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  • 1. Adlercreutz, Ludvig
    et al.
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Andersen, J.
    Ogink, R.
    Optimizing the Natural Gas Engine for CO2 reduction2016In: SAE Technical Papers, SAE International , 2016, Vol. 2016-April, no AprilConference paper (Refereed)
    Abstract [en]

    With alternative fuels having moved more into market in light of their reduction of emissions of CO2 and other air pollutants, the spark ignited internal combustion engine design has only been affected to small extent. The development of combustion engines running on natural gas or Biogas have been focused to maintain driveability on gasoline, creating a multi fuel platform which does not fully utilise the alternative fuels' potential. However, optimising these concepts on a fundamental level for gas operation shows a great potential to increase the level of utilisation and effectiveness of the engine and thereby meeting the emissions legislation. The project described in this paper has focused on optimising a combustion concept for CNG combustion on a single cylinder research engine. The ICE's efficiency at full load and the fuels characteristics, including its knock resistance, is of primary interest - together with part load performance and overall fuel consumption. In the process of increasing the efficiency of the engine the following areas have been of primary interest, increased compression ratio, thermal load at high cylinder pressure and the use of EGR to further increase efficiency. The overall goal in the project was to reduce the CO2-emissions while maintaining the performance and characteristics of the engine. The ambition is to reduce specific tail-pipe CO2-emissions in g/kWh by 50% compared to a modern gasoline engine. The goal was close to being reached at 45% reduction at full load and 25-34% on part load. This was done by theoretically downsizing the engine and increasing the specific performance of the engine.

  • 2. Adlercreutz, Ludvig
    et al.
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Stenlåås, Ola
    Particle Emission Measurements in a SI CNG EngineUsing Oils with Controlled Ash Content2019In: SAE Technical Papers, 2019Conference paper (Refereed)
    Abstract [en]

    Clean combustion is one of the inherent benefits of using a high methane content fuel, natural gas or biogas. A single carbon atom in the fuel molecule results, to a large extent, in particle-free combustion. This is due to the high energy required for binding multiple carbon atoms together during the combustion process, required to form soot particles. When scaling up this process and applying it in the internal combustion engine, the resulting emissions from the engine have not been observed to be as particle free as the theory on methane combustion indicates. These particles stem from the combustion of engine oil and its ash content. One common practice has been to lower the ash content to regulate the particulate emissions, as was done for diesel engines. For a gas engine, this approach has been difficult to apply, as the piston and valvetrain lubrication becomes insufficient. However, the low particle emissions from the combustion of CNG does allow for an investigation of particle contribution from engine oil ash content with only a minor particle contribution from the fuel itself. The hypothesis for this study is that there is a relationship between the engine oil ash content and the particulate emissions from a CNG engine. The investigation was conducted for several operating points with varying engine speeds and load on a single cylinder engine. The single cylinder approach was chosen to reduce sources of engine oil intrusion in the combustion chamber. The obtained results were not in line with the hypothesis, the particle emissions from the lower ash content oil did not decrease in number but the size of the particles did. The results also showed a spiking behavior in the particulate emissions, originating from the lubrication oil consumption past the piston rings. Mass flow through the engine proved to affect the particle size distribution as well as the total number of particles for all levels of oil ash content.

  • 3. Adlercreutz, Ludvig
    et al.
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Stenlåås, Ola
    Variation in Squish Length and Swirl to Reach Higher Levels of EGRin a CNG Engine2019Conference paper (Refereed)
    Abstract [en]

    Gaseous methane fuel for internal combustion engineshave proved to be a competitive source of propulsionenergy for heavy duty truck engines. Using biogascan even reduce the carbon footprint of the truck to near-zerolevels, creating fully environmentally friendly transport. Gasengines have already been on the market and proved to be apopular alternative for buses and waste transport. However,for long haulage these gas engines have not been on par withthe equivalent diesel engines. To improve the power and efficiencyof EURO VI gas engines running stoichiometrically, adirect way forward is adding more boost pressure and sparkadvance in combination with more EGR to mitigate knock.Using in-cylinder turbulence to achieve higher mixing rate,the fuel can still be combusted efficiently despite the increasedfraction of inert gases. In this paper, previous findings onin-cylinder air flows for diesel engine simulations are investigatedfor the applicability on to stoichiometric gas combustion.Two key parameters were identified, swirl and squish.By varying the levels of swirl with different squish lengths inthe piston design, the in-cylinder flow motion is altered toinvestigate its effect on stoichiometric gas combustion. Thetesting was performed on a single cylinder research engineoperated in the equivalent multi cylinder engine operatingpoints. The results show that previous modelling findings areverified on the pre-mixed gas combustion studied. By choosingswirl and squish for the design of the gas engine, it is possibleto increase the combustion speed and thus the fraction of EGRin the combustion charge, without the latter having a negativeimpact on the combustion.

  • 4.
    Aghaali, H.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, H. -E
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Improving turbocharged engine simulation by including heat transfer in the turbocharger2012In: SAE technical paper series, ISSN 0148-7191Article in journal (Refereed)
    Abstract [en]

    Engine simulation based on one-dimensional gas dynamics is well suited for integration of all aspects arising in engine and powertrain developments. Commonly used turbocharger performance maps in engine simulation are measured in non-pulsating flow and without taking into account the heat transfer. Since on-engine turbochargers are exposed to pulsating flow and varying heat transfer situations, the maps in the engine simulation, i.e. GT-POWER, have to be shifted and corrected which are usually done by mass and efficiency multipliers for both turbine and compressor. The multipliers change the maps and are often different for every load point. Particularly, the efficiency multiplier is different for every heat transfer situation on the turbocharger. The aim of this paper is to include the heat transfer of the turbocharger in the engine simulation and consequently to reduce the use of efficiency multiplier for both the turbine and compressor. A set of experiment has been designed and performed on a water-oil-cooled turbocharger, which was installed on a 2 liter GDI engine with variable valve timing, for different load points of the engine and different conditions of heat transfer in the turbocharger. The experiments were the base to simulate heat transfer on the turbocharger, by adding a heat sink before the turbine and a heat source after the compressor. The efficiency multiplier of the turbine cannot compensate for all heat transfer in the turbine, so it is needed to put out heat from the turbine in addition to the using of efficiency multiplier. Results of this study show that including heat transfer of turbocharger in engine simulation enables to decrease the use of turbine efficiency multiplier and eliminate the use of compressor efficiency multiplier to correctly calculate the measured gas temperatures after turbine and compressor. 

  • 5.
    Aghaali, Habib
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Exhaust Heat Utilisation and Losses in Internal Combustion Engines with Focus on the Gas Exchange System2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Exhaust gas energy recovery should be considered in improving fuel economy of internal combustion engines. A large portion of fuel energy is wasted through the exhaust of internal combustion engines. Turbocharger and turbocompound can, however, recover part of this wasted heat. The energy recovery depends on the efficiency and mass flow of the turbine(s) as well as the exhaust gas state and properties such as pressure, temperature and specific heat capacity. The exhaust gas pressure is the principal parameter which is required for the turbine energy recovery, but higher exhaust back-pressures on the engines create higher pumping losses. This is in addition to the heat losses in the turbochargers what makes any measurement and simulation of the engines more complex.

    This thesis consists of two major parts. First of all, the importance of heat losses in turbochargers has been shown theoretically and experimentally with the aim of including heat transfer of the turbochargers in engine simulations. Secondly, different concepts have been examined to extract exhaust heat energy including turbocompounding and divided exhaust period (DEP) with the aim of improved exhaust heat utilisation and reduced pumping losses.

    In the study of heat transfer in turbochargers, the turbocharged engine simulation was improved by including heat transfer of the turbocharger in the simulation. Next, the heat transfer modelling of the turbochargers was improved by introducing a new method for convection heat transfer calculation with the support of on-engine turbocharger measurements under different heat transfer conditions. Then, two different turbocharger performance maps were assessed concerning the heat transfer conditions in the engine simulation. Finally, the temperatures of turbocharger’s surfaces were predicted according to the measurements under different heat transfer conditions and their effects are studied on the turbocharger performance. The present study shows that the heat transfer in the turbochargers is very crucial to take into account in the engine simulations, especially in transient operations.

    In the study of exhaust heat utilisation, important parameters concerning turbine and gas exchange system that can influence the waste heat recovery were discussed. In addition to exhaust back-pressure, turbine speed and turbine efficiency, the role of the air-fuel equivalence ratio was demonstrated in details, because lower air-fuel equivalence ratio in a Diesel engine can provide higher exhaust gas temperature. The results of this study indicate that turbocompound engine efficiency is relatively insensitive to the air-fuel equivalence ratio.

    To decrease the influence of the increased exhaust back-pressure of a turbocompound engine, a new architecture was developed by combining the turbocompound engine with DEP. The aim of this study was to utilise the earlier phase (blowdown) of the exhaust stroke in the turbine(s) and let the later phase (scavenging) of the exhaust stroke bypass the turbine(s). To decouple the blowdown phase from the scavenging phase, the exhaust flow was divided between two different exhaust manifolds with different valve timing.

    According to this study, this combination improves the fuel consumption in low engine speeds and deteriorates it at high engine speeds. This is mainly due to long duration of choked flow in the exhaust valves because this approach is using only one of the two exhaust valves on each cylinder at a time.

    Therefore, the effects of enlarged effective flow areas of the exhaust valves were studied. Two methods were used to enlarge the effective flow area i.e. increasing the diameters of the blowdown and scavenging valves by 4 mm; and modifying the valve lift curves of the exhaust valves to fast opening and closing. Both methods improved BSFC in the same order even though they were different in nature. Fast opening and closing of the exhaust valves required shorter blowdown duration and longer scavenging duration. The modified lift curves provided less pumping losses, less available energy into the turbine and larger amplitude of the pulsating flow through the turbine.

    In order for defining a set of important parameters that should be examined in experimental studies, a sensitivity analysis was performed on the turbocompound DEP engine in terms of break specific fuel consumption to different parameters concerning the gas exchange such as blowdown valve timing, scavenging valve timing, blowdown valve size, scavenging valve size, discharge coefficients of blowdown and scavenging ports, turbine efficiency, turbine size and power transmission efficiency.

    Finally, to overcome the restriction in the effective flow areas of the exhaust valves, DEP was implemented externally on the exhaust manifold instead of engine exhaust valves, which is called externally DEP (ExDEP). This innovative engine architecture, which benefits from supercharging, turbocharging and turbocompounding, has a great fuel-saving potential in almost all load points up to 4%.

  • 6.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångstrom, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Demonstration of Air-Fuel Ratio Role in One-Stage Turbocompound Diesel Engines2013In: SAE Technical Papers, 2013, Vol. 11Conference paper (Refereed)
    Abstract [en]

    A large portion of fuel energy is wasted through the exhaust of internal combustion engines. Turbocompound can, however, recover part of this wasted heat. The energy recovery depends on the turbine efficiency and mass flow as well as the exhaust gas state and properties such as pressure, temperature and specific heat capacity.

    The main parameter influencing the turbocompound energy recovery is the exhaust gas pressure which leads to higher pumping loss of the engine and consequently lower engine crankshaft power. Each air-fuel equivalence ratio (λ) gives different engine power, exhaust gas temperature and pressure. Decreasing λ toward 1 in a Diesel engine results in higher exhaust gas temperatures of the engine.  λ can be varied by changing the intake air pressure or the amount of injected fuel which changes the available energy into the turbine. Thus, there is a compromise between gross engine power, created pumping power, recovered turbocompound power and consumed compressor power.

    In this study, the effects of different λ values and exhaust back-pressure have been investigated on the efficiency of a heavy-duty Diesel engine equipped with a single-stage electric turbocompounding. A one-dimensional gas dynamics model of a turbocharged engine was utilized that was validated against measurements at different load points. Two configurations of turbocompound engine were made. In one configuration an electric turbocharger was used and the amount of fuel was varied with constant intake air pressure. In another configuration the turbocharger turbine and compressor were disconnected to be able to control the turbine speed and the compressor speed independently; then the compressor pressure ratio was varied with constant engine fuelling and the exhaust back-pressure was optimized for each compressor pressure ratio.

    At each constant turbine efficiency there is a linear relation between the optimum exhaust back-pressure and ideally expanded cylinder pressure until bottom dead center with closed exhaust valves. There is an optimum λ for the turbocharged engine with regard to the fuel consumption. In the turbocompound engine, this will be moved to a richer λ that gives the best total specific fuel consumption; however, the results of this study indicates that turbocompound engine efficiency is relatively insensitive to the air-fuel ratio.

  • 7.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    A review of turbocompounding as a waste heat recovery system for internal combustion engines2015In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 49, p. 813-824Article in journal (Refereed)
    Abstract [en]

    Internal combustion engines waste a large amount of fuel energy through their exhausts. Various technologies have been developed for waste heat recovery such as turbocompounds, Rankine bottoming cycles, and thermoelectric generators that reduce fuel consumption and CO2 emissions. Turbocompounding is still not widely applied to vehicular use despite the improved fuel economy, lower cost, volume, and complexity higher exhaust gas recirculation driving capability and improved transient response. This paper comprehensively reviews the latest developments and research on turbocompounding to discover important variables and provide insights into the implementation of a high-efficiency turbocompound engine. Attention should be paid to the optimization of turbocompound engines and their configurations because the major drawback of this technology is additional exhaust back-pressure, which leads to higher pumping loss in the engines. Applying different technologies and concepts on turbocompound engines makes the exhaust energy recovery more efficient and provides more freedom in the design and optimization of the engines. Turbine efficiency plays an important role in the recovery of the wasted heat so turbine design is a crucial issue in turbocompounding. In addition, variability in geometry and rotational speed of power turbines allows for more efficient turbocompound engines in different operating conditions. The conclusion drawn from this review is that turbocompounding is a promising technology for reducing fuel consumption in the coming decades in both light- and heavy-duty engines.

  • 8.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Effects of Effective Flow Areas of Exhaust Valves on a Turbocompound Diesel Engine Combined With Divided Exhaust Period2014In: Proceedings from the FISITA 2014 World Automotive Congress, 2014Conference paper (Refereed)
    Abstract [en]

    Research and /or Engineering Questions/Objective: Exhaust gas energy recovery in internal combustion engines is one of the key challenges in the future developments. The objective of this study is to reveal the fuel-saving potential of a turbocompound Diesel engine combined with divided exhaust period (DEP). The exhaust flow is provided for two different manifolds via separate valves, blowdown and scavenging, at different timings. The main challenge in this combination is choked flow through the exhaust valves due to the restricted effective flow areas. Therefore, the effects of enlarged effective flow areas of the exhaust valves are studied.

    Methodology: A commercial 1D gas dynamics code, GT-POWER, was used to simulate a turbocharged Diesel engine which was validated against measurements. Then the turbocharged engine model was modified to a turbocompound engine with DEP. Using statistical analysis in the simulation (design of experiment), the performance of this engine was studied at different sizes, lift curves and timings of the exhaust valves and turbine swallowing capacity.

    Results: In the paper the effects of the effective flow areas of the exhaust valves are presented on the break specific fuel consumption, pumping mean effective pressure and the turbine energy recovery by increasing the valve size and modifying valve lift curve to fast opening and closing. This has been done in a low engine speed and full load. The main finding is that the flow characteristics of the exhaust valves in the turbocompound DEP engine are very important for gaining the full efficiency benefit of the DEP concept.  The turbocompound DEP engine with modified valve lift shape of the exhaust valves could improve the overall brake specific fuel consumption by 3.44% in which 0.64% of the improvement is due to the valve lift curve. Modified valve lift curves contribute mainly in decreasing the period of choked flow through the exhaust valves.

    Limitations of this study: The simulations were not validated against measurements; however, the mechanical and geometrical limitations were tried to keep realistic when manipulating the valve flow area events.

    What does the paper offer that is new in the field in comparison to other works of the author: In addition to the novelty of the engine architecture that combines turbocompound with DEP, the statistical analysis and comparison presented in this paper is new especially with demonstrating the importance of crank angle coupled flow characteristics of the valves.

    Conclusion: To achieve full fuel-saving potential of turbocompound DEP engines, the flow characteristics of the exhaust valves must be considered. The effective flow areas of the exhaust valves play important roles in the choked flow through the valves, the pumping work and the brake specific fuel consumption of the engine.

  • 9.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Externally divided exhaust period on a turbocompound engine for fuel-saving2014Conference paper (Other academic)
    Abstract [en]

    To improve exhaust heat utilization of a turbocharged engine, divided exhaust period (DEP) and turbocompound are integrated. The DEP concept decreases pumping loss created by the turbocompound. In the DEP concept the exhaust flow is divided between two different exhaust manifolds, blowdown and scavenging. One of the two exhaust valves on each engine cylinder is opened to the blowdown manifold at the first phase of exhaust stroke and the other valve is opened to the scavenging manifold at the later phase of exhaust stroke. This leads to lower exhaust back pressure and pumping loss. The combination of turbocompound engine with DEP has been examined previously and the result showed that this combination reduces the fuel consumption in low engine speeds and deteriorates it in high engine speeds. The main restriction of this combination was the low effective flow areas of the exhaust valves at high engine speeds.

    To overcome this restriction and increase the effective flow areas of the exhaust valves, DEP is employed externally on the exhaust manifold instead of engine exhaust valves. In externally DEP (ExDEP), both exhaust valves will be opened and closed similar to the corresponding turbocharged engine and the exhaust flow is divided by flow splits on the exhaust manifold. Two valves on the outlet ports of each flow split are added. One of them is a non-return valve (check valve) and the other one is synchronized with the cam shaft.

    In this study, the fuel-saving potential of ExDEP is analysed on the turbocompound engine at different engine speeds and loads and compared with the corresponding turbocharged engine, turbocompound engine and turbocompound DEP engine equipped. The results show that ExDEP has a great fuel-saving potential in almost all load points.

    ExDEP concept, itself, is a novel concept that there is no available literature about it. Moreover, combination of this new gas exchange system with turbocompound engines is an innovative extension of combined turbocompound DEP engines.

  • 10.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Improving Turbocharged Engine Simulation by Including Heat Transfer in the Turbocharger2012In: 2012 SAE International, SAE international , 2012Conference paper (Refereed)
    Abstract [en]

    Engine simulation based on one-dimensional gas dynamics is well suited for integration of all aspects arising in engine and power-train developments. Commonly used turbocharger performance maps in engine simulation are measured in non-pulsating flow and without taking into account the heat transfer. Since on-engine turbochargers are exposed to pulsating flow and varying heat transfer situations, the maps in the engine simulation, i.e. GT-POWER, have to be shifted and corrected which are usually done by mass and efficiency multipliers for both turbine and compressor. The multipliers change the maps and are often different for every load point. Particularly, the efficiency multiplier is different for every heat transfer situation on the turbocharger. The aim of this paper is to include the heat transfer of the turbocharger in the engine simulation and consequently to reduce the use of efficiency multiplier for both the turbine and compressor. A set of experiment has been designed and performed on a water-oil-cooled turbocharger, which was installed on a 2 liter GDI engine with variable valve timing, for different load points of the engine and different conditions of heat transfer in the turbocharger. The experiments were the base to simulate heat transfer on the turbocharger, by adding a heat sink before the turbine and a heat source after the compressor. The efficiency multiplier of the turbine cannot compensate for all heat transfer in the turbine, so it is needed to put out heat from the turbine in addition to the using of efficiency multiplier. Results of this study show that including heat transfer of turbocharger in engine simulation enables to decrease the use of turbine efficiency multiplier and eliminate the use of compressor efficiency multiplier to correctly calculate the measured gas temperatures after turbine and compressor.

  • 11.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Performance Sensitivity to Exhaust Valves and Turbine Parameters on a Turbocompound Engine with Divided Exhaust Period2014In: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 7, no 4, p. 1722-1733Article in journal (Refereed)
    Abstract [en]

    Turbocompound can utilize part of the exhaust energy on internal combustion engines; however, it increases exhaust back pressure, and pumping loss.  To avoid such drawbacks, divided exhaust period (DEP) technology is combined with the turbocompound engine. In the DEP concept the exhaust flow is divided between two different exhaust manifolds, blowdown and scavenging, with different valve timings. This leads to lower exhaust back pressure and improves engine performance.

    Combining turbocompound engine with DEP has been theoretically investigated previously and shown that this reduces the fuel consumption and there is a compromise between the turbine energy recovery and the pumping work in the engine optimization. However, the sensitivity of the engine performance has not been investigated for all relevant parameters. The main aim of this study is to analyze the sensitivity of this engine architecture in terms of break specific fuel consumption to different parameters concerning the gas exchange such as blowdown valve timing, scavenging valve timing, blowdown valve size, scavenging valve size, discharge coefficients of blowdown and scavenging ports, turbine efficiency, turbine size and power transmission efficiency. This study presents the sensitivity analysis of the turbocompound DEP engine to these parameters and defines a set of important parameters that should be examined in experimental studies.

  • 12.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Temperature Estimation of Turbocharger Working Fluids and Walls under Different Engine Loads and Heat Transfer Conditions2013In: SAE Technical Papers, 2013Conference paper (Refereed)
    Abstract [en]

    Turbocharger performance maps, which are used in engine simulations, are usually measured on a gas-stand where the temperatures distributions on the turbocharger walls are entirely different from that under real engine operation. This should be taken into account in the simulation of a turbocharged engine. Dissimilar wall temperatures of turbochargers give different air temperature after the compressor and different exhaust gas temperature after the turbine at a same load point. The efficiencies are consequently affected. This can lead to deviations between the simulated and measured outlet temperatures of the turbocharger turbine and compressor. This deviation is larger during a transient load step because the temperatures of turbocharger walls change slowly due to the thermal inertia. Therefore, it is important to predict the temperatures of turbocharger walls and the outlet temperatures of the turbocharger working fluids in a turbocharged engine simulation.

    In the work described in this paper, a water-oil-cooled turbocharger was extensively instrumented with several thermocouples on reachable walls. The turbocharger was installed on a 2-liter gasoline engine that was run under different loads and different heat transfer conditions on the turbocharger by using insulators, an extra cooling fan, radiation shields and water-cooling settings. The turbine inlet temperature varied between 550 and 850 °C at different engine loads.

    The results of this study show that the temperatures of turbocharger walls are predictable from the experiment. They are dependent on the load point and the heat transfer condition of the turbocharger. The heat transfer condition of an on-engine turbocharger could be defined by the turbine inlet temperature, ambient temperature, oil heat flux, water heat flux and the velocity of the air around the turbocharger. Thus, defining the heat transfer condition and rotational speed of the turbocharger provides temperatures predictions of the turbocharger walls and the working fluids. This prediction enables increased precision in engine simulation for future work in transient operation.

  • 13.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    The Exhaust Energy Utilization of a Turbocompound Engine Combined with Divided Exhaust Period2014Conference paper (Refereed)
    Abstract [en]

    To decrease the influence of the increased exhaust pressure of a turbocompound engine, a new architecture is developed by combining the turbocompound engine with divided exhaust period (DEP). The aim of this study is to utilize the earlier stage (blowdown) of the exhaust stroke in the turbine(s) and let the later stage (scavenging) of the exhaust stroke bypass the turbine(s). To decouple the blowdown phase from the scavenging phase, the exhaust flow is divided between two different exhaust manifolds with different valve timing. A variable valve train system is assumed to enable optimization at different load points. The fuel-saving potential of this architecture have been theoretically investigated by examining different parameters such as turbine flow capacity, blowdown valve timing and scavenging valve timing. Many combinations of these parameters are considered in the optimization of the engine for different engine loads and speeds.

    This architecture produces less negative pumping work for the same engine load point due to lower exhaust back pressure; however, the exhaust mass flow into the turbine(s) is decreased. Therefore, there is a compromise between the turbine energy recovery and the pumping work. According to this study, this combination shows fuel-saving potential in low engine speeds and limitations at high engine speeds. This is mainly due to the choked flow in the exhaust valves because this approach is using only one of the two exhaust valves at a time. To reveal the full potential of this approach, increasing the effective flow area of the valves should be studied.

  • 14.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Turbocharged SI-Engine Simulation with Cold and Hot-Measured Turbocharger Performance Maps2012In: Proceedings of ASME Turbo Expo 2012, Vol 5, ASME Press, 2012, p. 671-679Conference paper (Refereed)
    Abstract [en]

    Heat transfer within the turbocharger is an issue in engine simulation based on zero and one-dimensional gas dynamics. Turbocharged engine simulation is often done without taking into account the heat transfer in the turbocharger. In the simulation, using multipliers is the common way of adjusting turbocharger speed and parameters downstream of the compressor and upstream of the turbine. However, they do not represent the physical reality. The multipliers change the maps and need often to be different for different load points. The aim of this paper is to simulate a turbocharged engine and also consider heat transfer in the turbocharger. To be able to consider heat transfer in the turbine and compressor, heat is transferred from the turbine volute and into the compressor scroll. Additionally, the engine simulation was done by using two different turbocharger performance maps of a turbocharger measured under cold and hot conditions. The turbine inlet temperatures were 100 and 600°C, respectively. The turbocharged engine experiment was performed on a water-oil-cooled turbocharger (closed waste-gate), which was installed on a 2-liter gasoline direct-injected engine with variable valve timing, for different load points of the engine. In the work described in this paper, the difference between cold and hot-measured turbocharger performance maps is discussed and the quantified heat transfers from the turbine and to/from the compressor are interpreted and related to the maps.

  • 15.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Serrano, Jose R
    Universitat Politècnica de València.
    Evaluation of different heat transfer conditions on an automotive turbocharger2014In: International Journal of Engine Research, ISSN 1468-0874, E-ISSN 2041-3149, Vol. 16, no 2, p. 137-151Article in journal (Refereed)
    Abstract [en]

    This paper presents a combination of theoretical and experimental investigations for determining the main heat fluxes within a turbocharger. These investigations consider several engine speeds and loads as well as different methods of conduction, convection, and radiation heat transfer on the turbocharger. A one-dimensional heat transfer model of the turbocharger has been developed in combination with simulation of a turbocharged engine that includes the heat transfer of the turbocharger. Both the heat transfer model and the simulation were validated against experimental measurements. Various methods were compared for calculating heat transfer from the external surfaces of the turbocharger, and one new method was suggested.

    The effects of different heat transfer conditions were studied on the heat fluxes of the turbocharger using experimental techniques. The different heat transfer conditions on the turbocharger created dissimilar temperature gradients across the turbocharger. The results show that changing the convection heat transfer condition around the turbocharger affects the heat fluxes more noticeably than changing the radiation and conduction heat transfer conditions. Moreover, the internal heat transfers from the turbine to the bearing housing and from the bearing housing to the compressor are significant, but there is an order of magnitude difference between these heat transfer rates.

  • 16.
    Andrae, Johan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Johansson, David
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Björnbom, Pehr
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
    Risberg, Per
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Kalghatgi, Gautam
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Cooxidation in the auto-ignition of primary reference fuels and n-heptane/toluene blends2005In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 140, no 4, p. 267-286Article in journal (Refereed)
    Abstract [en]

    Auto-ignition of fuel mixtures was investigated both theoretically and experimentally to gain further understanding of the fuel chemistry. A homogeneous charge compression ignition (HCCI) engine was run under different operating conditions with fuels of different RON and MON and different chemistries. Fuels considered were primary reference fuels and toluene/n-heptane blends. The experiments were modeled with a single-zone adiabatic model together with detailed chemical kinetic models. In the model validation, co-oxidation reactions between the individual fuel components were found to be important in order to predict HCCI experiments, shock-tube ignition delay time data, and ignition delay times in rapid compression machines. The kinetic models with added co-oxidation reactions further predicted that an n-heptane/toluene fuel with the same RON as the corresponding primary reference fuel had higher resistance to auto-ignition in HCCI combustion for lower intake temperatures and higher intake pressures. However, for higher intake temperatures and lower intake pressures the n-heptane/toluene fuel and the PRF fuel had similar combustion phasing.

  • 17. Anton, N.
    et al.
    Fredriksson, C.
    Larsson, P. -I
    Genrup, M.
    Christiansen Erlandsson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Twin-scroll turbocharger turbine stage evaluation of experimental data and simulations2018In: Institution of Mechanical Engineers - 13th International Conference on Turbochargers and Turbocharging 2018, Institution of Mechanical Engineers , 2018, p. 487-502Conference paper (Refereed)
    Abstract [en]

    In this study a novel comparison of CFD, measured data and a ID-model is presented for a Twin-scroll turbocharger turbine stage. Both full and single admission flow divisions were taken into consideration and shown to represent "on-engine" conditions in the high and low engine rpm range respectively for a heavy-duty 6-cylinder diesel engine. With this in mind, the turbine stage was evaluated for each flow division at several rotational speeds. Both high and low pressure ratios were run. Emphasis is made on high pressure ratios as it is the most relevant case with regards to the energy levels of the exhaust flow. The purpose of the study was to gain insight into the differences and similarities between gas stand measurements, a ID-model and CFD considering performance and turbine stage parameters. The study concludes that the results from the measurements in the gas stand and ID-model, obtained best correlation with the CFD results at low turbine pressure ratios. At high pressure ratios significant deviations were observed. In order to check for discrepancies, both frozen rotor and stage interfaces were considered in the CFD-model, with an additional variant taking the rotor-volute tongue clocking into account. All interfaces resulted in the same trends, although the frozen rotor approach provided the best correlation with measured data. The clocking effect was seen not to affect the results to a great extent in this case. The main difference between the CFD and measurements in combination with the ID model-prediction primarily occur at the rotor inlet. The pressures were predicted to be substantially higher by the CFD calculations due to reduced pressure losses in the volute. Especially taking effect at high turbine pressure ratios which is most relevant for turbocharger applications and therefor the mapping process in the gas stand. This can be one of the reasons for significant deviations in efficiency, turbine parameters etc. at high pressure ratios as effectively more energy will be available to the rotor for a given turbine stage pressure ratio. In general best coherence was achieved for the full admission case. Even so, trends of main parameters such as efficiency, flow capacity and turbine parameters point in the same direction comparing CFD with calculations and measured results for both full and single admission. 

  • 18.
    Anton, Nicholas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Engine Optimized Turbine Design2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The focus on our environment has never been as great as it is today. The impact of global warming and emissions from combustion processes become increasingly more evident with growing concerns among the world’s inhabitants. The consequences of extreme weather events, rising sea levels, urban air quality, etc. create a desperate need for immediate action. A major contributor to the cause of these effects is the transportation sector, a sector that relies heavily on the internal combustion engine and fossil fuels. The heavy-duty segment of the transportation sector is a major consumer of oil and is responsible for a large proportion of emissions.

    The global community has agreed on multiple levels to reduce the effect of man-made emissions into the atmosphere. Legislation for future reductions and, ultimately, a totally fossil-free society is on the agenda for many industrialized countries and an increasing number of emerging economies.

    Improvements of the internal combustion engine will be of importance in order to effectively reduce emissions from the transportation sector both presently and in the future. The primary focus of these improvements is undoubtedly in the field of engine efficiency. The gas exchange system is of major importance in this respect. The inlet and exhaust flows as the cylinder is emptied and filled will significantly influence the pumping work of the engine. At the center of the gas exchange system is the turbocharger. The turbine stage of the turbocharger can utilize the energy in the exhaust flow by expanding the exhaust gases in order to power the compressor stage of the turbocharger.

    If turbocharger components can operate at high efficiency, it is possible to achieve high engine efficiency and low fuel consumption. Low exhaust pressure during the exhaust stroke combined with high pressure at the induction stroke results in favorable pumping work. For the process to work, a systems-based approach is required as the turbocharger is only one component of the engine and gas exchange system.

    In this thesis, the implications of turbocharger turbine stage design with regards to exhaust energy utilization have been extensively studied. Emphasis has been placed on the turbine stage in a systems context with regards to engine performance and the influence of exhaust system components.

    The most commonly used turbine stage in turbochargers, the radial turbine, is associated with inherent limitations in the context of exhaust energy utilization. Primarily, turbine stage design constraints result in low efficiency in the pulsating exhaust flow, which impairs the gas exchange process. Gas stand and numerical evaluation of the common twin scroll radial turbine stage highlighted low efficiency levels at high loadings. For a pulse-turbocharged engine with low exhaust manifold volume, the majority of extracted work by the turbine will occur at high loadings, far from the optimum efficiency point for radial turbines. In order for the relevant conditions to be assessed with regards to turbine operation, the entire exhaust pulse must be considered in detail. Averaged conditions will not capture the variability in energy content of the exhaust pulse important for exhaust energy utilization.

    Modification of the radial turbine stage design in order to improve performance is very difficult to achieve. Typical re-sizing with modifying tip diameter and trim are not adequate for altering turbine operation into high efficiency regions at the energetic exhaust pulse peak.

    The axial turbine type is an alternative as a turbocharger turbine stage for a pulse-turbocharged engine. The axial turbine stage design can allow for high utilization of exhaust energy with minimal pressure interference in the gas exchange process; a combination which has been shown to result in engine efficiency improvements compared to state-of-the-art radial turbine stages.

  • 19.
    Anton, Nicholas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Birkestad, Per
    The 6-Inlet Single Stage Axial Turbine Concept for Pulse-Turbocharging: A Numerical Investigation2019Conference paper (Refereed)
  • 20.
    Anton, Nicholas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Fredriksson, Carl
    Larsson, Per-Inge
    Genrup, Magnus
    Christiansen Erlandsson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    The Sector Divided Single Stage Axial Turbine Concept: A Feasibility Study For Pulse-Turbocharging2018Conference paper (Refereed)
  • 21.
    Anton, Nicholas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Fredriksson, Carl
    Larsson, Per-Inge
    Genrup, Magnus
    Christiansen-Erlandsson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Twin-Scroll turbocharger turbine stage evaluation of experimental data and simulations2018Conference paper (Refereed)
  • 22.
    Anton, Nicholas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Fredriksson, Carl
    Larsson, Per-Inge
    Genrup, Magnus
    Hultqvist, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Twin-scroll turbine performance evaluation from gas stand data 2016Conference paper (Refereed)
  • 23. Anton, Nicholas
    et al.
    Genrup, M.
    Fredriksson, C.
    Larsson, P. -I
    Erlandsson-Christiansen, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Exhaust volume dependency of turbocharger turbine design for a heavy duty otto cycle engine2017In: Proceedings of the ASME Turbo Expo: Turbomachinery Technical Conference and Exposition, GT 2017, ASME Press, 2017, Vol. 2C, article id V02CT44A015Conference paper (Refereed)
    Abstract [en]

    This study is considering turbocharger turbine performance at "on-engine" conditions with respect to turbine design variables and exhaust manifold volume. The highly unsteady nature of the internal combustion engine will result in a very wide range of turbine operation, far from steady flow conditions. As most turbomachinery design work is conducted at steady state, the influence of the chosen turbine design variables on the crank-angle-resolved turbine performance will be of prime interest. In order to achieve high turbocharger efficiency with the greatest benefits for the engine, the turbine will need high efficiency at the energetic exhaust pressure pulse peak. The starting point for this paper is a target full load power curve for a heavy duty Otto-cycle engine, which will dictate an initial compressor and turbine match. Three radial turbine designs are investigated, differing with respect to efficiency characteristics, using a common compressor stage. The influence of the chosen turbine design variables considering a main contributor to unsteadiness, exhaust manifold volume, is evaluated using 1D engine simulation software. A discussion is held in conjunction with this regarding the efficiency potential of each turbine design and limitations of turbine types.

  • 24.
    Anton, Nicholas
    et al.
    Scania CV AB, SE-15138 Sodertalje, Sweden..
    Genrup, Magnus
    Lund Univ, Energy Sci, SE-22100 Lund, Sweden..
    Fredriksson, Carl
    Scania CV AB, SE-15138 Sodertalje, Sweden..
    Larsson, Per-Inge
    Scania CV AB, SE-15138 Sodertalje, Sweden..
    Christiansen Erlandsson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    AXIAL TURBINE DESIGN FOR A TWIN-TURBINE HEAVY-DUTY TURBOCHARGER CONCEPT2018In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBOMACHINERY TECHNICAL CONFERENCE AND EXPOSITION, 2018, VOL 2B, ASME Press, 2018, article id UNSP V02BT44A008Conference paper (Refereed)
    Abstract [en]

    In the process of evaluating a parallel twin-turbine pulse-turbocharged concept, the results considering the turbine operation clearly pointed towards an axial type of turbine. The radial turbine design first analyzed was seen to suffer from sub-optimum values of flow coefficient, stage loading and blade speed-ratio. Modifying the radial turbine by both assessing the influence of "trim" and inlet tip diameter all concluded that this type of turbine is limited for the concept. Mainly, the turbine stage was experiencing high values of flow coefficient, requiring a more high flowing type of turbine. Therefore, an axial turbine stage could be feasible as this type of turbine can handle significantly higher flow rates very efficiently. Also, the design spectrum is broader as the shape of the turbine blades is not restricted by a radially fibred geometry as in the radial turbine case. In this paper, a single stage axial turbine design is presented. As most turbocharger concepts for automotive and heavy-duty applications are dominated by radial turbines, the axial turbine is an interesting option to be evaluated for pulse charged concepts. Values of crank-angle-resolved turbine and flow parameters from engine simulations are used as input to the design and subsequent analysis. The data provides a valuable insight into the fluctuating turbine operating conditions and is a necessity for matching a pulse-turbocharged system. Starting on a 1D-basis, the design process is followed through, resulting in a fully defined 3D-geometry. The 3D-design is evaluated both with respect to FEA and CFD as to confirm high performance and durability. Turbine maps were used as input to the engine simulation in order to assess this design with respect to "on-engine" conditions and to engine performance. The axial design shows clear advantages with regards to turbine parameters, efficiency and tip speed levels compared to a reference radial design. Improvement in turbine efficiency enhanced the engine performance significantly. The study concludes that the proposed single stage axial turbine stage design is viable for a pulse-turbocharged six cylinder heavy-duty engine. Taking into account both turbine performance and durability aspects, validation in engine simulations, a highly efficient engine with a practical and realizable turbocharger concept resulted.

  • 25.
    Anton, Nicholas
    et al.
    Scania CV AB, SE-15138 Sodertalje, Sweden..
    Genrup, Magnus
    Lund Univ, Energy Sci, SE-22100 Lund, Sweden..
    Fredriksson, Carl
    Scania CV AB, SE-15138 Sodertalje, Sweden..
    Larsson, Per-Inge
    Scania CV AB, SE-15138 Sodertalje, Sweden..
    Christiansen Erlandsson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    ON THE CHOICE OF TURBINE TYPE FOR A TWIN-TURBINE HEAVY-DUTY TURBOCHARGER CONCEPT2018In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBOMACHINERY TECHNICAL CONFERENCE AND EXPOSITION, 2018, VOL 8, AMER SOC MECHANICAL ENGINEERS , 2018Conference paper (Refereed)
    Abstract [en]

    In this study, a fundamental approach to the choice of turbocharger turbine for a pulse-charged heavy-duty diesel engine is presented. A standard six-cylinder engine build with a production exhaust manifold and a Twin-scroll turbocharger is used as a baseline case. The engine exhaust configuration is redesigned and evaluated in engine simulations for a pulse-charged concept consisting of a parallel twin-turbine layout. This concept will allow for pulse separation with minimized exhaust pulse interference and low exhaust manifold volume. This turbocharger concept is uncommon, as most previous studies have considered two stage systems, various multiple entry turbine stages etc. Even more rare is the fundamental aspect regarding the choice of turbine type as most manufacturers tend to focus on radial turbines, which by far dominate the turbochargers of automotive and heavy-duty applications. By characterizing the turbine operation with regards to turbine parameters for optimum performance found in literature a better understanding of the limitations of turbine types can be achieved. A compact and low volume exhaust manifold design is constructed for the turbocharger concept and the reference radial turbine map is scaled in engine simulations to a pre-set AFR-target at a low engine RPM. By obtaining crank-angle-resolved data from engine simulations, key turbine parameters are studied with regard to the engine exhaust pulse-train. At the energetic exhaust pressure pulse peak, the reference radial turbine is seen to operate with suboptimum values of Blade-Speed-Ratio, Stage Loading and Flow Coefficient. The study concludes that in order to achieve high turbine efficiency for this pulse-charged turbocharger concept, a turbine with efficiency optimum towards low Blade-Speed Ratios, high Stage Loading and high Flow Coefficient is required. An axial turbine of low degree of reaction-design could be viable in this respect.

  • 26.
    Arimboor Chinnan, Jacob
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Simulation and validation of in-cylinder combustion for a heavy-duty Otto gas engine using 3D-CFD technique2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Emission from automobiles has been gaining importance for past few decades. This has gained a lot of impetus in search for alternate fuels among the automotive manufacturers. This led to the increase usage of Otto gas engine which uses natural gas as fuel. New engine designs have to be optimized for improving the engine efficiency. This led to usage of virtual simulations for reducing the lead time in the engine development. The verification and validation of actual phenomenon in the virtual simulations with respect to the physical measurements was quite important. 

    The aim of this master thesis is to suggest the combustion model parameters after evaluating various combination of combustion and ignition models in terms of computational time and accuracy. In-cylinder pressure trace from the simulation is compared with the measurement in order to find the nest suited combination of combustion and ignition models. The influence of ignition timing, number of engine cycles and boundary conditions on the simulation results are also studied.

    Results showed that ECFM combustion model predicts the simulation results more accurately when compare to the measurements. Impact of ignition timing on various combination of combustion and ignition model is also assessed. Stability of various combustion simulation models is also discussed while running for more engine cycles. Comparison of computational time is also made for various combination of combustion and ignition models. Results also showed that the flame tracking method using Euler is dependent on the mesh resolution and the mesh quality. 

    Recommendations and suggestions are given about the mesh and simulation settings for predicting the combustion simulation accurately. Some possible areas of improvement are given as future work for improving the accuracy of the simulation results. 

  • 27.
    Bernemyr, Hanna
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Characterization of Tailpipe Exhaust Particles using a Rotating Disc Diluter and a Volatility Tandem DMA (v-TDMA)2006In: SAE 2006 Transactions Journal of Fuels and Lubricants, 2006, Vol. 2006-01-3367Conference paper (Refereed)
    Abstract [en]

    A v-TDMA instrument has been used to study the tailpipe exhaust particles of a heavy-duty Diesel engine equipped with a continuously regenerating trap (CRT) running at two different steady state conditions: high speed / medium load and medium speed / high load. The sample was extracted directly out of the engine and conditioned by use of a rotating disc diluter. This paper deals with measurements where the parallel mode of the v-TDMA instrument was used. A temperature of 350 °C was applied in the heated section of the v-TDMA to study the thermal stability of the particles. Dilution between 86 and 1740 times were applied to see if the amount of dilution affected the particle behavior. The CRT reduces the number concentration of accumulation mode particles by 90%. When using the CRT, high numbers of nucleation mode particles are measured that can be volatilized at 350° in the v-TDMA instrument. For nucleation mode particles, changing the dilution from 86 to 386 times can suppress particle formation by up to 90%. The present work shows that the rotating disc diluter together with the v-TDMA instrument are promising tools for study of exhaust particles sampled directly out of the engine.

  • 28.
    Binder, Christian
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. Scania CV AB.
    Experiments on Heat Transfer During Diesel Combustion Using Optical Methods2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Transportation is a crucial part of modern societies. This includes their economies. Trade and the transportation of goods have a great influence on prosperity. Nevertheless, the transportation sector with road transport in particular is heavily dependent on fossil fuels and emits a significant amount of greenhouse gases. One approach to mitigate the negative environmental impact of road transport is to increase the efficiency of its most common propulsion system, that is the internal combustion engine. Due to its dominant role in the road freight transportation sector, this thesis directs its attention to heavy-duty diesel engines. In-cylinder heat losses are one of the main factors that reduce engine efficiency. Therefore, the objective of this thesis is to gain a better understanding of the processes that influence in-cylinder heat losses by resolving them in time and space using optical methods. In diesel engines, most of the in-cylinder heat losses are transferred to the piston. As a result, this thesis focuses specifically on that component.

    In this research project, the task to determine in-cylinder heat losses to the piston in heavy-duty diesel engines is divided into two parts. The most important part consists of fast surface temperature measurements on the piston using phosphor thermometry. The heat transfer coefficient inside the piston cooling gallery defines an additional steady-state boundary condition.

    The work presented in this thesis includes therefore efforts to improve in-cylinder surface temperature measurements and an assessment of their accuracy and precision. Furthermore, it comprises of experimental results from measurements on steel pistons and a piston with an insulating thermal barrier coating. Results reveal spatial differences of the heat transfer during diesel combustion. Measurements at the impingement point indicate a strong influence of flame impingement on local heat transfer. A correlation is detected between heat transfer and cycle-to-cycle variations of flame impingement.

    The thesis also reports efforts to determine the heat transfer coefficient inside the piston cooling gallery. Using an infrared camera a method is presented to spatially resolve convective heat transfer inside this cooling channel.

  • 29.
    Binder, Christian
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. Scania CV AB.
    Abou Nada, Fahed
    Lund University.
    Richter, Mattias
    Lund University.
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Norling, Daniel
    Scania CV AB.
    Heat Loss Analysis of a Steel Piston and a YSZ Coated Piston in a Heavy-Duty Diesel Engine Using Phosphor Thermometry Measurements2017In: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 10, no 4, p. 1954-1968Article in journal (Refereed)
    Abstract [en]

    Diesel engine manufacturers strive towards further efficiency improvements. Thus, reducing in-cylinder heat losses is becoming increasingly important. Understanding how location, thermal insulation, and engine operating conditions affect the heattransfer to the combustion chamber walls is fundamental for the future reduction of in-cylinder heat losses. This study investigates the effect of a 1mm-thick plasma-sprayed yttria-stabilized zirconia (YSZ) coating on a piston. Such a coated piston and a similar steel piston are compared to each other based on experimental data for the heat release, the heat transfer rate to the oil in the piston cooling gallery, the local instantaneous surface temperature, and the local instantaneous surface heat flux. The surface temperature was measured for different crank angle positions using phosphor thermometry. The fuel was chosen to be n-heptane to facilitate surface temperature measurements during non-skip-fire, thermally stabilized operating conditions. Assuming one-dimensional heat transfer inside each piston, the local instantaneous surface heat flux was calculated using the heat transfer rate to the oil in the piston cooling gallery and the surface temperature measurements. The results from this study show that the surface temperature variation is similar for both pistons. The instantaneous heat flux during combustion is however significantly greater for the steel piston than the coated piston. The heat release analysis also indicates that combustion is slower for the piston with the yttria-stabilized zirconia coating.

  • 30.
    Binder, Christian
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. Scania CV AB.
    Henrik, Feuk
    Lund University.
    Richter, Mattias
    Lund University.
    Phosphor Thermometry for In-Cylinder Surface Temperature Measurements in Diesel Engines2019In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501Article in journal (Other academic)
    Abstract [en]

    Surface temperature measurements in technically relevant applications can be very  hallenging and yet of great importance. Phosphor thermometry is a temperature measurement technique that has previously been employed in technically relevant applications to obtain surface temperature. The technique is based on temperature-dependent changes in a phosphor’s luminescence. To improve the accuracy and precision of temperature measurements with this technique, the present study considers, by way of example, the impact of conditions inside the cylinder of a diesel engine on decay time based phosphor thermometry. After an initial, general assessment of the effect of prevailing measurement conditions, this research investigates errors caused by soot luminosity, extinction, signal trapping and changes of phosphors’ luminescence properties due to exposure to the harsh environment. Furthermore, preferable properties of phosphors which are suitable for in-cylinder temperature measurements are discussed. 16 phosphors are evaluated, including four which – to the authors’ knowledge –have previously not been used in thermometry. Results indicate that errors due to photocathode bleaching, extinction, signal trapping and changes of luminescence properties may cause an erroneous temperature evaluation with temperature errors in the order of serval tens of Kelvin.

  • 31.
    Binder, Christian
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. Scania CV AB.
    Matamis, Alexios
    Lund University.
    Richter, Mattias
    Lund University.
    Norling, Daniel
    Scania CV AB.
    Comparison of heat losses at the impingement point and in between two impingement points in a diesel engine using phosphor thermometry2019Conference paper (Refereed)
    Abstract [en]

    In-cylinder heat losses in diesel engines reduce engine efficiency significantly and account for a considerable amount of injected fuel energy. A great part of the heat losses during diesel combustion presumably arises from the impingement of the flame. The present study compares the heat losses at the point where the flame impinges onto the piston bowl wall and the heat losses between two impingement points. Measurements were performed in a full metal heavy-duty diesel engine with a small optical access through a removed exhaust valve. The surface temperature at the impingement point of the combusting diesel spray and at a point in between two impingement points was determined using phosphor thermometry. The dynamic heat fluxes and the heat transfer coefficients which result from the surface temperature measurements are estimated. Simultaneous cylinder pressure measurements and high-speed videos are associated to individual surface temperature measurements. Thus each surface temperature measurement is linked to a specific impingement and combustion events. An analysis of the surface temperature in connection with the high speed images reveals the great impact of flame impingement on instantaneous local heat flux at the impingement point. Absence of such an effect in between two impingement points implies an inhomogeneous temperature field.

  • 32.
    Binder, Christian
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. Scania CV AB.
    Matamis, Alexios
    Lund University.
    Richter, Mattias
    Lund University.
    Norling, Daniel
    Scania CV AB.
    Study on heat losses during flame impingement in a diesel engine using phosphor thermometry surface temperature measurements2019In: SAE Technical Papers, ISSN 0148-7191Article in journal (Refereed)
    Abstract [en]

    In-cylinder heat losses in diesel engines decrease engine efficiency significantly and account for approximately 14-19% [1, 2, 3] of the injected fuel energy. A great part of the heat losses during diesel combustion presumably arises from the flame impingement onto the piston. Therefore, the present study investigates the heat losses during flame impingement onto the piston bowl wall experimentally. The measurements were performed on a full metal heavy-duty diesel engine with a small optical access through a removed exhaust valve. The surface temperature at the impingement point of the flame was determined by evaluating a phosphor's temperature dependent emission decay. Simultaneous cylinder pressure measurements and high-speed videos are associated to the surface temperature measurements in each cycle. Thus, surface temperature readings could be linked to specific impingement and combustion events. The results showed a sharp increase of the surface temperature during the flame impingement and an abrupt decrease as the flame disappeared.

  • 33.
    Binder, Christian
    et al.
    Scania CV AB.
    Vasanth, E.
    Norling, Daniel
    Scania CV AB.
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Experimental Determination of the Heat Transfer Coefficient in Piston Cooling Galleries2018In: SAE Technical Papers, ISSN 0148-7191Article in journal (Refereed)
    Abstract [en]

    Piston cooling galleries are critical for the pistons’ capability to handle increasing power density while maintaining the same level of durability. However, piston cooling also accounts for a considerable amount of heat rejection and parasitic losses. Knowing the distribution of the heat transfer coefficient (HTC) inside the cooling gallery could enable new designs which ensure effective cooling of areas decisive for durability while minimizing parasitic losses and overall heat rejection. In this study, an inverse heat transfer method is presented to determine the spatial HTC distribution inside the cooling gallery based on surface temperature measurements with an infrared (IR) camera. The method utilizes a piston specially machined so it only has a thin sheet of material of a known thickness left between the cooling gallery and the piston bowl. The piston - initially at room temperature - is heated up with warm oil injected into the cooling gallery. The transient of the piston’s outer surface temperature is captured with an IR camera from the top. Combining the temperature transient of each pixel, the HTC is later obtained through an inverse heat transfer solver based on one-dimensional heat conduction inside the piston material. To the authors’ knowledge, the current study presents the first application of an inverse heat transfer method for spatially resolved and experimentally determined heat transfer coefficients inside a piston cooling gallery. Preliminary measurements at standstill to demonstrate the method display an area of increased heat transfer where the entering oil jet impinges onto the wall of the cooling gallery.

  • 34.
    Crescenzo, Domenico
    et al.
    KTH.
    Olsson, Viktor
    KTH.
    Arco Sola, Javier
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Wu, Hongwen
    KTH.
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Lycke, Eric
    Leufven, O.
    Stenlåås, Ola
    Turbocharger Speed Estimation via Vibration Analysis2016In: SAE technical paper series, ISSN 0148-7191, Vol. 2016-April, no AprilArticle in journal (Refereed)
    Abstract [en]

    Due to demanding legislation on exhaust emissions for internal combustion engines and increasing fuel prices, automotive manufacturers have focused their efforts on optimizing turbocharging systems. Turbocharger system control optimization is difficult: Unsteady flow conditions combined with not very accurate compressor maps make the real time turbocharger rotational speed one of the most important quantities in the optimization process. This work presents a methodology designed to obtain the turbocharger rotational speed via vibration analysis. Standard knock sensors have been employed in order to achieve a robust and accurate, yet still a low-cost solution capable of being mounted on-board. Results show that the developed method gives an estimation of the turbocharger rotational speed, with errors and accuracy acceptable for the proposed application. The method has been evaluated on a heavy duty diesel engine.

  • 35.
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    A computer-controlled bowing machine (MUMS)1992In: STL-QPSR, Vol. 33, no 2-3, p. 61-66Article in journal (Other academic)
    Abstract [en]

    MUMS is a  bowing machine, i.e., a  machine that bows (plays) a  violin in a controlled  and  repeatable  manner  by  mechanical means. Traditionally, the main application of bowing machines has  been in studying  string vibrations and violins under  reproducible conditions. MUMS uses  a normal bow to  excite  the violin, which also allows a comparison of different bows and their influence on the string vibrations. The position and velocity of the bow and the force between bow and string ("bow pressure") can be specified and controlled within close limits. MUMS consists of two parts; a converted printer which contains the mechanical support of the bow and motors for bow motion and force, and a PC-computer which controls the motion by software servos.

  • 36.
    Cronhjort, Andreas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. Scania CV AB.
    Dahlén, Lars
    Diesel Flame Studies in an Optical Engine2004Conference paper (Refereed)
    Abstract [en]

    A diesel engine with optical access through an extended piston has been developed. It is based on a heavy duty truck engine and the purpose is to generate calibration data for computer simulation of spray combustion, hereby facilitating reliable combustion prediction using Computational Fluid Dynamics (CFD). Conventional photography using a solid-state camera was adopted to image the combustion. As the upper surface of the glass window in the piston is flat, the compression ratio of the engine is reduced to 12:1, in order to avoid that the spray plumes hit the glass surface. To compensate for the lowered compression ratio, the inlet pressure as well as the inlet temperature were increased. As top dead center conditions regarding gas density and temperature are desired to be maintained, this approach results in an increased overall air-to-fuel ratio. Additionally, the cylinder pressure decay due to the piston movement becomes slower than it should be at the present engine speed. However, despite these drawbacks, the engine allows for spray combustion studies under realistic diesel engine conditions regarding pressure and temperature. In the preliminary study the inlet pressure was 400 kPa absolute and the temperature was 450 K, resulting in a compression pressure of about 8.6 MPa at top dead center when the engine runs at 1200 rpm. To predict the air mass in the cylinder as accurately as possible, the exhaust back pressure is always kept equal to the inlet pressure. To minimize the thermal load on the piston, fuel is injected only during cycles when an image is exposed. This is also beneficial when estimating the air mass in the cylinder, as the temperature of the rest gas from the preceding cycle is quite low. In the preliminary study a nozzle with eight orifices fitted to a common-rail injector was used to generate the sprays. The orifice diameter was 190 µm. The rail pressure was 160 MPa and the injected amount of fuel was 80 mg. The resulting combustion was dominated by diffusion flames.

  • 37.
    Cronhjort, Andreas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Gåsste, Jan
    Konstanzer, Dennis
    Advanced control system for optical diesel spray analysis in a pressurized vessel1997Conference paper (Refereed)
    Abstract [en]

    An advanced control system to enable systematic photographic studies of diesel injections has been developed. The system automatically generates series of photos under predefined conditions. The injections are made in a pressurized vessel. The temperature in the vessel can be varied between 30 °C and 100 °C and the gas pressure between 0.1 MPa and 5 MPa. The entire system is controlled by a computer, and therefore the safety level is very high when performing experiments under extreme conditions. During the injection sequence the system can be remote controlled and monitored from another computer. The timing of the image acquisition is adjustable with an accuracy of 1 µs. Up to four separate flashes can be used to achieve multiple exposures of the film. The four flashes can also be fired simultaneously in order to increase the optical energy in the flash. When using double exposure at a low level of optical magnification the spray tip velocity can be determined. If the double exposure facility is used in conjunction with a high magnification the droplet speed can be measured.

    The system has been used to study the spray penetration into air at 60 °C and 4.2 MPa. The air density corresponds to full load conditions in a direct injected 2 liter per cylinder heavy duty diesel engine. The peak injection pressure was 140 MPa. To minimize the influence of cycle to cycle variations the median values of several images have been used. The results have been compared with computer simulations.

  • 38.
    Csontos, Botond
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Contaminants Affecting the Formation of Soft Particles in Bio-Based Diesel Fuels during Degradation2019Conference paper (Refereed)
  • 39. Dembinski, H.
    et al.
    Ängström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Swirl and injection pressure impact on after-oxidation in diesel combustion, examined with simultaneous combustion image velocimetry and two colour optical method2013In: SAE Technical Papers: Volume 2, 2013, S A E Inc , 2013, Vol. 2, p. 2013-01-0913-Conference paper (Refereed)
    Abstract [en]

    After-oxidation in Heavy Duty (HD) diesel combustion is of paramount importance for emissions out from the engine. During diffusion diesel combustion, lots of particulate matter (PM) is created. Most of the PM are combusted during the after-oxidation part of the combustion. Still some of the PM is not, especially during an engine transient at low lambda. To enhance the PM oxidation in the late engine cycle, swirl together with high injection pressure can be implemented to increase in-cylinder turbulence at different stages in the cycle. Historically swirl is known to reduce soot particulates. It has also been shown, that with today's high injection pressures, can be combined with swirl to reduce PM at an, for example, engine transient. The mechanism why the PM engine out is reduced also at high injection pressures is however not so well understood. In this work flow field data during combustion and after-oxidation together with soot and temperature measurements was combined to examine how flow field affects soot formation and oxidation. Swirl number was varied together with injection pressure and the engine tests were done in a HD optical engine. The load was set to 10 bar & 20 bar IMEP at low lambda without EGR, typically transient load points. A high speed colour camera captures picture of the combustion seen through a glass piston-bowl. The flow field was extracted with combustion image velocimetry (CIV) that traces the glowing soot particulates (or the light luminosity difference) by cross correlation between two pictures from the high speed colour camera. From the same pictures the KL factor and flame temperature were simultaneously calculated with the 2-colour method. Both CIV and the 2-colour method are line of sight optical methods that catches flow, soot and temperature from the light observed through the piston. It was found that in the after-oxidation part of the cycle, the flow in the piston bowl deviates strongly from solid body rotation (that can be assumed to be the case before injection). With increased injection pressure this deviation from solid body rotation increased at constant swirl number. When swirl number was increased, the deviation from solid body rotation increased even further. This seems to be an important factor during the after-oxidation part of the combustion by amplifying the turbulence. The flame temperature together with KL factor (a measure of soot density inside the cylinder) was also influenced when the flow field in the cylinder was changed. With increased injection pressure, from 500 bar to 1000 bar, the maximum KL was amplified during combustion with 50%, but the measured tail pipe soot was decreasing from 1.22 FSN to 0.49 FSN. This together with increased solid body deviation for the 1000 bar case, at the after-oxidation part of the combustion, leads to the conclusion: The flow field during the late part of the cycle has strong impact on tail pipe soot emissions. What was created during the diffusion combustion has less impact on the tail pipe soot compared to the flow field effects during after-oxidation.

  • 40.
    Dembinski, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Flow measurements using combustion image velocimetry in diesel engines2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work shows the in-cylinder airflow, and its effects on combustion and emissions, in a modern, heavy-duty diesel engine. The in-cylinder airflow is examined experimentally in an optical engine and the flow field inside the cylinder is quantified and shown during combustion, crank angle resolved. Cross-correlation on combustion pictures, with its natural light from black body radiation, has been done to calculate the vector field during the injection and after-oxidation period. In this work, this technique is called combustion image velocimetry (CIV). The quantified in-cylinder flow is compared with simulated data, calculated using the GT-POWER 1-D simulation tool, and combined with single-cylinder emission measurements at various in-cylinder airflows. The airflow in the single cylinder, characterised by swirl, tumble and turbulent intensity, was varied by using an active valve train (AVT), which allowed change in airflow during the engine’s operation. The same operation points were examined in the single-cylinder engine, optical engine and simulated in GT-POWER.

    This work has shown that the in-cylinder airflow has a great impact on emissions and combustion in diesel engines, even at injection pressures up to 2,500 bar, with or without EGR and load up to 20-bar IMEP. Swirl is the strongest player to reduce soot emissions. Tumble has been shown to affect soot emissions negatively in combination with swirl. Tumble seems to offset the swirl centre and the offset is observed also after combustion in the optical engine tests. Injection pressure affects the swirl at late crank angle degrees during the after-oxidation part of the combustion. Higher injection pressure gives a higher measured swirl. This increase is thought to be created by the fuel spray flow interaction. The angular velocity in the centre of the piston bowl is significantly higher compared with the velocity in the outer region of the bowl. Higher injection pressure gives larger difference of the angular velocity.

    Calculated swirl number from the CIV technique has also been compared with other calculation methods, GT-POWER and CFD-based method. The result from the CIV technique are in line with the other methods. CFD-based calculations, according to [62], has the best fit to the CIV method. The GT-POWER calculations shows the same trend at low swirl number, but at high swirl number the two methods differs significantly.

  • 41.
    Dembinski, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    In-cylinder Flow Characterisation of Heavy Duty Diesel Engines Using Combustion Image Velocimetry2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In-cylinder flow in diesel engines has a large impact on combustion and emission formation. In this work, the flow is characterised with a new measurement method called combustion image velocimetry (CIV). This technique is used to explain how airflow introduced during induction affects soot emissions and interacts with injection pressures up to 2500 bar. The CIV measurements enable flow analysis during the combustion and post-oxidation phases. The flow velocities inside the cylinder of a heavy duty optical engine, was measured with a crank angle (CA) resolution of 0.17° at injection pressures of 200–2500 bar and up to nearly full load (20 bar indicated mean effective pressure (IMEP)), were investigated with this method. The flow field results were combined with optical flame temperature and soot measurements, calculated according to Planck’s black body radiation theory.

    At the high injection pressures typical of today’s production standard engines and with rotational in-cylinder flow about the cylinder axis, large deviations from solid-body rotational flow were observed during combustion and post-oxidation. The rotational flow, called swirl, was varied between swirl number (SN) 0.4 and 6.7. The deviation from solid-body rotational flow, which normally is an assumption made in swirling combustion systems, formed much higher angular rotational velocities of the air in the central region of the piston bowl than in the outer part of the bowl. This deviation has been shown to be a source for turbulent kinetic energy production, which has the possibility to influence soot burn-out during the post-oxidation period.

    The measured CIV data was compared to Reynolds-averaged Navier–Stokes (RANS) CFD simulations, and the two methods produced similar results for the flow behaviour. This thesis describes the CIV method, which is closely related to particle image velocimetry (PIV). It was found in this work that the spatial plane in the cylinder evaluated with CIV corresponds to a mean depth of 3 mm from the piston bowl surface into the combustion chamber during combustion. During the post-oxidation phase of combustion, the measured spatial plane corresponds to a mean value of the total depth of the cylinder. The large bulk flow that contributes to the soot oxidation is thereby captured with the method and can successfully be analysed. The link between changes in in-cylinder flow and emissions is examined in this work.

  • 42.
    Dembinski, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    An Experimental Study of the Influence of Variable In-Cylinder Flow, Caused by Active Valve Train, on Combustion and Emissions in a Diesel Engine at Low Lambda Operation2011Conference paper (Refereed)
    Abstract [en]

    Spray and mixture formation in a compression ignition engine is of paramount importance for diesel combustion. In engine transient operation, when the load increases rapidly, the combustion system needs to handle low lambda (λ) operation while avoiding high particle emissions. Single cylinder tests were performed to evaluate the effect of differences in cylinder flow on combustion and emissions at typical low λ transient operation. The tests were performed on a heavy duty single cylinder test engine with Lotus Active Valve Train (AVT) controlling the inlet airflow. The required swirl number (SN) and tumble were controlled by applying different inlet valve profiles and opening either both inlet valves or only one or the other. The operating point of interest was extracted from engine transient conditions before the boost pressure was increased and investigated further at steady state conditions. The AVT enabled the resulting SN to be controlled at bottom dead centre (BDC) from ~0.3 to 6.8 and tumble from ~0.5 to 4. The fuel injection pressure was varied from 500 bar up to 2000 bar, with increments of 500 bar, for each SN and tumble setting. No exhaust gas recirculation was used in following tests. GT-POWER was used to calculate SN, tumble, and turbulent intensity with the different valve settings. The input data for the GT-POWER flow calculations were measured in a steady-state flow rig with honeycomb torque measurement.

    The main conclusion of this study was that the air flow structure in the cylinder, characterized by SN, tumble, and turbulent intensity, has a significant effect on the resulting engine combustion and emissions for the investigated range of fuel injection pressures. By increasing SN above 3, while maintaining tumble at low levels, the engine could be run with richer air/fuel mixtures without further increasing smoke emissions at injection pressures 1000 bar and above. Also, NO

    xemissions decreased at λ below 1.3; ignition delay time decreased at higher tumble and turbulent levels; and higher levels of swirl resulted in more rapid combustion, decreasing smoke emissions at injection pressures over 1000 bar. Smoke emissions increase at higher engine speeds (above 1200 rpm) and high SN (above 6). The results of this study demonstrate that the mixing process controlled by in-cylinder flow (swirl and tumble) has a dominant effect on combustion.

  • 43.
    Dembinski, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Optical study of swirl during combustion in a CI engine with different injection pressures and swirl ratios compared with calculations2012In: SAE Technical Papers, Detroit: Society of Automotive Engineers, 2012Conference paper (Refereed)
    Abstract [en]

    Spray and mixture formation in a compression-ignition engine is of paramount importance in the diesel combustion process. In an ngine transient, when the load increases rapidly, the combustion system needs to handle low operation without producing high NO x emissions and large amounts of particulate matter. By changing the in-cylinder flow, the emissions and engine efficiency are affected.

    Optical engine studies were therefore performed on a heavy-duty engine geometry at different fuel injection pressures and inlet airflow characteristics. By applying different inlet port designs and valve seat masking, swirl and tumble were varied. In the engine tests, swirl number was varied from 2.3 to 6.3 and the injection pressure from 500 to 2500 bar. To measure the in-cylinder flow around TDC, particle image velocimetry software was used to evaluate combustion pictures. The pictures were taken in an optical engine using a digital high-speed camera. Clouds of glowing soot particles were captured by the camera and traced with particle image velocimetry software. The velocity-vector field from the pictures was thereby extracted and a mean swirl number was calculated. The swirl number was then compared with 1D simulation program GT-POWER and CFD based correlations. The GT-POWER simulations and CFD based correlation calculations were initiated from steady-state flow bench data on tested cylinder heads.

    The main conclusions from this study were that the mean swirl numbers, evaluated with the PIV software from combustion pictures around TDC, agreed with CFD based correlations and the low swirl numbers also correlated with the 1D-simulation program. Most of the induced swirl motion survives the compression and combustion, while the induced tumble does not survive to the late combustion phase. The tumble however, disturbs the swirl motion and offsets the swirl centre. This offset survives the compression and combustion. The diesel sprays that are injected symmetrically in the combustion chamber are thereby exposed to the swirl asymmetrically. This study also shows that the angular velocity at different piston bowl radii deviates from solid body rotation. The angular velocity is higher closer to the centre and decreases to be at the lowest value at the outer piston bowl edge. When the injection pressure is increased, the deviation from solid body rotation increases due to spray effects.

  • 44.
    Dembinski, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Swirl and Injection Pressure Effect on Post-Oxidation Flow Pattern Evaluated with Combustion Image Velocimetry, CIV, and CFD Simulation2013Conference paper (Refereed)
    Abstract [en]

    In-cylinder flow pattern has been examined experimentally in a heavy duty optical diesel engine and simulated with CFD code during the combustion and the post-oxidation phase. Mean swirling velocity field and its evolution were extracted from optical tests with combustion image velocimetry (CIV). It is known that the post-oxidation period has great impact on the soot emissions. Lately it has been shown in swirling combustion systems with high injection pressures, that the remaining swirling vortex in the post-oxidation phase deviates strongly from solid body rotation. Solid body rotation can only be assumed to be the case before fuel injection. In the studied cases the tangential velocity is higher in the centre of the piston bowl compared to the outer region of the bowl. The used CIV method is closely related to the PIV technique, but makes it possible to extract flow pattern during combustion at full load in an optical diesel engine. Injection pressure was varied from 200 up to 2500 bar at 1000 rpm without EGR. Swirl was varied between 1.2 and 6.4 at BDC. The CFD simulation was a sector simulation on the same in-cylinder geometry and boundary conditions as in the optical engine.

    The main findings show that with increased injection pressure, together with swirl, the angular velocity increases in the centre of the piston bowl meanwhile the angular velocity decreases slightly in the outer region. The total angular momentum decreases slightly when injection starts and the total rotational kinetic energy increases significantly. The redistribution of the angular velocity is caused by the driving force from the injection. When the swirling bulk flow acts on the injected spray/flame, its orbit is slightly directed to the leeward side of the swirl. When the flame is directed back to the cylinder centre, by the bowl, it has thereby an offset from where it is injected. This offset together with the high flow velocity from the flame increases the angular velocity in the central region of the combustion chamber. The angular velocity in the outer part of the bowl decreases slightly when angular momentum is moved into the centre of the bowl were the velocity increases. This deviation in angular velocity has been observed in both the CFD results and in the CIV results were it survives into the post-oxidation phase with slow dissipation during the expansion stroke. The dissipation is a source for late cycle turbulence generation that affects the soot oxidation.

  • 45.
    Dembinski, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    The effects of injection pressure on swirl and flow pattern in diesel combustionIn: International Journal of Engine Research, ISSN 1468-0874, E-ISSN 2041-3149Article in journal (Other academic)
  • 46.
    Dembinski, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Razzaq, H.
    In-Cylinder Flow Pattern Evaluated with Combustion Image Velocimetry, CIV, and CFD Calculations during Combustion and Post-Oxidation in a HD Diesel Engine2013Conference paper (Other academic)
    Abstract [en]

    In-cylinder flow pattern was evaluated during diesel combustion and post-oxidation in a heavy duty optical engine and compared with CFD calculations. In this work the recently developed optical method combustion image velocimetry (CIV) is evaluated. It was used for extracting the flow pattern during combustion and post-oxidation by tracing the glowing soot clouds in the cylinder. The results were compared with CFD sector simulation on the same heavy duty engine geometry. Load was 10 bar IMEP and injection pressure was varied in two steps together with two different swirl levels. The same variations were done in both the optical engine and in the CFD simulations.

    The main results in this work show that the CIV method and the CFD results catch the same flow pattern trends during combustion and post-oxidation. Evaluation of the CIV technique has been done on large scale swirl vortices and compared with the CFD results at different distances from the piston bowl surface. The flow field according to CIV is shown to resemble the flow quite near the optical piston bowl surface during the diffusion combustion period in the CFD results. During the after-oxidation period, the observed CIV data coincide with mean velocity data from CFD, calculated on the total depth from cylinder head to piston surface. Both methods indicate that the in-cylinder flow is strongly deviating from solid body rotation during the diffusion flame and after-oxidation period. This deviation is not so significant before injection. During the after-oxidation period, the deviation from solid body rotation increases with injection pressure.

  • 47.
    Ericsson, Gustav
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Westin, Fredrik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Optimizing the Transient of an SI-Engine Equipped with Variable Cam Timing and Variable Turbine2010In: SAE International Journal of Engines, ISSN 1946-3936, Vol. 3, no 1, p. 903-915Article in journal (Refereed)
    Abstract [en]

    As the engines of today decrease in displacement with unchanged power output, focus of today's research is on transient response. The trend of today is to use a turbocharger with high boost level. For SI-engines a regular WG turbocharger has been used, but in the future, when the boost level increases together with higher demand on the transient response, a Variable Nozzle Turbine (VNT) will be used together with Variable Valve Timing (VVT). As the degree of freedom increases, the control strategies during a transient load step will be more difficult to develop. A 1D simulation experiment has been conducted in GT Power where the transient simulation was "frozen" at certain time steps. The data from these time steps was put in a stationary simulation and the excessive energy was then bled off to obtain the same conditions for the engine in the stationary simulation as if the engine where in the middle of the transient. This method allows a faster and easier way to obtain a good control strategy for the VNT turbine and the VVT during a transient load step. The method can be used to find VNT/VVT settings strategies for the transient control with a good and robust result.

  • 48.
    Gundmalm, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Divided Exhaust Period on Heavy-Duty Diesel Engines2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Due to growing concerns regarding global energy security and environmental sustainability it is becoming increasingly important to increase the energy efficiency of the transport sector. The internal combustion engine will probably continue to be the main propulsion system for road transportation for many years to come. Hence, much effort must be put in reducing the fuel consumption of the internal combustion engine to prolong a future decline in fossil fuel production and to reduce greenhouse gas emissions.

    Turbocharging and variable valve actuation applied to any engine has shown great benefits to engine efficiency and performance. However, using a turbocharger on an engine gives some drawbacks. In an attempt to solve some of these issues and increase engine efficiency further this thesis deals with the investigation of a novel gas exchange concept called divided exhaust period (DEP). The core idea of the DEP concept is to utilize variable valve timing technology on the exhaust side in combination with turbocharging. The principle of the concept is to let the initial high energy blow-down pulse feed the turbocharger, but bypass the turbine during the latter part of the exhaust stroke when back pressure dominates the pumping work. The exhaust flow from the cylinder is divided between two exhaust manifolds of which one is connected to the turbine, and one bypasses the turbine. The flow split between the manifolds is controlled with a variable valve train system.

    The DEP concept has been studied through simulations on three heavy-duty diesel engines; one without exhaust gas recirculation (EGR), one with short route EGR and one with long route EGR. Simulations show a potential improvement to pumping work, due to reduced backpressure, with increased overall engine efficiency as a result. Although, the efficiency improvement is highly dependent on exhaust valve size and configuration due to issues with choked flow in the exhaust valves. The EGR system of choice also proves to have a high impact on the working principle of the DEP application. Furthermore, the DEP concept allows better control of the boost pressure and allows the turbine to operate at higher efficiency across the whole load and speed range. The option of discarding both wastegate and variable geometry turbine is apparent, and there is little need for a twin-entry type turbine since pulse interference between cylinders is less of an issue.

  • 49.
    Gundmalm, Stefan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Divided Exhaust Period: Effects of Changing the Relation between Intake, Blow-Down and Scavenging Valve Area2013In: SAE World Congress 2013, 2013Conference paper (Refereed)
    Abstract [en]

    In a previous paper we showed the effects of applying the Divided Exhaust Period (DEP) concept on two heavy-duty diesel engines, with and without Exhaust Gas Recirculation (EGR). Main findings were improved fuel consumption due to increased pumping work, improved boost control and reduced residual gas content. However, some limitations to the concept were discovered.  In the case of high rates of short route EGR, it was apparent that deducting the EGR flow from the turbine manifold impaired optimal valve timing strategies. Furthermore, for both of the studied engines it was clear that the size and ratio of blow-down to scavenging valve area is of paramount importance for engine fuel efficiency.

    In this paper, the DEP concept has been studied together with a long route EGR system. As expected it gave more freedom to valve timing strategies when driving pressure for EGR is no longer controlled with the valve timing, as in the short route case. However, when evaluating different combinations of intake, blow-down and scavenging valve area, the optimal relation proves to be strongly dependent on the current EGR system and EGR rates. Hence, for different engine setups the trade-off between total intake and total exhaust area needs to be re-evaluated for optimal engine fuel efficiency. This paper also presents general trends in how different valve timing strategies and EGR rates affect both pumping work and boost pressure.

  • 50.
    Gundmalm, Stefan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Divided Exhaust Period: Effects of Changing the Relation between Intake, Blow-Down and Scavenging Valve Area2013In: SAE International Journal of Engines, ISSN 1946-3936, Vol. 6, no 2, p. 739-750Article in journal (Refereed)
    Abstract [en]

    In a previous paper we showed the effects of applying the Divided Exhaust Period (DEP) concept on two heavy-duty diesel engines, with and without Exhaust Gas Recirculation (EGR). Main findings were improved fuel consumption due to increased pumping work, improved boost control and reduced residual gas content. However, some limitations to the concept were discovered. In the case of high rates of short route EGR, it was apparent that deducting the EGR flow from the turbine manifold impaired optimal valve timing strategies. Furthermore, for both of the studied engines it was clear that the size and ratio of blow-down to scavenging valve area is of paramount importance for engine fuel efficiency. In this paper, the DEP concept has been studied together with a long route EGR system. As expected it gave more freedom to valve timing strategies when driving pressure for EGR is no longer controlled with the valve timing, as in the short route case. However, when evaluating different combinations of intake, blow-down and scavenging valve area, the optimal relation proves to be strongly dependent on the current EGR system and EGR rates. Hence, for different engine setups the trade-off between total intake and total exhaust area needs to be re-evaluated for optimal engine fuel efficiency. This paper also presents general trends in how different valve timing strategies and EGR rates affect both pumping work and boost pressure.

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