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Flow-structures Generated by Valve and Piston Motion in an Exhaust Port of a Truck Engine
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0001-7715-863X
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0001-7330-6965
KTH, School of Engineering Sciences (SCI), Mechanics.
2013 (English)In: Proceedings of the 4th International Conference on Jets, Wakes and Separated Flows-IV, 2013Conference paper, Published paper (Refereed)
Abstract [en]

The exhaust port of a truck internal combustion engine forms the interface between the combustion engine and the turbocharger. Approximately 30-40% of the energy potential is lost in the exhaust gasses after combustion, which can be partially recuperated in a turbocharger. Hence, energy losses in the connection are highly undesired. However, due to the high occurring velocities and the complex geometry, flow separation, flowstructure formation, and secondary flow motion are the major sources of energy losses. Within the exhaust process, the valves open while the piston continues moving in the combustion camber. This process is often analyzed by modeling the piston and valves at fixed locations, but conserving the total mass flow. Using advanced methods, this process can be simulated numerically in a more accurate manner. This study compares Large Eddy Simulation based data, assessing the implied differences due to the choise of method for simulating the exhaust process from an engine cylinder. A simple case using fixed positions for valve and piston is contrasted with the cases where static valve and moving piston, and moving valve and moving piston are considered, respectively. The generated flow phenomena are  compared within the cases.

Place, publisher, year, edition, pages
2013.
Keyword [en]
Exhaust gas energy, Turbocharged engines, Automotive exhaust systems
National Category
Engineering and Technology
Research subject
SRA - Energy
Identifiers
URN: urn:nbn:se:kth:diva-134840OAI: oai:DiVA.org:kth-134840DiVA: diva2:668326
Conference
4th International Conference on Jets, Wakes and Separated Flows, ICJWSF2013,September 17-21, 2013, Nagoya, Japan
Note

QC 20131204

Available from: 2013-11-29 Created: 2013-11-29 Last updated: 2014-06-03Bibliographically approved
In thesis
1. Numerical Studies of Flow and AssociatedLosses in the Exhaust Port of a Diesel Engine
Open this publication in new window or tab >>Numerical Studies of Flow and AssociatedLosses in the Exhaust Port of a Diesel Engine
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the last decades, the focus of internal combustion engine development has moved towards more efficient and less pollutant engines. In a Diesel engine, approximately 30-40% of the energy provided by combustion is lost through the exhaust gases. The exhaust gases are hot and therefore rich of energy. Some of this energy can be recovered by recycling the exhaust gases into turbocharger. However, the energy losses in the exhaust port are highly undesired and the mechanisms driving the total pressure losses in the exhaust manifold not fully understood. Moreover, the efficiency of the turbine is highly dependent on the upstream flow conditions.

Thus, a numerical study of the flow in the exhaust port geometry of a Scania heavy-duty Diesel engine is carried out mainly by using the Large Eddy Simulation (LES) approach. The purpose is to characterize the flow in the exhaust port, analyze and identify the sources of the total pressure losses. Unsteady Reynolds Averaged Navier-Stokes (URANS) simulation results are included for comparison purposes. The calculations are performed with fixed valve and stationary boundary conditions for which experimental data are available. The simulations include a verification study of the solver using different grid resolutions and different valve lift states. The calculated numerical data are compared to existent measured pressure loss data. The results show that even global parameters like total pressure losses are predicted better by LES than by URANS. The complex three-dimensional flow structures generated in the flow field are qualitatively assessed through visualization and analyzed by statistical means. The near valve region is a major source of losses. Due to the presence of the valve, an annular, jet-like flow structure is formed where the high-velocity flow follows the valve stem into the port. Flow separation occurs immediately downstream of the valve seat on the walls of the port and also on the surface of the valve body. Strong longitudinal, non-stationary secondary flow structures (i.e. in the plane normal to the main flow direction) are observed in the exhaust manifold. Such structures can degrade the efficiency of a possible turbine of a turbocharger located downstream on the exhaust manifold.

The effect of the valve and piston motion has also been studied by the Large Eddy Simulation (LES) approach. Within the exhaust process, the valves open while the piston continues moving in the combustion chamber. This process is often analyzed modeling the piston and valves at fixed locations, but conserving the total mass flow. Using advanced methods, this process can be simulated numerically in a more accurate manner. Based on LES data, the discharge coefficients are calculated following the strict definition. The results show that the discharge coefficient can be overestimated (about 20 %) when using simplified experiments, e. g. flow bench. Simple cases using fixed positions for valve and piston are contrasted with cases which consider the motion of piston and/or valves. The overall flow characteristics are compared within the cases. The comparison shows it is impossible to rebuild the dynamic flow field with the simplification with fixed valves. It is better to employ LES to simulate the dynamic flow and associated losses with valve and piston motion.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. x, 81 p.
Series
Trita-MEK, ISSN 0348-467X ; 2013:19
Keyword
Internal Combustion Engine, Exhaust flow, Exhaust Valve, Exhaust Port, Large Eddy Simulation, Valve and Piston Motion, Total Pressure Losses, Energy Losses, Discharge coefficient, Flow Losses, Flow structures, Air Flow Bench, Engine-like Conditions
National Category
Engineering and Technology
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-134844 (URN)978-91-7501-957-4 (ISBN)
Public defence
2013-12-17, F3, Lindstedtsvägen 26, Kungliga Tekniska Högskolan, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20131204

Available from: 2013-12-04 Created: 2013-11-29 Last updated: 2013-12-04Bibliographically approved

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