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Flow measurements using combustion image velocimetry in diesel engines
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
2012 (English)Licentiate 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.

Place, publisher, year, edition, pages
Stockholm: Department of Machine design, Royal Institute of Technology , 2012. , 80 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2012:03
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-90817OAI: oai:DiVA.org:kth-90817DiVA: diva2:506694
Presentation
2012-03-01, B319 Gladan, Brinellvägen in 83, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20120302

Available from: 2012-03-02 Created: 2012-02-29 Last updated: 2013-11-12Bibliographically approved
List of papers
1. 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 Operation
Open this publication in new window or tab >>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 Operation
2011 (English)Conference paper, Published 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.

Place, publisher, year, edition, pages
Society of Automotive Engineers of Japan, Inc., 2011
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-86208 (URN)10.4271/2011-01-1830 (DOI)2-s2.0-84881194304 (Scopus ID)
Conference
SAE Japan
Note
QC 20120215Available from: 2012-02-15 Created: 2012-02-13 Last updated: 2013-12-10Bibliographically approved
2. Optical study of swirl during combustion in a CI engine with different injection pressures and swirl ratios compared with calculations
Open this publication in new window or tab >>Optical study of swirl during combustion in a CI engine with different injection pressures and swirl ratios compared with calculations
2012 (English)Conference paper, Published 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.

Place, publisher, year, edition, pages
Detroit: Society of Automotive Engineers, 2012
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-89095 (URN)2-s2.0-84877175283 (Scopus ID)
Conference
SAE 2012 World Congress, Detroit, USA, April 24-26, 2012
Note
QC 20120308Available from: 2012-04-24 Created: 2012-02-14 Last updated: 2013-12-10Bibliographically approved
3. The effects of injection pressure on swirl and flow pattern in diesel combustion
Open this publication in new window or tab >>The effects of injection pressure on swirl and flow pattern in diesel combustion
(English)In: International Journal of Engine Research, ISSN 1468-0874, E-ISSN 2041-3149Article in journal (Other academic) Submitted
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-90887 (URN)
Note
QS 2012 QS 20120326Available from: 2012-03-02 Created: 2012-03-02 Last updated: 2017-12-07Bibliographically approved

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