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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
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
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. 2011-01-1830- p.
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-86208DOI: 10.4271/2011-01-1830Scopus ID: 2-s2.0-84881194304OAI: oai:DiVA.org:kth-86208DiVA: diva2:500548
Conference
SAE Japan
Note
QC 20120215Available from: 2012-02-15 Created: 2012-02-13 Last updated: 2013-12-10Bibliographically approved
In thesis
1. Flow measurements using combustion image velocimetry in diesel engines
Open this publication in new window or tab >>Flow measurements using combustion image velocimetry in diesel 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:nbn:se:kth:diva-90817 (URN)
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
2. In-cylinder Flow Characterisation of Heavy Duty Diesel Engines Using Combustion Image Velocimetry
Open this publication in new window or tab >>In-cylinder Flow Characterisation of Heavy Duty Diesel Engines Using Combustion Image Velocimetry
2014 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. vi, 97 p.
Series
TRITA-MMK, ISSN 1400-1179 ; 2013:17
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-136978 (URN)978-91-7501-963-5 (ISBN)
Public defence
2014-01-15, Q1, Osquldasväg 4, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20131210

Available from: 2013-12-10 Created: 2013-12-10 Last updated: 2014-01-20Bibliographically approved

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