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In-cylinder Flow Characterisation of Heavy Duty Diesel Engines Using Combustion Image Velocimetry
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
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: urn:nbn:se:kth:diva-136978ISBN: 978-91-7501-963-5 (print)OAI: oai:DiVA.org:kth-136978DiVA: diva2:677626
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
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
4.
The record could not be found. The reason may be that the record is no longer available or you may have typed in a wrong id in the address field.
5. In-Cylinder Flow Pattern Evaluated with Combustion Image Velocimetry, CIV, and CFD Calculations during Combustion and Post-Oxidation in a HD Diesel Engine
Open this publication in new window or tab >>In-Cylinder Flow Pattern Evaluated with Combustion Image Velocimetry, CIV, and CFD Calculations during Combustion and Post-Oxidation in a HD Diesel Engine
2013 (English)Conference paper, Published 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.

Series
SAE Technical Paper, 2013-24-0064
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-136975 (URN)10.4271/2013-24-0064 (DOI)2-s2.0-84890334405 (Scopus ID)
Conference
SAE 11th International Conference on Engines & Vehicles; Capri, Napoli, Italy, September 15-19, 2013
Note

QC 20131210

Available from: 2013-12-10 Created: 2013-12-10 Last updated: 2013-12-10Bibliographically approved
6. Swirl and Injection Pressure Effect on Post-Oxidation Flow Pattern Evaluated with Combustion Image Velocimetry, CIV, and CFD Simulation
Open this publication in new window or tab >>Swirl and Injection Pressure Effect on Post-Oxidation Flow Pattern Evaluated with Combustion Image Velocimetry, CIV, and CFD Simulation
2013 (English)Conference paper, Published 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.

Series
SAE technical paper
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-136977 (URN)10.4271/2013-01-2577 (DOI)2-s2.0-84890339703 (Scopus ID)
Conference
SAE/KSAE 2013 International Powertrains,Fuels & Lubricants Meeting
Note

QC 20131210

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

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CiteExportLink to record
Permanent link

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Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
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  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
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  • text
  • asciidoc
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