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Laser Diagnostics of HCCI and Partially Premixed Combustion

Hildingsson, Leif (2006)
Abstract
The work presented in this thesis deals with measuring in-cylinder combustion species and events using different laser-based diagnostic methods. A variety of engine operating modes, like HCCI and partially premixed diesel combustion, have been investigated.



In the very first measurements, in-cylinder flow-fields were compared to CFD and steady-state blow rig results. After that, the ignition and combustion process of HCCI was investigated using laser-induced fluorescence (LIF) of formaldehyde and hydroxyl. In the low-temperature reactions that precede the main combustion, formaldehyde (HCOH) was seen to form homogeneously over the viewed area. Hydroxyl, OH, is formed in the high temperature regions that mark the main... (More)
The work presented in this thesis deals with measuring in-cylinder combustion species and events using different laser-based diagnostic methods. A variety of engine operating modes, like HCCI and partially premixed diesel combustion, have been investigated.



In the very first measurements, in-cylinder flow-fields were compared to CFD and steady-state blow rig results. After that, the ignition and combustion process of HCCI was investigated using laser-induced fluorescence (LIF) of formaldehyde and hydroxyl. In the low-temperature reactions that precede the main combustion, formaldehyde (HCOH) was seen to form homogeneously over the viewed area. Hydroxyl, OH, is formed in the high temperature regions that mark the main combustion; it was determined that OH is formed in areas from which formaldehyde had disappeared. By using different start of injection timings, different degrees of homogeneity could be obtained for HCCI combustion and the effects of this were examined using the above mentioned laser-technique. The engine-out NOx level was monitored to see what in-homogeneity level could be tolerated before getting too much NOx. Going from early injections towards late, a distinct change in the homogeneity was seen with injection at 70 CAD and around 50 CAD NOx levels started to increase. Later, LIF measurements were performed on combustion modes other than HCCI, these studies also included the use of exhaust gas recirculation (EGR). The modes that were examined and compared with port and DI HCCI were UNIBUS combustion using two fuel injection events and low-temperature diesel combustion with one injection 8 crank angles before top dead centre.



The feasibility of using formaldehyde, or other partially-oxidized fuel elements, as a naturally occurring fuel tracer were investigated by comparing the distribution of those species with that of the common fuel tracer toluene. The distributions of the two species are similar to each other in HCCI meaning that formaldehyde could be a tracer candidate. In low-temperature diesel, it seems like a good tracer; however more research is needed on the impact of polyaromatic hydrocarbons.



In the last part, high-dilution low-temperature diesel combustion was studied and during this time the first planar flow measurements in a firing diesel engine were obtained. Furthermore, LIF measurements of partially-oxidized fuel and LII of soot were performed. The initial distribution of partially-oxidized fuel was found to correlate well with regions of heat release that were identified from the flow field divergence. In the later stages of combustion, soot and partially-oxidized fuel were found to be concentrated in the cylinder centre and no bulk flow exist, at least not for our piston design, that transport this fluid to regions where oxidation could take place. Partially-oxidized fuel was also found in the squish region which can be a source of emissions of CO and unburned fuel. It was also seen that single-cycle measurements show good similarity to the mean results.



In the very last study that is presented, the flow structures of two low-temperature diesel operating conditions are compared at two swirl ratios. Differences are seen in the reverse-squish flow as well as in the fluid motion near the bowl rim. The main influence of decreasing the swirl was that the fluid motion at the bowl rim was altered. (Less)
Abstract (Swedish)
Popular Abstract in Swedish

Undersökningarna som presenteras i avhandlingen behandlar mätning av produkter från och händelser i förbränningsprocessen genom att använda laserbaserade mätmetoder. Ett antal olika körfall, som HCCI och partially premixed combustion (PPC), har undersökts.



I de första mätningarna som presenteras jämförs uppmätta flödesfält i cylindern med resultat från CFD och blåsriggskörningar. Därefter undersöks tändnings- och förbränningsprocessen i HCCI med hjälp av LIF av formaldehyd och hydroxyl. I de lågtemperaturreaktioner som inträffar innan huvudförbränningen sågs formaldehyd (HCOH) bildas homogent i det undersökta området. Hydroxyl, OH, bildas i de regioner med... (More)
Popular Abstract in Swedish

Undersökningarna som presenteras i avhandlingen behandlar mätning av produkter från och händelser i förbränningsprocessen genom att använda laserbaserade mätmetoder. Ett antal olika körfall, som HCCI och partially premixed combustion (PPC), har undersökts.



I de första mätningarna som presenteras jämförs uppmätta flödesfält i cylindern med resultat från CFD och blåsriggskörningar. Därefter undersöks tändnings- och förbränningsprocessen i HCCI med hjälp av LIF av formaldehyd och hydroxyl. I de lågtemperaturreaktioner som inträffar innan huvudförbränningen sågs formaldehyd (HCOH) bildas homogent i det undersökta området. Hydroxyl, OH, bildas i de regioner med högtemperaturreaktioner som markerar huvudförbränningen; bildandet av OH sågs i områden från vilka formaldehyd hade försvunnit. Genom att använda olika insprutningstidpunkter kunde olika grader av homogenitet erhållas och effekterna av detta studerades m.h.a. ovan nämnda lasermätmetod. Även emissionsnivåerna av NOx mättes för att avgöra hur stor inhomogenitet som kunde tolereras innan för höga NOx-nivåer erhölls. Genom att gå från tidig mot sen insprutning sågs en tydlig ändring av homogenitetsgraden vid insprutning vid 70 CAD och runt 50 CAD började NOx-nivån öka. Senare utfördes LIF-mätningar även av andra körfall än HCCI, dessa studier innefattade även användning av recirkulerade avgaser (EGR). De körfall som jämfördes med port- och direktinsprutad HCCI var UNIBUS, med två insprutningar, och lågtemperatur dieselförbränning med en insprutning 8 CAD före övre dödläget.



Möjligheten att använda formaldehyd, eller andra delvis oxiderade bränsledelar, som en naturligt förekommande bränsletracer undersöktes genom att jämföra fördelningen av dessa ämnen i cylindern med fördelningen av en vanlig tracer, i detta fall toluen. Fördelningen av de ämnena två liknar varandra i HCCI vilket innebär att formaldehyd kan vara en möjlig bränsletracer. I lågtemperatur dieselförbränning kan det också vara en tänkbar tracer, men fler undersökningar krävs om inverkan av polyaromatiska kolväten på den uppmätta signalen.



Lågtemperatur dieselförbränning med hög EGR-nivå studerades i den senare delen av avhandlingsarbetet och under denna tid gjordes de första flödesmätningarna i ett plan i en dieselmotor under förbränning. LIF-mätningar av delvis oxiderat bränsle och LII av sot genomfördes också. Regioner med delvis oxiderat bränsle fanns korrelera väl med regioner med värmefrigörelse; de senare identifierades från divergensen i flödesfältet. I den senare delen av förbränningen fanns sot och delvis oxiderat bränsle koncentrerat mot cylinderns centrum och inget flöde fanns som skulle kunna transportera dessa produkter till områden där oxidation kan fortgå. Delvis oxiderat bränsle upptäcktes även i squish-regionen och detta kan vara en källa till utsläpp av CO och obränt bränsle. En god överrensstämmelse sågs mellan enskilda mätningar och deras medelvärden.



I den allra sista undersökningen som presenteras jämförs flödesstrukturen för två olika lågtemperatur dieselkörfall, båda med låg och hög swirl. Skillnader sågs i reverse-squish flödet och i flödet runt kanten på bowlen. Den största skillnaden som sågs vid en minskning av swirltalet var att flödet vid bowl-kanten ändrades. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Professor Taylor, Alexander, Imperial College, London
organization
publishing date
type
Thesis
publication status
published
subject
keywords
low temperature combustion, Motorer, Motors and propulsion systems, Teknik, Technological sciences, PIV, in-cylinder flow structures, hydroxyl, OH, partially-oxidized fuel, formaldehyde, HCOH, LIF, diesel combustion, partially premixed combustion, PPC, HCCI, framdrivningssystem
pages
220 pages
publisher
Department of Energy Sciences, Lund University
defense location
Room M:A, M-building, Ole Römers väg 1, Faculty of Engineering, Lund University
defense date
2006-06-02 10:15:00
external identifiers
  • other:ISRN:LUTMDN/TMHP--06/1041--SE
ISBN
91-628-6849-7
language
English
LU publication?
yes
additional info
id
21fb1d4c-e534-420e-a7c9-0940ac55a146 (old id 546852)
date added to LUP
2016-04-01 16:13:53
date last changed
2018-11-21 20:39:46
@phdthesis{21fb1d4c-e534-420e-a7c9-0940ac55a146,
  abstract     = {The work presented in this thesis deals with measuring in-cylinder combustion species and events using different laser-based diagnostic methods. A variety of engine operating modes, like HCCI and partially premixed diesel combustion, have been investigated.<br/><br>
<br/><br>
In the very first measurements, in-cylinder flow-fields were compared to CFD and steady-state blow rig results. After that, the ignition and combustion process of HCCI was investigated using laser-induced fluorescence (LIF) of formaldehyde and hydroxyl. In the low-temperature reactions that precede the main combustion, formaldehyde (HCOH) was seen to form homogeneously over the viewed area. Hydroxyl, OH, is formed in the high temperature regions that mark the main combustion; it was determined that OH is formed in areas from which formaldehyde had disappeared. By using different start of injection timings, different degrees of homogeneity could be obtained for HCCI combustion and the effects of this were examined using the above mentioned laser-technique. The engine-out NOx level was monitored to see what in-homogeneity level could be tolerated before getting too much NOx. Going from early injections towards late, a distinct change in the homogeneity was seen with injection at 70 CAD and around 50 CAD NOx levels started to increase. Later, LIF measurements were performed on combustion modes other than HCCI, these studies also included the use of exhaust gas recirculation (EGR). The modes that were examined and compared with port and DI HCCI were UNIBUS combustion using two fuel injection events and low-temperature diesel combustion with one injection 8 crank angles before top dead centre.<br/><br>
<br/><br>
The feasibility of using formaldehyde, or other partially-oxidized fuel elements, as a naturally occurring fuel tracer were investigated by comparing the distribution of those species with that of the common fuel tracer toluene. The distributions of the two species are similar to each other in HCCI meaning that formaldehyde could be a tracer candidate. In low-temperature diesel, it seems like a good tracer; however more research is needed on the impact of polyaromatic hydrocarbons.<br/><br>
<br/><br>
In the last part, high-dilution low-temperature diesel combustion was studied and during this time the first planar flow measurements in a firing diesel engine were obtained. Furthermore, LIF measurements of partially-oxidized fuel and LII of soot were performed. The initial distribution of partially-oxidized fuel was found to correlate well with regions of heat release that were identified from the flow field divergence. In the later stages of combustion, soot and partially-oxidized fuel were found to be concentrated in the cylinder centre and no bulk flow exist, at least not for our piston design, that transport this fluid to regions where oxidation could take place. Partially-oxidized fuel was also found in the squish region which can be a source of emissions of CO and unburned fuel. It was also seen that single-cycle measurements show good similarity to the mean results.<br/><br>
<br/><br>
In the very last study that is presented, the flow structures of two low-temperature diesel operating conditions are compared at two swirl ratios. Differences are seen in the reverse-squish flow as well as in the fluid motion near the bowl rim. The main influence of decreasing the swirl was that the fluid motion at the bowl rim was altered.},
  author       = {Hildingsson, Leif},
  isbn         = {91-628-6849-7},
  language     = {eng},
  publisher    = {Department of Energy Sciences, Lund University},
  school       = {Lund University},
  title        = {Laser Diagnostics of HCCI and Partially Premixed Combustion},
  year         = {2006},
}