Combustion of Diesel sprays under real-engine like conditions: analysis of low- and high-temperature processes

Transcription

1 ILASS Europe 21, 23rd Annual Conference on Liquid Aomizaion and Spray Sysems, Brno, Czech Republic, Sepember 21 Combusion of Diesel sprays under real-engine like condiions: analysis of low- and high-emperaure processes M. Weclas *, J. Cypris and T.M.A. Maksoud * Georg Simon Ohm Universiy of Applied Sciences Nuremberg Faculy of Mechanical Engineering, Insiue of Vehicle echnology (IFZN) Kesslerplaz 12, 9489 Nuremberg, Germany Faculy of Advanced Technology Universiy of Glamorgan, Ponypridd, CF37 1DL, Wales, UK Absrac Mixure preparaion as creaed by Diesel injecion (sprays) as well as low- and high-emperaure oxidaion processes play a criical role in conrolling of engine combusion process, especially in corresponding exhaus emissions. The presen paper describes unique invesigaion on low-emperaure reacions (cool- and blueflames), hermal auo igniion and hea release of a non-premixed mixure under Diesel-engine like condiions. The experimens have been performed in a special high-pressure, high-emperaure consan volume (adiabaic) combusion chamber. The sysem simulaes he hermodynamic condiions ha can be found in a real engine cylinder a he momen of injecion begin (mosly close o he TDC of compression). Analysis of he process dynamics is of special ineres. For process analysis a model of a muli-sep oxidaion (igniion) has been consruced. In his model wo measured parameers are invesigaed: pressure disribuion and pressure gradien boh vs ime afer injecion sars. The whole process is analysed from he ime zero defined as a rigger signal for Diesel injecor (sar of injecion). The process has been analysed under differen es condiions: a consan iniial chamber pressures for a wide range of iniial emperaures, a consan chamber emperaure for differen iniial chamber pressures, a consan iniial chamber pressures as well as for a consan amoun of injeced fuel or for a consan air access raion. Addiionally, he delay ime and slopes have been analysed o describe he reacions dynamic. The auhors also defined crieria for hermal auo igniion process as well as for a ransiion from cool-flames o blue-flame reacions as well as o high-emperaure oxidaion process. The auhors have proposed a PPC-Posiive Pressure Coefficien (in analogy o a NTC) indicaing an influence of he combusion chamber pressure on he reacions dynamic. Inroducion Mixure preparaion process creaed by Diesel injecion significanly influences following processes including low- and high-emperaure oxidaion. The ime beween fuel injecion begin and he high-emperaure hea release process is defined as an igniion delay period. During his ime period a number of complex chemical and physical (especially for a non-premixed mixure) processes mus be performed. For example chemical reacions (so-called pre-igniion or low-emperaure oxidaion processes) are performed in order o prepare proper condiions for a hermal igniion (or auo igniion) process (depending on he emperaure and pressure condiions). From he poin of view of physical processes a fuel supply process (injecion), sprays disribuion in space, aomizaion, fuel vaporizaion and mixing wih air mus be considered. These processes are of special complexiy in he case of Diesel-like process where he resuling combusible mixure is highly non-homogeneous and is disribuion is ime-space dependen [1,2]. The presen paper describes unique invesigaion on low-emperaure reacions (cool- and blue-flames), hermal igniion and hea release of sprays under Diesel-engine like condiions. The low-emperaure oxidaion is usually reaed as a wo-sage process: a cool- and blue flames sage are followed by he high emperaure oxidaion (depends on he emperaure and pressure as well as on he mixure composiion) [3-8]. For he fuure clean combusion process (overall called homogeneous combusion processes) he chemisry of he pre-igniion reacions as well as conrolled auo igniion are key facors for conrolled process (especially in he case of variable engine loads and speeds). The process of auo igniion of a hydrocarbon fuels is chemically very complicaed and hundreds of chemical species paricipae in housands of reacions. The mos imporan reacions in he igniion process of hydrocarbon fuels have been seleced in [5]. Engine simulaor: high-emperaure, high-pressure consan volume combusion chamber There is a number of various ypes of rapid compression machines or combusion chambers known in he lieraure ha have been employed o sudy of low, inermediae- and high-emperaure chemisry [9-13]. In or- * Corresponding auhor: miroslaw.weclas@ohm-hochschule.de 1

2 ILASS Europe 21 Combusion of Diesel sprays under real-engine like condiions der o perform very deailed invesigaions on low-emperaure and high-emperaure oxidaion processes under engine like condiions having wide flexibiliy in seing he es condiions (especially iniial pressure and emperaure) a special high-pressure high-emperaure consan volume adiabaic combusion chamber has been buil and equipped wih Diesel common-rail injecion sysem. The sysem simulaes he hermodynamic condiions a he ime insance of injecion begin (mosly close o he TDC of compression in a real engine), however, he pressure and emperaure can be chosen independenly one anoher. Scheme and view of he combusion chamber is shown in Fig.1. Air supply Exhaus CR Injecor Pressure ransducer Elcronic conrol & daa acquisiion Cooling sysem for injecor & pressure sensor Termocouple Gaske ZrO 2 cover elecric conacs Combusion chamber Conrol & measuremen compuer CR injecion sysem Synheic air elecric conacs Pressure chamber Spark plug for igniion Hea isolaion Adiabaic High pressure pump wih driver & fuel ank Figure 1. Lef-Cross-secion of combusion chamber; Righ- Overall view of he es rig wih combusion chamber (engine simulaor) The es rig consiss of wo separae chambers: combusion chamber and insulaion (adiabaic) chamber. A view of he chamber head is shown in fig.2. Rail Pressure sensor Waer cooled injecor Air supply valve Pressure ransducer Exhaus valve Thermocouple for combusion chamber Combusion chamber head 2 Flow rae meer Figure 2. A view of he combusion chamber head The measuremen sysem can be divided in hree separae sub-sysems: sysem conrol; injecion sysem; measuremen sysem (see fig.3). Tes condiions and phenomenological model of he process Experimenal invesigaion presened in his paper considers Diesel engine-like condiions, however, no air moion in form of swirl or squish have been applied. The luck of air moion in he es chamber for promoing of fuel and air mixing allows analysis of a pure effec of Diesel sprays on a low- and high-emperaure oxidaion as well as on hermal auo igniion process. Special aenion is focussed on he analysis of process dynamics. I is well known in he lieraure ha depending on fuel chemical composiion, pressure and emperaure in combusion chamber wo differen mechanisms for igniion of hydrocarbon fuels may be seleced [8]: a single-sep and a muli-sep process. For process analysis a model of a muli-sep oxidaion (and igniion) has been consruced as presened in Fig.4. Characerisic poins and invesigaed parameers have been defined, as presened in his figure. The model does no include he range of so called slow combusion process.

3 ILASS Europe 21 Combusion of Diesel sprays under real-engine like condiions Injecion sysem, componens, hardware Injecion conrol Supply conrol ON / OFF Genoec conrol uni Injekor -5V Air or mixure supply synheische Luf -1bar Exhaus sysem Chamber heaing sysem Type E Type E Type E Type R Kisler Cooling sysem pc/bar - mv / 1Hz mv / 1Hz mv / 1Hz mv / 1Hz -1V 2kHz V Insrumenszei Naional USB-9211A Da s Bil d ka nn nic h an ge Insrumenszei Naional USB-6251 M-Series Da s Bil d ka nn nic h an ge Verbrennungs- Combusion Das Bild kann nich angezeig werden. Dieser Compuer verfüg möglicherweise chamber über kammer zu wenig Arbeisspeicher, um das Bild öffnen o Das Bild kann nich angezeig Prüfsands- werden. rechner Dieser Compuer verfüg mögliche e RS 232 RS W Spark plug igniion sysem Cooling sysem 1 DC moor; 2 high pressure pump; 3 pressure sensor; 4 filre; 5 fuel supply puimp (low pressure); 6 fuel ank; 7 supplier; 8 rail pressure seing valve; 9 common rail; 1 rail pressure sensor; 11 CR injecor; 12 fuel cooling; 13 pressurevalve;14 premixed mixure; 15 synheicair; 16 exhaussuckingsysemand gas analysaor; 17 power supply; 18 heaingelemen; 19 spark plugsupply; 2 spark plug; 21 piezo pressure ransducer; 22 cooling sysem of pressure ransducer: pump, waer ank, connecros;23 cooling sysem of fuelinjecor: pump, waerank, connecros; 24 charge amplifier; 25 conrollingpc; Figure 3. Subsysems of he engine simulaor (complee es rig) Definiion of characerisic poins in he model is given in Table 1. Zero-pressure line corresponds o he iniial chamber pressure measured a he poin of sar of fuel injecion (measured are hen he pressure changes in he chamber). Zero-ime poin corresponds o he ime insance a he poin of sar of fuel injecion (process is hen measured in ime afer injecion sars). p D dp/d p comb BF comb Comb CF TI BF p BF p CF p v C IB B A IB A C TI D CF BF comb v V CF BF 3 CF BF Comb oal oal ch (= v + CF + BF ) + phys Figure 4. Model of a muli-sep oxidaion (and igniion) processes used for pressure hisory analysis in he presen invesigaion The following characerisic parameers are seleced in his model: in general, he whole process consiss of four characerisic phases: iniial phase concerning sar of injecion and vaporizaion process (period beween poins IB and A); cool flame reacions (beween A and poin C); blue flame reacions (beween poins C and TI); high-emperaure oxidaion (from poin TI). 3

4 ILASS Europe 21 Combusion of Diesel sprays under real-engine like condiions duraion (ime window, period) of hese phases is described by characerisic duraion imes : v is he duraion of he firs phase; CF is he duraion of cool flame reacions; BF is he duraion of blue flame reacions; oal is he oal igniion delay defined as a sum of ch = v + CF BF and phys ; comb is he combusion duraion defined by he duraion of hea release process slope of paricular oxidaion process described by angle characerizing he rae of oxidaion process; CF, BF and comb are seleced; also a mean slope in bar/ms is considered characerisic ime of paricular phase of he process couned from he zero-ime poin a injecion begin (poin IB). This characerisic ime insances are measured by locaion of poins B, C and TI wih respec o he zero ime-line; characerisic pressures changes (pressure changes afer fuel injecion): p v negaive pressure change in he chamber characerized by a minimum pressure in he chamber resuling from he iniial vaporizaion of he injeced fuel; p CF pressure increase in he chamber resuling from he main par of cool flame oxidaion reacions; p BF pressure increase in he chamber resuling from he blue flame oxidaion reacions; p comb pressure increase in he chamber resuling from he high emperaure reacions (hea release). Table 1. Definiion of parameers in he model of fig.4. Poin /Parameer Descripion / definiion IB Sar of fuel injecion (zero-pressure line) pib TIB A B C TI D CF BF comb v CF BF comb ch phys CF BF comb pv pcf pbf pcomb Pressure chamber a he pin of sar of fuel injecion Gas emperaure in he chamber a he pin of sar of fuel injecion Poin of minim of pressure in he combusion chamber afer fuel injecion Poin of crossing of zero-pressure line afer fuel injecion Poin of ransiion from cool- o blue-flame reacions (low emperaure oxidaion) Poin of hermal igniion: ransiion from blue flame reacions (low emperaure oxidaion) o high emperaure oxidaion (hea release) Poin of maximum pressure in he chamber as a resul of high emperaure oxidaion Angle a which he slope line of cool flame reacions crosses he ime axis Angle a which he slope line of blue flame reacions crosses he ime axis Angle a which he slope line of high emperaure oxidaion crosses he ime axis Duraion of iniial vaporizaion phase Time window beween minimum of pressure and crossing of zero-pressure line Duraion of main par of cool flame reacions Duraion of iniial (premixed) phase of combusion (high emperaure oxidaion) Duraion of cool flame reacions Duraion of blue flame reacions Duraion of combusion (high emperaure oxidaion) Duraion of chemical igniion delay Duraion of physical par of igniion delay Characerisic ime of cool flame reacions Characerisic ime of blue flame reacions Characerisic ime of combusion (high emperaure oxidaion) Negaive pressure change in he chamber Pressure change in he chamber during main par of cool flame reacions Pressure change in he chamber during blue flame reacions Pressure change in he chamber during premixed phase of combusion Processes afer sar of fuel injecion in he chamber has been invesigaed under wo differen condiions: a consan emperaures T IB for differen chamber pressures p IB and consan amoun of injeced fuel m fuel. Temperaure range T IB = 2 C o 8 C; pressure range p IB = 5bar o 2bar. a consan chamber pressures p IB for differen emperaures T IB and consan air access raio. Temperaure range T IB = 2 C o 8 C; pressure range p IB = 5bar o 2bar. In a consan volume adiabaic combusion chamber he pressure gradiens (dp/d) corresponds o hea release rae (dq/d). Maximum of pressure gradien represen maximum of hea release rae. The characer of pressure gradien disribuion may also indicae characerisic process o be invesigaed. As used below, a single-peak (maximum) disribuion of pressure gradien indicaes hermal igniion for a single-sep igniion process or no igniion (low-emperaure oxidaion only) in he case of muli-sep process. Bi-modal disribuion of pressure gradien maxima indicaes a muli-sep igniion process including hermal igniion. 4

5 ILASS Europe 21 Combusion of Diesel sprays under real-engine like condiions Special aenion has been focused on he pre-igniion reacions and he ransiion from cool- o blue-flames as well as from blue-flame o high-emperaure oxidaion processes. The dynamic of hese reacions has been invesigaed in deail. The characerisic ime () describes principally he delay ime afer injecion begins of a given kind of reacion. Especially imporan is here invesigaion of relaive disance ( ) or raio ( 1 / 2 ) of characerisic imes of boh reacions. In following, his characerisic ime raio is called as dimensionless ime. Transiion from one reacion o anoher one (e.g. from low-emperaure oxidaion blue-flames o highemperaure oxidaion represened by hermal igniion) requires close one-anoher locaion of delay imes. Wide spacing of characerisic imes for boh kinds of reacions probably prevens from his ransiion. According o he model presened in figure 4 he following crieria for ransiion from low-emperaure o high-emperaure oxidaion processes are seleced: comb BF ~ 1 single - sep igniion comb comb 1 no hermal igniion 1 muli-sep igniion BF BF Process analysis: effec of iniial chamber pressure Because of he limied space of he paper his is impossible o describe he process a all invesigaed emperaures T IB. For he reason of he paper examples of measured process, only are presened in his chaper. An example of pressure hisory measured a consan emperaures T IB =7 C for variable pressures p IB and consan air access raio non-premixed charge) is shown in Figure 5. The process is analysed for consan air access raio wha means variable amoun of fuel injeced in he combusion chamber for differen chamber pressures p IB. Pressure gradien [bar/ms] Pressure [bar] Figure 5. Pressure hisory (op) and pressure gradien disribuion (boom) a differen iniial chamber pressures p IB a consan chamber emperaure T IB =7 C This figure shows pressure chamber hisory (op) and pressure gradien changes (boom) in ime afer fuel injecion begins (poin IB) a seleced iniial chamber pressures p IB. The higher he chamber pressure p IB he shorer is delay ime for hea release and higher rising of corresponding chamber pressure. The hea release rae represened by slope of he curves also increases wih increasing p IB. The pressure gradien in an iniial phase of he process shows a single peak disribuion a high chamber pressures p IB characerisic for a single-sep igniion process (premixed par of he charge). A lower pressures (5 and 1bar), however, a very fla plaeaux in pressure gradien disribuion is observed before occurring of maximum peak. The higher pressure p IB he faser is oxidaion process and he higher chamber pressure p comb. Considering disribuion of he characerisic ime comb i is observed (Fig.6) ha he higher he iniial chamber pressure p IB he shorer delay of he igniion process. This ime shorens almos linearly wih increasing pressure. The second parameer used for he process dynamics analysis is he reacion rae characerized by a slope comb (see Fig 6). The higher chamber pressure he higher slope of he reacion curve, i.e. he hea release rae increases wih increasing iniial chamber pressure p IB. 5

6 ILASS Europe 21 Combusion of Diesel sprays under real-engine like condiions comb [ms] pressure p IB [bar] comb [deg] pressure p IB [bar] Figure 6. Lef-Disribuion of characerisic ime comb; Righ- Disribuion of slope comb ; boh vs iniial chamber pressure p IB a consan chamber emperaure T IB =7 C This relaionship is no linear: in he range of lower pressures (p IB <1bar) he reacion rae is relaively low (on he level of 6 o 7 degrees) and increases wih increasing pressure, whereas a higher chamber pressures he slope increases slower wih chamber pressure and maximum slope is on he order of 88 degrees. Invesigaion of mean slopes corresponding o pressure changes in millisecond indicaes ha even a high chamber pressures he reacion sill significanly acceleraes. The maximum chamber pressure p comb linearly increases wih increasing pressure p IB (please noe ha he mixure is non-premixed and no swirl has been applied o promoe he mixing process). An overview of he characerisic ime disribuion versus chamber pressure in a wide range of iniial chamber emperaures T IB is given in Figure T IB =3, = [ms] 15 1 [ms] 2 15 T=35 C pressure p IB [bar] pressure p IB [bar] Figure 7. Disribuion of characerisic ime vs iniial chamber pressure p IB a differen iniial chamber emperaures T IB and consan air access raio =1.5 T=4 C T=45 C T=5 C Firsly, he characerisic ime disribuion a he lowes invesigaed iniial chamber emperaure T IB =3 C is analysed. There are differen characerisic ranges of he process o be seleced: lowes pressure p IB =2.9bar: delay ime is very long on he order of 25ms slighly higher pressures p IB < 5bar: delay ime is reduced o approximaely 5ms; wih increasing chamber pressure he delay ime rapidly reduces a pressure p IB =5bar: delay ime is he shores (~4ms) pressures in he range p IB =5bar o 15bar: delay ime is shor having a low level plaeaux he highes pressures pib > 18bar: delay ime again increases (>1ms) The auhors propose o inroduce a PPC parameer Posiive Pressure Coefficien in analogy o NTC (Negaive Temperaure Coefficien). PPC indicaes ha in a seleced range of pressures p IB he delay ime of a low-emperaure oxidaion process is he shores and probably he rae of hese reacions is he highes. Even furher increasing in pressure p IB (or ) increases ime and decreases angle PPC will even more visible a lower chamber emperaures T IB. I may be concluded ha he lowes invesigaed emperaure T IB =3 C is a criical emperaure for cool-flame reacions in he middle range of invesigaed pressures. A he lowes pressures (p IB <5bar) here is probably a ransiion from a slow-combusion process o cool-flames (by increasing chamber pressure) and is characerized by a very long delay ime. This emperaure range for a cool flame reacion is similar o ha repored in [14]. In he pressure range from 5bar o 18bar here is a range of cool-flame reacions. Conrary o ha, a he highes pressure p IB a rapid increase of reacion delay would sugges exisence of NTC or possible ransiion o blue-flame reacions. 6

7 ILASS Europe 21 Combusion of Diesel sprays under real-engine like condiions Process analysis: effec of iniial chamber emperaure In his secion a non-premixed low- and high-emperaure oxidaion processes under Diesel engine-like condiions are invesigaed a consan pressure p IB in a wide range of iniial chamber emperaures T IB. As an example, he process is invesigaed a high chamber pressure p IB =18bar for a consan amoun of fuel injeced in o he combusion chamber. The process is analysed in emperaure range T IB from 3 C o 8 C. An overview of he chamber pressure and pressure gradien hisories afer injecion begins is given in fig.8. Pressure [bar] Pressure gradien [bar/ms] [ms] Temperaure T IB [ C ] Figure 8. Lef-Pressure hisory (op) and pressure gradien disribuion (boom) a differen iniial chamber emperaures a p IB =18bar and consan mass of fuel m fuel =23.3mg; Righ- Disribuion of characerisic ime I could be expeced ha in a such a wide range of emperaures differen kinds of reacion occur a differen hermodynamic condiions. The following characerisic pars of he process have been seleced: he lowes emperaure T IB =3 C: delay ime is very long (approximaely 6ms) and he reacion rae is low (because of he ime scale his is no ploed in fig.8) emperaure T IB =35 C: delay ime is shorer (approximaely 2ms) and he reacion rae is higher emperaure T IB =4 C: delay ime is shorer (approximaely 7ms) and he reacion rae is slighly higher emperaure T IB =45 C: delay ime is shorer (approximaely 3ms) and he reacion rae is slighly higher higher emperaures 45 C < T IB < 6 C: delay ime is on he order of 2ms and he reacion rae only slighly changes high emperaures 6 C T IB < 7 C: delay ime is on he order of 1.5ms and he reacion rae only slighly changes highes emperaures T IB > 7 C: delay ime is shorened o below 1.5ms and he reacion rae does no pracically change. The process in a very early sage jus afer injecion sars is also emperaure dependen. A low emperaures T IB 4 C he negaive pressure ( P v ) is almos consan in a very long ime period being on he level of p v =-.3bar o -.2bar. Disribuion of pressure gradien shows characerisic behaviour depending on he emperaure range: a high emperaures a single peak disribuion is observed, and in he middle emperaure range a bi-modal disribuion is indicaed, however, he spacing beween boh peaks is shor in ime. Because of a very long delay ime (~66ms) of he process a he lowes chamber emperaure T IB =3 C he lowes limi of his diagram has been se a T IB =35 C. The higher he chamber emperaure he shorer he delay ime, however, here is a range of emperaure T IB < 5 C where his ime gradually (almos linearly) decreases wih increasing iniial chamber emperaure. A higher emperaures he delay ime comb is only weakly emperaure dependen and reaches values around 2ms level. Similar behaviour is observed for delay ime BF. As indicaed in his figure, he dimensionless ime a high chamber pressure is almos consan on he level of indicaing possible hermal igniion process. Please noe ha a his high chamber pressure (p ib =18bar) here is no indicaion for exisence of a negaive emperaure coefficien. The angle comb increases wih increasing emperaure being almos consan a he level of 87 degrees for emperaures T IB > 5 C. The disribuion of BF shows much more complex characer. A he highes emperaures he low-emperaure reacion rae is very low suggesing ransiion o a single-sep igniion process, as already indicaed above. Reducing he emperaure he reacion rae (blue-flame) increases indicaing ransiion o a muli-sep igniion process. For furher reducing of he empera- 7

8 ILASS Europe 21 Combusion of Diesel sprays under real-engine like condiions ure from 6 C o 45 C he reacion rae shows a local maximum a 55 C and hen a local minimum a 45 C. Furher reducing he emperaure again significanly increases he reacion rae o he level of 7deg. Concluding remarks In he paper auhors described unique invesigaion on low-emperaure reacions (cool- and blue-flames), hermal auo igniion and hea release of a non-premixed mixure under Diesel-engine like condiions. The experimens have been performed in a special high-pressure, high-emperaure consan volume (adiabaic) combusion chamber simulaing engine condiions near he op dead cenre of compression sroke. The sysem simulaes he hermodynamic condiions o be found in a real engine a he momen of fuel injecion begin. For process analysis a model of a muli-sep oxidaion (igniion) has been consruced and wo measured parameers are invesigaed: pressure hisory and pressure gradien disribuion as a funcion of ime afer injecion sars. The process has been analysed under differen es condiions: a consan iniial chamber pressures for a wide range of iniial emperaures, a consan chamber emperaure for differen iniial chamber pressures as well as for a consan amoun of injeced fuel or for a consan air access raio. Addiionally, he delay ime and slopes have been analysed o describe he reacions dynamic. The auhors defined crieria for hermal auo igniion process as well as for a ransiion from cool-flames o blue-flame reacions and o high-emperaure oxidaion process. The auhors have also proposed a PPC-posiive pressure coefficien (in analogy o a NTC) indicaing an influence of he combusion chamber pressure on he reacion dynamics. References [1] Weclas, M., 22 nd European Conference on Liquid Aomizaion and Spray Sysems, Como, Ialy, Sepember 28, 6-7. [2] Weclas, M., Cypris, J. In. Journal of Engine Research 11: (29). [3] Baldwin, R. R., Walker, R. W., 14h (Inernaional) Symposium on Combusion. Pisburgh, PA, 1973, pp [4] Wesbrook, K. C., Pi, W. J., Leppard, W. R., The Auo-Igniion Chemisry of Paraffinic Fuels and Pro- Knock and Ani-Knock Addiives: A Deailed Chemical Kineic Sudy, SAE Paper No (1991). [5] Wesbrook, C.K., Proceedings of he Combusion Insiue 28: (2). [6] Griffihs, J.F., Halford-Maw, P.A., Rose, D.J., Combus. Flame 95: (1993). [7] Minei, R., Carlier, M., Ribaucour, M., Therssen, E. and Soche, L.R., Combus. Flame 12: (1995). [8] Goldsborough, S.S., Auoigniion of lean iso-ocane-air mixures in an RCEM, 27 Fall Meeing of he Wesern Saes of he Combusion Insiue Sandia naional Laboraories, Livermore, Paper no. 7F-62 (27). [9] Park, P. and Keck. J.C., Igniion Delays for Iso-ocane: Measuremen Using a Rapid Compression Machine and Predicion Using a Reduced Chemical Kineic Model, SAE Paper No (1991) [1] Donovan, M. T., He X., Zigler, B. T., Palmer, T. R., Wooldridge, M. S., Areya A., Combusion and Flame 137: (24) [11] Lim, O.T., Sendoh, N., Iida, N., Experimenal Sudy on HCCI Combusion Characerisics of n-hepane and iso-ocane Fuel/Air Mixure by he use of a Rapid Compression Machine, SAE Paper No (24) [12] Würmel, J., Simmie, J.M., Curran, H.J., Inernaional Journal of Vehicle Design 44: (27). [13] Mial G., Sung, C.J., Combusion Science and Technology 179: (27). [14] Harmann, L., Lucka, K., Mengel, C., Köhne H., Proceedings of he 5 h European solid oxide fuel cell forum, Lucerne, (22). Acknowledgemen M. Weclas hanks he Federal Minisry of Educaion and Research (BMBF) and German Federaion of Indusrial Research Associaions (AiF) for financial suppor of he presened invesigaion (Projec No.17N227). 8