Transient Temperature Measurement of Unburned Gas in an Engine Cylinder Using Fiber-Optic Heterodyne Interferometry

Transcription

1 Transien Temperaure easuremen of Unburned Gas in an Engine Cylinder Using Fiber-Opic Heerodyne Inerferomery by Nobuyuki Kawahara, Eiji Tomia, Hiroshi Kamakura, isuru Ichimiya Deparmen of echanical Engineering, Okayama Universiy Tsushima-Naka 3, Okayama JAPAN Absrac Various global environmenal issues are relaed o he use of inernal combusion engines, including air polluion and energy concerns. Wih homogenous charge compression igniion (HCCI) engine, i is possible o operae wih ulra lean premixed mixures and o lead low NOx and soo-paricle emissions. The combusion process in he HCCI engine is due o auo-igniion of an unburned mixure. The occurrence of auo-igniion is dependen on he emperaure and pressure hisories of he unburned mixures. Therefore, i is necessary o measure he emperaure hisory of he unburned mixure in he HCCI engine. In he presen sudy, he emperaure of he unburned mixure in a homogeneous charge compression igniion (HCCI) engine, fueled wih dimehyl eher (DE), was measured using fiber-opic heerodyne inerferomery. The echnique is based on refracive index measuremens using laser inerferomery along a line of sigh. The emperaure hisory of gas can be deermined from he pressure hisory in he engine, he gas composiion, and he laser inerference inensiy. The measuremen accuracy of he developed sysem was sufficien o deermine he emperaure hisory of unburned mixure in HCCI operaion. The uncerainy of his mehod is wihin ±15 K. The resoluion of emperaure measuremens is approximaely.5 K, and is dependen on boh he sampling clock speed of he A/D converer and he lengh of he es secion. Opical fiber for preserving polarizaion He-Ne laser λ /4 RG H λ /2 : irror AO PBS PF : Polarizing filer PF PBS : Polarizing beam splier SL : icro-lens PT Reference λ/4 : 1/4 wave rearder signal λ/2 : 1/2 wave rearder RG : Rod glass PT : Phoo-ransisor PBS PF PT Tes signal SL Fig. Developed fiber opic heerodyne inerferomeer 1

2 1. Inroducion Temperaure measuremens of urbulen combusion processes can provide imporan informaion abou chemical kineics conrolling fuel oxidaion and polluan formaion, and he opimizaion of pracical devices. However, an accurae ime-resolved emperaure hisory of gas is difficul o obain experimenally. Tradiionally, sound velociy and infrared emission absorpion mehods have been used o measure he unburned mixure emperaure in inernal combusion engines. Livengood (1958) and Glucksein and Walcu (1961) used a sound-velociy mehod o measure he gas emperaure in a cylinder. The unburned mixure emperaure has also been measured using iodine absorpion specra (Chen e al., 1954), a wo-wavelengh infrared mehod (Agnew, 196), and an infrared radiaion pyromeer (Burrows e al., 1961). ore recenly, a ligh-scaering mehod ha uses sponaneous vibraional and roaional Raman scaering, laser Rayleigh scaering, coheren ani-sokes Raman specroscopy (CARS) and laser-induced fluorescence (LIF) has been developed (Chiger, 1991, Eckbreh, 1996, Zhao and Ladommaos, 21). Several researchers have used CARS mehod o deermine he unburned mixure emperaure (Luch, e al., 1987, Bood, e al., 1997, Nakada, e al., 199, Akihama and Asai, 1993). echnique is paricularly well suied o engines, because i produces a srong signal. However, he accuracy of CARS in an engine cylinder is only ±4 K (Akihama and Asai, 1993) and i is limied o single-poin and single-sho measuremens. Two-dimensional emperaure measuremens have become possible using fluorescence hermomery because of is inrinsically high signal-o-noise raio. Schulz e al., (1996) used LIF wih a unable KrF excimer laser o obain quaniaive imaging of he niric oxide concenraion disribuion and emperaure field in an SI engine. Kaminski e al. (1998) used a wo-line aomic fluorescence (TLAF) echnique o measure he emperaure inside an inernal combusion engine. These mehods have he poenial o provide quaniaive wo-dimensional emperaure disribuion, bu ime-series analysis is limied by he laser repeiion rae. Laser inerferomery (Goldsein, 1983, Fomin, 1998) offers high poenial resoluion and provides a non-inrusive emperaure measuremen echnique. Garforh (1976) used modified ichelson inerferomery o measure he ransien densiy in he unburned gas region of a spherical combusion chamber, and obained he ransien gas emperaure from he equaion of sae and pressure daa. Hamamoo e al. (1989) measured he unseady emperaure change of a gas during compression and expansion using ach-zehnder inerferomery; however, hey encounered difficulies because he measuremens were usually sensiive o mechanical vibraion. Hamamoo e al. (1994) and Tomia e al. (1994, 2) addressed some of hese problems by using modified ach-zehnder inerferomery wih polarizaion-preserving fibers and Köser prisms o measure he emperaure change of a compressed unburned gas during flame propagaion and o invesigae he knock phenomenon. However, i is difficul o apply his sysem o anoher combusion sysem due o he special opical arrangemen. Heerodyne inerferomery (Kawahara, e al. 2) is more fairly insensiive o flucuaions in signal inensiy caused by mechanical vibraion. Thus, a fiber-opic heerodyne inerferomery sysem was developed o measure he emperaure hisory of he unburned end-gas in an engine cylinder during flame propagaion (Kawahara, e al., 22). A polarizaion-preserving fiber was used o deliver he es beam o and from he es secion in order o improve he applicabiliy of his sysem. In he presen paper, he same fiber-opic heerodyne inerferomery sysem was used o measure he emperaure of he unburned mixure in a homogenous charge compression igniion (HCCI) engine (Thring, 1989) fueled wih dimehyl eher (DE). Wih HCCI i is possible o operae wih ulra lean premixed mixures and o lead low NOx and soo-paricle emissions. The combusion process in he HCCI engine is due o auo-igniion of an unburned mixure. The occurrence of auo-igniion is dependen on he emperaure and pressure hisories of he unburned mixures. Therefore, i is necessary o measure he emperaure hisory of he unburned mixure in he HCCI engine. oreover, DE (CH 3 OCH 3 ), one of he oxygenaed fuels, is an aracive alernaive fuel because of smoke-free combusion, reducion of NOx and easy compression igniion. Since DE shows very srong low emperaure oxidaion, he HCCI sudy of DE may give useful informaion on he general role of cool flame in HCCI operaion. 2

3 2. Experimenal ehod and Procedure 2.1 Principles of Temperaure easuremen The principles of using opical inerferomery o measure gas emperaure are shown in Fig. 1. Inerferomeric mehods allow variaion in he refracive index along he line of sigh o be measured. When he unburned gas mixure is compressed by he pison, he densiy of he gas in he combusion chamber changes, affecing he refracive index. The refracive index is influenced simulaneously by boh emperaure and changes in species concenraions. The difference beween he opical pahs of he es and reference beams varies, and corresponds o changes in he refracive index in unburned mixure and he inerference ligh inensiy. When he reference and a es beam have inensiy I, he inerference inensiy, I, is expressed as [ ( b ) ] I = 2 I 1+ cos 2πf + ψ where f b and ψ τ denoe he bea frequency and he change of phase shif in he es secion, respecively. The change of phase shif of he heerodyne signal over a given ime, ψ Η, is relaed o ψ by ψ = πfb( ) d 2 2πf br ( ) d where f br and f b denoe he bea frequency of he reference and es secions, respecively. The change of phase in he es secion, ψ, is also expressed by (1) (2) ψ = 2πΦ / λs = 2πnL / λs (3) where Φ is he change in he opical pah lengh, L is he lengh of he es secion, λ s is he wavelengh of he es beam, and n is he change in he refracive index in he es secion. Unburned gas mixure compressed wih he pison Inerferomery Gladsone-Dale Equaion Ideal gas law Refracive index Densiy Temperaure Gas composiion Pressure Fig.1 Principle of emperaure measuremen using laser inerferomery 3

4 The relaionship beween he refracive index and densiy can be approximaed using he Gladsone-Dale equaion, n ρ RG PR G (4) = 1+ = 1+ RT where R G is he Gladsone-Dale consan (cm 3 /mol)(gardiner, e al., 198), which is deermined by he wavelengh of he laser and he gas species. The variables, R, P, and T denoe he mean molecular weigh, mean gas consan, pressure, and emperaure in he es secion, respecively. The value of he Gladsone-Dale consan for each gas is given in deail for each laser wavelengh in reference (Gardiner, e al., 198). When he gas mixure is composed of many species, he Gladsone-Dale consan of he mixure is expressed as R = R x G Gi i (5) where x is he mole fracion of each gas and he subscrip i indicaes he i-h species of he mixure. The emperaure of he mixure can be obained from Eqs. (2), (3), and (4), 2πPR GT L T = 2 P R L + T R π ψ λ G (6) When he pressure P and emperaure T of he iniial sae are known, he emperaure of he gas can be calculaed from measuremens of he pressure and he change in bea frequency of he inerfering ligh. 2.2 Fiber-Opic Heerodyne Inerferomery Figure 2 shows he configuraion of he fiber-opic arrangemen in he combusion chamber. A frequency sabilized He-Ne laser, wih a wavelengh λ of nm and an oupu power of 1 mw, provides a linear polarized beam for he measuremens. The AO sysem for heerodyne inerferomery produces wo beams. In his experimen, he frequency of he firs beam is shifed by 8.1 Hz, and ha of he second by Hz. These beams mee a he polarized beam splier and creae a bea frequency of 25. khz. The difference beween he iniial frequencies can be alered o creae oher bea frequencies (12.5 ~ 1 khz), if desired. Afer he polarized beam splier, he beam is spli ino wo by he half mirror. One beam is deeced by a phoo-ransisor as a reference signal; he oher is used for modified ichelson inerferomery. The reference signal beam passes ouside he combusion chamber and is refleced by a mirror. The beam used for ichelson inerferomery passes hrough he es secion, is refleced by a mirror, and hen passes back hrough he es secion again. The delivery of he es beam poses a possible problem in heerodyne inerferomery since, any change in he posiion of he opical sysem in relaion o he combusion chamber affecs he resuls due o he sensiiviy of he signal. The polarizaion of he signal is imporan; herefore, a 1.5 m polarizaion-preserving fiber is used o deliver he es beam o and from he es secion in he combusion chamber. The 1/4 wave rearder, used previously for a es beam wihou he fiber sysem (Kawahara, e al., 2), is replaced by a 1/2 wave rearder in he fiber-opic sysem, so ha he polarizaion angle of he fiber coincides wih he es beam. A disribued index lens is fixed a each end of he fiber o generae a collimaion beam and o inroduce he beam ino he fiber. This disribued index lens has an anireflecion coaing o decrease he cross-alk effec. The es beam passes hrough he fiber and mees he reference beam a he polarized beam splier, where he wo beams inerfere wih each oher. The inerfering ligh is guided o a phooransisor, and changes in he inensiy are deeced. The main problem of his sysem is coherence lengh of laser due o he differen lengh of he es and reference beams. The frequency sabilized He-Ne laser used in hese ess has a long coherence lengh (over 1 km); hus, he difference beween he pah lenghs of he es and reference beams is insignifican. The reference signal, es signal and pressure daa are colleced using an A/D converer (maximum sampling rae: 5 khz). These daa are hen analyzed using in-house sofware. 4

5 He-Ne laser : irror AO PBS PF : Polarizing filer PF PBS : Polarizing beam splier SL : icro-lens PT Reference λ/4 : 1/4 wave rearder signal λ/2 : 1/2 wave rearder RG : Rod glass PT : Phoo-ransisor H λ /4 λ /2 PBS PF PT Tes signal SL Fig. 2 Developed fiber-opic heerodyne inerferomeer Opical fiber for preserving polarizaion RG 3. Unburned ixure Temperaure easuremen in a HCCI Engine Cylinder This experimen used a specially designed compression-expansion engine ha can only auo-ignie once. Wih his engine can observe he phenomena of one cycle in one experimenal run. A schemaic diagram of he engine is shown in Fig. 3. The engine had a bore and sroke of 78 and 85 mm, respecively, and he compression raio was 1.1:1. The consan volume combusion chamber in his engine was he same as ha described in (Kawahara, e al., 22),. The laser beam used for fiber-opic heerodyne inerferomery passed hrough glass rods in he combusion chamber. The glass rods are fixed wih liquid packing and hin Teflon gaskes in order o preven leakage of he fuelair mixure. The axis of he laser beam in he es region was 4.3 mm from he upper wall and 2.7 mm from he side wall; his posiion was chosen o be ouside he hermal boundary layer near he wall. The lengh of he gas layer in he es region, L, was mm. The engine cylinder was conneced o a mixure ank by a pipe. Iniially, a homogeneous mixure was inroduced ino he ank and cylinder hrough an open valve, wih he pison se a op dead cener (TDC). The engine was driven by an elecric moor while he valve was open. Afer a given ime, he valve was closed when he pison was a boom dead cener (BDC). The mixure was hen compressed sufficienly o raise he mixure emperaure above is igniion poin. Auo-igniion was disribued hroughou he cylinder volume, saring a he hoes regions. The mixure was inroduced wihou swirl, because he valve was locaed a he cener axis of he cylinder. The engine was operaed a 6 rpm. The pressure signals in he cylinder, inerference inensiy, crank angle, TDC, BDC, and valve closure were recorded by an A/D converer, wih a sampling ime of 2 microseconds and daa resoluion of 12 bis. The cylinder and mixure ank were iniially charged wih a homogeneous dimehyl eher (DE)-air mixure (equivalence raio φ =.3). DE-air mixure was iniially heaed up a 348K by he elecric heaer. The emperaure of he fuel-air mixure a he sar of compression (base sae) had o be deermined in advance, because he fiber-opic heerodyne inerferomery sysem measured only he change in emperaure from he base sae. In his experimen, he valve was closed a 5

6 Bore: 78 mm Sroke: 85 mm DC elecric Compression Valve-sopper Power supply raio: 1.1 Valve Solenoid Pressure ransducer Thermocouple Valve-closure signal Spark elecrode ixure ank Crank angle pulse Elongaed pison Elecric moor (Variable speed) Flywheel TDC signal BDC signal Roary encoder Fig. 3 A schemaic diagram of he es engine BDC of a cerain cycle. Using a resisance wire as a hermomeer, he emperaure a BDC of he valve closure cycle was 3.8 K lower han he iniial gas emperaure in he mixure ank (Tomia, e al., 1994). This value was used for he emperaure a he sar of compression. The emperaure afer valve closure was obained from he pressure daa and he heerodyne signal, as given by Eq. (6). Figure 4 indicaes he pressure hisory and he hea-release rae in he cylinder of he es engine. The combusion of he DE-air mixure was characerized by a clearly disinguished wo-sage igniion, which is visible from he wo peaks in he hea release rae curve. The firs peak indicaes he hea released during he firs sage of igniion, which is also described by he low emperaure (T<1 K) chemical kineics. The main igniion sage follows he firs sage. A lower emperaures (up o 9 K), he igniion is conrolled by degeneraive chain branching processes. The figure shows clearly ha HCCI combusion occurred in he es engine, using an ulra-lean premixed mixure and DE as fuel. Figure 5 indicaes he pressure hisory and he measured phase shif beween he reference and es signals a an engine speed of 6 rpm. BDC corresponds o a crank angle of 18 and TDC corresponds o 36. The phase shif increased slighly wih he pressure rise during he firs sage of compression. Alhough noise from mechanical vibraion conribued o he inerference signal when he valve was closed a BDC, he effec was wihin he limis 6

7 PressurePa 3 Pressure Hea release rae (BDC) Crank Crank angledeg (TDC) Fig. 4 easured pressure and hea release rae in he cylinder of es engine Hea release raej/deg ψrad ψ, 6 3 ψ ψ Pressure PressurePa (BDC) Crank angledeg (TDC) Fig. 5 easured phase shif and pressure of unburned mixure in he cylinder of es engine 7

8 allowed for measuremen. The effec of he impac when he valve closed and he operaing vibraion of he engine were herefore sufficienly resrained o permi accurae heerodyne inerferomery measuremens. The emperaure hisory of he unburned mixure from a crank angle of BDC o he firs igniion sage was calculaed using Eq. (6) and is ploed wih black circles in Figure 6. The ransien emperaure deermined by heerodyne inerferomery was compared wih he emperaure calculaed using he mean emperaure from he sae equaion for an ideal gas. The mean emperaure is also he bulk emperaure in he engine cylinder. The mean emperaure was similar o ha measured by inerferomery before a crank angle of 3, bu he emperaure obained by he presen sysem was lower han he mean emperaure before he firs sage of igniion. This was because he measuremen locaion was near he wall, where he emperaure is expeced o be lower han he mean emperaure. Heerodyne inerferomery provided he mean emperaure along a line of sigh, and he presen resuls demonsrae ha his mehod can measure he emperaure hisory of he unburned mixure in a HCCI engine. 4. easuremen Accuracy The accuracy of he developed fiber-opic heerodyne inerferomery sysem depends on (1) he accuracy of pressure measuremens, (2) he sabiliy of he AO sysem, (3) he gas composiion, and (4) he relaionship beween he bea and sampling frequencies. (1) Accuracy of pressure measuremens The pressure hisory of he combusion chamber is required in order o esimae he emperaure of he gas. The accuracy of pressure measuremens depends on ha of he pressure ransducer, which has a specified non-lineariy of less han 1% a full scale. Even if he pressure measuremen had an error of ±2.5 kpa, which would be an over- TemperaureK Eqof ideal gas Heerodyne Hea release rae (BDC) Crank angledeg (TDC) Hea release rae, J/deg Fig. 6 Temperaure change of unburned mixure in he cylinder of es engine 8

9 esimae, he accuracy of he emperaure daa would sill be ±2.%. The accuracy of he heerodyne inerferomery sysem was found o be largely dependen on he accuracy of he pressure measuremens. (2) Sabiliy of he AO sysem If he bea frequency of he AO sysem is unsable, he gas emperaure esimaes will be poor. In his sysem, he sabiliy of he AO sysem was.2 ppm; herefore, he sabiliy effecs of he AO sysem were negligible. (3) Gas composiion The Gladsone-Dale consan varies wih gas composiion. In his analysis, he composiion of he unburned mixure was assumed o be consan. In an HCCI engine, igniion is conrolled by degeneraive chain branching processes a low emperaure. Low-emperaure oxidaion processes occur in an engine cylinder during firs sage combusion. Therefore, he effec of he Gladsone-Dale consan mus be considered. For example, if he equivalence raio of he es gas (DE-air mixure) varies from.3 o.25, he Gladsone-Dale consan changes from o cm 3 /mol, respecively. In his case, he error inroduced by assuming a consan equivalence raio of.3 was approximaely.6%. (4) Relaionship beween he bea and sampling frequencies The relaionship beween he bea and sampling frequencies affecs he emperaure measuremen resoluion. Opimizaion of he wo frequencies improves he accuracy of a sysem. In his sudy, he iniial bea and sampling frequencies were 25 and 5 khz, respecively. A oal of 2 sampling poins were obained during one period of he bea frequency before he spark. However, during he compression by he pison, only 18 sampling poins were obained, owing o an increase in he bea frequency of he es signal. If 1/18 of he bea signal period is considered o be he resoluion of he emperaure measuremens, hen he measuremen resoluion, which changes wih densiy, is abou.5 K. Fig. 8 indicaes he change in he measuremen resoluion, T, wih pressure, P, for emperaure T, K Sampling frequency: 5 khz Iniial bea frequency : 25 khz T, K 5 T, K T, K P, kpa Fig. 7 Resoluion for emperaure of unburned mixure 9

10 measuremens of he unburned gas mixure compressed by he pison. The value of T changes wih densiy; i was approximaely.45 ~.8 K for hese ess. These values indicae ha our sysem can measure emperaure a a beer resoluion han repored for he ach-zehnder opical sysem wih polarizaion-preserving fibers and Köser prisms (Tomia, e al., 1994). The resoluion of emperaure and ime could be improved by using an A/D converer wih a higher sampling rae, and by increasing he lengh of he es secion. 5. Conclusions Non-inrusive measuremen of ransien gas emperaures was successfully developed wih a fiber-opic heerodyne inerferomery sysem. The measuremen accuracy of he developed sysem was sufficien o deermine he emperaure hisory of unburned mixure in HCCI operaion. There was good agreemen beween he measured emperaure and he mean emperaure calculaed from he sae equaion for an ideal gas. The uncerainy of his mehod is wihin ±15 K. The resoluion of emperaure measuremens is approximaely.5 K, and is dependen on boh he sampling clock speed of he A/D converer and he lengh of he es secion. Fiber-opic heerodyne inerferomery sysems would be useful in sudies of auo-igniion kineics in HCCI engines. This mehod can also be used for oher applicaions ha require a ransien emperaure record wih a fas response ime. Acknowledgmens Financial suppor of his research by he Indusrial Technology Research Gran Program of he New Energy and Indusrial Technology Developmen Organizaion (NEDO) of Japan is graefully acknowledged. References Livengood, J.C., Taylor, C.F., and Wu, P.C. (1958). easuremen of Gas Temperaure in an Engine by Velociy of Sound ehod, SAE Trans, 66, Glucksein,.E., and Walcu, C. (1961). End-gas Temperaure-pressure hisories and heir relaion o knock, SAE Trans., 69, Chen, S.K., Beck, N.J., Uyehara, O.A., and yers, P. (1954). Compression and End-Gas Temperaure from Iodine Absorpion Specra, SAE Trans., 62, Agnew, W.G. (196). End Gas Temperaure easuremen by Two-Wavelengh Infrared Radiaion ehod, SAE Trans, 68, Burrows,.C., Shimizu, S., yers, P.S., and Uyehara, O.A. (1961) The easuremen of Unburned Gas Temperaure in an Engine by an Infrared pyromeer, SAE Trans., 66, Chiger, N. (1991). Combusion easuremens, Hemisphere Publishing Corp. Eckbreh, A.C. (1996), Laser Diagnosics for Combusion Temperaure and Species, 2nd Ed., Gordon and Breach Publishers. Zhao, H. and Ladommaos, N. (21), Engine Combusion Insrumenaion and Diagnosics, Sociey of Auomoive Engineers, Inc. Luch, R.P., Tees, R.E., Green, R.., Palmer, R.E., and Ferguson, C.R. (1987). Unburned Gas Temperaure in an Inernal Combusion Engine. I: CARS Temperaure easuremens, Combus. Sci. and Technol., 55, 41. 1

11 Bood, J., Bengsson, P-E., auss, F., Burgdorf, K., and Denbra, I. (1997). Knock in Spark-igniion Engines: Endgas Temperaure easuremens using Roaional CARS and Deailed Kineic calculaions of he auoigniion process, SAE paper Nakada, T, Io, T., and Takagi, Y. (199). Unburn Gas Temperaure easuremens Using Single Sho CARS in a Spark Igniion Engine, Proc. of In. Symp. on COODIA 9, Akihama, K., Asai, T. (1993), Improvemen in Temperaure easuremen Accuracy of Q-Branch CARS Thermomery (Effecs of Specral Resoluion of Deecion Sysem), JSE Inernaional Journal, B 36-2: Schulz, C., Sick, V., Wolfrum, J., Drewes, V., Zahn,., and aly, R. (1996), Quaniaive 2D Single-Sho Imaging of NO Concenraions and Temperaures in a Transparen SI Engine, Proc. Comb. Ins. 26: Kaminski, C. F., Engsroem, J. and Alden,. (1998), Spark Igniion of Turbulen ehane/ Air ixures Revealed by Time-Resolved Planer Laser-Induced Fluorescence and Direc Numerical Simulaions, Proc. Comb. Ins. 27, Goldsein, R.J. (1983). Fluid echanics easuremens, Hemisphere Publishing Corp. Fomin, N.A. (1998). Speckle Phoography for Fluid echanics easuremens, Springer-Verlag. Garforh, A.. (1976). Unburn Gas Densiy easuremens in a Spherical Combusion Bomb by Infinie-fringe Laser Inerferomery, Combus. and Flame, 26, Hamamoo, Y., Tomia, E., and Okada, T. (1989). The easuremen of he Transien Temperaure of Gas by Laser Inerferomery, JSE In. J., Ser. II, 32-2, Hamamoo, Y., Tomia, E., and Jiang, D. (1994). Temperaure easuremen of End Gas under Knocking Condiion in a Spark-Igniion Engine by Laser Inerferomery, JSAE Review, 15-2, Tomia, E., Hamamoo, Y., and Jiang, D. (1994). Temperaure and Pressure Hisories of End Gas under Knocking Condiion in a S.I. Engine, Proc. of In. Symp. on COODIA 94, Tomia, E., Hamamoo, Y., and Jiang, D. (2). easuremen of Temperaure Hisory of Unburned Gas Before Knocking in a Spark-Igniion Engine Using Laser Inerferomery, eas. Sci. Technol., 11, 1-7. Kawahara, N., Tomia, E., Kamakura, H. (2). Transien Temperaure easuremen of Unburned Gas Using Opic Heerodyne Inerferomery, 1h In. Symp. on Appl. of Laser eas. on Fluid ech., in CD-rom, (2). Kawahara, N., Tomia, E., Kamakura, H. (22). Unburned Gas Temperaure easuremen in a Spark-igniion Engine Using Fiber-Opic Heerodyne Inerferomery, eas. Sci. Tech., 13-1, pp Thring, R.H. (1989), Homogeneous Charge Compression Igniion (HCCI) Engines, SAE Paper Gardiner, W.C.Jr, Hidaka, Y., and Tanzawa, T. (198). Refraciviy of Combusion Gases, Combus. and Flame, 4,