End-Gas Temperature Measurements in a DOHC Spark-Ignition Engine Using CARS

CARS temperature measurements were carried out both in a constant volume combustion chamber and in a spark-ignition engine. The CARS temperature measurement under engine-like condition was validated by comparing the unburned gas temperatures for premixed propane-air flame in a constant volume combustion chamber obtained by CARS with predicted temperatures of 2-zone flame propagation simulation model. There was good agreement between the predicted temperatures and the mean values of 10 CARS measurements. The standard deviation of 10 measurements at each measuring timing was about ±40 K. End-gas temperatures were measured by CARS technique in a conventional 4-cylinder DOHC spark-ignition engine with the engine motoring and firing. The measured motoring temperature matched well with the adiabatic core temperature calculated from the measured cylinder pressure. The engine was fueled with primary reference fuel (PRF80) of 80% iso-octane and 20% n-heptane by volume. The engine was operated under 1200 rpm, wide open throttle condition and spark ignition timing was varied. CARS spectra of 150 consecutive cycles at different crank angles were acquired. Cylinder pressure was measured simultaneously with CARS signal and used as a parameter on fitting CARS spectrum to the library of theoretical spectra. Significant heating by pre-flame reaction in the end gas was observed in the late part of compression stroke under both knocking and non-knocking condition. Standard deviations of burned end-gas temperatures were larger than those of unburned end-gas temperatures due to the cyclic variation of combustion and turbulent flow after combustion.