Accurate CARS thermometry was developed in order to measure the unburned gas temperature in an engine. CARS system was modified by using single-longitudinal-mode pump beam, by eliminating nonresonant components with polarization technique and by improving the spectral resolution of the detection system. This modification greatly improved the accuracy of temperature measurement of the averaged and single-shot CARS from ±100K to ±20K, from ±150K to ±40K, respectively.

Unburned gas temperature in a single-cylinder engine was measured by accurate CARS thermometry. As a result, it was experimentally proved that the unburned core gas was compressed adiabatically. The temperature difference between the knock and non-knock and non-knock cycles, and the heat release due to end-gas reactions were measured exactly.

The reduced chemical kinetic model for auto-ignition, developed by Cowart et al., was investigated in terms of not only knock onsets but also the unburned gas temperature. The adjustment of the isomerization reaction in their model was required to give agreement between the predicted and observed knock onsets and temperature. However, the model calibrated in this study was not able to represent a steep temperature rise at auto-ignition. Knock onsets on a cycle-by-cycle basis was predicted within the accuracy of 2.5 deg. crank angle using the calibrated model. Finally, the effects of non-uniformity of the unburned gas temperature and the mixture for knock occurrence were discussed.

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