Diesel Combustion Fluctuation Analysis by Optical Fiber Thermometer : Relationship between Flame Temperature Fluctuation and Excess Air Ratio of the Burned Zone

Fluctuation of flame temperature was measured in the combustion chamber of a DI diesel engine by means of the optical fiber thermometer, and combustion pressure history was measured as well. By using the two-zone model, the excess air ratio of the burned zone was analyzed based on the experimental pressure history, and it was compared between the two cases with and without pilot injection. It is shown that the excess air ratio in the case of pilot injection is smaller than the one in the standard injection depending the ignition delay. And it is also found that the excess air ratio of the burned zone is well correlated with the RMS values of pressure and flame temperature fluctuations