Effect of the ambient O_2 concentration and pressure on the spray combustion characteristics of diesel fuel was experimentally examined using a high-temperature, high-pressure combustion vessel. The sequential images were captured by using a high-speed color video camera and were analyzed using the two color method to quantify the temporal variation of the soot temperature and KL factor. Based on a series of systematic experiments, it is confirmed that O_2 concentration is the dominant factor affecting both the ignition delay and combustion period. The volumetric fraction of O_2 in ambient air has great effect on flame temperature and NO_x emission, however ambient pressure has little effect on both values. On the contrary both of the volumetric fraction of O_2 in ambient air and the ambient pressure have large effect on soot production.
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