Visualization on the influence of the post-injection timing on diesel engine combustion

Post-injection can improve the properties of diesel soot emissions. In this paper, studies on the effect of different post-injection timings on in-cylinder combustion characteristics in an optical engine, were conducted by alternating the post-injection timing under the same injection amount and applying high-speed photography. From the two-color technique, the soot temperature and KL factor were obtained from flame images and were used to analyze the in-cylinder flame temperature and soot characteristics of different post-injection timings. The results reveal that with the spray interval angle increasing, the distribution of flame temperature and the total amount of the KL factor show twin peaks, and the total amount of the KL factor decreases faster in the late period, which means the soot oxidation rate is accelerated.