Experimental study of the diesel spray combustion and soot characteristics for different double-injection strategies in a constant volume combustion chamber

In this work, broadband luminosity was used to detect ignition delay and diffused back-illumination extinction imaging was employed to measure soot property with different double-injection strategies in a constant volume combustion chamber under different ambient conditions. The interaction between the two-stage injections have been studied experimentally with two key parameters, dwell time and first injection duration. Results show that in two-stage injection cases, a faster flame propagation speed and a more homogeneous soot concentration distribution were observed in the second injection. Besides, averaged KL value in soot regions of the second injection is slightly less than that of the first one. The first injection has a better effect on the ignition delay of the second injection under low ambient pressure. Meanwhile, the soot onset time of the second injection is advanced more obviously. However, compared with the first injection, the advance amount of the ignition delay and the soot onset time of the second injection shows no particular sensitivity with ambient temperature. With longer pilot injection duration, the initial sooting location of the main injection shows a slight reduction but the total soot mass seems to be constant with the variation of the pilot injection duration. (C) 2019 Energy Institute. Published by Elsevier Ltd. All rights reserved.