Effects of dual-direct injection parameters on performance of fuel Jet Controlled Compression Ignition mode on a high-speed light duty engine

Fuel Jet Controlled Compression Ignition (JCCI) was proposed to control the combustion phasing of premixed charge. In this mode, a small quantity of jet-injection diesel fuel was used to ignite the premixed charge, which was prepared by the main pre-injection blended fuels of diesel and ethanol-gasoline. Experiments of JCCI mode combined with dual-direct injection strategy were conducted on a modified single-cylinder naturally aspirated diesel engine. Effects of jet-injection and pre-injection parameters on the combustion and emission characteristics were investigated in detail under four engine load conditions at the rated speed of 3000 r/min. Experimental results showed that the diesel fuel jet-injection could control the ignition timing and combustion phasing robustly at all the four engine load conditions. The combustion process was composed of two stages, the jet fuel spontaneous combustion stage and the pre-mixture combustion stage. Besides, sensitive analysis of the jet-injection and pre-injection parameters on the JCCI mode performance were also accomplished. Advancing the jet-injection timing could shorten the combustion duration and improve the indicated thermal efficiency (ITE), but along with an increase in the nitrogen oxides (NOx) emissions, especially at higher engine loads. As the pre-injection energy ratio was upgraded, the local equivalence ratio and the diffusion-controlled combustion could be reduced, resulting in the reduction of soot emissions. Sensitivity interval was introduced to access the effects of pre-injection timing. Beyond this interval, the pre-injection timing showed insignificant effects on the combustion characteristics and emissions. With the increase of pre-injection pressure, more pre-injection fuels penetrated into the crevice and near liner regions, and the total hydrocarbon (THC) emissions were increased. Finally, the enhanced reactivity of pre-injection fuels was demonstrated to effectively reduce THC emissions at lower engine loads.