Control of Ignition Timing and Combustion Phase by Means of Injection Strategy for Jet-Controlled Compression Ignition Mode in a Light Duty Diesel Engine 2020-01-0555

Controllability of ignition timing and combustion phase by means of dual-fuel direct injection strategy in jet-controlled compression ignition mode were investigated in a light-duty prototype diesel engine. Blended fuel with lower reactivity was delivered in the early period of compression stroke to form the premixed charge, while diesel fuel which has higher reactivity was injected near TDC to trigger the ignition. The effects of several important injection parameters including pre-injection timing, jet-injection timing, pre- injection pressure and ratio of pre-injection in the total heat value of injected fuel were discussed. Numerical Simulation by using CFD software was also conducted under similar operating conditions.

The experimental results indicate that the jet-injection timing shows robust controllability on the start of combustion under all the engine load conditions. Pre-injection timing/pressure/ratio show little impact on the start of combustion due to low reaction activity of premixed charge. Early pre-injection timing and larger pre-injection pressure lead to wall-wetting and poor vaporization of pre-injected fuel especially at light duty conditions, as a result, combustion duration increases, and CO/THC emissions enhance. Larger pre-injection ratio in the total heat value of injected fuel prolongs combustion duration and enhances CO/THC emissions at lower engine load, reduces combustion duration and CO/THC emissions at higher engine load. The numerical simulation results demonstrate the two-stage combustion process described according to the experimental results. The two-stage combustion process of diesel jet JCCI mode is featured by the evolution of intermediate species such as H2O2 and OH, and the main emission products such as CO and NOx. At last, the effects of injection parameters on JCCI combustion characteristics are summarized.