Effects of pilot injection timing on the combustion noise and particle emissions of a diesel/natural gas dual-fuel engine at low load

For diesel pilot ignited dual-fuel engines, pilot injection timing is a very important parameter to control the initial combustion process. In this study, the combustion noise and particle emissions characteristics of a diesel/natural gas dual-fuel engine with varying pilot injection timing at low load (BMEP = 0.357 MPa) were experimentally investigated. The in-cylinder pressure, heat release rate (HRR), pressure raise rate (PRR), ignition delay, combustion duration and brake thermal efficiency (BTE), as well as THC, CO, NOx and particle emissions were analyzed. The maximum pressure rise rate was presented as a measure of combustion noise and the electrical low-pressure impactor (ELPI) was employed to illustrate the particle number and mass distributions. The experimental results indicated that the combustion noise is obviously deteriorated with advanced pilot injection timing. However, the particle number and mass concentrations could be reduced significantly with advanced pilot injection timing. In addition, the maximum reduction of particle number was more than 75%. Therefore, according to experimental study of combustion noise and particle emissions, it is not rational to excessively advance the pilot injection timing. Meanwhile the combustion noise can be considered as a limiting factor when advancing the pilot injection timing.