Insights into the effects of direct injection timing on the characteristics of deposited fuel film and Particulate Matter (PM) emissions from a Dual-Fuel Spark Ignition (DFSI) engine

Particulate Matter (PM) emissions have been a global concern for environmental protection and public health. By utilising Laser-Induced Fluorescence (LIF) method and PM spectrometer analyser, this study provided new insights into the effects of direct injection timing (t(DI)) on the characteristics of deposited fuel film and engine PM emissions. The experimental results show that deposited fuel with a close impingement distance (D) has a more irregular edge and nonuniform distribution. Both deposited film mass and area would be decreased by increasing D or decreasing the injection duration (t(inj)). For a fixed t(inj), a steady reduction can be found in the deposited mass ratio (R-df) with the increase of D. Moreover, the impact of D on R-df becomes a bit stronger by increasing t(inj) from 1.2 ms to 3.0 ms. An appropriate direct injection timing is very beneficial to reduce PM number (N-P) and PM mass (M-P) of DFSI engine. By delaying tDI from -340 degrees CA to -300 degrees CA, the maximum reduction of total N-P and M-P can be up to 63.77% and 90.68%, respectively. By further delaying t(DI) to -280 degrees CA is difficult to provide a sufficient time for fuel-air mixture prior to ignition, which would cause a considerable increase of PM emissions.