Optimising microscopic spray characteristics and particle emissions in a dual-injection spark ignition (SI) engine by changing GDI injection pressure

Regarding reducing particle emissions from dual-injection spark ignition engines, most of the existing research focused on the benefits of using alcohol fuels. However, a comprehensive study of the effects of fuel injection pressure on microscopic spray characteristics and particle emissions in dual-injection spark ignition engines fuelled with gasoline has not been reported before. In this paper, with the assistance of phase Doppler particles analyser system and fast particle analyser, a study of optimising microscopic spray characteristics and particle emissions in a dual-injection spark ignition engine fuelled with gasoline by changing GDI injection pressure was conducted. The results show that by increasing injection pressure from 5.5 MPa to 18 MPa, both normal and tangential components of droplet velocity increase, but the possibility of spray impingement would not increase a lot. Higher injection pressure would increase the probability of small droplets, and more droplets would collapse with a mode of continuous ripping or break down abruptly. From jet’s central axis to sides, Sauter mean diameter increases first, then reduces outside the spray boundary. Increasing injection pressure from 5.5 MPa to 18 MPa reduces total particle number concentration, which is 53.98% and 45.44% at 2 bar and 10 bar, respectively. Meanwhile, the peak of particle number distribution curve decreases from 3.01×106 to 1.43×106 at 2 bar, whilst reducing from 1.08×106 to 5.33×105 at 10 bar. Overall, this paper comprehensively analyses the effects of fuel injection pressure on microscopic spray characteristics and particle emissions, whilst offering a practical approach to reduce particle emissions in dual-injection SI engines fuelled with gasoline.