Combustion and soot evolution during engine cold starts: effects of injection timing and pressure in wall-impinging sprays

Wall-impinging spray occurrence increases significantly during cold start operations in heavy-duty diesel engines, particularly with varying injection strategies. Therefore, computational simulations were employed to investigate the above problems. The results indicate that injection timing primarily influences soot formation by the competing effects of spray-wall interaction and fuel film evaporation. Advancing the injection timing from −6 °CA to −13 °CA intensifies spray-wall interaction, which improves fuel-air mixing and consequently reduces soot emissions to a minimum at −13 °CA. At −20 °CA, the increased fuel film mass and evaporation rate dominate soot formation, leading to higher soot emissions. Premature injection timing at −24 °CA promotes intense premixed combustion, which accelerates the oxidation of soot and film vapor, leading to a second decrease in soot emissions. The influence of injection pressure on soot emissions is governed by two competing effects: the promotion of fuel-air mixing and the increase in fuel film mass. However, raising the pressure beyond 60 MPa causes a surge in fuel film mass and evaporation, which contributes to soot formation. Soot emissions are lowest at 60 MPa. The highest IMEP and lowest soot emissions are obtained at injection timing −13 °CA combined with injection pressure 60 MPa in this heavy-duty engine study.