An experiment of how fuel injection pressure affects the performances of gasoline compression ignition(GCI) was conducted

including the characteristics of combustion

engine knock

thermal efficiency and emissions. It was conducted on a modified single-cylinder engine with the compression ratio of 17. The results show that with the increase in the injection pressure

the air-fuel mixture forms much more quickly

the auto-ignition timing advances towards the top dead center

and the combustion duration becomes shorter. All of those lead to a higher thermal efficiency at first and a slightly lower one later. However

high injection pressure will lead to multipoint auto-ignition

causing higher maximum pressure rise rate and severe engine knock

which requires a delayed injection timing. The combustion becomes more sensitive to injection timing as the injection pressure rises

and the higher variation in coefficient of cyclic indicates mean effective pressure or knock is more likely to appear

resulting in more difficulty in combustion control. Through data analysis

no significant effects of the injection pressure on knocking frequency is found. Besides

increased injection pressure will reduce HC and CO emissions

but result in a certain increase in NOx emissions.