A turbocharged downsizing
spark ignition (SI) engine combined with
direct injection technology has the potential to improve the power
and fuel economy and reduce emissions. However, gasoline engines are
prone to knocking under low-speed and high-load conditions, which
limits the application and development of downsizing SI engines. In
this study, numerical simulation methods are used to explore the feasibility
of water injection in the intake port to reduce the knock tendency
of gasoline direct injection (GDI) engines and to explore the effects
of different water injection pressures on combustion and emissions.
First, the GDI engine is induced to knock by increasing the compression
ratio and advancing the spark timing. Then, the influences of low
position and no angle (LPNA) and high position and angled water injector
arrangements on engine combustion are explored. When the water injector
arrangement is LPNA, the turbulent kinetic energy near the spark plug
is higher, the equivalence ratio is more evenly distributed, and the
engine knock intensity is smaller. Finally, when the arrangement of
the water injector is LPNA, the effects of water injection pressure
on the knock, combustion, and emissions of the GDI engine are explored.
The results show that when the water injection pressure is 5 bar,
the knock intensity of the engine is the smallest, the cycle work
is the highest, and the emissions of NO
x
and unburned hydrocarbon are the lowest.