Stratified lean combustion characteristics of a spray-guided combustion system in a gasoline direct injection engine

Gasoline direct injection (GDI) systems have higher power and fuel efficiency than multi-point injection (MPI) systems. The direct injection of fuel into the combustion chamber leads to improved fuel economy because intake air is cooled by fuel evaporation. Direct fuel injection also improves knock resistance and volume efficiency. Furthermore, spray-guided direct injection (DI) combustion systems allow stratified lean combustion operation due to their ability to eliminate wall-wetting and form ignitable stratified mixtures near spark plugs.In this research, a spray-guided combustion system with a piezo-type gasoline direct injector was investigated for its applicability to stratified lean combustion engines. Tests were conducted at constant engine speeds and load conditions (2000 rpm, IMEP 0.28 MPa) that reflect typical operating conditions for passenger vehicles. Fuel economy and combustion stability were evaluated for various injection pressures at each excess air ratio. It is possible to create a sufficiently rich mixture for ignition in the vicinity of the spark plug, even under overall ultra-lean mixture conditions (λ = 3.0). Exhaust gas recirculation (EGR) and retarded ignition timing were considered to achieve a reduction in nitrogen oxide (NOx) emissions. EGR with optimized ignition timing was most effective when a spray-guided combustion system was employed.

► Stable lean combustion in a spray-guided type GDI engine was achieved with late and high pressure fuel injection strategy.
► Even though the spray penetration decreased at higher backpressures, fuel impingement still caused smoke emissions.
► When applying the spray-guided combustion system, EGR reduced NOx and THC more effectively than retarded ignition.