Impact of Port Fuel Injection and In-Cylinder Fuel Injection Strategies on Gasoline Engine Emissions and Fuel Economy

As the emission regulations for internal combustion engines are becoming increasingly stringent, different solutions have been researched and developed, such as dual injection systems (combined port and direct fuel injection), split injection strategies (single and multiple direct fuel injection) and different intake air devices to generate an intense in-cylinder air motion. The aim of these systems is to improve the in-cylinder mixture preparation (in terms of homogeneity and temperature) and therefore enhance the combustion, which ultimately increases thermal efficiency and fuel economy while lowering the emissions.

This paper describes the effects of dual injection systems on combustion, efficiency and emissions of a downsized single cylinder gasoline direct injection spark ignited (DISI) engine. A set of experiments has been conducted with combined port fuel and late direct fuel injection strategy in order to improve the combustion process. Several steady state points were selected for this study to represent the typical engine conditions in use. Direct injection timings were varied to find the best injection timing for optimum in-cylinder conditions and therefore optimum efficiency at each speed and load. The results show that net indicated specific fuel consumption (NISFC) could be decreased by up to 9% at 1000 rpm and 8.83 bar NIMEP (net indicated mean effective pressure) using the optimized PFI/late DI injection. At the other test points, NISFC was similar to those with DI-only operation despite higher in-cylinder pressures and slightly shorter combustion durations. In terms of emissions, there was an increase of CO when using both PFI and late DI, while HC decreased slightly at the same conditions. The smoke number shows a significant reduction at most cases compared to the direct injection-only operation.