Particulate emissions from a GDI engine equipped with an upstream fuel source 2019-01-1180
Public health risk and resulting stringent emission regulations for internal combustion engines pose a need for solutions to reduce particle emissions (PN). Current PN control approaches include increased fuel pressures, optimization of spray targeting, multiple injections and tumble flaps in addition to gasoline particulate filters (GPF).
In this paper, a single-cylinder spark-ignited GDI engine is equipped with a custom inlet manifold and a port fuel injector located 500 mm upstream. The engine was used to measure and analyze particulate emissions under stationary medium/high load operation for several varied parameters with focus on the mass split between Direct Injection and the upstream fuel source. Since an upstream injector results in substantially better mixing quality, the mass split between the injectors provided a way to control the mixing quality. The experiments also included particulate measurements with a thermodenuder and a catalytic stripper, removing major part of the volatile organic compound (VOC) from the raw emissions. In this way particle numbers (PN) from both raw emissions and solid particulates in addition to size distributions from solid PN could be measured and analyzed.
The results demonstrate and quantify the benefits with fuel mass split on the particulates showing that the PN can be decreased by almost 10 times at 1500 rpm and 7 bar IMEP using 50% fuel mass split between the injectors. Even a 10% of fuel mass contribution from the upstream injector showed a significant reduction in PN. At other combinations of dual injection for a given load point, as the percentage of port injected fuel mass increases, PN decreases. However, this reduction in PN is sensitive to engine operating speed whereas solid PN is observed to be independent of engine speed. Such an effect on PN suggests improved mixing causes less rich zones and or wall wetting inside the cylinder compared to 100% Direct Injection operation.