Despite the known benefits of direct injection spark ignition engines, PFI (port fuel injection) remains a relevant concept for cost-sensitive market segments. PN emissions limits is already expected for future emission legislations also for PFI engines (in China). This paper explains the mechanisms of PN production correlated with: CFD experiments on NA engine (natural aspirated engine) and turbo engine, Visiolution from AVL, Test bench measurements with gas analysis and PN measurement.
Previous studies showed impact of the spray layout, injection timing, charge motion, operating points of the engine, temperature and fuel effect. This paper mainly focuses on the spray design of the injector through the pattern, the homogeneity of injector pattern having the main contribution in relationship with PN reduction.
It is shown with several spray configurations including height and width cross section variations that homogeneous distribution should be accompanied of low fuel quantities everywhere across the spray pattern in order to reduce the fuel deposit in intake pipes and combustion chamber and hence the risk of pool fires, main sources of particulates emissions.
Thanks to the more uniform lower thickness fuel film deposit in the intake duct and combustion chamber, the new spray design approach shows less sensitivity of PN emission with load, speed and temperature of the engine, as well as equivalence ratio and fuel quality (expressed through PM index value).
In the high load area of a turbocharged engine significant PN improvement is shown: several orders of magnitude of PN reduction is measurable on steady state test bench. The reduction of PN is seen on hot & cold condition on cycle on chassis dyno (WLTP, or simulation on chassis dyno of the RDE test) for two main fuels with different qualities (high and low PMindex) the results on other pollutants being unchanged even in transient condition.