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Strategies Towards Meeting Future Particulate Matter Emission Requirements in Homogeneous Gasoline Direct Injection Engines

Since the introduction of the EURO 5 emission legislation particulate matter emissions are no longer only a concern in the development of Diesel engine powertrains. In addition to particulate mass (PM) requirements the new European legislation will also foresee the implementation of a particulate number (PN) requirement for all spark ignition (SI) vehicles with the introduction of EURO 6. Measurements with state of the art gasoline engine powered vehicles show that conventional MPFI engines are already below the future proposed limits while gasoline engines with direct injection are above these limits and will require additional development efforts. This paper discusses both fuel system component requirements as well as control strategies in support of reducing particulate emissions. On the component side, mixture formation in regard to evaporation rate and penetration is a key factor. On the control side, injection timing and injection splitting are important parameters, especially under cold catalyst heating conditions. Encouraging test results show that significant improvements in regard to particulate matter emissions can be made. For the particulate mass emission a value significantly lower than the proposed limit can be achieved, while the proposed particulate number limit is significantly more challenging. The demonstrated vehicle results detailed below show that the proposed EURO 6 targets can be met by gasoline engines with direct injection by careful further optimization of the involved hardware and calibration without adding an additional after-treatment system.