Guy Hoffmann

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.

Fuel System Pressure Increase for Enhanced Performance of GDi Multi-Hole Injection Systems

The progressive trend towards the GDi engine downsizing, the focus on better fuel efficiency and performance, and the regulatory requirements with respect to the combustion emissions have brought the focus of attention on strategies for improvement of in-cylinder mixture preparation and identification and elimination of the sources of combustion emissions, in particular the in-cylinder particulate formation. This paper discusses the fuel system components, injector dynamics, spray characteristics and the single cylinder engine combustion investigation of a 40 [MPa] capable conventional GDi inwardly-opening multi-hole fuel injection system. It provides results of a study of the influence of fuel system pressure increase between 5 [MPa] to 40 [MPa], in conjunction with the injector static flow and spray pattern, on the combustion characteristics, specifically the particulate and gaseous emissions and the fuel economy. The combustion data shows the marked effect of fuel pressure increase on reduction of the combustion emissions and improvement of fuel consumption. It also illustrates an influence of the injector specifications that is evident at all system pressures.

A Comparative Study of the Fuel Pressure and Temperature Effects on the GDi Multi-Hole Spray

The gasoline direct injection (GDi) engine cold-start emissions of unburned hydrocarbons (UHC) and particulate emissions, prior to the full catalyst warm-up, are a substantial source of engine emissions and the primary challenge to meet the Euro6D and US Tier5 emission regulations. Figure 1 presents typical accumulated particulate emissions from a GDi engine, with homogeneous combustion operation, under the new European drive cycle (NEDC). It illustrates the large proportion of particulate emissions during the engine cold-start phase.