The global warming and the drain on fossil fuel resources are serious concerns which lead to a desire to improve the fuel efficiency of vehicles and reduce exhaust emission. Considering the market penetration of battery electric vehicles (BEV) and the Well to Wheel CO2 emission, hybrid electric vehicles (HEV) are expected to be the majority for the next decades. As a result, the development of an internal combustion engine is still highly required. The gasoline direct injection (GDI) engine is a promising solutions for complying with future CO2 regulations.

However one of the biggest challenges in GDI engines is to reduce PN (Particulate number) emission. EU commission started the PN emission limit from 2017 with Real Driving Emission (RDE) in the frame of Euro 6d-Temp, which required the Gasoline Particle Filter (GPF) application for most of the gasoline vehicles. The regulation will become further stringent after 2020 by extending the acceptable temperature range down to -7℃. Therefore, the PN reduction technology under extreme cold condition needs to be developed. In this paper, within a collaboration between Hitachi and Technische Universität München (TUM), high fuel pressure up to 50MPa and the multiple injection up to 5 times are investigated as promising countermeasures.

First, the spray measurement was carried out, to clarify the effect of the high fuel pressure and multiple injections on the spray. The penetration reduction could be confirmed only at low load conditions, which was not the case at middle to high loads. With the increase of the injection amount, the benefit of the shorter injection duration by higher pressure seems to be cancelled by the high injection velocity. Therefore the multiple injection is necessary to actively control the penetration and reduce the spray wall impingement.

Next, the thermodynamic engine test for PN emission measurement and the endoscope measurement for PN source identifications are carried out. For realizing the cold environment condition, an engine cooling facility was installed to the single cylinder research engine, which can cool down the engine head down to -7℃. The PN reduction effect of the high fuel pressure up to 50MPa was investigated by the optical measurement. PN could be reduced at low load due to the better homogeneity and less wall wetting, but the tendency was not consistent at mid-high load. The reason was estimated to be the longer penetration, cancelling the benefit of better evaporation and causing wall wetting.

The DoE-based optimization of the multiple injection strategy was carried out, as the initial screening of the promising multiple injection concept. The response surface model was built up, and promising injection concepts were obtained. The optimized injection strategy with triple injection showed the best PN reduction effect.
Based on the DoE results above, the promising injection strategies were further investigated with higher fuel pressure and larger number of injections. Finally 5 times injection with 50MPa showed the significant PN reduction at the high load area.

Mr. Naoki Yoneya, Hitachi, Ltd., JAPAN; Mr. Sebastian Blochum, Technical University of Munich, Institute of Internal Combustion Engines, GERMANY; Prof. Dr.-Ing. Georg Wachtmeister, Technical University of Munich, Institute of Internal Combustion Engines, GERMANY; Mr. Yoshihito Yasukawa, Hitachi Automotive Systems Europe GmbH, GERMANY; Mr. Yuki Sugiyama, Hitachi Automotive Systems, Ltd., JAPAN