An overview of STEP II activity of JCAP gasoline working group is presented. The main evaluation of STEP II was conducted with advanced gasoline-powered vehicle and fuel technologies for reducing exhaust emissions. 4 models of prototype vehicles were prepared for evaluation. 3 of them were SIDIs with lean NOx catalysts and another was MPI with three way catalyst. All test vehicles were designed with the target of 1/6 emission level of the FY 1978 Japanese regulations.
Sulfur effects were evaluated by 30000km mileage accumulation tests using 2ppm, 22ppm and 86ppm sulfur gasolines. Exhaust emissions of SIDI vehicles were largely affected by the sulfur content but the degree of effect differed between vehicles. For further reduction of SIDI emissions, investigations about “Package technology” of vehicle and fuel - sulfur durability improvement of lean NOx catalyst and sulfur reduction of fuel - with consideration about “Well to Wheels” CO2 are necessary.
Effects of Aromatics (8, 30, 50%), T50 (72, 101, 124 degree C), T90 (119, 150, 183 degree C) and MTBE (0, 6.2, 13.1%) on exhaust emission were also evaluated. Results showed individual tendencies of fuel property effects with each vehicle. It is assumed that the difference is caused by various advanced combustion and after-treatment systems as well as the level of accuracy and diversification of their respective control systems. Elemental study on combustion analysis is necessary for further mechanism analysis.