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Combustion chamber deposits (CCD) in wall-guided stratified charged direct injection spark ignition (DISI) engines affect combustion significantly because CCD may disturb the air-fuel mixture formation and, as a result, cause emission deterioration. For the design of engines and fuels, it is therefore important to determine the effects of CCD on emissions from DISI engines. In this study, the effects of CCD on emissions from a DISI engine using different fuel distillation properties were investigated. The study results show that, during stratified charged operation, an increase in CCD increased the total hydrocarbon (THC) emissions under high speed conditions and the NOx emissions under the low speed conditions.

This paper presents a study of antiknock performance under various octane numbers and compression ratios in a direct injection spark ignition (DISI) gasoline engine. The relationship between the octane number and engine performance in the DISI engine-the engine torque and the break specific fuel consumption (BSFC)-was investigated in comparison with a multipoint injection (MPI) engine. Due to the improvement in the charging efficiency and the advance of the ignition timing by cooled aspiration, the engine torque of the DISI engine was improved over that of the MPI engine. It was also found that the octane number requirement (ONR) was reduced. In addition, the possibility of engine performance enhancement at high compression ratios was studied. At high compression ratios, the engine torque is reduced due to the heavy knocking when low octane gasoline is used. However, an improvement in the engine torque has been observed with high octane gasoline.

The effects of gasoline volatility (T50 and T90), sulfur content and hydrocarbon types on CO, NOx, total hydrocarbon and speciated hydrocarbons were investigated. The properties of the test gasoline were varied in the range of the Japanese marketplace gasoline, which are characterized by low T50, T90 and low sulfur content. Sulfur content is, especially, regulated under 100 ppm. The Japanese 10.15 mode emissions under hot-transient conditions were measured by using a vehicle equipped with a three-way catalyst. The results indicated that the sulfur content was more effective on exhaust CO, total hydrocarbon and NOx emissions than T50, T90 or hydrocarbon types of gasoline were. The sensitivity to sulfur was different depending on the speciated hydrocarbons. Increasing the sulfur content significantly raised exhaust paraffines, but had no significant effect on olefins. Among the aromatics, the exhaust benzene was most sensitive to sulfur.