Study on the Effects of Ethanol-gasoline Octane Number on Anti-knock Performance in Direct-injection Gasoline Engine

Abstract

ABSTRACT The high strength technology for gasoline engines improves the thermal efficiency, while at the same time, increasing the knocking tendency. To improve the anti-knock performance of gasoline engines, blending mixture of fuels are needed with higher requirements. In this paper, ethanol/TRF fuel was selected as the gasoline substitute and the effects of fuel octane number and ethanol content on anti-knock performance were simulated in a three-dimensional engine model. The results show that when knock occurs, the knock amplitude is larger at the intake port and the knock onset is earlier at the exhaust port. With the enhancement of anti-knock performance, abnormal combustion such as spontaneous ignition of the end-gas mixture is suppressed, where the turbulent kinetic energy increases in the combustion chamber but decreases at the edge of the cylinder. Also, it is indicated that increasing the RON by 1, mixing 2% volume ethanol, and increasing MON by 1 orderly improve the thermal efficiency. Based on the research and optimization, an evaluation index of anti-knock performance for ethanol-gasoline fuel (EOI*) is proposed, which is suitable for modern engines. From this index, the chemical effect contributes most in the anti-knock performance of ethanol-gasoline mixtures, while the evaporative cooling effect and sensitivity are less and less dominant.