Insights into the underlying reaction kinetics of gasoline–ethanol interactions and their effects on the auto-ignition characteristics of gasoline/ethanol blends

Abstract

Ethanol-blended gasolines show enhanced anti-knock behavior in spark-ignition engines. Fundamental experimental investigations on their auto-ignition behavior are however scarce in the literature. In addition, previous numerical studies present diverse explanations for the effects of ethanol blending on the ignition delay times of gasoline/ethanol blends. These factors motivate the present study, aiming to extend the knowledge on the ignition of gasoline/ethanol blends and the understanding of the underlying reaction kinetics. For this purpose, ignition delay time measurements of the mixtures of a real gasoline fuel blended with ethanol were carried out in a shock tube and a rapid compression machine for range of conditions with respect to temperature, pressure, equivalence ratio, and blending ratio. Numerical modeling of the fuel ignition was performed based on a chemical mechanism, which is proposed in this study to predict the obtained data accurately. The reported datasets, in conjunction with the numerical analyses, demonstrate the significant mitigating impact of ethanol blending on the gasoline reactivity in the low- and intermediate-temperature ranges. It is found that, while the ignition delay times at intermediate temperatures are influenced by both physical dilution and chemical kinetic effects, the retarded ignition at low temperatures below 700 K is solely attributed to the chemical interaction of gasoline surrogate and ethanol in terms of OH radical competition. The OH radical scavenging character of ethanol also leads to a non-linear blending behavior. At high temperatures, the blending of ethanol accelerates the auto-ignition slightly, owing to its moderately higher reactivity at these conditions.