Progress and recent trends in reactivity-controlled compression ignition engines

Abstract

Low-temperature combustion is an emerging engine technology that has the ability to yield low NOx and soot emissions while maintaining high fuel efficiency. Low-temperature combustion strategies include homogeneous charge compression ignition, premixed charge compression ignition, reactivity-controlled compression ignition and partially premixed combustion. These low-temperature combustion strategies use early fuel injections to allow sufficient time for air–fuel mixing before combustion. According to the literature, some low-temperature combustion strategies are not promising for future automotive and power generation applications due to difficulties in controlling the heat release rate and the lack of a combustion phasing control mechanism. To mitigate these problems, the reactivity-controlled compression ignition combustion concept was introduced. Reactivity-controlled compression ignition is a dual-fuel partially premixed combustion concept, which uses port fuel injection of a low-reactivity fuel (e.g. gasoline, natural gas and alcohol fuels) and direct injection of a high-reactivity fuel (e.g. diesel and biodiesel) with blending inside the combustion chamber to increase the combustion duration and to provide phasing control. Combustion phasing is controlled by the relative ratios of the two fuels, and the combustion duration is controlled by spatial stratification between the two fuels. This article begins by an overview of the different low-temperature combustion strategies and demonstrates some advantages of reactivity-controlled compression ignition, over homogeneous charge compression ignition and premixed charge compression ignition combustion strategies in regard to fuel flexibility and combustion controllability. A comprehensive review of recent research on various aspects of reactivity-controlled compression ignition and comparisons of thermal efficiency and pollutant emissions over conventional diesel combustion is also presented. This article presents the significance of reactivity-controlled compression ignition strategy as a promising solution for future automotive engines and discusses future research directions.