Experimental study on compound HCCI (homogenous charge compression ignition) combustion fueled with gasoline and diesel blends

Abstract

Because the energy crisis and environmental pollution are significant concern, a next-generation combustion mode for internal combustion engines that can simultaneously reduce exhaust emissions and substantially improve thermal efficiency has attracted increasing attention. In the last two decades, diesel-fueled HCCI (homogenous charge compression ignition) combustion has been widely researched. It has been determined that diesel HCCI combustion has the potential to improve NOx and soot emissions at low-to-medium loads; however, it suffers from higher HC (hydrocarbon)/CO (carbon monoxide) emissions, narrow operating ranges, and uncontrollable ignition timing and combustion rates due to low volatility and high ignitability. For this reason, 30%–50% (v/v, briefly G30, G40, and G50) gasoline/diesel fuel blends are used in a novel technology of a compound HCCI combustion mode, in which port fuel injection and in-cylinder direct injection are combined. The combustion and emission characteristics of the compound HCCI combustion using blend fuels are investigated on a single-cylinder engine. The effect of the gasoline volume in the blends, the premixed ratio, and the overall fuel supply rate on compound HCCI combustion are initially evaluated, and the effects of the intake air boost on G30 compound HCCI combustion is also investigated.The experimental results indicate that the maximum heat release rate, maximum in-cylinder pressure, and NOx emissions of G40 and G50 compound HCCI combustion significantly increase when compared to that of G30 compound HCCI combustion. Moreover, it is determined that the intake air boost has great potential to reduce the NOx and soot emissions of compound HCCI combustion simultaneously. CO and HC emissions of optimized G30 compound HCCI combustion with/without boost are relatively higher compared to that of traditional DICI (direct injection compression ignition) combustion. The NOx and soot emissions of optimized G30 compound HCCI combustion with intake air boost are far lower than those of the DICI diesel engine. Specifically, the NOx emissions can be maintained within 100 ppm, and the soot emissions are below 10% at the full load ranges.