Premixed ignition characteristics of blends of gasoline and diesel-like fuels on a rapid compression machine

Abstract

Fuel ignition process is of importance in premixed diesel low-temperature combustion strategies because longer ignition delay could provide more fuel and air mixing time. Using blends of gasoline and diesel-like fuels might be a possible way for the ignition delay extension. In this study, a rapid compression machine is employed to investigate the characteristics of premixed ignition processes of blends of n-heptane and commercial gasoline. The proportion of gasoline in blended fuels and the compression ratio in this rapid compression machine are varied to investigate the effects of fuel component and compression ratio on ignition processes. It is found that blended test fuels have two-stage increases in their cylinder pressure traces, indicating that a low temperature heat release process exists before the main combustion stage. Increased gasoline proportion in test fuels reduces peak cylinder pressure and maximum pressure rise rates, while the 1st, 2nd, and overall ignition delay are extended. Increased compression ratio elevates the peak cylinder pressure and shortens the 1st stage, 2nd stage, and overall ignition delays. The maximum pressure rising rates are also increased with compression ratio, so when the low gasoline proportion test fuels are used, knock combustion tends to occur at high compression ratio conditions. However, as long as the gasoline proportion increases to a sufficient level, knock combustion is avoided.