Effects of direct injection timing and premixed ratio on combustion and emissions characteristics of RCCI (Reactivity Controlled Compression Ignition) with N-heptane/gasoline-like fuels

This paper presents an experimental study on the combustion and emissions characteristics of Reactivity Controlled Compression Ignition (RCCI) combustion with n-heptane/gasoline-like fuels are researched on a single-cylinder engine. The effects of injection timing and premixed ratio are investigated. The experimental results indicate that with the advance of the direct injection timing, the ignition delay increases for all three fuels and ethanol has the longest ignition delay. The CO (carbon monoxide) and soot emissions gradually decrease while the NOx emissions increase for the three different fuels. However, HC (hydrocarbon) emissions monotonically decrease with gasoline but initially increase and then decrease with the alcohol fuels. When comparing gasoline and ethanol with the same premixed ratio and direct injection timing, the combustion phase with ethanol as port fuel occurs later than that of gasoline, especially with a higher premixed ratio. Moreover, ethanol has lower NOx and soot emissions than those of gasoline, indicating that ethanol as an alternative fuel can improve emissions in the RCCI combustion mode.