Detailed experimental analysis of combustion characteristics of port fuel injected HCCI engine with n-butanol DEE blends for emission reduction

Homogeneous charge compression ignition engines are a promising combustion model with both low emissions and high thermal efficiency advantages. The main problem with Homogeneous charge compression ignition is that there is no physical mechanism to control the combustion phase. In addition, operating range is narrow. Auto-ignition is directly affected by fuel properties. Fuel properties also have a significant effect on operating range. In this study, second generation biofuel butanol and high reactivity diethylether fuel pair were selected in order to both control combustion phase and extend the operating range. The results demonstrated that increasing the proportion of butanol in the fuel blend allows for better control of the combustion phase. Butanol delayed the combustion process, causing the majority of heat release to occur around top dead center. This led to an improvement in thermal efficiency and a reduction in emissions. The highest indicated thermal efficiency was recorded as 43.2 % with the use of 45 % butanol 55 % diethyl ether blend fuel. The widest operating range was achieved with 30 % butanol 70 % diethyl ether blend fuel, where butanol helped to keep knocking just below the safety threshold of 9 bar/°CA. To reduce total energy losses, a compromise was made on intake temperature, which limited further extension of the operating range. Despite this, all test fuels yielded zero NOx and soot emissions. Particularly under conditions with thermal efficiency above 30 %, HC and CO emissions decreased. However, under ultra-lean mixture conditions, misfire events caused a reverse trend, resulting in increased HC and CO emissions.