Experimental investigation on the combustion and emissions characteristics of an N-butanol/CTL dual fuel engine

The effects of n-butanol/coal to liquid (CTL) dual fuel combustion mode on combustion and emissions characteristics were experimentally investigated at medium load. The CTL was produced by the Fischer-Tropsch process and the N-butanol was obtained by the biological fermentation. The optimized combustion boundary conditions mainly include n-butanol ratio, EGR rate and start of injection (SOI). The results showed that the premixed combustion ratio (PCR) of CTL is lower than the conventional diesel, which is beneficial to reduce the peak value of in-cylinder pressure and rate of pressure rise (ROPR). Port fuel injection of n-butanol improves the homogeneity of the mixture gas, which is contributing to increasing the PCR, shortening the combustion duration, thereby suppressing the generation of particles and improving the volumetricity of combustion. Introducing EGR effectively suppresses the excessive ROPR caused by the pre-injection of n-butanol and broadens the range of n-butanol premixed fraction. In the comparison of pure CTL mode, combining with the suitable EGR rate and SOL the combustion mode of n-butanol/CTL dual fuel can simultaneously reduce NOx and particulate emissions. Among them, a higher n-butanol ratio needs to be combined with a higher EGR rate to obtain a better comprehensive emission performance, and increasing the n-butanol ratio promotes the conversion of particulate to nuclear mode. After optimization of the combustion boundary conditions, the NOx emission of the n-butanol/CTL dual fuel mode at the n-butanol ratio of 30% is reduced by 49.5%, and the particulate matter emission is reduced by 40.9%, relative to the pure CTL mode.