Dual-fuel engines fueled with n-butanol/n-octanol and n-butanol/DNBE: A comparative study of combustion and emissions characteristics

The dual-fuel combustion mode has drawn much attention due to its high thermal efficiency and low emissions. In this study, to realize the dual-fuel combustion, n-butanol was selected as the port-injected fuel (PIF); whereas two C8-biofuels, i.e., n-octanol and di-n-butyl ether (DNBE), were used as the direct-injected fuels, respectively. A comparative study between n-butanol/n-octanol and n-butanol/DNBE fueled dual-fuel engines in terms of their combustion and emissions characteristics was numerically carried out with the KIVA4-CHEMKIN code. The energy fractions of PIF varied from 0 to 0.4 at 1500 rpm and 2280 rpm. The results show that with the PIF increasing, the peak pressure and CO emissions increase, while the combustion duration gets shorter. Though adding more n-butanol contributes to a lower global fuel reactivity, the ignition delay is still shortened. Compared with the n-butanol/n-octanol engine, the n-butanol/DNBE engine exhibits a shorter ignition delay due to the high reactivity of DNBE. Also, it has a lower maximum pressure rise rate and longer combustion duration for its diffusion combustion phase. Consequently, a higher indicated thermal efficiency and much lower CO emissions are observed in the n-butanol/DNBE dual-fuel engine, with the expense of a slight increase in NOx emissions.