Experimental investigation of reactivity controlled compression ignition with n-butanol/n-heptane in a heavy-duty diesel engine

Highlights: • Reactivity controlled compression ignition shows two combustion regimes. • Double direct injection shows good control of combustion phasing. • High exhaust gas recirculation rate is required to phase combustion properly. • Ultra-low soot/nitrogen oxides emissions can be achieved from 4 to 12 bar. • Above 50% gross indicated efficiency can be achieved from low to medium loads. Butanol is a potential alternative fuel to be applied in the internal combustion engine for its sustainability and low-sooting propensity. In this paper, n-butanol is port injected as low reactivity fuel and n-heptane is directly injected into cylinder as high reactivity fuel to achieve high thermal efficiency as well as low soot/NO_x emissions. To understand the effects of charge preparation parameters and load range of this reactivity controlled compression ignition combustion, experiments are performed in a single cylinder heavy-duty diesel engine. The results show that single direct injection causes either too early combustion phasing or excessive HC/CO emissions. Increasing the inlet boosting pressure is beneficial to obtain high thermal efficiency but HC/CO emissions deteriorate remarkably. The double direct injection strategy can phase the combustion properly and obtain high gross indicated efficiency without sacrificing CO emissions too much. Additionally, a high exhaust gas recirculation rate is necessary to achieve proper control of combustion phasing as the reactivity of n-butanol is not low enough. It is found that the n-butanol/n-heptane reactivity controlled compression ignition can be operated from low to medium loads. And the sensitivity of combustion phasing to the direct injection timing decreases as the load increases. At medium–high load, combustion couldn't be phased after the top dead center, which leads to high pressure rise rates and high peak pressures. Extremely low particulate matter and NO_x emissions are observed throughout this tested load range and a gross indicated efficiency over 50% can be observed from low to medium load.