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/NOx 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 NOx emissions are observed throughout this tested load range and a gross indicated efficiency over 50% can be observed from low to medium load.