The effects of diesel injection strategies on the combustion and pollutant emission characteristics of a modified heavy-duty reactivity controlled compression ignition engine fueled with natural gas/diesel are studied. Natural gas with low reactivity is assumed to be inducted into the engine through the intake port, while diesel fuel with high reactivity is directly injected into the engine using a double injection strategy. Several parameters were studied including the premixed natural gas amount, the first and second injection timings and the injected diesel mass split between the two injections. The results showed improved engine efficiency with reductions in soot and oxides of nitrogen emissions could be achieved with the injection strategies studied, but hydrocarbons and carbon monoxide emissions were deteriorated. Three factors, namely first start of injection timing, second start of injection timing and the diesel injection fuel fractions, had pronounced effects on reactivity controlled compression ignition engine combustion performance and emissions. To reduce soot and oxides of nitrogen emissions, increasing the natural gas percentage, advancing first and second starts of injection timing beyond a certain point and increasing fuel fraction in first start of injection timing are preferred, but they had an adverse effect on hydrocarbons and carbon monoxide emissions. (C) 2015 Elsevier Ltd. All rights reserved.