The aim of this study is to evaluate a heavy duty diesel engine operation under reactivity controlled compression ignition combustion fueled with diesel oil and natural gas enriched with hydrogen and nitrogen addition. In this study, a single cylinder heavy– duty diesel engine is set to operate at 9.4bar gross IMEP (Mid- Load). The amount of injected diesel oil per cycle into the engine combustion chamber assumes to be fixed and hydrogen and nitrogen (75:25 volumetric proportion of hydrogen: nitrogen) along with exhaust gas recirculation are gradually added to natural gas while the total fuel energy content is kept fixed. The results show that by adding hydrogen and nitrogen to natural gas, without the exposure to the excessive combustion noise, the hydrogen energy share can be enhanced up to 40.24% and the gross indicated efficiency more than 50% is achievable. Moreover, without significant engine power losses, the engine emission levels such as NOx, carbon monoxide, unburned hydrocarbon, and formaldehyde are reduced significantly.