Reactivity controlled compression ignition (RCCI) is one of the most promising low temperature combustion (LTC) strategies to achieve higher thermal efficiencies along with ultra low oxides of nitrogen (NOx) and particulate matter emissions. Small single cylinder diesel engines of air-cooled type are finding increasing applications in the agriculture pump-set and small utility power generation owing to their lower cost and fuel economy advantages. In the present work, a small single cylinder diesel engine is initially operated under conventional combustion mode at rated speed, varying load conditions to establish the base line reference data. Then, the engine is modified to operate under RCCI combustion mode with a newly designed cylinder head to accommodate a high pressure, fully flexible electronically controlled direct diesel fuel injection system, a low pressure gasoline port fuel injection system and an intake air pre heater. Using a National Instruments (NI) controller, the engine operating parameters in terms of direct injected diesel fuel timings, injection pressures, port injected gasoline fuel timings, intake air temperatures and gasoline to diesel fuel ratio at each load conditions are optimized to achieve maximum brake thermal efficiency. The obtained results show that the engine could be operated under RCCI combustion mode over its complete load range at rated speed with a 14.7% higher brake thermal efficiency, near zero NOx and smoke emissions along with a lower rate of pressure rise as compared to conventional combustion. Thus, the present work demonstrates that RCCI is feasible to achieve and has a greater potential to significantly improve fuel economy along with achieving near zero NOx and smoke emissions in small single cylinder diesel engines. Copyright © 2017 SAE International.