Achieving simultaneous reduction of NOx,CO and unburned hydrocarbon (UHC) emissions without compromising engine performance at part loads is the current focus of dual fuel engine research.The present work focuses on an experimental investigation conducted on a dual fuel (diesel-natural gas) engine to examine the simultaneous effect of inlet air pre-heating and exhaust gas recirculation (EGR) ratio on performance and emission characteristics at part loads.The use of EGR at high levels seems to be unable to improve the engine performance at part loads.However,it is shown that EGR combined with pre-heating of inlet air can slightly increase thermal efficiency,resulting in reduced levels of both unburned hydrocarbon and NOx emissions.CO and UHC emissions are reduced by 24％ and 31％,respectively.The NOx emissions decrease by 21％ because of the lower combustion temperature due to the much inert gas brought by EGR and decreased oxygen concentration in the cylinder.