One of the methods to achieve curtailment of diesel engine emissions is the conversion of conventional diesel engines to using natural gas as a supplement to normal diesel fuel. In this type of engines most of the engine power output is provided by the gaseous fuel, while a pilot amount of diesel fuel is used as ignition source of the gaseous fuel-air mixture. However dual fuel operating mode, in comparison to conventional diesel one, suffers from low brake thermal efficiency and high carbon monoxide emissions. By applying a two-zone phenomenological model, the present work studies the effect of air inlet preheating and exhaust gas recirculation on the performance and exhaust emissions of a pilot ignited dual fuel diesel engine. The main objectives are to record and comparatively evaluate the relative impact that each one of the above mentioned parameters has on the engine performance characteristics and emitted pollutants. Moreover, it deals with the determination of an optimum combination between the examined parameters, so that probable undesirable effects on engine performance characteristics are avoided. By comparing the investigation results, it is revealed that the simultaneous increase of both parameters examined could be a promising solution to improving engine efficiency (increase up to 5%) and reducing CO emissions (decrease up to 10%) from a pilot ignited dual fuel diesel engine, without imparting any serious problem to engine operational lifetime. The conclusions from the study may be proved valuable for the application of this technological solution to existing diesel engines. (C) 2013 Elsevier Ltd. All rights reserved.