The Effect of Exhaust Gas Recirculation on Combustion and Emission of RCCI Engine Fueled with Diesel-CNG Fuel

RCCI as low temperature combustion is one of the common methods for reducing nitrogen oxides and soot pollutants. In this study, the effect of exhaust gas recirculation on combustion and emission of an RCCI engine, fueled with diesel and CNG was investigated. The investigated engine is a single-cylinder engine with diesel direct injection to the combustion chamber as high-reactivity fuel and a port fuel injection of CNG fuel as low-reactivity fuel. The start of injection, the injection shape, and the injection duration of both injectors are controlled by the developed ECU. Since the engine tested has good stability in the premix ratio of 60% and is capable of operating with high EGR percentage, it was selected for investigation. The results of this study show that with an increase of the exhaust gas recirculation rate from 0 to 34%, the amount of IMEP and thermal efficiency decrease by about 18%. As the EGR increases, the start, middle, and end of the combustion are delayed due to the decrease in oxygen content inside the combustion chamber. With the increase of EGR, the temperature of the combustion chamber decreased so that increasing CO and UHC production, showing an increase of 86 and 300%, respectively, while NOx decreases by 350%.