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With a view to understanding the air-fuel mixing behavior and the effects of the mixture quality on the emissions formation and engine performance, a new quantitative factor of the in-cylinder air-fuel homogeneity named Homogeneity Factor (HF) has been developed. Its characteristics under various injection conditions and air swirl motions within the cylinder have been investigated with CFD simulation. The results have shown that air-fuel homogeneity is essentially affected by the spatial and temporal fuel distribution within the combustion chamber. Higher injection pressure, longer dwell time and increased pilot fuel quantities can contribute to better mixing quality resulting in increased HF and optimum engine performance with low fuel consumption and soot emissions. With regard to the in-cylinder air motion, increasing swirl ratio enhances the air-fuel mixing quality which has been reflected in the variation of the HF.

Diesel engine emissions are directly influenced by the air fuel mixture within the cylinder chamber. Increasing concern over the environment impacts of the exhaust pollutants has enforced the setting of emissions legislation since the 1960s. In the last decades emissions legislations have become stricter which resulted to the introduction of multiple injection strategies and exhaust gas recirculation (EGR) in the cylinder in order to abate emissions produced. In this study, the effect of injection rate for double in-cylinder injection in combination with various EGR and bio-diesel fuel rates has been studied using CFD simulations. Taguchi orthogonal arrays have been used for reducing the number of simulations for possible combinations of different rates of injection quantities, EGR composition and bio-diesel quantities. Oneway analysis of variance technique (ANOVA) has been used to estimate the importance of the above factors to the emissions output and performance of the engine.