Effects of the swirl ratio and spray angle on the mixture stratification in a diesel–NG RCCI engine

Abstract

Reactivity Controlled Compression Ignition (RCCI) engine is the newest technology to settle the issue of excessive NOx emission of conventional diesel engines. In the present work, the effects of swirl ratio and spray angle on the performance and stratification of diesel–natural gas RCCI engines are investigated numerically. The local and global stratifications are measured by the field of equivalence ratio and its standard deviation (SD), respectively. It is concluded that the ignition delay and the location of ignition depend on the local and global stratifications controlled by the swirl ratio and spray angle. The increase in the swirl ratio increases the ignition delay by decreasing the value of equivalence ratio SD, $$ \phi $$ -SD, before ignition. On the other hand, the variation of spray angle controls the combustion duration by changing the sequence and the lag between the two ignition events happening in the bowl and squish area. Moreover, it is found that the position of the maximum stratification on $$ \phi $$ -SD curve is well correlated with CA50. Finally, the best operation is with a swirl ratio in the range 0.7–0.85 and spray angle of 145° which results in suppressed emissions and an efficiency above 50%.