Computational Study of a Multiple Fuel Injector Concept under High-Load and High-EGR Conditions

A new concept utilizing multiple fuel injectors was proven effective at reducing heat transfer losses by directing spray plumes further away from the combustion chamber walls. In this concept, two injectors are mounted close to the rim of the piston bowl and point in opposite directions to generate swirling in-cylinder bulk motion. Moreover, a new flat-bowl piston design was also proposed in combination with the multiple fuel injectors for even larger improvements in thermal efficiency. However, all tests were performed at low-to-medium load conditions with no significant EGR. Modern engine concepts, such as the double compression-expansion engine (DCEE), have demonstrated higher thermal efficiency when operated at high-load conditions with a large amount of EGR for NOx control. Thus, this study aims to assess the effectiveness of the multiple-fuel-injector system under such conditions. In this study, a number of 3-D CFD simulations are performed using the RANS technique in CONVERGE. The computational domain is based on the modified Volvo D13 engine geometry that is used as a combustor unit of the DCEE. The results of this study show that the injection strategies used previously with the multiple-fuel-injector concept perform poorly at high-load conditions due to inadequate mixing. Moreover, the flat-bowl piston design proposed previously does not seem to improve heat transfer losses at these conditions. Thus, several alternative piston bowl designs are investigated, some of which are shown to reduce heat losses and improve mixing. Finally, a number of perspective strategies are recommended to be implemented with the multiple-fuel-injector concept for efficiency maximization.