Effects of EGR, compression ratio and boost pressure on cyclic variation of PFI gasoline engine at WOT operation

To reduce the cyclic variation is an effective way to improve the fuel economy and combustion of spark ignition engines. In this paper, the effect of exhaust gas recirculation (EGR), compression ratio and boost pressure on cyclic variation was investigated by means of both experiments and simulation for a port fuel injection (PFI) engine. The mechanisms of these effects were analyzed by computational fluid dynamics (CFD) tools. A Ricardo E6 PFI engine was used as the experimental prototype. The experiments were performed with six EGR ratios, three compression ratios and two boost pressures for a given equivalence ratios. The experiments were operated with the same parameters as that of the simulation. Results showed that the simulation work agree well with the experiment. Both simulation and experiment results showed that an increase of EGR ratio will increase cyclic variation for its lower laminar flame speed. However, the combination of EGR with either an appropriate compression ratio or boost pressure can achieve a relatively low cyclic variation.