Numerical evaluation of the potential of late intake valve closing strategy for diesel PCCI (premixed charge compression ignition) engine in a wide speed and load range

A full-engine-cycle multidimensional model was applied to investigate the effect of late (intake valve closing) IVC on combustion and emission characteristics in a diesel (premixed charge compression ignition) PCCI engine in a wide speed and load range. The results indicate that the in-cylinder swirl ratio and turbulence kinetic energy are significantly enhanced with increased engine speed, while only swirl ratio is slightly affected by the variation in IVC timing. In PCCI combustion mode, ignition timing varies with engine load and speed, and late IVC strategy leads to a noticeable delay in ignition timing by decreasing the effective compression ratio over all the operating range. Late IVC is a very effective approach for reduction of (nitrogen oxides) NOx emissions in the whole operating range, but the benefit of soot reduction with late IVC only locates in the low-to-medium load range. Moreover, it is found that indicated specific fuel consumption is effectively decreased with the employment of late IVC strategy in the medium-to-high load and low-to-medium speed range. Overall, by delaying ignition phasing and decreasing combustion temperature from late IVC timing, the high NOx emissions at medium load, and low fuel efficiency at low speed can be avoided for PCCI combustion.