The Effect of Variable Enhanced Miller Cycle Combined with Egr Strategy on the Cycle-by-Cycle Variations and Performance of High Compression Ratio Engines Based on Asynchronous Valve Opening Strategy

Abstract

A novel design of the variable enhanced Miller cycle (VEMC) achieved by the asynchronous intake valve is adopted in the test spark ignition (SI) engine with different high compression ratios (CR12.5 and CR14.5). The influences of high compression ratio and VEMC on the combustion cycle-to-cycle variations (CCV) of a GDI gasoline engine are conducted and compared to the original Otto cycle (OC). Meanwhile, the impact of the coupling application of exhaust gas recirculation (EGR) and VEMC on the combustion and emission performance is also discussed. Results show that the high geometric compression ratio VEMC engine with large valve opening interval angle not only reduces the cyclic variation at low load effectively compared with the OC cycle, but also significantly improves operational stability at medium and high loads due to its excellent anti-knock ability. Besides, the coupling application of VEMC and EGR in the high GCR engine can significantly reduce NOx emissions compared to only use the VEMC, which gains a reduction of 68.7% at 12 % EGR rate.

Keywords: Asynchronous intake valve, Variable enhanced Miller cycle, High compression ratio, Combustion stability, Exhaust Gas Recirculation