Effect of Miller cycle and exhaust gas recirculation on combustion characteristics of a gasoline direct-injection engine

A numerical method is used to investigate the effect of variation Miller cycle and Exhaust gas recirculation (EGR) on fuel economy and combustion characteristics of a turbocharged gasoline direct-injection (GDI) engine, in which one-dimensional (1D) and three-dimensional (3D) model are established in GT-Power and CONVERGE software, respectively. The simulation values of the model are validated well with experimental results at part load and full load conditions. The results demonstrate that fuel economy is improved with Miller degree increasing at 50% loads because of the reduction of pumping loss. Further studies have shown that, especially at +/- 58 degrees CA Miller degrees, early intake valve closure (EIVC) has a better performance than late intake valve closure (LIVC) on fuel economy. In addition, EGR can further decrease fuel consumption based on miller cycle because of further decline for pumping loss and combustion phase optimization. Meanwhile, LIVC can match wider EGR rates than EIVC in terms of good fuel economy. Compared to the baseline scheme, the brake specific fuel consumption is reduced by 4.3% with LIVC58 + 7% EGR. And combustion process of the LIVC58 + 7% EGR also gets optimized which result in lower maximum in-cylinder temperature due to the advance of CA50 and delay of combustion duration.