A numerical study on the effect of thermal and charge stratification on the HCCI natural gas engine

The applications of homogeneous charge compression ignition (HCCI) engine are still limited due to the absence of a definite means to control ignition timing and narrow the operating region. It was found that thermal stratification and charge stratification strategies bring forward good potential to achieve the staged combustion with reduced pressure-rise rates. In this study, a single cylinder engine and a CFD simulation are applied to investigate the combustion processes in the stratified HCCI engine. To obtain thermal and charge stratification on the combustion chamber, exhaust gas recirculation (EGR), glow plug and simulated reformer gas (RG) of CO-H-2 mixture are used. Increasing EGR at constant lambda line decreases the maximum achievable power, while at the constant increasing lambda at each constant EGR decreases the indicated mean effective pressure. EGR expands combustion duration hence smoother and quieter operation is achieved. Increasing reformer gas blend fraction considerably expands the operating region toward the lean side. Advancing combustion timing at constant energy flow and intake temperature stem from using glow plug in the combustion chamber, while with increasing mean in-cylinder temperature, combustion duration is prolonged.