Mechanical & Indusrial Engineering, Babol Noshirvani University of Technology
Combustion in homogeneous charge compression ignition (HCCI) engine is controlled auto ignition of well-mixed fuel, air and residual gas. Since onset of HCCI combustion depends on the auto ignition of fuel/air mixture, there is no direct control on the start of combustion process. Therefore, HCCI combustion becomes unstable rather easily especially at lower and higher engine load. Charge stratification has the potential to extend the load limits of HCCI combustion by improving the control over the combustion phase as well as reducing the maximum of pressure rise. In this study, a combination of experiment and numerical simulation was carried out to investigate the effect of fuel stratification using reformer gas and EGR on HCCI natural gas combustion. It was found that fuel stratification in this case increased the autoignition property of natural gas. On the lean operation boundary, reformer gas and EGR blending enhanced the autoignition by advancing combustion timing at identical initial conditions compared to pure natural gas that expanded the lean boundary of the operating region.