A numerical study on RCCI engine fueled by biodiesel/methanol

A 3-D numerical simulation platform based on the KIVA4-CHEMKIN code was constructed by incorporating a newly developed skeletal chemical kinetics mechanism to study the reactivity controlled compression ignition (RCCI) engine performance, combustion and emission characteristics. In the present study, methanol is assumed to be induced into the engine through the intake port, while biodiesel is directly injected into the engine by the end of the compression stroke. The skeletal biodiesel and methanol dual fuel chemical reaction mechanism coupled with CO, NO_x and soot formation mechanisms was developed and validated by comparing the ignition delay predicted by the developed mechanism with that of the detailed biodiesel and methanol mechanisms, and also by comparing the simulation results of KIVA-CHEMKIN with the experimental results under different engine operating conditions. A good agreement has been achieved in terms of ignition delay, in-cylinder pressure and heat release rate (HRR). The methanol mass fraction was varied from 0% to 80% at an interval of 20% to form different reactivity stratification. Simulation results revealed that under 10% load conditions, the increasing methanol reduced the peak pressure and heat release rate, whereas under 50% and 100% loads, the peak pressure both appeared at 60% methanol induction. Also, the reactivity distribution and ringing intensity were discussed, aiming at investigating the fuel gradient effects and knocking level, respectively. For the emissions, a general decreasing trend on CO emission was observed at both 50% and 100% loads while at 10% load, a slight increasing trend was shown. In respect of NO_x, it appeared that the emission under medium and high loads showed no tangible change with port methanol increase. However, a remarkable drop was observed at 10% load. Besides, the RCCI with more port-injection methanol showed a good ability to reduce soot emission.