Evaluation of the necessity of exhaust gas recirculation employment for a methanol/diesel reactivity controlled compression ignition engine operated at medium loads

Three-dimensional computational fluid dynamics simulation was conducted to investigate the improvement of engine performance by managing exhaust gas recirculation rate and methanol fraction in a methanol/diesel reactivity controlled compression ignition engine. By defining fuel efficiency and ringing intensity as the restricted boundaries, the operating ranges of exhaust gas recirculation rate and methanol fraction under various initial temperatures were determined to simultaneously achieve high fuel economy and avoid engine knock. The results indicated that the fuel efficiency and ringing intensity were dominantly affected by the combustion phasing, and they was nearly insensitive to the variations of exhaust gas recirculation rate and initial temperature at a constant combustion phasing. The necessity of exhaust gas recirculation employment at medium loads was dependent on the level of initial temperature. When initial temperature was less than the critical value (380 K in this study), optimal engine performance could be achieved by only adopting high methanol fraction without introducing exhaust gas recirculation. Once initial temperature was beyond the critical value, exhaust gas recirculation was imperative to avoid excessive ringing intensity. Through simultaneously optimizing methanol fraction and exhaust gas recirculation rate, the combined strategy exhibited more advantages in fuel efficiency, nitrogen oxides, and ringing intensity under a wide range of initial temperature.