Experimental investigations of mineral diesel/methanol-fueled reactivity controlled compression ignition engine operated at variable engine loads and premixed ratios

Global warming and stringent emission norms have become the major concerns for the road transport sector globally, which has motivated researchers to explore advanced combustion technologies. Reactivity controlled compression ignition combustion technology has shown great potential to resolve these issues and deliver high brake thermal efficiency and emit ultra-low emissions of oxides of nitrogen and particulate simultaneously. In this experimental study, baseline compression ignition combustion mode and reactivity controlled compression ignition combustion mode experiments were performed in a single-cylinder research engine using mineral diesel as high-reactivity fuel and methanol as low-reactivity fuel. All experiments were carried out at constant engine speed at four engine loads (brake mean effective pressure: 1-4 bar). For efficient combustion and lower emissions, four premixed ratios (r(p) = 0, 0.25, 0.50, and 0.75) were tested to assess optimized premixed ratio at different engine loads. In these experiments, primary and secondary fuel injection parameters were maintained identical. Combustion results showed that reactivity controlled compression ignition combustion was more stable compared to compression ignition combustion and resulted in lesser knocking. Reactivity controlled compression ignition combustion delivered higher brake thermal efficiency and lower exhaust gas temperature and oxides of nitrogen emissions, especially at maximum engine loads. Addition of methanol as secondary fuel reduced particulate emissions. Particulate analyses depicted that reactivity controlled compression ignition combustion mode emitted significantly lower accumulation mode particles; however, emission of nucleation mode particles was slightly higher. A significant reduction in particulate mass emitted from reactivity controlled compression ignition combustion was another important finding of this study. Particulate number-mass distributions showed that increasing the premixed ratio of methanol led to a dominant reduction in particulate number concentration compared to particulate mass. Analysis for critical performance and emission characteristics suggested that optimization of the premixed ratio of methanol at each engine load should be done in order to achieve the best results in reactivity controlled compression ignition combustion mode.