Numerical study on diesel ignited methane-hydrogen tri-fuel RCCI combustion

In this paper, the diesel ignited methane-hydrogen reactivity-controlled compression ignition (RCCI) combustion is numerically simulated to study the combustion characteristics of the internal combustion engine under different hydrogen addition ratios. Moreover, the typical combustion characteristics are compared to identify the normal combustion and detonation combustion in this combustion mode. The results show that the moments of ignition, and the end time of combustion is advanced proportionally with the hydrogen addition from 0% to 40%. In particular, the oxidation time of the CH2O, which is the key component produced in the low-temperature reaction is advanced accordingly. The key component of OH, which corresponds to the high-temperature reaction is getting to advances as well. The emission analysis indicates that the addition of the hydrogen increase the NOx emissions, while decreases the CO, THC, and soot emissions. Interestingly, with the proportion of hydrogen up to 60%, the heat release rate in the cylinder shows three peaks and the pressure increase rate exceeds the normal combustion value, which represents the detonation occurs in the cylinder, and the main combustion period changes significantly compared with the normal combustion. In detonation combustion, the generation time of OH is further advanced with a significant higher mass fraction than the normal combustion. The detonation with higher hydrogen fraction increases NO_X emissions dramatically due to the high-temperature during the combustion process.