Effect of compression ratio and hydrogen addition on performance and different phases of hydrogen/diesel combustion in reactivity controlled compression ignition engine

Abstract Reactivity controlled compression ignition (RCCI) engines use a minimum of two fuels with dissimilar reactivities. The current experimental study examined the effects of compression ratio (CR), hydrogen flow rate, and load on performance, knocking tendency, emissions, and different phases of co-combustion in a hydrogen–diesel RCCI engine employing conventional diesel in-cylinder injection and hydrogen induction into the manifold, which reduces the system cost. A constant-speed stationary engine was selected for this study because it has rarely been studied. Compared with the existing literature, wider ranges of hydrogen flow rates (up to 30 slpm) and CRs (15–20) were investigated in this study. The results indicate that the maximum brake thermal efficiency was obtained at low hydrogen flow rates (3–5 slpm). Under part-load conditions, the maximum heat release rate and cylinder pressure decreased with an increase in the hydrogen flow rate. At high loads and high CRs, a second peak was observed in the heat release curve, the magnitude of which increased with the hydrogen flow rate owing to H2 + air-premixed combustion. The knocking tendency increased with an increase in the hydrogen flow rate and a decrease in the CR. These findings can potentially help in identifying the best operating conditions for stationary constant-speed compression ignition engines adapted for H2–diesel RCCI operations, as these engines find wide application in rural economies for powering electric generators, water pumps, and agricultural equipment.