Effect of Exhaust Gas Recirculation on Hydrogen–Diesel Combustion in a Reactivity Controlled Compression Ignition Engine

The effect of exhaust gas recirculation, load and hydrogen flow rate on emissions, different stages (phases) of hydrogen–diesel–air combustion, knocking tendency and performance is investigated in a diesel–hydrogen reactivity-controlled compression ignition engine. Experiments were conducted on a stationary engine for wider ranges of exhaust gas recirculation rates (0–30%), hydrogen flow rates (0–30 slpm), and loads (0–100%) which are studied scarcely in the literature. Findings show that with an increase in exhaust gas recirculation rate, the brake thermal efficiency decreases and the efficiency is found to drop by 6% when the exhaust gas recirculation is maximum when compared with neat diesel operation. A second peak is noticed in the heat release rate at a high hydrogen flow rate and 100% load due to the hydrogen + air premixed combustion, and the magnitude of the second peak decreases with increasing exhaust gas recirculation rate. When compared with neat diesel operation, an extreme reduction of up to 80% in nitrogen oxide emissions was observed at an exhaust gas recirculation rate of 30%. Ringing intensity decreased by up to 30% with exhaust gas recirculation which reduces the knocking tendency at high hydrogen flow rates.