Effect of H2 addition on combustion and exhaust emissions in a heavy-duty diesel engine with EGR

Abstract The effect of the addition of hydrogen (H 2 ) on the combustion process and nitric oxide (NO) formation in a H 2 -diesel dual fuel engine was numerically investigated. The model developed using AVL FIRE as a platform was validated against the cylinder pressure and heat release rate measured with the addition of up to 6% (vol.) H 2 into the intake mixture of a heavy-duty diesel engine with exhaust gas recirculation (EGR). The validated model was applied to further explore the effect of the addition of 6%–18% (vol.) H 2 on the combustion process and formation of NO in H 2 -diesel dual fuel engines. When the engine was at N = 1200 rpm and 70% load, the simulation results showed that the addition of H 2 prolonged ignition delay, enhanced premixed combustion, and promoted diffusion combustion of the diesel fuel. The maximum peak cylinder pressure was observed with addition of 12% (vol.) H 2 . In comparison, the maximum peak heat release rate was observed with the addition of 16% (vol.) H 2 . The addition of H 2 was a crucial factor dominating the increased NO emissions. Meanwhile, the addition of H 2 reduced soot emissions substantially, which may be due to the reduced diesel fuel burned each cycle. Furthermore, proper combination of adding H 2 with EGR can improve combustion performance and reduce NO emissions.