Study on the Combustion and Emission Characteristic of a Heavy-Duty Natural Gas/Ammonia RCCI Engine with Diesel Ignition

As a carrier of hydrogen, ammonia has great potential in reducing pollution and carbon. This paper investigates the impact of diesel compression ignition on the combustion and emission performance of a natural gas/ammonia mixture RCCI engine through numerical simulation. The energy fraction of ammonia is set from 0% to 100% in the study to evaluate the feasibility of ammonia application in heavy-duty natural gas/diesel RCCI engines. A natural gas/n-heptane/ammonia reaction mechanism that includes 89 species and 611 reactions was innovatively established, which can accurately simulate the ignition process. The results indicate that under all engine load conditions, as the ammonia energy fraction increases, the cylinder pressure and thermal efficiency of the engine decrease, and the power performance gradually weakens. Under high load conditions, when ammonia is added to premixed natural gas, as the ammonia energy fraction increases, the characteristic frequency near the resonance mode gradually disappears, which is beneficial for reducing the knock trend and ringing intensity of engines. However, due to the increase in incomplete combustion increase, the ammonia energy fraction should not be too large at high loads.