Numerical Simulation of Ammonia-Hydrogen Engine Using Low-Pressure Direct Injection (LP-DI)

Ammonia (NH3), a zero-carbon fuel, has great potential for internal combustion engine development. However, its high ignition energy, low laminar burning velocity, narrow range of flammability limits, and high latent heat of vaporization are not conducive for engine application. This paper numerically investigates the feasibility of utilizing ammonia in a heavy-duty diesel engine, specifically through low-pressure direct injection (LP-DI) of hydrogen to ignite ammonia combustion. Due to the lack of a well-corresponding mechanism for the operating conditions of ammonia-hydrogen engines, this study serves only as a trend-oriented prediction. The paper compares the engine's combustion and emission performance by optimizing four critical parameters: excess air ratio, hydrogen energy ratio, ignition timing, and hydrogen injection timing. The results reveal that excessively high hydrogen energy ratios lead to an advanced combustion phase, reducing indicated thermal efficiency. Additionally, the injection of hydrogen during the intake stroke causes a decrease of ammonia during the intake process, while delaying the injection timing during the compression stroke results in uneven air-fuel mixture distribution, both contributing to a decline in indicated thermal efficiency. Under specific operating conditions of an excess air ratio of 1.0, 20% hydrogen energy ratio, -14°CA ATDC spark ignition timing, and -180°CA ATDC hydrogen injection timing, the engine achieved a maximum indicated thermal efficiency of 47.8%.