Numerical Investigation of the Effects of the Ammonia Injection Rate Shape and Timing on the Performance of an Ammonia-Hydrogen Dual-Fuel Engine

There is an increasing interest in using ammonia in combustion systems, specifically in internal combustion engines, as an alternative to fossil fuel. It has numerous benefits to manifest as a competent rival against hydrogen. However, an ignition promoter, such as hydrogen addition, is still needed for stable combustion. As the engine using ammonia also suffers from high NOx emissions, in this study, the effects of ammonia injection rate shape and timing on emissions of an ammonia-hydrogen dual-fuel engine were numerically investigated. The base engine was a diesel engine whose intake parameters, such as intake temperature and pressure, were adjusted to adapt to utilize ammonia-hydrogen as fuel. Hydrogen was assumed to be premixed with the intake charge (port injected), and ammonia was directly injected into the cylinder within a definite time. The governing equations were solved by writing a MATLAB code, and the combustion mechanism was implemented in Cantera. The results showed that the ammonia injection with a cubic injection rate shape (increasing the ammonia mass injection rate gradually like a cubic curve) could reduce the in-cylinder pressure by 16.5%. The split ammonia injection between 350 and 370 crank angle degrees (350:360–368:370) produces the least NO and NO₂. This scheme is the best injection strategy since, besides the lowest NO and NO₂ emissions, its peak in-cylinder pressure is only 1% more than the scheme with the least in-cylinder peak pressure (cubic injection rate shape).