Experimental and numerical study on direct injection of liquid ammonia and its injection timing in an ammonia-biodiesel dual injection engine

Ammonia is an alternative carbon-free fuel that can be easily stored in a liquid phase, unlike hydrogen, and then directly utilized in diesel engines. Hence, a single-cylinder diesel engine was retrofitted for direct injection of liquid ammonia with pilot ignition of biodiesel in dual fuel combustion mode. The effects of the liquid phase of ammonia and ammonia energy share (AES) on combustion, emissions, and engine performance were investigated and compared with pure biodiesel operation. Moreover, various ammonia injection timings were studied to improve ammonia/biodiesel combustion and reduce emissions. A CFD model was developed and validated with experimental data to study ammonia/biodiesel sprays, combustion characteristics, and emissions formation. The results showed higher AES significantly reduced the local cylinder temperature due to the strong cooling effects of ammonia, therefore, a maximum AES of 50% was achieved. Increasing AES to 50% decreased combustion duration and combustion phasing by 26.2 and 4.4 CAD, respectively. However, it deteriorated the indicated thermal efficiency (ITE) by 1.3 percent point compared to pure biodiesel. Furthermore, retarding ammonia injection from −25 to −10 CAD significantly reduced NOx, CO, and ammonia emissions by 31.4%, 39.6%, and 31.3%, respectively. Ultimately, the optimal operating condition was suggested when ammonia was injected at −10 CAD and biodiesel at −16 CAD with AES of 50%.