Combustion and stability characteristics of ammonia-diesel emulsion fuels containing varied water contents in a small diesel engine

The use of ammonia as a fuel in diesel engines involves challenges such as instability and low combustion energy, leading to incomplete combustion. The concept of an ammonia-diesel emulsion fuel (ADEF) has been proposed, but the water content of such fuels has not yet been optimised. This study identifies the ideal level of water in an ADEF to improve combustion stability and enhancing micro-explosions benefits. ADEF samples comprising mixtures of diesel, a 1% aqueous ammonia solution and 0%, 5%, 10%, 15%, 20%, 25% or 30% water were evaluated in a diesel engine at a constant speed of 2400 rpm under loads of 0, 3.84, 6.4, and 8.9 Nm. The data were compared with results for pure diesel fuel as a reference. Formulations containing 0%, 5% or 30% water proved unviable due insufficient stability leading to engine shutdown. In contrast, moderate water contents of 10% and 15% yielded optimal combustion characteristics at loads up to 6.4 Nm. Under ideal conditions, the peak pressures for the ADEFs 10% and 15% water (7.10 and 7.17 MPa, respectively) were comparable to that of diesel (7.17 MPa) with minimal cycle-to-cycle variation. The cycles analysis show that lower-water (0–5%) sample tend to exhibit misfires at 0 and 3.84 Nm loads, while showed a knocking cycle at 6.4 Nm load. High-water ADEFs (20–25%) led to excessive cooling of combustion temperatures, and increased misfires cycles as load increased. This study identified the optimal water proportion in ADEF to dilute ammonia and reduce its adverse impact on combustion.