Work

Characteristics of high-pressure spray combustion of liquid ammonia blended with methanol/propane in a marine engine

Year: 2025

Type: article

Abstract: Mixing lower hydrocarbons with ammonia (NH3) improves the ignition characteristics and burning velocity of NH3 in premixed flames. However, the effect of mixing lower hydrocarbons with NH3 in the high-pressure dual-fuel (HPDF) mode of marine engines, involving intricate physical and chemical processes, remains underexplored. To investigate the effect of lower hydrocarbon mixing with NH3 on spray combustion in the HPDF mode of marine engines, this study conducted combustion tests on NH3/methanol (CH3OH) or NH3/propane (C₃H₈) fuel blends in a rapid compression and expansion machine that can simulate a medium-speed marine engine. Fuel blends of NH3/CH3OH and NH3/C₃H₈ were injected directly into the cylinder. The ignition was assisted by a pilot diesel injection and the diffusion combustion of the spray of NH3/lower hydrocarbons was captured using a shadowgraph method. In addition to the heat-release analysis, exhaust emissions were analyzed using a Fourier-transform infrared (FTIR) exhaust gas analyzer. The use of NH3/CH3OH fuel blends improved the flammability of NH3 by shortening the ignition delay, shortening the main combustion duration, improving the heat-conversion rate, and reducing the nitrogen oxide emissions per unit of released heat. NH3/C₃H₈ blends occasionally exhibited deteriorated combustibility, especially at C₃H₈ mixing ratios of 30 wt%, with prolonged combustion duration and reduced heat-conversion rates. This may be due to an increase in the stoichiometric air requirement and shortening of the liftoff. The mixing of CH3OH or C₃H₈ with NH3, or an extended pilot injection, enables sustained combustion of the main fuel, thereby preventing a reduction in the heat-release rate.

Source: Fuel

DOI: 10.1016/j.fuel.2025.134808