Near-nozzle flash-boiling flow of iso-octane, methanol, and ammonia in the engine combustion network spray G injector.

This article focuses on the near-nozzle flow and spray behavior of volatile renewable fuels—ammonia (NH₃) and methanol (CH₃OH)—compared to iso-octane, using three-dimensional computational fluid dynamics (CFD) simulations with the Engine Combustion Network’s (ECN) eight-hole Spray G injector. The study examines subcooled (non-flash-boiling) and flash-boiling injection conditions, highlighting that the ratio of saturation pressure to ambient pressure (R_p) is critical for initiating flash-boiling, while the enthalpy of vaporization (h_fg) and a related Jakob number (J_a*) govern the intensity of vaporization and spray expansion behavior. Results show that subcooled sprays exhibit oscillatory, overexpanded jets influenced by injector geometry, whereas flash-boiling sprays are steadier and can be either underexpanded or overexpanded depending on fuel properties and operating conditions; notably, high R_p values lead to bell-shaped, underexpanded sprays with complex shock structures and spray collapse. These findings underscore the importance of fuel thermophysical properties in optimizing injection strategies for ammonia and methanol to achieve efficient combustion and reduced emissions in internal combustion engines.