Experimental characterization of direct injection liquid ammonia sprays under non-reacting diesel-like conditions

Abstract

Ammonia is seen as a promising fuel to replace fossil fuels internal combustion engines, given the advantages of zero carbon emission and extensive experience in its synthesis at large scale. The ignition of ammonia in direct injection engine is still a challenge due to its unfavorable combustion characteristics, but the investigation of ammonia spray characteristics is an important step to shed light on the optimum combustion strategy. In this paper, the evolution of direct injection ammonia sprays was measured at engine-like conditions generated in a constant pressure facility by means of diffused back-illumination imaging and schlieren. In a first step, ammonia spray behavior is compared against that of Diesel fuel. Experimental results show a slower penetration of ammonia mainly due to a lagging starting penetration phase, which cannot be later recovered. In terms of liquid length, initial stages show the same pattern as for ammonia, while a shorter stabilized liquid length can be observed. Parametric trends over different operating conditions show a similar behavior to Diesel against ambient density and temperature, as well as with injection pressure and nozzle diameter. Such results, backed up by the application of a 1D spray model developed for Diesel-like fuels, suggest that ammonia sprays under non-reacting conditions have a mixing-controlled evolution.