Effect of preheated air temperature on a liquid ammonia flash spray in a swirl combustor

Abstract

Ammonia is a suitable carbon-free alternative fuel for power equipment. Direct combustion of liquid ammonia has the potential to reduce system costs and heat loss of gas turbine (GT). However, its tendency to flash and the high latent heat of vaporization can lead to combustion deterioration. Previous research suggests that stabilizing a liquid ammonia flame requires swirling and preheated air. So far, the influence mechanism of preheated air on liquid ammonia swirl spray remains inadequately explored. To fill this research gap, this study conducted a large eddy simulation (LES) to investigate the effect of preheated air temperature ($T_a$) on a liquid ammonia flash spray in a swirl combustor. The influence of $T_a$ on the spray morphology and the axial velocity, diameter, and temperature distributions of the droplets were investigated to understand the spray characteristics. Besides, the effects of $T_a$ on the evaporation characteristics, the properties, and the possible ignition performance of the mixture were studied. The results show that with the increase of $T_a$, the heating capacity of air is enhanced, leading to a greater proportion of droplets reaching flash boiling conditions. This greatly optimizes the evaporation process, resulting in more complete evaporation and significantly smaller volume. The bulk air flow velocity is increased, causing the expansion of the inner recirculation zone (IRZ), and the gaseous temperature and mixture concentration distribution are optimized. In addition, the low gaseous ammonia concentration makes ignition difficulty at $T_a$ = 300 K. The high $\left|\tau \right|$ value ($\tau$ is the shear stress) and large inner recirculation zone area lead to a larger $RegionM$ and a smaller $RegionL$ at $T_a$ = 300 K compared to the case of $T_a$ = 500 K.