Experimental study on the explosion characteristics of NH3/DME/air mixtures

Abstract

Co-firing ammonia (NH3) fuel with dimethyl ether (DME) is a promising approach of achieving clean combustion. However, the fundamental explosion characteristics of NH3/DME blends have not been well understood. This paper presents an experimental study of the explosion characteristics of NH3/DME blends using a spherical constant-volume combustion chamber. The effects of equivalence ratio (ϕ = 0.7–1.5), initial pressure (Pu = 0.05–0.5 MPa), and DME fraction (XDME = 0–100%) on the explosions were examined. The results show that peak explosion pressure Pmax, maximum pressure rise rate (dP/dt)max, and deflagration index KG, vary non-monotonically with equivalence ratio, and reach peak values at around ϕ = 1.1–1.2. DME addition has a positive effect on explosion intensity. Both (dP/dt)max and KG show a linear increase trend with increasing DME, while the growth rate of Pmax decreases with DME fraction. The relatively higher increase in Pmax between 0 %DME and 20 %DME is mainly due to greater heat release. Pmax increases with increasing initial pressure, and this is because of the increase in mixture mass promoting the heat release, and the enhanced possibility of effective collision between molecules of gas mixtures. The influence of initial pressure on (dP/dt)max and KG depends on the equivalence ratio. Both (dP/dt)max and KG show a linear increase with increasing initial pressure at ϕ = 1.0 and 1.5, whereas they are insensitive to initial pressure at ϕ = 0.7. This is because the decrease in laminar burning velocity leads to a significant increase in explosion time at ϕ = 0.7 compared to ϕ = 1.0 and 1.5. In addition, the actual explosion pressure is closely associated with non-negligible heat loss during flame propagation, and the heat loss decreases with the addition of DME, but increases with increasing initial pressure.