Experimental and kinetic study on the extinction characteristics of ammonia-dimethyl ether diffusion flame

Abstract

Combustion with dimethyl ether is regarded as one of the effective means to improve the combustion stability of ammonia gas. In-depth understanding of the combustion characteristics of ammonia-dimethyl ether mixture, especially the extinction limits, is the basis for the development of related combustion technology. In this work, the extinction limits of diffusion flames of NH3, DME and NH3-DME mixture were obtained through experiments, and a kinetic model was developed to accurately describe the combustion characteristics of NH3-DME, especially for the extinction limits. The extinction characteristics of NH3-DME mixture were analyzed based on this model. The experimental results show that blending DME in the fuel or increasing the oxygen concentration in the oxidant can effectively expand the combustion limits of the NH3 diffusion flame. When the oxygen mole fraction in the oxidant is increased to 27%, the strain rate at extinction of the NH3 diffusion flame is 3.3 times of the original value. When NH3 is mixed with 10% volume fraction of DME, the increase is 3.9 times. Numerical analysis shows that the chemical and thermal effects of DME promote the combustion of NH3-DME mixture, and when the DME mole fraction in fuel exceeds 33%, the effect of chemical effect is bound to exceed the thermal effect. With the increase of the strain rate, the reaction zone of the flame becomes thinner, the escape rate of active radicals increase, and the heat release rate of per unit mass of fuel decreases, which leads to the continuous decrease of the flame temperature and eventually leads to flame extinction. The addition of DME increases the thickness of flame, increases the amount of radical generation and improves the heat release rate of the reaction process, thus promoting the combustion and improving the stability of NH3 diffusion flame.