Experimental investigations of plasma-assisted ammonia combustion using rod-electrode-type microwave plasma source

Abstract

Ammonia have been attractive as one of the alternative fuels for reducing greenhouse gas (GHG) emissions. However, ammonia combustion has lower combustion performance than common hydrocarbon fuels. Furthermore, it may emit nitrous oxide (N2O), which is one of the GHGs. This paper presents the experimental investigations of plasma-assisted ammonia combustion (PAAC) using a rod-electrode-type microwave plasma source (MPS) at atmospheric pressure. The equivalence ratios of premixed ammonia/dry air (NH3/Air) gas are set below the stoichiometric combustion of NH3 to reduce toxic NH3 in the combustion gas. Under the condition of the equivalence ratios, the experiments are focused on reducing the unburned NH3 and produced N2O concentrations in the combustion gas. In the experiments, the unburned NH3, nitrogen oxide (NOx) (the sum of nitric oxide (NO) and nitrogen dioxide (NO2)), and N2O concentrations in the combustion gas are investigated in terms of the flow velocity of premixed NH3/Air gas inside the rod-electrode-type MPS and the transmission power to the rod-electrode-type MPS. In conclusion, the rod-electrode-type MPS is identified to be useful for PAAC. The NH3 and N2O concentrations in the combustion gas reach approximately 25 and 4 parts per million (ppm), respectively, under the conditions of the equivalence ratio of 1.0, flow velocity of approximately 0.167 m/s, and transmission power of about 84 W. At that time, the NOx concentration is approximately 4300 ppm, and the power transmission efficiency is approximately 68 %.