Combustion of NH3/DME and NH3/DME/NO mixtures

Abstract

The objective of this work is to study the oxidation of ammonia and dimethyl ether mixtures (NH₃/DME) both in the absence and the presence of monoxide of nitrogen (NO). For this purpose, laboratory experiments have been conducted in a quartz flow reactor setup in the 875–1425 K temperature range at atmospheric pressure, modifying the oxygen excess ratio (λ), and the NH₃/DME mixture ratio with and without NO. The experimental results have been simulated with a literature-based kinetic mechanism. The results show that the presence of DME and an oxygen excess ratio affect the conversion of NH₃, shifting its oxidation to lower temperatures, which decrease as the DME concentration in the mixture and λ increase. Interactions between ammonia and DME seem to be important under the studied conditions, presumably involving the formation and thermal decomposition of methyl nitrite (CH₃ONO). These interactions affect the oxidation of ammonia at low temperatures, consume and produce NO, which would determine the final NO emission. When there is NO in the NH₃/DME mixtures, NO is reduced up to 60 %, also favouring the oxidation of ammonia, but with an almost imperceptible effect of NO in the case of DME. The addition of different concentrations of DME also affects the oxidation behaviour of ammonia in NH₃/DME/NO mixtures. In general, the conversion of both NH₃ and DME is highly determined by the concentration of OH radicals, although thermal decomposition is also relevant for DME.