The oxidation of NH3/CO/O2/H2O system in a plug flow reactor: Experimental and kinetic modeling study

Ammonia, as a carbon-free fuel, is easier to store and transport than hydrogen. Due to the high ignition energy and low reactivity of ammonia, adding hydrogen or carbon-based fuels as combustion aids may improve the ignition and burnout of ammonia. CO is an important intermediate product in the co-combustion process of ammonia and carbon-based fuels. Research on NH3/CO co-combustion will further promote the application of such co-fuel in propulsion systems and power generation. In this work, experimental results were supplemented with novel flow reactor results on the effect of NH3 on CO oxidation in the absence of NO, and explained based on a detailed chemical kinetic model. The effects of temperature (1023-1223 K), NH3 concentration (250-1500 ppm), and water content (1 %-10 %) on CO oxidation, NH3 conversion, and NO generation were analyzed. In the NH3/CO system, the properties of CO always dominate. As the NH3 content increases, NH3 gradually inhibits the oxidation of CO by seizing free radicals (O, H, OH) and converting into NH2. NH2 further interacts with free radicals to convert into NH or HNO, and ultimately into NO. An increase in temperature will decrease the release of NO and CO and gradually decrease the conversion of NO from NH3. However, ammonia concentration had little effect on the ratio of ammonia conversion to NO. When H2O increases from 1 % to 2 %, it has a significant inhibitory effect on the production of NO and promotes the oxidation of CO. When the water concentration increases from 5 % to 10 %, the inhibitory effect reaches saturation. The present work evaluates the amine subset of the reaction mechanism under the studied conditions and provides experimental data under different NH3/CO ratios, which can be used to construct and verify the reaction mechanism of mixed fuels of carbon-based fuels and ammonia.