Flow Reactor Study of NH₃/DEE Oxidation Chemistry

The pursuit of environmentally sustainable alternatives to conventional fuels is essential today. Ammonia emerges as a promising candidate, though its inherent disadvantages must be addressed. Co-firing ammonia with fuels exhibiting superior thermochemical properties is one of the most widely accepted solutions. The present study investigates the oxidation of ammonia and diethyl ether mixtures (NH₃/DEE). To this end, a quartz flow reactor was employed at atmospheric pressure, within a temperature range of 875-1425 K. The oxygen excess ratio (λ) and the NH₃/DEE mixture ratio were systematically varied during the experiments. The results show an increase in the reactivity of ammonia when mixed with DEE. During pyrolysis, DEE is inhibited by competition for H radicals, which are essential for initial conversion steps. DEE undergoes thermal decomposition without a significant radical pool, while NH₃ reactivity remains low. With the increase of the oxygen excess ratio, fuel oxidation occurs at lower temperatures. Hydroxyl (OH) and atomic oxygen (O) radicals are crucial in NH₃ oxidation, while the presence of DEE derivatives further promote this oxidation, although both fuels exhibit competitive behavior regarding radical consumption. Variations in λ do not cause a significant effect in the oxidation temperature of DEE, with OH radicals playing a central role in the minor differences observed. Hydrogen abstraction via interaction with H radicals is the most important consumption reaction of DEE, mainly occurring at the secondary carbon position. Conversely, the production and interaction of derivatives at other positions contribute to the most inhibitory reactions in DEE oxidation. The NH₃/DEE ratio has a significant impact on ammonia oxidation, particularly under high DEE dilution conditions (NH₃/DEE = 10). OH and H radicals drive oxidation, while an increased DEE concentration leads to CH₃ radical formation, enhancing fuel consumption. A literature-based kinetic mechanism, modified in the present work, was employed to represent and interpret the current results accurately.