Study on ammonia and dimethyl ether oxidation and kinetic interaction up to 100 atm

In this work, NH₃ and DME dual fuel oxidation and kinetic coupling are experimentally studied by using a supercritical pressure jet-stirred reactor (SP-JSR) at 20 and 100 atm, over a temperature range of 500–900 K, and at fuel-lean and stoichiometric conditions with NH₃ to DME molar ratios of 4 and 0.62, respectively. An HP-Mech model for high-pressure NH₃/DME oxidation is developed based on our previous studies and it shows generally better performance than other models in the literature on high-pressure oxidation experiments. Due to DME's strong low-temperature reactivity, it dramatically enhances the oxidation of NH₃ at low temperature. However, the effect of NH₃ on DME oxidation varies with temperature. At low temperatures, NH₃ inhibits low-temperature reactivity by consuming OH radicals. In addition, the NH₂ and NO_x formation from NH₃ further suppresses the low-temperature DME reactivity by reducing alkylperoxyl and O₂QOOH radicals via RO₂ + NH₂ = RO + H₂NO, RO₂ + NO = RO + NO₂ and O₂QOOH + NO = 2CH₂O + HO₂ + NO₂. At intermediate temperatures, due to enhanced kinetic coupling of NH₂/NO_x/HO₂ chemistry, DME oxidation is significantly promoted. It is found that there are two major NH₂/NO_x/HO₂ coupling pathways for OH radical production brought by NH₃: (1) NH₂ + HO₂ = H₂NO + OH and (2) NH₂ + NO₂ = H₂NO + NO with NO + HO₂ = OH + NO₂. Moreover, the resulting H₂NO will further contribute to OH production via the H₂NO/NO_x/HONO coupling pathways: H₂NO + NO₂ = HNO + HONO, HNO + NO₂ = HONO + NO, and HONO (+M) = OH + NO (+M). These new NH₂/NO_x/HO₂ and H₂NO/NO_x/HONO pathways play a critical role in promoting DME oxidation at intermediate temperatures. Novelty and Significance Statement: Blending NH₃ with DME can significantly enhance the reactivity of NH₃ and facilitate its practical application in advanced internal combustion engines. NH₃/DME oxidation is studied in a novel supercritical pressure jet-stirred reactor up to 100 atm, a much higher pressure than previous studies. An interesting non-monotonic effect of NH₃ addition on fuel oxidation has been found. Unique kinetic couplings of NH₂/HO₂/NO_x and H₂NO/NO_x/HONO brough by NH₃ and DME blending are identified to play important roles in radical generation and reactivity promotion. The valuable experimental data and key kinetics revealed in the current work can tremendously improve our understanding of NH₃/DME oxidation via NO_x/RO₂ and NH₂/H₂NO/HO₂/NO_x kinetic couplings at low to intermediate temperatures.