Effects of mixture composition on oxidation and reactivity of DME/NH 3 /air mixtures examined by a micro flow reactor with a controlled temperature profile

Effects of mixture composition and equivalence ratios on oxidation and reactivity of dimethyl ether (DME)/ammonia (NH 3 ) mixtures are investigated based on weak flame responses observed in a micro flow reactor with a controlled temperature profile (MFR). For observations, the NH 3 fractions in fuel blends are varied as 0-50%. Three equivalence ratios ( phi = 0.5, 1.0 and 1.2) are examined. A combined chemical reaction model for DME/NH 3 mixtures is developed and used to simulate oxidation of DME/NH 3 mixtures in MFR. Under the stoichiometric conditions, the DME oxidation is promoted and the mixture reactivity is enhanced as the NH 3 fractions in fuel blends increase from 0 to 15%. As the NH 3 fractions further increase from 15 to 50%, CO oxidation is inhibited; the mixture reactivities are suppressed strongly. Chemical reaction analyses indicate that NOx produced by the NH 3 oxidation converts less-reactive radicals into more-reactive radicals (HO 2 -> OH and CH 3 -> CH 3 O) through the NO-NO 2 catalytic loop at the intermediate temperatures of 80 0-10 0 0 K. However, with larger NH 3 fractions in fuel blends, the OH radical consumption by NH 3 increases, thereby inhibiting CO oxidation. Moreover, when the equivalence ratios are varied, mixture reactivity is more inhibited as equivalence ratios increase, although they change only slightly irrespective of the equivalence ratios in neat DME cases. With richer equivalence ratios, more OH radicals are consumed by DME, CH 2 O, NH 3 , and H 2 . Moreover, the CO oxidation is inhibited in the intermediate temperature zone when NH 3 is blended because CO has lower priority for OH radical consumption among these species as a result of its high activation energy. Results of this study demonstrate the strong potential of NH 3 to control reactivity of hydrocarbon mixtures over a wide range by changing the mixture composition and equivalence ratios. (c) 2021 The Authors. Published by Elsevier Inc. on behalf of The Combustion Institute. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Automated summary

The oxidation and reactivity of DME/NH3 mixtures are affected by mixture composition and equivalence ratios. The presence of NH3 in fuel blends promotes DME oxidation up to a certain point, but beyond that, it inhibits CO oxidation and suppresses mixture reactivities strongly. The study demonstrates the potential of NH3 to control reactivity of hydrocarbon mixtures over a wide range by adjusting mixture composition and equivalence ratios.