Abstract
This work investigates the reaction kinetics of the thermal decomposition of dimethoxymethane (DMM) and 1,2-dimethoxyethane (1,2-DME), which are both representative molecules of the promising clean polyether fuels. Pyrolysis experiments are carried out with helium diluted mixtures containing individual fuels in a flow tube at two different pressures of 760 Torr and 30 Torr. By varying the temperature distributions along the flow tube, the resulting species composition is sampled downstream the reactor and analyzed by a photoionization mass spectrometer. A kinetic model, including sub-mechanisms for the thermal decomposition of both fuels, is proposed, which can well characterize important measurements, such as the fuel decomposition reactivity and the speciation of crucial products. Under identical conditions, 1,2-DME exhibits a higher decomposition reactivity than DMM, because of the characteristic C-C bond fission as well as the easier hydrogen abstraction reactions by methyl radical. Some fuel-specific intermediates are observed, including methyl formate in DMM pyrolysis, methyl vinyl ether and methoxy acetaldehyde in 1,2-DME pyrolysis. These species mainly come from fuel radical dissociations following the hydrogen abstractions from the central (-CH2O-) and (-CH2CH2O-) moieties in DMM and 1,2-DME, respectively. The formation of some other intermediates are closely related to the consumption of these fuel-specific species. Particularly, the decomposition of methyl formate produces high concentrations of methanol in DMM pyrolysis. In 1,2-DME pyrolysis, the consumption of methyl vinyl ether and methoxy acetaldehyde brings about the formation of C-2 oxygenated intermediates such as acetaldehyde, ethenol and ketene. Higher concentrations of unsaturated C-2 (ethylene and acetylene) and larger hydrocarbon intermediates present in 1,2-DME pyrolysis, due to the existence of C-C bond in the fuel molecule. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.