Decarbonisation potential of dimethyl ether/ hydrogen mixtures in a flameless furnace: Reactive structures and pollutant emissions

摘要

This article sheds light on the combustion characteristics of dimethyl ether and its mix-tures with methane/hydrogen under flameless conditions at different equivalence ratios. It was found that combustion of 100% dimethyl ether in flameless conditions minimises the NO formation, keeping it less than 10 ppm with no CO or unburned hydrocarbons. Pro-gressive addition of methane was found to reduce the NO, reaching up to zero value at 50% methane in molar fraction along with a marginal CO2 reduction. However, large amounts of CO were found for higher methane levels, greater than 60% CH4 in molar fraction. Reactive structures based on OH* chemiluminescence revealed that adding methane re-sults in increased ignition delay times and, consequently, a more distributed reaction zone characterised by reduced temperature gradients. No visible flame was observed for pure dimethyl ether as well as dimethyl ether/methane mixtures. Furthermore, a more intense and narrower reaction zone, characterised by the presence of a visible flame, was formed upon hydrogen addition. Adding hydrogen by 50% in molar fraction did not cause a noticeable rise in NO levels; however, CO2 was lowered by about 18%. Further addition of hydrogen resulted in increased peak temperatures of about 1700 K and higher NO emis-sions of about 50 ppm. Additionally, a skeletal Chemical Reactor Network was built and simulated with the commercial software CHEMKIN Pro to investigate the effect of the different mixtures and operating conditions on NO formation from a chemical point of view. N2O pathway was observed to be the root source of NO emissions for pure DME and DME/CH4 mixtures, however; the thermal pathway became gradually more important as hydrogen concentration was increased in the mixture.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.