Effects of wall temperature profile on weak flame structure of stoichiometric dimethyl ether/air mixture in a micro flow reactor

[Display omitted] •Effect of wall temperature profile on DME weak flame structure was investigated.•Three-stage DME oxidation consists of one cool flame and two hot flames.•Under large temperature gradient, the cool flame moves to high temperature zone.•The second-stage oxidation disappears with under large wall temperature gradient.•Maximum wall temperature affects the heat release rate of hot flame significantly. Combustion characteristics of stoichiometric dimethyl ether (DME)/air mixture in a cylindrical micro-channel with linear wall temperature profiles were numerically investigated under an inlet velocity of 2.0 cm/s. The effects of wall temperature gradient and maximum wall temperature on flame structure were scrutinized. Stabilized three-stage oxidation of weak flame, which consists of one cool flame and two hot flames, was observed. With the increase of wall temperature gradient, the cool flame moves to higher temperature location because the residence time at local temperature becomes shorter. Moreover, the second-stage oxidation of hot flame disappears when the wall temperature gradient is great enough. Detailed analysis of reaction pathways and heat release rate demonstrates that under elevated wall temperature gradient, the reaction delay makes the cool flame to sustain at higher wall temperature position. As for the hot flame, the intensification of HCO decomposition under a larger wall temperature gradient produces more H and CO. The H radical accelerates the consumption of CH3OCH3 and CH2O, which can further strengthen the total reaction and result in the mergence of the two heat release rate peaks of hot flames. When the wall temperature gradient is fixed, the heat release rate of hot flame is significantly influenced by the maximum wall temperature. The second heat release peak of hot flame will disappear if the maximum wall temperature is low enough because the low wall temperature could not provide enough energy for the direct decomposition of HCO and initiation of the chain reaction of CO oxidation.