Low-dimensional modelling of flame dynamics in heated microchannels

Abstract

This paper presents simulations of stoichiometric methane/air premixed flames into a microchannel at atmospheric pressure. These simulations result from numerical resolutions of reduced-order models. Indeed, combustion control into microchannels would be allowed by fast simulations that in turn enable real-time adjustments of the device's parameters. Former experimental studies reported the occurrence of a Flame Repetitive Extinction/Ignition (FREI) phenomenon provided that a temperature gradient is sustained at the channel's walls. Conducting unsteady one-dimensional simulations including complex chemistry, a late numerical study tried to explain the occurrence of this phenomenon. The present study therefore explores low-dimensional models that potentially reproduce the FREI phenomenon. Provided a calibration of some empirical constants, an unsteady two-dimensional model including one-step chemical reaction is shown to decently reproduce the FREI regime all along the range of mixture flow rates investigated by the experimental studies. Complementing the aforementioned numerical study, furthermore, when the channel's diameter is varied, the two-dimensional model unveils an unstable regime that a one-dimensional model cannot capture. As two-dimensional hydrodynamics appears to play a key role into the flame's dynamics, therefore the heat rate released by the microcombustor, one-dimensional models are not believed to deliver an adequate strategy of combustion control into such microchannels.Comment: 37 pages, 12 figure