Effects of equivalence ratio variation on lean, stratified methane-air laminar counterﬂow ﬂames
Richardson, E.S., Granet, V.E., Eyssartier, A. and Chen, J.H. (2010) Effects of equivalence ratio variation on lean, stratified methane-air laminar counterﬂow ﬂames. Combustion Theory and Modelling, 14, (6), 775-792.
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The eﬀects of equivalence ratio variations on ﬂame structure and propagation have been studied computationally. Equivalence ratio stratiﬁcation is a key technology for advanced low emission combustors. Laminar counterﬂow simulations of lean methane-air combustion have been presented which show the eﬀect of strain variations on ﬂames stabilized in an equivalence ratio gradient, and the response of ﬂames propagating into a mixture with a time-varying equivalence ratio. “Back supported” lean ﬂames, whose products are closer to stoichiometry than their reactants, display increased propagation velocities and reduced thickness compared with ﬂames where the reactants are richer than the products. The radical concentrations in the vicinity of the ﬂame are modiﬁed by the eﬀect of an equivalence ratio gradient on the temperature proﬁle and thermal dissociation. Analysis of steady ﬂames stabilized in an equivalence ratio gradient demonstrates that the radical ﬂux through the ﬂame, and the modiﬁed radical concentrations in the reaction zone, contribute to the modiﬁed propagation speed and thickness of stratiﬁed ﬂames. The modiﬁed concentrations of radical species in stratiﬁed ﬂames mean that, in general, the reaction rate is not accurately parametrized by
progress variable and equivalence ratio alone. A deﬁnition of stratiﬁed ﬂame propagation based upon the displacement speed of a mixture fraction dependent progress variable was seen to be suitable for stratiﬁed combustion. The response times of the reaction, diﬀusion, and cross-dissipation components which contribute to this displacement speed have been used to explain ﬂame response to stratiﬁcation and unsteady ﬂuid dynamic strain.
|Subjects:||T Technology > TJ Mechanical engineering and machinery|
|Divisions:||University Structure - Pre August 2011 > School of Engineering Sciences
|Date Deposited:||16 Jun 2011 13:39|
|Last Modified:||15 May 2014 15:02|
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