Branched-chain ignition in strained mixing layers

Mellado Ramírez, José Damián and Sánchez Pérez, Antonio Luis and Kim, J.S. and Liñán Martínez, Amable (2000). Branched-chain ignition in strained mixing layers. "Combustion Theory and Modelling", v. 4 ; pp. 265-288. ISSN 1364-7830.


Title: Branched-chain ignition in strained mixing layers
  • Mellado Ramírez, José Damián
  • Sánchez Pérez, Antonio Luis
  • Kim, J.S.
  • Liñán Martínez, Amable
Item Type: Article
Título de Revista/Publicación: Combustion Theory and Modelling
Date: 2000
Volume: 4
Faculty: E.T.S.I. Aeronáuticos (UPM)
Department: Motopropulsión y Termofluidodinámica [hasta 2014]
Creative Commons Licenses: Recognition - No derivative works - Non commercial

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Abstract. The time-dependent evolution of the radical pool in an initially inert hydrogen-air counterflow mixing layer subject to variable strain is investigated analytically. Although the initial chemistry description contains three different chain carriers, namely, H, O and OH, it is shown that the ignition problem can be accurately described in terms of a single radical-pool variable that incorporates steady-state assumptions for the radicals O and OH. Use of this non-standard procedure reduces the problem to the integration of a single conservation equation, whose solution depends on the existing Damkohler number A, defined as the ratio of the diffusion time across the mixing layer to the characteristic branching time. Ignition takes place when A remains predominantly above a critical value of the order of unity. The exponentially growing radical pool, which extends across the mixing layer, can be described analytically by separation of variables in configurations with a slowly varying strain rate, providing a solution that is used to investigate the parametric dependences of the ignition time. Weakly strained solutions are studied separately by addressing the asymptotic limit of large Damkohler numbers. It is seen that the reaction zone then becomes a thin layer of relative thickness A- 1 ' 4 centred at the location where the branching rate is maximum. The analysis employs asymptotic expansions in decreasing powers of A for the shape and for the exponential growth rate of the radical pool. The accurate description of the solution necessitates computation of three terms in the asymptotic expansion for the growth rate, yielding predictions for the ignition time that remain accurate even for values of A of the order of unity.

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Item ID: 1308
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Deposited by: Biblioteca ETSI Aeronauticos
Deposited on: 15 Jan 2009
Last Modified: 20 Apr 2016 06:46
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