Dynamics of thermal ignition of spray flames in mixing layers

Martínez-Ruiz, D.; Urzay, J.; Sánchez Pérez, Antonio Luis; Liñán Martínez, Amable y Williams, F.A. (2013). Dynamics of thermal ignition of spray flames in mixing layers. "Journal of Fluid Mechanics", v. 734 ; ISSN 0022-1120. https://doi.org/10.1017/jfm.2013.500.

Descripción

Título: Dynamics of thermal ignition of spray flames in mixing layers
Autor/es:
  • Martínez-Ruiz, D.
  • Urzay, J.
  • Sánchez Pérez, Antonio Luis
  • Liñán Martínez, Amable
  • Williams, F.A.
Tipo de Documento: Artículo
Título de Revista/Publicación: Journal of Fluid Mechanics
Fecha: 2013
Volumen: 734
Materias:
Escuela: E.T.S.I. Aeronáuticos (UPM) [antigua denominación]
Departamento: Motopropulsión y Termofluidodinámica [hasta 2014]
Licencias Creative Commons: Reconocimiento - Sin obra derivada - No comercial

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Resumen

Conditions are identified under which analyses of laminar mixing layers can shed light on aspects of turbulent spray combustion. With this in mind, laminar spray-combustion models are formulated for both non-premixed and partially premixed systems. The laminar mixing layer separating a hot-air stream from a monodisperse spray carried by either an inert gas or air is investigated numerically and analytically in an effort to increase understanding of the ignition process leading to stabilization of high-speed spray combustion. The problem is formulated in an Eulerian framework, with the conservation equations written in the boundary-layer approximation and with a one-step Arrhenius model adopted for the chemistry description. The numerical integrations unveil two different types of ignition behaviour depending on the fuel availability in the reaction kernel, which in turn depends on the rates of droplet vaporization and fuel-vapour diffusion. When sufficient fuel is available near the hot boundary, as occurs when the thermochemical properties of heptane are employed for the fuel in the integrations, combustion is established through a precipitous temperature increase at a well-defined thermal-runaway location, a phenomenon that is amenable to a theoretical analysis based on activation-energy asymptotics, presented here, following earlier ideas developed in describing unsteady gaseous ignition in mixing layers. By way of contrast, when the amount of fuel vapour reaching the hot boundary is small, as is observed in the computations employing the thermochemical properties of methanol, the incipient chemical reaction gives rise to a slowly developing lean deflagration that consumes the available fuel as it propagates across the mixing layer towards the spray. The flame structure that develops downstream from the ignition point depends on the fuel considered and also on the spray carrier gas, with fuel sprays carried by air displaying either a lean deflagration bounding a region of distributed reaction or a distinct double-flame structure with a rich premixed flame on the spray side and a diffusion flame on the air side. Results are calculated for the distributions of mixture fraction and scalar dissipation rate across the mixing layer that reveal complexities that serve to identify differences between spray-flamelet and gaseous-flamelet problems.

Más información

ID de Registro: 32544
Identificador DC: http://oa.upm.es/32544/
Identificador OAI: oai:oa.upm.es:32544
Identificador DOI: 10.1017/jfm.2013.500
URL Oficial: http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9039269&fileId=S0022112013005004
Depositado por: Biblioteca ETSI Aeronauticos
Depositado el: 31 Oct 2014 07:37
Ultima Modificación: 31 Oct 2014 07:37
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