Publication: Numerical analyses of deflagration initiation by a hot jet
Loading...
Identifiers
Publication date
2012-08-07
Defense date
Advisors
Tutors
Journal Title
Journal ISSN
Volume Title
Publisher
Taylor & Francis
Impact
Export
Abstract
Numerical simulations of axisymmetric reactive jets with one-step Arrhenius kinetics
are used to investigate the problem of deflagration initiation in a premixed fuel–air
mixture by the sudden discharge of a hot jet of its adiabatic reaction products. For the
moderately large values of the jet Reynolds number considered in the computations,
chemical reaction is seen to occur initially in the thin mixing layer that separates the hot
products from the cold reactants. This mixing layer is wrapped around by the starting
vortex, thereby enhancingmixing at the jet head, which is followed by an annular mixing
layer that trails behind, connecting the leading vortex with the orifice rim. A successful
deflagration is seen to develop for values of the orifice radius larger than a critical
value aϲ in the order of the flame thickness of the planar deflagration δL. Introduction
of appropriate scales provides the dimensionless formulation of the problem, with
flame initiation characterised in terms of a critical Damk¨ohler number ∆ϲ = (aϲ/δL)²,
whose parametric dependence is investigated. The numerical computations reveal that,
while the jet Reynolds number exerts a limited influence on the criticality conditions,
the effect of the reactant diffusivity on ignition is much more pronounced, with the
value of ∆ϲ increasing significantly with increasing Lewis numbers Le. The reactant
diffusivity affects also the way ignition takes place, so that for reactants with Le ≳ 1 the
flame develops as a result of ignition in the annular mixing layer surrounding the developing
jet stem, whereas for highly diffusive reactants with Lewis numbers sufficiently
smaller than unity combustion is initiated in the mixed core formed around the starting
vortex. The analysis provides increased understanding of deflagration initiation processes,
including the effects of differential diffusion, and points to the need for further
investigations incorporating detailed chemistry models for specific fuel–air mixtures.
Description
Keywords
Deflagration, Ignition, Transient hot jet, Starting vortex, Differential diffusion
Bibliographic citation
Combustion Theory and Modelling (2012), vol.16, n.6, pp.994-1010