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Ignition and combustion in a laminar mixing zone

Marble, Frank E. and Adamson, Thomas C., Jr. (1954) Ignition and combustion in a laminar mixing zone. Jet Propulsion, 24 (2). pp. 85-94. ISSN 0095-8751. http://resolver.caltech.edu/CaltechAUTHORS:20100120-092445763

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Abstract

The analytic investigation of laminar combustion processes which are essentially two- or three-dimensional present some mathematical difficulties. There are, however, several examples of two-dimensional flame propagation which involve transverse velocities that are small in comparison with that in the principal direction of flow. Such examples occur in thc problem of flame quenching by a cool surface, flame stabilization on a heated flat plate, combustion in laminar mixing zones, etc. In these cases the problem may be simplified by employing what is known in fluid mechanics as the boundary-layer approximation, since it was applied first by Prandtl in his treatment of the viscous flow over a flat plate. Physically it consists in recognizing that if the transverse velocity is small, the variations of flow properties along the direction of main flow are small in comparison with those in a direction normal to the main flow. The analytic description of the problem simplifies accordingly. The present analysis considers the ignition and combustion in the laminar mixing zone between two parallel moving gas streams. One stream consists of a cool combustible mixture, the second is hot combustion products. The two streams come into contact at a given point and a laminar mixing process follows in which the velocity distribution is modified by viscosity, and the temperature and composition distributions by conduction, diffusion, and chemical reaction. The decomposition of the combustible stream is assumed to follow first-order reaction kinetics with temperature dependence according to the Arrhenius law. For a given initial velocity, composition, and temperature distribution, the questions to be answered are: (1) Does the combustible material ignite; and (2) how far downstream of the initial contact point does the flame appear and what is the detailed process of development. Since the hot stream is of infinite extent, it is found that ignition always takes place at some point of the stream. However, when the temperature of the hot stream drops below a certain value, the distance required for ignition increases so enormously that it essentially does not occur in a physical apparatus of finite dimension. The complete development of the laminar flame front is computed using an approximation similar to the integral technique introduced by von Kármán into boundary layer theory.


Item Type:Article
Additional Information:(Reprinted from JET PROPULSION, March-April, 1954). Copyright, 1954, by the American Rocket Society, Inc., and reprinted by permission of the copyright owner. Presented at the 8th ARS National Convention, New York, N. Y., December 3, 1953. This investigation was carried out, in part, under the financial sponsorship of the Ordnance Corps, U. S. Army.
Group:Guggenheim Jet Propulsion Center
Funders:
Funding AgencyGrant Number
Ordnance Corps, U.S. ArmyUNSPECIFIED
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Guggenheim Jet Propulsion Center50
Record Number:CaltechAUTHORS:20100120-092445763
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20100120-092445763
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17230
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:28 Jan 2010 17:51
Last Modified:26 Dec 2012 11:42

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