LaminarNonpremixedFlamesILect21ME525SP2011

- ME 525 Combustion Lecture 21 Laminar Nonpremixed Flames Introduction Nonreacting Jets Simplified Description of Laminar Nonpremixed Flames Prof

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School of Mechanical Engineering, Purdue University ME 525: Combustion Lecture 21: Laminar Nonpremixed Flames – Introduction, Nonreacting Jets, Simplified Description of Laminar Nonpremixed Flames Prof. Robert P. Lucht Room 87, Mechanical Engineering Building School of Mechanical Engineering Purdue University West Lafayette, Indiana Email: [email protected] Phone: 765-494-5623 March 29, 2011 1/36
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School of Mechanical Engineering, Purdue University Lecture Topics • Qualitative characteristics of laminar nonpremixed flames. • Review of conserved scalar concept. • Nonreacting jet mixing solution. • Simplified theoretical description of a laminar nonpremixed flame. 2/36
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School of Mechanical Engineering, Purdue University Laminar Jet Diffusion Flames (Nonpremixed Jet Flames) 3/36
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School of Mechanical Engineering, Purdue University Counterflow Nonpremixed Flames Opposed jet nonpremixed flame 4/36
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School of Mechanical Engineering, Purdue University Counterflow Nonpremixed Flames Tsuji burner flame: 5/36
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School of Mechanical Engineering, Purdue University Review of Conserved Scalar, Definition of Mixture Fraction • Concept of conserved scalar is very useful for nonpremixed flames because it varies continuously through the flame zone. A conserved scalar is a quantity defined such that there are no sink or source terms in the conservation equation for that quantity. • Examples: - absolute enthalpy (in the absence of viscous dissipation and thermal radiation) - element mass fraction (in the absence of nuclear reactions) - mixture fraction 6/36
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School of Mechanical Engineering, Purdue University Review of Conserved Scalar, Definition of Mixture Fraction • In premixed flames conserved scalars are constant throughout the flowfield (neglecting differential diffusion effects), in nonpremixed flames they very continuously as mixing and chemical reaction occurs. Definition of mixture fraction f : mass of material from fuel stream = mass of mixture in differential volume element f 7/36
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School of Mechanical Engineering, Purdue University Review of Conserved Scalar, Definition of Mixture Fraction • Consider the three-"species" reaction:   11 k gf uel kg oxidizer kg products   • For this system the mixture fraction will be: 1 1 F Pr f YY     8/36
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School of Mechanical Engineering, Purdue University Review of Conserved Scalar, Definition of Mixture Fraction • Conservation equation for the mixture fraction. Assume all species diffuse at the same rate:  1 2 FF F Pr Pr Pr dY d mm dx dx dx d dx dx dx        D 9/36
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School of Mechanical Engineering, Purdue University Review of Conserved Scalar, Definition of Mixture Fraction • Divide the product species conservation equation by and add to the fuel species conservation equation: • Substituting for the mixture fraction we obtain:    11 03 1 FP r r Pr F dY Y Y d m dx dx dx m m          
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This note was uploaded on 12/27/2011 for the course ME 525 taught by Professor Lucth during the Fall '11 term at Purdue University-West Lafayette.

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- ME 525 Combustion Lecture 21 Laminar Nonpremixed Flames Introduction Nonreacting Jets Simplified Description of Laminar Nonpremixed Flames Prof

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