Book contents
- Frontmatter
- Summary Contents
- Detailed Contents
- Introduction
- Overview of the Book
- 1 Overview and Basic Equations
- 2 Decomposition and Evolution of Disturbances
- 3 Hydrodynamic Flow Stability I: Introduction
- 4 Hydrodynamic Flow Stability II: Common Combustor Flow Fields
- 5 Acoustic Wave Propagation I – Basic Concepts
- 6 Acoustic Wave Propagation II – Heat Release, Complex Geometry, and Mean Flow Effects
- 7 Flame–Flow Interactions
- 8 Ignition
- 9 Internal Flame Processes
- 10 Flame Stabilization, Flashback, Flameholding, and Blowoff
- 11 Forced Response I – Flamelet Dynamics
- 12 Forced Response II – Heat Release Dynamics
- Index
- Solutions
- References
9 - Internal Flame Processes
Published online by Cambridge University Press: 05 October 2012
Book contents
- Frontmatter
- Summary Contents
- Detailed Contents
- Introduction
- Overview of the Book
- 1 Overview and Basic Equations
- 2 Decomposition and Evolution of Disturbances
- 3 Hydrodynamic Flow Stability I: Introduction
- 4 Hydrodynamic Flow Stability II: Common Combustor Flow Fields
- 5 Acoustic Wave Propagation I – Basic Concepts
- 6 Acoustic Wave Propagation II – Heat Release, Complex Geometry, and Mean Flow Effects
- 7 Flame–Flow Interactions
- 8 Ignition
- 9 Internal Flame Processes
- 10 Flame Stabilization, Flashback, Flameholding, and Blowoff
- 11 Forced Response I – Flamelet Dynamics
- 12 Forced Response II – Heat Release Dynamics
- Index
- Solutions
- References
Summary
Chapter 8 considered ignition and the processes associated with autoignition and forced ignition of a nonreactive mixture. In this chapter, we focus on premixed and non-premixed flames and the key physics controlling burning rates and extinction processes. Section 9.1 summarizes basic issues associated with the structure and burning rate of steady, premixed flames in one-dimensional flow fields. This includes discussions of the effects of pressure, temperature, and stoichiometry on burning rates. Section 9.2 discusses how these one-dimensional characteristics are altered by stretch; that is, fluid mechanic shear or flame curvature. We then discuss how these lead to changes in burning rate and, for large enough levels of stretch, cause the flame to extinguish. Section 9.3 treats the effects of unsteadiness in pressure, fuel/air ratio, and stretch rate. Specifically, we discuss how the flame acts as a low pass filter to disturbances in most cases, and that its sensitivity to disturbances diminishes with increasing frequency. These results have important implications for many combustion instability phenomena, in which the flame is perturbed by time varying flow and composition variations.
We then move to non-premixed flames. Section 9.4 reviews non-premixed flames in the fast chemistry limit, and Section 9.5 discusses finite rate kinetic effects. This section shows that large gradients in fuel and oxidizer concentrations can lead to flame extinction.
- Type
- Chapter
- Information
- Unsteady Combustor Physics , pp. 247 - 292Publisher: Cambridge University PressPrint publication year: 2012
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