Book contents
- Frontmatter
- Contents
- Preface
- INTRODUCTION
- 1 CHEMICAL THERMODYNAMICS
- 2 CHEMICAL KINETICS
- 3 OXIDATION MECHANISMS OF FUELS
- 4 TRANSPORT PHENOMENA
- 5 CONSERVATION EQUATIONS
- 6 LAMINAR NONPREMIXED FLAMES
- 7 LAMINAR PREMIXED FLAMES
- 8 LIMIT PHENOMENA
- 9 ASYMPTOTIC STRUCTURE OF FLAMES
- 10 AERODYNAMICS OF LAMINAR FLAMES
- 11 COMBUSTION IN TURBULENT FLOWS
- 12 COMBUSTION IN BOUNDARY-LAYER FLOWS
- 13 COMBUSTION IN TWO-PHASE FLOWS
- 14 COMBUSTION IN SUPERSONIC FLOWS
- References
- Author Index
- Subject Index
8 - LIMIT PHENOMENA
Published online by Cambridge University Press: 06 July 2010
- Frontmatter
- Contents
- Preface
- INTRODUCTION
- 1 CHEMICAL THERMODYNAMICS
- 2 CHEMICAL KINETICS
- 3 OXIDATION MECHANISMS OF FUELS
- 4 TRANSPORT PHENOMENA
- 5 CONSERVATION EQUATIONS
- 6 LAMINAR NONPREMIXED FLAMES
- 7 LAMINAR PREMIXED FLAMES
- 8 LIMIT PHENOMENA
- 9 ASYMPTOTIC STRUCTURE OF FLAMES
- 10 AERODYNAMICS OF LAMINAR FLAMES
- 11 COMBUSTION IN TURBULENT FLOWS
- 12 COMBUSTION IN BOUNDARY-LAYER FLOWS
- 13 COMBUSTION IN TWO-PHASE FLOWS
- 14 COMBUSTION IN SUPERSONIC FLOWS
- References
- Author Index
- Subject Index
Summary
So far we have been concerned only with situations involving intense burning. In this chapter we shall study the transition between burning and nonburning states, namely phenomena involving ignition, extinction, flame stabilization and blowoff, and flammability.
There are many practical situations exhibiting ignition and extinction phenomena in our daily lives. For ignition, we can cite the striking of a match, turning on the gas stove by a pilot light or spark discharge, firing within an internal combustion engine through compressive heating or again by spark discharge, and the initiation of fires and explosions in mines, grain elevators, and upon the rupturing of fuel tanks by electric or frictional sparks. For extinction, we can cite firefighting through spraying of water and chemicals and the quenching of chemical reactions by the relatively cold wall of combustion chambers.
At the fundamental level, ignition can be achieved in one of two ways. One can either supply an amount of heat to part or all of a combustible mixture. The supply can be either momentary or continuous. The heated mixture responds Arrheniusly, reacts faster, and produces more heat. At the same time, however, being hotter it also tends to lose more heat to the walls and colder parts of the gas. Thus if the rate of heat generation exceeds that of cooling, then an accelerative, runaway process occurs that eventually leads to a state of intense burning.
- Type
- Chapter
- Information
- Combustion Physics , pp. 303 - 365Publisher: Cambridge University PressPrint publication year: 2006