DIFFUSION FLAMES AND DROPLET BURNING

In a restricted sense, a diffusion flame may be defined as a nonpremixed, quasisteady, nearly isobaric flame in which most of the reaction occurs in a narrow zone that can be approximated as a surface. This is the class of flame problems that will be discussed in the present chapter. The coupling-function formulation (Section 1.3) provides a convenient framework within which these problems can be studied. Coupling functions usually are more useful for initially unmixed systems than for initially premixed systems because, as we shall see, the chemical reaction rate is often of negligible importance in answering certain questions raised for diffusion flames. 

Even within our restricted definition, so many diffusion-flame problems exist that we do not have enough space to consider them all. Therefore, we shall merely illustrate the analytical procedure by means of three examples (Sections 3.1-3.3). The problem of droplet burning (Section 

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