On the Formation of Nitrogen Oxides During the Combustion of ...

2.1 Classification of Combustion Processes
Droplet Vaporization and Burning
Recalling the schematic of Figure 1.1, Liñán and Williams [253] provide the
following summary on the process of liquid fuel injection and spray combustion.
The authors state that a quantitative prediction of the histories of all of
these processes is difficult, but progress is being made by addressing different
aspects separately:
• Atomization
• Vaporization
• Heat transfer
• Droplet-air mixing
• Vapor-air mixing
• Ignition
• Turbulent diffusion flames
• Premixed combustion
• Production of NO x and other pollutants
• Extinction
The majority of these combustion processes take place in the gas phase, and
the combustion products are typically gaseous [253, 443]. Law and Sirignano
[233, 236, 402, 403, 405] and Faeth [126, 127] give a detailed review of the fundamentals
of droplet vaporization and combustion. Discussing the major elements
of an integrated approach, Sirignano [403] points out the necessity of
treating unsteady, multi-dimensional, turbulent reacting flows with polydisperse,
multi-component sprays. A model has to account for transient droplet
heating and vaporization, liquid-phase mass diffusion, and droplet drag and
trajectory in a numerically efficient manner. Furthermore, Law and Faeth
[235] recall that droplet vaporization and combustion is a classical problem of
heterogenous combustion, in particular when assuming quasi-steadiness and
spherical symmetry. This simplifies the mathematical aspects of the problem.
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