Emissions from Nonpremixed Flames
NOx Emissions from Nonpremixed Hydrocarbon Flames
A variety of methods are used to study NOx emissions from nonpremixed
hydrocarbon flames. Of particular interest is the prediction of
emissions from practical combustors including diesel engines and
household appliances. A number of experimental measurements of
emissions from laminar and turbulent jet diffusion flames were made.
Numerical studies of one-dimensional flames have been performed using
detailed and reduced mechanisms. Rate-ratio asymptotics are used to
develop relationships which indicate how emissions scale with
dissipation rate, pressure, and dilution among other
quantities. Relationships such as these can be used in engineering
models to predict emissions.
CO and N2O Emissions from Nonpremixed Hydrocarbon Flames
Species such as CO and N2O are in near equilibrium within diffusion
flames. As a result, the emissions are governed by the quenching of
the reactions which consume these species on the lean side of the
flame. Rate-ratio asymptotics can be used to predict the emissions of
these species by considering the flux of these species at the point
where the reactions are quenched (i.e. the consumption reaction
becomes asymptotically slow relative to the transport). This point is
generally referred to as the cross over point, where radical
consumption and production switch dominance. As the scalar
dissipation rate (the characteristic diffusional time scale) increases
these emissions are found to increase.
Click here to download a postscript
version of Dr. Hewson's thesis which contains much more information on these
topics.
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