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Dr. Kal Seshadri
Department of Mechanical and Aerospace Engineering
University of California a San Diego
La Jolla, California 92093-0411
Structure and Extinction of Partially Premixed Flames
Abstract
Experimental, numerical and analytical studies on extinction
of laminar partially premixed flames were carried out. The studies employed
the counterflow configuration. A premixed fuel-rich mixture of methane
(CH4), oxygen (O2), and nitrogen (N2) was injected from one duct while a
fuel-lean mixture of CH4, O2 and N2 was injected from the other duct. The
levels of partial premixing were given by the equivalence ratios r of the
fuel-rich mixture and l of the fuel-lean mixture. Previous studies have
established that the scalar dissipation rate at extinction depends on the
stoichiometric mixture fraction, ξst and the adiabatic temperature, Tst. To
clarify the influence of partial premixing on extinction, studies were
carried out at fixed values of ξst and Tst. For r-1 = 0, experiments show
that the value of the strain rate at extinction, aq, increases with
increasing l. For l = 0, experiments show that the value of the strain rate
a extinction, aq, decreases with increasing r-1. Numerical calculations were
carried out using a detailed chemical-kinetic mechanism and an one-step
chemical-kinetic mechanism. The values of aq calculated using the detailed
mechanism were found to agree well with experiments. The values of aq
calculated using the one-step mechanism do not agree with experiments. In
fact, calculations with the one-step mechanism show the values of aq to
decrease with increasing l, and increase with increasing r-1. Results of a
previous activation-energy asymptotic analysis of partially premixed flames
were used to obtain critical conditions of extinction. The asymptotic
results were found to agree with those calculated numerically using the
one-step mechanism. Rate ratio asymptotic analysis (RRA) was carried out
using reduced chemistry. Results of RRA were found to agree with those
calculated numerically using the detailed mechanism. The differences in
critical conditions of extinction obtained using the detailed mechanism and
he one-step mechanism are attributed to differences in flame structure.
Wednesday, October 8, 2003
Bourns Hall, Room A265
10:10 a.m.-11:00 p.m.
(Refreshments will be served at 10:00 a.m.) |
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