Behavior of preheated premixed flames at lean conditions

Document Type

Conference Proceeding

Publication Date

1-1-2013

Abstract

The ultra-lean combustion regime extends below the conventional lean flammability limit, where viable flames require substantial preheating of the reactant mixture. A large number of simulations of adiabatic laminar flames with detailed reaction kinetics and pseudo-randomly distributed inlet temperatures (Tin = 300-1000K) and equivalence ratios (φ = 0:12-1:0) is used to investigate fundamental aspects of lean and ultra-lean combustion of methane/air mixtures. Common features of flame characteristics are studied as a function of inlet temperature, equivalence ratio, mass flux and peak temperatures, which are used to parameterize the solution space. Holding individual parameters constant, a comparison of flame structures reveals that a characteristic temperature at the transition from preheating zone to the active reaction zone is reliably predicted by the local mass flux. Another characteristic temperature marking complete reaction of the fuel is predicted by the peak temperature. Overall, findings demonstrate that a parameterization using initial temperature and/or equivalence ratio fails to predict parameters of the inner reaction zone. Yet, results show that key features within the flame structure of premixed combustion are essentially unchanged throughout the lean and ultra-lean regime, where burning rates determine the temperature at which the preheating layer transitions into the active reaction zone. It is shown that peak temperatures determine characteristics of the active reaction zone irrespective of the mixture stoichiometry.

Publication Source (Journal or Book title)

8th US National Combustion Meeting 2013

First Page

2477

Last Page

2488

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