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Old   May 20, 2004, 08:05
Default Ignition modeling
Julie Polyakh
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The Methodology volume defines the "Fraction" in the ignition model as follows (p. 10-7):

"For modeling purposes, it is often necessary to initiate the reaction by specifying an ignition mechanism. This consists of one or both of the following options: Reducing the fuel concentration by a user-specified fraction in the ignition region of the solution domain. The reduced fuel concentration is an artifice that signals the fact that a small proportion of the fuel has already been burned by the ignition mechanism and is therefore necessary to start off the combustion simulation process..."

I'm not sure that I understand this right. Let me give you an example to clarify it. Suppose that the fuel mass concentration in the ignition cell type is 0.08 before the ignition. The "Fraction" parameter value is 0.05 (as it is given in Tutorial 9). Than at the beginning of the ignition, set let's say to iteration #100, the fuel mass concentration becomes 0.08-0.05=0.03. Am I right? If I am than the ignition fraction value should be very small in order to keep fuel mass fraction close to the stoichiometric value.

The next question is about air initialization. Is it legitimate to introduce a small fraction of fuel (for example, it's stoichiometric value) into the air in order to ensure better convergence and ignition?


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