Equivalence ratio in partially premixed flame system

AI Thread Summary
The discussion centers on calculating the equivalence ratio in a plasma-assisted combustion setup using counterflow burners with a specific oxidizer and fuel composition. The equivalence ratio is typically defined as the fuel-to-oxidizer ratio compared to a stoichiometric ratio, but the presence of premixed methane complicates this calculation. It is noted that the equivalence ratio can vary throughout the flame, particularly in partially premixed cases. Instead of relying solely on the equivalence ratio, using the Takeno flame index or a mixture fraction can provide better insights into the combustion regime. Understanding these variations clarifies the confusion surrounding the calculation of a constant equivalence ratio.
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Hi, I'm learning the basics of plasma assisted combustion so I've been reading up on a few articles related to it.
My question is regarding this article http://enu.kz/repository/2011/AIAA-2011-971.pdf
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Using a setup consisting of a pair of counterflow burners, the composition of the oxidizer stream was fixed at O2/Ar/He/CH4(0.26:0.32:0.4:0.02) while the fuel stream was CH4 diluted by Ar (fuel mole fraction varied from 0.2 to 0.4). In this experiment, both oxidation and fuel reforming occurs. How do I find the equivalence ratio for both cases?

Oxidation: CH4 + 2O2→ CO2 + 2H2O
Fuel reforming: 2CH4 + O2→ 4H2 + 2CO

The equivalence ratio is defined as (fuel-to-oxidizer ratio)/ (fuel-to-oxidizer ratio)st and usually methane will be the fuel and oxygen as oxidizer, but in this case the oxidizer itself is premixed with methane so how do I calculate the equivalence ratio? Please help. I get so confused.
 
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The equivalence ratio is different everywhere in your flame. In partially premixed cases, it is more useful to use the Takeno flame index as a measure for the combustion regime, or use the mixture fraction together with the equivalence ratio to characterize the flame.
 
bigfooted said:
The equivalence ratio is different everywhere in your flame. In partially premixed cases, it is more useful to use the Takeno flame index as a measure for the combustion regime, or use the mixture fraction together with the equivalence ratio to characterize the flame.
I see! I never thought about different parts having different equivalence ratios before. No wonder I couldn't get a constant value. It makes more sense now. Thank you so much!
 

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