Equivalence ratio in partially premixed flame system

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SUMMARY

The discussion focuses on calculating the equivalence ratio in a partially premixed flame system, specifically using a setup with counterflow burners and a fixed oxidizer composition of O2/Ar/He/CH4 (0.26:0.32:0.4:0.02). The equivalence ratio is defined as the fuel-to-oxidizer ratio divided by the stoichiometric fuel-to-oxidizer ratio. In this scenario, the oxidizer is premixed with methane, complicating the calculation. Participants suggest utilizing the Takeno flame index and mixture fraction to better characterize the combustion regime and understand the varying equivalence ratios throughout the flame.

PREREQUISITES
  • Understanding of plasma assisted combustion principles
  • Familiarity with counterflow burner setups
  • Knowledge of chemical reaction equations for oxidation and fuel reforming
  • Concept of equivalence ratio in combustion systems
NEXT STEPS
  • Research the Takeno flame index and its application in combustion analysis
  • Study mixture fraction calculations in partially premixed flames
  • Explore advanced combustion modeling techniques for varying equivalence ratios
  • Examine the effects of different fuel and oxidizer compositions on combustion efficiency
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Researchers and engineers in the field of combustion science, particularly those focusing on plasma assisted combustion and flame characterization techniques.

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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
1-s2.0-S0010218011002203-gr1.jpg

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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