Equivalence ratio in partially premixed flame system

In summary, the individual is learning about plasma assisted combustion and has been reading articles on the topic. They have a question about finding the equivalence ratio in an experiment where both oxidation and fuel reforming occur. The article they reference uses a setup with a pair of counterflow burners and a fixed composition of the oxidizer stream with a varying fuel stream. The equivalence ratio is defined as the ratio of fuel-to-oxidizer ratio to the stoichiometric fuel-to-oxidizer ratio, but in this case, the oxidizer is premixed with methane. The individual is confused about how to calculate the equivalence ratio in this scenario. They are advised to use the Takeno flame index or mixture fraction to characterize the flame in partially premixed cases
  • #1
fyyfifowffums
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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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  • #2
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.
 
  • #3
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!
 

FAQ: Equivalence ratio in partially premixed flame system

What is the definition of equivalence ratio in a partially premixed flame system?

The equivalence ratio in a partially premixed flame system is the ratio of the actual fuel-air ratio to the stoichiometric fuel-air ratio. It is typically denoted by the symbol φ and is used to quantify the chemical balance between the fuel and the oxidizer in a combustion process.

Why is the equivalence ratio important in a partially premixed flame system?

The equivalence ratio is important in a partially premixed flame system because it directly affects the rate of combustion. A higher equivalence ratio means there is more fuel present in the system, leading to a faster and more intense combustion. On the other hand, a lower equivalence ratio means there is less fuel, resulting in a slower and less efficient combustion process.

How does the equivalence ratio affect the stability of a partially premixed flame?

The equivalence ratio plays a crucial role in the stability of a partially premixed flame. A moderate equivalence ratio (around 0.5-0.7) is usually necessary for maintaining a stable flame. If the equivalence ratio is too low, the flame may go out due to insufficient fuel. Conversely, if the equivalence ratio is too high, the flame may become too intense, leading to instability and potential flame extinction.

What is the optimum equivalence ratio for a partially premixed flame system?

The optimum equivalence ratio for a partially premixed flame system depends on various factors such as the type of fuel, the oxidizer, and the geometry of the system. In most cases, an equivalence ratio between 0.5 and 0.7 is considered optimal for achieving stable and efficient combustion.

How can the equivalence ratio be controlled in a partially premixed flame system?

The equivalence ratio in a partially premixed flame system can be controlled by adjusting the fuel and air flow rates. By increasing or decreasing the fuel flow rate, the equivalence ratio can be changed accordingly. Additionally, the use of advanced control systems and feedback mechanisms can also help maintain a desired equivalence ratio in real-time.

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