Short answer
When designing combustion systems or selecting fuels, consider the Lewis number to predict and control flame stability, particularly in dynamic or turbulent environments.
- Field
- Classic Design
- Source
- Eurasian Chemico-Technological Journal (2014)
- Method
- Computational fluid dynamics (CFD) simulations and statistical analysis of direct numerical simulations (DNS).
- Evidence
- Strong effect
The deviation of a fuel's Lewis number from unity significantly influences the 'polarisation effect' during flame-vortex interactions, impacting heat release uniformity and potentially leading to local flame extinction. This classic design research insight is drawn from a 2014 study published in Eurasian Chemico-Technological Journal. Using Computational fluid dynamics (cfd) simulations and statistical analysis of direct numerical simulations (dns)., researchers explored how this design variable affects real-world outcomes. The key design takeaway: When designing combustion systems or selecting fuels, consider the Lewis number to predict and control flame stability, particularly in dynamic or turbulent environments.
Lewis Number dictates flame-vortex interaction and extinction risk
The deviation of a fuel's Lewis number from unity significantly influences the 'polarisation effect' during flame-vortex interactions, impacting heat release uniformity and potentially leading to local flame extinction.
Eurasian Chemico-Technological Journal · 2014
Key Findings
- 01The 'polarisation effect,' where heat release rate is enhanced in some areas and reduced in others due to flame curvature and strain rate, is strongly dependent on the fuel's Lewis number.
- 02A greater deviation of the Lewis number from unity leads to a stronger polarisation effect, increasing the risk of local flame extinction.
- 03Local flame extinction can occur in both thermodiffusively stable and unstable flames.
- 04Mixing fuels with different Lewis numbers can enhance heat release homogeneity, making the combustion less sensitive to curvature and reducing extinction events.
Application
Design takeaway
When designing combustion systems or selecting fuels, consider the Lewis number to predict and control flame stability, particularly in dynamic or turbulent environments.
How to apply
When designing burners or engines, analyze the Lewis numbers of potential fuel mixtures. Aim for mixtures that minimize the deviation of the effective Lewis number from 1.0 to promote uniform combustion and reduce extinction risk.
Project actions
- 01When researching fuels for a combustion project, look up their Lewis numbers.
- 02Consider how the interaction of flames with air currents (like from fans or turbulence) might affect your design, especially if you're using fuels with extreme Lewis numbers.
Method & Evidence
Variables
Strengths & Limitations
Strengths
- +Provides a quantitative measure (PEN) for the polarisation effect.
- +Investigates a range of Lewis numbers, including extreme values.
Limitations
The simulations used are simplified models of real-world combustion. Factors like three-dimensional effects, impurities in fuel, and varying pressures were not fully explored.
Reliability & validity
The study's validity relies on the accuracy of the DNS simulations. Reliability is supported by statistical analysis of simulation data.
Think critically
If a fuel has a Lewis number far from 1.0, and the 'polarisation effect' leads to extinction, how might a designer counteract this without changing the fuel itself?
Design Principles
"Control flame stability and heat release uniformity by managing fuel properties (Lewis number) and their interaction with flow dynamics (vortices)."
Understanding how fuel properties like the Lewis number affect flame behavior under dynamic conditions is crucial for designing safer and more efficient combustion systems. This insight can guide material selection and mixture design to achieve more stable and predictable combustion processes.
What This Means for Your Design
Imagine a flame being pushed and pulled by swirling air. If the fuel isn't balanced right (its Lewis number is too high or too low), some parts of the flame will burn much hotter and brighter, while others will dim or even go out. Mixing fuels can help make the burning more even.
How to use in your project
- 1.Reference this study when discussing the choice of fuel or the stability of combustion in your design project, especially if your design involves dynamic airflow or heat generation.
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Quick Cite
Paragraph starter
The interaction between flames and vortices, as quantified by the 'polarisation effect,' is significantly influenced by the fuel's Lewis number. Fuels with Lewis numbers deviating from unity exhibit uneven heat release, increasing the risk of local flame extinction. This suggests that for improved combustion stability and efficiency in design projects, careful selection or blending of fuels to achieve a Lewis number closer to 1.0 is advisable.
Source
Eurasian Chemico-Technological Journal
Quantification of the Local Heat Release Rate During Flame-Vortex Interactions at Different Lewis Numbers and Equivalence Ratios
journal · 2014
View sourceQuestions About This Research
- What does the research say about lewis number dictates flame-vortex interaction and extinction risk?
- When designing combustion systems or selecting fuels, consider the Lewis number to predict and control flame stability, particularly in dynamic or turbulent environments. Evidence: Eurasian Chemico-Technological Journal (2014).
- Why does "Lewis Number dictates flame-vortex interaction and extinction risk" matter for design?
- Understanding how fuel properties like the Lewis number affect flame behavior under dynamic conditions is crucial for designing safer and more efficient combustion systems. This insight can guide material selection and mixture design to achieve more stable and predictable combustion processes.
- How can designers apply this research?
- When designing combustion systems or selecting fuels, consider the Lewis number to predict and control flame stability, particularly in dynamic or turbulent environments.
- What were the main findings?
- The 'polarisation effect,' where heat release rate is enhanced in some areas and reduced in others due to flame curvature and strain rate, is strongly dependent on the fuel's Lewis number.. A greater deviation of the Lewis number from unity leads to a stronger polarisation effect, increasing the risk of local flame extinction.. Local flame extinction can occur in both thermodiffusively stable and unstable flames.. Mixing fuels with different Lewis numbers can enhance heat release homogeneity, making the combustion less sensitive to curvature and reducing extinction events.
- What research method was used?
- Computational fluid dynamics (CFD) simulations and statistical analysis of direct numerical simulations (DNS)..
- How strong is the evidence?
- Evidence strength is rated Strong effect, based on a 2014 journal from Eurasian Chemico-Technological Journal.
- What should I do differently in my next project?
- When designing burners or engines, analyze the Lewis numbers of potential fuel mixtures. Aim for mixtures that minimize the deviation of the effective Lewis number from 1.0 to promote uniform combustion and reduce extinction risk.
- What are the limitations?
- The study focused on two-dimensional simulations and specific fuel types (hydrogen, methane, propane) and artificial cases. Real-world combustion environments are more complex.