Flame stretch

Definition

Flame stretch refers to the elongation or distortion of a flame due to the influence of local flow velocities and turbulence. This phenomenon affects how flames propagate, interact with surrounding flow fields, and can significantly impact combustion characteristics, especially in turbulent environments where fluctuations in velocity can stretch or compress the flame front.

5 Must Know Facts For Your Next Test

1. Flame stretch can lead to increased burning rates as the flame interacts with turbulent eddies, making it crucial for understanding combustion in engines and industrial burners.
2. In premixed flames, flame stretch modifies the local flame structure by changing the curvature of the flame front, which can alter heat release rates and emissions.
3. Flame stretch is particularly important in modeling combustion processes where turbulence and reaction kinetics are interdependent, often requiring complex simulations to capture its effects.
4. In laminar flows, flame stretch effects are minimal, but as turbulence increases, the significance of flame stretch on combustion efficiency becomes more pronounced.
5. Understanding flame stretch helps in optimizing combustion systems for better performance and lower emissions by controlling how flames respond to turbulent flow conditions.

Review Questions

• How does flame stretch influence the characteristics of combustion in turbulent flows?
  • Flame stretch influences combustion characteristics by affecting the propagation speed and stability of the flame. In turbulent flows, fluctuations in velocity create varying degrees of stretch and compression in the flame front. This leads to increased burning rates and altered heat release patterns, which can enhance combustion efficiency but may also result in higher emissions if not managed properly.
• Discuss the relationship between flame stretch and turbulent flame speed in practical combustion systems.
  • Flame stretch is closely related to turbulent flame speed because it directly affects how quickly a flame can propagate through a mixture. In practical combustion systems, an increase in turbulence typically results in higher flame stretch, leading to an increased turbulent flame speed. Understanding this relationship is essential for optimizing combustion processes to achieve efficient burning while minimizing emissions.
• Evaluate the role of flame stretch in flame wrinkling and its implications for improving combustion technologies.
  • Flame stretch plays a significant role in flame wrinkling by altering the curvature of the flame surface, which increases the effective surface area available for reaction. This enhancement leads to more efficient heat release and can improve overall combustion performance. By understanding how to control flame stretch and its associated wrinkling effects, engineers can design better combustion systems that minimize pollutants while maximizing energy output.

Related terms

Turbulent Flame Speed: The speed at which a flame propagates through a turbulent medium, influenced by factors like turbulence intensity and flame stretch.

Burning Velocity: The speed at which a premixed fuel-air mixture burns, impacting how quickly a flame front advances.

Flame Wrinkling: The distortion of a flame surface caused by turbulence, which increases the surface area and enhances the rate of heat release during combustion.