Spherical Flame Stretch Rate Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 26, 2026Spherical Flame Stretch Rate Calculator
Lab context: constant-volume combustion bombs ignite a fuel-air mixture at a central point and record the resulting spherical flame as it expands outward - a standard method for measuring laminar burning velocity experimentally. As that flame grows, its surface stretches, and the stretch rate itself needs to be corrected for to get an accurate unstretched burning velocity.
The Formula
K = 2 × SL / R
Worked Example
A flame with 0.4 m/s burning velocity at a 25 mm radius: K = 2 × 0.4 / 0.025 = 32 per second.
As the same flame continues expanding to a larger radius, this stretch rate falls - which is exactly why experimentalists extrapolate measured burning velocity back to zero stretch (infinite radius) rather than using measurements taken early in the expansion.
How to Use This Calculator
- Enter laminar burning velocity in m/s.
- Enter the current flame radius in mm.