[6] The flame stretch is also discussed by Bernard Lewis and Guenther von Elbe in their book.
[7] All these discussions treated flame stretch as an effect of flow velocity gradients.
The stretch can be found even if there is no velocity gradient, but due to the flame curvature.
is the laminar propagation speed of unstretched premixed flame.
The formula for flame stretch was first derived by John D. Buckmaster in 1979.