text: The burning velocity of the stretched flame can be derived by subtracting suitable terms from the unstretched flame speed, for small curvature and small strain, as given by
  where
  * is the burning velocity of unstretched flame
  * is the term corresponding to the imposed strain rate on the flame due to the flow field
  * is the Markstein length, proportional to the laminar flame thickness , the constant of proportionality is Markstein number 
  * is the flame curvature, which is positive if the flame front is convex with respect to the unburnt mixture and vice versa.