Computation of laminar premixed flame extinction limits in the unburnt-to-unburnt opposed flow configuration with upstream heat loss

Numerical methods are used to examine the combined effects of stretch and upstream heat loss on the properties of an otherwise adiabatic, stoichiometric, laminar, premixed methane-air flame. A symmetric unburnt-to-unburnt opposed flow configuration is investigated in which fresh combustible mixture is discharged towards the stagnation plane from identical, coaxial, plug flow nozzles maintained at constant temperature, and separated by a fixed distance. A continuation method is used, in tandem with Newton solutions for individual flame structures, to study the flame behaviour as the stretch rate (or nozzle inlet velocity) is varied. High and low stretch extinction limits are observed as positions of vertical tangency in the steady state solution curves of flame property versus stretch rate. The complete series of solutions forms a set of isolae with both stable and unstable branches.