Effects of dilution on the extinction characteristics of strained lean premixed flames assisted by catalytic reaction

As a fundamental study relevant to micro-combustor application, the effects of mixture dilution on the lean extinction characteristics is studied for a stagnation-point flow system with a methane/air mixture over a platinum surface. For steady conditions, the level of flammability extension by surface reaction depends strongly on the mixture dilution, such that the benefit of catalyst-assisted lean combustion can be fully realized only with a diluted system. As for the effects of surface heat loss, while it lowers the overall flammability of the system, it was found that the level of flammability extension by surface reactions is rather insensitive to the surface thermal conditions. These observations are explained by consideration of characteristic time scales calculated from the fuel consumption rate. The extinction response to oscillatory strain rate also shows consistent behavior. Unsteady extinction behavior in response to equivalence ratio fluctuations showed an expected trend overall. It is also found that the benefit of flammability extension by catalytic reaction can become greater as the level of unsteadiness increases. 2006 Published by Elsevier Inc. on behalf of The Combustion Institute.