Ignition and Burning of a Layer of Incomplete Combustion Products

Abstract

An ignition criterion for lean premixed and diffusion flame burning is developed using classical empirical relations for lean premixed flammability limits and an analogy between limit premixed and diffusion flames first noted by Simmons and Wolfhard. The ignition criterion is validated by comparison with ignition experiments using a layer of products of incomplete com- bustion. The criterion, developed to allow prediction of the ignition of the upper layer in compart- ment fires, is compatible with zone fire models. Three modes of layer burning were observed. Mode one burning was a ring flame surrounding the buoyant diffusion flame feeding the layer. Mode two burning occurred when the ring flame deformed to include finger-like extensions away from the plume. Mode three was burning of layer gases at the layer/air interface. All three modes were diffusion flames. The rate of burning was controlled by the flammability of the layer such that the ignition criterion was just satisfied during layer burning.