Effects of Particle Size on the Ignition of Static CH4/Air and H2/Air Mixtures by Hot Particles

Abstract

ABSTRACT Understanding and characterizing the non-homogenous ignition of flammable mixtures by hot particles are important for industry safety. In this study, one-dimensional transient simulations considering detailed chemistry and transport are conducted for the ignition of static methane/air and hydrogen/air mixtures by hot particles with different radii. The objective is to assess the effects of particle size on the ignition delay time for the hot particle-induced ignition process. Unlike the nearly homogenous ignition in shock tubes or rapid compression machines, the non-homogeneous ignition caused by a hot particle depends on not only chemical kinetics but also transport of reactive species. It is found that 1D hot particle ignition is much slower than the 0D homogenous ignition (in which the mixture temperature is the same as the fixed particle temperature) since there is radical loss near the particle surface caused by mass diffusion. The ignition delay time for hot particle ignition is found to strongly depend on the particle radius and temperature. This is interpreted through the change of radical loss with particle radius and temperature. Moreover, to characterize the hot particle ignition, we introduce a Damköhler number which is the ratio between two characteristic times for chemical reaction and mass diffusion. The change of the normalized ignition delay time for 1D hot particle with the Damköhler number is discussed; and a linear relationship is observed for certain conditions.