Numerical Simulation of the Ignition of Fuel/Air Gas Mixtures Around Small Hot Particles

Abstract

Abstract This study presents the simulation and detailed analysis of the ignition of initially quiescent fuel/air mixtures by small, stationary, laser-heated spherical particles. Our simulations cover a wide parameter space by varying the kind of fuel, stoichiometry, heating rate, radical surface destruction efficiencies as well as particle size. The results agree well with experimentally determined particle surface temperatures at the time of ignition over the whole range of parameters. The surface temperatures required for ignition strongly depends on the kind of fuel and increases in the order hydrogen, acetylene, ethylene, ethane, propane and methane. It also increases with decreasing particle size. By contrast, mixture stoichiometry and heating rate have a minor influence on the ignition temperatures. Comparisons with two-dimensional direct numerical simulations show that fast, but fully coupled one-dimensional simulations are sufficient to capture the details of the ignition event, permitting a systematic investigation for large number of conditions. At small particle radii (r≤2 mm) there exists a simple mapping of only two parameters, an apparent activation energy and a factor comprising thermo-physical properties of the gas phase that is able to estimate the particle surface temperature required for ignition. Such a map might be used for the safety assessment of ignition hazards by small hot particles as function of fuel, stoichiometry and particle size.