Analysis of dropwise ignition versus external ignition for dilute multicomponent fuel sprays

An attempt has been made to identify conditions for dropwise ignition and spray ignition. Both pure as well as multicomponent fuels are considered. For dropwise ignition, an existing ignition criterion has been modified to account for the nonlinear dependence of reaction rate on fuel and oxygen concentrations and to account for the multicomponent nature of the fuel. The external or spray ignition is considered through the zero heat flux condition at the ignition source. The effect of chemical kinetics is examined by employing reaction schemes with unity as well as nonunity exponents of fuel and oxygen concentrations. Results indicate that for most of the conditions considered, the individual droplet ignition is favored over the external ignition. Only when the drop diameter is smaller than 30 μm does the spray ignite earlier than droplets. The addition of a small amount of a volatile component significantly enhances the ignitability of both modes. However, the effect is stronger for the dropwise ignition mode.