Measurements of minimum ignition energy by using laser sparks for hydrocarbon fuels in air: propane, dodecane, and jet-A fuel

Abstract

Minimum ignition energy of fuel–air mixtures involving propane, dodecane, and jet-A fuels has been measured at a range of pressures and equivalence ratios. The minimum ignition energy obtained by using laser sparks shows consistently larger values than corresponding data using electrical sparks for propane–air mixtures at 1 atm and at lower pressures, similar to existing measurements in the literature, perhaps due to the different electromagnetic and thermal conditions that exist within and near the spark plasmas. The heavier hydrocarbon fuels exhibit progressively larger optimum equivalence ratio corresponding to the minimum in the ignition energy, away from the stoichiometric equivalence ratio. The minimum ignition energy of jet-A fuel has also been measured by using laser sparks, and shows a nearly parabolic variation as the temperature and pressure conditions cause a shift in the fuel–air ratio from lean (with respect to an optimum fuel–air ratio) to the rich side. The minimum ignition energy is observed to be ∼2 mJ at ∼25°F above the so-called flashpoint at 1 atm. The fuel loading (the amount of liquid fuel per total chamber volume) affects the ignition characteristics of the jet-A fuel in that a decrease in the fuel loading is accompanied by an increase in the minimum ignition energy. This is attributable to relative decrease in the amounts of light-end hydrocarbon species at low fuel loadings.