Quenching distances, minimum ignition energies and related properties of propane-air-diluent mixtures

Abstract

The ignition by high voltage inductive-capacitive sparks of the quiescent stoichiometric C3H8-air mixture diluted by various amounts of additives (He, Ar, N2, or CO2) is examined at various initial pressures within 0.5–1.5 bar in a cylindrical vessel of volume ~0.28 L. The quenching distances (QDs) of C3H8-air and C3H8-air-diluent mixtures are determined by means of flanged electrodes technique. Experimental QDs are compared with the computed ones, obtained by a previously described model. Using the QD, the minimum ignition energies (MIEs) are evaluated using a correlation model. At constant pressure, dilution results in the increase of both QD and MIE. Among the examined diluents, CO2 has the most important effect, followed by N2, Ar and He. For each diluted mixture the QDs and MIEs depend on initial pressure, according to a power law. The baric exponents of the QD are further used to determine the overall reaction orders of C3H8-O2 reaction in flames. The overall activation energies of this process are determined from the semi-logarithmic dependence of the QDs versus reciprocal average flame temperatures. The overall kinetic parameters of propane-oxygen reaction are influenced by diluent addition.