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

The ignition by high voltage inductive-capacitive sparks of the quiescent stoichiometric C3H8-air mixture diluted by various amounts of additives (He, Ar, N-2, or CO2) is examined at various initial pressures within 0.5-1.5 bar in a cylindrical vessel of volume similar to 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 N-2, 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-O-2 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.