Combustion of Turbulent Lean Mixtures by Plasma Jet Ignition

In order to confirm quantitatively the performance and characteristics of the plasma jet ignition in turbulent lean mixtures, combustion tests were carried out with varying the governing parameters of the plasma jet ignition. three plasma cavity sizes of 37, 75, and 170 mm³, three orifice diameters of 1, 2, 5 and 4 mm, and three discharge energies of 0.3, 0.6 and 0.9 J were tested in a disk-shaped combustion bomb with lean methane-air mixtures. A characteristic lifetime and a characteristic length of the plasma jet and an entrainment volume of the mixture into the plasma jet were defined theoretically and expressed by the parameters of the plasma jet igniter. From a series of combustion test, the lean flammability limit, the comparing parameter, and a combustion index are well correlated with these characteristic values, where the comparing parameter shows the degree of combustion enhancement by the plasma jet ignition in its initial stage and the combustion index represents the total combustion performance of the plasma jet ignition.