The Initiation of Combustion by a Hot Turbulent Mixing Element

Abstract

Abstract The ignition characteristics of the turbulent element produced by a pulsed plasma source are modelled using a simple Arrenhius reaction rate formulation and the entrainment hypothesis. It is shown that critical ignition conditions depend on the heat content of the combustible mixture and the ratio of the energy and momentum injected by the plasma source. The model indicates formation times of the order of milliseconds during which times extinguishing cases cannot easily be distinguished from combusting cases. During this time the chemical reactions are controlled by the turbulent mixing alone. This furnishes a tentative explanation of anomalously long ignition delay times sometimes observed with pulsed plasma jet ignition systems. Experimental observations confirm the broad features of the theoretical model, in particular the validity of the similarity assumptions and the scaling factors predicted for the element behavior.