Search Results

Research on ignition, flame growth and flame propagation in engine-like turbulence has produced widely varying correlations between turbulence parameters and flame speed. Some previous work has shown that the burning velocity observed in a given turbulence level depends on the flame size as well as the turbulence intensity and scale. This explains some of the previous experimental discrepancy and emphasizes the importance of measuring flame growth and turbulence effects over the range of interest for a given modelling requirement. This paper reports on an experimental study of flame growth from ignition sparks in spatially uniform, decaying turbulence similar to that found in engine combustion chambers. High speed schlieren video and pressure trace analyses were used to study 3-dimensional turbulent flame growth in a constant volume, cubical combustion chamber. Lean methane-air mixtures of 60%, 70%, 80%, 90% and 100% stoichiometric compositions were ignited at 1 atm and 300 K.

Formation of pulsed plasma jets, or puffs, was examined using several visualization techniques. Self-light streak photography was first employed to record salient global features of the development and structure of the jet. This provided information on the motion of the luminous gas particles in its core, revealing that plasma jets can have two distinct modes, being either totally subsonic or embodying a supersonic efflux manifested by the recorded streaks of Mach discs. At a fixed power pulse of electrical energy discharge in the plenum chamber, the outcome depends on the constriction imposed by an orifice at its outlet. Whereas the difference between the two types of jets was quite small, penetration in the subsonic case was found to be definitely larger than in supersonic.