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High speed schlieren video and pressure trace analyses were used to study the effects of turbulence on burning velocity in a fixed volume combustion chamber. Lean methane-air mixtures of equivalence ratios of 0.76 and 0.96 were ignited at 1 atm and 23°C. Schlieren images of flame growth were recorded on video at 2000 frames per second while combustion chamber pressure was simultaneously recorded. The turbulence intensity at ignition was set at 0 m/s to 4 m/s intensity with integral scale around 7.6 mm by pulling a perforated plate across the chamber prior to ignition. In the analysis, the turbulence parameters were adjusted for the effect of decay and rapid distortion in a closed vessel during combustion. Results of both video and pressure trace analyses show a linear relationship between turbulent burning velocity and turbulence intensity as expected. Moderate changes in equivalence ratio had a negligible effect on this relationship.

Previous research on the effects of enhanced ignition systems has produced some conflicting results, possibly related to the various diagnostic methods used. In this investigation, several methods were used to measure the effects on flame development for different spark ignition circuits in quiescent and turbulent premixed gaseous mixtures. Sparks from a standard ignition circuit, typical of automotive use, were compared with sparks from a breakdown ignition circuit and from a plasma jet ignition circuit. It is shown that burning velocity calculation methods based on pressure trace analysis tend to be biased by any effects which provide a more spherical flame growth; particularly by projecting the spark kernel into the mixture away from the spark plug. Thus, the pressure trace-based burning velocity measurements gave false indications when comparing flames growing from dissimilar ignition systems.