The influence of spark discharge characteristics on minimum ignition energy in flowing gases

Abstract

The electrical aspects of spark ignition in flowing combustible mixtures have been investigated in a specially designed, closed circuit wind tunnel in which a fan was used to drive the gas through a 9 cm square working section at various levels of pressure and at velocities up to 100 m/sec. The turbulence intensity in the ignition zone was varied between 1% and 15%. Turbulence scales ranged from 0.2 cm to 0.8 cm. The methods employed in the generation and measurement of turbulence have been fully described elsewhere [5]. The ignition unit supplied capacitance sparks of “rectangular” form whose energy and duration could be varied independently. The optimum spark duration for minimum ignition energy was found to be independent of turbulence intensity, but to vary appreciably with pressure, velocity and mixture strength. Measurement of the energy released during a spark discharge showed that it was linearly proportional to gap width and increased slightly with increase in pressure and velocity. The energy required to effect spark ignition was reduced by the use of electrode materials having low conductivity and low boiling point, and also by locating the spark electrodes with their axes parallel to the direction of the flow.