A study of the electrical characteristics of an oxy-fuel flame

Electrical phenomena useful for oxy-fuel process sensing are demonstrated at signal level voltages applied to an oxy-fuel cutting torch. The current-voltage characteristic of the flame between the torch and work is recorded while varying torch-to-plate standoff, fuel-oxygen ratio, total flow rate, and plate temperature. At ±10 V, typical currents are on the order −100 μA to 25 μA, and the I-V characteristic exhibits three regimes. At low currents, the relationship between voltage and current is linear. At positive currents, transition to saturation is heavily curved around 10-20 μA. Negative currents do not totally saturate in this voltage range, but there is an abrupt transition to a new slope, which we describe as “partial” saturation. The properties of these regimes demonstrate strong repeatable links to standoff and fuel-oxygen ratio. Flow rate and plate temperature also demonstrate correlation to these electrical properties despite substantial scatter.