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.