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Abstract This is a study of the suitability of preheat flame electrical resistance as a potential method for measuring the standoff distance an oxyfuel cutting torch and a work piece. Careful scrutiny of forty-seven individual experiments demonstrate that when cut quality is good, there is a linear repeatable relationship between the two with uncertainty about ±0.3 mm (0.015 in.). As the cut quality degrades, the formation of top-edge dross reduces the electrical path length in the flame, and momentary reduction in the reaction rate in the kerf reduces the free electrons in the flame, causing increases in flame resistance. In these conditions, measurement uncertainty reduces to ±1 mm (0.040 in.) or worse. 

This is a study of the suitability of preheat flame electrical resistance as a potential method for measuring the standoff distance an oxyfuel cutting torch and a work piece. Careful scrutiny of forty seven (47) individual experiments demonstrate that when cut quality is good, there is a linear repeatable relationship between the two with uncertainty about ± .3mm (.015in). As the cut quality degrades, the formation of top-edge dross reduces the electrical path length in the flame, and momentary reduction in the reaction rate in the kerf reduces the free electrons in the flame, causing rises in flame resistance. In these conditions, measurement uncertainty reduces to ± 1mm (.040in) or worse. 

This paper presents a computational model to study ion and electron transportation and current-voltage characteristics inside a methane-oxygen flame. A commercial software is used to develop the model by splitting the simulation into the combustion and electrochemical transportation parts. A laboratory experiment is used to compare the results from the model. The initial and boundary conditions represented in the model are similar to the experimental conditions in the laboratory experiment.

In the combustion part, the general GRI3.0 mechanism plus three additional ionization reactions are applied and results are then used as input into the electrochemical transportation part. A particular inspection line is created to analyze the results of the electrochemical transportation part. Ion, electron number density, and current density are studied along the interval from −40V to 40V electric potential. The ions are heavier and more difficult to move than electrons. The results show that at both torch and work surfaces charged sheaths are formed and cause three different regions of current-voltage relations.

 

This two-part paper presents precise measurements of the ion currents passing between the torch and work piece of the preheat flame of an oxyfuel cutting torch as a means for replacing contemporary sensing suites. Part II presents the results of a novel spinning disc Langmuir probe technique to construct spatially resolved measurements of the flame's ion density distribution. A bias voltage is applied to a .254mm diameter wire protruding from a spinning disc, and as the wire is passed through the flame, the measured currents (on the order 10uA) are collected. The process is repeated with incremental wire depths in the flame to construct the entire planar cross-sectional ion density. Measurements reveal intense ion concentrations in the inner cones that rapidly decay by an order of magnitude in the surrounding flow. The outer cone forms a hollow cylinder of weak ion concentration that declines with distance from the inner cones in a manner consistent with recombination. 

This two-part paper presents precise measurements of the ion currents passing between the torch and work piece of the preheat flame of an oxyfuel cutting torch as a means for replacing contemporary sensing suites. Part I shows that the current-voltage characteristic of the flame exhibits sharp discontinuities common to semi-conductors that we study in various configurations including preheat, pierce, cut, and loss-of-cut. Standoff measurements are made by applying a sinusoidal current signal between the torch and work piece while the resulting voltage amplitude is an indication of flame resistance. Uncertainties are estimated to range from 0.5mm to 1mm (.02in to .04in). Signals for ready-to-pierce and precursors for loss-of-cut are also produced due to the generation of secondary ions from chemical activity at the work piece.