Simulation of Ion Current in Oxyfuel Flame Subject to an Electric Field

Though it is more than a century old, oxyfuel's (or 'flame-cutting's') unparalleled performance on thick steel has rendered it an enduring favorite in shipyards, building construction, rail, defense, and countless other heavy industries. The harsh operating environment, such as the open flames and extreme heat, limit the ability of contemporary sensor suites to provide reliable data essential for process feedback control and automation. Due to persistent shortcomings in the available sensing technologies, mechanized oxyfuel cutting systems have never benefited from the degree of autonomy demonstrated by their competing processes, such as the laser, water jet, and plasma cutting.   Thus, an experienced labor force is still needed in order to operate the mechanized oxyfuel cutting systems, as a result having a major impact on the system efficiency and reliability. 

Since typical sensors are highly unreliable in the harsh environment near the high temperature flame, an alternative method is to find the co-dependence between critical parameters and the electrical characteristics of the flame, which can be easily measured using data acquisition unit and power supply. Experimental data in the literature show the current-voltage (IV) characteristic correlates with different critical parameters of oxyfuel flame in the preheat process and when cutting steel. To replicate the experimental results and further investigate the electric characteristics, such as migration of the ions and ion distributions, a comprehensive two-dimensional computational simulation is proposed. Simulations of ion currents in oxyfuel flame subject to an electric field, with and without surface reactions, are performed using Star CCM. This includes the same physical settings of the experiment to validate the computational model. Both the reduced surface chemical mechanism and the reduced combustion chemical mechanism with ion exchange reactions are included. The Coulomb force acting on both the ions and electrons due to the electrical field in the system is also applied in the simulations. 

The results of this study illustrate the detailed electrical characteristics of the premixed methane-oxygen oxyfuel cutting flame subject to an electric field when the surface reactions are considered. By using these computational results to illustrate and better understand the physical behavior of the oxyfuel cutting flames, a more validated current voltage relationship is generated. This relationship could then be embedded into a control algorithm to detect the critical process parameters and may facilitate a step forward toward achieving the autonomous oxyfuel cutting process in the future, with envisioned major impacts on the system efficiency and reliability.