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1. A Study of the Efficacy of Flame Electrical Resistance for Standoff Measurements During the Oxyfuel Cutting Process

   https://doi.org/10.1115/1.4053216  

   Martin, Christopher R.; Untaroiu, Alexandrina; Xu, Kemu; Mahbobur Raman, S. M. (July 2022, Journal of Manufacturing Science and Engineering)

   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. 

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2. Semiconductor aspects of the oxyfuel cutting torch preheat flame; Part I: Measurements between torch and work

   Martin, Christopher; Pond, Teresa; Tomas, Jacob; Schmit, Jenna; Miguel, Erikson; Untaroiu, Alex; Xu, Kemu (June 2020, Proceedings of the ASME Manufacturing Science and Engineering Conference)

   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. 

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3. Numerical Study of the Effects of Confinement on Concurrent-Flow Flame Spread in Microgravity

   https://doi.org/10.1115/1.4047645  

   Li, Yanjun; Liao, Ya-Ting T.; Ferkul, Paul (November 2020, Journal of Heat Transfer)

   null (Ed.)

   Abstract The objective of this work is to investigate the aerodynamics and thermal interactions between a spreading flame and the surrounding walls as well as their effects on fire behaviors. A three-dimensional transient computational fluid dynamics (CFD) combustion model is used to simulate concurrent-flow flame spread over a thin solid sample in a narrow flow duct. The height of the flow duct is the main parameter. The numerical results predict a quenching height for the flow duct below which the flame fails to spread. For duct heights sufficiently larger than the quenching height, the flame reaches a steady spreading state before the sample is fully consumed. The flame spread rate and the pyrolysis length at steady-state first increase and then decrease when the flow duct height decreases. The detailed gas and solid profiles show that flow confinement has multiple effects on the flame spread process. On one hand, it accelerates flow during thermal expansion from combustion, intensifying the flame. On the other hand, increasing flow confinement reduces the oxygen supply to the flame and increases conductive heat loss to the walls, both of which weaken the flame. These competing effects result in the aforementioned nonmonotonic trend of flame spread rate as duct height varies. Near the quenching duct height, the transient model reveals that the flame exhibits oscillation in length, flame temperature, and flame structure. This phenomenon is suspected to be due to thermodiffusive instability. 

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4. Nanofiber z-threaded CFRP and the multifunctionality for advanced air mobility

   Hsiao, Kuang-Ting (September 2024, Society of Plastics Engineers (SPE®) International www.4spe.org)

   Carbon fiber reinforced polymer (CFRP) is one of promising lightweight materials for advanced air mobility (and electrical vehicles) due to the high strength, low density, and corrosion resistance. On the other hand, CFRP is more expensive than many lightweight alloys, difficult to join, less fire-resistant, lower conductivities in thermal and electrical energy, more sensitive in processing defects, and more difficult to inspect its structural damages. To improve the multifunctionality desired by advanced air mobility, CFRP could be modified with nanoparticles. Nanofiber z-threaded CFRP (ZT-CFRP) technology utilizes millions of long carbon nanofibers to z-directionally thread through all carbon fibers in per square-centimeters of ZT-CFRP prepreg. The ZT-CFRP enhanced the mechanical properties, thermal conductivity, and electrical conductivity. The unique 3D-multicscaled fiber-reinforced microstructure also provide additional performance such as enhanced resistance against the property degradation caused by void, enhanced flame-retardance, improved adhesive-joint (i.e., bond line) strength, and enhanced thermal infrared damage/defect evaluation resolutions. This paper will overview the ZT-CFRP performances along with the state of ZT-CFRP prepreg process development including the scaled up roll-to-roll hot-melt manufacturing process of the ZT-CFRP prepreg. Its potentially useful multifunctional attributes for advanced air mobility will also be discussed in this paper. 

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5. Simulating the Effect of Electric Bias Voltages on the Electrical Characteristics of Oxyfuel Preheat Flame Using Reduced Combustion Mechanism

   https://doi.org/10.1115/1.4062963  

   Rahman, S. M.; Warrier, Rohith; Untaroiu, Alexandrina; Martin, Christopher R. (November 2023, Journal of Fluids Engineering)

   Abstract A three-dimensional computational model is presented in this paper that illustrates the detailed electrical characteristics, and the current–voltage (i–v) relationship throughout the preheating process of premixed methane-oxygen oxyfuel cutting flame subject to electric bias voltages. As such, the equations describing combustion, electrochemical transport for charged species, and potential are solved through a commercially available finite volume computational fluid dynamics (CFD) code. The reactions of the methane-oxygen (CH4–O2) flame were combined with a reduced mechanism, and additional ionization reactions that generate three chemi-ions, H3O+, HCO+, and e−, to describe the chemistry of ions in flames. The electrical characteristics such as ion migrations and ion distributions are investigated for a range of electric potential, V ∈ [−5 V, +5 V]. Since the physical flame is comprised of twelve Bunsen-like conical flames, inclusion of the third dimension imparts the resolution of fluid mechanics and the interaction among the individual cones. It was concluded that charged “sheaths” are formed at both torch and workpiece surfaces, subsequently forming three distinct regimes in the i–v relationship. The i–v characteristics obtained from this study have been compared to the previous experimental and two-dimensional computational model for premixed flame. In this way, the overall model generates a better understanding of the physical behavior of the oxyfuel-cutting flames, along with more validated i–v characteristics. Such understanding might provide critical information toward achieving an autonomous oxyfuel-cutting process. 

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