Characterization of an Oxyacetylene Torch for High Temperature Material Testing

Abstract

Executive SummaryFree-Stream Oxyacetylene Flame Characterization Oxyacetylene torches are commonly used for testing of candidate thermal protection system materials. The oxyacetylene torch test facility at the University of Arizona has been characterized in terms of free-stream flame velocity, pressure, oxygen content, and heat flux, studying the effect of the flame environment on the material response and behavior. The following are key methods and results from the study: 1. Particle tracking velocimetry was performed using a high-speed camera and seeding the flame with high temperature ceramic particles. Results show that the velocity of the flame is highest at the torch tip and decreases as a function of increasing distance. 2. A pressure transducer was used to measure the stagnation point pressure of the free-stream flame. Results show that the pressure is highest at the tip and decreases as a function of increasing distance. Off-axis tests were also performed 0.5 cm and 1 cm below the torch axis centerline and show that the off-axis pressure is the same as ambient conditions. 3. Oxygen concentration within the flame was measured using two methods, an oxygen sensor and lambda sensor. On-axis results from both sensors agree from 5 – 8 cm from the tip, beyond 8 cm the oxygen sensor reported a higher oxygen concentration than the lambda sensor. Oxygen concentration increases with increasing distance from the torch tip. And oxygen concentration increases as a function of increasing radial distance. 4. A heat flux gauge was introduced to the flame for measurement of the free-stream heat flux. Results show that the heat flux is highest close to the tip and decreases as a function of increasing distance. Sample Collection and Gas Chromatography A technique was developed for gaseous sample collection of the flame and efforts were made to characterize collected samples via gas chromatography–mass spectrometry. Results were inconclusive, due to an inability to separate low mass permanent gases with the equipment available. However, highest separation did occur via a split injection method with high split ratio and a low flow rate. Though the separation was not adequate for analysis, the results indicate advances in method development for future work. Material Results Graphite and various proprietary carbon-carbon composites were tested within the torch to validate free-stream characterization. Fick’s First Law of Diffusion was used to calculate the ablation rate of graphite samples, and experimental results are comparable. Composites were tested at two test positions corresponding to a high and low heat flux. Of the various composites tested, ablation rates were either the same between heat fluxes, or increased at the higher heat flux.