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Ignition Capability of Mechanically Generated Sparks Landing in Fuel Beds

Abstract

The primary focus of this study is to analyze the ignition capability of different metal particles and how a shower of metal particles generated from grinding can cause ignition of wildland fuels. To this end, this thesis focuses on describing the experimental apparatus and procedures developed to investigate the ignition capability of different metals in combination with different wildland fuels. Moreover, the experimental data results are presented in a manner to improve future analytical and numerical models. A detailed thermal and statistical analysis will be included as a part of the full project report. The experiments were performed using three different type of metals which are stainless steel, copper, and cold rolled steel. The grinding of these materials generated hot particles that were directed downwards into a collection box containing wildland fuels. The fuels consist of the following: Lehmann lovegrass, wildoats, timothy grass and cheatgrass. For the first set of experiments, the interaction between the metals and fuels at different fuel temperatures were studied. It was found that cold rolled steel and stainless-steel particles possessed the highest ignition capabilities. For the second set of experiments, the fuel moisture was varied considerably (20% - 80%), and it was determined that cold rolled steel particles could considerably ignite the fuels at high fuel moisture percentages. For the last set of experiments, the distance between the fuel bed and grinder was varied to match that of real-life applications. It was concluded that cold rolled steel could ignite fuels up to distances of 100 cm. For all metals, particles were collected and examined under a microscope at 400x magnification. Results indicate that the diameter of the particles from cold rolled and stainless steel ranged from 0.0625 mm to 0.80 mm and were considerably smaller than that of copper, which ranged from 0.4375 mm to 2.5 mm. Physical processes conclude that cold rolled steel and stainless steel achieve higher initial temperatures than those of copper due to differences in the toughness of the material. The tougher metals absorb a higher amount of separation energy before fracture and increase the probability of the particles combusting.

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