Spherical gas-fueled cool diffusion flames

An improved understanding of cool diffusion flames could lead to improved engines. These flames are investigated here using a spherical porous burner with gaseous fuels in the microgravity environment of the International Space Station. Normal and inverse flames burning ethane, propane, and n-butane were explored with various fuel and oxygen concentrations, pressures, and flow rates. The diagnostics included an intensified video camera, radiometers, and thermocouples. Spherical cool diffusion flames burning gases were observed for the first time. However, these cool flames were not readily produced and were only obtained for normal n-butane flames at 2 bar with an ambient oxygen mole fraction of 0.39. The hot flames that spawned the cool flames were 2.6 times as large. An analytical model is presented that combines previous models for steady droplet burning and the partial-burning regime for cool diffusion flames. The results identify the importance of burner temperature on the behavior of these cool flames. They also indicate that the observed cool flames reside in rich regions near a mixture fraction of 0.53. & COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

An improved understanding of cool diffusion flames, investigated in the microgravity environment of the International Space Station using a spherical porous burner, has the potential to enhance engine performance. The experiments included various fuel and oxygen concentrations, pressures, and flow rates, and utilized diagnostics such as intensified video cameras, radiometers, and thermocouples. The results revealed the presence of spherical cool diffusion flames, with particular conditions required for their production, and highlighted the significance of burner temperature and rich regions near a mixture fraction of 0.53.