Cool Pool Diffusion Flames

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Most of the engines that power land, air, and sea transportation have low thermal efficiencies and consume nonrenewable fuels. A newly discovered class of flames, called cool diffusion flames, could contribute to dramatic increases in these efficiencies – from upper thirties to sixty per cent – and accelerate the adoption of renewable fuels. These flames could also improve the understanding of wildland fire spread and smoldering mechanisms. Cool diffusion flames were discovered in 2012 aboard the International Space Station. They have unusually low temperatures between 500 – 1000 K, compared to 2000 K for traditional flames. Their discovery has already resulted in an improved understanding of ignition, but further progress has been impeded by the high cost and complexity of the experimental facilities required. This project will reduce this cost by developing a novel facility that burns fuel pools in cool flame mode. It will also improve the understanding of cool diffusion flames by performing detailed measurements and comparing them with computational simulations.The first objective of this project is to develop new ways to observe cool diffusion flames above pools of liquid fuels bounded above by a heated ceiling. This will enable any laboratory to build such a facility inexpensively. Many liquid fuels will be considered, including pure hydrocarbons, traditional transportation fuels, and renewable bio-derived fuels. It is unknown which of these fuels can burn in air as cool diffusion flames, and at what temperatures and mixture fractions. It is also unknown whether they may support slightly hotter flames, called warm diffusion flames, and whether they can exist without an external heat source. The second objective will be to characterize the flame details, namely, the flame temperatures, compositions, burning rates, and emissions. The third objective will be to perform autoignition simulations with Cantera software using various chemical kinetics models and to compare the predictions with the measurements. These simulations will fill gaps in the measurements and help evaluate and develop models of cool flame chemistry. The broader impacts of this project include improving engine efficiency, increasing the use of renewable fuels, and involving graduate students and undergraduates from diverse backgrounds.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.