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Using a cool instrument to take a new look at rocket fuels

With the hope of developing better future rocket fuels, a group of researchers is developing instrumentation to test super cold fuel mixtures.

Led by Jake Leachman, assistant professor in the School of Mechanical and Materials Engineering, the researchers received support from the Joint Center for Aerospace Technology Innovation (JCATI) and from Aerojet Corporation to develop the instrumentation, which will be able to look at gelled mixtures of new kinds of high energy density fuels, like hydrogen and methane mixtures.

To send a rocket into space requires a fuel with high specific energy and energy density. Rocket fuels have changed little in the past 40 years, but recent advances have created new lightweight and strong fuel tanks that can store fuels at high pressures. With a significantly lower cost for liquid natural gas, aerospace companies are interested in investigating new types of gelled fuel mixtures.

“For many years, we didn’t have a lightweight container to allow us to store these new kinds of high pressure fuels,’’ says Leachman. “We didn’t have the logistics. The new tanks have created a new opportunity.’’

Leachman is interested in testing mixtures of methane and hydrogen at cold temperatures. The gelled mixture would be similar to wet snow, with methane being the ice slush and the hydrogen behaving like water. By mixing the two fuels, one can increase its energy density, which makes it a more attractive possible fuel with many possible applications. Nobody has done careful density measurements of such a fuel, with only one data set since 1960.

To measure the energy densities, Leachman is retrofitting an instrument that precisely measures density and sorption, or the ability of a material to hold or take up another substance. Leachman first saw the instrument as an undergraduate at the University of Idaho in the late 1990s. The instrument, called a Rubotherm Isosorp 2000, has since been sitting unused for several years. To retrofit it, the researchers are “strapping a refrigerator to it,’’ he says. Then, they can measure mixtures at temperatures as low as 3 Kelvin, or -454 degrees Fahrenheit. Using the same basic way of measuring that Archimedes discovered in his bathtub, the researchers will precisely measure density by seeing how much liquid their materials displace.

“Once retrofitted, this instrument will be unique and advantageous to the aerospace industry in the state,’’ says Leachman. “The potential gains to established aerospace technologies are substantial, and the capabilities resulting from this work could be substantial for the aerospace community in Washington State for years to come.’’