A cold look at hydrogen

  • 30-Jun-2008 07:24 EDT

Timothee Pourpoint, a Senior Research Scientist in Purdue’s School of Aeronautics and Astronautics, adjusts valves needed to direct the flow of hydrogen and nitrogen in a bulk high-pressure hydrogen storage and feed system at the university’s Maurice J. Zucrow Laboratories.

Purdue University engineers are conducting experiments using a hydrogen facility that became operational in 2007 to help NASA create designs to improve the cooling efficiency and performance of the J-2X rocket engine, which will be used for future missions to Mars and the moon. More efficient cooling improves performance and reduces the need for costly overhauls.

The hydrogen facility allows Purdue researchers to study fundamental processes in hydrogen-oxygen engines, such as the J-2X and the engine that will be used by astronauts during their descent to the moon.

In addition to its use as a fuel in these engines, liquid hydrogen serves as a coolant before entering the combustion chamber, also known as “regenerative cooling.” The -420°F liquid hydrogen circulates through channels in a cooling jacket surrounding the combustor, absorbing heat and raising its temperature before it is injected into the chamber.

The Purdue research focuses on accurately measuring the heat flux, which is caused by differences in temperature between the hot combustion gases and the cooled walls of the combustor. Combusted gases in the rocket’s chamber reach 6000°F, which is more than three times higher than the melting temperature of the combustor’s copper wall.

Measurements are used to improve detailed computational models of how propellants mix inside the combustor. The work also aims at better understanding the behavior of coolant inside channels surrounding the combustor.

“Extreme heating takes place in specific locations, and this localized heating tends to limit the combustor life,” said William Anderson, an Associate Professor in Purdue’s School of Aeronautics and Astronautics. “Without knowing exactly how the overheating occurs, we tend to overcool the whole combustor. This limits how much propellant energy can be converted into useful thrust.”

High-purity hydrogen is provided by the hydrogen facility, located at Purdue’s Maurice J. Zucrow Laboratories. The hydrogen source is made possible by an intricate feed system designed by Timothee Pourpoint, a Senior Research Scientist in the School of Aeronautics and Astronautics who is in charge of the hydrogen facility. Another major focus of the facility is work funded by General Motors to develop an automotive hydrogen-storage system. Hydrogen gas not used for rocket research is piped 1000 ft away to the Hydrogen Systems Laboratory for the GM hydrogen research.

“Because of the facility, we are able to conduct research on a scale that is directly comparable to the J-2X,” said Anderson. “The facility allows significant hydrogen-flow rates at pressures exceeding 5000 psi.”

It is critical to measure the heat flux because engineers need to know how much liquid hydrogen or liquid oxygen to flow through the outside of the engine to keep it cool. Purdue researchers measured how much the heat flux varied at different points on the inner wall of the combustion chamber when propellant was being fed into the chamber with a carefully designed set of injectors.

“Until now, these detailed measurements were made using only one injector element, whereas this experiment contains seven elements,” said Anderson. “Having seven elements allows you to get precise spatial measurements to tell you how the heat flux changes due to interactions between elements and how it changes relative to the location of the injector elements.”

The J-2X rocket is an upgraded version of the J-2 rocket, which was part of the Saturn V vehicles that carried astronauts to the moon in the Apollo missions (see “NASA begins rocket testing” on page 18 in the January/February 2008 AEM). The J-2X is part of the Ares rocket that will be used to launch the Orion spacecraft to the International Space Station after the end of the Space Shuttle program in 2010. The rocket also will be needed to carry materials into Earth orbit for retrieval by other spacecraft bound for the moon and Mars.

Measurements taken in the experiments will help engineers more precisely size the cooling jacket for optimal cooling in the J-2X. Better cooling could be achieved by changing the size of the tubing or channels to match areas of highest and lowest heating. Better computational models would enable engineers to see how a design would perform before building the engine.

“It costs millions of dollars to build these engines and additional millions of dollars to test them,” said Anderson. “So before building a rocket engine, you want to have a good idea of how it’s going to perform.”

The research is being funded through NASA’s Constellation University Institute Program, which supports rocket research at universities around the nation. Missions using the J-2X rocket are planned for the next decade.

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