LIQUID HYDROGEN AS A PROPULSION FUEL,1945-1959

 

Part I : 1945 - 1950

2. Air Force Research on Hydrogen

 

 

Hydrogen-Air

 

[18] In the initial days of the contract, the studies of hydrogen as a fuel related to its ignition and burning in air for possible application to jet engines. The work began with 67 tests of gaseous hydrogen injected, ignited, and burned in an air stream. No data were published, but presumably there were no problems. In the next series of experiments, liquid hydrogen was injected in open air ahead of a stream of air from a [19] small pipe (about 7.5 cm in diameter), and later the liquid hydrogen was injected in the air flowing within the pipe. The liquid hydrogen flow was very small (about 2 grams per second) and when the liquid hydrogen was directed as a straight jet, an icicle-from moisture in the air-formed on the injector and impeded the flow. A splash plate was placed in front of the liquid hydrogen jet to spread it radially into the air stream and this gave better results. Combustion was maintained over a wide range of hydrogen-air mixture ratios.7

 

An unsuccessful attempt was made to use hydrogen in a pulsejet engine, the type of engine used in the German V-1. The inlet of a pulsejet consists of a number of flapper, or one-way, valves. When air enters through these, fuel is injected and the mixture ignited. The rise in pressure from combustion closes the flapper valves and the hot gases flow rearward through the nozzle, producing thrust. When operated on gasoline, the rapid series of explosive bursts was very noisy-as anyone can attest who experienced them popping along overhead in World War II. The Ohio State investigators obtained a tiny pulsejet engine marketed for model airplanes and substituted hydrogen for the fuel. It would not work because the very wide flammability limits of hydrogen resulted in continuous, rather than intermittent, burning. The investigators concluded that the narrow range of flammability of gasoline was responsible for establishing cyclic combustion by flaming out at lean and rich mixtures; it was these characteristics that made the pulsejet work.

 


group photo of researchers

Fig. 4. Staff of Ohio State University's rocket laboratory. ca. 1950. First row, L to R: Lester Cox, shop supervisor; Darwin Robinette. Student; James Pierce, student; Arthur Brooke. test mechanic William L. Dovle, chief engineer; Philip Petre, student. Standing; Lawrence Anthony, rocket shop supervisor; Ross Justus, machinist; Harold Smeck, engineer; James Sweet, test mechanic William Strauss, engineer ; unidentified. (Courtesy of Arthur Brooke.)


 

[20] In the latter part of 1948, large-scale equipment was built to investigate hydrogen as a fuel for ramjets. A few tests were made, but were discontinued when the facilities were needed to test a liquid-hydrogen pump.

 

To sum up the hydrogen-air burning experiments, they were qualitative observations and verified only what was already well known-hydrogen burns in air over a wide range of conditions. The nature of the experiments and their cessation in favor of another project indicated a lack of interest in hydrogen as a fuel for air-breathing engines.

 

Other hydrogen-air experiments were made to assess the hazards of handling hydrogen. Tests of hydrogen-air explosions were made using a liter of liquid hydrogen an open-mouth dewar. Ignition of the evaporating hydrogen resulted in a quiet flame, whereas hydrogen containing 10 percent solid air exploded with violence. Johnston was well aware of these characteristics as the following incident, part of the legend about him, illustrates.

 

Johnston supplied liquid hydrogen not only for his own experiments but also for the low-temperature experiments of other groups on the campus. One day a fire broke out at the top of a liquid hydrogen dewar of about 25 liters capacity being used for some materials testing. The fire department was called and the dewar was hurriedly rolled out into a parking lot. The firemen and a crowd were standing in a circle about the dewar, obviously puzzled about what to do next, when a passing car suddenly stopped in the middle of the street and a man got out. He pushed through the crowd, approached the dewar, pulled out his handkerchief and used it to snuff out the flame. He returned to his car and departed without having said a word. None in the crowd recognized Professor Johnston.8


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