High energy fuels

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Under the name High-Energy-Fuel (abk: HEF ), the US Air Force developed propellants for jet and rocket engines of all kinds in the 1950s, which have a higher energy content than the hydrocarbon-based fuels, such as. B. JP-4 . The US Navy has been running its own project under the name ZIP since 1952.

Basics

Aircraft and rocket fuels should be liquid at normal temperatures and have as little volume per unit of mass as possible.

Carbon has a calorific value of 32.8 MJ / kg, whereas hydrogen has a reaction energy with oxygen of 120 MJ / kg. Because of the low calorific value of the carbon they contain, hydrocarbons release significantly less reaction energy per unit of mass than hydrogen. However, hydrogen is only liquid in the temperature range between −253 ° C and −259 ° C and its density is still low even then. However, unbranched hydrocarbons (n-alkanes) are liquid with chain lengths of 5 to 16 carbon atoms at 20 ° C and have a relatively high density.

Therefore, a HEF hydrogen compound that contains an element with a high reaction energy instead of carbon would have a higher reaction energy than hydrocarbons. Boron has the highest reaction energy after hydrogen with 60.4 MJ / kg. However, hydrogen boride compounds themselves are unsuitable because they are likely to self-ignite in air.

The solution was to use borane, hydrogen and carbon alkyl boranes. The new boron-based fuel should increase range when used in the afterburner by 16% and when used in the entire engine by 30%.

development

Because of the almost identical density and volume to JP-4, five different alkylboranes were developed . These were numbered as HEF-X. Each number represented an alkyl borane. HEF-1 for ethyldiborane , HEF-2 for propylpentaborane , HEF-3 for ethyldecaborane , HEF-4 for methyldecaborane and HEF-5 for ethylacetylenedecaborane .

properties

HEF-3 had a reaction energy of 58.1 MJ / kg and HEF-4 even one of 60.4 MJ / kg. Whereas the then standard fuel of the US Air Force, JP-4 only has a calorific value of 41.8 MJ / kg. However, all alkyl boranes are very toxic. For example, HEF-3 is ten times more toxic than cyanide. Some of the combustion products are partially liquid and solid in the engine. The combustion product boron trioxide is easily deposited on engine parts due to its high melting point. In addition, the combustion product boron carbide, which is solid due to its even higher melting point, can damage the engine. The combustion of HEF also creates unmistakable black smoke in afterburners. The combustion product boron trioxide is also toxic. ZIP Fuel burns with a green flame.

The End

In 1959 the HEF program was discontinued. The North American XB-70 , which was to use HEF fuel (HEF-3) in the afterburner and later HEF-4 in the entire engine, therefore used the new kerosene JP-6, which was developed in the meantime and which was more energetic than JP-4. With another tank, she could almost reach the planned range. The ramjet engines of Bomarc should have been switched on HEF; there were also other aircraft that were supposed to use high-energy fuels. Some of them didn't get past the project or planning stage.

Individual evidence

  1. ↑ Dennis R. Jenkins, Tony R. Landis: Warbird Tech Series Volume 34, North American, XB-70 VALKYRIE , Specialty Press, North Branch, Minnesota, USA, 2002. ISBN 1-58007-056-6 , page 98
  2. ↑ Wesley Griswold, "Super-Potent 'Zip' Fuels Pack More WHOOSH" , Popular Science , October 1957, pages 86-89 and 250
  3. ↑ Wesley Griswold, "Super-Potent 'Zip' Fuels Pack More WHOOSH" , Popular Science , October 1957, pages 86-89 and 250
  4. ↑ Dennis R. Jenkins, Tony R. Landis: Warbird Tech Series Volume 34, North American, XB-70 VALKYRIE , Specialty Press, North Branch, Minnesota, USA, 2002. ISBN 1-58007-056-6 , page 98
  5. ^ Dennis R. Jenkins, Tony R. Landis: Warbird Tech Series Volume 34, North American, XB-70 VALKYRIE , Specialty Press, North Branch, Minnesota, USA, 2002. ISBN 1-58007-056-6 , page 99
  6. ↑ Dennis R. Jenkins, Tony R. Landis: Warbird Tech Series Volume 34, North American, XB-70 VALKYRIE , Specialty Press, North Branch, Minnesota, USA, 2002. ISBN 1-58007-056-6 , pages 99-100 .
  7. ^ Entry on diboron trioxide in the GESTIS substance database of the IFA , accessed on December 28, 2011(JavaScript required) .
  8. ↑ Wesley Griswold, "Super-Potent 'Zip' Fuels Pack More WHOOSH" , Popular Science , October 1957, pages 86-89 and 250
  9. ↑ Dennis R. Jenkins, Tony R. Landis: Warbird Tech Series Volume 34, North American, XB-70 VALKYRIE , Specialty Press, North Branch, Minnesota, USA, 2002. ISBN 1-58007-056-6 , page 100
  10. ^ Abandoned & Little-Known Airfields