Zip fuel

Under the name of High -Energy Fuel ( abk: HEF ) developed the U.S. Air Force in the 1950s fuels for jet and rocket engines of all kinds that have a higher energy content than the fuels based on hydrocarbons, such as JP- fourth The U.S. Navy operating under the name since 1952 ZIP her own project.

Basics

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

Carbon provides a calorific value of 32.8 MJ / kg, whereas hydrogen has an energy of reaction with oxygen of 120 MJ / kg. Hydrocarbons put about because of the low heating value of the carbon contained significantly less reaction free energy per unit mass than hydrogen. But only hydrogen in the temperature range between -253 ° C and -259 ° C and its density is liquid even still low. However, straight-chain hydrocarbons ( n- alkanes) are liquid at chain lengths of from 5 to 16 carbon atoms, at 20 ° C and have a relatively high density.

Therefore, would have a hydrogen compound that contains an element with a high reaction power instead of carbon, a higher reaction energy as hydrocarbons. The highest reaction energy for hydrogen has boron at 60.4 MJ / kg. However, boron-hydrogen compounds are not suitable, as they are, with certain probability, to the air to ignite spontaneously.

Therefore, the solution has been the use of alkyl boranes of boron, hydrogen and carbon. The new boron-based fuel should increase the range when using the afterburner by 16% and when using the whole engine by 30%.

Development

Because of to JP -4 almost identical density and volume were developed five different alkylboranes. These were numbered as HEF -X. Each number was for a alkylborane. HEF -1 for Ethyldiboran, HEF -2 for Propylpentaboran, HEF -3 for Ethyldecaboran, HEF -4 for Methyldecaboran and HEF -5 for Ethylacetylenedecaboran ..

Properties

HEF- 3 had a reaction energy of 58.1 MJ / kg and HEF -4 even a 60.4 MJ / kg. Whereas the former standard fuel of the U.S. Air Force, JP -4 only has a calorific value of 41.8 MJ / kg. However, all alkylboranes are very toxic. For example, exceeds HEF -3 toxicity of cyanide tenfold. Some of the products of combustion in the engine are partially liquid and solid. The combustion product boric oxide deposits because of its high melting point slightly to engine parts from. In addition, the firm because of its even higher melting point boron carbide combustion product can damage the engine. The combustion of HEF generated in afterburners also highly visible black smoke. The combustion product trioxide is also toxic. ZIP Fuel burns with a green flame.

End

In 1959, the HEF program was discontinued. The North American XB- 70 in afterburner and later HEF- 4 should use the whole engine fuel HEF ( HEF -3), so took advantage of the now developed new kerosene JP -6, which was more energetic than JP -4. With another tank they could almost reach the projected range. The ramjets the Bomarc would have to be changed over to HEF; in addition, there were other planes that should take advantage of High -Energy Fuels. Some of them did not come about the project or planning stage.

Swell

• Aviation fuel