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  • Author or Editor: R. Bellajrou x
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Abstract  

Engine Viking of Ariane 4 is supplied with asymmetrical dimethylhydrazine (UDMH) (CH3)2NNH2. An addition of a small amount of hydrazine hydrate N2H4H2O was proposed to increase the thermal stability of UDMH. The mixture where the mass ratio (CH3)2NNH2/N2H4H2O is equals to 75/25, is called UH25. These propelling agents are unstable when they are heated and the optimisation of burning conditions requires a good knowledge of their vaporisation and of their thermal decomposition kinetics.

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Abstract  

Monomethylhydrazine (MMH) (CH3)NHNH2 is currently used as fuel for spacecraft engine combustion chambers. The Aestus engine of the upper stage of Ariane 5 is fed with MMH under pressure of 16 bars. The propellant, initially at room temperature, is about 393 K when introduced into the combustion chamber, due to heating up through the regenerative circuit. As MMH is unstable above 373 K, it has been necessary to check its decomposition rate and vapor pressure under such conditions. The vapor pressure of this propellant has been measured in a pressure vessel and the thermal decomposition rate was determined with the same device up to 500 K.

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