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Is Rocket Grade Hydrogen Peroxide and Liquid Hydrogen a hypergolic propellant combination? I recall, seeing the combination somewhere on the www, however I couldn't retrace the source where I saw it.

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I'm going to say yes, depending on how loose you want to be with definitions. Hydrogen peroxide as rocket fuel is decomposed by passing it through a metal catalyst screen, producing water, oxygen, and heat. At 90% concentration the temperature is around 800C (see figure 2). The autoignition temperature for kerosene is 210C. It worked for the Bristol Siddeley Gamma engines used in Britain's Black Arrow, and which used 85%. So it's not that hydrogen peroxide and kerosene will spontaneously ignite, but that the decomposition temperature of hydrogen peroxide is high enough to ignite the kerosene. On the other hand, you just put a catalyst on the injector, it's not like you have to shoot a pyrophoric slug into the combustion chamber.

Edit: I said kerosene. I don't know why I said kerosene. Actually, I know why -- because I didn't read the question carefully. But the answer doesn't really change.

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As far as I know the answer is no.

The autoignition temperature of Hydrogen is 536 °C according to Wikipedia.

Although this temperature could vary with pressure, I am also unaware of LOX/LH2 being hypergolic, hence adding water to the mixture (you asked about hydrogen peroxide) should not make things that much easier.

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  • $\begingroup$ It's possible that the hydrogen would catalyze the decomposition of the peroxide, which produces oxygen and steam at something not far from that autoignition temperature. $\endgroup$ Jan 11 '19 at 13:47
  • $\begingroup$ @SteveLinton You could add some other catalyst as well to start the combustion, but if a certain amount of transferred heat needs to be given for the reaction to start, I'd argue that by definition it would not qualify as an hypergolic mixture. $\endgroup$
    – Mefitico
    Jan 11 '19 at 14:48
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    $\begingroup$ I'm not sure what you mean by tranferred heat, If you run peroxide over a catalyst, it releases enough energy to heat itself to about 600C, so if you then added some hydrogen it would very possibly auto-ignite with the oxygen in the decomposition products, so you wouldn't need an additional igniter. $\endgroup$ Jan 11 '19 at 14:59
  • $\begingroup$ To clarify: A combustion essentially sustains itself by producing enough heat to activate more of the same chemical reaction, causing a chain effect, but it requires ignition to begin. Hypergolic implies spontaneuous combustion, so the activation energy should be around the available energy of the involved particles. You make a fair point that by heating one element and then mixing you technically did not use an external ignition, but I believe this is somewhat a borderline case. I'm also unaware of this being technically feasible. $\endgroup$
    – Mefitico
    Jan 11 '19 at 15:06

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