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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3 Answers
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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 800 °C (see figure 2). The autoignition temperature for kerosene is 210 °C. 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 hydrogen will spontaneously ignite, but that the decomposition temperature of hydrogen peroxide is high enough to ignite the hydrogen. 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. $\endgroup$ Commented Jan 11, 2019 at 13:47
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$\begingroup$ @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. $\endgroup$– MefiticoCommented Jan 11, 2019 at 14:48
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1$\begingroup$ 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. $\endgroup$ Commented Jan 11, 2019 at 14:59
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$\begingroup$ 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. $\endgroup$– MefiticoCommented Jan 11, 2019 at 15:06
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No.
For a propellant (i.e. oxidizer and fuel) combination to be hypergolic, either one of the following two conditions need to be met:
- One of the propellants reacts rapidly and exothermically with the other OR
- One of the propellants induces rapid, exothermic decomposition of the other
Hydrogen does not react directly with hydrogen peroxide (unless you can generate highly reactive hydrogen atoms which only exist at high temperatures). Also, liquid hydrogen is not a good catalyst for hydrogen peroxide decomposition. Besides, the very low temperatures of liquid hydrogen will hinder decomposition and reaction rates.
However, one way of making this propellant work is by first using a metal catalyst to decompose the peroxide. The heat and oxygen generated from this can then be used to reliably ignite the liquid hydrogen. But then again, going by the strict definition, that's not a hypergolic combination.
