Hydrogen-Oxygen Rocket Engines

In summary, an experiment showed that when two gases are combusted, a small amount of water is left behind. This water vapor is what propels the rocket.
  • #1
Hi !
I remember an experiment in school where two volumes of Hydrogen and one of Oxygen were mixed in a test tube set upside down on (at the time !) a platter full of mercury.
A spark in two electrodes on top of the tube would trigger an IMPLOSION and the mercury would jump upward to fill the volume. Miracle: in a residual space probably due to the imperfection of the ratio of the mixture, small droplets of WATER were visible!
My question concerns Hydrogen/Oxygen rocket engines. I never got a satisfying answer to this question:
I understand that the usual mixtures of propulsion create an instantaneous violent & important expanding volume of mainly CO2 being expelled on the back of a rocket and create a reaction thus a propulsion.
But how something that I understood apparently wrongly as a reduction / IMPLOSION can push a rocket ??
Jacques D. Paris France
Thx to your old folks for coming o:)
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  • #2
2 parts Hydrogen combusted with 1 part Oxygen forms water. H_2 O remember? The water left in the tube was the PRODUCT of the combustion of the gases. Why did the Mercury fill the tube? Because the volume occupied by the water was less then that occupied by the original gases.

The combustion of O and H releases a LOT of energy, it is this energy which propels the space shuttle. The white plume of exhaust gases is WATER vapor, not CO_2
  • #3
Thanks for your answer Integral. In:
I understand that the usual mixtures of propulsion
I was referring to most others ie:Black Powder generating expulsed gases.
Bye and thanks again.
  • #4
For the experiment in the OP, the water condenses (as Integral said) because even though the reaction produces a lot of energy for the material consumed, it isn't a lot compared to the heat capacity of the test tube and mercury, so the water vapor quickly cools and condenses.
  • #5
Let's look at this in more detail using the ideal gas law.

The chemical reaction is 2H2 + O2 = 2 H20.

The pressure of an ideal gas is given in many places, for instance

PV = nRT, or if we count in molecules, rather than moles, PV = NkT

For our example, it's convenient to count in molecules, N, rather than moles, n, so the correct formula is PV = NkT.

Now, when the above reaction occurs, N goes down - N is intially 3, and goes down to 2.

But T goes up - way up. T starts at 300K at room temperature, and increases to about 3000K (per http://hypertextbook.com/facts/1998/JamesDanyluk.shtml )

If we hold the volume constant, we can ask what happens to the pressure. P = NkT/V, where V is a constant. So P is proportional to the product of N T. The decrease in N by a factor of 2/3 is more than made up by the 10x increase in T.

I would predict that high speed photos would show the mixture initally expanding (pushing the mercury down, before it cooled off and contracted).
  • #6
when 2 things bond the energy used to create the bond is released =]
  • #7
I would predict that high speed photos would show the mixture initally expanding (pushing the mercury down, before it cooled off and contracted).
Thanks pervect and everyone.
This talks to my down to ground way of understanding things, :wink: . ( I do not have a formal scientific education or diploma just curious of everyhing)
I was of course aware that energy is pushing the rocket It cannot be denied :approve:
Over time, it is usually the only answer I got but it did not feed my curiosity. I would grumble using my sparse (or spare) neurones something like...
"""So, if one would violently dissipate a tremendous amount of Joules from enormous capacitors in a suppositely as big gas discharge flash device thus generating an intense radiation of this energy light in the reflector's direction would this crazy lampost be pushed violently backward"""
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Related to Hydrogen-Oxygen Rocket Engines

1. What is a hydrogen-oxygen rocket engine?

A hydrogen-oxygen rocket engine is a type of rocket engine that uses a mixture of hydrogen and oxygen as its propellant. This mixture is ignited and produces a powerful thrust, which propels the rocket into space.

2. How do hydrogen-oxygen rocket engines work?

Hydrogen-oxygen rocket engines work by combining liquid hydrogen and liquid oxygen in a combustion chamber. The mixture is then ignited, creating a controlled explosion that produces a high-velocity exhaust gas. This gas is expelled through a nozzle, providing the thrust needed to propel the rocket forward.

3. What are the advantages of using hydrogen-oxygen rocket engines?

Hydrogen-oxygen rocket engines have several advantages over other types of rocket engines. They are highly efficient, producing a high specific impulse (a measure of how efficiently a rocket uses its propellant) and therefore allowing for longer and more powerful flights. They also produce clean exhaust, consisting mainly of water vapor, making them more environmentally friendly than other rocket engines.

4. What are the challenges of using hydrogen-oxygen rocket engines?

One of the main challenges of using hydrogen-oxygen rocket engines is the need to store and handle the highly volatile and cryogenic fuels. Liquid hydrogen must be kept at extremely low temperatures (-253°C) and liquid oxygen at slightly higher temperatures (-183°C), requiring specialized storage facilities and handling procedures. Additionally, the combustion of hydrogen and oxygen produces extremely high temperatures, making it necessary to use materials that can withstand these extreme conditions.

5. What are some examples of rockets that use hydrogen-oxygen rocket engines?

Several rockets, including some of the most powerful in the world, use hydrogen-oxygen rocket engines. These include the Saturn V rocket, which was used for the Apollo missions to the moon, and the Space Shuttle, which used hydrogen-oxygen engines for its main propulsion system. Currently, the Falcon 9 and Falcon Heavy rockets, developed by SpaceX, also use hydrogen-oxygen rocket engines.

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