Model Rocket Propulsion: The Power of Hydrogen and Oxygen Combustion

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Discussion Overview

The discussion centers around the feasibility and mechanics of using hydrogen and oxygen combustion for propulsion in model rockets. Participants explore the implications of combustion chamber design, efficiency, and the nature of rocket propulsion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether hydrogen combusted with surrounding oxygen can propel a model rocket forward and sustain propulsion.
  • Another participant notes that while hydrogen combustion is faster than propane, a properly designed combustion chamber is necessary for significant thrust.
  • A participant inquires about the efficiency of the combustion process in a large chamber and whether the rapid expansion of gases affects oxygen entry from the air.
  • It is suggested that the fuel must enter the combustion chamber at supersonic speed to effectively pull in air and create a ram effect, which is crucial for propulsion.
  • A participant clarifies that the proposed design does not fit the traditional definition of a rocket engine, as it relies on external oxidizers rather than carrying both fuel and oxidizer onboard.
  • One participant seeks clarification on the term "ram effect" and its relevance to the discussed propulsion method.

Areas of Agreement / Disagreement

Participants express differing views on the efficiency and design requirements for hydrogen combustion in model rockets, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

Limitations include assumptions about combustion chamber design, the efficiency of different fuels, and the conditions under which the ram effect operates. The discussion does not resolve these technical details.

Who May Find This Useful

Individuals interested in model rocketry, propulsion systems, and combustion dynamics may find this discussion relevant.

sid_galt
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If say hydrogen is ejected out of the tail of a model rocket and combusted with O2 of the surrounding air, will that propel the model rocket forward and will the propulsion be sustainable?
 
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It is a fairly common method using propane. Try searching for pressure jet. Hydrogen will combust much faster so some adjustments will probably be needed.

To get any significant thrust you need a properly designed combustion chamber.
 
Last edited:
Thank you for the reply.

So in effect, the expansion of hot gases is fast enough that it poses no significant barrier to the entry of oxygen in the combustion chamber from the outside air?

For a fairly large combustion chamber, is the process more efficient than say 40-50%?
 
The fuel must enter the combustion chamber at supersonic speed to pull in the air and generate the ram effect that makes it work. The propane ones I have seen had a very low efficiency.
 
You are referring to bringing oxygen from the outside, mixing it with hydrogen in a combustion chamber and expelling that?

I see no reason why it wouldn't work. It's not a 'rocket' engine if you use that design, however. 'Rocket' implies both fuel and oxidizer are carried onboard.
 
Bjørn Bæverfjord said:
The fuel must enter the combustion chamber at supersonic speed to pull in the air and generate the ram effect that makes it work. The propane ones I have seen had a very low efficiency.

what is "ram effect"?
 

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