# Time needed for a pressured N2O cylinder to reach the apex of its travel as a projectile...

## Main Question or Discussion Point

Hello, I am trying to understand the maths/physics/chemistry behind this situation. Here is the scenario. I have 8 grams of pressurized N2O in a cylinder at 60 bar/ 900 psi. If the temperature stays constant (let's say 50-70°C, or at a temperature where the N2O can stay as pressurized as possible) what is the maximum distance (on the Y axis... I am trying to go up not sideways) the cylinder could go up. With accounting as less weight as possible (0.5Kg for say or less).

Also if possible would anyone know the expected/guess time it would take for it to reach that distance?

I know this might sound complex or not depending who you are. I am just trying to find the height this tiny cylinder could reach up and after time want to increase the cylinder size, however if I understand the basics or know how to calculate the basics I can self teach myself. Thank you for any help. Also the hole where the N2O would be exiting would be 1 mm by 1 mm big. As this should give a strong air flow of N2O leaving the cylinder.

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mjc123
Homework Helper
I hope this question is purely hypothetical...

DrClaude
Mentor

anorlunda
Staff Emeritus
We asked for a more clear exlplanation, because this sounded dangerous. Here's the OP's explanation.

Hi, and no sorry about that. I am not trying to literally build a rocket. I am trying to figure this out for my high school project. We have to come up with a project for the end of the year. The project is that we need to mathematically explain something that isn't used today to prove why it is not used. For example, I chose if instead of the first stage rocket on the Falcon 9 (SpaceX) if it was a compression gas used instead if they could save money. So I am not building any rocket whatsoever I just need the math of it to eventually find a good medium of possible or impossible
With that, I am re-opening this thread.

anorlunda
Staff Emeritus
In that case, you can answer the question without pressures, temperatures, flows, cylinders or any of that dangerous stuff.

I'll give you a hint. Just compare the energy densities, joules per kg. Compare the energy released per kg when burning rocket fuel, to the energy required to compress one kg of gas to the storage pressure. There are many other complications, but start there. Use Wikipedia and Google to figure out those energy densities, then post your answer here.

berkeman
In that case, you can answer the question without pressures, temperatures, flows, cylinders or any of that dangerous stuff.

I'll give you a hint. Just compare the energy densities, joules per kg. Compare the energy released per kg when burning rocket fuel, to the energy required to compress one kg of gas to the storage pressure. There are many other complications, but start there. Use Wikipedia and Google to figure out those energy densities, then post your answer here.
Hi thank you, after doing a bit of research I found that for N2O it gave 396.3 kJ/kg to compress and I found that the Falcon 9 rockets gave 7600 kN of thrust.

anorlunda
Staff Emeritus
Hi thank you, after doing a bit of research I found that for N2O it gave 396.3 kJ/kg to compress and I found that the Falcon 9 rockets gave 7600 kN of thrust.
That's a good start, see if you can find jJ/kg of the fuel used in the Falcon 9. You need the same units, kJ/kg to compare them directly.

That's a good start, see if you can find jJ/kg of the fuel used in the Falcon 9. You need the same units, kJ/kg to compare them directly.
Ok after looking online I found it was around 46 kJ/kg. So N2O has more force?

anorlunda
Staff Emeritus
Ok after looking online I found it was around 46 kJ/kg. So N2O has more force?
Are you sure? Perhaps 46 MJ/kg.

Are you sure? Perhaps 46 MJ/kg.
So after looking at the Wikipedia link it should be around 142 MJ/kg... So its a lot more than N2O now.

berkeman
anorlunda
Staff Emeritus
So after looking at the Wikipedia link it should be around 142 MJ/kg... So its a lot more than N2O now.
Much better.

Since the difference is so big, there is no need to examine the fine details to decide which is better.

Another way to check your answer. if N2O was better, why isn't is used for real space rockets?

Next time when your write your OP, think how the question might be interpreted or misinterpreted. You need to be explicit enough for people to know the context of your question.

berkeman
Much better.

Since the difference is so big, there is no need to examine the fine details to decide which is better.

Another way to check your answer. if N2O was better, why isn't is used for real space rockets?

Next time when your write your OP, think how the question might be interpreted or misinterpreted. You need to be explicit enough for people to know the context of your question.
that makes sense then. And yes I will think of this in the future. It is my bad. English is not my first language.

anorlunda