Comments by "zenith parsec" (@zenithparsec) on "Real Engineering"
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@you_beg_my_pardon
By not giving the fuel enough oxidizer to burn completely, the nozzle doesn't get as hot but some of the fuel is only partially burned, resulting in soot.
They could have used it as fuel by adding more oxygen to the mixture. But if they did, the exhaust would have been hot enough to melt the nozzle.
Also, changing these ratios was how it could change how much power it was producing.
Rocket speed and positions are usually planned to optimize the fuel and velocity needed to get into the desired orbit.
Because the atmosphere gets thinner as you go up., and because the rocket is accelerating, there is a drag force on the rocket from moving fast through the air starts to reduce, instead of increase. (The math isn't too hard, but basically the graph for air density at some altitude gets smaller faster than the rate drag is getting bigger. This drag is the "Max Q" they talk about. Basically.)
Typically the engines will be told to push less around those places, both to reduce load on the vehicle and to save the thrust for when it makes more difference.
Trying to capture the soot and save it would not be useful. There's 4000 pounds of fuel going through each of 5 engines per second, turning into 5800F (or 3200C) exhaust at an altitude of up to 42 miles.
Some of that is now soot. Good luck collecting it.
Getting stuff into space is hard.
(sorry this is so long. ;] )
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@cindyjuanez4623 They don't want it to burn clean, because as I said, it would melt the rocket. And nitrous is N2O, which means 2/3rd of the atoms are nitrogen. You need two molecules of them to give you the same amount of oxygen as you get from one molecule of... oxygen.
You're not dumb. as an oxidizer N2O has been considered and tested for many applications, but it doesn't tend to get used because when going into space, you want the highest chance of reaching it. The best way to do that is to use to most powerful propellant by weight that you can. LOX is denser and adds more "go faster" than N2O does.
I'm simplifying many some things as much as I can without bending any important truths.
Given relative atomic masses and their respective densities when liquid, LOX wins by about 60% in my quick back of the envelope check from Wikipedia numbers.
When burned, the nitrogen released isn't a big fan of reacting with the carbon and hydrogen (whether from propane or kerosene, or from liquid hydrogen.) It will react with the oxygen though, and produce nitric oxide (NO) and nitrogen dioxide (NO2), but I can't find anything immediately about where this would happen... if I had to guess I would say outside the rocket, at the edge where there's atmospheric oxygen, because I think the hydrocarbon would burn in N2O preferentially over N2O self-reducing, but I don't know about at rocket pressures and temperatures. It is literally rocket science, so I have an excuse. All nitrogen oxides have have numerous biological and environmental effects like making acid rain and destroying ozone, causing smog, and tending to cause a bad day for living things in general.
But it's a legit oxidizer. It's just not as good as what they could easily do. The major advantage is that it's really easy to store, compared to LOX.
Hybrid rockets often use it. (Imagine a solid fuel booster and a LOX/RP-1 liquid fuel booster had a baby. It would have an oxidizer tank, and instead of having the fuel and oxidizer mixed into the fuel grain, it just has fuel. Straight paraffin wax poured into the tube [with channels cut out of it for the oxygen) is all you need for a hybrid.)
Hybrids are simpler than liquid fueled rockets: It's takes fewer resources to make them. They are more complicated than solid fuel motors.
When you start a solid rocket motor, you're lighting a candle and waiting for it to burn all the way down.
A hybrid motor can stop (or even control the throttle ) at any point by controlling how much oxygen is being sent to the combustion chamber.
Why don't orbital rockets use N2O, Because it's not as efficient as LOX. It's not a dumb idea, but it's not done because it's not as good as easy enough alternatives.
Isp is "specific impulse" which measures (roughly) "how much 'go faster' do I get for each mass-unit of "go faster stuff", and the bigger the number, the better the propellant is. For reasons, the unit is "seconds" written as s. You typically get told the Isp at sea level, and in a vacuum.
At sea level, the rocket exhaust has to get out of the rocket, but in front of it is the atmosphere, pushing inward at about 14 lb/sq in of pressure.
The J2 engine's rocket nozzle is 6'5" in diameter. That's a whole lot of pressure you need to displace and keep displacing while inside the atmosphere. . And because you are using some of your potential thrust energy just to keep the air out of the way (it's to do with the dot product of the vectors. ) so the exhaust can get out and push you into space... which means you can't use it for lift because it's tired now.
So sea level numbers are lower. )
As these numbers vary due to the rocket specifics, these numbers should be considered illustrative. (Inecaise forgot where I got them. )
LOX/Paraffin hybrid has vacuum Isp of 360s , but N2O/Paraffin gives you only 310s. I'm not a hybrid motor person, but I saw some charts and comments in a paper or two which mentioned hard starts (that's when it the fuel detonates instead of deflagrates on ignition) being common. You don't want that. (But that's potentially just an engineering problem.)
1) It wouldn't be as efficient to use N2O instead of LOX because you need to carry so much extra mass.
2) The "not burning cleanly" was deliberate, to stop it melting.
3) And your rocket would probably still fail its emissions test because of all the nitrogen oxides.
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