A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Space Science » Policy
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Rocket Fuel



 
 
Thread Tools Display Modes
  #1  
Old December 15th 19, 05:02 PM posted to sci.space.policy
William Elliot[_4_]
external usenet poster
 
Posts: 86
Default Rocket Fuel

Kerosene fuel for rockets is deliberately burned oxygen poor so the
unburnt fuel will add mass to the rocket's exhaust to give it more
thrust. To avoid the waste of incomplete combustion and get higher
fuel efficiency with greater thrust, dust could be inserted into or
near the combustion chamber instead of unburnt fuel.
  #2  
Old December 15th 19, 07:24 PM posted to sci.space.policy
Alain Fournier[_3_]
external usenet poster
 
Posts: 548
Default Rocket Fuel

On Dec/15/2019 at 11:02, William Elliot wrote :
Kerosene fuel for rockets is deliberately burned oxygen poor so the
unburnt fuel will add mass to the rocket's exhaust to give it more
thrust. To avoid the waste of incomplete combustion and get higher
fuel efficiency with greater thrust, dust could be inserted into or
near the combustion chamber instead of unburnt fuel.


I doubt that you could find a kind of dust that would be well suited for
this purpose. The ideal non burning mass would be helium. What you want
is something that will convert the energy of the combustion into thrust.
So you want very simple and light molecules. If you have big and complex
molecules, a lot of the combustion energy will be used up into getting
those molecules to vibrate (hot molecules tend to do that). You don't
want the the energy to make the molecules vibrate, you want it to make
the molecules go out fast.

If you add helium, the helium won't vibrate since a helium molecule is a
single helium atom, and because it is light, a hot helium atom will move
very fast. By Newton's law, if the helium atom goes out fast in one
direction, the rocket has to get a big push in the other direction. So
that would be nice. But you don't add helium to the burning gases
because if you put some helium in the mix, you increase the likelihood
that oxygen molecules hit helium instead of hitting kerosene and go out
unburned. And you don't want big heavy oxygen molecules going out
carrying energy by vibrating instead of going out carrying energy by
going out fast.

With extra kerosene, mostly all the oxygen will be burnt, and mostly all
the kerosene will be at least partly burnt. The partly unburned kerosene
will be simple light molecules such as hydrogen or free carbon atoms.


Alain Fournier
  #3  
Old December 15th 19, 09:58 PM posted to sci.space.policy
[email protected]
external usenet poster
 
Posts: 75
Default Rocket Fuel

On Sunday, December 15, 2019 at 11:02:40 AM UTC-5, William Elliot wrote:
Kerosene fuel for rockets is deliberately burned oxygen poor so the
unburnt fuel will add mass to the rocket's exhaust to give it more
thrust. To avoid the waste of incomplete combustion and get higher
fuel efficiency with greater thrust, dust could be inserted into or
near the combustion chamber instead of unburnt fuel.


Pure reactants as hot an exhaust level findable is the basic goal.
To add an impurity to cause a higher thrust is ok if it does
not alter the primary combustion. Generally impurities are like
adding noodles to boiling water, it cools the exhaust.

Adding something like aluminium might change the game. It
is proven helpful in solid fuel mixtures. An aluminum
screen in the exhaust flow might be allowable.
  #5  
Old December 16th 19, 01:44 AM posted to sci.space.policy
[email protected]
external usenet poster
 
Posts: 75
Default Rocket Fuel

On Sunday, December 15, 2019 at 6:42:14 PM UTC-5, JF Mezei wrote:
On 2019-12-15 11:02, William Elliot wrote:
Kerosene fuel for rockets is deliberately burned oxygen poor so the
unburnt fuel will add mass to the rocket's exhaust to give it more
thrust.



It was explained to me here before. Fuel rich mixture passes some
unburnt fuel through the nozzle, and much ends up burning in the engine
bell.

As the fuel burns in engine bell, it puts pressure on the top of the
bell as it is accelerated downward, hence adding to the force pushing
rocket upwards.


There is a term that I forget. It has to due
with combustion chamber internal dynamics.

It is analogous to a gun's ammunition dynamics.
A casing's volume and shape has a large effect
on firing pressures.

The outcome is the fact that fuel energy release
will not equate to rocket thrust.
  #6  
Old December 16th 19, 06:25 AM posted to sci.space.policy
Scott Kozel
external usenet poster
 
Posts: 62
Default Rocket Fuel

On Sunday, December 15, 2019 at 1:24:11 PM UTC-5, Alain Fournier wrote:
On Dec/15/2019 at 11:02, William Elliot wrote :
Kerosene fuel for rockets is deliberately burned oxygen poor so the
unburnt fuel will add mass to the rocket's exhaust to give it more
thrust. To avoid the waste of incomplete combustion and get higher
fuel efficiency with greater thrust, dust could be inserted into or
near the combustion chamber instead of unburnt fuel.


I doubt that you could find a kind of dust that would be well suited for
this purpose. The ideal non burning mass would be helium.


Where would they get enough helium for this? It is a rare element on Earth
and there is no chemical process to synthetically produce more of it.
  #7  
Old December 17th 19, 02:14 AM posted to sci.space.policy
Sylvia Else[_3_]
external usenet poster
 
Posts: 87
Default Rocket Fuel

On 16/12/2019 3:02 am, William Elliot wrote:
Kerosene fuel for rockets is deliberately burned oxygen poor so the
unburnt fuel will add mass to the rocket's exhaust to give it more
thrust. To avoid the waste of incomplete combustion and get higher
fuel efficiency with greater thrust, dust could be inserted into or
near the combustion chamber instead of unburnt fuel.


The cost of the fuel barely factors into launch costs, so there's little
benefit to improving fuel efficiency from the perspective of cost of
fuel. Further, providing an alternative to the unburnt fuel involves
increased complexity (and hence risk) and weight for the extra equipment.

Sylvia.
  #8  
Old December 22nd 19, 06:21 PM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 2,307
Default Rocket Fuel

In article ,
says...

On 2019-12-16 20:14, Sylvia Else wrote:

The cost of the fuel barely factors into launch costs, so there's little
benefit to improving fuel efficiency from the perspective of cost of
fuel.




I was told that the current setup has fully optimized fuel efficiency.
Having the "perfect" fuel/O2 mixture would produce a nice clean blue
flame out the exhaust, but that exhaust ends having to expand in the
engine bell and that would pull down on the top of engine bell.


This is simply not true. If it were true, a cold gas thruster wouldn't
work. Since cold gas thrusters are a state of the art way to provide
for a simple reaction control system, we know they work.

By having leftover fuel leaving the nozzle, it combusts in the engine
bell which not only fills the void, but also pushes up on the engine
bell as it too gets pushed down to exit.


This makes no sense. Where does the excess fuel get oxidizer to combust
in the bell? There is no source for this.

You're thinking of excess fuel which continues to burn in the earth's
atmosphere, which is 20% oxygen.

Unless, of course, you have a cite for this.

Consider that the rocket scientists have fully optimized the engines,
and Musk even goes as far as wanting the kerozene super cooled to
increase its density so they can carry more fuel. So the fuel-rich
mixture that results in imperfect combustion of some fuel in the engine
bell is a desired outcome because it increases engine efficiency.


Yes, because of the excess hydrogen in the exhaust. Lighter molecules
in rocket engine exhaust is a "good thing". This is why LOX/LH2 engines
are used in upper stages and why those engines are run hydrogen rich.

If my camping stove is able to burn kerosene with a blue flame, then I
am pretty sure they can do the same with rocket engines if they wanted to.


That orange color in the exhaust in the atmosphere is the kerosene which
was used for film cooling of the engine bell burning orange in the
presence of atmospheric oxygen. Since it's already exiting the nozzle,
it is also much cooler than it is in the actual combustion chamber.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
  #9  
Old December 24th 19, 12:03 AM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 2,307
Default Rocket Fuel

In article ,
says...

On 2019-12-22 12:21, Jeff Findley wrote:

This makes no sense. Where does the excess fuel get oxidizer to combust
in the bell? There is no source for this.


I asked in this group not that long ago why the fancy rocket engines
can't burn kerosene in a nice clean blue flame since even my camping
stove is able to do that.


Yes.

I was told that they purposefully have fuel rich environment so there is
combustion that happens in the bell to to expand that fuel, thus
maintaining a more optimal pressure in the bell, and this fuel, in
burning/expanding would also get accelerated downward after pushing up
on the engine bell.


You remember wrong. I can't imagine anyone telling you that because
it's wrong.

So not only accelerated by the "clean" combustion going out the
combustion chamber exhaust, but gets second acceleration as it burns in
the engine bell.


There might be some combustion in the bell, but that's not why you want
fuel rich combustion. That's wanted due to the lighter molecules and
disassociated atoms (i.e. hydrogen molecules and atoms).

Where does it gets its oxygen? That was not discussed. It was pointed
that this was one big reason for different engine bells in vacuum
engines vs sea level.


Nope. Again, I can't imagine anyone explaining it this way because it's
simply wrong.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Rocket enging fuel? Christopher[_5_] Technology 2 November 6th 10 08:16 PM
least polluting rocket fuel [email protected] Technology 22 February 14th 06 09:16 AM
REQ: Rocket Fuel & Propulsion [email protected] Space Shuttle 3 August 28th 05 10:11 PM
graphite as rocket fuel? [email protected] Technology 10 February 1st 05 07:23 AM
Polynitrogen Rocket Fuel sanman Policy 174 December 11th 04 01:14 PM


All times are GMT +1. The time now is 10:47 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.