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