At 03:09 AM 09/28/2018, Lars Osborne wrote:
Expect more regarding their kick-pump autogenous system soon.Â
In the context of the evident concern regarding helium
availability, it occurs to me that it might be feasible
to use a pumped system to develop the pressurization for
a primarily pressure-fed rocket. (For example, LOX
pressurized with GOX...). If a small flow of propellant
is drawn off by a high-pressure pump and run through a
heat exchanger to vaporize it, the gas will be at almost
the same pressure (less the drop in the heat exchanger)
and can thus pressurize the main tank.
This should require less power than pumping the entire
propellant flow from a low initial pressure, so the
power should be reduced by the ratio of the liquid
and vapor densities. (In practice, there would be a
loss due to requiring more than the net expulsion
volume of pressurizing gas, of course, but the inlet
liquid flow could still be a relatively small part of
the total flow.)
Also, come to think of it, once the system reaches the
steady state full power condition, the pump only needs
to overcome losses in the heat exchanger, as it has
the pressurized supply available as its inlet feed...
and this condition might even be approximated during
startup with a suitable profile, using (perhaps) a
preliminary pumped flow to develop initial tank
pressure, to where the engine can be ignited and
supply heat to maintain vaporization. Such a system
would never need to pump the full chamber pressure,
even at the fractional flow needed for the pressurizing
cycle... the pump power requirement could be rather
low, compared to fully pump-fed systems, and there
would be no consumable high-pressure gas requirement.
(I wonder if a small electric pump could do the job at
a favorable weight, relative to the high-pressure gas
tank and regulator of a "conventional" pressure-fed
system.)
I was gonna say it wouldn't work for non-volatile
propellants like peroxide, but you could use something
volatile and inert (like LN2 etc.) in the pressurant
tank / heat exchanger loop, and tap off gas to pressurize
the main tanks: again, the total condensed pressurant
volume could be significantly less than the main propellant
expulsion volume... and the pressurant tank would only need
to operate at the engine system pressure (unlike a gaseous
source such as high-pressure nitrogen and a regulator).
But ("there's always a 'but'..." - J. Clark) the tank
would operate at low temperature, hence probably requiring
insulation (which would offset the weight advantage of the
reduced pressure).
-dave w
On Thu, 18 Oct 2012, John Carmack wrote:
> I would like to see investigation done on fully gasifying one or both of
> the propellants by the engine before combustion to mitigate the two
> phase flow injection issues.
It may be simpler to use engine heat to fully gasify a small fraction of
both, and use the resulting warm gas for tank pressurization. Avoiding a
separate pressurant doesn't have to imply classical self-pressurization;
giving the propellant some help is a reasonable alternative. There are
disadvantages (thermal issues in the tank, need for good diffusers) but
also advantages (constant feed pressure and density, no two-phase flow).