Water Injection Thread

[Greg Hermann]

>Thanks, Greg, for the good discussion.  I never thought about the Mach 1
>stuff in the exhaust housing.  At Mach 1, though, flow through a nozzle is
>only dependant on density (upstream pressure).  Velocity cannot increase
>with pressure drop but flow can still increase as density increases.  In
>other words, sucking harder will not produce more flow but pushing harder
>will, albeit at a reduced rate (kink in curve) since velocity cannot
>increase.

Also dependent upon temperature, since Mach 1 increases with increasing
temp, but you knew that---

And since increasing the back-pressure on an engine will increase the EGT
(due to less downward T/P shock during blowdown), at least with a
turbocharger turbine nozzle, the flow will increase a bit more linearly
with increasing backpressure than your statement implies when dealing with
an engine /turbocharger pairing.

(I have a FAIRLY decent handle on what is happening qualitatively here, but
PLEASE don't ask for NUMBERS!!!)

The "pushing harder" (higher density) to get more flow through the nozzle
part would mean more back-pressure on the recip part of the engine, which
would mean more pumping losses, and hence less net output. (which, in turn,
translates to lower efficiency), which brings us back full circle! Exactly
why I SUSPECT that a well done pressure recovery accumulator on a good set
of turbo headers might make for a net gain!!

Thanks for the discussion, Gary. The back and forth definitely stretches
the knowlege envelope quite a bit!!
WHICH IS FUN!!!

I think the REAL unexplored gain is in (more efficient) pressure recovery
from the Mach .75 velocity in the gas spiral at the turbine outlet, though.
The circumferential component of the flow in that gas is distinctly greater
than the axial component. Some way of straightening the helical flow out,
and turning all (more) of that velocity back into static pressure would
truly be a FREE increase in the pressure ratio across the turbine, with all
of the performance improvements that that implies!!! Plus, I do not think
that a device for doing it would take up all that much space! Also, no
moving parts involved and decently low temps, so ALMOST as reliable as
taxes!
>
Greg

>Gary Derian <gderian at cybergate.net>
>
>
><big snip>
>>
>>DO NOT misunderstand me, these wanderings are theoretical conjecture at
>>best--if I shut up and build something, test it, and it proves out, then I
>>would (and will!) be more forceful about it!
>>>
>>Regards, Greg
>>