Water Injection Thread

[Greg Hermann]

Gary Derian wrote---

Wouldn't the sound energy in the exhaust from a tuned system direct more
energy to the exhaust turbine?
>Turbines may like to have a steady flow but shouldn't additional energy
>help?

Additional energy is always good--I think the real question here is how
good you can make your convergent-divergent collector nozzle and how good
you  can make the convergent nozzle from the accumulator to the turbine--if
the gain in turbine efficiency from having a steady feed pressure and
velocity exceeds the nozzle losses, you will have won, if not, converging
the collector directly into the turbine nozzle might well do better.

Somehow, I think that building some stuff, and instrumenting it properly,
and testing it would be a whole lot easier than trying to do the calcs!!!

 I thought that was the idea behind dual scroll exhaust housings.

It kind of is, but I think the idea of the split housings is even more to
prevent interference between exhaust pulses from adjacent cylinders in the
firing order as they are fed into the turbine nozzle(s).

A megaphone would convert velocity into pressure but the exhaust ultimately
>has to speed up again (and drop pressure) to flow through the exhaust
>housing.

It sure does--but what calcs I HAVE done indicate that the gas velocity
coming out of the turbine feed nozzle(s) needs to about match the velocity
of the tips of the turbine blades for decent turbine efficiency to
happen--this velocity is again about Mach .75  AVERAGE in a typical case.
Get too much pulsation at this point, and you will begin to get Mach 1
(choked) flow--ain't no more gas gonna go through the nozzle--so things
will get seriously constipated during part of the pulse, and screw up the
header tuning. At Mach .75, it wouldn't really take much pulsation at all
to produce an increase in back pressure, either, even if you are not
pulsing it strongly enough to choke it.

Which is kinda why I think smoothing the flow out might be a net win, even
though there are losses through two more nozzles to make up for.

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