Water injection (was: Re: fuel cooling intake air)

[Axel Rietschin]

From: "Bruce Plecan" <nacelp at bright.net>
> > > But you excluded it in your first statement.
> > I implied it. The AFR is supposed to be maintained, some way or another,
> > with or without water.
>
> No you specificly said just timing

Re-read it. I never excluded anything. I just didn't mention it because it
is totally obvious, at least to me, that with more boost goes more fuel. As
I also said, it's an ECU job and it's been mapped for this.

> Now,
> > would you use such an ECU to run a highly tuned race engine, if
regulation
> > allows you to use a more sophisticated unit?
>
> Lots of other details involved other then the ge wow factor. There are
> applications were brutialy simple out weights, risking sensor failures.
(ie
> experimential aviation, and yes they use fiinely tuned race engines)

Things tends to get more sophisticated, nowadays, but we jump from cars to
tractors to airplanes here. I confess I don't know what kind of combustion
control (or whatever) is used on rocket engines, nor do I care. Now can you
please mention the name and type of one or more electronic engine management
systems likely to be found in a modern turbocharged car, that don't use ACT
as an input parameter?

> > No? Are you saying that injecting water in the air charge at some point
in
> > the intake system, after the turbo, will cause the turbine wheel to
> > accelerate? Please explain.
>
> The intake chage by being cooler will have less pressure, in most high
> performance turbo applications there, is a limiting factor based on boost.
> So yes the turbo will be spinning faster.

So evaporating water will not cause an _increase_ of pressure instead?
Actually, you just added something (steam) that takes 100% of the room made
up by the temperature decrease (like the "pushing a rock uphill" metaphor),
and displaced oxygen in the process (the original point of this discussion).
So no, the turbo will not be spinning any faster.

And, by the way, what is the "limiting factor based on boost"? air speed at
the turbo intake? compressor wheel speed? losses in the induction system?
engine's VE, fuel available? detonation?, exhaust back pressure? turbine
housing flow?

> > a dedicated sequential ECU [for WI]

> ME, overkill, IMHO.
> Get so clever and precise, anything slightly wrong and total system shut
> down.  Nope.

Different point of views.

I've read Mr. Harris and Summer's messages with great interest, and also Mr.
Colon's answer. I stand corrected, water is not inert and does participate
in accelerating the combustion process, enabling more energy to be release
in the short timeframe encountered at high engine speed. It show I'm not up
to speed with the thermochemistry of the combustion process, and I learned
something. Now, what's the engine speed where water start to do something
mesurably useful? Does this speed fall in the diesel engines operating
range? Below that speed, what the water is useful for, beside as an
in-cylinder coolant and detonation retardant?




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