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

Bruce Plecan nacelp at bright.net
Tue Jul 11 00:32:25 GMT 2000



> Ok, so you are running a lot of boost on a small diesel.  Do you know if
> you are running near stoich?

We tune for performance, so far no resonably priced WB available.

A plume of black smoke has as much to do
> with injection droplet size and combustion temperature as it does
> air:fuel ratio.

This is a competion vehicle not an engineering project, I use it as example
rather then making pie in the sky statements, is all.

> > And do you have
> > > control of injection timing with respect to manifold pressure?
> > No
> > >  I suspect that cooler combustion temps might be a good thing with a
> > > diesel if it it still fuel lean of stoich, so that you aren't
combusting
> > > piston tops as well as diesel fuel.
> > Running right our ETGs are just like a SI ICE.
> OK, but that's not combustion temperature.

Gees, I realize that, but it shows where we are relative to the thermal
limits of the engine.

> >  In a mixture that has very little
> > > extra oxygen, such as a spark ignition engine, then the displacement
of
> > > oxygen is not such a good thing for making power, as a rule of thumb.
> > > The point of the turbo was to get more oxygen in the engine in the
first
> > > place, after all. If you are very fuel lean and oxygen rich, then
> > > perhaps this displacement of oxygen is not such a penalty as in a
spark
> > > ignition engine.
> > But we're not that lean, we're to the stage of really driving the CR up
with
> > the amount of fuel and water were adding.  We're also running, 18:1 CR,
> > instead of the more common 16.

> Are you running the higher CR for easier starting?  Sounds like a rather
> high compression ratio when you are looking for power.

Easier starting?  no
Sounds like,   no
*this is a refined result*.

> >  But one could argue that it serves a similar function
> > > as EGR at that point, by reducing peak combustion temperatures. Which
> > > brings us back to why bother trying to force the air in the engine if
> > > you only want to displace it with an inert gas or water vapor.
> > Mr Harris took care to explain that earlier.
> Yes, and the part about volvo and the cooled EGR was a perfect example
> of displacing oxygen and cooling combustion to advance the ignition
> timing to get the power back while going back to stoich from fuel rich
> while still avoiding detonation. Helps lots when you want to pass an
> emissions test and you are pushing the thermal envelope of an engine
> design.
> > >  I might also say that the point of spraying the water at the
> > > intercooler probably winds up producing water vapor, not puddles, if
> > > done correctly.
> > In fooling around with the Wi, and various high pressures, the mist
really
> > wasn't having that much of a cooling effect abainst ones skin, like
you'd
> > imagine.  We were working outside in 90+ temps, and you'd tought if
would
> > make a huge difference.
> > I've watched and seen how much water it takes to cool an air to water
> > systems water radiator off.  I takes a bunch of water to make any real
> > difference.  Granted these are 4L engines, and just around 400-450 HP.
To
> > really make a drastic difference it going to take throwing, a serious
amount
> > of water at it.  Spraying a mist into anything means it will accumulate
on
> > those surfaces, and drip down.
> The point of the water is to absorb energy when it boils off. Either
> ahead of the intercooler in the air, or at the intercooler surface. I
> should imagine that at 60psi, your intercooler is warmer than your skin.
> So it might just do a better job of evaporating the water.

Again, I'm trying to get across, what in practice happens, rather then
interuptions, or just misstatements of fact.
grumpy

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