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

[Seth]

Bruce Plecan wrote:
> 
> > I have been watching this thread. I was wondering if you might be a bit
> > more specific about your application.
> 
> 87 Buick GN,  3.8L, Auto, engine mildly hotrodded pocket porting, big
> downpipe exhuast, fuel pump, Should be a easy to run 12 sec 1/4 mile ET car
> 
> Diesel, 436 CID, very carefully put together, 60 PSI of boost,  uses about a
> gal of water every 30 secs at WOT.  200PSI WI, and very finely mists the
> Water.  We run right at 2:1 fuel water.  Mechanical Injection pump, so
> far....
> 
>  I have a feeling that the needs of
> > a spark ignition engine at high rpm might be different from a highly
> > boosted diesel.
> 
> Not that I've seen.
> 
>  I am wondering if at full boost you manage a
> > stoichiometric air fuel ratio (or fuel rich?) with the diesel, or are
> > you still very fuel lean as most normal diesels are.
> 
> Leaving the line the plum is probably 6-8' in diameter, and 50+' tall, so no
> we're nothing like you'd imagine a normal diesel is.



Ok, so you are running a lot of boost on a small diesel.  Do you know if
you are running near stoich? A plume of black smoke has as much to do
with injection droplet size and combustion temperature as it does
air:fuel ratio. 



  
> 
> 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. 

> 
>  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.

> 
>  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.   
> 
>  The commercially available systems I have seen try to
> > evaporate the water in the air just ahead of the intercooler. Whatever
> > is left probably boils off. Not saying that others aren't different,
> > just what I have have seen.
> 
> Who makes that system?.
> Grumpy

I'll get you a name. One that comes to mind was for 2nd generation turbo RX-7s.


-Seth


> 
> >
> > -Seth
> >
<big snip>
> 
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