Why no water injection?

[sportyaccordy]

Here's what happen when you dump water onto a grease fire

http://www.youtube.com/watch?v=_lab6T9FQMI&feature=related

Here's the scientific cliff notes of it

In an engine, water injection does a lot of good things. Cools down the combustion chamber (enabling more boost or compression or w/e, also reducing emissions), and more importantly, through the absorption of the heat, turns the vapor into steam, which through expansion adds power & in theory should increase efficiency.

I don't know the stoichiometric ratios for fuel/water/air that are ideal, but assuming a 1:1 ratio or something reasonable could work why the hell haven't manufacturers all jumped onto this yet? It's already in practice in the aviation industry & t3h b00st w3rld, is there something I'm missing?

[Submariner]

Interesting question: I can't picture the cost or complexity being too great of an issue. 

If I remember basic physics correctly, constant, rapid changes in temperature (and to a lesser extend, pressure) can dangerously stress the material that experiences it.  Do speciality/aviation engines have protections against this, or is it simply a non-issue?

[giant_mtb]

Becuz we hav intercoolerz.

[68_427]

Where's the water going to come from?  A possibly heavy water tank?  You would also have extra lines/injectors.  Would it be injected through the intake or be DI?  It'd be really complicated to make it all worth it.

[GoCougs]

My very limited knowledge of it (primarily WWII aircraft) says that its benefit is for hyper performance engines (i.e., extremely high compression ratio/high cylinder pressure) which is to say the benefit is basically zero for a standard performance engine.

The comment on "steam charging" I'd question because the heat used to vaporize the water is heat taken from the combustion process; I'm not so sure there would be a net gain in cylinder pressure (that is, on a properly running engine).

[sportyaccordy]

Well correct me if I'm wrong- I'm def no combustion expert- but isn't the bulk of the work extracted in a combustion engine from expansion? Heat wise, the water injection would def sap some of the heat of combustion- but odds are that is heat that was gonna flow into the block as waste heat (a significant portion- 50% of the input energy in my experience from cogen)- so as far as combustion goes, any means of converting heat into expansion will aid in crankshaft output efficiency, unless there's something I'm missing.

Why didn't I think of this in college, this would have made for an excellent master's thesis.

[Galaxy]

The Saab 99 turbo S used water injection.

[Galaxy]

The comment on "steam charging" I'd question because the heat used to vaporize the water is heat taken from the combustion process.

I am not certain but I think the heat used would otherwise be lost to the coolant system, or the exhaust.


Edit: I missed that Sportyaccord already wrote that.

[Galaxy]

One potential problem with water injection:




I suppose today one could tweak them to not prosuce so much soot. However a simply diesel soot filter will probably not be sufficient.

[sportyaccordy]

Where the hell does the soot come from? 

And I have found some online communities about water injection, but nothing definitive about its effect on fuel economy.

From the kits I have seen, its main advantage is in bringing down super/turbocharged intake temps. But that is with the water injection happening before the throttle plate. I would be curious to see what the effects would be of injection after the throttle. I imagine less than positive effects on fuel atomization (though the water injection could be delayed), but positive effects on combustion chamber temps and other things. I don't think the mixture could handle a volume of water significant enough to add a ton of power, but a more sophisticated approach could definitely be a plus in the fuel economy dept, esp in the context of these new turbo engines. Imagine... 13:1 compression, 10lbs of boost off a small turbo, aggressive timing from idle to redline at any load, all for something like an Elantra  Gonna look into this more.

[Galaxy]

Where the hell does the soot come from? 

Good question. I am assuming that the water causes some of the combustion to be incomplete. That effect would get counteracted by making the combustion that does get completed more efficient.