[the_zerox]

Can anyone tell me why water injectors (into the intake or TB) do not damage an engine ie, common sense would tell me that you would have problems with oil and water mixing or rust right?

Z

 

[Mike 94PGT]

Can anyone tell me why water injectors (into the intake or TB) do not damage an engine ie, common sense would tell me that you would have problems with oil and water mixing or rust right?

Z

In properly executed water injection systems, no damage occurs for several reasons:

First, the water is atomized by either a nozzle/pressure arrangement (similar to how a spray bottle works) or ultrasonically (like those heatless humidifiers you might have seen) and enters the intake tract as a fine mist. Even if it made it all the way to the combustion chamber in this form, it would still be compressible as opposed to a volume of liquid water.

One of the key things about water injection is that the general idea is to not have the water enter the combustion chamber in even an atomized form but as a vapor. When you boil a pot of water, the "steam" you see doesn't actually appear until a little bit above the surface of the water and is simply vapor that has condensed back to an atomized liquid form. You can't actually see the vapor because its, for all intents, a gas. The bubbles you see in boiling water...they're water vapor bubbles, not air.

In order for the atomized water to vaporize, it needs to absorb heat from its surroundings - the air in the inlet tract - and this is what water is quite good at doing, with a fairly high latent heat of vaporization. Because of this, the intake air can be cooled quite a bit (of course, how much depends on the heat of the incoming air: compressed air (i.e. turbocharged) is far hotter than ambient air and thus more heat transfer can occur if more water is added.)

As far as rust, the combustion chamber of an operating engine is an environment where that doesn't much support the formation of oxides of iron. Indeed, one of the byproducts of normal combustion is water. The heat of combustion, oil washing, wiping action of the rings and even the mixture swirl all ensure that the water isn't resident on the cylinder walls long enough to start oxidizing the iron.

The oil will be fine too. If enough water is injected to wash as a liquid into the sump, the engine probably would have grenaded due to hydro-static lock so water-dulited oil is the least of the engine's concerns. The amount of water injected is (should be!) really small.

Of course, in the old days (back in the 70s , it wasn't uncommon to take a garden hose set to a trickle (and I mean a trickle!) and feed that directly into the air horn of the carb while revving the engine. The general idea was that the water would flash-vaporize in the combustion chamber and would literally steam-clean the piston crowns and heads etc. I'd never do that now, but lots of engines survived the process

 

[the_zerox]

water injection non turbo

So mike, would it be possible/suitable to place a water injector in a non turbo situation to cool the incoming air, and why dont more people do this (is anyone in this list doing it already?) more oftern rather than adding cold air inductions? (which as it is difficult to get access to on a MX6 is a real problem.

Dean

 

[Mike 94PGT]

Re: water injection non turbo

So mike, would it be possible/suitable to place a water injector in a non turbo situation to cool the incoming air, and why dont more people do this (is anyone in this list doing it already?) more oftern rather than adding cold air inductions? (which as it is difficult to get access to on a MX6 is a real problem.

Dean

It's possible (anything is possible) but here's the problem. The air entering the engine is at or fairly near ambient temperature most of the time. There are exceptions as when sitting in traffic and things get toasty under the hood, but by and large, its generally fairly close to ambient. Water in a glass on a table doesn't vaporize very fast - it can take days (long) for the water to evaporate. In the same way, the amount of vaporization that would occur in the inlet tract under ambient or near ambient conditions would be small. As such, the amount of heat removed from the air is small and the cooling effect negligible. The engine ingests the water droplets harmlessly where they flash into steam and, if anything, may help reduce carbon buildup.

What you need is something that boils at a considerably lower temperature. N2O (nitrous) is one such material. Water boils at 100 degrees C while nitrous boils at -88 degrees C. Thus, as the nitrous enters the intake tract, it almost instantly vaporizes and in the process takes alot of heat out of the air as it does so. In addition to supplying easily-dissociated oxygen to the engine (N20 splits into N2 and O in the heat of the combustion chamber), the cooling effect is almost as important.

There are other materials. Isopropanol (isopropyl or "rubbing" alcohol) is a bit better than water with a boiling point of about 82 degrees C. Not nearly as good as nitrous, but better than water. Think of it this way: put a drop of water on the back of your hand and blow on it. It feels a bit cooler. Now repeat it with a drop of rubbing alcohol: it feels alot cooler. This is due to the increased vaporization rate of the isopropanol.


In summary, water or even alcohol injection on a normally aspirated car of nominal compression (like, say the 9.2:1 KL03) won't really benefit from water injection. They may get a bit out of alcohol injection (maybe some washer fluid which is diluted alcohol) but it'll be a smallish effect.

 

[the_zerox]

ambient temprature?

Mike,
How can the air be at ambient temprature, I thought we needed to try really hard to reduce the temp of the air (ie. cai or spacers) entering the mx6's engine?

Dean

 

[Mike 94PGT]

Re: ambient temprature?

Mike,
How can the air be at ambient temprature, I thought we needed to try really hard to reduce the temp of the air (ie. cai or spacers) entering the mx6's engine?

Dean

It's true that a CAI helps, though I don't know that I believe all of the gains of, say, a HS CAI, are due to the fact that it's sucking under-car air or if they are due to the much smoother & less restrictive path the air takes on the way to the TB. The OEM air intake on the MX6 & PGT is actually pretty good as far as taking in cool air from in front of the radiator. What's not good is the convolutions the air goes through as it enters that airbox, changing directions several times and then entering the VAF. I'm sure it all heats up, and maybe it can even get pretty hot during a traffic jam in August in Phoenix, but I still don't think the air is getting all *that* hot.

Under way, the air entering a normally aspirated engine isn't too much above the outside ambient air. Most of the intake tract is cooled as the air rushes in while the car is under way and the engine is under load.

Of course, the air is heated inside the intake runners and that's what the phenolics are supposed to help with (though I've not seen actual instrumented data showing the temperature drop inside the runner afforded by these things, people do report the manifold is cooler to the touch.)

Sure, the air is heated in the manifold but I don't personally think it's heated to the extent that water injection will help immensely, mostly because water's boiling point is so high. As I said earlier, other cooling agents like isopropanol or even washer fluid might do better. Actually, I'd be interested to see dyno plots showing a N/A motor with a hot engine before and after water injection and then after alky/washer fluid injection. Might be very interesting...

 

[twinturbo6]

I love that guy!! Everytime he logs on we all learn something.... MIKE i appreciate you taking the time to so thoroughly inform us, while not be superior about. thank you