Water Injection - What does it do?

I believe that was covered in the 'Popular Mechanics' article that debunked all of the 'fuel saving' devices tested. Much of this stuff is still being advertised even though it had only a possible application in carbureted engines.

Water injection came as an extra measure of high power and ping reduction in piston engine military airplanes. The throttle (I'm doing this from memory... it's been a long time) went from idle to cruise to maximum - then there was a button interlocked further position marked 'WEP' which stood for War Emergency Power. You used that one only when you were in peril of having your ass shot off! What it did was open the throttle all the way, increase the supercharger/ turbo boost and dump about 50 gallons of water into the intake over the next 3 minutes. The water mist did a couple of things. It flashed to steam and added an extra measure of compression. It also absorbed some heat energy in the process of turning to steam which reduced peak cylinder temperature and reduced pinging.

Neat idea but absolutely has no place in a modern automobile street engine. Can cause more problems than it could ever hope to fix. Aside from possible water lock and corrosion, there is also the aspect of how to winterize the water reservoir. You could add alcohol to it and then it further tips the cost - benefit scale in the wrong direction.

Just as a point of interest, google for "war emergency power" or 'engine "water injection"'

Oppie

Dunno much about it. I dont think a stock engine would take much if any advantage from it. The cons would be greater I think.

Pro's: Cooler Cumbustion Carbon Remover

Con's: Rust Moisture in Oil Set up cost

Unknowns: Fuel Mileage HP

If it would give better gas mileage I think the automakers would jump right on it.

Well, that depends. On your car as it came from the factory, I would tend to agree.

But on a very high compression or forced induction motor - that's a different story.

First paragraph on this page does a good job describing the use:

It was covered in PM TV show last week as a debunked gadget along with the tornado, etc. and they expressed concern over potential damage if not hooked up correctly. It was used in WWII to extend gas mileage in fighter planes. I first learned about this in the '80s when an old friend garage built such a device as designed by his father, a WWII pilot/mech. for his , lol, K-car. He claimed it worked but never proved it.

marx404

Wasn't there an olds motor in the 50's that had something like this?

You need to get up to speed on water injection. Especially when used on diesel engines.

Would you care to point me to some information please? I may be wrong at times but never wishy-washy . Oppie

In many respects, Water injection works like EGR does in modern street engines. It lowers the peak combustion temperature under high power and controls ping. Water inj does have the result of aditional expansion (ie power) but this is not a fuel saver as you have to supply additional energy to vaporize the water. Bottom line is that it may improve power but not fuel economy.

The WW-II use of water (usually combined with alcohol) injection was strictly for detonation suppression at high power settings. It cooled the charge in the cylinders while the alcohol raised the effective octane rating of the fuel/air mixture. It certainly did NOT improve fuel economy and was good only for short duration (full military power).

Note that those aircraft used either superchargers or turbo superchargers to boost the intake manifold pressure to 60 or more inches of mercury (15 in is sea level ambient).

Detonation susceptibility increases with charge pressure and temperature and decreases as octane increases.

Forget about it for improving fuel economy!

I saw a 1940's airplane engine on display at the Intrepid Sea and Space Museum in New York City. Don't recall what it was from but it had a 2-stage induction system; first stage was a turbocharger and second stage was a supercharger. As you said, that could easily get 60 psi at a cruise altitude.

For improved economy have any of you tried fuel preheating. Saw an article on it and built a heater with good luck on 2 cars: 74 Mercury Capri (had Ford Pinto engine) and a 78 VW Dasher Wagon (standard VW water-cooled 4). It used radiator fluid to raise the temperature of incoming fuel a bit. There was about 1 foot of jacket so it probably didn't heat it too much.

As the engine (and radiator fluid) came up to temperature the idle speed increased. Gas mileage was up about 20% as I recall. It was all downstream from the fuel pump to avoid vapor lock. Never had a problem other than the increased idle speed.

Didn't have the guts to try it with a fuel injected Rabbit given the high pressure fuel system. And the funky fittings for the lines. If it works why don't companies work it into their fuel systems?

And last, how about heating incoming air a bit more? That should help, too.

Jim

I never considered fuel pre-heat on a modern engine since the fuel is always flowing in a loop (pump from the tank, take off what you need for the injectors, fuel pressure regulator and dump back into tank). Too much pre-heat and you heat up the fuel in the tank excessively (which just might be a problem).

Heated air induction is a far safer way to get the same effect. Oppie

That's probably your answer right there.... it doesn't work. And a 20% improvement sounds very improbable.

And as for heating air, seems to me you need enough to vaporize fuel, but beyond that it's counterproductive because air becomes less dense and you don't want that. That's why turbochargers have intercoolers, to lower intake temperature.