Water Injection - What does it do?

"Orval Fairbairn" > wrote in message
news
> In article >,
> "Oppie" > wrote:
>
>> 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.
>>
>>
>> "marx404" > wrote in message
>> ...
>> > 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.
>
>
> 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

"Jim, N2VX" > wrote in message
...
> 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

"Jim, N2VX" > wrote in message
...
>
> 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?

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


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

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.