I have seen many posts about adding water to a gas engine...some wrong some right. So to set teh record right I'll add what I know about the topic. I have built and used several water injection systems. It does work and will not (when use properly) destroy an engine. I used it in my turbo charged Subaru (450HP 360ft/lbs four cyl) I built the car from the ground up, so i feel i am qualified to give an account of what it does/how it works.
First a quick lesson on combustion: Ideal Air fuel ratio for gasoline is 14.7:1, that is the point where the it is burning most efficiently. Most engines must use a much richer ratio some as rich as 9:1 (under certain load conditions). The excess fuel is used to cool the engine and prevent denotation.
denotation: AKA: KNOCK, knock is a condition where the air fuel mixture explodes before the it is suppose to(which will VERY quickly destroy an engine). knock can be prevented in a number of ways. the simplest is to use a higher octane gas. The higher the number the less explosive a fuel is, hence the less chance it will explode in the combustion chamber prematurely. Additionally, you (or your car's computer) can retard timing, add fuel or in a turbo engine lower boost. OOOORRRRR you can add water to the air fuel mixture making it less explosive.
Which brings me to water injection. Water injection is spraying an ATOMIZED mist of water into the intake. This atomization is achieved by spraying it through a nozzle at high pressure. Atomization is VERY important you can't have a drip or a drop of water. Since water doesn't compress than one or two drops in a cyl will force the water past the rings and\or valves (which is what I'd guess happen to your friend with the 350). the mist of water will essentially raise the flash point of the air fuel mixture, having the same effect as a higher octane fuel. which is why most people see a few extra MPG when they put the 'good stuff' in the tank.
SO let me put the pieces of the puzzle together for you. adding small amounts of water lowers the flash point of your air fuel mixture. Remember that knock is the premature combustion of the air fuel mixture, lowering the flash point will make this less likely.
Since modern gas engines are controlled by a computer that 'listens' for knock then adds fuel (making it richer than 14.7:1), and/or retards timing both causing reduced power. So its easy to see that if your motor is using more fuel to make less power that fuel economy is reduced.
Normally aspirated engines are limited by how fast they can take in air. Turbocharged engines are limited by the octane or 'ping-resistance' of the fuel/air mixture. Water injection helps push that limit further.
No point in water injecting a normally aspirated engine (except maybe a nice steam cleaning of the combustion chamber!).
Shutdown,
A friend of mine, back in the late 60' early 70's had a Datsun 4 door sedan. He expiremented with turbos starting with one off of a Corvair spyder and then moved up to What I think was an Air research.
He had the heads o-ringed to prevent blow outs and he had a home brewed water injection set up. He started with a beer keg in the trunk, a ford windshield washer motor and a jet off an old holley carb. It was triggered with a mechanical micro switch at half throttle. It was very crude but it worked.
I don't remember how many lbs boost he was running but I seem to remember it was very high.
We went to the old Orange County Raceway on grudge night and he ran against my 67 SS396. Of course I blew him away off the line but he was within a car length by the end of the 1/4. Those were fun times!
Lady Vixen and the Rat
2006 Arctic Fox 29-5T (Lady Vixen)
2002 K3500 w/8.1 "It's a gasser!"(The Rat)
Normally aspirated engines are limited by how fast they can take in air. Turbocharged engines are limited by the octane or 'ping-resistance' of the fuel/air mixture. Water injection helps push that limit further.
No point in water injecting a normally aspirated engine (except maybe a nice steam cleaning of the combustion chamber!).
Not true. By that logic a naturally aspirated engine would NEVER knock because it would never get enough air (to be lean enough) to do so.
All engines (NA or turbo) are capable of achieving 14.7:1 AFR. You are correct that bigger power gains can be had with forced induction engines because it gives you a 3rd variable to adjust (timing, fuel ratio AND BOOST). However gains can be noted while adjusting only fuel and timing.
Even with water spray you won't be able to get to 14.7:1 at high load/rpm with out knock, closer yes.
And YES, it does steam clean, which is a good thing too.
Formerbiker:
I miss smoking Cameros, vettes, stangs and even the occasional viper in a 4 banger. the looks the drivers you was worth a million!
the systems don't have to be complicated to work, but they better you can manage them the better they'll serve you. my system was controlled by a microprocessor, based on throttle position, boost and intake air temp.
* This post was
edited 05/08/08 09:28am by shutdown *
and to think back in the mid 70s my uncle basically set up a water drip system into his Buicks carburetor and had a cable to his distributor timing. As he would change how much water drip he could readjust the timing. it worked pretty good and it sure did keep the engine clean, but unfortunately his only problem with it was remembering to turn it off... LOL Oh the good ol days.
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Chris, Lori and the Greyhounds
94' Dodge Ram 2500 4X4 Cummins T/D
05' 30' Coachman Capri
Water injection was used in Radial Airplane engines during the Korean and Vietnam war (A-1 Skyraider fighter). It increased the horsepower from 3000 to 3300 during combat.
Shutdown, does water raise or lower flash point? You said it both ways. Higher octane fuel actually lowers BMEP so higher octane actually gets poorer mileage in a given engine that uses lower octane fuel. I will bet Sundowner1 can fill us in on the valve and valve seat erosion caused by water injection.
I used water imjection for years in my ford 460. Atomized might be nice, but mine was atomized only slightly. We're talking two streams of water spraying right into the secondaries. More water than a windshield squirter. The system was driven by an electric pump that is sometimes used as a fuel pump. A vacuum feed from the carb triggered a solenoid valve. In the mountains, it was not unusual to use 4 gallons of water to 30 gallons of gas.
As for not improving the power in a non-supercharged engine, that's simply wrong. I had the MSD adustable timing module and could adjust timing on the fly, from a control in my lap. With water, I could advance the timing 6+ degrees over what would take w/o water. The idle RPMs went up and the engine was "sharper." Towing was noticeably better. IT was easy to tell when the water tank was empty. Knock city. I never did notice much, if any, MPG increase, the 460 uses a storm drain for a carb. I read that WI works for diesel but I can't see how it could. My PSD has plenty of power already. :-).
CROSSBOLT wrote: Shutdown, does water raise or lower flash point? You said it both ways. Higher octane fuel actually lowers BMEP so higher octane actually gets poorer mileage in a given engine that uses lower octane fuel. I will bet Sundowner1 can fill us in on the valve and valve seat erosion caused by water injection.
Karl
Sorry water RAISES the flash point. Meaning that because water won't burn when mixed with something that will that something (gas) will the mixture becomes less explosive and taking a higher temp before ignition will occur.
Perhaps more correctly I should have used the term "autoignition" instead of "flash point". if memory serves for 87 octane gas that magic temp (for autoignition) is 470 degrees F. Maybe that temp is for 93 octain??? The two words are not interchangeably but are very closely related. Anyway, in an attempt to make this as easy to understand and by as many people as I can the whole concept is a bit over simplified.
You are right. When no other variable is changed a fuel with a higher flash point fuel will not burn as quickly or as hot, which will result in lower MPG AND power output.
BUTTTT since modern engine control computers 'listen' for knock and will lean the AFR and advance timing until it hears it the end result is increased increased power and MPG. Forced induction engines do better with water injection than do naturally aspirated ones, it gives you(or the computer) a 3rd variable (boost) to adjust.
As for valve seat erosion, can't say. It was never an issue for me after about 30K miles of running water injection.
Sundowner1 wrote: Water injection was used in Radial Airplane engines during the Korean and Vietnam war (A-1 Skyraider fighter). It increased the horsepower from 3000 to 3300 during combat.
Water injection was used extensively in supercharged aircraft engines, both air-cooled radial (P&W, Wright, Bristol, BMW and Japanese equivalents) and liquid-cooled inline (D-B particularly) to ALLOW a HP increase, by overboosting, for short periods of time. The injection of a coolant (water, water-methanol, water-ethanol) did not by itself increase power output, rather enabled an increase buy supercharging to higher pressures.
The practice continued in use during the postwar era on the large radial engines needed to get heavy military and commercial transports off the ground, including DC-6 and DC-7, Super Constellation, StratoCruiser, KC-97, C-121, B-50 et al.
Water injection to support high boost goes back a long way in aviation practice, at least as far as the Schneider Cup races of the '30's.
Other hot rod practices like nitrous oxide boost, and nitromethane oxidants (mixed in fuel or injected) also go back to military and competition aircraft prior to WW-II.
FWIW, GM put a methanol-water injection system into the turbocharged Olds Cutlass 215 cid V-8, in the early '60's, even though maximum boost was about 7 PSI. This allowed them to keep a higher compression ratio for efficiency, since the turbocharger seldom got into boost in ordinary driving. Even with full throttle right off the line, we could seldom get the pressure gauge into the boost range under 4000 rpm, and the transmission would upshift as soon as it got there, and boost would fall off. Turbocharger = sales gimmick?
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