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Redline Dreamz wrote:

LegacyT wrote:Injecting water and alcohol is made to cool the CYLINDER WALLS during the combustion cycle. The atomized water/alcohol mix breaks down durning combustion. The water breaks down to hydrogen and oxygen and the alcohol binds with the left over oxygen. The 2 Hydrogen atoms are what do the cooling, in a similar fashion that nitrogen in nitrous oxide does, just not nearly as effective. The alcohol alone is a combustable, but when bonded with the extra oxygen atom it becomes a lubracant, but still burns. Injecting water alone will cause a SEVERE LEAN STATE which can and will break and/or burn holes in things. Using a alcohol/nitromethan mix cools and lubracates even better than the water alcohol mix however it is less than cost effctive being that a 1 gallon jug of alcohol/nitromethan/oil (40%/40%/20%) is about $20 bucks and change. Injecting Nitrogen alone is the same idea as injecting strait oxygen.... ALL SORTS OF LEAN. There is testing of using CO2 in hopes of the carbon atom becoming a super lubracant but is not proven to work yet.

Thats just a summary of how the injection system works and why you use it the way you do.

ummm I think that water injection is to cool the intake charge, not only to avoid detonation but to make the air more dense supporting more fuel. Its not to "cool the cylinder walls." thats what coolant is for. not like combustion is going to cool them down even if it is not as hot. the water does not break down in the combustion, it is merely a spectator. water vapor in the cylinder does have the added benefit of "steam cleaning" carbon in the cylinder. also alcohol is not as efficient as h2oin removing heat, i.e. water has a higher specific heat capacity. its not as widely available or cheap as water.

Actually, there's some good research out there indicating that the water does in fact break down... I need to find these sources and read up on them, but I have heard of people reducing the amount of injected fuel and instead injecting more water, and actually making more power. The water helps speed up the combustion reaction somehow... Interesting, since water is normally a product of the oxidation reaction.

Wow. Heated discussion. How many here have actually used water injection? Alcohol injection?

In my opinion, water and alcohol injection are different - water injection *can* help take some heat from the inlet charge, however, it's main purpose, in my experience, has been to reduce the tendency of knock or detonation. With a certain amount of water in the combustion chamber, it requires heat to change it from liquid to gas form, so it absorbs some heat from the chamber. Because it does not "ignite" it acts like increasing the octane in the combustion chamber. The finer the mist, the better the process (more contact surface area, can absorb heat more efficiently).

Problems usually stem from too much water injected to be turned to steam, so some of it gets into the sump, can promote corrosion in the engine, etc.

Alcohol injection is something entirely different. Alcohol is a fuel that is burnt. It has a very high octane rating, but less energy (per cubic unit) than gasoline. Therefore, to get the same power as with gasoline, a much larger amount of alcohol has to be injected (in its stead). Alcohol does allow (and really needs to be effective) much higher compression ratios. Like 14 or 15:1 instead of 10:1 on gasoline (NA). Now, alcohol could be injected to help with the combustion process on a gasoline engine, it would act much like an octane booster, without the worry of water - getting too much wouldn't be as detrimental.

That is what I recall from the top of my head. If I am wrong, please point it out and correct me, but don't be a jerk about it.

Is water injection for automobiles the same as the water injection used in planes in WWII? I'd have to read up on it again but from what I remember they had the ability to use water injetion on their engines to get a boost in performance for a short time in emergency situations. I think the engines tended to seize up after they landed, though. I don't remember which country/ies did this. I'll have to talk to my aviation friend and try and get the info again.

-Ryan

Some WWII fighters were supercharged, so maybe they used it for the same reason Subaru does? They would have to store the water somewhere so it wouldn't freeze at high altitudes. I know some aircraft used NOS at high altitudes for quick bursts of emergency power, but I didn't know they used water injection. I have a thing for those old fighters, so it would be interesting to know.

Steve

I have heard about use of water injection in fighters too. It was discontinued because they couldnt justify carrying the extra weight of water. also jet engines made that technology obsolete. they could overfuel jet engines and use the afterburners creating the same effect, but on a larger scale and not have to carry an unnecesssary liquid on board. I think this ishow I heard it but I could be wrong, it was a while ago.