effictivness of water injection

[kachok25]

I have long been a beliver in the potnetial of water injection as a means of increasing boost while reducing knocking, I used to get laughed at for bringing this up but recently I have noticed that at leased in some circles the idea has cought on but the one thing that I don't know for sure is how much additional boost I could use with water injection. I read a technical book addressing the subject and it mentioned increasing the maxamum pre-ignition pressure from 150 psi to 280 psi using a reasonable amount of water, does this mean that I can almost double my boost or are there other factors that I am not considering, because if that is the case that would make water injection more potant than any octaine booster and even some racing fuels. Someone correct me if my hypothisis is flawd, or if there is any downside except the small amout of air that water vapor displaces let me know.

[Reed]

water injection is a great idea but it should not be used as an octane booster. it is great for a turbo system that is running at its absolute maximum boost level and using water injection to create a margin of error for bad fuel or a sudden drop in fuel pressure or for anything else that may go wrong. Many people see it as a bandaid for a bad tune. Of course water injection can be used to increase boost but I would say to use for safety reasons or maybe for a slight and momentary increase in boost.

[Schister66]

If you're talking about spraying water over an intercooler in order to cool it and prevent heat soak, then that idea has already been put into action. The Subaru WRX STi has water injection on the IC in order to prevent heat soak on their little top mount......

If i completely missed the point, let me know

[kachok25]

Originally Posted by Schister66

If you're talking about spraying water over an intercooler in order to cool it and prevent heat soak, then that idea has already been put into action. The Subaru WRX STi has water injection on the IC in order to prevent heat soak on their little top mount......

If i completely missed the point, let me know

No you missed the idea completly. I am talking about spraying a fine mist of water into the intake runners, this in drawn into the cylinders cooling off the hotspots that are the cause of detonation much more effective (in theory) than just cooling the the air in the innercooler by 20-30 degrees (although it does that too) as water evaporates it absorbes ALOT of heat somthing that gas does not do well. Ususaly people mix alcohol into the water this serves several purposes; first it keeps the water from freezing in cold weather, alcohol is part oxygen so it carries more oxygen in a liquified form, and it provides aditional knock protection by supplying a little extra fuel to the mix ensuring that you do not have a lean mixture. The whole idea sounds great and if properly used is supposed to be very effective, but unfortunetly Formula one banned water injection in its infency so it is not a race proven technology. Hence alot of tuners still treat is like snake oil or a bandaid for a bad setup, but the fact reamins that it can dramaticaly raise the detonation threashold of gasoline engines (from 150psi to 280psi with 87 octaine @2000RPM If memory serves)

[kachok25]

Originally Posted by Reed

water injection is a great idea but it should not be used as an octane booster. it is great for a turbo system that is running at its absolute maximum boost level and using water injection to create a margin of error for bad fuel or a sudden drop in fuel pressure or for anything else that may go wrong. Many people see it as a bandaid for a bad tune. Of course water injection can be used to increase boost but I would say to use for safety reasons or maybe for a slight and momentary increase in boost.

Well if it can create a significant margin of error where there was not one before allowing the use of maxamum boost, is that not raising the boost pressure in effect? And if you can safely advance your ignition timing a few degrees in that not creating more power? I have one more technical question if anyone can anwser it I know that the water vopor displaces some of the air in the cylinders but it also cools the air in the intake runners condensing it, what is the difference in the effect of displacement vs condensing (or vice versa), in other words how much more does it displace vs condense? I used to be able to remember the formula for that but it has been a long time since I finnished collage chemistry and my math is a little fuzzy.

[Reed]

I am not sure about that but i do recall reading something about the water turning to steam in the cylinder and slightly increasing the effective compression.

[Schister66]

well if you spray water in there you're going to have left over water and that's going to cause rust....

[beef_bourito]

I don't think it makes much of a difference in terms of how much air you can fit, if anything it allows more because the air's cooler. you use such a small amount of water that the cooling effect makes the air alot denser. also it does increase compression a but because you can't compress water but it's very small.
I'd say that you could very easily use water or alcohol injection as a tuning mechanism or to increase power. sure it does make your engine safer and it protects against knocking and such but who uses it for that?

One thing about water/alky injection is that it cools the air alot and also cools exhaust temperatures, this means that if you inject too early, you'll have a laggy turbocharger, you should injectslightly before you reach the max boost you can run without water injection (3-5psi under) and then keep it going while you're running up to full boost. this would make it so you have quick spooling and really high boost and power.

If you wanted you could have everything automated so you can flip some switches and dramatically change the performance of your car. you could have an electric boost controller so you can run really low boost or high boost, then you could have your alcohol injection running with only a certain ammount of pressure so unless you're actually racing you won't be wasting alcohol, water or fuel.

[kachok25]

Originally Posted by beef_bourito

I don't think it makes much of a difference in terms of how much air you can fit, if anything it allows more because the air's cooler. you use such a small amount of water that the cooling effect makes the air alot denser. also it does increase compression a but because you can't compress water but it's very small.
I'd say that you could very easily use water or alcohol injection as a tuning mechanism or to increase power. sure it does make your engine safer and it protects against knocking and such but who uses it for that?

One thing about water/alky injection is that it cools the air alot and also cools exhaust temperatures, this means that if you inject too early, you'll have a laggy turbocharger, you should injectslightly before you reach the max boost you can run without water injection (3-5psi under) and then keep it going while you're running up to full boost. this would make it so you have quick spooling and really high boost and power.

If you wanted you could have everything automated so you can flip some switches and dramatically change the performance of your car. you could have an electric boost controller so you can run really low boost or high boost, then you could have your alcohol injection running with only a certain ammount of pressure so unless you're actually racing you won't be wasting alcohol, water or fuel.

Personaly I dont think that the 20-40 degree difference in exaust temp is going to make a lick of difference in how quickly the turbo spools, and even if it did the pressure drop on the intake side (due to the air being condensed) would offset it (less load on the turbo allowing for faster accelaration). And with the addition of alcohol to the mix it would spool faster, because although alcohol cools the air going in it also carries oxygen in with it (eythal is one third oxygen I think) that would actualy raise the exaust gas temp and thus pressure having the completly opposite effect as the one you described. Even boost control is limited in what it can do by the compression ratio, boost level, and octaine of the fuel. Basicly it cannot just delete pre-ignition and if water injection can give it an edge in the range of 5psi it is a worth wile investment in my book, at leased for high hp applacations.

[kachok25]

Originally Posted by Schister66

well if you spray water in there you're going to have left over water and that's going to cause rust....

Think about that for one second. Water injection is only activated under boost the only way that water would stay in the engine is if you cut off the engine while under boost, and if you are dumb enough to do that you have bigger problems than a little rust in your engine, you have just crystalized the oil in your turbocharger for starters, and if your turbo shares oil with your engine you are screwd Also think about this when you drive on a rainy day does your engine take in water? If you live in the deep south with near 100% humidity is you engine taking in water? How many engines that you know of have blown due to rust in the combustion chamber? Of all the problem that I have see I have never seen that one. Make sence?

[kachok25]

Originally Posted by Reed

I am not sure about that but i do recall reading something about the water turning to steam in the cylinder and slightly increasing the effective compression.

If you can find me any links on that I would be very intrested in seeing them, but I think you will find that there is not a great deal of increased pressure before TDC because water is a vapor form acts just like any other gas when the temp is raised. One mole occupies 22.4 liters at STP (standard temparature and pressure) just like oxygen or nitrogen. The only thing that might raise the pressure a little is that once completly vaporized it would take roughly 60% less heat to raise the pressure of water vapor as it would oxygen (water molecular weight in 10 while O2 weight is 16), but the amout of water is not enough to make this a significant problem I would think. But like I said maby there is somthing that I am not taking into consideration so if you can find that link I would love to see it.

[Black Lotus]

Stole this from the Innovate Motorsports forum awhile back.
Remember, that this is talking about the use of EXCESS fuel used to prevent an abnormal combustion event.
When you increase boost, you are increasing power, so you still need to add fuel to keep the BSFC in line. You should not use water to take the place of this additional fuel. You'll have a lean fuel mixture and the engine will eventually fail...::
------------------------------------------
Application Note: You CAN be too Rich
By Klaus Allmendinger, VP of Engineering, Innovate Motorsports

Many people with turbochargers believe that they need to run at very rich mixtures. The theory is that the excess fuel cools the intake charge and therefore reduces the probability of knock. It does work in reducing knock, but not because of charge cooling. The following little article shows why.

First let’s look at the science. Specific heat is the amount of energy required to raise 1 kg of material by one degree K (Kelvin, same as Celsius but with 0 point at absolute zero). Different materials have different specific heats. The energy is measured in kJ or kilojoules:

Air ~ 1 kJ/( kg * deg K)
Gasoline 2.02 kJ/( kg * deg K)
Water 4.18 kJ/( kg * deg K)
Ethanol 2.43 kJ/( kg * deg K)
Methanol 2.51 kJ/( kg * deg K)

Fuel and other liquids also have what's called latent heat. This is the heat energy required to vaporize 1 kg of the liquid. The fuel in an internal combustion engine has to be vaporized and mixed thoroughly with the incoming air to produce power. Liquid gasoline does not burn. The energy to vaporize the fuel comes partially from the incoming air, cooling it. The latent heat energy required is actually much larger than the specific heat. That the energy comes from the incoming air can be easily seen on older carbureted cars, where frost can actually form on the intake manifold from the cooling of the charge.

The latent heat values of different liquids are shown here:

Gasoline 350 kJ/kg
Water 2256 kJ/kg
Ethanol 904 kJ/kg
Methanol 1109 kJ/kg
Most engines produce maximum power (with optimized ignition timing) at an air-fuel-ratio between 12 and 13. Let's assume the optimum is in the middle at 12.5. This means that for every kg of air, 0.08 kg of fuel is mixed in and vaporized. The vaporization of the fuel extracts 28 kJ of energy from the air charge. If the mixture has an air-fuel-ratio of 11 instead, the vaporization extracts 31.8 kJ instead. A difference of 3.8 kJ. Because air has a specific heat of about 1 kJ/kg*deg K, the air charge is only 3.8 C (or K) degrees cooler for the rich mixture compared to the optimum power mixture. This small difference has very little effect on knock or power output.

If instead of the richer mixture about 10% (by mass) of water would be injected in the intake charge (0.008 kg Water/kg air), the high latent heat of the water would cool the charge by 18 degrees, about 4 times the cooling effect of the richer mixture. The added fuel for the rich mixture can't burn because there is just not enough oxygen available. So it does not matter if fuel or water is added.

So where does the knock suppression of richer mixtures come from?

If the mixture gets ignited by the spark, a flame front spreads out from the spark plug. This burning mixture increases the pressure and temperature in the cylinder. At some time in the process the pressures and temperatures peak. The speed of the flame front is dependent on mixture density and AFR. A richer or leaner AFR than about 12-13 AFR burns slower. A denser mixture burns faster.

So with a turbo under boost the mixture density raises and results in a faster burning mixture. The closer the peak pressure is to TDC, the higher that peak pressure is, resulting in a high knock probability. Also there is less leverage on the crankshaft for the pressure to produce torque, and, therefore, less power.

Richening up the mixture results in a slower burn, moving the pressure peak later where there is more leverage, hence more torque. Also the pressure peak is lower at a later crank angle and the knock probability is reduced. The same effect can be achieved with an optimum power mixture and more ignition retard.

Optimum mix with “later” ignition can produce more power because more energy is released from the combustion of gasoline. Here’s why: When hydrocarbons like gasoline combust, the burn process actually happens in multiple stages. First the gasoline molecules are broken up into hydrogen and carbon. The hydrogen combines with oxygen from the air to form H2O (water) and the carbon molecules form CO. This process happens very fast at the front edge of the flame front. The second stage converts CO to CO2. This process is relatively slow and requires water molecules (from the first stage) for completion. If there is no more oxygen available (most of it consumed in the first stage), the second stage can't happen. But about 2/3 of the energy released from the burning of the carbon is released in the second stage. Therefore a richer mixture releases less energy, lowering peak pressures and temperatures, and produces less power. A secondary side effect is of course also a lowering of knock probability. It's like closing the throttle a little. A typical engine does not knock when running on part throttle because less energy and therefore lower pressures and temperatures are in the cylinder.

This is why running overly-rich mixtures can not only increase fuel consumption, but also cost power.

[kachok25]

Very intresting tech page but who says that the water has to be injeected before the fuel? If the fuel has already vaporized who is to say that you could not inject the water afterwards and have it enter the cylinder as droplets? Afterall it is the cooling inside the cylinder that gives it its infamus knock resistence not the cooling of the inital air charge, and it should not interfear with the evaporation of the fuel much? Plus it would have less of an air displaceing effect as a liguid mist anyway in fact it would be a negligable amount. Plus the latent heat required to evaporate the fuel would easly be created as a bi-product of the compression from the turbo/supercharger anyway, even with a world calss innercooler. And remember I am not asking for the sake of peak thermal effecency I am talking about raw HP, so if using water injection reduces my thermal effecenty by 3% but allows me to increase the amount of air I am burning by 10% I would consider that a great tradeoff. If I am missing somthing please point it out to me. Thanks for all the imput guys keep it up. Oh one more thing how would water injection affect emissions in a low CR turbocharged street car?

[CBFryman]

Originally Posted by kachok25

No you missed the idea completly. I am talking about spraying a fine mist of water into the intake runners, this in drawn into the cylinders cooling off the hotspots that are the cause of detonation much more effective (in theory) than just cooling the the air in the innercooler by 20-30 degrees (although it does that too) as water evaporates it absorbes ALOT of heat somthing that gas does not do well. Ususaly people mix alcohol into the water this serves several purposes; first it keeps the water from freezing in cold weather, alcohol is part oxygen so it carries more oxygen in a liquified form, and it provides aditional knock protection by supplying a little extra fuel to the mix ensuring that you do not have a lean mixture. The whole idea sounds great and if properly used is supposed to be very effective, but unfortunetly Formula one banned water injection in its infency so it is not a race proven technology. Hence alot of tuners still treat is like snake oil or a bandaid for a bad setup, but the fact reamins that it can dramaticaly raise the detonation threashold of gasoline engines (from 150psi to 280psi with 87 octaine @2000RPM If memory serves)

Ethanol is not, in anyway, composed of oxygen.
WI Benefits inthe Folowing ways:
-Cools the incomming air, ever been at a theme park on a hot day and they had thoes things spraying a fine mist of water into the air and you would walk by them and it would cool you off, same deal.
-The water creates more steam in the combustion chamber cleaning up more of the carbons and other crap that may be built up in the combustion chamber
-water in gas form can only be compressed so far before it becomes liquid agian, once the water is liquid we all know that it doesnt liketo compress at all. this means the compression ratio is "raised" making the burn more efficent.
-Water is often mixed iwth ethanol, which is added fule
-when alcohol evaporates it cools the surrounding air, and gasoline does not.
-all of this cooling the water/alcohol is doing reduces hot spots and therefor knocking

WI is often used in boosted engines and high compression engines, the problem with NA and Supercharged engines that do not have knock sensors to cut back timing and WI is that once your run out of water you are SOL...i think Curtis had some bad experences like that.
if i remember right it was something about 11.5:1 compression and 83 octane or similar.

[Reed]

instead of water, would it be possible to fill your WI system with race gas? what would be the benefits/downfall of doing this?