Water injection

[FahlinRacing]

I know there are a couple threads on this, however I know the reason mainly is to keep things from melting on high power production mills. However, I know the arguement on guys who favor the system and the ones who say you can't make power with water because you can't burn water. I had this lurking question in my thoughts today at work talking to a friend about an engine.

Anyways, since H2O is two hydrogen and one oxygen, would the combustion process break the water down and allow the oxygen molecules become useful for continuing power production with our power stroke?

 

[GregLocock]

wiki:

"At elevated temperatures water molecules split into their atomic components hydrogen and oxygen. For example at 2200 °C about three percent of all H2O molecules are dissociated into various combinations of hydrogen and oxygen atoms, mostly H, H2, O, O2, and OH. Other reaction products like H2O2 or HO2 remain minor. At the very high temperature of 3000 °C more than half of the water molecules are decomposed,"

You will have a very unhappy little engine if much of the gas is at 2000 deg C, never mind 3000. You could add some powdered platinum to improve the dissociation rate at lower temperatures.

http://www.eng-tips.com/viewthread.cfm?qid=189819

has some interesting numbers



Cheers

Greg Locock


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[MikeHalloran]

My theory is that finely divided liquid water absorbs a lot of heat as it boils and becomes steam, thereby preventing or suppressing or extinguishing what would otherwise be a detonation event. I.e., using heat of vaporization, but no significant dissociation or other chemistry involved. Suppressing detonation _allows_ the engine to run at elevated power levels, but doesn't produce any extra power by itself, except maybe for expansion of the steam. You have of course detected that there are other theories, galore. Feel free to develop your own.





Mike Halloran
Pembroke Pines, FL, USA

 

[140Airpower]

Greg, interesting data. One factor to consider is the dissociation rate at very high pressures. IIRC, Ricardo calculated or measured a much lower rate due to the pressure. Nevertheless, the dissociation of water and the approach to dissociation cause a lot of heat to be absorbed and decreases the temperature rise even after the water is already completely evaporated. Water also acts as a diluent, just getting in the way of the reactants and as a reaction product itself its presence lowers the reaction rate.
Your idea about a Platinum catalyst is interesting. Lowering the energy barrier to H2O dissociation should make it all the more effective.

FahlinRacing There is nothing to be gained from the extra Oxygen when water dissociates. The best energy yield is for the Oxygen to recombine with the Hydrogen. Net energy = zero. However, the afor mentioned reduction in combustion temperature and concurrently peak pressure, lowers the efficiency of the engine. The power gain is due to the ability of the engine to withstand more boost or CR without detonation.

BTW when all is considered, mixing alcohol, a fuel -especially Methanol, will get you more ultimate power than water alone despite the fact that water alone is a better anti-detonate. This is due to the trade-offs wrt efficiency.

 

[patprimmer]

The water and alcohol both also evaporate in the manifold to some degree. This both cools, thereby increasing the air density, but also displaces air, thereby diluting the charge. I think (without hard data at my fingertips) that water increases the density by a larger factor than it displaces air, while alcohol displace more air than they increase the density of.

Hence water increases VE while alcohol reduces it, however alcohol ads energy per unit of oxygen burned vs oxygen burned by hydrocarbon fuel.

Regards
Pat
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[FahlinRacing]

Interesting stuff, thanks guys for posting. So at 2200 C (3992 F) things begin to seperate, but, we seem to still not be able to use the oxygen molecules coming from water like we would with already consumable air molecules.

I am believing that nothing changes between the diesel engine and a gas engine in terms of water injection since the ICE uses the water to prevent detonation through latent heat of vaporization?

If we benefit from anything produced here would the steam produced be larg enough to see a difference even with a small amount of water steam still expands quite a bit in comparison Hmmmm. Thanks for giving me some stuff to think about to at work.

Jim

 

[patprimmer]

The latent heat of vaporisation cools the charge as the water evaporates. This drop in temperature causes the air to contract or the pressure to reduce, meanwhile the steam produced causes the The water to expand, hence rebuilding the pressure to where it was.

Regards
Pat
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[140Airpower]

The total picture with water injection is very messy. You have the effect of cooling the charge in a supercharged engine, making it more dense AND lowering the potential to detonate. You have the effect of delaying heat build up ahead of ignition due to water's slowing the chemical decomposition of the fuel (especially gasoline). You have the lowering of peak temp and pressure allowing more boost and/or CR. You have the reduced loss of energy through chamber walls due to lower peak temp. You have the effect of more energy flow out of the exhaust (in the form of greater pressure at exhaust valve opening) that in turbo applications should increase the efficiency of the turbo setup.

As for the steam engine effect, after combustion, the mixture is so hot everything is a gas. The water from combustion and the injected water are not different. What counts is the pressure, not the composition of the gas (although the specific heats of steam are slightly different from N2 and CO2). As mentioned, the extra water REDUCED the peak pressure. The trade off of reduced peak pressure and increased late pressure should be a net loss. To get around the reduced peak pressure problem and get the benefit of steam expansion, the Crower 6-Stroke engine separates the combustion and steam expansion processes.

 

[FahlinRacing]

Bummer, well thank you for the insight once again. I never came across thought of the reduction in cylinder temps because of the water evaporation, forgot I could compare it to how fuel evaporates within the chamber. I will just stick to drinking the water for now. Seems like quite the ride for the process on hoping to gain anything more than detonation supression.

 

[hemisboats]

You may want do do some research on HH0 Generation. I've been doing a lot of reading lately on the subject. The trick appears to strike the correct balance between energy used (to split the elements) and energy received from the HHO produced! Pretty interesting stuff...

 

[patprimmer]

The energy required to separate water into hydrogen and oxygen is exactly the same as the energy obtained by burning them together less any losses in the process. It's called the law of conservation of energy sand is high school physics. It's also called the first law of thermodynamics.

Some claim that hydrogen being added to the mix in the chamber catalyses the reaction to burn the hydrocarbon (there is already plenty of oxygen there from the air) but I have never seen credible evidence to support this. I have seen credible evidence it makes no difference at all, therefore claims by people selling such devices are snake oil.

Regards
Pat
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[BigClive]

The main thing I noticed about water injection when I did some experiments with it a few years ago was that it did terrible things to the engine oil in the sump very quickly - turning the oil into a creamy emulsion. So you have to be careful not to inject too much water.

 

[140Airpower]

BigClive, this is an important observation. The normal accumulation of water in the sump is exacerbated by water injection. The appropriate measure is to be sure the oil temperature is always above about 160F. This is usually not much of a problem in normal driving after warmup.

 

[hemisboats]

BigClive, seems to me that about 25 years ago there was a water injection system on the market that claimed in Create roughly 15% power, thus savings. However, it was a long time ago and they no longer make the system either because it didn't work (scam) or computers adjust the system to account for the water. I think the water was turned to steam prior to ejection as you cannot compress water and straight water would cause the water to blow by the rings.

I think Patprrimmer was right,"snake oil"! IMHO

 

[patprimmer]

Yep as said before, there is already plenty of water in blow by. This accumulates in the oil even without water injection, but it obviously collects at a faster rate with water injection.

Either way, the oil must warm up to flash off the water before there is enough to cause emulsification. It must flash of at a reasonable rate so it does not destroy the oil film on the bearing journal as it flashes off.

The journal is the point where the oil most likely reaches water boiling point and to much water will turn to a lot of steam at 212 deg f. To much steam and not enough oil left on the journal will destroy bearings.

Regards
Pat
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