Water injection

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
Circlotron
Expert
Expert
Posts: 774
Joined: Tue Feb 05, 2013 6:56 am
Location: Melbourne, Australia

Re: Water injection

Post by Circlotron » Mon Jun 18, 2018 9:30 am

That's rather interesting. A bit more complicated than I first thought.
Here's a snippet I've posted in the past that seems to add weight to what you say. Someone else's words.
The effectiveness of spark ignition is directly related to the availability of free hydrogen. Molecules containing tightly bound hydrogen such as methanol, nitromethane, and methane are far more difficult to ignite than those with less bonds.

During combustion - water - H2O ( present and formed ) is extremely active in the oxidation of the hydrocarbon. The predominant reaction is the following:

OH + H ==> H2O
H2O + O ==> H2O2
H2O2 ==> OH + OH
Loop to top and repeat.

The OH radical is the most effective at stripping hydrogen from the HC molecule in most ranges of combustion temperature.

Another predominant process is the HOO radical. It is more active at lower temperatures and is competitive with the H2O2 at higher temps.

OO + H ==> HOO
HOO + H ==> H2O2
H2O2 ==> OH + OH

This mechanism is very active at both stripping hydrogen from the HC and for getting O2 into usable combustion reactions.

Next consider the combustion of CO. Virtually no C ==> CO2. Its a two step process. C+O ==> CO. CO virtually drops out of early mid combustion as the OH reactions are significantly faster and effectively compete for the available oxygen.

Then consider that pure CO and pure O2 burns very slowly if at all. Virtually the only mechanism to complete the oxidisation ( Glassman - Combustion Third Edition ) of CO ==> CO2 is the "water method".

CO + OH ==> CO2 + H
H + OH ==> H20
H2O + O ==> H2O2
H2O2 ==> OH + OH
Go to top and repeat.

This simple reaction accounts for 99% + of the conversion of CO to CO2. It is important in that fully two thirds of the energy of carbon combustion is released in the CO ==> CO2 process and that this process occurs slow and late in the combustion of the fuel. Excess water can and does speed this
conversion - by actively entering into the conversion process thru the above mechanism.

The peak flame temperature is determined by three factors alone - the energy present and released, the total atomic mass, and the atomic ratio – commonly called CHON for Carbon, Hydrogen, Oxygen, and Nitrogen. The chemical reactions in combustion leading to peak temperature are supremely indifferent to pressure. The temperatures and rates of normal IC combustion are sufficient to cause most of the fuel and water present to be dissociated and enter into the flame.

As can be seen above, water is most definitely not only not inert but is a very active and important player in the combustion of hydrocarbon fuel. Ricardo and others have documented that under certain conditions ( normally supercharged ) water can replace fuel up to about 50% and develop the same power output, or that the power output can be increased by up to 50% addition of water. This conditions were investigated by NACA and others for piston aircraft engines. It is important to note that these improvements came at the upper end of the power range where sufficient fuel and air was available to have an excess of energy that could not be converted to useable pressure in a
timely manner.

Scotthatch
Pro
Pro
Posts: 311
Joined: Sat Apr 14, 2018 11:12 pm
Location: 7000 ft up

Re: Water injection

Post by Scotthatch » Mon Jun 18, 2018 10:48 am

NACA went away in 1958 so you are talking old research... and my first worry about that much water would be corrosion. My next thought is you are talking about power levels in very crude big inefficient cylinders of the aircraft of the day that are not anywhere like what we run today ... anything I have ever seen on water vapor carbs or injection is that it made a lot less power then gas .....

Going back to something more normal then the above ...

Water vapor point is like 200 degrees
Ethanol Vapor point is like 175 degrees
Methanol vapor point is like 150 degrees

All depending on boost or vacuum at the moment

Water in all likelihood would be lucky to vaporize in the intake on NA motor ... I think this is why the mix works well ... methanol cools the charge ... water cools the cylinder ... both slow down the burn .... I have always seen better results from mix then just water ..

Truckedup
Guru
Guru
Posts: 1734
Joined: Mon Jan 21, 2013 2:41 pm

Re: Water injection

Post by Truckedup » Mon Jun 18, 2018 1:06 pm

Scotthatch wrote:
Mon Jun 18, 2018 10:48 am


Water in all likelihood would be lucky to vaporize in the intake on NA motor ... I think this is why the mix works well ... methanol cools the charge ... water cools the cylinder ... both slow down the burn .... I have always seen better results from mix then just water ..
slowing down the burn means more ignition timing advance ,yes? And a slower burn time is more favorable to detonation, yes?
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire

Schurkey
Guru
Guru
Posts: 1256
Joined: Sun Mar 01, 2009 2:42 am

Re: Water injection

Post by Schurkey » Mon Jun 18, 2018 3:21 pm

mike hohnstein wrote:
Sun Jun 17, 2018 6:06 pm
Tell you this, 645" diesel V-8 turbo, charge air cooler, propane injection and shooting windshield washer fluid in with a two jet system @ the cac outlet. Boost goes up 3# with the water on. EGT's 200 degree's cooler,
Boost goes up even though the working fluid--exhaust gas--has less temperature. Tells me that the volume of exhaust gas including steam spooling the turbo is much higher than hotter, more-expanded exhaust without steam. And you have higher boost even though on the intake side, the fluid is supposedly contracting the intake charge.
God bless turbochargers.

Or are we thinking that the added water, vaporizing, adds so much volume to the intake charge that the pressure rises? That's not such a fun thought.
gruntguru wrote:
Mon Jun 18, 2018 12:32 am
When water vaporises in the intake, it cools the charge and shrinks it by more than the extra volume occupied by water vapor. So the net effect is an increase in air mass to the engine.
I have trouble wrapping my head around this. Given that water expands tremendously, while air (especially) and fuel don't expand as much, you'd need very, very little water vaporizing to cause all that cooling/contracting of the fuel/air mix.
Fireonthemountain wrote:
Mon Jun 18, 2018 2:24 am
Turbo-Rocket Fluid and steam engines what will they think of next.... =D> =D>
I still have a couple bottles of Turbo-Rocket Fluid. Sold most of 'em.
Image
joe 90 wrote:
Mon Jun 18, 2018 6:33 am
Carbon reacts with water at high temp (at a lot less than 3000)to give CO and H2.
It's an endothermic reaction, it uses energy. You get the energy back with the combustion of CO and H2.


Maybe as low as 706 deg C?

http://www.madsci.org/posts/archives/20 ... .Ch.r.html
No wonder adding water cleans carbon from the chamber. I thought it was a matter of steam-cleaning, the carbon blew out the exhaust in chunks 'n' pieces, maybe partially-dissolved. Never dreamed it would enter into the combustion process.

Circlotron wrote:
Mon Jun 18, 2018 9:30 am
That's rather interesting. A bit more complicated than I first thought.
Here's a snippet I've posted in the past that seems to add weight to what you say. Someone else's words.
The effectiveness of spark ignition is directly related to the availability of free hydrogen. Molecules containing tightly bound hydrogen such as methanol, nitromethane, and methane are far more difficult to ignite than those with less bonds.

During combustion - water - H2O ( present and formed ) is extremely active in the oxidation of the hydrocarbon. The predominant reaction is the following:
...
Thanks for that.

user-23911

Re: Water injection

Post by user-23911 » Mon Jun 18, 2018 5:31 pm

Water is also used in the cracking of heavy hydrocarbons to make lighter ones, part of the oil refining process.

gruntguru
Member
Member
Posts: 147
Joined: Fri Apr 10, 2015 7:56 pm

Re: Water injection

Post by gruntguru » Tue Jun 19, 2018 12:32 am

Schurkey wrote:
Mon Jun 18, 2018 3:21 pm
gruntguru wrote:
Mon Jun 18, 2018 12:32 am
When water vaporises in the intake, it cools the charge and shrinks it by more than the extra volume occupied by water vapor. So the net effect is an increase in air mass to the engine.
I have trouble wrapping my head around this. Given that water expands tremendously, while air (especially) and fuel don't expand as much, you'd need very, very little water vaporizing to cause all that cooling/contracting of the fuel/air mix.
The answer lies in the latent heat of vaporisation of water. It takes more than 2,200 KJ of heat energy to vaporise 1 kg of water. It takes about 1 KJ of heat energy to raise the temperature of 1 kg of air by 1 degree Celsius.

So (ball park) if 1% water is added to intake air and it completely vaporises, you are taking 2,200 x 1% = 22 KJ of heat out of each kg of air, dropping the temperature by about 22 degrees. The change in air density is proportional to the change in absolute temperature so if we start with 100*C and end with 78*C the density increases by (100 + 273)/(78 + 273) = 1.06 or 6% density increase.

Meanwhile the water vapor has added less than 1% to the intake air volume (water vapor is slightly lighter than air).

user-23911

Re: Water injection

Post by user-23911 » Tue Jun 19, 2018 1:35 am

gruntguru wrote:
Tue Jun 19, 2018 12:32 am
The answer lies in the latent heat of vaporisation of water. It takes more than 2,200 KJ of heat energy to vaporise 1 kg of water.

That value for water is about double the value for methanol.
So to get the same cooling effect by evaporating methanol alone, you'll need to evaporate double the mass of it.

F-BIRD'88
Guru
Guru
Posts: 6209
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: Water injection

Post by F-BIRD'88 » Tue Jun 19, 2018 2:56 am

Thats all glorious and all.... except once you realize methanol is a fuel, too.
it can burn and be part of the combustion too.
The 50-50 deal works out pretty good, overall.

user-23911

Re: Water injection

Post by user-23911 » Tue Jun 19, 2018 3:45 am

It goes in the fuel tank....the methanol.
That's where it belongs. Mixed with the low octane petrol.

Truckedup
Guru
Guru
Posts: 1734
Joined: Mon Jan 21, 2013 2:41 pm

Re: Water injection

Post by Truckedup » Tue Jun 19, 2018 5:54 am

F-BIRD'88 wrote:
Tue Jun 19, 2018 2:56 am
Thats all glorious and all.... except once you realize methanol is a fuel, too.
it can burn and be part of the combustion too.
The 50-50 deal works out pretty good, overall.
Where does oxygen come from to go with the methanol so the mixture isn't too rich/? is extra oxygen released with all the chemical reactions mentioned above?
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire

user-23911

Re: Water injection

Post by user-23911 » Tue Jun 19, 2018 7:37 am

If you're using EFI, in particular the speed density variant of EFI, it's really not compatible with water injection due to the way it works (Cooling the charge in the manifold increases the density, but the computer has no way of knowing how much by) . It's going to lean out the AFR when it turns on. Adding methanol or ethanol to the mix will tend to richen it back up.
That's yet another big disadvantage of speed density systems and a big plus for MAF based EFI.

If you're starting with a MAF based EFI system and the AFR is correct then adding water and methanol will make it richer, same with a carburettor.

Truckedup
Guru
Guru
Posts: 1734
Joined: Mon Jan 21, 2013 2:41 pm

Re: Water injection

Post by Truckedup » Tue Jun 19, 2018 8:31 am

joe 90 wrote:
Tue Jun 19, 2018 7:37 am
If you're using EFI, in particular the speed density variant of EFI, it's really not compatible with water injection due to the way it works (Cooling the charge in the manifold increases the density, but the computer has no way of knowing how much by) . It's going to lean out the AFR when it turns on. Adding methanol or ethanol to the mix will tend to richen it back up.
That's yet another big disadvantage of speed density systems and a big plus for MAF based EFI.

If you're starting with a MAF based EFI system and the AFR is correct then adding water and methanol will make it richer, same with a carburettor.
So a richer mixture may not be ok if it causes power to drop off..Obviously on some engines, richer helps to limit detonation but that what the water/alcohol spray is used for...
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire

F-BIRD'88
Guru
Guru
Posts: 6209
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: Water injection

Post by F-BIRD'88 » Wed Jun 20, 2018 3:11 am

Truckedup wrote:
Tue Jun 19, 2018 5:54 am
F-BIRD'88 wrote:
Tue Jun 19, 2018 2:56 am
Thats all glorious and all.... except once you realize methanol is a fuel, too.
it can burn and be part of the combustion too.
The 50-50 deal works out pretty good, overall.
Where does oxygen come from to go with the methanol so the mixture isn't too rich/? is extra oxygen released with all the chemical reactions mentioned above?
Good question.. When you inject methanol and water you can then back off on the gasoline fuel used at WOT that is used for cooling (WOT overfuel), to a significant extent. The methanol is very high octane. and also does carry its own oxygen , too.

Scotthatch
Pro
Pro
Posts: 311
Joined: Sat Apr 14, 2018 11:12 pm
Location: 7000 ft up

Re: Water injection

Post by Scotthatch » Wed Jun 20, 2018 11:05 am

Truckedup wrote:
Mon Jun 18, 2018 1:06 pm
Scotthatch wrote:
Mon Jun 18, 2018 10:48 am


Water in all likelihood would be lucky to vaporize in the intake on NA motor ... I think this is why the mix works well ... methanol cools the charge ... water cools the cylinder ... both slow down the burn .... I have always seen better results from mix then just water ..
slowing down the burn means more ignition timing advance ,yes? And a slower burn time is more favorable to detonation, yes?

I guess the answer to timing advance is yes but I think more along the lines of the timing I should be able to run and not retarded to make it run without......

The other part depends on the type of detonation that is happening ... is it because the mix is lit off by a hot spot ... is it compression ignition ..... or is the burn pressure wave lighting off the rest of the mix early?

The basic idea of octane is that it is harder to burn and therefore the burn is slower but that is not how peak HP is made .... up to the point of an uncontrollable burn a higher speed burn does better and will make a higher peak pressure so it is a fine line between to fast and to slow and this is tuned with timing and fuel .....

The other part of cooling the cylinder is just getting the parts to hold up .... as power goes up or forced up with boost or nos the temperature will also climb and this is hard on ring gap needed and piston temp and clearance and exhaust valve temperature so by doing something to help cool the parts it all holds up better

Scotthatch
Pro
Pro
Posts: 311
Joined: Sat Apr 14, 2018 11:12 pm
Location: 7000 ft up

Re: Water injection

Post by Scotthatch » Wed Jun 20, 2018 11:06 am

joe 90 wrote:
Tue Jun 19, 2018 7:37 am
If you're using EFI, in particular the speed density variant of EFI, it's really not compatible with water injection due to the way it works (Cooling the charge in the manifold increases the density, but the computer has no way of knowing how much by) . It's going to lean out the AFR when it turns on. Adding methanol or ethanol to the mix will tend to richen it back up.
That's yet another big disadvantage of speed density systems and a big plus for MAF based EFI.

If you're starting with a MAF based EFI system and the AFR is correct then adding water and methanol will make it richer, same with a carburettor.

This is a very interesting take on what happens and worth remembering when doing this

Post Reply