water injection pre turbo

[YelloRolla]

There are some specifics to making it work.
For example; are all the cars that are running draw through carby turbo doing the same damage to the compressor as those who have failed with water injection? If not then what is the difference?
Plain water has a very high surface tension, and it doesn't evaporate (and evaporation is what we want to achieve to bring the inlet temps down) all that quickly. So adding a percentage of alcohol to the water helps with both of these issues.

For those who like the numbers. My friends Datsun, fitted with an SR20 running at a C/R of 10.5:1 uses no conventional intercooler, yet it runs 11.0 at 120mph. This is no pretty set up, it uses an atmo motor with a very old T3 on it. I guess that he has something working.

Although I concede that this doesn't address the longevity issue, you can make things work even though the magazine article's authors weren't so successful.

[project_x]

i know its from another forum but a good read

http://www.ausrotary.com/viewtopic.php?t=38929&start=0

sometimes magazine articles are not the be all and end all, but hey information is out there and its up to the induvidual to decide what is best.. i think post or pre has its pros and cons but the water injection pricipal has alot more benifits in general, more so what it does for the cylinder pressure as well.

see what you think

[JustenGT8]

It's not rocket science guys. You have a water droplet hitting softish alloy moving at 100,000+rpm...makes that droplet look pretty solid.

The smaller the droplet the smaller the problem it's that simple.

The only aspect that would worry me (and i swear by WI having run it on my past 2 turbo cars) is the day your pre-turbo water injection setup decides not to atomise well (very cold, partial blockage, act of god) is the day you kiss your compressor wheel goodbye.

[1jzracing]

It's not rocket science guys. You have a water droplet hitting softish alloy moving at 100,000+rpm...makes that droplet look pretty solid.

The smaller the droplet the smaller the problem it's that simple.

The only aspect that would worry me (and i swear by WI having run it on my past 2 turbo cars) is the day your pre-turbo water injection setup decides not to atomise well (very cold, partial blockage, act of god) is the day you kiss your compressor wheel goodbye.

AGREED!

.... maybe usable in a low milage high stress drag application or something where compressor life insignificant

[whatthe?]

So the lesson here is that although more expensive a post-turbo injection kit is going to pay for itself over time?

[project_x]

from what i have seen first hand , no compressor damage evident at 15km mark so the system that was used gets the thumbs up for me.. it may have alot to to do with the ammount of water used and the way it is atomised as well as the nozzles fail safe design.
( no acts of god ) have a read of the link i put up , its actually quite a good read.

it seems that the benifts of water injection would definatly aid the guy wanting to push standard pistons further as the reduction of peak cylinder pressure and raising the average at the same time as well as allowing more timing and leaner afrs.. seems too good to be true, but it works

[project_x]

from what i have seen first hand , no compressor damage evident at 15km mark so the system that was used gets the thumbs up for me.. it may have alot to to do with the ammount of water used and the way it is atomised as well as the nozzles fail safe design.
( no acts of god ) have a read of the link i put up , its actually quite a good read.

it seems that the benifts of water injection would definatly aid the guy wanting to push standard pistons further as the reduction of peak cylinder pressure and raising the average at the same time as well as allowing more timing and leaner afrs.. seems too good to be true, but it works

taken from another thread by bill shurvington(ausrotary)

K Stage 1

Intro: This has been covered before, but just to set the scene. Water is NOT passive in combustion, it aids the

conversion of CO to CO2, which is where most of the energy of combustion is released. It also helps cool

things down( in the process reducing the work done in the compression stroke) and prevents detonation.

You can replace a significant amount of the fuel with water allowing you to run at the best power AFR rather

than running overly rich and losing power. Disclaimer: I give not a stuff what is said on WI equipment vendors websites, so if I disagree with aquamist so be it. They are a pump manufacturer.

Pre-turbo WI: Compression in a turbo is usually adiabatic. This means that the air is heated as it is

compressed, which takes power from the shaft and requires removing through an intercooler. If you inject

water before the turbo, then you can move compression to near isothermal, so very little heat is added, and

less power is taken from the turbine to compress the air for the same boost level. You can loose the

intercooler and therefore suffer less pressure drop between compressor and inlet. All of which gives you the possibility to get more power out the same turbo.

Water has a very high latent heat of vapourisation, but once you have reached the saturation pressure in air, then you gain no more cooling at that point. However Dalton's law comes to the rescue at this point and if you bung in some other miscible fluids, say methanol and acetone, then each has its own saturation pressure, and you get an accumulative cooling effect. A little petrol would do the job if you added a second injector for it.

And here we hit the first problem. You need fine atomisation to avoid potential blade damage. For this you need an airshrouded injector, such as VW used in some of their CIS systems (hunting applications list for those). RX7s have an airpump that can be turned to this application. Other option is to weld a bung into the scroll as most of the compression happens here.

I need to run some numbers on exactly the effect of various fluids here, but imagine if you had cut the power needed to get the PSI wanted by a 1/3. You would get spool up at 2/3 of the gas flow before and could run at higher boost once you had spooled.

Post turbo WI: Here you are adding water to deal with combustion and detonation reduction. Ideally you would inject directly into the chambers to minimise any charge displacement. The OMP drilling in the housing would work nicely for this if you run premix. In terms of sizing you would be wanting to replace about 30% of the fuel with water, so size accordingly.

Quick note on A/R changes with WI: If you inject water directly into the exhaust, then it rapidly expands and turns to steam. In doing so it takes heat out of the exhasust, but the volume gain more than makes up for this. Tricky to implement, but can be used to change the effective A/R of the turbine, giving you a much wider operating range. MSD do a system for 2 strokes that uses this effect to change the effective tuned length of the exhaust to improve scavenging.

That's me out of time for now, but have a think and ask some questions. Remember, if you say 'but Mazda/aquamist/the lad with a supra on my block don't do it this way' I shall laugh maniacally and point you to the work of Sir Harry Ricardo on the rolls royce merlin engine in the late 30's. He was a genius.

Part 2b: water is good for your bang

below is a great mail written by Bob Harris a few years back explaining, in far more lucid prose than I could ever hope for. Key points to note in the text:

1. Water speeds up the key reactions releasing energy to the crank in a sharper peak. This means more power at the wheels. Note the comment that 2/3 of the energy released in combustion comes late in the cycle without water present at the beginning. This is less of a problem in a rotary than a piston, but you still lose leverage on the eccentric (note I haven't looked at it from a heat lost to the rotor perspective).

2. Water injection has been shown to give very significant increases in max power

3. At >35% WI it has been shown you can run under boost all the way back to stoich without detonation in piston engines. No reason a rotary shouldn't be similar. Extrapolating this you can see that you can also run more advance (more power) and also use AFR to control power output, rather than run stupidly rich just to prevent engine death, or backing off the spark so you loose lots of the HP you paid for.


Quote:

Let us take a quick look at ignition. Those who have a Heywood can look it up
- mines on loan so going by memory. The first thing that happens is a plasma
cloud is formed by the arc consisting of super heated electron stripped atoms.
When this cloud "explodes" a ball of high energy particles is shot outward.

The highest energy particles are the hydrogen atoms - and they penetrate the
charge about 5 times as far as the rest of the particles. As they lose energy
and return to normal temps - about 5000 k - they begin to react chemically
with any surrounding fuel and oxygen particles. 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 predominate 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 predominate 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 O
H 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 oxidization ( Glassman - Combustion Third
Edition ) of CO ==> CO2 is the "water method".

CO + OH ==> CO2 + H
H + OH ==> H20
H2O + O ==> H2O2
H2O2 ==> OH + OH
goto 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 definitily 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 usable pressure in a
timely manner.

As a side note - Volvo recently released some SAE papers documenting the use
of cooled EGR to both reduce detonation and return to a stoic mixture under
boost in the 15 psi range - while maintaining approximately the same power
output. Notice - they reduced fuel and still get the same power output.

When you consider that EGR consists primarily of nitrogen, CO2, and water ( to
the tune of about two gallons formed from each gallon of water burned ), you
might draw the conclusion that it also was not "inert". They peaked their
tests at about 18% cooled EGR - which would work out to about 36% water
injection and got about the same results under similar conditions that the
early NACA research got.





Makes you think doesn't it

Bill

[brett_celicacoupe]

i found something relevant to this old discussion.

effects of pre turbo WI:

[oldcorollas]

as for the chemical stuff... it is not just thermodynamics you need to be concerned with, but kinetics...
we use mixtures of H2, H2O, CO, and CO2 to choose oxygen partial pressures... but the reactions don't reach equilibrium that quickly... so need to be careful when saying that is one of the causes of the effects...

[twentyEight]

i found something relevant to this old discussion.

effects of pre turbo WI:

Brett,

Well done on those pics, that's exactly the effect I had seen in the magazine article...

[brett_celicacoupe]

the story on those pics is unknown so he might have had a garden hose nozzle.

then again he might have had the best nozzle money can buy

[JustenGT8]

Even the best nozzle can get a partial block and the day it does is the day it water jets your compressor wheel...hardly worth the risk when a post turbo setup is so easy these days.

[brett_celicacoupe]

make sure you put one before your supercharger when you put it on justen

i know i will be

[JustenGT8]

Already plumbed in

[worldwalker]

what sort of after market computer should be run with WI? I'm thinking of fitting on a 3s in an MR2, mainly because of the limited effect the intercooler has on the system. My understanding is that 3s run far to rich anyway, would there be a safe limit prior to needing an after market computer?