Water/meth injection: a theoretical and practical discussion

[bobhatton]

Just chiming in.. no water does not need to boil to evaporate. It is evaporating all the time just at room temperature. Just not at a noticable rate.

Water has 3 states, ice, water and steam. So if it has not boiled it is still water

[T.F.S.]

Turbos sometimes get a little bit hot, they also pull quite a vacuum which allows the water to boil at a much lower temperature and then we have explosive evaporation at the tips of the blades..

The simple evidence for this is that pre compressor water injection has proved many times to result in moving the true operating point to the left on the compressor map.

For more info please read here.
http://www.aquamist.co.uk/vbulletin/sho ... .php?t=251

[dazzz]

Just chiming in.. no water does not need to boil to evaporate. It is evaporating all the time just at room temperature. Just not at a noticable rate.

Water has 3 states, ice, water and steam. So if it has not boiled it is still water

Water is constantly evaporating and condensating at the same time. The rate a which it does this depends on the energy within the water If the rate of evaporation is greater than the rate of condensation the water will disappear.

[dazzz]

Turbos sometimes get a little bit hot, they also pull quite a vacuum which allows the water to boil at a much lower temperature and then we have explosive evaporation at the tips of the blades..

The simple evidence for this is that pre compressor water injection has proved many times to result in moving the true operating point to the left on the compressor map.

For more info please read here.
http://www.aquamist.co.uk/vbulletin/sho ... .php?t=251

Surely you're looking to cool the air after the turbo, once the air is pressurised and heated. To do this the water would need to be fluid/mist when it comes into contact with the hot air. If it was injected before the turbo and atomised before the turbo, all the cooling is done before the turbo. This would also change the density of the air.

Also a lot of the water mist would be cooling the turbo itself.

Still intersted to find out the change in effective octane when injecting methanol.

[2mad]

water does not need to boil to evaporate.

Agreed


http://www.straightdope.com/columns/rea ... ling-point

[T.F.S.]

The issue I am trying to deal with here is Bobs comment that there is no cooling of the inlet air via water injection.

The air is heated inside the turbo is it not? If we cool it there we are doing as good a job as anywhere else, even better in some respects as it has other advantages, the RAF chose this injection point also.

Octane depends on the amount of methanol you inject I would imagine.

[dazzz]

I am ex RAF. I do know a little more than I'm letting on.

I understand what you saying.

Let's say you have a long pipe coming off your turbo, goes all around the engine bay and boot then into the throttle. The amount of time the air has to be cooled is quite a bit.

If you've got a pipe coming off the turbo, over the top of the engine and straight into the throttle, the time it takes for the air charge to reach the throttle is tiny so the time period for cooling is very very small.

I don't think the water has the space or time to make a significant change to the charge temps.

Why is it you don't use a water to air intercooler also.?

[T.F.S.]

Any info you could add on what the RAF did would be mega interesting.

I deemed that I didn't need it, methanol seemed to reduce the intake temps so well I could run without it, seems like I was right or the engine would have gone bang, it ran for years like that.

[dazzz]

What would you do if you needed to take the car on a long journey. Say to nurburgring.

I wasn't propulsion in the raf, as I say I'm not really to clued up on the ins and outs. I started as avionics then went for commission. I can tell you anything you need to know about administering alcohol to the human body though.

I'll ask someone I know to explain the theory and how much fluids are used. I don't know what temps a turbo fan engine runs at but I imagine its higher than a 3sgte.

Could you post a photo of your setup with a few labels.

[T.F.S.]

I dont drive to/around the nurburgring, it was a fast road car.

I have a whole bunch of pics and data logs on the thread I linked earlier.
http://www.imoc.co.uk/forums/viewtopic. ... &start=140

[ashley]

Just chiming in.. no water does not need to boil to evaporate. It is evaporating all the time just at room temperature. Just not at a noticable rate.

Water has 3 states, ice, water and steam. So if it has not boiled it is still water

So (and this is all a question): when we are talking about water evaporating in the inlet tract (injecting after the turbo/ before the TB), it stays as liquid suspended in the charge air (similarly to humidity)? So any cooling effect is similar to the evaporation effects we see on our own bodies when moisture evaporates.

We are NOT talking a phase change in the inlet tract, and the significantly larger cooling effects that this entails in all the complicated calculations that have been linked to. Phase change from water to steam requires significant energy as an input, and so would only occur within the combustion chamber- which is where we would expect to see the real benefits of water injection.....?

In other words:

When injecting water post turbo & pre TB, it may give a minor intercooling effect in so much as it cools the air to the extent that the water injected was already at a lower temperature.

The main effect is the additional water is now present in the combustion chamber during combustion, and is converted to steam as part of combustion, so absorbing some of the energy that would otherwise manifest itself as increased combustion chamber temperatures.

Or as Bob says: water has no intercooling effect, the effects are all within the cylinders.


Or have I completely misunderstood?


(And note- I'm talking about the effects in relation to water, not methanol)

[T.F.S.]

Every paper or site I look at says otherwise, intercooling effects of water injection seem very well documented.

[ashley]

So which part have I misunderstood? Is water going through a phase change in the inlet tract? Genuine question

[T.F.S.]

I would assume so, all I know is that there seems to be many papers that document the cooling effect, even wiki (which is not peer reviewed) documents it.

I cant find any tests to support otherwise though, can anyone else?

[GeorgeL]

So which part have I misunderstood? Is water going through a phase change in the inlet tract? Genuine question

Yes mate it is due to pressure not temperature

Which is why it does indeed have a cooling affect. (Water on its own)


(No doubt bob will argue with me on it. That's why I haven't posted but I've read a lot of poo recently regarding this)

[dazzz]

I've had a quick browse through the topic you posted.

Thing for me is a lot of your data is based on temp readings which I don't know are accurate or not.

But then you write this

Just adding this graph that a lot of you might find interesting.

Image Replaced With URL For Quote http://www.pballandmore.com/images/wate ... essure.jpg

It goes some way to show why it is that my engine is in one piece where other MR2 engines have simply gone pop...like I said in page one, its all about cylinder pressure and detonation.

The water cools the walls of the cylinder preventing the cracking some engines suffer, it cools the piston, it cools the inlet, lowers EGT, reduces cylinder pressure, increases the octane of the fuel, reduces knock.

When used pre turbo it also spools the turbo earlier as it changes the density of the charge, changes the mach speed of the compressor, allows the turbo to flow more/hold on to its power for longer and pushes the turbo towards an isothermic state.

If you also add methanol into the mix it just makes the turbo go mad!

Turbo cars need WI...

I would agree with the first part of this 100%

I don't know what happens to the turbo, I'm not big on turbos.

[dazzz]

I believe this is why you're getting the performance you are. I'm guessing the methanol is also making a massive difference.

With your car, what would happen if you were to also add in a usual smic? Surely you'd get better results, you'd have more chance of cooling the charged air before ignition?

[T.F.S.]

I wanted fastest spool, to test the theory I removed the eBay SMIC and went hard.

If it was replaced the efficiency of the intercooler would be decreased with the pre intercooler injection points maybe.




Also high pressure increases the boiling point of water, this makes evaporation less likely.

[ashley]

So which part have I misunderstood? Is water going through a phase change in the inlet tract? Genuine question

Yes mate it is due to pressure not temperature

Explain that to me...you have increased pressure under boost, which increases the boiling point of water, so making phase change less likely...or is my A-level physics letting me down?

[raptor95GTS]

WWII aircraft used WI in the inlet of the supercharger, achieved 100degF air intake temperature drops. I'd guess those engineers used the right equipment to measure their data

Not necessarily, technology has moved on "slightly" in the last 60 years or so...

aye technology might have moved on, human brain power might not have moved on in step