Water/meth injection: a theoretical and practical discussion

[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

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?

Pressure differential between the pump pressure and inlet pressure through the jet which creates an expansion.

Your a level is correct

[ashley]

So are you saying that because the pressure drops across the injection nozzle, the water effectively turns to steam as it is injected? Not what I have seen when playing with water, injectors and a pump on my bench!

Or are you saying it is more liekly to evaporate (and so it stays as a liquid)?

[raptor95GTS]

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assume so, all I know is that there seems to be many papers that document the cooling effect, even wiki (which is not peer reviewed) documents it.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

Water injection worked by reducing cylinder inlet temperature, thereby delaying the onset of detonation. As the water evaporated in the induction passages of the engine, it providing a prodigious amount of cooling to the fuel charge due to the latent heat of vaporization of the water. Cylinder inlet temperatures went from about 350􀁱F to about 100􀁱F. This increased the detonation margin to the point that up to 150 inHg of manifold pressure could be used. When water injection was in use, the engine was markedly smoother, and the interior of the combustion chambers stayed extremely clean with no carbon or arnish build-up on the piston crowns, valves, or ring packs. Frank remembers that “There was no hard carbon whatsoever. You could clean the top of a piston down to bare metal by wiping it with a cloth”.

German engineers tried water injection (Wassereinspritzung) on their gasoline engines, but with limited success. Germans, who were very good at uilding highprecision pumps, had perfected direct fuel injection for their large aircraft engines. German engineers injected water directly into the cylinders as well. Since the water did not have time to evaporate and cool the induction air, the large cylinder inlet temperature reduction was not achieved.

frank walker Pratt & Whitney Aircraft engineer.

[dazzz]

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?

Water injection worked by reducing cylinder inlet temperature, thereby delaying the onset of detonation. As the water evaporated in the induction passages of the engine, it providing a prodigious amount of cooling to the fuel charge due to the latent heat of vaporization of the water. Cylinder inlet temperatures went from about 350􀁱F to about 100􀁱F. This increased the detonation margin to the point that up to 150 inHg of manifold pressure could be used. When water injection was in use, the engine was markedly smoother, and the interior of the combustion chambers stayed extremely clean with no carbon or arnish build-up on the piston crowns, valves, or ring packs. Frank remembers that “There was no hard carbon whatsoever. You could clean the top of a piston down to bare metal by wiping it with a cloth”.

German engineers tried water injection (Wassereinspritzung) on their gasoline engines, but with limited success. Germans, who were very good at uilding highprecision pumps, had perfected direct fuel injection for their large aircraft engines. German engineers injected water directly into the cylinders as well. Since the water did not have time to evaporate and cool the induction air, the large cylinder inlet temperature reduction was not achieved.

frank walker Pratt & Whitney Aircraft engineer.

The last paragraph is very interesting.

[dazzz]

Maybe...

Rather than thinking about the air temps rising then being cooled by the water, what if because you are injecting water pre turbo the water is being put under pressure at the same time as the air so to speak. Maybe this would stop the temps rising so high in the first place

[GeorgeL]

The pressure drop across the injector (which acts like An orifice plate) turns the water from a full bore liquid to a mist spray.

It's just like an air cooling unit that doesn't use a refrigeration unit by means of dropping temperature. Instead it uses atomised water (large surface area) to do the job.

There are a lot of tangents being thrown into this thread though which seems to be confusing it all.

[ashley]

Cool...I'll walk away from it

[T.F.S.]

Maybe...

Rather than thinking about the air temps rising then being cooled by the water, what if because you are injecting water pre turbo the water is being put under pressure at the same time as the air so to speak. Maybe this would stop the temps rising so high in the first place

Maybe.

I know that the English/Americans were injecting pre comp too, maybe the Germans were injecting post comp which could explain the difference in results if any of that info is to be believed.

[2mad]

Heres another application using the same sort of high mist jet w/i uses for cooling air temps for outdoors spaces .

The quote "Mist Systems work by forcing water through our specially designed mist nozzles. This produces a fog-like mist of ultra fine water droplets that average 25 microns or less in size. High pressure mist cooling reduces the droplet size even further, to as small as 5 microns. Using just one gallon of water, our mist systems create a surface area larger than a football field. As you can imagine, the rate of evaporation is extremely fast."

During this rapid evaporation process, the "fog" of minute water droplets quickly absorbs the energy (heat) in the environment and evaporates, turning into water vapor (gas). The energy (the heat) that is used to convert the water into a gas is eliminated, whereby the air in the environment is cooled.


The original article.. http://southerncoolmist.com/how-pre-coo ... -work.html

[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

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)

That all sounds right to me.


The only way to see if anything injected into the inlet tract is decreasing the temperature and therefore increasing the air flow into the engine is to measure the air going into the engine with and without the fluid injection.

[bobhatton]

During this rapid evaporation process, the "fog" of minute water droplets quickly absorbs the energy (heat) in the environment and evaporates, turning into water vapor (gas).

The only "GAS" that water can turn into is steam and if i remember right the steam expands by 1400 times the volume of the water so will displace a very large amount of the inlet air.

[Danbob]

Before reading this thread I believed the following (read it in a book and it made sense to me)

Injecting post compressor, Pre Throttle Body:

1: The water stays a liquid (finely atomised liquid but still a liquid) until it enters the combustion chamber (Running 1.2 Bar boost, water would not become a gas until 123 Deg C + if the water had become a gas, it's volume would be hugely increased)

2: Water has a much higher specific heat capacity than air, so when the fine mist of water is mixed with the intake airflow, heat energy is transferred from the air to the water, and because the water's higher Specific heat capacity, it's temperature will not rise as much as the air's temperature falls. - Therefore the net temperature of the mixture will fall.



The only argument I've seen in this thread which would answer the above is Bob's - That between the post IC injection point, and the intake port, there is not enough time for the heat transfer to occur.

[Danbob]

During this rapid evaporation process, the "fog" of minute water droplets quickly absorbs the energy (heat) in the environment and evaporates, turning into water vapor (gas).

The only "GAS" that water can turn into is steam and if i remember right the steam expands by 1400 times the volume of the water so will displace a very large amount of the inlet air.

Beat me to it!

The only way to see if anything injected into the inlet tract is decreasing the temperature and therefore increasing the air flow into the engine is to measure the air going into the engine with and without the fluid injection.

So could we test the amount of air flow into the engine with and without WI by measuring the engine power output with ignition timing fixed and at a boost where the engine is not knock limited?

[bobhatton]

Before reading this thread I believed the following (read it in a book and it made sense to me)

Injecting post compressor, Pre Throttle Body:

1: The water stays a liquid (finely atomised liquid but still a liquid) until it enters the combustion chamber (Running 1.2 Bar boost, water would not become a gas until 123 Deg C + if the water had become a gas, it's volume would be hugely increased)

2: Water has a much higher specific heat capacity than air, so when the fine mist of water is mixed with the intake airflow, heat energy is transferred from the air to the water, and because the water's higher Specific heat capacity, it's temperature will not rise as much as the air's temperature falls. - Therefore the net temperature of the liquid will fall.



The only argument I've seen in this thread which would answer the above is Bob's - That between the post IC injection point, and the intake port, there is not enough time for the heat transfer to occur.

The temperature deferential, or total heat available in the boosted air flow is too low and the time they are both together is too short a time to give any cooling, but once the water is in the combustion chamber the temperature is so high that the water will boil very fast even under the greater pressure in there, absorbing large amounts of heat, reducing the combustion pressures and therefore reducing the octane requirements of the engine.

[bobhatton]

During this rapid evaporation process, the "fog" of minute water droplets quickly absorbs the energy (heat) in the environment and evaporates, turning into water vapor (gas).

The only "GAS" that water can turn into is steam and if i remember right the steam expands by 1400 times the volume of the water so will displace a very large amount of the inlet air.

Beat me to it!

The only way to see if anything injected into the inlet tract is decreasing the temperature and therefore increasing the air flow into the engine is to measure the air going into the engine with and without the fluid injection.

So could we test the amount of air flow into the engine with and without WI by measuring the engine power output with ignition timing fixed and at a boost where the engine is not knock limited?

The normal way on an engine dyno is with the inlet venture, Wilson grid or whatever the dyno has fitted to measure air flow,
I cannot think of any other way as any changes are going to be very small.

[Odin_S]

Didnt really want to get inbetween the mud slinging match but, I've previous not been interested in WI but with the idea it at the very least cools the cylinder walls perhaps not preventing cracking but at least helping stop it, I'm all ears

I'm in the process of a 400bhp build on a gt3076 on a PP SMIC and someone steer me to best non intrusive setup or should i just save my money for a CC?

[jimGTS]

I read somewhere, don't know how true.

But it also helps clean the internals, essentially a steam clean everytime it's used. Helping to remove deposits and evening out compression in each cylinder (basically helping and removing battle carbon build up on the pistons).


Many people are banging on about whether it cools the intake temps or not, but surely more important is whether it helps keep detonation at bay.

Many moons ago, on my rev5, tuning on the dyno, we switched Wi on and off.
Although Ryan (2bar tuning) didn't mention any change in intake temps, he did note reduced knock/det situations. Same boost/timing! Simply on and off test. Only for a pull or 2 to be fair.

So what about swinging this arguement around and consider it's reduced det possibilities, if you don't agree/believe/know it drops temps at least.

I have to say, on my power fc on my old car, intake temp reading on the commander, i don't remember any sort of decrease in intake temps. It certainly was not significant otherwise I would have remembered in sure.

I run wi today to help keep det at bay and to clean the engine, if I see lower temps, great, if not, not an issue.

So in saying that. I imagine a cc setup running wi would be quite bullet proof if tuned well.

[Danbob]

I don't think anybody would argue with you that WI reduces det. That fact is well proven a and is the main purpose of Wi.

The reason the charge cooling argument has gone on so long is because that is the aspect that is harder to prove

[raptor95GTS]

jimGTS - I know you're a bit particular about bits on your car, which WI kit did you go with? Or did I miss that in the last 7 pages lol!

[jimGTS]

On my old rev5 I had a progressive aem kit.

Currently have a basic coolingmist kit supplied by TFS.