Water/meth injection: a theoretical and practical discussion

[ashley]

Tell me about it- it would be great to devise an experiment to finally prove it one way or t'other...at the moment all I can see is two very compelling, but opposing arguments as to what water injection actually achieves!

I was thinking how to prove it- I think you'd need to set up a test rig with compressed air flowing through a tube, with a water injection nozzle in the tube, and some means of removing the water droplets from the air after the nozzle. You'd then use 3 thermocouples- one before the injector to give you a pre-injection air temp, one after the injector to replicate what we currently see (water + air), then one after the water droplet filter to measure the temperature of just the air.

If water vapourisation does indeed produce an inter-cooling effect then you should see a temperature drop between the first and last thermocouples.

But...how do you remove the water droplets withour effecting the air temperature? Would a fine filter work?

[2mad]

Tell me about it- it would be great to devise an experiment to finally prove it one way or t'other...at the moment all I can see is two very compelling, but opposing arguments as to what water injection actually achieves!

I was thinking how to prove it- I think you'd need to set up a test rig with compressed air flowing through a tube, with a water injection nozzle in the tube, and some means of removing the water droplets from the air after the nozzle. You'd then use 3 thermocouples- one before the injector to give you a pre-injection air temp, one after the injector to replicate what we currently see (water + air), then one after the water droplet filter to measure the temperature of just the air.

If water vapourisation does indeed produce an inter-cooling effect then you should see a temperature drop between the first and last thermocouples.

But...how do you remove the water droplets withour effecting the air temperature? Would a fine filter work?

Love the way your thinking I had the same thought, problem is the mesh filter stopping the water would be cooled by the water then cool the air passing through it
Like I said i think this is a proper catch 22

But for anyone reading this wondering should I spray water/meth the answer is YES how it works is obviously debatable but it works brilliant, its better than driving your car on the coldest winters day on the hottest summers day.

[GeorgeL]

I'll try not be too geeky with this... So in simple:

Heat travels from hot to cold

Heat absorption and rejection is more affective the larger the surface area you have.

So having an injection of water/meth gives you a light mist (large surface area) which is at a lower temperature than the "dry" air it is going to be getting sprayed into.

The temperature of the "dry" air before the water/meth injection will be dropped as the state/phase transition of liquid water/meth to water/meth vapour occurs as the air passes through the water/meth.

In a small system like our cars, the heat energy transfer isn't massive but it's enough to drop the charge temperature significantly.

To answer the question... Water/meth injection DOES cool the inlet air.


I'm currently trying to design a non-intrusive sub cooling system for my BMIC which instead of using water/meth uses a compressed gas coil with a pressure drop across it.

[2mad]

Cheers George I new I was right lol

Looking forward to seeing your non-intrusive sub cooling system, that sounds fascinating

[GeorgeL]

Bob is also correct in what he originally said though about potentially dropping power. It's all about getting the volume being sprayed in spot on. Tbh though given that we are not in this at a Motorsport level with a deep bank account for research and development I'd say we are doing ok .. A single jet before the TB operating on boost pressure vs throttle position is fine.

Haha thought I'd make it sound fancy. It's quite basic.. Just awkward to try and squeeze in and the added weight of a compressed gas bottle isn't ideal. As always... Pros and cons

[ashley]

The temperature of the "dry" air before the water/meth injection will be dropped as the state/phase transition of liquid water/meth to water/meth vapour occurs as the air passes through the water/meth.

This assumes (and as I think Bob disputes) that the liquid is actually evaporating prior to entry into the cylinders, or whether it is entering the cylinders still in suspension.

I don't dispute that injecting water/meth gives benefits, I'm just curious to understand the actual mechanism through which this benefit is achieved...I'm also nervous that the apparent drop in IATs that is seen is not actually a function of the charge temperature dropping...this means that if I'm logging IATs to monitor engine health I may be using incorrect data when injecting water/meth.

Ultimately you are right- it's an academic argument for our cars, and I will probably continue to inject water/meth pre-TB...but I do like to understand why!!

[GeorgeL]

It's like running your car on a cold damp morning where the air is "dense" and there is a lot of moisture in the air as opposed to running it on a warm dry day where the air isn't as "dense"

You can really feel and see the difference in performance if logging

[JD]

Well, this thread is interesting

On another note I've been quoted £75 for welding in the boss for the injector. Is that a bit steep? I know ally welding is a bit of an artform.

[Nic]

Well, this thread is interesting

On another note I've been quoted £75 for welding in the boss for the injector. Is that a bit steep? I know ally welding is a bit of an artform.

That's very expensive for what is a simple and quick job, I recently had a bracket repaired on an aluminium intercooler which cost me £10 cash. Try to find a one man operation local to you.

[2mad]

Well, this thread is interesting

On another note I've been quoted £75 for welding in the boss for the injector. Is that a bit steep? I know ally welding is a bit of an artform.

That's very expensive for what is a simple and quick job, I recently had a bracket repaired on an aluminium intercooler which cost me £10 cash. Try to find a one man operation local to you.

Holly cow that is pricey, most welders charge £30 ish per half hour and its not going to take much more than that to weld in a boss
Are they going to tap the threads for you or is the boss already threaded.

Edit .. I would be very surprised if a back street garage charged you more than £30

[JD]

As I thought. The boss is already threaded, and I have the correct tap now anyway, so would have done that part myself if it wasn't.

Eeeeh back to looking up welders.

[2mad]

Yeah get looking at your local back street garages £75 pre-theaded is Crazzy.

Edit.. My mate runs a back street garage and my brother inlaw run a top performance tuning shop , so maybe I just get really good deals. But £75 seems a bit excessive .

[bobhatton]

I'll try not be too geeky with this... So in simple:

Heat travels from hot to cold

Heat absorption and rejection is more affective the larger the surface area you have.

So having an injection of water/meth gives you a light mist (large surface area) which is at a lower temperature than the "dry" air it is going to be getting sprayed into.

The temperature of the "dry" air before the water/meth injection will be dropped as the state/phase transition of liquid water/meth to water/meth vapour occurs as the air passes through the water/meth.

In a small system like our cars, the heat energy transfer isn't massive but it's enough to drop the charge temperature significantly.

To answer the question... Water/meth injection DOES cool the inlet air.


I'm currently trying to design a non-intrusive sub cooling system for my BMIC which instead of using water/meth uses a compressed gas coil with a pressure drop across it.

Methanol will drop the charge air temperature, but it is a fuel and should be treated as an injected fuel.

Water never has and never will cool the charge air temperature, all its work is done in the cylinders.

Because Methanol and water do different things the injection point and when and how they are injected are not the same. The only reason they are used together is because they mix together.

[bobhatton]

Not arguing- just want to understand why we see lower IATs when injecting water then? Is the water "fooling" the sensor?

To answer my own question: the IAT sensor is also reading the temperature of the water being injected, so the reading is no longer a pure inlet air temperature- it's an average of the air temperature (higher) and the water droplet temperature (lower).

My interpretation anyway...

So...is water injection actually producing an inter-cooling effect at all?? If my explanation is correct, then no it is not.

Starting to understand Bob's prior comments on this now (I think)

I find this theory very interesting, is the IAT sensor is being cooled by the water and not the incoming charge of compressed air
I have been thinking on this and its a proper catch 22, How can I devise an experiment to read just air temp with out the sensor being cool by the sprayed water/meth (18c in the tank temp ish)

If it is the case the the IAT sensor is being cooled by the water/meth it would make for a much more efficient setup to fit a resistor instead of the temp sensor, clamped to 25c and fit 4x 0.3mm injectors, one in each of the 4 runners like bob suggested .

Personally I think water/meth cools the incoming charge but inlight of this new theory I cannot prove it


Kev.



Edit.. For the record the k type thermocouple sensor I used for the vid I posted ^ was about the size of a grain of sand sandwiched between two thin pieces of plastic .
I really couldn't say how much the sprayed water/meth affected it temp wise, at the time I didn't think it would be by much.

If the inlet air is cooled the total mass, weight of the air going into the engine will increase, so all you need to do is to measure this air flow with and without water or methanol injection.

I and lots of others have done this over the years so we know what happens.

[2mad]

Haha thought I'd make it sound fancy. It's quite basic.. Just awkward to try and squeeze in and the added weight of a compressed gas bottle isn't ideal. As always... Pros and cons

Defiantly start a new thread or pm me, sounds wicked, if I can drop my intake temps im in

[JD]

Bob if you have the time to go into detail, I'd be interested to read about some of the setups you've built over the years and how these worked, because you keep dropping tidbits of info without ever really expanding on it. I do understand what you are talking about.

For instance, where would your injection points be if injecting separately? Pure methanol before the throttle plate and water directly into the manifold? That would seem to make sense based on what you've said. I don't suppose many people with road cars would like a tapped tank of pure methanol in their cars. So, for road cars, it is safer and more practical to inject together, so methanol can both cool the intake charge and increase octane, and water can provide additional cooling in the cylinder when evaporated there at higher temp?

[JD]

Haha thought I'd make it sound fancy. It's quite basic.. Just awkward to try and squeeze in and the added weight of a compressed gas bottle isn't ideal. As always... Pros and cons

Defiantly start a new thread or pm me, sounds wicked, if I can drop my intake temps im in

seconded. do start a thread on that

[2mad]

Methanol will drop the charge air temperature, but it is a fuel and should be treated as an injected fuel.

Absolutely I tuned my car to take advantage of the meth .

So what your saying is meth will cool intake temps?

Just trying to get to the bottom of this Bob and you have way more experience with this than me.

Ps. For anyone that interested, on boost using a mines ecu 10.8 afr was the magic number with 50/50 water/meth sprayed at 0.4 bar using a 0.7 jet (440cc injectors using a hks vpc).
I know all cars are different but it might help (11.5 afr on boost no water/meth)

Any lower afr the car lost power and any higher afr the car lost power

[GeorgeL]

I'll start a thread on it once I've got something put together. At the moment it's only on paper

No doubt I'll be told that it's wrong aswell lol

[raptor95GTS]

for water injection, read about the the stuff they did for WWII fighter engines, guy called Frank Walker. WEP Bear in mind, aircrews lives depended on this, not just pride on a 1/4 mile run so when they did it, they did it right.