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Water/alcohol injection for supercharged engines
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Author:  PetenSoaf [ Fri Apr 27, 2007 6:05 pm ]
Post subject:  Water/alcohol injection for supercharged engines
Does anyone here know much about the practicalities of water/methanol injection?
I've put one of Ben Aford's SC12 supercharger setups on an otherwise *very* standard 998 in my Moke. The system, as it stands, will comfortably make 15psi of boost at WOT with a few revs on board. Of course, with the 8-point-something compression of a 998 means that detonation starts hammering away at anything over about 8psi. Undoubtedly, this isn't helped by the massive post supercharger temps that can be achieved - I have seen the supercharger to head manifold get over 100 degrees on a hard run.

Now, I've cobbled together a home made water injection setup consisting of an old EFI fuel pump, a pressure switch and a fogging nozzle capable of delivering 50ml of water per minute at about 40psi into the supercharger intake. I've set this up to trigger at 5psi and, with it running, I can happily push up to 11-12psi without detonation - the manifold is significantly cooler - I haven't seen over 80 degrees with the water running.

Does anyone have any experience with running a water/methanol mix iin a system such as this?

As I understand it, water has a far greater heat capacity than methanol so it will essentially absorb more heat before it flashes to steam, thereby cooling the intake charge more. . .but methanol is, in effect, a high-octane fuel, so injecting it should raise the detonation threshold somewhat. . .common sense says there is an 'ideal' water/methanol blend that can be used. . .

Any ideas??
Author:  JC [ Fri Apr 27, 2007 7:16 pm ]
Post subject: 
No idea. However, there is a 'intelligent' box you can buy that takes an intake manifold temp (or air intake) reading couples that with boost pressure and injects the mixture at a pre-determined level.

The reason for taking the inlet temp reading is so you aren't using the water/methanol at low temps when its not really required.

I shall find the link.
Author:  JC [ Fri Apr 27, 2007 7:20 pm ]
Post subject: 
Could be one of these articles, couldn't be bothered reading through them...

http://autospeed.drive.com.au/A_107970/cms/article.html

http://autospeed.drive.com.au/cms/article.html?&A=0527
Author:  Mokesta [ Fri Apr 27, 2007 7:25 pm ]
Post subject: 
A mate of mine used to run WM injection in a Starion with high boost and no intercooler. He used a 50/50 mix after trying different ratios. Pure methanol gave more power on cold nights but allowed too much detonation when temps were higher.

I think you just have to ensure that the water is clean and not too salty or mineralised. Many EFI pumps run the terminals in the fluid because petrol isn't a conductor. Salty water is and you may burn out the pump.

Does your fogger nozzle or other part of your system include a check valve? An anti-siphon valve is needed of you run the nozzle on the engine side of the butterfly, but you don't.
Author:  PetenSoaf [ Fri Apr 27, 2007 7:38 pm ]
Post subject: 
In regards to the water burning the pump out - I'm using water that is about as clean as it gets - 'Milli-Q' water (has been through reverse-osmosis and anion-exchange filters). That being said, I fully expect that the pump wont last long - after all it is designed to pump fuel and will probably rust solid fairly quickly. This is really only a test system to see what works best - after I've sorted it, I can buy a proper150psi water injection pump.
No check valve is needed either - tank is lower than the supercharger (it's in the rear footwell, behind the drivers seat) and there isn't enough vacuum to draw a significant volume of water out of the tiny fogging nozzle at idle.
By the way your mate's Startion reacted, it looks like the theory is correct - water for cooling, methanol for power.
Author:  DOZ [ Fri Apr 27, 2007 8:57 pm ]
Post subject: 
Spraying water/methanol is so retro, like from the 80's dude. Get with the program and get an intercooler. :lol:

Spraying water makes steam - thats cool (well the air is cooler) but the problem is steam is superheated water vapor, and it don't contribute to making power, it just displaces air. You get less air charge in as some is displaced by the steam, hence less power for the same boost (compared to using an intercooler). There is an advantage if the water vapour enters the combustion chamber in that on combustion it adds pressure by forming steam but compared to petrol/air combustion pressure it's bugger all.

Methanol is not much better, it displaces air too when turning to vapor but since it has an OH molecule it burns itself so does contribute to power. The energy released in this process would be less than the energy if you had the equivalent intercooled air and petrol though. It is highly corrosive so I would make it a 50/50 mix and make sure you keep it from leaking into the engine!

If you inject NO2, thats a different story as you should already know it does the same thing as the water injection (ie - cools the charge) but it also adds lots of oxygen to the mix, so you just need to add some more fuel.

I guess if you want to continue with it you need to be able to remotely adjust the amount of water/methanol mix and boost as you go, you will find a balance point where the engine won't take any more of either. The problem doing this is that at high engine speed the detonation will not be audible and will result in damaged pistons, even broken ring lands so be careful.

Regards

Daniel
Author:  PetenSoaf [ Fri Apr 27, 2007 9:29 pm ]
Post subject: 
You're a braver man than me if you're game enough to intercool a draw through super/turbo charged engine. . .
Author:  slinkey inc [ Fri Apr 27, 2007 11:01 pm ]
Post subject: 
As I recal Ben uses it on his race car.

I've seriously considered it, but with my current compression it doesnt detonate of full boost, being a 1330 and my timing is pretty, err. retarded aswell.

I would like to do it on another motor later with more boost. A motor built for supercharging.

And as said above intercooler, out of the question.
Author:  DOZ [ Sat Apr 28, 2007 10:30 am ]
Post subject: 
Ok guys, you obviously don't know what laughing out loud means - usually it means a joke or sarcasm, take your pick....

If you read my post properly you would see I said to use 50/50 mix and have a remote adjustment (usually a throttling device such as a needle valve) to vary the amount going in.

Image

Some people use different sized nozzles to vary the qty injected but this takes forever to make adjustments as you have to pull the nozzle out and change it. Where you place the nozzle/s will also change the intercooling effect, I would start close to the blower.

The other parts such as the pump etc you already have.

Take it to a dyno with a couple of different pulleys and slowly up the boost and add the water/methanol mix, find the point where no more power/torque is made and the engine is not detonating.

Also make sure it doesn't leak into the motor when it's turned off or you'll end up with all sorts of problems such as corroded pistons/rings.

Nb - I have had experience with this on turbo cars but gave up years ago as most of the cars ended up with an air-air intercooler.

Daniel
Author:  slinkey inc [ Sat Apr 28, 2007 12:25 pm ]
Post subject: 
DOZ wrote:
Ok guys, you obviously don't know what laughing out loud means - usually it means a joke or sarcasm, take your pick....

Daniel



Ah fair enough, I wasn't offended I thought you were laughing at us for not using an intercooler, because you may not have known that we can't.

Water injection can sit as a shelved idea I'm thinking about programable igntion at the moment.
Author:  69elf [ Sun Apr 29, 2007 6:52 am ]
Post subject: 
I'm no expert, but I believe that there are water cooled intercoolers and while I know you can't add an intercooler to the blow through sc kits, I wondered if someone talented could make a water cooled inlet manifold for the sc12 kits to drop the inlet temperature?
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