Well I've read all 5 pages of that above... interesting approaches, of which there are two basic ones
Hill'n'folks and Gregs!
I've been checking this out from across the Atlantic, on the UK and Euro side, remembering that Ricardo himself was probably the first to look into WI for IC engines in any detail, and his graph plot of overfuelling aero engines and then when that reached its limits of detonation suppression, substituting water injection. We're talking 1930's here and that plot still stands and is frequently reprinted to show what benefits are attainable in a spark ignition engine -
Pratt and Whitney, Rolls Royce and subsequently the Germans were the main champions of this, P&W developing it to a very high level - in fact it was the difference between some of their engines surviving war power settings - or not :roll:
Applied to a diesel things are a bit different, but not much.
The difference between Hill'n and Greg is obviously
1) cost DIY Vs Pro approach
.. which cannot be resolved, you're on one side or the other depending on thickness of your wallet;
2) Where and how to inject
Something that hasn't been mentioned, as such, is that 2) is very much influenced by whether short term boost cooling or long term steady state WI is anticipated.
Whilst Hill'n uses it mainly 'just for passing', this is no substitute for an intercooler when a diesel is in a heavier vehicle than a car. Even my AAZ Transporter (vanagon), a draggy shape weighing nearly 2 tons empty, requires 9-10 psi to cruise at the legal limit over here (70 mph).
Long term WI needs to be efficient and reliable at these boost and power levels, and Greg has his figures spot on, between 150 and 300 cc/min to give sufficient equivalence to a good IC.
He also advises higher pressures, better atomising nozzles and some means of ensuring that WI is boost related and cannot inject below a threshold boost - in fact atmospheric pressure would be the minimum, but 7-10 psi makes sense.
And post turbo injection - this is Aquamist's solution too (and unless for a 'bad' hot underbonnet installation, post intercooler too).
Aquamist in the UK were responsible for supplying the equipment for all the World Rallye car WI systems, so successful they all went that way eventually, and have now been regulated against in that sport.
They are also repsonsible for the WI systems of the recent Diesel World Speed Record 350mph by JCB Diggers (Ricardo, still an important IC engine research outfit, developed the engines). Apparently the tyres ability to transmit more power prevented further spped incraeses, not power.
Their top pump isn't cheap, but the main thrust of their equipment is high pressure, high reliability and nozzles that atomise extremely well under those high pressures. This is Formula One type stuff, the pump designed from scratch as the ultimate WI pump. they do a cheaper higher capacity one too, but their Race Pump is the dog's (about $300). Their control systems and instrumentation also extends to Formula One type levels, but as I say, World Rally Championship regs have now banned these systems (proof of the pudding!)
As Greg says you need at least 10 bar (150 psi) to do the job properly, to keep the flow rates down you need the massive surface area of fine droplets.
This cools the charge, but there is a lot more going on in the cylinder than a lower charge temperature when 25 to 50% of fuel weight of water is being injected. In fact benefits are still accruing beyond these quantities, if the engine and boost flows are sufficient to utilise them. 100% is possible but eventually the engine will flood, not come to harm, but simply unable to handle that quantity.
One of the main benefits is that the cylinder pressure curve is smoothed out, peak temps come down, but energy absorbed in the early stages of combustion is released later... this can only be beneficial and those having trouble with rod/ring and bottom end strength, as well as head temp issues at high boost levels should really look into this seriously.
Injecting pre-turbo at significant and useful quantities long term has definitely been seen to to erode compressor impellers. For a few seconds here and there, maybe not.
Also, 10% methanol to prevent freezing is probably the best compromise, thats what they tend to use, water has all the other properties required and as a substitute for an intercooler, where WI automatically starts above a certain boost level, 50/50 starts to get expensive as well as a pain in the butt to organise.
But the key to really good WI efficiency, is good control of flow rate, boost dependent and extremely highly atomised before entering the cylinder - you then get charge density benefits + additional in cylinder power enhancement without any risk of overdoing it.
This is not saying Hill'n isn't having great fun developinga and using his grassroots WI system - it sure sounds like it works, as a quick and cheap way of cooling things down and getting better charge density. But its not the way that the pros have found works best when the chips are really down.
http://www.aquamist.co.ukHas some excellent information, but hard to find on their site... look at technical and resources. Here are the JCB diesel World Record breaker links if you are intersted:-
http://www.aquamist.co.uk/dieselmaxhttp://www.jcbdieselmax.com/html/home.php
