Article on The Internet Mini Encyclopædia
I've been reading up on water injection over the last couple of days and what I have read pretty much backs up what I already knew. I've also discussed it with a certain tuner who'd rather not be named. Here's the gist:
Water injection is used to cool the combustion chambers on some high compression turbo engines, not the charge as some people think - that's the job of the intercooler or charge cooler. The idea is that the water will cool the surfaces within the combustion chamber in much the same way as excess fuel does. However using water rather than excess fuel has three advantages:
1. Water is a lot cheaper than fuel.
2. Water doesn't produce nasty emissions.
3. Water will not wash the oil off the bore like excess fuel will, so water injection will give a longer engine life than simply running rich.
A few years ago there was a lot of talk about using water in lean burn engines to allow engines to run leaner mixtures without running too hot and pinking, or worse still burning valves or even melting holes in the pistons. Of course when you are trying to set up an engine for maximum economy running richer is not an option, so point 1 above applies doubly. Points 2 and 3 are still as valid in this application. And this is where we come to the snake oil comes into it. Some people who have heard about the use of water injection in high performance blown engines have jumped to the erroneous conclusion that water injection alone is a performance aid in it's own right. The performance benefits on a blown engine are indirect, if you have and engine that starts to detonate at say 10psi so you have set peak boost to 9.5psi, simply bolting on water injection will not increase performance, what it will allow you to do is increase peak boost.
I have seen kits sold as an aid to economy, of course this only works if the mixture is leaned out accordingly. Although there has been talk of water injection allowing you to run higher compression ratios I can find not mention of this is my reference materials, nor can I see how it would work. In order to run higher compression you need a higher octane rated fuel (that's what octane ratings are after all) and I can't see how water would increase the octane rating of fuel.
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