|
Typical water injection systems spray a mist of water droplets into the intake. This mist, consisting mostly of fine droplets of liquid water, doesn't do a whole lot by itself, because typically you'd spray at most a 1:4 ratio of water to fuel. The water mist that does vaporize will cool off the intake charge, but not by a lot. Most of the cooling occurs within the combustion chambers themselves, as the water mist absorbs heat from the charge being compressed, and then vaporizes. If you could optimize the spark and fuel maps to take advantage of this cooling effect, then you could get some modest fuel economy gain there.
Now, you could set it up so that you would inject very hot water into the intake. Although it is counterintuitive, this may also give some fuel economy gain because the hot water mist will more completely vaporize than with traditional water injection. This will displace the air in the intake such that less oxygen is being drawn in than before, and your throttle plate would have to open a bit more to compensate. This would lower intake manifold vacuum, and since the engine would not longer have to work as hard to make that intake vacuum, it would use less fuel than before.
I use a variant of the second type, but I use fuel instead. The 12-hole fuel injectors spay a very fine mist into heated intake air, which causes the fuel to mostly evaporate. This lowers the amount of work each piston has to perform to suck in the intake charge, and has the added benefit of more uniformly mixing the fuel air mixture. I saw a 11% improvement in fuel economy by switching to these injectors, and am going to press on with an auxiliary hot water injection system to verify this idea will work.
|