If any of you have looked into water injection systems you know that there are no systems out there currently made for enhancing fuel economy. Everything out there is built to cool down the intake air charge so the engine can suck in cooler/denser air which creates more horsepower. This is not really what we want our system to do. I'd like to throw out my ideas on water injection and see what everyone thinks. Please comment if you feel anything I say is incorrect or you wish to clarify anything.
Lets start out with what we want the water injection to do and why. For us, we want water injection to replace the large droplets of fuel that will not aid in generating power. Fuel vapors are what create most of the power. These large droplets of fuel burn too slowly to produce (much) power and are still burning by the time the exhaust valve opens. The burning droplets exit the combustion chamber and continue to burn through the exhaust system. This is simply wasted fuel. If we can replace the large droplets of fuel with water we eliminate the waste. But, if these large droplets contribute so little to power output, why do we need them at all? Well, these large droplets of fuel absorb the heat created when the air/fuel mixture explodes. Without them the explosion releases too much heat for the surrounding metal to absorb and eventually something fails and you throw a rod, crack a piston, etc. This is what happens when a fuel mixture leans out too much. So, we inject water (in some form) to absorb this heat.
Now, onto the actual water injection system, and the problems with the commercially avaliable units. The commercially avaliable units made today are, as I mentioned before, made to cool down the air intake charge (for the most part). The better units meter the amount of water injected based on engine load. This is a necessity for our own application. The problem I see in most commercial units is that they inject water before or at the throttle body. Most modern intake manifolds are not designed to flow airborn liquids through them as previous carburated or throttle body injected manifolds were. This ends in unequal water distribution between cylinders. The result is that some cylinders will run hotter than others due to lack of water. Another problem is that they are not meant to be run constantly. They turn on during high engine loads and then turn back off when engine loads are light. This would not be the case in our situation. We would want the water to always be being injected, but as mentioned before it would be metered by engine load. This brings up the duribility of the components of the commercial units. Will it hold up under constant use? There is also the question of how well the water is metered for injection. A lot of commercial units use the map sensor and adjust water injection based off it's signal. That again is not enough for us. I don't believe this is a very accurate way of metering water injection. Water injection for fuel economy must be treated as precisely as fuel injection if we are to attain good effeciency and results from the system.
Now for my ideas:
Injection location - I think a properly designed system will inject water in the same general location of the fuel injectors. In most cases this is the area where the intake manifold and head meet. This ensures proper water delivery to each cylinder in modern engines not designed with a 'wet' intake manifold. This of course presents problems like complexity and increase price.
Constant use - I'm not sure where you can find a water pump designed to run constantly that will give you the pressure needed, work off 12V, and be inexpensive.
Water metering - This is where I really think improvments can be made. In order to maintain peak thermal effeciency of the engine we would want to control the water injection while referencing exhaust gas temperature. As far as I know, no commercial system does this. However, it makes perfect sense to me.
So, thats basically my very complicated setup ideas...