Aquamist System 1s
By Chris Henry

First, things first... what is a water injection system? Water injection has been around for over 50 years. A fine mist of water is sprayed into the incoming air. The water then evaporates which effectively cools the air and some often remains in a liquid mist form where it actively absorbs heat during combustion. Both ways, it reduces the temperature inside the cylinder which reduces the chances of predetonation or ping. Another effect of water injection cooling is more power. Water injection produces more power a few different ways. First, the air coming into the engine is cooled. Cooler air is more dense and contains more oxygen. The second way water injection can improve power is by allowing more advanced timing or more boost. Basically, running with water injection is like running high octane gas.

Let me quickly point out that water injection is mainly used in turbo charged or supercharged applications because they need it most and benefit most from it. A normally aspirated low to medium compression engine will not generally benefit from this system. Aquamist System 1s is the system we installed on our test vehicle, a 2001 Grand Cherokee with a 7 psi supercharged 4.7L V-8.

The Aquamist System 1s kit

When it comes to water injection. Ask around and you will soon find out that Aquamist is the world renowned leader. They produce more systems than anyone else and have perfected water injection by using high powered pumps that inject the water at over 60 psi. The high pressure water injected using the atomizing jet creates a fine mist that lower quality, lower powered system can't compare to.

For this application, we decided to use the .7mm jet size which injects
water at a rate of about 265 ml/minute.

The pump is very high quality and has quite some heft. The Aquamist kit doesn't cut any corners.

The pressure switch (shown above) turns on the pump when boost exceeds 5 psi, so the water only injects when you really need it.

Here is the wiring schematic for the system.

The injection jet is placed after the K&N filter and
before the air intake of the supercharger.

A bypass switch and bicolor indicator LED
were mounted in dash (not included in kit).

The fine mist of water is sprayed into the air rushing into the supercharger, the Kenne Bell twin screw supercharged then compresses and heats the air as this is done. Some if not all of the water evaporates during this compression, what doesn't evaporate is then sucked into the cylinder where the water molecules absorb the heat in the cylinder. This evaporation process is refered to as gaseous intercooling.

Still skeptical? How about some high school physics. Remember PV=nRT? Well if you do, you know that as the P (pressure) rises then T (temperature) must also rise. Now, the supercharger itself is not 100% efficient. Let us assume it is 70% efficient and we are working with 7.5 psi of boost.

That means that air entering the supercharger at 77 degrees exits it at 171 degrees. Ouch, that is hot! So if this fine mist of water sprayed at 265 ml/minute into the supercharger inlet evaporates completely, it would theoretically cool the charge 82 degrees, that is an 89 degree difference! Ok, now imagine the difference between running a quarter mile in 10 degree weather and 99 degree weather. It is huge, to be exact, it is a 20% air density increase! Sound impossible, check out this page and do the math.

So, does this equate perfectly to 20% more power? Will it make the 325hp blown 4.7L V-8 crank out an extra 65 hp? Well, in all honesty, day in and day out, no. I expect the largest factor is that not all of the water evaporates, some water droplet will find their way all the way to the engine, some of the water droplets will stick to walls of the intake. Some days, the humidity is really high and less of the water will evaporate. Also, the Kenne Bell supercharger has two auxilliary fuel injectors which inject fuel prior so there is already some cooling going on. It is interesting to note, I find a bit more power on dry days, normally people find more power on wet days. Is there a difference in power, yes. The current weather condition really affects the actual performance gain. Further testing is coming, but I would say it packs on another honest 15 horsepower on a warm dry day.

The main reason for the injection system is actually some added insurance against predetonation which can kill a supercharged engine. The added heat and pressure that a supercharger tacks greatly increased the chance of predetonation. Either methanol or isopropyl alcohol can be added during winter months to prevent it from freezing. I actually tapped the windshield washer fluid tank and now use it for both the windshield washer pump and the Aquamist pump. Currently I'm running just water, but when the days get colder, rubbing alcohol will go into the mix. I also wired a switch in series with the relay to allow you to disable the system. This is handy if your tank is low and don't want to burn out your Aquamist pump. A twin (green and red) element LED was always mounted in the dash, it is green if the switch is on, when the pump switches on under boost, the red element lights also it mixed with the green light to make an amber color indicating that the system in injecting.

The last and probably largest potential power gaining options left to explore are advancing the timing or upping the boost. Because the system cools the air and in cylinder combustion, it effectively raises the octane level of the gas and the system quite possibly could support 10 lbs. of boost using plain premium gas. I have to test whether water injection can prevent predetonation at such a high boost that typically calls for race fuel. Another option is to reprogram the PCM to a use more aggressive timing. The recent PCM flashes are very conservative.

In conclusion, the system has somewhat limited applications. It is made for forced induction vehicles. The System 1s can be had for under $500. Aquamist also offers more sophisticated systems but for this relatively low boost application, this system was perfect. Let's face it, $500 is cheap insurance again predetonation and the extra horsepower is huge added bonus.

http://www.aquamist.co.uk