Friday, August 25, 2006

Coolingmist water injection

I was just having a look on Coolingmist's website at their water injection system, since it's significantly cheaper than the Aquamist system. What caught my eye is this water tank that they sell, which is designed to sit in the boot of the car AND accommodate the water injection pump. I quite like the idea.

However, I'm not overly impressed with their control system. As far as I can make out, it does not monitor the duty cycle of the fuel injectors like the Aquamist 2d system does; it only measures boost pressure and inlet temperature (and/or exhaust temperature). Although you can set up the system to follow maps, these appear to be relative to boost pressure.

I don't think this is a good idea. From what I've read, there's not much to be gained running water injection below 1 bar inlet pressure... you're better off running a high octane fuel. So in my mind, there's no point even running water injection unless the boost goes above 1 bar. Once above 1 bar, it seems that World War II research shows that best results come from following a fixed ratio of water to fuel. Therefore, the more fuel you inject in the cyclinder, the more water you inject, but in a fixed ratio (in the order of 10%).

I know on my car that I don't need to have my foot hard on the throttle to attain 1 bar boost. Therefore, the water injection system needs to be able to monitor the amount of fuel that is being injected into the engine in order to know how much water to inject. The Aquamist system does this by monitoring the control signal sent from the engine management system to one of the fuel injectors (and multiplies this by six (well, three actually, since during one revolution there's only 3 induction strokes) for the Ghibli, since it has six cylinders. From what I can make out, the Coolingmist system doesn't do this. I'm also not too impressed with the blocked nozzle detection that they offer... it has no automoated fail safe if water stops flowing. With the Aquamist system I can set it up to trigger my E-Boost to run safe boost pressure if water stops flowing.

So, despite the cost difference, I'm going to stick with the Aquamist system. Regarding the tank, the Coolingmist boot mounted option is nice, but I've been giving some more thought on this and I think that the Ghibli's windscreen washer tank should be accessible enough to utilise instead. I'm therefore now thinking that I'll mount the pump in the engine bay instead of the boot. This will necessitate running thick, heavy duty cable from the battery in the boot, but I don't suppose this is too much of an issue. Since manufacture of the water tank for the boot was one of the barriers for me ordering the system, then bypassing this requirement means that I'm one step closer to ordering the kit! I just need to check that I can indeed access the windscreen washer tank (item 35 in the drawing above, located between the body panels in the driver's side front wing, hopefully accessible from the wheel arch), since I'll probably have to remove it in order to install the barb connection for the supply hose to the pump and in order to install the float switch to warn when the tank is getting empty (and to switch the system to fail safe). To get to the windscreen washer tank I'll have to remove item number 22 in the drawing below.

The other barrier to ordering the Aquamist kit is the location of the water injection nozzles. I would like to use two, one on each of inlet pipes where I have the blow off valves fitted. This means sending them off to Forge to have some flat spots welded on and then holes drilled and tapped. So instead, I'm thinking of using a single nozzle located on the Y-piece just infront of the throttle body. I think there's a flat, thick walled section on this piece already which would be suitable for locating the nozzle.

So a couple of things for me to try out, maybe this weekend?

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