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Water injection electrical; Metering water supply
Topic Started: Mar 28 2014, 03:22 PM (526 Views)
sheananigans


So I'm looking to equip my geo with water/ methanol injection. I've read quite a bit into it and it seems the general way of doing it is to have a injection nossel spray into the intake (more or less). To me this seems like it would work, but not good enough for my tastes. I would like to be able to meter the water that enters the engine the same way the fuel is metered in order to retain proper water to fuel ratio through multiple engine States, eg: rpm change, hot cold, load change, etc...

The way I want to do this is to use a fuel injector with all stainless steel construction to meter the water. I would do this creating a circuit in which a relay powered by the ig switch would provide 12v+ to the water injector with a potentiometer in line. The ground would then be fed into the switched ground source for the fuel injector to the ecu. By doing this I'm hoping to have the fuel injector and water injectors pulse width be the same. And then using the potentiometer I would then be able to vary the length of travel on the pintle valve of the water injector to control flow and keep the water to fuel ratio proper.

Now my questions are this,

1. Would the added amperage from the second injector fry the ecu ground source?
2. Would the potentiometer successfully allow me to control flow by modifying the length of travel of the pintle valve in the injector?
3. Do I have this completely ass backwards? Haha

Maybe mweb will chime in? :rocker
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Hanuman
"The Almighty Grounds Cleaner"

how about a old carburetor to meter the water flow?
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Coyote X


a potentiometer will not be able to handle the current. But you can get expensive large ones that can, they still won't work the injector like you want. Injectors need the full 12V.

The way I planned on eventually building a water injection system was to use a fuel pump and variable pressure regulator and a injector smaller than the stock tbi injector so I have a complete system pumping water instead of gasoline. With the adjustable pressure regulator I could get the injector to spray 10% the flow of the stock injector and it could be wired directly to the tbi injector wires so the computer operates both of them the same. Of course it also needs a switch on the throttle to cut the water at idle. Really other than the water maybe corroding up the fuel pump or injector there isn't much of a reason that a system like that won't work reliably. If the computer can't handle the load of two injectors it would be a simple matter of adding a power transistor to operate the second injector.
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t3ragtop
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Turbo3 and Twincam Tweaker

you cannot adjust pintle travel. the pintle is either open or closed, the pulse width dictates the time open and pressure dictates the flow rate.

even peak and hold circuits keep the pintle off it's seat for the entire injection pulse event. peak and hold pops a lot of current at first to move the pintle at it's highest speed and then tapers the current so that the overall event draws less current so as to not blow something up.

saturation operation uses less current overall and uses a more simple electrical circuit.

the problem that you will likely run into is that the injection driver transistor in the ecu won't play well with 2 coils in parallel. as a resistive load the second coil will cause current to go up. as an inductive load, the second coil will mess with the first injector's pulse width in a non-linear fashion.

the injector's coil is measured in impedance, not resistance, and as such it involves an ac component which interacts with the coil in applied voltage as well as frequency. as the pulse width frequency goes up and pulse width becomes longer, the control current goes up as a constant of frequency.

when you introduce a second coil with different operating impedance there is an interaction between the collapsing magnetic fields that taxes the flyback circuit and usually either blows the driver transistor or the weaker of the 2 injector coils.

i'm not saying that you can't do it but it would definitely be a crap shoot.

an adjustable resistor won't be the correct device. all it will do is add resistance to the circuit. there's a lot more involved than basic dc electricity when it comes to injector control.
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sixtharmy


I assume that, since you want to inject a methanol/water solution, you're looking for supercharging like that of a WWII fighter plane. If that's the case, then I would think that most of your injection would be taking place during hard acceleration. If so, then you could probably get away with injecting some specific quantity of solution per minute any time you go to wide open throttle. I'd suggest a pump activating/deactivating switch in some way attached to the throttle position sensor. For the electronic sorts of reasons given by others earlier, I don't think you could directly tap the TPS potentiometer in your 94. However, you might be able to kluge an additional sensor in a piggyback arrangement. If you go that route, then I believe that the TPS from the 89-91 models are simple on/off switches at WOT. Constant flow rate could then be controlled by an aerating jet and a high pressure pump. Flow rate can be calculated from apperture and pressure drop at the jet. Appropriately sized jets could probably be found in old carburetors, and I've heard that home expresso makers are a good source of compact high pressure pumps. Mind you I'm just blue skying here. You'd need to find some reference for the optimum MeOH/Water to fuel mixture for an ICE and you'd also need to know the fueling table flow rates for WOT. Regardless, I don't think you'll actually see much supercharging with such an injection setup. But I've never tried it, so I don't really know. Experiment and enjoy. I hope some of you more knowledgable guys will chime in here, since I could easily be leading sheananigans astray.
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t3ragtop
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Turbo3 and Twincam Tweaker

if he was dealing with a boosted operation i would suggest a hobb's switch.

on a normally aspirated set up i'd be inclined to use a microswitch and relay.

the simplest set up uses a pressurized tank with a valve on the line to the injection nozzle. on/ off operation at a given set point and a given flow rate follows the "kiss" principle. ;)
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sixtharmy


Yeah I thought I might be over thinking this, but in my defense I'd just finished reading all the stuff on PWM injector operation. Also, I've been trying to think of something to do with the neat tiny high pressure pump in my broken Italian expresso machine.
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doviatt
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Can you not just pour water into your gasoline?
Remind me, what are you trying to accomplish?
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rmcelwee
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You are making this WAY over complicated. I would say that even if you were trying to use 20 PSI boost pressure on your Geo for some reason a simple on/off switch would work just fine (or at least a two stage). Is your budget more or less than $5,000 for this system?
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me2


http://www.motherearthnews.com/diy/water-injection-system-zmaz79ndzraw.aspx#axzz2xJyfvdTa

I tried this many years ago on a 1971 Dodge Dart. It did not seem to help my gas mileage but then I was also young and stupid.
I had the valve next to the steering column and my bottle of water on the passenger floor where I could watch the flow of air through the stone.
I could crank the valve up so much that it would suck water to the point of the car running rough.

I wonder if someone could use a system like this with one of your fancy computer software to watch what it is doing to performance- and thereby learn how to use it optimally- manually.
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