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Old 12-15-2009, 04:32 PM   #1
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Default Progressive Pressure Water Injection

So I've got this old Vortec FMU laying around...

So what Im thinking is that I could essentially use it to make a water injection system that is progressive with boost pressure. The Pressure switch would switch on the water pump at say 5psi at which point it would be operating at a base pressure, but as the boost increases the FMU would increase the water pressure and consequently the amount of water being injected.

I assume Im going to need a pretty high pressure pump in order to have good atomization initially and still give it headway to increase with boost.

But anyway,give me some input. Hopefully Im not having a Hyper moment here
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Old 12-15-2009, 04:35 PM   #2
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The downfall for this idea, is that you need high pressure to properly atomize the water. So you would need a FMU that can handle already high pressures of like 100+ psi. What you are proposing is essentially a different implementation of already existing progressive controlled systems. They work by controlling pump speed which in turn controls pump pressure, or by sort of sending the pump a PWM signal to control output. Both are very rough implementations, with uneven atomization throughout the delivery range, and poor control overal of output. It might work though. Give it a try.
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Old 12-15-2009, 04:44 PM   #3
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Hm, I always assumed other progressive systems worked by pulsing a solenoid at varying frequencies, like its done with nitrous. Which if anybody has ever seen a dyno of such systems you realise how poor power delivery is. Which is why I thought this would be significantly better.
So I guess progressive systems already use progressive pressure.

Are there issues with control using a PWM signal? I would imagine that there is a non-linear relationship between motor speed and pumping.
The RRFPR/FMU would be a very linear relationship.
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Old 12-15-2009, 04:45 PM   #4
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nope the DO progressive controller alters the voltage of the pump, IIRC
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Old 12-15-2009, 04:52 PM   #5
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Ok, maybe I'm an idiot and can't see the obvious answer here.

How is an FPR going to alter pressure at the WI pump? I know how the vortec works on a fuel system with a RETURN line. How exactly would you plumb this into the WI plumbing?
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Old 12-15-2009, 05:01 PM   #6
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Quote:
Originally Posted by jayc72 View Post
Ok, maybe I'm an idiot and can't see the obvious answer here.

How is an FPR going to alter pressure at the WI pump? I know how the vortec works on a fuel system with a RETURN line. How exactly would you plumb this into the WI plumbing?
you would basically set it up just like a fuel system. It would have a static FPR with the FMU on the return, so you would have a return to the reservoir.
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Old 12-15-2009, 05:32 PM   #7
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Quote:
Originally Posted by Full_Tilt_Boogie View Post
The RRFPR/FMU would be a very linear relationship.
That's correct. However the relationship between pressure and flow volume is non-linear. Doubling pressure does not double flow.
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Old 12-18-2009, 03:07 AM   #8
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Quote:
Originally Posted by Joe Perez View Post
That's correct. However the relationship between pressure and flow volume is non-linear. Doubling pressure does not double flow.
I though for liquids (incompressible) there is a linear relationship between pressure and flow, but I may be wrong, Im not sure what principle explains the relationship between pressure and flow
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Old 12-18-2009, 03:07 PM   #9
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Joe is absolutely right. Flow does not increase linearly with pressure. For empirical confirmation, look at some of the nozzle charts that show flow versus delta-P. They are not linear.

Here is the equation for incompressible flow through an orifice. Key equation feature, the flow rate is a function of the square root of the pressure differential. Not linear.


More information here. It is a discussion on orifice plates, but the same principle applies.
Orifice plate - Wikipedia, the free encyclopedia

As with any non-linear curve you can make short interval linear extrapolations to approximate the difference in flow. But, the farther you extrapolate, the larger the error.
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Old 12-18-2009, 03:20 PM   #10
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ooooh I see, so in other words the electronic way is a better route to a linear increase because you could program the speed of the pump vs. map in order to make a linear relationship, or any other type of curve you want.

I guess ill just try to sell this FMU to some poor soul, haha
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