Progressive Pressure Water Injection

[Full_Tilt_Boogie]

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

[neogenesis2004]

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.

[Full_Tilt_Boogie]

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.

[Braineack]

nope the DO progressive controller alters the voltage of the pump, IIRC

[jayc72]

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?

[Full_Tilt_Boogie]

Originally Posted by jayc72

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.

[Joe Perez]

Originally Posted by Full_Tilt_Boogie

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.

[Full_Tilt_Boogie]

Originally Posted by Joe Perez

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

[ZX-Tex]

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.

[Full_Tilt_Boogie]

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