[Diy_efi] Basic Speed-Density equations?

[Perry Harrington]

You don't need RPM if you are doing a continuous injection system.

The RPM is just to tell the computer to shoot n number of M millisecond
squirts.

If you base it purely off MAP and assumed VE, a CIS system should work.

As your MAP becomes closer to atmosphere, you need more fuel, less MAP,
less fuel.

Since this is an airplane engine that you want to maintain a constant speed,
your VE will be constant and the MAP will determine the load.

I presume you ARE using a variable pitch prop?

You will just need to tune the system to provide a certain amount of fuel in
relation to the MAP.  Since your cylinder is the valve, and probably
not adjustable, you should tune the volume via fuel pressure.

--Perry

On Fri, Jun 14, 2002 at 02:12:50PM -0500,  Brian Michalk wrote:
> > Jim,
> >
> > Read the first couple of pages in Bruce & Al's paper on implementation
> 
> Read it, good reference.
> 
> If I base fuel flow on MAP, air temperature and RPM, I can come to a value
> that will at a minimum produce power let's say 90% of maximum power.  Let's
> say that for my purposes this is excellent enough to keep my airplane from
> falling out of the sky.
> 
> If I use MAP, temp and RPM, how do I do this without electricity?  I don't
> think I can.  Map and temp seem possible, but RPM needs to be some
> mechanical actuator based on a mechanical rate.  Maybe some centrifugal
> arrangement would work ... maybe it's not as far fetched as I think.  What
> does everyone else think?
> 
> What I'm working on is the backup scenario to my EFI injection that is
> already finished.
> I've got it worked out on paper to use a rolling diaphragm cylinder that
> actuates a fuel metering valve.  The cylinder has a canister referenced to
> some known pressure.  Let's assume sea level pressure at 60 degrees
> fahrenheit.  The good part is that this compensates for temperature also.
> The other half of the cylinder would be referenced to MAP.  I am planning to
> throw away the RPM part and go on MAP alone.  Remember, this is the backup
> system.  I'm not interested in efficiency, just reliability.  I could of
> course go with a mixture adjustment knob, but I'm trying to engineer that
> out of the system.
> 
> 
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-- 
Perry Harrington			Data Acquisition & Instrumentation, Inc	
perry at dainst dot com					 http://www.dainst.com/		 

Those who would give up essential liberty to purchase a little temporary safety
deserve neither liberty or safety. Nor, are they likely to end up with either.
                             -- Benjamin Franklin

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