What I am having a hard time emotionally accepting here is the brute
strength of the diaphragm spring required.
When one takes a carb apart one is not used to finding
an intake valve spring inside generating dozens of pounds
of force. What you usually find is a bunch of
little wimpy springs. That is the very amazing aspect
to this carb. When you think about it the intake manifold
negative pressure is a powerful force. Obviously it takes
several HP to pump the intake manifold down to several psi.
BTW If a way could be found to idle a gasoline engine with
a wide open throttle (like a diesel engine) the pumping loses
could be drastically reduced as would the idle fuel consumption.
The other thing that strikes me about this carb design
is its analog computer nature. It has infinite resolution.
None of this stair step analog to digital converter stuff.
If all works as it should the spring will stay deflected
at it's max deflection and the sum of the spring force (about 60 pounds)
and the intake manifold vacuum pneumatic force on the back side of
the diaphragm should equal the force on the front side of the
diaphragm due to fuel chamber pressure supplied by the high
pressure fuel pump. The forward spring force and the pneumatic
back force on the diaphragm remain in balance. As the intake manifold
absolute
pressure increases reducing the pneumatic force on the back side of
the diaphragm the spring force increases.
For the diaphragm to remain stationary
the sum of the forces on both sides will be equal.
This is Newton's Third law of motion. I'll paraphrase.
For every action there is an equal and opposite reaction
for an object to remain stationary.
If the hydraulic pressure in the fuel chamber
becomes less due to fuel squirting out the main jets the
the diaphragm moves forward opening the needle
valve and the fuel pump replenishes the supply pushing
the diaphragm back in balance with the pneumatic and spring
force on the back side.
Stunningly simple. However Excedrin head ache number 400 to understand.
I am waiting to hear from someone where I am going wrong :)
Paul Lamar ...No rotor no motor.
Paul,
After studying and sleeping on this carb, some thoughts.
1. it is going to be very difficult to control mixture with this. The
spring
can't be bottomed, or it's not a spring and the vac is just pulling the
diaphragm to a stop. This also leads to "if the vac fully retracts the
diaphragm, where does the fuel for idle come from?"
2. the carb won't work at 15 psig fuel pressure. That much pressure will
make the needle so sensitive to the opening orifice that you will never
control fuel flow at part throttle. Also, the 15 psig will force the fuel
out the imulsion tubes as well as the jets. A system with that much
pressure
would have no imulsion tubes and would just be an injection system.
3. with an electric fuel pump on, and the engine not running, what
prevents
the carb from filling the engine with raw fuel? There is no vacuum to pull
the diaphragm and the needle will be open.
Hope this helps, but I think a mechanical fuel injection system will be
easier.
Larry
Good questions Larry Thanks for thinking about it.
1) There are two scenarios where the spring can bottom. One is; if the
vacuum is
high enough the backward force on the diaphragm could bottom the spring.
Since sea level pressure is 15 psi absolute on the front side of the
spring
and there is a pure vacuum on the back side of the spring the strength and
spring
rate of the spring is chosen to deal with that scenario.
When the diaphragm is in an aft position and the spring is partially
compressed
the needle valve is normally closed limiting the compressive force on the
spring. Even if the pressure is absolute zero on the back side of the
diaphragm.
Another scenario is; if the the float needle valve fails and the engine is
pumping
a pure vacuum (the spring could bottom). Of course the main jets are then
squirting a maximum amount of fuel and the engine would quit as it would
be
way too rich. The pressure on the back side of the diaphragm would then
rise to
15 psi absolute and the fuel pump pressure would be limited to 32 psi
absolute
squirting fuel out of the main jets. In that case some sort of automatic
switch could shut off the pump. The mixture control could be backed off to
full lean removing all force from the spring on the diaphragm. The
diaphragm
would then bottom on the back stop.
I had that happen in a Cessna 172 I was flying only in that case the float
sank. The fuel pressure on the carb was only 2 psi or so due to the high
wing
tanks. The engine still ran long enough by manipulating the mixture
control
to allow me to make a safe emergency landing at the nearest airport.
In the case of this carb with a failed needle valve you would have to
manually
switch the fuel pump on and off to achieve the same results.
Fortunately float needle valves are extremely simple and reliable.
Another scenario is a failed fuel supply pressure regulator.
Pretty much the same scenario. Same emergency procedure.
Fortunately these devices are also very reliable.
These failure modes are not unique to this carb. Many of the same
things would happen in an EFI system.
2) The main jets are upstream of the air injectors. Upstream of the main
jets
the pressure is 15 psi. The air injectors are located down stream from
the main jets. Down stream from the main jets the air pressure is
atmospheric because they are just a fraction of an inch away from the
throat.
In this way this carb differs from a pure fuel injection system. In a pure
fuel
injection system the orifices are the last thing in the fuel flow
plumbing.
There is a slight exception however and that is the Continental AC style
injectors
that entrain a bit of atmospheric air right at the orifice. I'll include a
scan
of that injector. It is very similar to the air injection scheme I am
using.
3) You are absolutely right about this. Don't turn the electric pump
on until the engine is turning over. A lot of EFI systems do the same
thing. They turn the pump on briefly to build fuel pressure and then
turn it off as soon as the engine RPM comes up to idle speed. I am still
thinking about this and I may come up with some other solution.
Thanks again for thinking about this Larry. I hope other people
will come up with possible failure modes because as far as I can
tell nobody has built and used the exact same system.
It is a real pleasure having a bunch of talented engineers
on here analyzing my hair brained schemes.
Paul Lamar ...No rotor no motor.
P.S. most EFI fuel pressure regulators work in exactly the same
way. As MAP increases so does fuel pressure.
Sounds like you're reinventing the wheel.
George Lazik
Which wheel do you suggest we use? :)
It must be dual 55 mm throat, lean able and side draft.
Also it must cost less than $500.
Paul Lamar ...No rotor no motor.
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