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My work on a Fuel Flow meter indicates that the basic Pulse width determination is essentially independent of RPM. The engine only "knows" about the current intake/rotation cycle. The pulse width for a single injection event is basically determined by manifold pressure and the rotational displacement.
With the Air density system approach the EC2 uses, the manifold pressure is used as an indication of the amount of air the rotor chamber captures during one rotation. The volume of the air capture during one rotation is constant (the rotary is a positive displacement pump). The amount of air captured by the constant volume is dependent on of the density of the air in the manifold. If the air density in the manifold is low (idle) the 40 CID (displacement of one rotor) only contains a small amount of air/fuel. IF the air density in the manifold is high (WOT) then the 40 CID contains a larger amount of air/fuel.
At low manifold pressure (idle) the pulse width is shorter in duration because there is less air/oxygen ingested by the rotor to burn the fuel, at high manifold pressure (WOT) the pulse width is longer in duration. RPM takes care of itself in that the injectors are triggered each rotation period, so if the engine is rotating faster the injectors are triggered faster (once per rotation in any case), if the engine is rotating slower the injectors are triggered less frequently. So rpm sort of takes care of itself. Now there is some adjustment to the pulsewidth based on rpm because the Ve of the intake system IS rpm dependent. This is where you may need to adjust the fuel Map quantity for a certain manifold/rpm setting because the Ve at that setting is different than another rpm.
I'd say your understanding of the fuel injection process is on the money.
Ed
----- Original Message ----- From: "Blake Lewis" <blake.lewis@gmail.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, September 22, 2006 2:28 AM
Subject: [FlyRotary] Re: Fuel Pressure Regulator Vacuum or Boost??
I am just learning this stuff. This is my line of thoughts on the subject.
The amount of fuel that will flow through the injector during a
pulse width, is proportional to the pressure differential across the
injector.
(Delta Pressure) * (Pulse Time) = constant * Volume
Without the "Vacuum Regulator", at Idle when you have a vacuum
(less pressure) the Delta Pressure would be bigger, flowing more fuel
per pulse time.
I guess the computer wants a constant flow rate. The manifold
pressure could change significantly during the intake cycle. Cycle
time inversely proportional to rpm. The pulse width is proportional to
rpm. So, as we need more fuel we have less time to inject it. And
during the injection time, whithout the vacuum regulator, the flow
rate would change, being less predictable for the computer.
I think you would want the injector open over most of the intake
cycle to get the best mix. Maybe starting a little late so as not to
be flowing fuel during the exhaust overlap. I'll pick 79% for the duty
cycle of the injector. Since the rotary's manifold is always in the
intake cycle we would want the injector open 79% of the time. Which is
also 79% of the intake cycle.
In one rotor rotation:
close open close open close open
7% 26.33% 7% 26.33% 7% 26.33%
But in one shaft rotation it is:
close open
21% 79%
Is this what you want at full power WOT?
Now I understand the desire for staged injectors. At lower rpms you
can keep the lower flow injector open longer getting a better mix.
-- Blake C. Lewis
--
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