Good explanation and I agree with everything except the part about RPM not being used by the EC2. Engine speed is a primary input to the system, hence the term "speed - density system". After giving it some more thought, I think the long distance between injector and port has a large part to play in this problem. It causes the fuel delivery to the engine to be out of phase with what the engine is doing. At very low throttle, the volume of air in the runner can represent almost all the air that the chamber is going to inhale in one cycle. Since the injection pulse calculated and injected for that cycle is at the far end, the engine is not actually going to get that load of fuel until the NEXT cycle. If conditions are changing rapidly (which can definitely happen at low rpm) the charge for one cycle can be very different than for the next one. In addition to this factor, the injected charge is sitting in the runner waiting for the next cycle and has a chance to condense on the walls of the runner. These are the factors that made me advise against moving the injectors out to the far end of the runners. Tracy ----- Original Message ----- From: Russell Duffy Sent: Tuesday, March 30, 2004 12:31 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: No rev-2 flying yet (Tracy, see comments inred) My guess is that it appears that when closing the throttle very rapidly, you probably end up with an overly rich intake manifold air/fuel mixture. This may occur because in one fraction of a second you are opearting at WOT (lots of fuel flow) and the next down to idle. So the rpm drops down in to the LOW, LOW range due to the rapid decrease in manifold pressure caused by the rapid throttle closure and still rapidly pumping rotors. So its down in the low rpm range with a rich mixture and then since the rpm is so low, the manifold pressure may well creeep back up to the 16-17" Hg range simple because there is not enough rpm to keep the manifold pressure lower. So now the system is seeing higher manifold pressure. Since the system only really uses the manifold pressure (and not rpm) in its calculation, the higher manifold pressure convinces itself that you have opened the throttle a bit (while you actually have not) and so it dumps in a bit more fuel. This keeps the mixture overly rich as there is really not as much air coming into the system. Once you crack the throttle a bit, more air flow leans out the mixture, rpm increases, manifold pressure actually decrease back to 14-15" Hg and the system stabilizes. GREAT explanation!!! That's got to be exactly what's happening. Thanks, Rusty (now I can ignore that "problem")
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