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From: Ed Anderson [mailto:eanderson@carolina.rr.com]
Sent: Monday, July 06, 2009 3:17 PM
To: 'Rotary motors in aircraft'
Subject: Long Response -avoid reading unless Hopelessly addicted to EC2/3
folklore was [FlyRotary] Re: Below staging
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Below staging
Hi Steve,
No offense, but I'm quite sure the EC2 doesn't know if the injectors
are powered or not. The disable switches operate on the power leads to
the injectors and the EC2 pulls the other side of the injector to
ground to fire it. There's no input to tell the EC2 whether power is
applied or not. What it does know is that the cold start switch is
activated. In Tracy's wiring scheme, that happens automatically when a
disable switch is activated. You have to do it manually but it amount
to the same effect. Your description is exactly the way it is supposed
to work.
Hi Bob, (I'm baaaccccckkkkk).
No offense, Bob {:>), whether the EC2 does or does not sense injector line
voltage, I do not know. But, I don't see why the EC2 could not easily tell
if there is power to the injectors.
Any time the EC2 is not grounding its' side of the injector (causing it to
inject) there is 12+ Volts at the EC2 injector pin on the EC2 box - Unless
you have turned the disable switch for that pair of injectors off (no
voltage to injectors). Until the EC2 grounding pulse there is no current
flow and therefore no voltage drop across the injector. So if there is 12+
volts on one side then there is 12+ volts on both sides including at the EC2
injector pin. Once the ground pulse is sent then the voltage is dropped
across the injectors and there is indeed near zero volts on the EC2 pin.
So I would think it would be easy for the EC2 to sense whether there is 12
volts on that pin between injector pulses and if there is 12+ volts, then
the EC2 would know it is powered up.
Now whether the EC2 does this or not, again, I do not know, but it would
seem very easy to do. I know I do that on my EFISM - in fact sensing the
voltage level of the pulse train is how I measure the pulse duration and use
for my calculations.
You might also note that with the engine warmed up and idling with the
cold start switch off, you can turn off the secondary injectors and the
engine will run fine whether the cold start switch is on or off. The
fact that it runs fine with the secondaries off and the cold switch on
emphasizes that the cold start function doesn't double the pulse width
below the staging point. That would deliver too much gas to the engine.
Bob, I believe the normal default mode for the EC2 is above the staging
point with all four injectors firing. So the nominal pulse duration is that
required to keep these four injectors providing the required fuel and that
is the "normal" state. Every thing else are "special states".
Now we come to some special EC2 operating states. The two primary operating
states, it would appear to me are:
1. Operating above staging manifold pressure
2. Operating below staging manifold pressure
Above Staging Point.
State: Above staging with 4 injectors power on and nominal pulse duration,
cold start function inactive. Engine runs fine.
If you now turned off one pair of injectors, you are removing its power and
therefore disabling that pair and also grounding the cold start circuit
which activates the cold start function. The EC2 then doubles the normal
pulse duration to compensate for the OFF disable switch cutting off half of
the injectors. So fuel flow is still basically what we had before disabling
one pair. Engine runs fine.
Now you turn the disabled pair back on, this applies power to the injectors
and ungrounds the cold start circuit, therefore the pulse duration is cut in
half and drops back to the nominal duration for 4 injectors. Engine runs
fine.
Now you leave both injector pair on and reach up and manually turn on the
cold start switch on the PCM control panel again activating the cold start
function. Power in this state is available to both pair (all 4) injectors,
and the cold start function doubles the nominal pulse duration. So with all
four injectors with power on, this doubling of the pulse duration ends up
feeding double the fuel amount to the engine that would normally be provided
by 4 injectors. Engine may NOT run so fine.
Ok, still above staging point, all injectors are on and firing but too much
fuel. Cold start switch on PCM panel back to off/inactive. Pulse duration is
cut by ½ back to the nominal pulse duration for 4 injectors. Engine Runs
Fine.
Below Staging Point (this appears to be the state of contention)
The engine drops below the staging point. Two things happens (I believe).
1. The EC2 no longer fires the secondary pair (but power is still on them),
2. The EC2 doubles the pulse duration (over that nominal for the 4
injectors) which then compensates for having 1/2 of the injectors no longer
firing.
So the fuel flow is the same (ideally) immediately above and below the
staging point due to the action of doubling the pulse duration and halving
the number of injectors - when you drop below staging point. So far, no
cold start function is involved (I think {:>)) Engine Runs fine.
Ok, we are now below staging point cooking along on two primary injectors (I
know you disagree with this point, Bob, but bear with me) When you drop
below that staging point the EC2 automatically doubles the nominal pulse
duration because you have stopped using the 2 secondary injectors.
Normally you are using the two primary injectors below staging. So we still
have the same fuel flow below with 2 injectors that we had above staging
point with 4 injectors - so fuel flow both sides of the staging point is the
same (ideally). Engine runs fine.
Now, while below staging, you manually turn off the primary injectors by
turning off their disable switch. This removes power from the primary
injectors and grounds the cold start circuit. But - wait, I postulate that
below staging the cold start circuit is already in effect (doubling the
pulse duration). So there is no further doubling and the EC2 senses power
removed from the primary injectors, senses power is still there on the
secondary injectors and immediately starts firing the secondary injectors.
Engine Runs Fine.
NOW IF this theory is correct then turning on the cold start switch on the
PCM panel with only one pair of injectors operating below staging - should
do nothing regarding the pulse duration as its already double that that
nominally required for 4 injectors. Engine Runs Fine.
Now, the above is incorrect and turning on the cold start using the PCM
panel switch, does double the already doubled pulse duration (for just two
injectors) then the engine should get too much fuel. OR if turning on the
cold start switch automatically turns on the secondary injectors below
staging then again - too much fuel. Engine may not run fine.
But IF the 1st hypothesis is a correct hypothesis then it would at first
appear there would be no value in having a cold start switch during starting
because below staging point there is no quadrupling (double of the already
doubled pulse duration) of the pulse duration and no excess fuel flow.
However, IMPORTANT POINT - if you recall when you are first attempting to
start your engine you ARE ABOVE the staging point (manifold pressure wise).
In fact, your manifold pressure is nearly the same as WOT (actually probably
closer) while trying to start. So being above the staging point turning on
the cold start will indeed double the fuel flow - and since we are above the
staging point both injector pairs can fire - assuming there is power to both
pairs. So until your engine starts to run (and pulls the manifold pressure
down) having the cold start switch on when attempting to start will double
your fuel flow (and possible flood your engine if kept up too long). It
will do this because at initial starting the manifold pressure is not below
staging point.
You mentioned that the staged indicator was on with the primaries off
and the cold switch on. Did you notice if the staged indicator was on
with the secondaries off and the cold switch on? I would expect that
it was. I think that's an indication that both banks of injectors are
active even though below the staging point. Only those injectors that
are powered through the disable switches will operate.
I agree, it's not absolutely necessary to understand exactly how the
various boxes work to use them. I'm an electronics guy though and it's
of interest to me. I didn't even think about the below staging issue
until Mark Supinski asked a question on the AeroElectric list about a
problem he was having using a single three way switch for the injector
disable function. Turns out he wasn't activating the cold start either
and the engine would always die if he disabled the primaries. That's
when it struck me that when cold start is active, both banks of
injectors have to be operating from the EC2 side to make injector
disable work even when below staging.
Ed Anderson isn't quite convinced I have it right either. If I can't
convince him, I'll have to change my story. Or, Tracy will come
back from vacation and straighten me out. :)
Bob W.
Hey, Bob, I would rephrase such that it reads that "Ed Anderson is not quite
certain that HE has it right" and that is one reason why we are having this
discussion {:>) But, I agree there is only one infallible source for the
information.
Ok, that's it for me. Now, we'll have to wait for the guru to come down
from the mountain (or at least back from Colorado) to find out. Would not
surprise me greatly to find out all our theories are defunct {:>)
Great discussion, Bob, Steve, great list.
Best Regards
Ed
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