Hi Bill,
I could be wrong, but, I’m fairly
certain that the position of the Ec2 manual mixture control does not
necessarily have any deterministic relationship to air/fuel ratio of the EC2. The
resulting air/fuel ratio is a combination of (among other things) the MCT bin
(pointed to by manifold pressure) in which the engine is operating plus
the effect of the manual mixture control knob.
The narrow band O2 sensor response curve
is pretty crappy for any sort of linear interpolation – but, most have a
range of from a few 10 millivolts to approx 1.1 volt. With the higher
voltage 1.0 representing higher air/fuel ratios – somewhere in the
vicinity of 12 – 10 :1 air/fuel ratio. Stioch (14.7:1)
voltage is normally around 0.45 volts (or 450 millvolts) and that is generally
the only value that is really rather accurate on a narrow band O2 sensor.
So with my EFISM if the air/fuel ratio
indictor is in the middle of its range on the display, it should be yellow in
color. I also have a feature that when looking at the air/fuel indicator
screen (the one with fuel flow and fuel used values displayed), if you press
button b3 and b4 together you will get displayed in the air/fuel ratio window
of the actual voltage being read from the O2 sensor. So if the EFISM
indicator is yellow and in the middle the voltage should read somewhere close
to 450 mv. IF it is green and near the right hand limit the voltage
will probably be reading around 900 mv indicating an higher air/fuel
ratio. If red and to the left side then it will be reading less than 450
mv.
However, remember that the curve for the
narrow band O2 sensor is not very suitable for interpolation. The wide
band O2 sensor is much better and therefore you can get more accurate
indication of air/fuel ratio.
So almost all narrow band O2 air/fuel
ratio indictors are only useful in giving you a relative indication of leaner
or richer.
In fact, I am considering a future
modification/option/user selectable Narrow band or wide band O2 sensor for the
EFISM. Initially the wide band O2 sensors were in the $250 -$300 range,
but now have dropped down to around $80 for the borsch model which makes them
more cost feasible.
I probably did not answer your question,
but that is as close as I could come.
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Bill Bradburry
Sent: Friday, October 16, 2009
8:57 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Stoich
A/F Ratio?? : [FlyRotary] Re: where's the missing power?
Good point, Ed.
How much change does the mixture knob on the EC-2/3 allow? Say
for instance, if Mike was at 14.7 at full throttle with the mixture knob at the
center position, how far would he have to turn the knob to the right to achieve
12.65 AFR? I ask this because the A/F gage will not read that
mixture. It will be topped out well before that mixture ratio
occurs. How do you determine best power mixture?
Bill B
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Friday, October 16, 2009
8:35 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Stoich A/F
Ratio?? : [FlyRotary] Re: where's the missing power?
Hi Mike,
I guess I’m missing something - If
your mixture monitor shows stoich at full throttle, then it’s not solely
an airflow problem – it appears to me that it’s the lack of
sufficient fuel. IF you are at stoich 14.7:1 A/F ratio then that means you have
more oxygen available in your system to support burning more fuel = more
power. You should be able to enrich the mixture particularly at
full throttle (assuming you are wanting full power at full throttle) to around
12.65:1 air/fuel ratio for best power. I know you know all of this - that
is why I am puzzled by your statement that you feel it’s an airflow
problem when on the surface with the Stoich ratio it would appear it’s a
lack of sufficient fuel.
Ed.
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Mike Wills
Sent: Thursday, October 15, 2009
11:22 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: where's
the missing power?
Sorry for my absence on a topic I started. My nephew
had a skateboarding accident last weekend and is in the hospital in a
chemically induced coma until his brain swelling is under control. And I
thought car powered airplanes were dangerous. Stay away from skateboards.
Tracy - My
mixture monitor shows stoich at full throttle. I suspect an airflow issue
rather than fuel.
Al - my vacuum gauge is located in the plenum directly
behind the throttle plates.
Lynn - I agree
that the TB inlet is horrible and needs a bell mouth. The inlet is also pretty
obstructed by the cowl which isnt visible in the pics I sent. I think I'll make
an attempt to clean this up some and see if it gets me anywhere. If not I'll
live with it for a while.
Kelly - always tough to determine if the problem is an
engine issue or if the load is simply too much for the engine to overcome. I'm
going to experiment with the shallow dive several have suggested and see what
happens.
----- Original Message -----
Sent: Tuesday, October
13, 2009 4:21 PM
Subject: [FlyRotary] Re:
where's the missing power?
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Al Gietzen
Sent: Tuesday, October 13, 2009 7:22
PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: where's
the missing power?
I dont have a regular manifold
pressure gauge, just an industrial type vacuum gauge ( I really gotta get an MP
gauge). Anyway, the vacuum gauge was indicating 4" of vacuum.
Where are you measuring the 4”
vacuum? If it is near the ports it is no unusual; if it is out before the
runners; something is wrong.
Al
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