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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