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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