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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