Received-SPF: pass
 receiver=logan.com; client-ip=75.180.132.123; envelope-from=eanderson@carolina.rr.com
Message-ID: <9B2574E1F0794D1A893010E7E83CD552@EdPC>
From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-4893035@logan.com>
In-Reply-To: <list-4893035@logan.com>
Subject: Re: [FlyRotary] staging and tuning
Date: Tue, 8 Mar 2011 09:32:14 -0500
MIME-Version: 1.0
Content-Type: text/plain;
	format=flowed;
	charset="iso-8859-1";
	reply-type=original
Content-Transfer-Encoding: 7bit
Importance: Normal

Well written and understandable bit of analysis, Steve.

 I discovered by observing the O2 mixture that my "bog" at the staging point 
was caused by the mixture going too lean(I have same size primary/secondary 
injectors).   Through trial and error I found that I could eliminate the bog 
by enrichen the mixture at that point by increasing the fuel map values for 
a few EC2 bins after the staging point.  This eliminated my bog, however, I 
never understood why it should be necessary, now thanks to your work and 
analysis, I do.

Ed

Edward L. Anderson
Anderson Electronic Enterprises LLC
305 Reefton Road
Weddington, NC 28104
http://www.andersonee.com
http://www.eicommander.com


--------------------------------------------------
From: "Steven W. Boese" <SBoese@uwyo.edu>
Sent: Sunday, March 06, 2011 7:49 PM
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: [FlyRotary] staging and tuning

> Bill and anyone else interested:
>
> The issues involved with mixture changes when the EC2 controller stages 
> can be understood by considering two simple concepts:
>
> 1. The first is the concept of injector lag, also referred to as injector 
> latency and injector dead time, as well as other names.  The fuel 
> injectors are not perfect.  They do not instantaneously respond to the 
> controller pulse.  That is, they take a measurable time to open after the 
> application of the pulse and they take a measurable time to close after 
> the pulse ends.  These two times are not equal and the result is that the 
> injector flows fuel for a smaller period of time than the injector pulse 
> width.  In addition, the injector flow rate is changing during the opening 
> and closing time periods.  Measurements of the amount of fuel delivered as 
> a function of pulse width show that the deficit in the amount of fuel 
> delivered for any pulse is the same whether the pulse width is long or 
> short.  For stock 40 lb Mazda injectors with a fuel pressure of 40 psi and 
> a system voltage of 13 volts, this loss in the amount of fuel delivered 
> corresponds to an injector lag or dead time of about 1.2 ms.
>
> This 1.2 ms is not trivial.  Consider a rotary engine running at 6000 rpm. 
> The time it takes for one revolution is 10 ms.  Limiting the injector 
> pulse to an 80% duty cycle limits the injector pulse width to 8 ms.  The 
> effect of the injector lag is to decrease the amount of fuel delivered by 
> 1.2/8 x 100 or 15% at 8 ms pulse width,  1.2/4 x 100 or 30% at 4 ms pulse 
> width, and 1.2/1.2 x 100 or 100% at 1.2 ms pulse width.  It is obvious 
> that the shorter the pulse width, the larger the fuel deficit.
>
> 2. The second concept to realize is that the EC2 controller does not take 
> injector lag into account.  This has been demonstrated with my EC2's at 
> default settings by measuring the injector pulse width on either side of 
> the staging transition.  It has also been demonstrated by pulse width 
> measurements taken when engaging the injector back up function where the 
> change from using two to using four injectors is forced to occur without a 
> change in manifold pressure or change in MAP table address.  These 
> measurements show that, before tuning, the EC2 staging transition is a 
> transition to using all the injectors at half the pre-transition pulse 
> width.  The essential point here is that even if the primary and secondary 
> injectors are the same size, staging, by using twice as many injectors at 
> half the pulse width does not result in the same fuel flow, but rather a 
> substantial fuel flow decrease.  Using the above data, this is easily seen 
> by considering what would happen if staging took place at an initial pulse 
> width of 1.2 ms.  After staging, the fuel flow would then be zero.
>
>
> Before tuning and with primary and secondary injectors of the same size, 
> the effect of injector lag is always for the controller to deliver less 
> fuel than it calculates as being needed.  This problem becomes 
> progressively worse as the injector pulse width decreases.  When the 
> secondary injector flow rating is larger than that of the primary 
> injectors, the mixture change due to staging, while predictable, is not 
> intuitive.  This is because the tendency to go lean due to the injector 
> lag effect accompanying the pulse width being cut in half is now combined 
> with the tendency to go rich due to the two larger injectors now in use. 
> Whether the mixture goes leaner, richer, or is unchanged upon staging 
> depends not only on the difference in the primary and secondary injector 
> flow ratings but also upon the conditions (initial pulse width) under 
> which staging takes place.
>
> The discussion which follows is for the case of equal sized primary and 
> secondary injectors and initial tuning starting with default parameters:
>
> The percent decrease in fuel flow upon staging is most severe for low 
> initial fuel flow rates.  This explains the difficulty in achieving a 
> smooth staging process if the staging threshold is set too low.  Even for 
> reasonable initial fuel flow rates in the range of 6 to 10 gal/hr, the 
> fuel flow will decrease significantly.  If the mixture is rich enough when 
> staging takes place, the decrease in fuel flow may not result in a large 
> change in engine power output.  However, if the mixture is already 
> somewhat lean when staging occurs, the mixture may become very lean and 
> result in a marked decrease in power.
>
> I've used three methods to compensate for the injector lag.
>
> 1.  The first method is to follow the instructions in the manual.  Tuning 
> is started by adjusting modes 3 and 2.  After modes 3 and 2 have been 
> adjusted, then mode 1 or 9 is used to adjust the mixture correction table. 
> Tuning the mixture correction table can compensate for the fuel flow 
> decrease on staging caused by injector lag.  This results in a 
> discontinuity in the correction table at staging.  Since defining the step 
> in the mixture table can be difficult, programming the mixture somewhat 
> rich across this region is helpful.  Cruise operation at MAP values close 
> to the staging threshold then simply requires some adjustment of the 
> manual mixture control.  Because of the step in the mixture table at the 
> staging point, changing the staging threshold also requires retuning of 
> the mixture table in this region. Tuning the rest of the table compensates 
> for other factors such as changes in volumetric efficiency in addition to 
> injector lag.  Injector lag affects tuning of the entire table although it 
> is just not as obvious as its effect on staging.
>
> 2.  A second way to compensate for the effect of injector lag on staging 
> is to use the mode 6 secondary injector differential adjustment even with 
> primary and secondary injectors of matched flow rates.  Since the mode 6 
> setting only has effect above the staging threshold, and since the effect 
> of injector lag is to make the injectors act as if they became smaller 
> upon staging, mode 6 can be used to eliminate the step in the mixture 
> correction table.  This is possible because mode 6 has the ability to 
> compensate for smaller as well as larger secondary injectors compared to 
> the primaries.  Compensation for the effect of injector lag and other 
> factors is still necessary throughout the table, but the changes are 
> gradual and much easier to implement than a discontinuity.  This method 
> removes the injector lag effect upon staging and works quite well.
>
> The tuning procedure then becomes the same whether the primary and 
> secondary injector flow rates are different or identical:
>
> a.  Set the staging threshold at a MAP corresponding to the high end of 
> the primary injector flow limit using mode 7.  (For 40 lb injectors, about 
> 20" MAP works well.)
>
> b.  Adjust Mode 3 to get a mid scale O2 sensor reading at a MAP just below 
> the staging threshold MAP.
>
> c.  Adjust mode 6 to get a mid scale O2 sensor reading at a MAP just above 
> the staging threshold MAP.
>
> d.  Adjust mode 2 for best operation at minimum idle MAP.
>
> e.  Adjust the mixture table throughout the useable MAP range using mode 1 
> or 9 to keep the O2 sensor reading mid scale.  (To be honest, I skip step 
> "e" and simply use the manual mixture control to adjust the mixture in 
> cruise.)
>
>
> Steve Boese
> RV6A 1986 13B NA RD1A EC2
>
>
>
>
> --
> Homepage:  http://www.flyrotary.com/
> Archive and UnSub: 
> http://mail.lancaironline.net:81/lists/flyrotary/List.html
>