Gordon,

 

The traces in the image are for 5000 RPM of the eccentric shaft.  For each rotor, there is one combustion event for each revolution of the E-shaft.  For manifold pressures less than the staging threshold, there is one primary injector pulse for each rotor for each revolution of the E-shaft.  The amount of fuel delivered is determined by the length of that injector pulse, which, in turn, is primarily determined by manifold pressure.  With default settings, when the system transitions to manifold pressure just above the staging threshold, the primary and secondary injectors of a given rotor are both pulsed, the pulses occur at the same time, they are of equal duration, and the pulse duration is half of the duration of the single primary injector just below the staging threshold.  The other rotor receives the same signals, but offset by 180 degrees of E-shaft rotation.

 

The effect of the injector dead time is most evident at the staging threshold.  When the engine is running at a correct mixture at a manifold pressure just below the staging threshold, relatively long pulses to the primary injectors are delivered.  When the manifold pressure becomes greater than the staging threshold, the mixture goes lean because the primary and secondary injectors operating at half the pulse duration deliver less fuel than the primary injectors alone at the original pulse duration.  This is because the injector dead time is a larger percentage of the injector pulse when the pulse duration is short.  It should be emphasized that the forgoing assumes default settings.

 

The problem of the mixture going lean upon transitioning to using both the primary and secondary injectors can be dealt with in several ways.  I have found that adjusting mode 6 to achieve the correct mixture just above the staging threshold works best for me even if all the injectors are identical.  Adjusting mode 6 changes the pulse duration of both the primary and secondary injectors above the staging threshold and the change is same amount for both the primary and the secondary injectors.

 

This is the behavior of the version of EC2 that I have.  It is my understanding that Tracy has incorporated a dead time compensation in the latest versions.  As a result, the latest versions may be easier to tune, but this would have no effect on building an independent fuel totalizer based on injector pulse integration.

 

As long as the tuning process has not resulted in changing the injector pulse durations of the injectors of the two rotors (adjusting mode 4) the implication is that fuel flow can be determined by measuring the pulse duration of one primary injector, knowing the RPM,  knowing if the secondary injectors are in use or not, and applying a dead time correction.

 

I measured the injector dead time by determining the amount of fuel delivered at different pulse durations and extrapolating a plot of fuel delivered vs. pulse duration to zero fuel delivered.  The pulse duration at zero amount of fuel delivered was used as the injector dead time.  The dead times of identical models of injectors appears to be very consistent and may sometimes be found in the injector specifications.  The flow characteristics of a given injector can be affected by (among other things) system voltage and the difference between the fuel pressure and the manifold pressure.  The voltage should be well controlled in a properly operating electrical system, and the difference between the fuel pressure and manifold pressure is generally dealt with by using a manifold pressure compensated fuel pressure regulator such as the stock RX7 regulator.

 

Steve