Primarys and secondarys.. How?

[robert dingli]

Craig asks,
> 
> With an engine with a primary and secondary stage, do you need different
> fuel curves for the primary and secondary (IE in a Mazda rotary, where
> the primary and secondary have different port timing (~= two intake
> valves in a piston engine following different cam profiles).
> 

First, some background ..

Rotaries tend to have rather peculiar fuelling requirements. 
While parallel injection once per revolution works fine in a piston engine, 
we found that it resulted in unequal fuelling for a rotary.  Each rotor 
draws in air every revolution, 180 deg out of phase of the other, and produces
relatively large pressure pulsations in the intake manifold.  As a result
the fuel has the be injected either twice per revolution or sequentially. 
We settled on sequential injection for the primaries to avoid injector 
cut-off problems near idle and the larger non-linearity in fuel flow near 
100% duty cycle.  The single secondary output (which is used on only a 
fraction of applications) injects twice as often to provide equal fuelling.

As for fuel curves, the speed density mapping is calibrated empirically.
This system lumps the injector response, engine fuel requirements and
desired AFR as one overall adjustable parameter for each speed and load 
combination (128 in all).  As long as the secondary port always opens at 
the same (or similar) rpm, it is simply up to the user to incorporate any 
no-linearities into the map.

> 
> (PS- Rob, there is an RX3 in the latest FF+R with a wolf 3d in it.
> Writeup seemed pretty positive about the system).
> 

The efi system used is one of our earliest prototypes.  Since then, we
have added a fully mapped ignition system to the ECU which independently
controls the coils for distributorless rotary ignition with separate
leading and trailing adjustments. 


Robert
-- 
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             Robert Dingli           r.dingli at ee.mu.oz.au

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 344 7966                           (+613) 344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA
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