I have been curious about this, since there are injectors and pumps out there that can support lots of fuel and power, would it be better to place the injectors at or near the point of peak compression in the housing or at the intake portion of the housing like the newest Mazda rotary concept? What about angle? My thought is to do a combination direct and port EFI system for my next project.

       Steve Ross


   The problem is getting the fuel  thoroughly mixed with the air.

   Injectors at the beginning of the runners gives the lowest fuel burn
   for the HP generated.

   Not used in racing cars because the throttle response suffers.

   Paul Lamar

   Ok, so the motion generated by the rotor is not sufficient to help atomize the fuel? My thought was that with the high pressures generated by the gasoline direct injectors and the modern nozzle designs that the atomization characteristics would be better.

   I guess along this line, are there combustion chamber shapes that would be more ideal for direct injection?

   Steve Ross


   I suspect it has more to do with the time the fuel stays in contact with the air.
   I could be wrong.

   CW, John Deere and RPI spent millions investigating this sort of thing and they
   never bettered the Mazda BSFC. Mazda has tried several chamber shapes and the
   latest RX8 is a simple  rectangular bath tub of uniform depth relative to the face of
   the rotor.

   http://www.rotaryeng.net/Stratfied-charge-rotary.pdf

   http://www.rotaryeng.net/Direct-inj-strat-charge.pdf

   The answer to better efficiency is turbo compound F1 style. We should see that
   in 2017 or 2018 with the new RX9 or what ever they call it.



   Paul Lamar


Advantages of DISI. The high pressure used to inject directly into the
cylinder or rotor chamber atomizes the fuel into very small droplet
size which helps vaporization. Also the vaporization cools the combustion
chamber which helps draw more air in. Mazda with their Skyactiv technology
found significantly lower cylinder air temps at the end of intake and even
lower at the point of ignition compared to conventional port injection.
Part of the rotary emissions problem is the intake mixture that makes it
out the exhaust during overlap. With direct injection, the fuel can be aimed
away from the intake and timed to start close to the exhaust port being
covered. This looks to be one area Mazda has been pursuing on the new
engine. With direct injection you could go back to a p-port intake for more
power.

Dale Davies


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