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


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