12

Has Mazda (or any modifier/OEM of rotaries) tried DI (Direct Injection) into the
combustion chamber? Would it be a worthwhile “improvement”? It seems without the
valves, it would be better than DI in a piston engine. I have learned that amongst
others, that the Audi DI engine needs a ‘head job’ on the valves almost every 25K
because the valves are NOT cleaned by the intake manifold injectors as that engine is
DI…….and that the valves get ‘dirty’ very quickly!


Marc Wiese


It might. CW did a lot of direct injection. Might help with squish flow.

Paul Lamar


There are several DI strategies that could be worthwhile in a rotary engine. One of them is DISC (Direct Injection Stratified Charge). Which is a strategy that concentrates a rich mixture in the middle of the combustion chamber, close to the spark plug, surrounded by a lean mixture.  This strategy might be particularly useful in a rotary engine at part load because it allows for lean mixtures in the quench areas without having to worry about good ignition and stable combustion in the rest of the combustion chamber and allows you to open up the throttle body a bit more which should reduce pumping losses.
At full load you will want a richer mixture to achieve Lean or Mean Best Torque for maximum power. This is where PPC (Partially Premixed Combustion) might be a good strategy. This is a type combustion that is somewhere in between diesel style combustion and HCCI (Homogeneous Charge Compression Ignition) combustion.
With this strategy the fuel gets injected so that it only has time to partially mix. This ensures that there are pockets where the conditions are just right for CI (Combustion Ignition) without having the fast combustion rate and consequent high pressure rise rate of a homogeneous charge, which would destroy the engine and which is also why HCCI is only used with very lean mixtures btw. This requires a high compression ratio to work however but this is also where it gets it's higher thermal efficiency from.
I have a 13B DEI block in my basement that is fully converted to run both strategies, except for the high compression ratio unfortunately.
If my agenda allows, I might test the DISC-strategy end this year or maybe next year and if someone is interested I'll post the results here.
If I can find a good set high comp rotors, I might test PPC as well. Does anyone know where to get some for this motor?

Erwin Nijs


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