Yeah if I was wealthy I'd would have and now would be patenting some of my ideas. Oh well I'll just wait and someone else will figure it out. That's how it works for me. And funny how they gave up on their baby, the Wankel.

Rotarys in their current design just aren't feasible with today's emission and efficiency requirements. They were definitely cool in their day though.

Engines used as generators for electrics may allow expanded use of ported engines (two strokes, Wankels, etc) which can be clean and efficient when operated at fixed RPM and load. I'm pretty sure that is what's behind Mazda's idea to use a Wankel as a range extender.
https://www.carsguide.com.au/car-news/mazda-confir...

Okay, but what's the deal with the weird pocket in the piston crown?

Mike Halloran
Pembroke Pines, FL, USA

Must have something to do with the direct injection scheme. The linked article mentions it but does not explain it.

"A number of improvements to the Miata's combustion process were implemented, too. The shapes of the combustion chamber and piston feature a number of modifications to increase tumble flow speed, and thus, and knock resistance. A new high-pressure fuel injection strategy makes combustion more efficient, too.

There's some clever stuff going on with electronic controls here, too. At low RPMs, fuel is injected during the heat and pressure strokes, and just before the power stroke to create a richer mixture around the spark plug, creating more stable combustion. This was critical to give this engine a boost in low-RPM torque, but not at the expense of refinement and fuel economy."

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

All of the Mazda Skyactiv engines have that bowl in the piston. Under some operating conditions, they are controlling detonation by injecting fuel late in the compression stroke so that the bulk of it stays within that bowl and doesn't get out to the periphery of the cylinder, which is where detonation usually sets in. Can't detonate with no fuel in the air out there.

Bowl in the piston - anything to do with flame quenching?

"Quench" is old thinking. You don't want the flame to go out, you want it to keep burning until as much of the HC and CO are consumed as possible.

"Squish", on the other hand ... The bowl-in-piston arrangement promotes plenty of it. It's not quite to the same extent as with a diesel engine, but it is headed in that direction. Note the flanks on the sides of the dome; I'm quite sure these match up pretty closely with the chamber walls in that area.

In certain operating modes, the Skyactiv engines inject fuel late in the compression stroke, and a fair bit of it would remain within that bowl and close to the spark plug, with lots of charge motion to mix the fuel and air. There is no "quench" (old school hot-rodder thinking and terminology) because there is next to no fuel out in the far reaches of the chamber anyhow. Can't have detonation if there is no fuel to burn.

The Skyactiv-G engines don't use lean-burn; that's a no-no for the emission controls. The overall chamber has to be stoichiometric but it can be rich in the vicinity of the spark plug (easier ignition) and lean outside of that, and then the squish turbulence would mix it all up near TDC and allow the (already-ignited before TDC) combustion to complete.

"You don't want the flame to go out"... that is exactly what I was trying to tell. Won't the bowl increase the flame quenching distance?

Trying to intuit combustion behavior in a modern engine is futile in my opinion. These days, it's all done with chemical kinetics code integrated in CFD code. This is really the only way to understand the fine detail of how combustion proceeds in a modern engine.

Combustion systems don't design themselves, nor are they designed by CFD. They are still designed by people, based on hunches and experience. CFD can provide insight and can test ideas, if you trust it and use it wisely.

Steve

I think it's combustion modeling (CFD/Chemical Kinetics using Chemkin or similar), test on instrumented engines (such as the one shown at www.ntnu.edu/ept/internal-combustion-engine-labora...), update models based on measurements, and repeat. That's how we designed new systems during my career in research and development (not engines, but a similar process of modeling validated and refined by experiment).