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A good article. It barely addresses the elephant in the room however: The Toyota Prius and its Atkinson engine. The Atkinson engine is 99% the same as a regul

A good article. It barely addresses the elephant in the room however: The Toyota Prius and its Atkinson engine. The Atkinson engine is 99% the same as a regular engine (aka: Otto cycle), except the timing is different. Instead of closing the valves when the piston+cylinder is full of gasoline+air mix... the Atkinson engine waits a bit and "leaks" some gasoline+air back out before closing the intake valve, effectively burning only 70% of the fuel, but getting maybe 85%+ of the power of a regular Otto-cycle engine. Its a simple and cheap tweak to a traditional engine that grossly improves efficiency (but at huge costs to low-end torque). Basically, any regular ol' carmaker who is mass producing Otto cycle / regular ICE engines can easily tune their piston timing to be an Atkinson engine instead. I believe Toyota even has computerized controls today that switches between efficient Atkinson (lower-power but higher efficiency) modes and powerful Otto cycle (higher power but lower efficiency) modes, though this control isn't really used too often in practice. --------- This article makes a good point that Mazda has a culture of this... rotary engine. It does compare it (somewhat unfairly) to the Atkinson engine though (inside the Prius and RAV4), I don't think anyone expects any traditional engine (Otto or Rotary) to keep up with Atkinson Engine efficiency. Its a good try however. But it does raise the question of what benefits can this rotary engine give over other engine types.

aidenn0 3y ago
I am mildly annoyed that Toyota calls late intake valve closing (LIVC) an "Atkinson-cycle" Atkinson made 3 engines none of which are anything like a 4-stroke with LIVC. The closest is perhaps his two-stroke engine, which kept the exhaust valve closed during the power stroke and open for part of the compression stroke. The Miller-cycle is much closer to what the Prius uses than anything Atkinson made; it was a traditional 4-stroke with LIVC, but required a super-charger to generate power at low RPMs. The Prius has a CVT and electric motor, overcoming any issues at low RPMs. Also now that VVT is more common, many engines run with LIVC under certain conditions.
- jeffbee 3y ago
  And, of course, Mazda had been selling LIVC engines for years before the Prius appeared. Like all of Mazda's other weird engines they were expensive, bad, and unreliable.
  - whaleofatw2022 3y ago
    I was gonna say, pretty sure the millenia? Had some sort of Miller cycle
    - aidenn0 3y ago
      Good memory; Wikipedia agrees with you: "[The Miller cycle] was adapted by Mazda for their KJ-ZEM V6, used in the Millenia sedan, and in their Eunos 800 sedan (Australia) luxury cars[1] 1: https://en.wikipedia.org/wiki/Miller_cycle https://en.wikipedia.org/wiki/Miller_cycle
pmsh 3y ago
If the engines are direct injected rather than port injected, they can just delay fuel injection until the intake valve is closed, and no fuel should be pushed back into the intake manifold. I have read that modern Toyota engines use both port and direct injection, but am not sure what the Prius does.
- pfdietz 3y ago
  You want both to keep the intake valves clean, yes?

aidenn0 3y ago

I am mildly annoyed that Toyota calls late intake valve closing (LIVC) an "Atkinson-cycle" Atkinson made 3 engines none of which are anything like a 4-stroke with LIVC. The closest is perhaps his two-stroke engine, which kept the exhaust valve closed during the power stroke and open for part of the compression stroke. The Miller-cycle is much closer to what the Prius uses than anything Atkinson made; it was a traditional 4-stroke with LIVC, but required a super-charger to generate power at low RPMs. The Prius has a CVT and electric motor, overcoming any issues at low RPMs. Also now that VVT is more common, many engines run with LIVC under certain conditions.

jeffbee 3y ago
And, of course, Mazda had been selling LIVC engines for years before the Prius appeared. Like all of Mazda's other weird engines they were expensive, bad, and unreliable.
- whaleofatw2022 3y ago
  I was gonna say, pretty sure the millenia? Had some sort of Miller cycle
  - aidenn0 3y ago
    Good memory; Wikipedia agrees with you: "[The Miller cycle] was adapted by Mazda for their KJ-ZEM V6, used in the Millenia sedan, and in their Eunos 800 sedan (Australia) luxury cars[1] 1: https://en.wikipedia.org/wiki/Miller_cycle https://en.wikipedia.org/wiki/Miller_cycle

pmsh 3y ago

If the engines are direct injected rather than port injected, they can just delay fuel injection until the intake valve is closed, and no fuel should be pushed back into the intake manifold. I have read that modern Toyota engines use both port and direct injection, but am not sure what the Prius does.

pfdietz 3y ago
You want both to keep the intake valves clean, yes?