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Maybe something here is not understood. Atkinson cycle did not use variable valve timing. The offset crank is a means that accomplishes characteristics of Atkinson's design.
The change in valve timing which allow blow back into the intake manifold, combined with residual exhaust gas in the cylinder allows partial throttle positions with higher actual compression in the cylinders. This is done by having a higher actual compression ratio which is reduced by the actuation of the camshafts, with the fuel mixture diluted by higher percentages of exhaust gas in the combustion chamber when the piston is compressing the mixture.
Maybe not the best explanation but it is a "lean burn" scenario, without the NOX emissions issues of the classic lean burn design. Higher part throttle in cylinder compression, higher EGR content in the compressed mixture gives you the advantage of better "leverage" while using less fuel. The mixture will not heat up as high in combustion as a normal mixture but most of that is mitigated by the higher static compression.
To a certain degree this allows the throttle position to be more open for the same amount of power while power produced is lower due to higher EGR percentage and higher in cylinder compression.
With a static compression of 13.5 to 1 at 50% manifold vacuum that works out to 6.75 to 1, while a more typical 10 to 1 at 50% throttle would give you 5 to 1 actual compression (the amount of fuel & air actually compressed by the piston).
A normal engine idling with a static compression ratio of 10 to 1, with 22 inches of manifold vacuum at idle would produce 8/30 of the static compression. That's less than 3to 1 actual compression 80/30 to be exact, assuming atmospheric is 30 inches.
This is the direction most manufacturers are going to with super high compression ratios, Atkinson cycle, with one more critical improvement. Direct Injection, which the Prius engine does not have, allows fuel to be injected into the combustion chamber, but that is only part of it. Once you can inject fuel into the combustion chamber at pressures higher than the combustion temperature produces, then you can inject fuel any time after TDC, with no possibility of pre ignition. Mazda is doing this with SKYACTIV, with the last injection at something like 60% ATDC. This allows them to stretch out the combustion duration to produce a more even application of pressure to the top of the piston for greater efficiency, a longer push, in other words.
An engine swap from a Prius to another car, eliminating the hybrid components, while doable, would require some extraordinary capabilities, since the programming of the ECU depends on the hybrid synergy drive to cover specific portions of power application. It would be way beyond most peoples capabilities for probably not as great a benefit as might be imagined.
Get a manual Echo or Tercel and put one of the higher overall ratio Japanese home market transmissions in it and get 50+ MPG that way.
regards
Mech
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