Hybrid Gasoline Engine - Atkinson Cycle

Jim,

While I do believe there are a lot of writers that don't go the extra mile and give details on most subjects, the jist of what the reporter was saying is probably true--although I haven't read the article.

The Prius, and I believe the Escape, both use an Atkinson cycle engine. Most gasoline engines use the Otto cycle. The Atkinson cycle, I believe, is an Otto cycle engine that has been modified to allow the intake and exhaust valve timing to be variable. This allows the engine to operate at a maximum efficiency at variable power outputs. The typical Otto cycle engine has peak power and peak efficiency at different locations in its operating envelope. I.e., you'll get a lot of power out of the engine at some rpm and at some fuel input (gas pedal location) but it won't be operating at maximum efficiency.

The Atkinson engine tries to achieve maximum efficiency at whatever power output the engine is operating. I.e., you can have maximum efficiency whether you need 20 hp to travel on level ground or 70 hp to accelerate while going up a hill.

I hope this helps, and I hope others can correct me if I am wrong.

Steve

You might be interested in visiting this web site http://www,creedproject.org/stream_v7n2.pdf page 10and observe that whike every thing you say is true testing a prius on E85 actually incresed power by 20%.

Every thing in life involves trade offs

As stated by Steve its the larger expansion ratio of this simulated Atkinson Cycle that achieves the improved efficiency of the gas engine. Combined with lighter components that are used in the engine IMO. I suspect that the 13.5:1 c.r. is actual piston stroke versus TDC volume and wonder what the effective compression ratio is. Ordinary engines loose heat energy down the exhaust pipe, this Toyota engine gathers some of this with its larger expansion ratio and converts it into kinetic energy.
The trade off is reduced power vis-a-vis the engine capacity. However this does not matter with the electric motor to supply acceleration torque.
Although the engine cycle is called an Atkinson Cycle, it is not an Atkinson engine IMO. The Akinson engine per se is more defined by it's awkward linkage which proved to be impractical but did give actual variable suction and compression strokes. The Toyota engine arrives at the cycle through the back door so to speak by pushing some of the charge back into the inlet manifold as previously stated.

All cars will run better on E-85. Ethanol is a great oxygenate, and will increase output and power. On the flip side, is that it will lower mileage since it is "less explosive"

It's my belief that the Prius engine would be more accuratley called a Miller Cycle engine. That is a engine that has a shorter compression stroke than a power stroke. This is most often accomplished by holding the intake valve open in the early part of the compression stroke. I understand an Atkinson Cyle engine to be one that accomplishes intake, compression, power and exhaust in a single turn of the crankshaft.
Mazda which I believe has built engines which shorten the compresssion stroke has referred to
them as Miller Cycle engines.
I would like to hear comment on this from someone more knowledgable than I.
Thanks

E-85 gives lower gas milage because alchol has much less energy per gallon than gasoline.