|
Where to start...
Okay, take a 2L displacement Otto engine and convert it to the TRUE Atkinson cycle engine and its EFFECTIVE displacement now becomes something less, as a ratio between the shortened intake/compression stroke and the power/exhaust stroke, than 2L. Giving up the POWER of a 2L OTTO engine infavor of the efficiency, longer "burn" cycle of the Atkinson engine.
The current implementation does exactly the same thing, sacrificing POWER for FE.
Pumping losses.
When the piston is at BDC the travel direction of the crank is at 90 degrees to the angle required to move the piston upward in a compression cycle. Delaying the closing of the intake valve during this early period in the compression stroke results in lowering the pumping losses since the travel angle of the crank will be closer to linear for piston travel once compression actual begins.
An ideal engine would be able to vary the compression ratio as a function of cylinder A/F mixture charge level. An engine with a fixed compression ratio, say 10:1, is not very effective at/with low charge levels. SAAB is currently testing an engine that can vary the compression ratio as a function of charge level.
My point with the Atkinson cycle is: what is the use of an elongated burn cycle if the charge level was so low that the "burn" was complete at 2/3 piston travel..?? So it would be better to not delay the closing of the intake valve for partial throttle and thereby make more efficient use of the native compression ratio of 13:1.
What drives the tubine in a turbocharged engine...??
Partial or moderate throttle = No excess energy left over to be exhausted into the turbine, NO turbine power.
Think you're ever see a turbocharged Atkinson cycle engine..??
|