The variable valve timing engines are pretty clever and effective. Control of overlap, combustion chamber filling, residual exhaust gas amounts and prevention of raw air/fuel mixture making it out the exhaust. It's the way to have both an Atkinson Cycle Engine and an Otto Cycle engine.
For single speed, steady load engines. Engineers have tweaked the compression ratio and intake timing into Atkinson Cycle for years. Getting Atkinson Cycle to work on a variable speed, variable load engine requires the speed and accuracy of computer control.
I can't recall if it was Crower, Manley or who the west coast race engine parts builder was in the 1970's or 1980's. They drove a 350cu" delivery truck with 14.5 to 1 mechanical compression using modified 327 pistons. And a long duration intake cam lobe profile.
There is also work on stratified charge engines where the gasser doesn't use the throttle at cruise. The combustion chamber takes a full charge of air. Then a mist of fuel is kept very close to the sparkplug. If this mist of fuel was spread around the combustion chamber the ratio would be too low to burn.
Pumping losses are reduced as it heat losses to combustion chamber walls.
Hydrocarbon emissions are down as well as the fuel droplets don't "touch" the combustion chamber walls. Fuel that touches or is very close to combustion chamber surfaces either doesn't burn or only partly burns.
One of the reasons an engine fully up to temp is more efficient than when cold. Also why an engine is better off running with a 195F stat instead of a 160F stat or non at all.
True compression ratio maybe even lower at 2 to 1 at part throttle/idle.
The lower combustion chamber pressure and density is why flame travel is slower. This is why vacuum spark advance was introduced to increase part throttle efficiency.
There is some tinkering going on with six cycle gasoline and diesel engine with a much reduced cooling system. Water is injected and flashes to steam after the exhaust stroke. For another "power stroke".
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Today's Featured Article - The Day Mom Drove the 8N - by Brian Browning. My Dad was wanting to put in a garden but couldn't operate the 8N and handle the old horse drawn plow he had found and rigged up to use with the tractor. Well, he decided to go get Mom out of the house and have her drive the tractor while he walked behind the plow. You got to understand that while my Mom is a hard worker who will always help whenever she can... she had never operated farm machinery before that day. Dad got her out there, explained how the clutch was the same as in our o
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