The issue with small capacity engines is that the combustion chamber surface area to cc (volume) ratio goes goes up dramatically as cc's decrease.
What this means is that there is more surface area for heat to escape through, rather than push the piston the smaller you go.
ie:
Halving all the dimensions of a cylinder decreases its volume by 8X.
Its surface area by 4X
What this boils down to is that the efficiency of a really small engine of around 10cc IIRC is around 8%, vs over 30% for bigger car sized engines.
That's the efficiency of Thermoelectrics which have no moving parts and are silent.
ie: Fuel to electricity is as, to more efficient and a hell of a lot quieter and long lasting with a TEC if you're looking at a 10cc engine.
Then there's this HC fuel to heat/light to solar electricity: 40% efficient, currently..! which is very exiting!
If you want the most the most efficient, light powerful engine off the shelf today it's a 2-Stroke with a Tune Pipe.
NB!!!
Because its running at constant rpm its NOT nearly as DIRTY as everyone thinks and constant rpm means WAY-WAY simpler to tune for efficiency! ( that's true for any engine)
How's how and why it's so much cleaner:
If a 2-stroke is run at a constant rpm we can get most of the charge that is otherwise lost out the exhaust to return to the combustion chamber, with a Tune-Pipe.
But not all as there will be some dilution in the tune pipe.
If a tiny reed valve is added to the TRANSFER port;
then the first bit of lost to exhaust charge is not in fact charge but air.
The first bit to be lost is the last bit to be returned by the tune pipe.
So any dilution in the tune pipe is more with plain air than charge.
Meaning more to all charge is returned to the cylinder, by the tune-pipe before the exhaust port closes.
ie: in the video that 1st bit of green to escape, which is the last bit of green to be returned is plain air and any dilution is no longer a problem.
The other place where there is a problem is with the power stroke only being around half a downward stroke, vs a 4-stroke's full stroke, before the exhaust port opens.
This means that there is way less time for a complete and clean burn of all the charge.
If one were to add hydrogen; the burn is speeded up dramatically, making that initial exhaust escaping down the pipe cleaner.
Here some sort of onboard hydrogen or HHO/Hydroxy cell could be used.
NOT for economy, but for improved emissions...
( Do NB MIT etc's plasmatrons that are in fact efficient at onboard hydrogen production however)
That leaves the lubricating oil and soot as an issue.
They are MUCH heavier than the gasses in the exhaust.
So a centrifuge after the tune-pipe would be efficient at separating these particulates in the exhaust from the gasses, whence they could be returned to the intake.
( I suspect a centrifuge may also be a very effective muffler. Especially with some thought in that direction put into it's design.
I also NB the effectiveness of Helmholtz and /or Quarter Wave Resonators on fixed rpm exhaust etc noise )
What this means is that there is more surface area for heat to escape through, rather than push the piston the smaller you go.
ie:
Halving all the dimensions of a cylinder decreases its volume by 8X.
Its surface area by 4X
What this boils down to is that the efficiency of a really small engine of around 10cc IIRC is around 8%, vs over 30% for bigger car sized engines.
That's the efficiency of Thermoelectrics which have no moving parts and are silent.
ie: Fuel to electricity is as, to more efficient and a hell of a lot quieter and long lasting with a TEC if you're looking at a 10cc engine.
Then there's this HC fuel to heat/light to solar electricity: 40% efficient, currently..! which is very exiting!
If you want the most the most efficient, light powerful engine off the shelf today it's a 2-Stroke with a Tune Pipe.
NB!!!
Because its running at constant rpm its NOT nearly as DIRTY as everyone thinks and constant rpm means WAY-WAY simpler to tune for efficiency! ( that's true for any engine)
How's how and why it's so much cleaner:
If a 2-stroke is run at a constant rpm we can get most of the charge that is otherwise lost out the exhaust to return to the combustion chamber, with a Tune-Pipe.
But not all as there will be some dilution in the tune pipe.
If a tiny reed valve is added to the TRANSFER port;
then the first bit of lost to exhaust charge is not in fact charge but air.
The first bit to be lost is the last bit to be returned by the tune pipe.
So any dilution in the tune pipe is more with plain air than charge.
Meaning more to all charge is returned to the cylinder, by the tune-pipe before the exhaust port closes.
ie: in the video that 1st bit of green to escape, which is the last bit of green to be returned is plain air and any dilution is no longer a problem.
The other place where there is a problem is with the power stroke only being around half a downward stroke, vs a 4-stroke's full stroke, before the exhaust port opens.
This means that there is way less time for a complete and clean burn of all the charge.
If one were to add hydrogen; the burn is speeded up dramatically, making that initial exhaust escaping down the pipe cleaner.
Here some sort of onboard hydrogen or HHO/Hydroxy cell could be used.
NOT for economy, but for improved emissions...
( Do NB MIT etc's plasmatrons that are in fact efficient at onboard hydrogen production however)
That leaves the lubricating oil and soot as an issue.
They are MUCH heavier than the gasses in the exhaust.
So a centrifuge after the tune-pipe would be efficient at separating these particulates in the exhaust from the gasses, whence they could be returned to the intake.
( I suspect a centrifuge may also be a very effective muffler. Especially with some thought in that direction put into it's design.
I also NB the effectiveness of Helmholtz and /or Quarter Wave Resonators on fixed rpm exhaust etc noise )
