Small efficient engine rubber coupled to PM generator: what and efficiency quest

[Logic11]

If one wanted a small efficient gasoline engine to PM generator, today!
Sorry there's no such thing.
The surface area of the combustion chamber increases as the combustion chamber volume, in cc's here, decreases.
The smaller the engine, the more inefficient it is, due to heat loss through the big surface.
For our power needs we're looking at engines as found in Weed Wackers (cheap), chainsaws (?) and RC aircraft (not).

It doesn't end there.
Increased friction..? (..? is often a 'note to self)

Pumping losses below the single piston.
In a 2 cylinder, 1 piston is going up while the others coming down, so the air beneath them on has to move 1 cylinder over
There's nowhere to go in a single cylinder.
Vacuum is currently used to ameliorate that. (sucks oil out between the rings? Lubrication?)

(2 Reed valves turn it into a supercharger..!One in and one out to the intake.
Lubrication becomes an issue. That much oil in your intake wont work. Centrifuge..?

Or put a 4-stroke head on a 2-stroke and lube it like a 2-stoke.
While that might help efficiency some and power to weight, I digress! )

(Oh ye; Or just go 2-stroke. Constant rpm makes it way easier to clean up a 2-stroke.
The oily exhaust makes it so you can use structural frame tubing as an exhaust and Quarter wave resonator saving weight. That may work for other engines too depending on metal choice. But I digress again! )


Point is small pistons just aren't as efficient.

A rotary engine's power stroke is in the same... lobe I think? Its like the sleeve and head stay hot from constan power strokes if you get my meaning and its just a cool piston every time type thing
If the combustion wall runs hot that should make small rotaries more efficient than small piston engines..?
Friction is lower too IIRC? No reciprocating.
They're high maintenance so guys who enjoy building engines have them...

They do run smooth (low vibration) and are pretty compact.
This video of a tiny 1.4hp rotary makes you want to put gears in just for the sound!

I NB that high pitch noise is easier to damp. and constant noise easier to tune out. (for all engines mentioned)

There's that other rotary too..?

Linear engines:
Very efficient!
But you wont find one at the hardware store.
I think maybe the DIY trick here is to turn the virtual crankshaft like an electric motor would, sort of linear-ised...
Change to generator PDQ every 4th stroke. To supercaps 1st..??
Then start playing with the CRANK profile..!
A "We know how crank engines work so stick with that initially" kinda thing?

Lets not forget that everything from optimal AF ratio and spark timing to cam profiles and tuned length exhausts and intakes can all work together at their optimum, all the time..! at constant rpm,
EASILY!!!
Even with a cheap ol carb etc.
This works for all the above engines.
So which type and why???


Engine to generator:
Direct drive with a rubber coupling is most effectient, but both the engine and generator have optimal rpms.
Finding an engine and generator (PM motor?) that are optimal at the same rpm is no easy task however!?
So chain or belt drive makes things easy here. 96% efficient?
What would you guys do?

The generator:
Thats all up to others here, far more qualified than I.
I'm at sized for average KW, PM motor and engine..?

 

[Chalo]

Linear electric motors suffer reduced effectiveness when coupled to a crank, because they only reach their maximum speed for an instant with every stroke, with the remainder of the stroke at lower and changing speed. Given that the entire world runs on rotating generation equipment for a lot longer than any of us have been alive, I think you'd want to use some kind of rotary generator. When mass and energy efficiency are taken into account, it's a three phase AC generator that does it best.

Why you'd want to drive it with a small reciprocating engine, with its attendant noise, pollution, and inherently impaired efficiency, is beyond my understanding. I guess you're focused only on the good side of the equation. Maybe sniff around Stirling engines and see if you can find something that doesn't suck so much. They're purportedly more efficient than gasoline engines and definitely less obnoxious.

Rubber couplings introduce hysteresis loss and wear. Flywheels do the same job better.

 

[Logic11]

Linear electric motors suffer reduced effectiveness when coupled to a crank, because they only reach their maximum speed for an instant with every stroke, with the remainder of the stroke at lower and changing speed. Given that the entire world runs on rotating generation equipment for a lot longer than any of us have been alive, I think you'd want to use some kind of rotary generator. When mass and energy efficiency are taken into account, it's a three phase AC generator that does it best.

Why you'd want to drive it with a small reciprocating engine, with its attendant noise, pollution, and inherently impaired efficiency, is beyond my understanding. I guess you're focused only on the good side of the equation. Maybe sniff around Stirling engines and see if you can find something that doesn't suck so much. They're purportedly more efficient than gasoline engines and definitely less obnoxious.

Rubber couplings introduce hysteresis loss and wear. Flywheels do the same job better.

No-no;
I mean a virtual crankshaft...
ie: We have the ignition and EFI tech for real crankshafted engines. We also have the software for high pole count rotating motors, so a virtual 'sinusoidal' but physically linear crankshaft/motor to run the 3 non powered strokes is not a 'start from scratch' endeavor.

ie: Making a linear electric motor using current (rotational) software should be easy, so you can drive a non firing linear engine all day, with ease.

I'm guessing that some well placed diodes (to std active PFC etc circuitry) in the motor circuitry will allow for the power stroke to generate more electricity than the other 3 'motored' strokes take, as it does in stock 4-stroke engines today. (guessing)

The efficiency of a linear engine is (theoretically) WAY better than a std ICE with crankshaft:
Max torque from a crankshaft would be IF the conrod was at 90 degrees to the crank when the piston was at the std 20 deg after TDC where the max pressure on the conrod is currently produced during the power stroke in a std engine...

ie: In today's engines; max pressure is produced when the conrod is more trying to push the whole crankshaft down out of the engine, rather than when its at the 90 deg to the crankshaft optimal for turning it.
That's NOT an issue with linear engines, and is why there's so much research into them...

Also; when the conrod is at an angle relative to piston motion, there is a sideways force on the piston that translates in high friction (and wear) between the piston and sleeve.
That is also NOT an issue with linear engines...

Where their issue lies is in getting their piston to reciprocate in the predictable 'sinusoidal' manner all our software is already geared for...

(if you want to get technical about vibration free linear engines; 2 counter reciprocating pistons is where you end up and that means 2 virtual, electromagnetically driven crankshafts/pistons...)

All this takes a hell of a lot of picturing in your minds eye. I suggest a high grade blunt.

As for why:
The maths says: Producing onboard electricity is most eco for heavy vehicles where added weight is a smaller percentage of total weight.
For that to be true in say a velo or E-bike, the genset weight needs to be that of a small hydrogen balloon!
So no it's mostly not for the 1st world, although The Toecutter an co. might disagree.

Here in 'The New South Africa', that many people 'brand avoided' etc for, the power is more off than on.
So having a highly mobile efficient genset wherever you go is a big plus! Come visit SA if you don't believe me, I dare you!
(You also want to bring (sewage filled) pothole hopping active suspension with you)

Rubber couplings allow for the engine and genset to be slighty out of alignment. (the less so; the less your arguement holds water) Thats why you can go buy one right now...
If you want to engineer an ICE with the PM generator doubling as the flywheel you need to go buy a lathe and milling machine and probably a good fitter and turner just for a start! That's a lot more expernsive.

But (for once) thx for arguing: Lots of people were probably wondering the same things but not arsed to ask.