If it\’s got an engine. . .

Dorri probably likes it

Maximum Efficiency

Posted by ifitsgotanengine on September 12, 2006


It seems to me that the best engine from an efficiency standpoint is a single-cylinder engine. Practical experience bears this out – my Suzuki Savage 650 (single cylinder) got 70 mpg, while my Yamaha Maxim 650 (four cylinder) gets 48. Less moving parts mean less friction. less friction means more of the energy in that gallon of gas goes to moving the car down the road.

Less moving parts also means less parts to break.

Why do we not see three-liter singles in family sedans? Or five-liter singles in sports cars?

If you know anything about engines, you already know the answer to this. A large single-cylinder engine would vibrate so badly that it would shake the car apart.

What I propose is a hybrid single-cylinder engine. Couple a large single-cylinder engine up to an electric motor/generator. The electronics controlling the motor/generator would have to be fast enough to switch from motoring to generating every other engine revolution.

When the engine is on its power stroke, the motor/generator is acting as a generator, charging a capacitor (think really fast battery). On the other three strokes, the motor/generator is acting as a motor, since the engine isn’t doing anything productive.

The hybrid motor/generator isn’t there to improve efficiency through regenerative braking, as in other hybrids, it’s just there to smooth out the big single’s power pulses, allowing it to be used in civilized transportation.

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4 Responses to “Maximum Efficiency”

  1. Steve Gaalema said

    Wouldn’t there still be a lot of vibration just from the unbalanced piston?

    Even better (both from efficiency and vibration) would be one cylinder with opposing pistons enclosing the combustion. Little vibration and 1/2 the piston speed of a single piston.

  2. Dorri732 said

    You’re right, Steve. The engine would have to be dynamically balanced. Either with mallory metal in the crankshaft or balanced with the motor/generator.

    I like the idea of opposed pistons, but that gives us double the frictional area. (piston ring/cylinder wall). I’d have to do some tricky math to determine if the lower speed offset it, but I doubt it would.

    Thanks for the comments!

  3. Steve Gaalema said

    If you assume 1/2 the stroke of a single piston for each of the two pistons, then for the same total displacement, the wall frictional losses should be equal (since the distance over which frictional force is overcome is 1/2).

    Then to really reduce friction, eliminate the crankshaft, and extract power electromagneticly…

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