Unthrottled engine-generator

[mackerm]

This question was inspired by a display of antique "hit and miss" engines. In these engines, every power stroke gets the maximum fuel/air charge, but they don't fire on every cycle. Throttled engines, of course, fire on every cycle, but they seldom use the optimum fuel/air charge. Surely the best features of each could be combined.

Are there any engines which control their output strictly via the crankshaft? I imagine this would be most easily done by varying the inducing current in the alternator. If you wanted more power, you'd temporarily reduce the alternator's output, allowing the engine to speed up. And if you wanted less power, you'd briefly increase the output, forcing the engine to slow down.

The varying electrical frequency would be cleaned up with an inverter unit like the ones in small Honda generators.

 

[GregLocock]

The classic hit and miss governor interrupted the intake valve, in a gas engine. So it got no charge and no air when it was overspeed.

No, I haven't seen anyone use an electric brake of whatever form on an engine for normal use, although we do use electrical dynamometers for testing.

The fuel wasteage would be horrific.

Cheers

Greg Locock

 

[mackerm]

Where would the horrific fuel wastage come from? The power generated from slowing the engine to the required speed seems rather small. You could store it in a capacitor, but I doubt it would be worth the effort.

It seems an obvious idea to me. The next logical step after the current crop of throttled variable-speed generators with inverters. The main problem I see is that it's a difficult balancing act. You'd have to extract just the right amount of power so that the engine neither stalled nor revved uncontrollably.

 

[GregLocock]

You will have to absorb the power difference between the load at the braked speed, and the full power available at that speed. In an automotive application this is likely to be 70% of the power of the engine at that speed.

Either I have missed something or this is a very odd idea.

Cheers

Greg Locock

 

[mackerm]

"Braked speed" is not an accurate description. The idea is to produce exactly the amount of power you use. If you need 10 full-compression power strokes per second, that's the goal. Ditto if you need 50 full-compression power strokes per second.

I appreaciate the dialogue, by the way.

Mike Ackerman

 

[JayMaechtlen]

you mean, run the engine at whatever RPM produces the power you need most efficiently, and let the generator/inverter package output the needed frequency and voltage?

Kind of like the way a car with automatic transmission operates- the shift program selects ratios to make good use of the motor.

Should get much better efficiency at part loads, perhaps a bit worse efficiency at full load. (maybe full load is locked at an RPM that produces the desired frequency output, so no conversion losses?)

sounds reasonable to me...



Jay Maechtlen

 

[mackerm]

D'oh! An automatic transmission. That's accurate. Something along the lines of a diesel-electric locomotive's transmission. But I don't think diesel-electrics have been optimized the way I've been thinking. Many people are upset by the amount of noise and exhaust they produce when they're idling, which they do for long periods. Using electricity as a "virtual flywheel" could help lower the RPMs during light loads and idling.