> > Maybe some kind engineer or physics teacher can help me on this. I remember reading somewhere that a canoe is the most efficient boat design, the bicycle is the most efficient land transportation and the jet airliner is the most efficient means of air travel. All are based on people/miles for the least expenditure of energy, or something like that. Could this be true?
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> > I also remember that text books in the 1950's and '60's said that a steam engine was 10% efficient, a gasoline engine was 25% efficient and a diesel was 35% efficient. Considering the engineering imporvements in engines, have these percentages changed?
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> > I spend a great deal of time traveling by jet, car, and canoe, with an occasional short ride on a bicycle, so I am curious about such things. Sometime I even wonder how new and old motorscooters figure into all this.
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>Howard
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>
> [snip]
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> Anyway, although I was joking with my opening comment, "efficiency" actually is not a controversial scientific term. It doesn't mean, "What will get you somewhere fastest with the least amount of energy," as you seem to be assuming, as evidenced by your objection that a person paddling it will need to replenish his energy supply after a time. Efficiency is, in a system, the ratio of energy used to produce work to the energy wasted. If you paddle a canoe, you're wasting precious little of the energy: most of the waste will be what is required to counteract the forces of wind and current; barring that, there's just the friction of the canoe against the water, the canoe and your body against the air, and whatever energy is required for you to move your paddle from the point you take it out of the water at the end of one stroke and plunk it back in for the next.
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> Stick on a gasoline engine, and you may get there faster, you may not have to stop and rest ever, and you may feel a lot less exhausted at the end, but the efficiency of the system is still inferior, as gasoline engines waste three times as much energy as they utilize.


I'm curious how engineers actually go about *estimating* these work::energy ratios. How do we come to hear of reports like "combustion engines waste 3x more energy than they consume"? Would that be a piston-driven engine? Would rotary engines be more efficient? Howard originally asked the question:

"text books in the 1950's and '60's said that a steam engine was 10% efficient, a gasoline engine was 25% efficient and a diesel was 35% efficient. Considering the engineering improvements in engines, have these percentages changed?"

Those efficiency figures are so poor that they stick in the mind, but we've come a long way. Today parts can be designed and machined to more exacting tolerances. Gaskets are made from durable resin-polymers to fit more tightly. Oil lubricants maintain greater stability due to synthetics. Embedded CPUs monitor and warn of potential problems within the engine, and even from the start, CAD drafting tools can design an entire vehicule and all its parts... and have them all fit perfectly the first time the engine is built.

So I'd like to know HOW engineers approximate efficiency estimates, and what measuring yardstick do they use as reference. Because part of the figure-folklore that *I* once heard is: that machines with mechanical parts have a "20% efficiency", on average, whereas living organisms like us have at least 70% metabolic efficiency. Why?

Wolfspirit

"Rooting to bring back that good ole' Vorlon technology"