> > > 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?
> >
> > > 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?
> >
> > > 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.
> >
> >Howard
> >
> >
> > [snip]
> >
> > 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.
> >
> > 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"



they still waste 3X the energy - - -they just MAKE more energy. we can say they waste energy with no study simply by the fact that they produce heat- - heat requires energy to produce. Anything that heats up is wasting energy. (if you wanna verify that engines produce heat, touch yer tailpipe after you drive for awhile. . .but don't send me the burn unit bill ;) In fact, combustion engines by their veyr design HAVE to waste energy in order to produce any. . in order to move the pistons, you have to expand the gasses in the cylinder. . the way to do that is to set fire to it, thus the heat.

steam engines actually work on the same principle, but water is not as volitile as gasoline, and takes more energy to heat up enough for it to expand, so the steam engine isn't as efficient. And, when it DOES heat up enough to expand, it doesn't expand as fast as exploding gas does, so all that heat you used to expand it isn't creating as much energy as the gasoline engine.

Rotary engines and regular engines i'm not sure about. . they work on the same principle - -- gas explodes, driving the pistons. . the main difference is where the pistons are placed (many other diffs too, but they're not important to this convo)



a good way to measure engine efficiency is to know how much work it takes to move something a certain distance. Then you see how much gas the engine uses to move that thing that distance. Since it's known how much energy is in a gallon of gas, it's easy then to figure out how much energy was wasted when you used the engine to do the work. Then you know the efficiency.