Quote:
Originally Posted by sc_rufctr
I can't remember the teacher that said it but apparently there is that much energy in a tank of gas.
If you think about it we have cars that can travel above 200 mph on an engine that may be 20% efficient at best.
How fast could that car go if the engine was 99% efficient?
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As a side question. How efficient are modern rocket and jet engines?
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Not 18,000 mph.
What you need to understand is that heat engines work via thermodynamic principles. The maximum theoretical efficiency of any system comes from the Carnot cycle and is limited to the difference between the hottest temp in the cycle and the lowest temp, divided by the hottest temp, all in absolute numbers. Most of the cycles require input of energy (compression) and have losses which cannot be recovered (friction, heat of vaporization of water in combustion, etc).
Add to this that a car engine has to operate over a wide range of operating conditions.
Something the hybrid car is supposed to do it allow a smaller, more efficient, specially tuned engine to operate and store energy (in the batteries) so that the car car be still operated over a wide range of operating conditions. The problem is, it is still an internal combustion engine. It isn't THAT much more efficient.
If you look at the hybrids, you will find that they are more areodynamic, lighter, have higher pressure tires, etc. I don't know the details, but I expect better than 50% of the gains are created there. And let's also bring up regenerative braking.
If you took a Hybrid, removed the batteries and all of the other associated junk, and replaced it with a 60-70 hp 1.0l VTEC, with a 6 speed manual transmission, I expect you could get similar mileage. And it would be 1/2 the cost...
Most of the people in this country buy an SUV because they have a lifestyle which includes the need for one, at times. It would be more fuel efficient to have a tiny commuter care during the week, and the SUV for other times. But that means doubling the number of cars.
Or you could rent the SUV when you need it. But that is not convinient.
The best way to asses two different cars is not on just fuel efficency, but on the overall cost of ownership for a set period of time. Money is a pretty good indication of how much energy was required to build it, run it, maintain it, etc.