Quote:
Originally Posted by chrisl
That's a really unlikely claim. Using a frontal area of 35 square feet and a drag coefficient of 0.40, the truck would experience an aerodynamic drag of about 260 pounds at 85mph. Overcoming this would require about 59 horsepower at the wheels. Assuming an overall vehicle weight of 5000 pounds (which is really light for a 3/4 ton), and assuming you're on pretty efficient tires, the rolling resistance will be about another 35 pounds force, requiring another 8 horsepower at the wheels or so, for a total wheel power to maintain 85mph of about 67hp. Assuming a drivetrain efficiency of 85% (15% drivetrain loss), your snowmobile engine would have to be making about 79hp continuously to maintain 85mph (since all the energy in a non plug-in hybrid must ultimately be coming from the engine).
It'll take you just under 6 hours (5.88 hours, to be exact) to cover 500 miles at 85mph. During this period, with the engine making 79hp, the engine will output a total energy of 1.247 gigajoules (or 346.4 kWh if you prefer). Gasoline has an energy density of about 120.3 megajoules per gallon. If you had a 45% efficient engine (which would be incredibly high for a normal gas engine - large low speed marine diesels can approach 50%, but most gas engines are more like 20-30% at their peak efficiency point), you would get 54 megajoules of work out of the engine for each gallon of gas. To get the required 1.247 gigajoules, you would need 23 gallons of gas, giving a fuel efficiency of about 22 miles per gallon.
Keep in mind that the above involved a lot of optimistic assumptions. You could perhaps increase the efficiency further with careful aerodynamic mods, but you aren't going to get 4 times lower fuel consumption than my numbers above. Admittedly, if you load the car with a LOT of batteries (>250kWh), you could start with a full battery charge and 5 gallons of gas, and end a 500 mile drive having used 5 gallons of gas and a huge battery charge. Then it's not really realistic to say you got 100mpg though, since you really used 5 gallons of gas and a lot of electricity, and you could not have made it the distance on the gas alone. Besides, if it were that easy to make a pickup do 100mpg, do you really think Toyota would be selling a 45-50mpg Prius? It would sell a lot better if it did 150-200mpg, which would be easily doable if your claim above held up.
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The mechanical force was supplied by an electric motor mated to the manual transmission that was already in the truck. the Skido motor turned two B-52 alternators (EDIT: they were the starters, not the alternators), one generating electricity to power the electric motor, and one to recharge that huge ass-load of batteries we did start out with.
You are correct in stating we started with charged batteries, and for the purpose of high school calculations 23 years ago, we based our fuel economy on the number of miles covered after a consumer would have pulled out of their garage in the morning. ultimately ending on empty batteries that would have to be charged overnight by a consumer.
We did lighten, rake and aerodynamically treat the truck in order to get as low a COD as we could, but did not have access to a proper wind tunnel for testing - again, we were high school physics students
This is the same basic principle used by trains - run an ICE to turn a generator, and use electric motors for physical motivation. An ICE can be made quite efficient when you find the perfect RPM to just keep it going - not perfect, but far better than trying to cycle it up and down and constantly changing the load.