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Fuel Efficiency and Hybrid Cars


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How are hybrid cars that don't need to be recharged more efficient than a standard car? The energy from the batteries ultimately comes from gasoline anyways. Wouldn't it be less efficient to charge a battery with gas and then use the battery to power the car than to use gas directly?

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The way I understand it, because the engine is smaller than a conventional car, and the batteries are smaller than a full electric car, the hybridization makes everything efficient. Most conventional engines are sized for peak performance, which you really only use about 1% of the time. The hybrids actually use more battery power than engine power when you "floor it" to increase speed quickly. This means less pollution and gas usage, therefore more efficiency.

 

The hybrids also have the ability to convert the kinetic energy from braking into stored electricity. They even shut the engine off while stopped at red lights. They have special tires for low resistance.

 

Ultimately, car manufacturers love them because for every hybrid they make that gets 60+ mpg, they get to make a couple of 16 mpg conventional guzzlers allowed by the CAFE requirements.

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Okay there's a couple of reason why hybrids are more efficient than a regular gas engine.

 

1. The energy from braking can be converted back into electricity and used to recharge the batteries. This is referred to regenerative braking. Regular cars just use frictional braking and all the energy is wasted as heat.

 

2. The torque curves of an electric motor and gas engine compliment each other. Electric motors supply the most torque at low RPMs. Gas engines supply the most torque when they are in their 'power band'. This is usually at several 1000 rpm. By using a properly designed gas/electric hybrid you can have a total system output with a much larger power band. This means you use each motor at the points where it supplies the most power at the greatest efficiency. The electric motor gets you off the line quickly, but the gas engine carries you when you're cruising along.

 

3. If you cheat and use a wall socket to occasionally top off your battery, you win twice over. Gas engines are horribly inefficient if you look at the chemical energy of the gas compared to the output of the engine. Most of that energy goes off as heat. Power plants, on the other hand, are very efficient at converting chemical energy into electricity. If you use the energy derived from a power plant to charge your battery every now and then, it'll cost less than the gas you'd use, and it'll be derived from a much more efficient source.

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I seen one hybrid where the engine was just idling to produce electricity but would step up a few notches if more power was required than what the batteries required.

The engine wasn't connected to the wheels in any way. A bit like diesel-electric trains.

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Thanks for all your replies. I just assumed that batteries would be charged by the alternator, which works as a result of the combustion of gasoline. I couldn't figure out how it could be more efficient to translate the combustion into electric energy, then use that to power the car instead of using the energy directly from the combustion to power the car.

 

It makes a lot of sense to use breaks to harvest energy, that's a lot of untapped energy in regular cars. Thanks again everyone!

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I was kind of amazed that the hybrids use the electric motor for quick starts instead of the IC engine. And that the IC is used for cruising speeds instead of the battery. I don't know why I had that turned around in my mind. Mopeds, I guess.

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  • 2 weeks later...

Doesn't a Hybrid car have 2 engines, an electric one and a Petrol or Gas powered one??? The way I understood it was, when travelling under 50km/h the electric engine was used, and recharged by braking. At speeds over 50km/h the Gas engine was used, so when cruising around town where the speed limit is 50km/h you effectively do not use any gas.

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Doesn't a Hybrid car have 2 engines, an electric one and a Petrol or Gas powered one??? The way I understood it was, when travelling under 50km/h the electric engine was used, and recharged by braking. At speeds over 50km/h the Gas engine was used, so when cruising around town where the speed limit is 50km/h you effectively do not use any gas.

 

 

Um, yes.

 

If you read the thread, you would have seen that this was all covered.

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