Sunday, July 20, 2008

Hypermiling and such stuff

I found this very interesting graphic online. It shows where the energy in a car is going. The top is city driving and bottom is highway driving.

The first big thing that you can see is that only 4-7% of the energy actually ends up making the car go forward.

The second thing you can see is that standby - or idling - uses more energy in city driving than driving and braking. 17% of the energy into the car goes into idling.

The third thing you can see is how much energy is lost in the engine - over 60%, close to 70%. There is clearly a huge potential for industry to improve fuel economy by improving engine efficiency.

So what can we as drivers control? Only a few aspects

* Idling
* Aero resistance
* Braking

If we change our driving habits, we can reduce the loses.

Idling - if we can reduce our urban idling by 50%, frees up 8% more energy to flow into the rest of the system, about 1/2 of that will be lost in the engine, but this still gives a boost to 23% of the energy actually making it to the driveline instead of 19%. This means 17% goes through to driving the car.

Braking is the next area where you can gain a reasonable amount. Each time you use the brakes, you are wasting the energy you used to get up to speed. By driving with a fair amount of distance between you and the next car and by looking ahead to the lights and letting the car coast to the light, you can cut your braking in half again. These two things are the main differences between a hybrid and a regular car. They do not idle and they use the brakes to recharge the batteries.

If you idle less, and this does mean turning off the car each time you stop for even a few seconds, and if you drive as if the brakes do not work, you can very quickly get highway mileage for your car in the city. Saving 15 to 20% in fuel is easy.

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