Auto Manifesto

April 13, 2010

A Few Fuel Economy Details

Picked up some interesting tidbits in an SAE article on fuel economy. Fuel consumption, measured in grams per second, is about 0.2 for your typical idling car. That can jump to 2 or 3 g/s under light acceleration, a factor of 10 to 15 times as much. And the average driver launches at about 0.2 g.
Further, the engineers interviewed said that lowest speed in the tallest gear is the most efficient point for each vehicle's fuel consumption.

Cold weather also increases engine friction with the article estimating it is twice as much at 0 degrees C than it is in warm conditions.

Hybrid vehicle fuel economy is more sensitive to driver aggressiveness. For example, during hard braking energy that could be recaptured is wasted if the vehicle's regular friction brakes have to supplement the regenerative brakes.

A few more pieces of info: The average car loses about 4% fuel economy for basic electronics (engine control, brake lights, etc), while it can lose up to 15% when including the use of heated seats, audio, defrost and so on.  Neat stuff.



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