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Margery Conner Technical Editor Margery Conner's PowerSource streams the latest developments in electronic power design and related technologies. Follow Margery on Twitter at: http://twitter.com/margeryc.



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Thursday, October 18, 2007

Auto efficiency: Not much of the gas goes down the road

Oct 18 2007 1:58PM | Permalink |Comments (1) |


 Oil futures closed on another record high today, and where barrel prices go, gas-at-the-pump prices are sure to follow*. So, where does all the energy in a gallon of gas go after you put it in your car’s tank? Here’s what the US Department of Energy’s fuel economy web site says: Less than 13% of the energy from the fuel you put in your tank serves to actually move your car. The rest of the energy is lost to engine and driveline inefficiencies, idling, and a little bit to run accessories such as air conditioning.  Here’s the overall breakdown:

Car subsystem

Losses

Due to:

Engine

62.4%

Engine friction, moving air, wasted heat

Standby/idle

17.2%

 

Accessories

2.2%

e.g. air conditioning

Driveline losses

5.6%

 

… leaving 12.6% to actually move you down the road. I’m not saying to prove that the car is a hugely inefficient way of moving around – it is what it is, and mass transit and bikes are not universally practical – but to point out the enormous potential for improving automobile efficiency. Some of the improvements will come from aerodynamics and mechanical improvements, but a lot will depend on new electronic controls. For example, using an integrated starter that turns the engine off at a stoplight and automatically restarts when you step on the gas can improve on that 17% lost to idling.

Even without the move to hybrid vehicles, the imperative to make cars more efficient is accelerating the adoption of more and more electronic control into cars.

*I just learned of the “Rockets and feathers” metaphor, as used by Chris Knittel of the Institute for Transportation Studies at UC Davis: “Prices actually follow rises in crude oil prices very closely. They tend to lag behind decreases in the price of crude. This is a phenomenon we call rockets and feathers. Gas prices shoot up when crude oil goes up, but they float down slowly when crude oil prices fall.”


Related entries in: Automotive | Power Sources/Controllers | 


Reader Comments



at 11/14/2007 1:34:09 PM, Carlton said:
That''s a lot of losses, just in the engine!

Moving to "hybrid" alone is not a panacea, of course. The current hybrid vehicles really aren''t that much more efficient than a gasoline engine, having both a full engine and full electric motor. A series hybrid, where only the electric motor generates torque directly and a small engine is used just to recharge the batteries while in transit really would boost efficiency.

If the Chevy Volt works out, maybe we''ll see a bunch of series hybrids come out (hopefully, if they really are as efficient as they claim to be).

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