5 ms·

A mid-sized conventional gasoline car is more fuel efficient at 55MPH than at 45MPH. Pumping losses work that way. With improved aerodynamics, you could get t

A mid-sized conventional gasoline car is more fuel efficient at 55MPH than at 45MPH. Pumping losses work that way. With improved aerodynamics, you could get that even higher. https://afdc.energy.gov/data/10312 https://afdc.energy.gov/data/10312

TedDoesntTalk 5y ago
Incredible. Thanks for sharing. I had no idea. What is “pumping loss “?
- axiolite 5y ago
  > What is “pumping loss “? Unlike older scientific topics that have esoteric terminology, usually from the Latin, this one is pretty straight forward... It is the energy lost due to pumping. Basically, the overhead of keeping an engine running no matter how much distance of roadway you cover, but more on point, the extra losses due to running an engine outside of its peak power/performance range: https://www.cycleworld.com/2015/10/12/ask-kevin-what-is-pumping-loss-in-spark-ignition-piston-engines/ https://www.cycleworld.com/2015/10/12/ask-kevin-what-is-pump...
  - wumpus 5y ago
    Weird, does this apply to EV's, too?
    - axiolite 5y ago
      > does this apply to EV's, too? Not "pumping" losses, no. There is no intake air or exhaust gas to pump. EVs may experience an effect that is similar in practice, albeit much smaller... Things like headlights, HVAC, entertainment systems, etc., will draw more power the longer it takes you to get to your destination, so reducing your speed from 30 to 15 MPH might not be an efficiency win.
      - deleted 5y ago
        [deleted]
      - beerandt 5y ago
        No- those losses (less the engine idle speed) are relatively larger for electric, because alternator loss is already baked into the efficiency for ice engines.
    - hhhhhdsgs 5y ago
      its the opposite for EVs. Their range decreases as their speed increases due to the increased effect of wind resistance
    - elil17 5y ago
      I believe due to motor efficiency and losses from AC, media system, etc., the most efficient speed for most EVs and hybrids is around 25 mph. I’ve heard 10 and 35 suggested as well.
    - beerandt 5y ago
      No- electric motors generally perform better at lower speeds, gas at higher speeds. Especially so in direct comparison. Which is why hybrids often switch from electric to gas past some determined speed.
      - sudosysgen 5y ago
        That's only true because the electric motors don't have a gearbox but the gas engines do.
  - GhettoComputers 5y ago
    Would be very interesting to see some of the ideas that they wanted to base improved infrastructure on with older ideas of the future of technology. The convoys always fascinated me, and the entrenchment of older technology makes progression much harder when the existing infrastructure is heavily depended on and long term planning has never been a strength of the US.
swader999 5y ago
But much less efficient at 65 and 75. Pushing the wind eventually gets you.
adrianN 5y ago
At which speed a car is most efficient can essentially be chosen by the engineer designing it as far as I know.
- beerandt 5y ago
  For an engine rpm yes, for a moving body, not so much. Energy in a vacuum is proportional to velocity squared, and energy required with wind drag is iirc 4th power of velocity. So even with an engine designed to be most efficient when the car drives 65 mph, the efficiency of the system will quickly be controlled by drag forces as speed increases.

TedDoesntTalk 5y ago

Incredible. Thanks for sharing. I had no idea. What is “pumping loss “?

axiolite 5y ago
> What is “pumping loss “? Unlike older scientific topics that have esoteric terminology, usually from the Latin, this one is pretty straight forward... It is the energy lost due to pumping. Basically, the overhead of keeping an engine running no matter how much distance of roadway you cover, but more on point, the extra losses due to running an engine outside of its peak power/performance range: https://www.cycleworld.com/2015/10/12/ask-kevin-what-is-pumping-loss-in-spark-ignition-piston-engines/ https://www.cycleworld.com/2015/10/12/ask-kevin-what-is-pump...
- wumpus 5y ago
  Weird, does this apply to EV's, too?
  - axiolite 5y ago
    > does this apply to EV's, too? Not "pumping" losses, no. There is no intake air or exhaust gas to pump. EVs may experience an effect that is similar in practice, albeit much smaller... Things like headlights, HVAC, entertainment systems, etc., will draw more power the longer it takes you to get to your destination, so reducing your speed from 30 to 15 MPH might not be an efficiency win.
    - deleted 5y ago
      [deleted]
    - beerandt 5y ago
      No- those losses (less the engine idle speed) are relatively larger for electric, because alternator loss is already baked into the efficiency for ice engines.
  - hhhhhdsgs 5y ago
    its the opposite for EVs. Their range decreases as their speed increases due to the increased effect of wind resistance
  - elil17 5y ago
    I believe due to motor efficiency and losses from AC, media system, etc., the most efficient speed for most EVs and hybrids is around 25 mph. I’ve heard 10 and 35 suggested as well.
  - beerandt 5y ago
    No- electric motors generally perform better at lower speeds, gas at higher speeds. Especially so in direct comparison. Which is why hybrids often switch from electric to gas past some determined speed.
    - sudosysgen 5y ago
      That's only true because the electric motors don't have a gearbox but the gas engines do.
- GhettoComputers 5y ago
  Would be very interesting to see some of the ideas that they wanted to base improved infrastructure on with older ideas of the future of technology. The convoys always fascinated me, and the entrenchment of older technology makes progression much harder when the existing infrastructure is heavily depended on and long term planning has never been a strength of the US.

swader999 5y ago

But much less efficient at 65 and 75. Pushing the wind eventually gets you.

adrianN 5y ago

At which speed a car is most efficient can essentially be chosen by the engineer designing it as far as I know.

beerandt 5y ago
For an engine rpm yes, for a moving body, not so much. Energy in a vacuum is proportional to velocity squared, and energy required with wind drag is iirc 4th power of velocity. So even with an engine designed to be most efficient when the car drives 65 mph, the efficiency of the system will quickly be controlled by drag forces as speed increases.