5 ms·

An useless but fun observation: you can do the litres/100km division and arrive at units of area. A family car might have a fuel consumption of 0.05 mm^2. This

An useless but fun observation: you can do the litres/100km division and arrive at units of area. A family car might have a fuel consumption of 0.05 mm^2. This is the cross-section of the imaginary pipe of fuel along the highway that a car with no fuel tank would have to pick up as it travels.

keule 12y ago
https://what-if.xkcd.com/11/ https://what-if.xkcd.com/11/
dredmorbius 12y ago
Actually, what you're arriving at is energy use per unit distance. The unit of area result you're getting (correcting from original content) is a misuse of units: "liters/100km" is more properly "liters of fuel/100km", where liters-of-fuel is a shorthand for quantity (that is, mass) of fuel used per 100km -- it's more convenient to measure fluid volume than mass (though you'll find that aircraft will measure fuel by weight). And that is still a shorthand for "energy contained per unit of fuel over distance travelled". That reduces to energy/distance, or: ( kg × m ) / s^2. That doesn't have a unit applied to it, though it works out to mass times acceleration. So, as noted, "Liters of petrol" (or diesel) are actually a shorthand for "energy contained in a liter of fuel". There's an imperial unit for this, the barrel of oil equivalent, "barreloil" in GNU Units. This is equivalent to: • 6.12 billion Joules • 1.70 MWh • 5.8 million BTU • 0.000107 Hiroshima bombs • 0.21 tons of coal • 3.82e+28 electron volts • 1.46 million kilocalories (food calories) So, a 30 MPG car (7.8 liters/100km) is burning 0.049 barrels of oil per 100km, or roughly 83.4 kWh/100km. I happened to catch a recent video Robert Llewellyn posted to G+ on the VW e-Golf, an all-electric version of the Golf (previously the Rabbit in the US)[1]. He mentioned getting approximately 15 kWh/100km driving performance, with the manufacturer claiming efficiency as high as 12 kWh/100km. This means that, overall, the electric vehicle is a lot more efficient than a typical internal-combustion vehicle. Checking on Edmunds.com[2], the 2014 Golf Diesel 2.0L 6 speed manual is rated for 30/42 mpg -- the eGolf uses nearly 7x less energy (6.95x) on the road. Mind that generating and transmission losses run around 30%, so the net efficiency gain is only 4.87x, but that's still a lot more efficient than an oil-powered vehicle. The eGolf does offer far less range than the oil-powered version, however, as a result of the much lower energy storage density offered by batteries over liquid fuels. _______________________________ Notes: 1. https://plus.google.com/114018232303831249060/posts/SLeXV2o4jzF https://plus.google.com/114018232303831249060/posts/SLeXV2o4... http://www.youtube.com/watch?v=C2ZDVfa3x7Y http://www.youtube.com/watch?v=C2ZDVfa3x7Y 2. http://www.edmunds.com/volkswagen/golf/2014/?sub=diesel#specs-pod-anchor http://www.edmunds.com/volkswagen/golf/2014/?sub=diesel#spec...

keule 12y ago

https://what-if.xkcd.com/11/ https://what-if.xkcd.com/11/

dredmorbius 12y ago

Actually, what you're arriving at is energy use per unit distance. The unit of area result you're getting (correcting from original content) is a misuse of units: "liters/100km" is more properly "liters of fuel/100km", where liters-of-fuel is a shorthand for quantity (that is, mass) of fuel used per 100km -- it's more convenient to measure fluid volume than mass (though you'll find that aircraft will measure fuel by weight). And that is still a shorthand for "energy contained per unit of fuel over distance travelled". That reduces to energy/distance, or: ( kg × m ) / s^2. That doesn't have a unit applied to it, though it works out to mass times acceleration. So, as noted, "Liters of petrol" (or diesel) are actually a shorthand for "energy contained in a liter of fuel". There's an imperial unit for this, the barrel of oil equivalent, "barreloil" in GNU Units. This is equivalent to: • 6.12 billion Joules • 1.70 MWh • 5.8 million BTU • 0.000107 Hiroshima bombs • 0.21 tons of coal • 3.82e+28 electron volts • 1.46 million kilocalories (food calories) So, a 30 MPG car (7.8 liters/100km) is burning 0.049 barrels of oil per 100km, or roughly 83.4 kWh/100km. I happened to catch a recent video Robert Llewellyn posted to G+ on the VW e-Golf, an all-electric version of the Golf (previously the Rabbit in the US)[1]. He mentioned getting approximately 15 kWh/100km driving performance, with the manufacturer claiming efficiency as high as 12 kWh/100km. This means that, overall, the electric vehicle is a lot more efficient than a typical internal-combustion vehicle. Checking on Edmunds.com[2], the 2014 Golf Diesel 2.0L 6 speed manual is rated for 30/42 mpg -- the eGolf uses nearly 7x less energy (6.95x) on the road. Mind that generating and transmission losses run around 30%, so the net efficiency gain is only 4.87x, but that's still a lot more efficient than an oil-powered vehicle. The eGolf does offer far less range than the oil-powered version, however, as a result of the much lower energy storage density offered by batteries over liquid fuels. _______________________________ Notes: 1. https://plus.google.com/114018232303831249060/posts/SLeXV2o4jzF https://plus.google.com/114018232303831249060/posts/SLeXV2o4... http://www.youtube.com/watch?v=C2ZDVfa3x7Y http://www.youtube.com/watch?v=C2ZDVfa3x7Y 2. http://www.edmunds.com/volkswagen/golf/2014/?sub=diesel#specs-pod-anchor http://www.edmunds.com/volkswagen/golf/2014/?sub=diesel#spec...