(Cesgranrio - 2010)
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The age of speed: how to reduce global fuel consumption by 75 percent
September 11, 2008
Low-tech Magazine
Breaking speed records was an almost daily occurrence throughout the 20th century. Cars, ships, planes and trains became faster and faster, year after year. Because the power needed to push an object through air increases with the cube of velocity, this race to ever higher speeds raises energy consumption exponentially.
Engineers treat velocity as a non-variable, while in fact it is the most powerful factor to save a really huge amount of energy - with just one stroke, at minimal cost, and without the need for new technology. Lower speeds combined with more energy efficient engines, better aerodynamics and lighter materials could make fuel savings even larger.
Air resistance increases with the square of speed, and therefore the power needed to push an object through air increases with the cube of the velocity. If a car cruising on the highway at 80 km/h requires 30 kilowatts to overcome air drag, that same car will require 240 kilowatts at a speed of 160 km/h. Thus, a vehicle needs 8 times the engine power to reach twice the speed. In principle, this means that fuel consumption will increase fourfold (not eightfold, because the faster vehicle exerts the power only over half the time).
Over a distance of 1,000 kilometres, the slow car would consume 375 kilowatt-hours (12.5 hours multiplied by 30 kilowatts) and the fast car would consume 1,500 kilowatt-hours (6.25 hours multiplied by 240 kilowatts).
However, this extra fuel consumption can be diminished or even negated by, most importantly, more fuel efficient engines, lighter materials and better aerodynamics. Even though today’s cars are faster than those from decades ago, they consume a similar amount of fuel. This is the reason why almost everybody is talking about energy efficiency and aerodynamics, and not about speed.
But if you lower the speed, fuel consumption is decreased by the full 75 percent. More efficient technology cannot change that – unless in a positive way. If you combine a lower speed with more fuel efficient engines and better aerodynamics, fuel savings can become much larger than 75 percent.
A decrease of 75 percent in fuel consumption is not peanuts. More than 60 percent of world oil production is used for transportation, which means that total oil production would be almost halved (-45%). In combination with more efficient engines, better aerodynamics and lighter materials a 75 percent reduction of oil production is not unrealistic.
Yet, when the International Energy Agency argues that the average car sold in 2030 would need to consume 60 percent less fuel than the average car sold in 2005, it claims: “With current technologies, only plug-in hybrids are capable of this”.
This statement is wrong. We could lower the fuel consumption of cars (and other vehicles) by at least 75 percent, we could do it today, and we can do it with present technology.
© Kris De Decker (edited by Vincent Grosjean) http://www.lowtechmagazine.com/2008/09/speed-energy.html, access on April 6, 2010.
The calculation used by the author to support his major view on fuel consumption is that
a car can save up to 75% of its oil consumption if it has a hybrid fuel engine.
a car driven slowly needs only 25% the fuel it consumes when driven fast.
current cars are faster and consume much less than those of the past.
today’s vehicles can travel faster because they are made to consume 8 times more over half the time.
older cars would spend 4 times more fuel than modern cars because their engines were not energy efficient.
Gabarito:
a car driven slowly needs only 25% the fuel it consumes when driven fast.