Abstract
Transportation takes a considerable and increasing fraction of the energy use worldwide, and more than half the oil consumption. By far the largest part is used by cars powered by internal combustion engines. The advantage of using internal combustion engines is that the energy density of liquid fuels is extremely high. The disadvantage is that gasoline and diesel engines have a poor performance: 20 to 25% only. How does this compare with electric cars? What are the alternative transportation systems and their efficiencies anyway? In this lecture we analyse the efficiency of various transport systems, using elementary physics principles. We will look at cars, buses, trains and TGVs, ships and aircraft. In addition, the efficiency of human powered vehicles will be considered. New and promising developments in the field of Intelligent Transportation Systems, like Cooperative Adaptive Cruise Control, are also discussed.
Highlights
Summary. — Transportation takes a considerable and increasing fraction of the energy use worldwide, and more than half the oil consumption
If a family drives an average of 20000 km annually, it consumes ca. 1400 litres of gasoline
Experimental data for trains. – A double-decker train consisting of 4 cars (372 seats in total, 254 tons) turns out to have an energy efficiency of 158 passenger-km per litre of gasoline, if converted to electricity
Summary
Speed (in km/h) Fig. 1. – The resistance that a car experiences increases dramatically at higher speeds, due to the rapidly increasing air resistance or drag (blue curve). – The resistance that a car experiences increases dramatically at higher speeds, due to the rapidly increasing air resistance or drag (blue curve). 1. We notice that, when we drive through residential areas at lower speeds (below 50 km/h), the rolling resistance is dominant. We notice that, when we drive through residential areas at lower speeds (below 50 km/h), the rolling resistance is dominant It is clearly an advantage in this situation to have a light car (especially since it uses less energy during the frequent stop-and-go cycles). Things are not as bad as suggested by the steeply rising curve This is because the efficiency of an engine increases at higher speeds, since it has to work harder (the efficiency is zero when the engine is idling!). Some sort of speed limit may be a good idea after all, if we consider energy use
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