Car bumpers used to be made of steel. Most cars now have extruded aluminum or glass-reinforced polymer bumpers. Both materials have a much
higher embodied energy than steel. Take the weight of a set of steel bumpers to be 20 kg, and that of an aluminum one to be 14 kg. Table 10.11 gives the equation for the energy consumption per kg per km for a 1,000 kg car as 2.1
10-3
MJ/km. kg.
(a) Work out how much energy is saved by changing the bumper set of a 1,000 kg car from steel to aluminum, over an assumed life of 200,000 km.
(b) Calculate whether the switch from virgin steel to virgin aluminum has saved energy over life. You will find the embodied energies of steel and aluminum in the datasheets of Chapter 15. Ignore the differences in energy in manufacturing the two bumpers—it is small.
(c) Repeat the calculation for the bumpers made from 100% recycled steel and aluminum. The datasheets of Chapter 15 give the necessary energies
(d) The switch from steel to aluminum increases the price of the car by $60. Fuel cost depends on country; it varies at present between $0.5/ liter and $2/liter. Using a pump price of $1 for gasoline, work out whether, over the 200,000 km life, it is cheaper to have the aluminum bumper or the steel one.