Environmental Engineering Reference
In-Depth Information
10
Cargo
plane
1
Truck
Gas
pipeline
0.1
Container ship
Railroad
Oil
pipeline
0.01
Maritime tanker
0.001
1
10
100
1000
Velocity (m/s)
Figure 13.2
Relative energy consumption for different freight transportation methods at typical speed
ranges expressed in logarithmic scales.
Adapted from Chapman, 1989.
high-density fluid, drag forces are minimized by an adequate design that minimizes the
pressure drag and low speeds, which makes slow-moving cargo ships one of the most efficient
transportation methods.
Other important factors that affect the fuel economy of transportation vehicles are the ther-
modynamic efficiency of the engine(s) that converts fuel energy into power and the weight of
the vehicles themselves. When all the factors that affect fuel economy are combined, the
amount of energy used by a vehicle certainly is a function of the mass transported; but it is
severely affected by the velocity at which it is displaced. When different transportation meth-
ods are compared in terms of relative energy consumption, a vessel transporting bulk cargo
uses 1 unit of energy, a container ship would use 2.4 units, a train 3.1 units, and a truck
10 units of energy (Jacobs, 2007). Figure 13.2 shows a plot of the normalized ranges of energy
spent for different freight transportation methods at typical speed ranges for each method both
expressed in logarithmic scale. From the plot, it can be observed that a cargo aircraft uses two
orders of magnitude (100 times) more energy than a slow-moving marine tanker. The plot may
be in some way outdated because the efficiency of vehicles has changed significantly in the
last two decades; however, physics has not changed and the plot still illustrates the point.
