Environmental Engineering Reference
In-Depth Information
Climate Change, n.d.). The improvement of planes' fuel consumption comes from more effi-
cient engines and more aerodynamic airframes. Because the same types of planes are used for
cargo and for passengers transport, the parallel in fuel consumption is still valid.
Room for fuel consumption improvement still exists, so it is expected that the fuel effi-
ciency of planes will improve even more in the near future. According to IATA (2009), the
most significant gain of efficiency will come from new engine architectures (e.g., open rotor,
geared turbofan, and counter-rotating fan) and from “natural and hybrid laminar flow” sur-
faces that are expected to be in place by 2020.
Open-rotor engines are up to 25 percent more efficient than traditional turbofan engines
(Myron, 2009), but they are noisier and bulkier, which makes them unsuitable for under-wing
mounting. Instead open-rotor engines need rear-fuselage installation (Wall et al., 2009).
Geared turbofan engines offer fuel efficiencies 12 percent better than conventional turbofan
engines. These engines are equipped with a gear box system that allows the fan to rotate at
lower speeds than the compressor and turbine, which results in less fuel burned and 50 percent
less noise (“Aircraft engine firms fight on to improve green technology,” 2008). Natural and
hybrid laminar flow controls are drag reduction techniques that work by stabilizing the bound-
ary layer to delay the transition from laminar to turbulent flow over plane surfaces. By maxi-
mizing a laminar flow around the body of the aircraft (instead of a turbulent flow), skin drag
can be reduced by up to 16 percent (Young and Humphreys, 2004).
Fuel consumption of aircrafts is heavily penalized by weight. So, it is expected that by
using composite materials, the weight of airframes and engines will be reduced in the near
future and improve fuel consumption.
In existing aircrafts, it is more difficult to make energy improvements, and among the few
potential upgrades are the following:
Substitution of components with reduced-weight ones (IATA, 2009).
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Installation of wing extensions (winglets). These devices come in most new aircrafts or
can be retrofitted to existing ones with a consequent fuel consumption reduction of up to
5 percent (Myron, 2009).
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Trains
Trains are fuel efficient because of their low rolling resistance, almost horizontal rolling sur-
face or with low-grade slopes, circulation at constant speeds for long distances, rails that allow
heavier loads than roads, and low aerodynamic resistance in comparison to other vehicles
(e.g., trucks).
However, aerodynamic resistance in trains varies according to the types of carts and load-
ing patterns. As it happens with trucks, the gap between cars produces additional air resistance
that is a function of distance. This is especially important with intermodal trains.
Containers used in intermodal freight have the same height and depth but lengths vary. So
when loaded onto well cars, which can be 40- or 48-feet long, in single or double stacks sig-
nificant air gaps are left open between cars, which generate aerodynamic resistance. The mag-
nitude of this resistance is a function of the speed and becomes important at 70 mph, which is
typical of intermodal trains (Lai et al., 2008). A train pulling exclusively box cars or a coal
train has less air resistance than an intermodal train or a train with different types of cars
loaded with different types of cargo. The aerodynamic resistance of intermodal trains can be
25 percent higher than a train loaded with coal (Lai et al., 2008). Wind tunnel testing showed
that the gap between intermodal loads, the position in train, and the yaw angle of wind are the
most important factors that affect the train's aerodynamics (Lai et al., 2008).
