Environmental Engineering Reference
In-Depth Information
economy, and above 50 mph aerodynamic drag becomes the dominant one. For every 2 per-
cent reduction on aerodynamic drag, fuel economy increases by 1 percent (Cummins Engine
Company, 2007).
Aerodynamic drag and rolling resistance
Aerodynamic drag in trailer trucks is intensified by the large frontal area, poor aerodynamics
of the cab, external air cleaners and exhausts, gap between the cab and the trailer, gaps between
trailers, rearview mirrors, gap between the trailer and the road, and suction created by the flat
rear end. Reduction of aerodynamic drag can be accomplished by installing roof deflectors,
cab extenders, chassis fairings, trailer side skirts, underhood air cleaners, concealed exhaust
systems, aerodynamic mirrors, and trailer end caps (Cummins Engine Company, 2007;
Kenworth, 2008b). For new truck purchases, selection of sloped hoods, aerodynamic head-
lights, round corners, and curved windshields lead to better fuel efficiencies.
Truck's rolling resistance is caused by deformation of tires while rolling and the internal
friction between layers of rubber. Energy absorbed by deformation and internal friction is dis-
sipated as heat, which makes rolling resistance worse. Selection of low resistance tires made
from stiffer rubber compounds and replacement of tire configurations translates into a better
fuel economy. The use of wide-base tires mounted on aluminum rims instead of the standard
duals on steel rims decreases weight and has a lower coefficient of rolling resistance (Ogburn,
2008).
Ships
Marine shipping is one of the most energy-efficient types or transportation modes. It assists
with around 80 percent of world commerce and produces 3.3 percent of global emissions of
carbon dioxide from international and regional fleets (Mehling, 2009). The efficiency of fuel
consumed per tonne of cargo per kilometer in ships comes from the fact that ships can trans-
port large amounts of cargo at low speeds. Still emissions from ship engines are much dirtier
than any road engine and contribute to ocean pollution. Marine engines use “bunker fuel,”
which contains high levels of sulfur that translates into sulfur dioxide emissions, and when
burned produces high level of particle matter in the form of carbon and sulfate particles.
Bunker fuel is a fraction heavier than diesel during oil refining with a sulfur content of
3.5 percent for “Bunker C,” which is a low-cost and the most common fuel used in cargo
ships. Moving one tonne of cargo for one kilometer produces 225 times more sulfur dioxide
emissions than moving the same distance by truck (“Sailing ships with a new twist,” 2005). To
minimize this impact, regulations are limiting the emissions of sulfur dioxide from ships by
requiring desulfurized fuels with content of sulfur between 1 and 1.5 percent or by elimination
of sulfur dioxide from the combustion gases by using scrubbers.
The International Maritime Organization (IMO) has identified several operational and
technical measures that could reduce ships' fuel consumption and at the same time reduce
carbon dioxide emissions. From the operational viewpoint, logistics organization, which
includes fleet management and voyage optimization, can reduce fuel consumption signifi-
cantly on all ships. In new ships, technical measures that would reduced fuel consumption
include the reduction of speed, more hydrodynamic hull designs, and better propulsion sys-
tems (IMO, 2009).
Fuel cost takes about 60 percent of the total cost of running a cargo ship, and low sulfur
fuels are 50 percent more expensive than traditional Bunker C fuel (“Sailing ships with a new
