Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Feasibility
Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
The marine vessel technologies presented in this section are all viable and commercially
available. Two of the limiting factors to implementation of these technologies are the high
cost associated with these changes and the slow fleet turnover rate. Policies that provide
incentives for the retrofit of these technologies, or facilitate a more rapid fleet turnover,
will accelerate the environmental and economic benefits.
Given the international nature of marine shipping, improvements to the global fleet may
need to be encouraged through international agencies and organizations which are
involved in regulating vessel operations, fuel usage, and setting vessel construction
standards. International insurance and banking agencies also may be recruited to ensure
that financing policies facilitate the application of reduced GHG environmental
technologies.
Propulsion System Improvements
Overview
Many of the engine improvement technologies discussed in the locomotive section of this
report, such as common rail configuration, advanced turbo charging, and turbo
compounding, have been applied to newly constructed vessels or during engine retrofit
programs over the past decade. For example, Wärtsilä, the leading manufacturer of large
marine engines, began marketing a range of slow-, medium-, and high-speed common rail
engines in 2001. By 2008, Wärtsilä received orders for over 700 common rail engines.
Typically diesel engines provide power directly to a vessel’s propellers. For such vessels,
fuel consumption and emissions tend to be higher when the engines are not operating at
their optimum speed and load rating. In a diesel-electric configuration, however, a series
of diesel generators are run at an optimized level, providing power to an electric motor
which in turn drives the vessel’s propellers. Similar engine configurations have been used
in naval submarines, but it was not until the mid 1990s that this technology was applied to
cruise ships (Moretti, 2002; Kanerva, 2006; PJK, 2006). For example the largest cruise ship
currently in operation is the Royal Caribbean’s Freedom of the Seas, which is equipped with
6 Wärtsilä 46 V12 diesel engines that use a common rail fuel injection system (Royal
Caribbean, 2009). Each of these engines is rated at 12.6 megawatts, providing a total
output of over 100,000 horsepower (Wartsila, 2009).
The advantages in using diesel-electric systems apply to vessels that operate over a wide
range of loads such as cruise ships, tugs, and roll-on/roll-off ferries. For vessels that
primarily operate at a constant and optimal load such as containerships and tankers, total
plant efficiencies with traditional diesel propulsion may be higher than with diesel-electric
systems, such that there is little fuel advantage to using this configuration for these longdistance
vessels.
Hybrid systems also are being developed that are very similar to diesel-electric systems in
that they operate smaller, more efficient diesel engines to power a generator which in turn
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