For example, in the United States, a loaded test
(IM240) has been developed to simulate conditions under which high NO x emissions may occur.
Some authorities may also conduct random roadside checks, or use remote sensing devices to
screen for high emitters. In addition, onboard
diagnostics of emission-control systems are
increasingly used to alert drivers to failures.
In Europe emissions from ships and railway
locomotives are governed by the legislation for
non-road mobile machinery (Stages III and IV of
Directive 2004/26/EC). The Stage III standards
are further divided into two substages: Stage III
A and Stage III B. The Stage III B standards
introduce PM limit of 0.025 g/kWh, representing
a 90% emission reduction relative to Stage II. To
meet this limit value it is anticipated that engines
will have to be equipped with DPFs. Stage IV also
introduces a stringent NO x limit of 0.4 g/kWh,
which is expected to require NO x after treatment.
Given the long working lives of the engines in
question, these regulations will not have any considerable effect on emission levels for another
couple of decades [94]. Again, a process of worldwide harmonization of regulations has begun.
Emission standards for diesel engines used in
railway locomotives have also been established
by the International Union of Railways (UIC),
an association of European railway companies
[120]. The standards apply to all new engines
used in new vehicles or for repowering of existing
locomotives, and are binding to UIC members.
Emission standards for marine engines are
defined by the International Maritime Organization (IMO). The standards – for NO x and SO x –
are contained in the International Convention on
the Prevention of Pollution from Ships, known as
MARPOL 73/78 [121]. In addition, the first sulfur
emission-control area (SECA, with a maximum
fuel sulfur content of only 1.5% sulfur content) in
the Baltic Sea entered into force in 2006, and
further SECAs in the North Sea and English
Channel entered into force in 2007.
Fuel Legislation Engine and vehicle technologies
normally achieve their best emissions performance
with high-quality fuels [122]. One property on
which a great deal of attention has focused is the
sulfur content, partly due to the need to reduce PM
and SO 2 emissions and partly because fuel sulfur
has an adverse effect on certain types of engine and
exhaust aftertreatment technology [122]. In Europe,
the controls on fuel sulfur content have been periodically tightened, and in the latest step Directive
2003/17/EC required a full transition to “sulfurfree” petrol and diesel (having less than 10 ppm of
sulfur) by 2009. This should enable advanced technologies – such as lean-burn engines, particle traps,
and regenerative NO x storage systems – to meet
stringent exhaust emission limits.
Because of the contribution of shipping to pollution at large ports, EU Directive 2005/33/EC
limits the fuel sulfur content to 0.1% in marine
fuels for harbor regions in 2010.
Improved Combustion and Exhaust Aftertreatment It is expected that petrol and diesel
will power road transport for the foreseeable
future, and considerable reductions in emissions
might still be realized in the short term through
improved engine design, fuel injection systems,
electronic timing, etc. Developments in ship
engine technology include direct water injection
and humid air motors (in which water vapor is
used to cool the charge air and reduce the NOx
formation during combustion) [96].
The main exhaust aftertreatment technologies
that enable vehicle and engine manufacturers to
comply with the exhaust emission legislation are
three-way catalysts, oxidation catalysts, exhaust
gas recirculation (EGR), DPFs, and SCR. Whilst
such technologies are generally fitted during manufacture, retrofitting is a common pollutionreduction strategy. For example, DPFs have been
fitted to all of London’s 8,000 buses.
In EGR the recirculation of the exhaust air into
the combustion chamber reduces the amount of
oxygen available for NO x formation. It has been
fitted to light-duty diesel road vehicles in Europe
for some years. For trains, EGR can give significant reduction in emissions but can be relatively
expensive to retrofit. It may also not be possible to
fit EGR to many classes of train due to space
restrictions [123]. EGR is also applicable to
ships but is not yet in regular use.
DPFs physically capture particles in the
exhaust stream. They can be broadly divided
into two types: “full flow” and “partial flow.”
70
Air Quality, Surface Transportation Impacts on
(IM240) has been developed to simulate conditions under which high NO x emissions may occur.
Some authorities may also conduct random roadside checks, or use remote sensing devices to
screen for high emitters. In addition, onboard
diagnostics of emission-control systems are
increasingly used to alert drivers to failures.
In Europe emissions from ships and railway
locomotives are governed by the legislation for
non-road mobile machinery (Stages III and IV of
Directive 2004/26/EC). The Stage III standards
are further divided into two substages: Stage III
A and Stage III B. The Stage III B standards
introduce PM limit of 0.025 g/kWh, representing
a 90% emission reduction relative to Stage II. To
meet this limit value it is anticipated that engines
will have to be equipped with DPFs. Stage IV also
introduces a stringent NO x limit of 0.4 g/kWh,
which is expected to require NO x after treatment.
Given the long working lives of the engines in
question, these regulations will not have any considerable effect on emission levels for another
couple of decades [94]. Again, a process of worldwide harmonization of regulations has begun.
Emission standards for diesel engines used in
railway locomotives have also been established
by the International Union of Railways (UIC),
an association of European railway companies
[120]. The standards apply to all new engines
used in new vehicles or for repowering of existing
locomotives, and are binding to UIC members.
Emission standards for marine engines are
defined by the International Maritime Organization (IMO). The standards – for NO x and SO x –
are contained in the International Convention on
the Prevention of Pollution from Ships, known as
MARPOL 73/78 [121]. In addition, the first sulfur
emission-control area (SECA, with a maximum
fuel sulfur content of only 1.5% sulfur content) in
the Baltic Sea entered into force in 2006, and
further SECAs in the North Sea and English
Channel entered into force in 2007.
Fuel Legislation Engine and vehicle technologies
normally achieve their best emissions performance
with high-quality fuels [122]. One property on
which a great deal of attention has focused is the
sulfur content, partly due to the need to reduce PM
and SO 2 emissions and partly because fuel sulfur
has an adverse effect on certain types of engine and
exhaust aftertreatment technology [122]. In Europe,
the controls on fuel sulfur content have been periodically tightened, and in the latest step Directive
2003/17/EC required a full transition to “sulfurfree” petrol and diesel (having less than 10 ppm of
sulfur) by 2009. This should enable advanced technologies – such as lean-burn engines, particle traps,
and regenerative NO x storage systems – to meet
stringent exhaust emission limits.
Because of the contribution of shipping to pollution at large ports, EU Directive 2005/33/EC
limits the fuel sulfur content to 0.1% in marine
fuels for harbor regions in 2010.
Improved Combustion and Exhaust Aftertreatment It is expected that petrol and diesel
will power road transport for the foreseeable
future, and considerable reductions in emissions
might still be realized in the short term through
improved engine design, fuel injection systems,
electronic timing, etc. Developments in ship
engine technology include direct water injection
and humid air motors (in which water vapor is
used to cool the charge air and reduce the NOx
formation during combustion) [96].
The main exhaust aftertreatment technologies
that enable vehicle and engine manufacturers to
comply with the exhaust emission legislation are
three-way catalysts, oxidation catalysts, exhaust
gas recirculation (EGR), DPFs, and SCR. Whilst
such technologies are generally fitted during manufacture, retrofitting is a common pollutionreduction strategy. For example, DPFs have been
fitted to all of London’s 8,000 buses.
In EGR the recirculation of the exhaust air into
the combustion chamber reduces the amount of
oxygen available for NO x formation. It has been
fitted to light-duty diesel road vehicles in Europe
for some years. For trains, EGR can give significant reduction in emissions but can be relatively
expensive to retrofit. It may also not be possible to
fit EGR to many classes of train due to space
restrictions [123]. EGR is also applicable to
ships but is not yet in regular use.
DPFs physically capture particles in the
exhaust stream. They can be broadly divided
into two types: “full flow” and “partial flow.”
70
Air Quality, Surface Transportation Impacts on