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DIESEL ENGINE EMISSIONS
in early 2006. The average age of the
European Diesel fleet was estimated to be
27 years for locomotives and 16 years for
DMUs. The rail sector’s total pollutant
emission output was evaluated to be less
than 1% of the total emission release.
With an increasing replacement of existing
rolling stock by new vehicles, a gradual
improvement of the emission behaviour of
the fleet was anticipated in the mid-term.
Retrofitting the existing fleet, which in
some cases was technically not feasible,
was not considered to bring a net benefit.
Figure 1: Functional schematic of Miller-cycle
The Review Process of the Directive
started in 2006 under the responsibility of
engines up to 560 kW from those with regarding their exhaust emissions. the European Commission’s Joint
higher power. Emission limits of different values were Research Centre (JRC).
In parallel with these developments, introduced for locomotive engines and for To represent the opinion and needs of
the European Commission began to railcar engines (IIIA) between 2006 and operators and manufacturers, the UIC B
introduce legislation limiting pollutant 2009 and even stricter limits (IIIB) were 208 expert committee, together with
emissions for all Non Road Mobile envisaged for 1 January 2012. Rolling Stock Manufacturers (UNIFE) and
Machinery (NRMM). EC Directive 97/68, Simultaneously, it was decided to perform engine producers (EUROMOT) was asked
in force since 1998, excluded rail vehicles. an inventory on emissions by Rail vehicles to define the users’ standpoint. The
From the end of 1990s, a number of (Rail Diesel Study), an investigation of the following work stages were identified:
railways had been coming under the validity of the rail specific test cycle (cycle
a73
Assessment of modifications within the
scrutiny of environmentalists since a F in ISO 8178-4) as well as a critical engine that might lead to potential
growing source of complaints were being review of the new version of the Directive improvement of its pollutant emissions
a73
Assessment of exhaust after-treatment
systems and filters for railway
operations together with their impact
on fitment space in the vehicle, mass
and length
a73
Consequences for re-engining
a73
Consequences for procurement,
operational and maintenance costs
a73
Test cycle assessment
a73
Comparison and possible alignment
with North American legislation
NOx reduction
Significant NOx-reduction is achievable by
implementation of the so-called ‘Miller-
cycle’, originally devised to improve the
efficiency of SI-engines (spark ignited
engines), for diesel engines. Instead of
closing the inlet valve after the piston
Figure 2: Functional schematic of EGR
passed Bottom Dead Centre (BDC) on
its intake stroke, the valve closes long
made concerning diesel emissions from rail and their future limits to be completed by before BDC. This allows an expansion
vehicles in densely populated urban areas. the end of 2007. of the charge air leading to a lower
As a result, the revision (26/2004) of The inventory was performed by combustion temperature. The
the EU directive 97/68, included AEAT with support from the UIC, Rolling formation of NOx increases with the
provisions for railway vehicles in the Stock Manufacturers (UNIFE) and Engine combustion temperature.
directive and from this point on they Manufacturers (EUROMOT). The There are basically two methods of
became subject to statutory provisions resulting Rail Diesel Study was published applying the Miller process. The so-called
72 EUROPEAN RAILWAY REVIEW
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ISSUE 3
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2008
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