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DIESEL ENGINE EMISSIONS
‘early’ version, where the intake valve The exhaust gas also increases the specific the piston. EGR also tends to reduce the
closes before BDC (500 – 540°), or the heat capacity of the mix, lowering the amount of fuel burned in the power
‘late’ version, where the intake valve closes peak combustion temperature. Because stroke. This is evident by the increase in
much later than BDC. Both methods lead NOx formation progresses much faster at particulate emissions that correspond to
to a reduction in effective compression. In high temperatures, EGR limits the an increase in EGR. In modern diesel
the ‘early’ configuration, this results from generation of NOx. engines, the EGR gas is cooled through a
expansion of the charge up to BDC and heat exchanger to allow the introduction
then a compression starting from a lower ‘‘Significant NOx-reduction of a greater mass of re-circulated gas.
level of pressure and temperature, and in
is achievable by
A schematic of an EGR system is given in
the ‘late’ configuration it results from the
implementation of the
Figure 2 on page 72.
late closure of the intake valve at a time As both methods lead to a significant
when the piston is already moving
so-called ‘Miller-cycle’ ’’
decrease in combustion temperature, they
upwards once again. will not be able to lower particulate
Both procedures can be applied to Whereas the Miller-cycle would allow emissions since particulates are burnt off
diesel engines, where they reduce the compliance with IIIA limits without any at higher temperatures. To comply with
final compression temperatures and additional after-treatment, the trade-off on IIIB PM (particulate matter) limit values a
produce lower peak temperatures fuel consumption would be rather particulate filter (DPF) becomes necessary.
during combustion. prohibitive when applied to ensure
A second method to reduce NOx by compliance with IIIB. EGR would allow SCR systems
internal engine design is EGR. EGR works IIIB limits to be achieved, but it requires a Current exhaust after-treatment systems
by re-circulating a portion of an engine's much more sophisticated cylinder head are not specifically geared to railway
exhaust gas back to the engine cylinders. design with potential disadvantages in applications since the rail market is
Intermixing the incoming air with re- maintenance costs. There are other trade- relatively small. Therefore, other existing
circulated exhaust gas dilutes the mix with offs. Adding EGR to diesel reduces the after-treatment systems have to be
inert gas, lowering the adiabatic flame specific heat ratio of the combustion gases considered and their suitability for use on
temperature and (in diesel engines) in the power stroke. This reduces the railways assessed. The complete lack of
reducing the amount of excess oxygen. amount of power that can be extracted by operational experience, together with the
Together with a US-American customer, DEUTZ AG has developed a cutting-edge power concept
for diesel locomotives. Instead of a single conventional large engine, 100 locomotives were fi tted with
several Gensets powered by DEUTZ TCD 2015 Series engines.
The advantages are conclusive: through the modular setup only as much power is generated as is
actually needed. In daily use this leads to a fuel saving of 40%, and harmful emissions could be cut
by around 80%.
DEUTZ AG · Ottostraße 1 · 51149 Cologne · Germany · Phone +49 (0) 221 822-0 · Telefax+49 (0) 221 822-5850 · www.deutz.com · E-Mail: info@deutz.com
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