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Emissions
Strategy for London Taxis |
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STT Emtec´s Emission
Reduction Technology |
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Motor & Diesel Turbo ‘CLEANPOWER’ emission reduction system for Metrocab |
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P.C.O. Notices |
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| In
order to meet the implemented air quality
strategy for London Licensed Taxis, STT
Emtec AB has developed a robust, efficient
and cost effective emission technology
called CleanCab.
The CleanCab system is based upon known
technology such as turbo charging, exhaust
gas recirculation (EGR), intercooler
and an EGR cooling system which will
convert the existing engine to meet
the latest Euro 3 emission standard.
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General
description of the CleanCab system |
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| A
turbocharger is used to feed air into
the engine in order to keep the air-fuel
ratio at acceptable levels to optimize
combustion. The boost pressure is controlled
by the main STT Emtec electronic control
unit, ECU, operating a pulse width modulated
valve. The ECU is also controlling the
amount of exhaust gases to be recirculated
by the EGR valve.
The only parameters required to control
the Cleancab System are engine load,
engine speed and temperature. The exhaust
gases are cooled by an EGR cooler to
reduce the exhaust gas temperature before
it is mixed with the inlet air. In addition
an intercooler system is added to increase
the density of the compressed inlet
air. |
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| Background |
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| The
air quality strategy for London requires
all “black cabs” operating in London to
demonstrate emission performance equivalent
to current Euro 3 emission requirements
by January 2008. The reason is that the
London Taxis estimates to emit 12% NOx
and 24% PM of total road emissions in
central London.
As the fleet is a mixture of vehicles
with different emission levels, EU1,
EU2 and EU3, the used emission technology
need to meet reductions as below, in
accordance with N1 category III.
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| -28%(IDI) |
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| -46%
(IDI) |
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| -41%(IDI) |
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| -50%(IDI) |
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| A
number of options can be used to achieve
Euro 3 Standards, such as: |
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| Exhaust
aftertreatment including |
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- Diesel Particulate Filter, DPF |
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NOx reduction by, EGR (Exhaust Gas Recirculation),
SCR (Selective Catalytic Reduction by
urea) or NOx catalyst |
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| Euro
3 Technology upgrade on existing engines
including |
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| -Turbo
charging |
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Intercooler |
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Hi performance EGR |
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EGR cooler |
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The
Exhaust aftertreatment option however
requires specific conditions from the
driving cycle to be able to operate effectively
and robustly, the main requirement being
sufficiently good exhaust gas temperatures.
The New European Driving Cycle, NEDC,
however used by Millbrook as a representative
profile for the emission tests indicates
a very low average exhaust gas temperatures
in the order of 192 deg C. |
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| “Based
upon a concept study of the operating
conditions, including temperature profile
and Air Fuel Ratio conditions STT Emtec
AB made following conclusion” |
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| Exhaust
aftertreatment is not a durable solution
because: |
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The low exhaust gas temperatures are insufficient
to promote continuous and reliable regeneration
for a passive DPF system, and hence
such a system will require frequent cleaning
to prevent irretrievable damage to the
filter substrate. |
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EGR as a stand alone solution is not possible
due to low AFR (Air Fuel Ratio) on high
and full load operation conditions. |
| - SCR and NOx
catalyst are also depending on sufficiently
high exhaust gas temperature to operate. |
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| Upgrading
of existing engines using the following
features to meet Euro 3 Emission Standards
is considered to be the most robust solution. |
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| Turbocharger
system |
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purpose of turbo charging is not primarily
to increase engine power, but to increase
Air Fuel Ratio, AFR, at intermediate to
high load conditions to make it possible
to use Exhaust Gas Recirculation, EGR,
without significant increase in soot formation. |
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| Intercooler
system |
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| The
purpose of an intercooler is to cool down
the compressed air downstream of the turbocharger.
The cooled air will reduce the combustion
temperature as well as NOx formation,
and at the same time also increase Air
Fuel Ratio, AFR, due to higher density
of the compressed inlet air. Cooled inlet
air will also bring down the thermal stress
on the combustion components. |
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| Exhaust
Gas Recirculation, EGR, system |
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| The
purpose of Exhaust Gas Recirculation,
EGR, is to introduce exhaust gas, containing
CO2 and water vapor, into the combustion
chamber. As a result EGR absorbs heat
from the combustion process, lowering
the temperature and reducing NOx formation.
The EGR system must be able to deliver
the required EGR rates to reach the target
of Euro 3 emissions in combination with
turbo charging. |
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| EGR
cooler |
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EGR-coolers purpose is to decrease the
emissions of nitrogen oxides, carbon monoxide,
hydrocarbons and particulates. The cooling
has to be chosen carefully for optimum
reduction of nitrogen oxide emissions. |
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| Diesel
Oxidation Catalyst, DOC |
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| An
oxidation catalyst is used to reduce emissions
of CO and HC. It also affects the heavy
hydrocarbons adsorbed on the particulates.
Depending on the amount of hydrocarbons
adsorbed the total particulate matters
can be reduced by 10-30 %. The performance
of an oxidation catalyst is dependent
on the exhaust gas temperature. |
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| The
main feature of the system is that it
is based upon engine conversion and not
after treatment such as additive- or filter
system requiring maintenance and cleaning.
As a turbocharger and intercooler system
is included, the performance and driveability
will be improved, as the engine will
maintain power and torque. |
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| Summary
of features |
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Maintained power and torque |
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No exhaust after treatment |
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Based upon robust and known technology |
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No additive required |
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No increased operational or cost for filter
cleaning |
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Improved driveability |
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| STT
Emtec in Brief |
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| STT
Emtec is a Swedish technology company
with more than twenty five years of experience
from the automotive industry. The company
operates in the two business areas Emission
Systems and Engine Systems. Being an engineering-driven
company, both business areas base their
operations on STT Emtec´s own research
and development resources.
Emission Systems focuses on products
designed to reduce emissions from primarily
heavy-duty diesel vehicles. The system
developed by STT which is a Low Pressure
EGR system, DNOx®, reduces all regulated
diesel-engine exhaust emissions.
STT has supplied close to 3000 EGR systems
worldwide.
Engine Systems develops, manufactures
and markets high-performance systems
for Mitsubishi 4WD vehicles, among others.
The company’s Research and Development
Centre, Production and Sales Offices
are based in Sweden.
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STT
Emtec´s Emission Reduction Technology
– CleanCab
Approved by the EST and PCO |
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| In
order to meet the implemented air quality
strategy for London Licensed Taxis, STT
Emtec AB has developed a robust, efficient
and cost effective emission technology
called CleanCab.
The CleanCab system is based upon known
technology known as turbo charging,
exhaust gas recirculation (EGR), intercooler
and EGR cooling system, converting the
existing engine to the latest emission
standard, Euro 3, as requested. |
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| CONTACT ONE OF OUR LONDON DEALERS LISTED BELOW :- |
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| Cricklewood Carriers Cab Co |
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| Unit 5 Ducksbury Ind. Est. |
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