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Emission Reduction Solutions
The emission reduction market originates from a large
political will to reduce the impact of diesel emissions
on the environment. Global legislation and government
incentives (* see bottom of page)
to act as a driving force and open up two sections of
the diesel engine market; new engines - often termed
the OE (original equipment) market and those already
in existence - referred to as retrofit market. Therefore,
Clean Diesel Technologies are well placed to ensure
compliance and assist in the reduction of both PM and
NOx, both of which are currently of most concern to
the legislators. There are a number of ways to reduce
diesel emissions and below is a list of the latest technologies
used in both the OE and retrofit market:
- Particulate Traps/Filters:
As a general rule, particulate traps are only fitted
to diesel vehicles over 7.5 tonnes and to vehicles
of Euro I, II, III emission standards, although traps
for smaller diesel vehicles are now becoming available.
New vehicles can also be fitted with traps and they
are sometimes offered as an option on new diesel cars.
Particulate traps can achieve a reduction in carbon
monoxide (CO) and hydrocarbon (HC) emissions of 80%
and over 90% in particulate matter (PM).
A particulate trap is a ceramic filter within the
exhaust system of a diesel engine that captures particulates
before they can enter the atmosphere. The captured
particulates are burnt off during the operation of
the vehicle using advanced control systems, catalytic
coatings or fuel-borne catalysts (FBCs). If the captured
PM is not removed the filter will plug. Combinations
of FBCs with other systems provide the most reliable
regeneration.
Ash residue accumulates in particulate traps and needs
to be removed through regular maintenance.
Flow-thru filters are another type of filter typically
providing 60 - 75% reduction of particulates.
Grants or subsidies are often available for the supply
and fitting of a particulate trap to buses, medium
and heavy goods vehicles, refuse trucks and fire tenders.
- Oxidation Catalysts:
A catalytic converter that chemically converts hydrocarbons
and carbon monoxide into water and carbon CO2. Oxidation catalysts can be fitted
to any vehicle, although grants or subsidies are often
only available for vehicles over 3.5 tonnes. In Western
Europe, all new diesel light duty trucks and passenger
cars and vans must be fitted with an oxidation catalyst.
Oxidation catalysts can achieve a reduction of up
to 90% in carbon monoxide (CO) emissions and 90% of
hydrocarbons (HC). PM reductions, however, only 20
- 30%. For heavy-duty vehicles, oxidation catalysts
are very effective, especially on older engines. Oxidation
catalysts also remove the characteristic diesel smell
from the exhaust.
The device typically consists of a stainless steel
canister that contains a honeycomb-like structure
that provides a large surface area coated with precious
metals. This structure also has a special washcoat
that promotes a series of chemical reactions (known
as oxidation) to take place. These reactions convert
pollutants into harmless gases. Oxidation catalysts
require no maintenance.
- Fuel Borne Catalysts (FBC):
Fuel-borne catalysts employ metals, usually iron,
platinum and cerium to control vehicle exhaust emissions
of hydrocarbons, carbon monoxide, oxides of nitrogen
and particulate matter. The catalyst is either pre-mixed
with the fuel at the depot or via a dosing unit fitted
to the vehicle. Used on its own Clean Diesel Technologies'
Platinum Plus will give a 4-8% fuel economy improvement
as well as a reduction by up to 40% of smoke and regulated
emissions including a 10-20% particulate reduction
and 10-30% HC and CO reduction. When used in conjunction
with an oxidation catalyst improvements of up to 50%
reduction in particulates are achieved, with flow-thru-filters
between 60% and 75% and with a particulate filter
over 85%.
- Selective Catalytic Reduction
(SCR):
Selective catalytic reduction is a versatile emission
reduction technology that can be used on many types
of diesel vehicle. It is best suited to larger vehicles,
due to the need for a small separate tank of chemical
reductant.
An SCR system has the potential to reduce oxides of
nitrogen (NOx) emissions by between 50% and 90%, although
this will be dependent on the duty cycle as the system
is extremely temperature dependent. Some reduction
in emissions of particulate matter is also achieved,
even if a particulate trap is not fitted.
SCR uses a reductant (ammonia or urea), which is injected
into the exhaust gas to help reduce oxides of nitrogen
(NOx) over a catalyst. Some systems also use a particulate
trap to further reduce emissions. Unlike some other
emissions control equipment, fitting SCR should not
result in any increase in fuel consumption and by
allowing the engine to be tuned for maximum economy
can actually decrease fuel consumption.
Ongoing maintenance costs will involve regular replacement
of the reductant, either ammonia or urea. Replacement
of the ammonia gas cylinder or replenishment of the
liquid ammonia/urea tank will only be required around
every 9 -10,000 miles for a taxi, but will be much
more frequent for a heavy vehicle. As to the choice
of using urea or ammonia, it is likely that urea will
be more commonly used by manufacturers as it has much
lower health risks.
Clean Diesel Technologies' patented ARIS™ 2000
NOx reduction system is a low-cost urea injection
system, which reduces NOx to elemental nitrogen and
water vapour. At typical exhaust temperatures of 320-500°C
NOx reduction is between 70% and 90%.
- Re-engining:
Commercial diesel engines, buses in particular, usually
require a new engine at some time in their operational
life. A range of commercial diesel vehicles can be
re-engined including buses, medium and heavy goods
vehicles, refuse trucks and fire tenders.
Significant reductions in both NOx and PM are normally
realised when an old engine is replaced by new technology.
Some trials have shown that with careful matching
(perhaps with a revised gear-train) fuel consumption
may also be improved.
Re-engining involves replacing an older diesel engine,
with a newer, cleaner version. The replacement engine
needs to be at least two Euro levels higher than the
original engine, or of Euro III standard. All re-engining
projects must also be combined with a particulate
trap or oxidation catalyst to maximise the emissions
reduction benefit. This should also lead to an increase
in engine reliability.
Grants are often available towards the costs of re-engining
buses, medium and heavy goods vehicles, refuse trucks
and fire tenders.
* Programs in Europe, Japan
and the US have been established to verify the emissions
reduction performance of various technologies applied
to clean up existing engines.
These include:
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