Retrofits & Cleaner Fuels
A retrofitted engine is cleaner because it either has been fitted
with a device designed to reduce pollution and/or it uses a cleaner
fuel. There are a variety of ways to retrofit a diesel engine. Retrofit
options range in cost as well as effectiveness and some come with
special requirements. Through EPA's Voluntary
Diesel Retrofit Program,
EPA verifies retrofit
technology and certifies cleaner fuels to ensure that they produce the emission
reductions advertised by their manufacturer.
The following chart summarizes some clean fuel and clean technology
options.
| Clean Fuel / Clean
Technology Options |
Type of Engine |
Percent Reduction
in Emissions of Particulate Matter |
Percent Reduction
in Emissions of Nitrogen Oxides |
Approximate Cost
of Technology |
| Ultra-Low Sulfur Diesel (ULSD) |
Nonroad Diesel Engine |
About 5 to 9%
Enables the PM filter technology to work |
N/A |
8 to 20 cents per gallon more than regular diesel now |
| Particulate Matter Filter |
New or Used Diesel Engine - 1995 or newer models |
60 to 90% |
N/A |
$5,000 to $10,000
Must use ULSD fuel |
| Oxidation Catalyst |
New or Used Diesel Engine |
20 to 30% |
N/A |
$1,000 to $2,000 and can be used with regular diesel
|
| Compressed Natural Gas (with an oxidation
catalyst) |
New CNG Engines |
70 to 90% if using catalyst technology to reduce ultra
fine PM, formaldehyde, and methane - otherwise, methane
and aldehydes will be much higher than diesel engines |
About 60% reduction but are highly variable (sometimes
increases occur) |
$30,000 more than a diesel bus (cost of CNG fuel
similar to regular diesel fuel)
Very expensive special re-fueling infrastructure and
maintenance facilities are required |
| Biodiesel Fuel B20: 20% biodiesel,
80% regular diesel
B100: 100% biodiesel |
New or Used Diesel Engine |
B20 - 10%
B100 - 40% |
Biodiesel increases emissions of NOx slightly.
B20 blend +2%
B100 fuel +10% |
B20 - 5 to 30 cents per gallon more than regular diesel
B100 - 75 cents to $1.50 per gallon more than regular
diesel (B100 may not be an option in the winter season)
|
| Emulsified Diesel Fuel |
New or Used Diesel Engine |
About 50% |
About 10% |
20 cents per gallon more than regular diesel fuel |
|
 |
Diesel Oxidation
Catalysts |
|
| |
| Diesel oxidation catalysts are devices that use a chemical
process to break down pollutants in the exhaust stream
into less harmful components. Diesel oxidation catalysts
can reduce emissions of particulate
matter (PM) by 20 percent and hydrocarbons
(HC) by 50 percent and carbon
monoxide (CO) by approximately 40 percent. Oxidation catalysts cost
about $1,000 to $2,000, can be installed on any new or
used bus, and run on regular diesel fuel. Although installation
time can vary, field experience suggests it takes about
1 to 3 hours to install an oxidation catalyst. |
|
|
Diesel Particulate
Matter Filters |
|
| |
Diesel particulate matter filters are ceramic devices
that collect the particulate
matter in the exhaust stream The high temperature of the exhaust
heats the ceramic structure and allows the particles
inside to break down (or oxidize) into less harmful
components. They can be installed on new and used buses,
but must be used in conjunction with ultra-low
sulfur diesel (ULSD) fuel with a sulfur content
of less than 15 parts per million. The combination of
PM filters and ULSD can reduce emissions of PM, HC,
and CO by 60 to 90 percent.
PM filters come in a kit that includes mounting brackets
and an electronic monitoring device. The cost of the
kit can range from $5,000 to $10,000. Some buses may
need the more expensive filters to compensate for lower
exhaust temperatures. PM filters work best on engines
built after 1995. As a result, knowing the age and type
of each engine in the fleet as well as the drive cycles
of the buses is an important part of any retrofit project.
These factors determine whether or not buses are candidates
for filters. Although installation time can vary, field
experience suggests it takes about 6 to 8 hours to install
the filter. |
|
|
Ultra-Low Sulfur
Diesel (ULSD) Fuel |
|
| |
| As of October 2006, ULSD is available at the pump in most of New England. The primary purpose of ULSD is to enable or improve the
performance of aftertreatment technologies such as a PM
filter. The quantity of emissions reductions from the
use of ULSD alone will vary depending on the application,
level of sulfur reduction, and other fuel characteristics
of the replacement fuel (e.g., cetane number, aromatics,
PNA). Some case studies suggest that the use of ULSD alone
can reduce emissions of PM between 5 and 9 percent. While
ULSD-only emission reductions for PM are relatively modest
on a per-vehicle basis compared to aftertreatment retrofit,
the emission reductions can be significant if an entire
fleet is fueled with ULSD. |
|
|
Compressed Natural
Gas |
|
| |
| Another replacement option is to purchase new buses that
run on compressed natural gas (CNG) and have been fitted
with an oxidation catalyst to reduce pollution. CNG is
a mixture of hydrocarbons, mainly methane, and is produced
either from gas wells or in conjunction with crude oil
production. Vehicles powered by natural gas perform just
like vehicles powered by diesel fuel. The majority of
natural gas consumed in the United States comes from sources
within North America. Increased use of clean, domestically
produced fuels helps reduce our reliance on oil from overseas,
which is good for our nations energy security. Natural
gas buses can reduce emissions of particulate matter (PM)
by about 70 to 90 percent if they meet Clean
Fueled Fleet requirements or have catalysts. CNG engines that do not
have catalysts, may have higher formaldehyde, hydrocarbon,
and ultra-fine PM emissions than Clean Diesel engines
meeting EPA's 2007 emission standard for PM. The cost
of natural gas varies, but generally is comparable to
the cost of regular diesel fuel. However, the cost of
a new compressed natural gas vehicle can be much higher
than a comparable diesel vehicle. Additionally, CNG buses
require special refueling facilities as well as a special
maintenance facilities, both of which are expensive. |
|
|
Biodiesel Fuel |
|
| |
Biodiesel is a domestically produced, renewable fuel
that can be manufactured from new and used vegetable
oils and animal fats. Biodiesel is safe, biodegradable,
and reduces air pollutants such as PM, CO, HC and air
toxics. However, emissions of NOx increase with the
concentration of biodiesel in the fuel. Some biodiesel
produces more NOx than others, and some additives have
shown promise in modifying the increases.
Blends of 20% biodiesel with 80% petroleum diesel (B20)
can be used in unmodified diesel engines. Biodiesel
can be used in its pure form (B100), but may require
certain engine modifications to avoid maintenance and
performance problems. Pure blends of biodiesel may not
be suitable for the winter season. B20 reduces emissions
of PM by about 10 percent. However, B20 also increases
NOx emissions by approximately 2%. The B20 blend costs
about 15 to 30 cents per gallon more than regular diesel
fuel. B100 reduces emissions of PM by roughly 40 percent
and costs about 75 cents to $1.50 more than regular
diesel fuel.
|
|
|
Emulsified Diesel
Fuel |
|
| |
Emulsified diesel is a blended mixture of diesel fuel,
water, and other additives that reduces emissions of
PM as well as NOx. Emulsified diesel can be used in
any diesel engine, but the addition of water reduces
the energy content of the fuel, so some reduction in
power and fuel economy can be expected. Emulsified fuel
will stay mixed for a fairly long time. However, if
a vehicle sits dormant for months at a time the water
can settle out of the fuel and possibly cause problems.
Therefore school buses may want to phase out the use
of the fuel towards the end of the school year and then
reintroduce it in the fall. Case studies suggest that
emulsified diesel can reduce emissions of smog-causing
NOx by about 10 - 20 percent and PM by about 50 - 60
percent. Emulsified diesel costs roughly 20 cents more
per gallon than regular diesel fuel. |
|
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