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Retrofit Strategies
There are many options to consider that reduce diesel emissions. Retrofitting is loosely defined as any change that improves the emission performance of a diesel engine.
Strategies to reduce emissions from construction equipment include:
- Switching to Cleaner Fuels - using advanced fuels, such as ultra-low sulfur diesel (ULSD), biodiesel, liquid petroleum gas, and compressed natural gas.
- Retrofit Technologies - installing emissions reduction technologies on an engine, such as particulate filters and oxidation catalysts.
- Repowering - replacing an old engine with a newer, cleaner model.
- Replacing - replacing an old vehicle or equipment with a cleaner model.
- Reducing Idling - reducing the amount of idling time a vehicle normally operates.
- Repairing and Proper Maintenance - repairing an existing engine to meet its original standards and/or keeping equipment running efficiently though good preventative maintenance.
Retrofit Technologies
Aftertreatment technologies, or “retrofitting,” can be installed for existing equipment or vehicles to reduce particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO) or hydrocarbons (HC), in addition to other air pollutants. EPA and the California Air Resources Board (CARB) verify the emissions performance of retrofit devices through appropriate protocols and statistical analysis. Verified products have undergone rigorous testing to confirm the device's emissions performance. EPA and CARB coordinate their respective verification programs through a Memorandum of Agreement (MOA) (PDF, 3 pages, 200K, About PDF). Learn more about EPA verified products.
| Technology Reduction Strategy | Description | Pollutants Reduced | Additional Information |
|---|---|---|---|
| Diesel particulate filters (DPFs) | DPFs are honeycomb or mesh devices placed within the exhaust stream that physically trap and oxidize PM. | HC, CO, PM (55-90% or more reduction) | DPFs must be paired with ultra-low sulfur fuels. DPFs use either passive or active regeneration systems to oxidize the PM in the filters. Passive filters require higher operating temperatures to work properly. Filters require some maintenance. |
| Diesel Oxidation Catalysts (DOCs) | DOCs are devices that oxidize pollutants in the exhaust stream. Typically packaged with the engine muffler. | PM (10-50%), HC (50% or more) and CO (50% or more) | DOCs have an established record in the highway sector and are gaining in nonroad applications. Sulfur in fuel can impede the effectiveness of DOCs; therefore, the devices require fuels with sulfur levels of 500ppm or lower. DOCs can be coupled with closed crankcase filtration technologies (see below). |
| Closed Crankcase Ventilation (CCV) | In many diesel engines, crankcase emissions — or “blow-by” — are released directly from the engine through the “road draft tube.” CCV devices provide a cleaner engine environment by capturing and returning oil in blow-by gasses to the crankcase. CCV devices direct NOx, HC and toxics to the intake system for re-combustion instead of polluting the environment. PM is collected in a filter and removed from the crankcase vapors. | PM reductions of about 10%, depending on a number of factors. The emissions reductions will be increased if paired with a DOC. | CCV devices have the following benefits:
CCV devices may be used on newer equipment as a way to meet upcoming engine emissions standards. EPA’s 2007 Highway Heavy Duty Diesel rule requires that engine manufacturers consider crankcase emissions as a part of overall emissions that must be reduced. |
| Selective Catalytic Reduction (SCR) | Selective Catalytic Reduction (SCR) Systems inject urea (or some form of ammonia) into the exhaust stream that reacts over a catalyst to reduce NOx emissions. | PM (about a 25% reduction) and NOx (60% reduction) | Commonly used in stationary applications, such as power plants. ARB has verified an SCR system for certain nonroad applications. SCR systems require periodic refilling of an ammonia or urea tank. Often used in conjunction with a DOC or catalyzed DPF to reduce PM emissions. |
| Exhaust Gas Recirculation (EGR) | EGR devices recirculate a portion of engine exhaust back into the engine to cool peak combustion temperatures and thus, reduce NOx. | NOx (25-50%), PM reduction can be achieved when paired with a DPF. | EGR technology is being considered by some original engine manufacturers as a way to meet upcoming engine emissions standards. |
| Fuels | Description | Pollutants Reduced | Additional Information |
|---|---|---|---|
Low-sulfur fuels:
|
Switching to fuels that contain lower levels of sulfur reduces PM and enhances the effectiveness of retrofit technologies. | PM (5-9%) reduction depends on the baseline fuel sulfur levels. | Nonroad fuel sulfur content was reduced to 500 ppm in 2007 and will be reduced to 15 ppm in 2010. |
| Emulsified Diesel | Water and additives mixed with fuel to lower combustion temperatures. | NOx (9-20%), PM (16-58%) | Good for centrally fueled fleets using equipment that does not sit idle for more than 30 days. May affect peak horsepower in some applications. |
| Replacing equipment with electric, hybrid or alternative fuel equipment (Liquefied Natural Gas – (LNG), Compressed Natural Gas – (CNG), Propane) | Can replace diesels with those that use hybrid technology or alternative fuels. Propane is a byproduct of natural gas processing and petroleum refining. | Typically, NOx, PM, HC, CO. | Examples include LNG or LPG yard tractors, forklifts or loaders. Natural gas replacements may require fueling infrastructure. |
Maintenance/Repair/Rebuild
Engines that are properly maintained according to the manufacturer ' s recommendations perform better and typically emit fewer emissions. Rebuilding an engine may also significantly lower emissions and can be a cost-effective option for high-value equipment.
Unless engines are properly maintained, other measures to reduce emissions may be futile. A poorly maintained engine cannot be cleaned up by technology alone. Properly maintained or recently rebuilt engines lower emissions by burning fuel more efficiently and can reduce operation costs through improved fuel economy and extended engine life.
Common maintenance issues include:
- restricted air filters
- improper engine timing
- clogged, worn, or mismatched fuel injectors
- faulty fuel injection pumps
- defective or maladjusted puff limiters
- low air box pressure
- improperly adjusted valve lash or governors
- maladjusted fuel racks
- defective air fuel controllers
- poor fuel quality
- improper driving gear and air intake manifold links