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National Clean Diesel Campaign (NCDC)

Working Together for Cleaner Air


Reducing people's exposure to diesel exhaust is a public health goal that depends on controlling diesel emissions. Below are brief descriptions of ways to control the emissions.

Hydraulic Hybrid

EPA and its industry partners are field testing a clean, fuel efficient hydraulic hybrid yard hostler.


Proper engine maintenance is necessary for optimum fuel economy and extended engine life as well as to control emissions.  Keeping good maintenance records is important for tracking and scheduling manufacturer-recommended maintenance for warranty and retrofit purposes.  When properly maintained and operated, a diesel engine should have a long useful life.

Retrofit Technologies:

All new engines have been certified to comply with EPA emission standards in place at the time of certification. Retrofit technologies are products that may be added to further reduce emissions from certified engine configurations.

The most common retrofit technologies are retrofit devices for engine exhaust after-treatment. These devices are installed in the exhaust system to reduce emissions and should not impact engine or vehicle operation. Examples of retrofit devices include diesel particulate filters (DPFs) and diesel oxidation catalysts (DOCs).

Some engines are equipped with after-treatment technologies as part of their originally certified emission control system, and may not be eligible for retrofit. Retrofit technologies may also include crankcase emission control devices, engine component upgrades or other modifications that reduce emissions.

Retrofit technologies are evaluated by EPA’s National Clean Diesel Campaign (NCDC) and California Air Resources Board (CARB), and verified technology lists are maintained by each program. Because they are designed and evaluated to reduce emissions from certified engine configurations, retrofit technologies should be added only to properly maintained engines.

Engines: Repair, Rebuild and Repower

An engine with a malfunctioning or damaged component should be repaired quickly to avoid additional damage to the engine, vehicle and emission control system.

Diesel engines often can be rebuilt and continue to operate in the same capacity. An engine in need of rebuilding may have low power, increased emissions and increased fuel consumption. In some cases an engine can be rebuilt to comply with cleaner emission standards.

Replacing an older engine with a new one which has been certified to cleaner emission standards is another option for some equipment and vehicles. Repowering with a new engine may extended the life of the machine, reduce fuel consumption, and significantly reduce emissions.

Replace Vehicles and Equipment:

Replacing old vehicles or equipment with a new cleaner model can substantially reduce emissions and fuel consumption.

Operational Strategies and Idle Reduction:

Operational strategies are ways of improving operating efficiency that may reduce engine run time and emissions. Operational strategies include improving the flow of vehicles to reduce idle time or miles traveled while performing the same task.

Limiting engine idling can reduce emissions and fuel consumption. Idle reduction technologies are available that provide amenities such as cabin heat and air conditioning without operating the main engine.

Operational strategies may be unique for a given locality or business and may need periodic review to determine if additional changes are necessary to maintain or improve performance.

Cleaner Fuels:

Emissions may be reduced by using fuels with certain properties or by using alternative fuels. Ultra-low sulfur diesel (ULSD) fuel as well as biodiesel blends will reduce emissions. Engines certified to operate on alternative fuels such as liquid petroleum gas (LPG), compressed natural gas (CNG), and liquefied natural gas (LNG) can also reduce emissions.

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