SACE | Southern Alliance for Clean Energy

Diesel Solutions


The good news is diesel technology has improved dramatically over the past several years and there are now retrofit technologies and cleaner fuels available to reduce pollutants emitted from diesel engines.

The use of retrofits, such as diesel particulate filters (DPF), with ultra-low sulfur diesel, is one of the most cost-effective solutions to drastically reducing particulate matter from diesel engines. Other technologies like diesel oxidation catalysts (DOCs) are also available but do not have as high of removal efficiencies.

Diesel Particulate Filter (DPF): DPFs are ceramic devices that collect particulate matter (PM) 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.

DPFs can be installed on new and used diesel engines, but must be used in conjunction with ULSD. ULSD with a sulfur content of less than 15 parts per million, is now widely available from distributors and at retail locations. The combination of DPFs and ULSD can reduce emissions of particulate matter, hydrocarbons, and carbon monoxide by 60 to 90 percent. (Source: EPA)

DPFs work best on engines built after 1995.

Tier 2 filters, such as flow-thru filters/Diesel Multi Stage Filters (DMF): A flow-thru filter or DMF is a two stage metallic filter used to trap and reduce particulate matter. Each filter stage consists of alternating layers of a corrugated metal and a porous sintered metal fleece. These devices reduce particulate matter, hydrocarbons and carbon monoxide emissions by 50 percent and nitrogen oxide emissions by 20 percent. (Source: CARB)

Diesel oxidation catalysts (DOCs): DOCs are one of the most popular control options to date because of their low cost and ease of installation. DOCs are devices that use a chemical process to break down pollutants in the exhaust stream into less harmful components. With ULSD widely available, DOCs should only be considered when vehicles are not good candidates for DPFs, because they are less effective at emission reduction. Particulate matter is reduced by 20-40 percent, hydrocarbons by 50 percent and carbon monoxide by approximately 40 percent with the use of DOCs. (Source: EPA)

Close Crankcase Ventilation (CCV): A CCV reduces emissions of hydrocarbons and particulate matter produced from the engine crankcase or oil pan area. Typically, CCV technology is combined with a DPF or DOC to reduce in-cabin emissions.

The EPA and the California Air Resources Board (CARB) have verification processes for the approved use of diesel retrofit technologies:
EPA verified technologies
CARB verified technologies

There are a variety of other solutions that can also reduce the pollution from diesel engines and save money for the owners of diesel vehicles. Across the country, more cities and counties are adopting anti-idling ordinances to reduce the amount of time that buses idle while not in motion.

By limiting idle time, fleets can save thousands of dollars a year in maintenance and fuel costs, reduce pollution, and reduce wear and tear on the vehicles. Schools, local and state governments, and private companies can also implement their own policies to limit idling around their facilities.

Inspection and maintenance programs are also important and effective programs to implement to maintain clean diesel engines. Air quality across the region can be improved. Decision-makers have an obligation to act responsibly to clean the air and reduce emissions that contribute to health problems and environmental degradation. Protecting our region’s air quality is protecting our health and our way of life.