Diesel Vehicles and Equipment
Diesel vehicles and equipment are the work horses of our economy – collectively they play a significant role in agriculture, construction, transportation and infrastructure. The combined features of fuel efficiency, power, reliability and durability give diesel vehicles and equipment this distinction. Diesel fuel burns more efficiently and is safer than gasoline because it does not form flammable mixtures, but there is a price to pay. Despite progress in cleaner fuels and emission standards and technology, diesel engines remain one of the largest sources of fine particulate matter, considered to be a significant threat to public health. Diesel exhaust also contributes to ozone formation, acid rain and global climate change.
On-road diesel vehicles include tractor trailer trucks, school buses, dump trucks, and utility trucks. Off-road heavy-duty vehicles include military tanks, marine vessels, locomotives, and various construction, industrial, and agricultural equipment. Diesel engines are also found in stationary equipment like emergency generators.
Diesel Engines and Fuel
Diesel engines operate via combustion ignition, where the mixture of fuel and air is compressed enough to spontaneously combust. This differs from a spark-ignition (gasoline) engine which relies on a spark plug to facilitate the explosion. The advantage of diesel engines in heavy duty applications is the power generated by the high compression engine. Gasoline engines provide superior driving performance in light-duty applications, but diesel engines are the primary choice for heavy duty vehicles (vehicles greater than 8,500 lbs.) and equipment.
Conventional diesel fuel contains sulfur and other impurities which make the exhaust harmful and limit the viability of emission control devices. Standards put in place by the EPA have required the use of ultra-low sulfur fuel (ULSF) in highway diesel vehicles since 2006, and these requirements are being phased in for non-road, locomotive and marine engines as well. Low sulfur fuel burns cleaner and allows for the application of exhaust treatment technologies that limit the emission of particulates (particulate matter or PM) and smog-forming nitrous oxides (NOx).
Emission standards for diesel vehicles passed by EPA in 2000 will result in a 90 percent reduction in harmful diesel emissions in engines built beginning model year 2007. Although standards are vital for long-term air quality improvement, many diesel engines are expected to last up to one million miles with proper maintenance and engine rebuilding. This means that older, dirtier engines may be in operation for 15 to 30 more years. Therefore, it is important to also look at alternative measures, including retrofit technologies for reducing emissions from this legacy fleet. (see “Recommendations for Reducing Emissions from the Legacy Diesel Fleet,” Clean Air Act Advisory Committee, January 11, 2007).
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