Diesel is a fuel typically used in engines that power heavy machinery, agricultural equipment and heavy duty trucks. Diesel's use is prevalent, and this brings up concerns over its emission quality. One ingredient in diesel is sulphur. The amount of sulphur determines the grade or quality of the fuel, but other materials do as well, all of which combine to form standards. These standards, besides being designed to meet engine performance expectations, must also meet the Environmental Protection Agency's guidelines.
Diesel fuel was first regulated in 1993 after concerns arose over high sulphur content. In 2003 and then 2006, diesel was further regulated to ensure a lower sulphur content in conjunction with performance standards. The modern standards were updated as recently as March 2009.
The standards cover the biodiesel amount (no more than 5 per cent), sulphur content (10, 50 and 500 parts per million maximum), cetane index, density (minimum of 51), ash (100 ppm maximum), viscosity, carbon residue (.2 per cent maximum), water and sediment (.05 per cent maximum), conductivity, oxidation, colour, flash point and lubricity.
The standards apply to seven different types of diesel fuel. Grades No. 1-D S15, S500 and S5000 are designated as speciality light fuels. Grades No. 2-D S15, S500 and S5000 are middle fuels used in vehicles that require a higher sulphur content. Grade No. 4-D is a heavy fuel, used in slow and medium speed engines, which need a denser fuel.
The standards are a compromise between maintaining air quality and engine performance standards. The most significant regulation of diesel fuel was that of sulphur content in the past decade. The standards, in conjunction with fuel grade, provide a framework that minimises the amount of sulphur emissions.
Diesel fuel was used extensively in European automobiles until the 1990s. Regulations have made it less likely that automobiles and light-duty trucks will have diesel engines.
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