School Bus Fleet Retrofits
Retrofit school buses with pollution control technologies and use ultra-low sulfur diesel fuel (ULSD).
Diesel particulate filters used in combination with ULSD can reduce particulate matter by 70 to 90 percent. Retrofitting also includes the re-powering or rebuilding of an engine, replacing of vehicles early, and the use of cleaner fuels, but most commonly the term refers to the use of after- market pollution control technologies (retrofits).
Buses manufactured between 1994 and 2007 can be effectively upgraded with the use of pollution control devices like the DPF and cleaner fuels. For older buses that cannot be immediately replaced and that are not electronically controlled or do not meet the high temperature requirements, which are necessary for DPF use, school districts should investigate alternative retrofit and fuel options and costs for each type of bus in the fleet.
Emissions are not only emitted from the tailpipe, but a significant amount is also emitted directly from the engine (engine crankcase). These emissions can be reduced by installing a device called the Crankcase Filtration System. This retrofit reroutes and traps pollution from the crankcase back into the engine. If this technology is used in combination with the DPF, particulate matter inside school buses can be eliminated .
Diesel oxidation catalysts (DOCs) can be used with additional pollution control devices in order to provide measurable pollution reduction benefits. DOCs are less expensive, but according to manufacturers and U.S. EPA, they only reduce fine particles between 20-30 percent. DOCs can be used with crankcase filtration systemsto achieve further reductions. Retrofitting existing diesel engines will provide reductions far earlier than those promised by recently adopted federal regulations for highway and off-road diesel engines.
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