|
|
Controlling Bus Emissions
Starting with the 2007 model year, both Transport Canada and the U.S. Environmental Protection Agency (EPA) set stringent limits on Nitrogen Oxide (NOx) and Particulate Matter (PM) emissions from on-road trucks and buses. Through a combination of engine redesign, ultra-low sulfur diesel (ULSD) fuel and engine oils, these new vehicle technologies will significantly cut emissions.
To reduce particulate matter, all new Calgary Transit buses purchased from 2007 on, have Diesel Particulate Filters (DPFs) installed that capture soot and larger sulfate particles. These filters work by channeling engine exhaust through a porous material on the filter, trapping engine exhaust particulate matter and preventing its release into the environment. Soot accumulates in the filter and when sufficient heat is present, active regeneration occurs, burning off the soot and cleaning the filter.
These new engine technologies significantly reduce Calgary Transit’s vehicle emissions into the environment. For a number of years, Calgary Transit has been testing fleet emissions called “opacity” by measuring the density of gases leaving the exhaust systems. The lower the opacity, the cleaner the exhaust. Considering Calgary Transit’s current stringent engine tune-up and rebuild program, further drops in opacity levels will come from the decommissioning of older buses and replacing them with buses equipped with advanced engine technologies.
Ultra Low Sulphur Diesel (ULSD) Fuel
Both Canada and the United States have mandated that the maximum sulfur content of 15 ppm in diesel fuel. This ULSD enables catalytic exhaust technologies that allow diesel engine emissions to be dramatically reduced. This mandate also includes a large reduction in heavy-duty engine emission standards; Particulate Matter (PM) is reduced by 90% and Nitrogen Oxides (NOx) are reduced by 95% from their current levels. Transport Canada the US Environmental Protection Agency (EPA) and engine manufacturers are all relying on ultra low sulfur diesel as the enabler to make this a reality.
Diesel Particulate Filters (DPF)
To reduce particulate matter starting in 2007, on-road trucks and buses will have DPFs installed that capture soot and larger sulfate particles. These filters work by channeling engine exhaust through a porous material on the filter, trapping the engine exhausts particulate matter and preventing its release into the environment. Soot accumulates in the filter and when sufficient heat is present active regeneration occurs, burning off the soot and cleaning the filter.
While soot is burned off through a regeneration process, ash accumulates in the filter and will eventually cause an increase in exhaust back pressure (fuel economy penalty). Therefore it is anticipated that every 200,000 to 400,000 kilometers these filters will need to be removed for ash cleaning.
|
