Whether taking students on a long route for a field trip or a routine pickup and drop-off route, keeping the air around them as clean and as free of particulate matter as possible and maintaining the emissions-control equipment that does this is becoming even easier. Product offerings such as diesel particulate filters (DPFs) and mufflers get rid of up to 90% of particulate matter with minimal maintenance.

Additionally, engine pre-heaters help school bus operators keep their buses comfortable during cold weather without idling and prolong the life of DPFs by reducing the load on the engine. For example, Paul Baczewski, school bus account manager for Webasto, says, a recent study conducted by an independent emissions testing lab showed that the amount of particulate matter being introduced into a DPF at 70 F can be reduced by almost one-third simply by pre-heating the engine.

SBF spoke with officials from five suppliers of these products to get the latest details on their emission-control offerings.

Clean Diesel Technologies Inc.

Clean Diesel Technologies Inc. (CDTi) now offers the Purifilter™ EGR DPF for school buses, an update of the technology on its Purifilter™ model. Both are EPA-certified and provide California Air Resources Board (CARB)-certified level 3-plus performance, with more than 85% particulate matter reduction, Ian MacDonald, VP of sales and marketing at CDTi, says.

Purifilter™ includes a catalytic coating that oxidizes the gaseous pollutants to carbon dioxide and water, and lowers the ignition temperature of the soot and burns it off during operation. In addition, Purifilter™ EGR also features the coating and augments it with proprietary Mixed Phase Catalyst technology, an upstream diesel oxidation catalyst and thermal insulation, allowing it to operate at significantly lower temperatures than the Purifilter™. 

“The Purifilter™ requires 25% of the duty cycle to be over 280 C, while the Purifilter™ EGR can operate at either a condition of 10% above 300 C or 30% over 240 C,” MacDonald says.

Like Purifilter™, the Purifilter™ EGR is also a passive system, meaning minimal operator intervention is needed, even at lower temperatures. The Purifilter™ Plus model features an electrical plug-in that allows operators to only have to clean the filter from time to time, according to MacDonald.

Donaldson Co. Inc.

Donaldson’s latest product offerings for school buses include its LNF and LXF mufflers, Todd Lewis, sales manager, says.

The LNF and LXF mufflers reduce particulate matter emissions by more than 90%. The LNF is designed for model year 1993 to 2006 high nitrogen oxide engines, while the LXF is designed for model year 2002 to 2006 low nitrogen oxide engines.

Both muffler kits are equipped with an Emissions Device Monitor that indicates when DPF cleaning is required. The monitor also sends alerts to the vehicle operator through an in-cab display when abnormal or undesirable operating conditions are detected.

The LNF and LXF mufflers are passive systems. The exhaust gas temperature profile for the LNF is: greater than 235 C for at least 40% of the time or greater than 300 C for at least 10% of the time.

The temperature profile for the LXF muffler is: greater than 245 C for at least 40% of the time or greater than 310 C for at least 10% of the time.[PAGEBREAK]

ESW Group

With the school bus market being one of ESW Group’s largest, particularly in California, ESW offers three emission-control products that cover the entire bus duty cycle: the Thermocat E, Long Mile S and the Horizon, Adam Gross, director of sales at ESW Group, says. All three are EPA-certified and provide CARB-certified level 3-plus performance, with more than 85% particulate matter reduction.

The Horizon is an active product, using electrical plug-in regeneration, and the Long Mile S is a passive system; it regenerates by employing hotter exhaust temperatures.

Meanwhile, the Thermocat E is an active/passive hybrid. It is verified through CARB as an active product because it has an external fuel source that is used to regenerate the product, but it acts passively without any driver or operator interaction, Gross explains.

Neither the Thermocat nor the Horizon require a hot exhaust temperature to regenerate. Both allow for low-exhaust temperatures that come with route variations, from the long haul to a route that picks up kids around the neighhorhood.

Espar Heater Systems

Espar’s E-Guardian Plus series of pre-heaters is programmable to turn on at a set time on any given day, says John Dennehy, VP of marketing and communications.

The E-Guardian Plus D5 and M-II units, both CARB- and EPA-verified, are designed to provide powerful preheating and auxiliary internal heat for bus applications. The units are compact and lightweight, and provide automatic altitude compensation. Additionally, Espar’s M-II heaters offer six operating speeds for reduced battery draw and fuel consumption.

The units start preheating the coolant and circulating it around the engine block and through the coolant chain, which run through the length of the bus and back and to the heat exchange, so it preheats the engine and the bus without the engine idling because it is a completely separate entity from the engine, Dennehy explains.  

Espar’s Multi-Max controls the unit and allows operators to preset an entire fleet of buses with one button, Dennehy says.

Webasto

Webasto’s Thermo Top C is small, light in weight, and reduces the wear and tear (extends maintenance cycles) on DPFs by reducing the amount of emissions introduced into the DPF at startup, Baczewski says.

Thermo Top C pre-heats the engine to the starting temperature, considerably reducing the load on the engine caused by a cold start. The engine pre-heater also eliminates the need to idle the engine to heat the bus, which reduces both fuel consumption and CO2 emissions.

Additionally, Scholastic Series Heater, introduced specifically for the school bus industry in 1996, is designed to be a fully functional heating system that not only will pre-heat an engine but also heat the passenger compartment and maintain heat while the vehicle is operating.