During the 1980s, a new line of medium-duty diesel engines became the pre-dominant drive train component in Type C school buses and medium-duty trucks, once exclusively powered by heavy-duty gasoline engines. Just as the new engines began populating our industry fleets, the Environmental Protection Agency introduced regulations for medium- and heavy-duty diesel exhaust emissions. These progressive rules, introduced in equipment starting in 1990 and amended in 2000, will be finally promulgated in 2010. The final rule requires the diesel engine manufacturers to reduce nitrogen oxide (NOx) emissions at the tailpipe to no more than 0.2 grams of NOx per brake horsepower, 90 percent lower than the 2004 NOx rule, which introduced us to the diesel oxidation catalyst (DOC) and exhaust gas recirculation (EGR).

NOx is formed as a result of the high combustion temperature in diesel engines. The hotter the combustion temperature (power), the more NOx is created. To reduce NOx formed during the power generation process, manufacturers needed to lower peak combustion temperature or clean the NOx from the exhaust stream after the combustion process. Simply put, our school bus engine suppliers were faced with this challenge: should they not produce NOx in their engine at all or find a way to get rid of as much of it as they could after the combustion/power process produces it? The first option is through enhanced EGR, the second is selective catalyst reduction (SCR). Both SCR and EGR are proven to reduce NOx emissions. So, the only exception to meeting the NOx requirement for vehicles with engines manufactured after Jan. 1, 2010 will be, how have our bus suppliers decided to do it?

Soon, school bus buyers will have to make a choice between purchasing buses with EGR or SCR. As purchasers of school buses, you have seen price increases due to commodity costs, safety enhancements, technology changes and previous environmental mandates. You can expect that 2010 bus price increases will reflect the cost of SCR or EGR NOx emission reduction technology development as well as the specific emission reduction equipment required.

The EPA NOx emission regulation is only months away from being in place. As a result, our industry Type C and Type D bus suppliers are firmly committed to two very different technologies. The choice will be between IC Bus, with its engines built by Navistar Inc., that will use an expanded version of its exhaust gas recirculation technology, and both Blue Bird and Thomas Built Buses, who will be using selective catalyst reduction technology developed on Cummins-built diesel engines.

Our choices have not been made simpler by all the recent debate from the manufacturers on why their system is better. Typical of any new product introduced to our industry, it is the buyer and operator who will decide which available technology is the right one for their particular situation. School budgets are tight, and private capital is subject to close scrutiny in these difficult economic times. As operators, all of us need to consider the relationships and experience we have with our suppliers and how best to leverage them when it comes to deciding what equipment we should buy. School bus suppliers have a lot riding on their selected emission strategy; a strong supplier partnership should be one that survives tough times and significant product changes. You should also keep in mind that our manufacturers continue to invest in R&D on enhancing the combustion process, alternative fuels, hybrids, plug-ins, etc. There is a good chance that one or more of these “game changing” systems could change school bus power plant emission technologies in the very near future.

Our current bus suppliers have long since demonstrated their commitment to this industry. Gather information from them, meet with them, test drive new buses, attend trade shows and industry association meetings. Basically, do your homework and you will make the right decision for your future bus purchases.

Pudlewski moderated the 2007-2010 Engine Odyssey panel with bus and engine OEMs at the 2009 STN EXPO. He is the retired vice president of fleet operations for Laidlaw Education Services and First Student.

Reprinted from the August 2009 issue of School Transportation News magazine. All rights reserved.