Independent Testing Shows SCR Technology in Thomas Built Buses Offers Advantages Over EGR

During a recent independent study, researchers found the SCR technology used on Thomas Built Buses offered better fuel economy and cost efficiency than EGR.

A recent, independent, third-party test of a Thomas Built Buses Saf-T-Liner C2 against an IC Bus CE Series provided evidence that SCR technology delivers 7 to 27% better fuel economy and, when factoring in the cost of diesel exhaust fluid (DEF), is the more cost-effective choice for cost-conscious customers.

Thomas Built Buses commissioned the fuel economy evaluation of a Thomas Built Buses Saf-T-Liner C2, powered by a Cummins ISB6.7 liter engine, and an IC Bus CE Series, powered by a MaxxForce DT 7.6 liter engine. Both engines were 2010 diesel emissions compliant. The Thomas Built bus was equipped with selective catalytic reduction (SCR) technology and the IC bus was equipped with in-cylinder exhaust gas recirculation (EGR) technology.

The test results, provided by Bosch Automotive Proving Grounds in December 2011, showed that the Thomas Built C2 delivered a fuel economy advantage over the IC CE Series, regardless of the route (urban or highway) and transmission mode (Economy or Performance). The fuel economy advantage, after factoring in the cost of DEF, can add up to an annual operating cost savings of $603 to $1,417 per bus.

“Test results exceeded our expectations,” says Tom Hodek, Cummins general manager, Bus Business. “Since day one, we’ve been confident that our SCR technology offers a fuel economy advantage over alternate emissions reduction technology. This test further defines the advantages of a cleaner, cooler-running SCR engine.”

“We’ve believed for some time that the fuel economy of our buses was better, since we’d taken the SCR technology path,” says Jed Routh, Thomas Built Buses product planning manager. “This was validated when we heard about actual fuel economy advantages from customers who received the early EPA 2010-compliant Thomas Built buses.

“Our intention with this testing,” continues Routh, “was to provide measurable, verifiable information to help our customers choose the school buses that are best for their needs and budgets. That’s particularly important in today’s tough economy.”

SCR technology removes nitrogen oxide (NOx) emissions from the exhaust stream after it is formed during the combustion process, while EGR technology prevents formation of NOx. While both reduce NOx levels, each has a different effect on engine efficiency and fuel economy. Treating the exhaust after the combustion process (as happens with the SCR technology in the Thomas Built C2 buses) allows the engine to function at optimal combustion temperatures, increasing fuel efficiency and reliability.

As customers evaluate purchases based on the total cost of ownership of each vehicle, it should be noted that the improvement in fuel economy achieved with SCR technology provides a cost advantage to customers even with the added cost of the use of DEF.