Results released from third-party testing commissioned by Navistar indicate that diesel-powered IC Bus CE Series school buses using Advanced EGR technology could offer up to a 4.5 percent advantage in fluid economy over competing bus brands.
The research was conducted by the Transportation Research Center, Inc., (TRC) to gauge fluid economy, the measurement of diesel fuel plus liquid urea used by a vehicle's emissions reduction system, of the MaxxForce 7 with Advanced EGR versus SCR technology utilized in the Cummins ISB diesel engine to 2010 EPA emissions standards to reduce NOx.
Two competitors, school bus manufacturer Thomas Built Buses and diesel engine provider Cummins, Inc., both issued statements this week that refute Navistar's findings. Cummins has previously said its SCR solution trumps EGR when it comes to fuel economy. But Navistar said fluid economy is the proper way to compare today's new school buses that utilize different technologies to meet EPA 2010 emissions requirements.
Essentially, according to Navistar, fuel economy only tells part of the story because SCR buses that use liquid urea could increase operating costs above and beyond what fleets are already paying for diesel fuel. And SCR with urea can introduce additional requirements on operators with regard to storing the liquid at their facilities.
IC Bus published a five-page white paper on the testing.In addition to the up to 4.5 percent advantage in fluid economy in typical school bus conditions in the best case scenario, TRC determined that the MaxxForce 7 engine could offer a fluid-economy advantage of between 0.5 and 1.5 percent by using TMC Type IV testing methods, which are considered to most closely replicate real-world fuel economy because they factor in vehicle aerodynamics, powertrain and tires.
The independent, third-party research conducted in May at TRC's proving-ground facility in East Liberty, Ohio, compared an IC Bus CE Series powered by an EPA-compliant 2010 MaxxForce7 with Advanced EGR with a Blue Bird Vision and a Thomas Built Buses Saf-T-Liner C2, both of which are equipped with Cummins ISB engines. The difference between the two technologies is that EGR continually re-circulates gas exhaust into the engine’s combustion chamber until NOx is essentially burned up, and SCR uses liquid urea to treat the exhaust gas stream outside of the engine to reduce NOx to EPA-accepted levels of 0.02 grams.
In the latest round of test for IC Bus, Navistar said the three school bus brands were in similar mechanical condition, were loaded with equal ballast weights and side window openings were the same in each vehicle at all times. Each bus was tested on multiple runs of a 135-mile test route that was developed specifically to replicate typical school bus applications. The tests gauged idle time, frequent stop-and-go intervals and long routes at low average speeds ranging from zero to 50 miles per hour. Drivers also switched vehicles every 45 miles of the test route to eliminate driver influence on the test results.
The buses tested all were equipped with the same Goodyear tire models and sizes, exhaust, and Allison 2500PTS five-speed transmission. Vehicle test weights were all roughly 25,000 pounds. Differences besides the engines used included the alternators (320 amp 12V for IC Bus compared to 200 amp 12V for Blue Bird and 240 amp 12V for Thomas) and fuel tank size (65 gallons for IC Bus compared to 100 gallons for both Blue Bird and Thomas).
“These testing scenarios are purposely designed to create as close to real-world on-the-road applications as possible, with no attention to detail spared,” said John McKinney, president of IC Bus. “The test results confirm our commitment to our customers to deliver the most efficient buses on the road.
At this update, Ken Hedgecock, vice president of sales, marketing and service at Thomas Built Buses, told School Transportation News that the manufacturer has delivered more than 8,000 school buses that utilize SCR technology supplied by engine maker Cummins.
"We resolutely stand behind SCR as the best technology to maximize fuel efficiency and performance while meeting EPA 2010 federal emission standards," he added. "The choice is simple when all factors are considered. Most importantly, Thomas Built’s customers have voiced their preference for SCR buses and have recorded their endorsements of the technology for others to review when considering new bus acquisitions.
While STN was awaiting a formal response from Blue Bird, a representative from Cummins said the company's analysis of Navistar's fluid economy report concluded that Navistar failed to give complete information pertaining to vehicle and engine specifications as well as mention all pre-conditions for "objective testing."
"Validity of the testing and published results is questionable," said Thomas R. Hodek, GM of bus business at Cummins. "Cummins is fully confident that with the correct customer powertrain specifications, the fuel economy of the EPA 2010 ISB6.7 in a Thomas Built or Blue Bird bus can be significantly better than that of the MaxxForce 7 in an IC bus.”
Last summer, TRC conducted similar research commissioned by Navistar on the Class-8 International ProStar+ with MaxxForce 13 Advanced EGR engine.