Latest Fuel Economy Testing Compares SCR with EGR Diesel Engine Technology

Blue Bird released its own data that claims SCR technology of the Cummins ISB diesel engine can achieve a more than 12-percent overall increase in fuel economy than Advanced EGR technology, depending on the engines tested.

The tests were conducted at the Bosch Automotive Proving Grounds and complied with SAE J1526 recommended fuel consumption standards and procedures of three separate tests per route and compared the ISB 6.7L in a 2012 Blue Bird Vision with Navistar’s 6.7L MaxxForce 7 as well as with the 7.6L MaxxForce DT installed in similar size IC Bus CE Series.

Blue Bird said it tested stop-and-go urban routes at driving speeds of 25 mph, 30 mph and 40 mph for 27 miles each on an enclosed test track. Each three mile lap on the test track included seven stops to simulate student pick‐up and/or drop off. The highway test consisted of a “steady state route” that simulated a 59-mile activity trip at an average speed of 58 mph. Blue Bird noted that actual fuel economy results may vary depending on type of route, terrain, driver behavior, weather conditions and loading.

The company said its Vision conventional powered by the Cummins ISB resulted in 10.67-percent increase in fuel economy over the IC Bus CE Series with MaxxForce 7, which IC Bus said is its fuel leader. Urban routes showed 8.07 mpg for the Vision compared to 7.32 for the CE, and the highway tests showed 9.81 mpg in the Vision and 8.84 in the CE. Overall, the study claimed that the Vision got 9.19 mpg compared to 8.31 mpg for the CE.

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“The results from a third-party, SAE compliant fuel economy tests echoed the real world results our customers were already experiencing.  We are pleased to report a 11 percent and 13 percent advantage over our competitor’s Exhaust Gas Recirculation (EGR) concept. In a day when every dollar counts, these advantageous fuel economy results provide a significant cost savings that positively affect a district’s bottom line,” said John Kwapis, chief operating officer for Blue Bird.

He added that the IC Maxxforce 7 and DT did not experience a regeneration cycle, which he explained happens in normal operating conditions.

“The normal regeneration cycle consumes additional fuel and would have shown an even greater advantage for the Blue Bird solution,” Kwapis said.

The overall, annual fuel savings of the ISB, according to Blue Bird, was $864.23. Blue Bird said an operator could expect to pay $8,161.04 annual for every 20,000 miles traveled at the April national average of $3.75 per gallon, whereas that cost increased to $9,025.27 for the MaxxForce 7. Blue Bird also claimed that the Vision’s vehicle range was 924 miles based on fuel capacity of 100 miles and overall mpg. That compared to the claim that the CE only had a range of 820 miles based on the same capacity and overall mpg.

Cummins said its data is showing that 2-3 percent of diesel fuel used must be DEF. For example, the engine uses 100 gallons of diesel fuel over a period of time, the SCR system used two to three gallons of DEF in the same period. The cost of DEF also fluctuates across the country. Last year, the bulk price varied from $1.73 per gallon to $2.73 per gallon.

Blue Bird also compared the Vision ISB with a CE Series powered by the MaxxForce 7.6L DT engine, similar to a test published by Thomas Built Buses earlier this year. The Blue Bird test claimed that the fuel economy improvement increased to 12.64 percent overall and as high as 16.74 percent on urban routes. IC Bus previously said that comparing that Thomas’ similar test of the Cummins ISB 6.7L and the Maxxforce DT “is like comparing apples to oranges.” IC Bus claims its MaxxForce 7 V8 with a six-speed is Navistar’s fuel leader.

Meanwhile, Blue Bird said: urban routes in the Vision bus achieved 8.24 mpg versus 7.06 for the CE; highway routes in the Vision recorded 9.76 mpg compared to 8.84 for the CE; and, overall, the Vision recorded 9.24 mpg and the CE recorded 8.20 mpg. At a total cost of $8,116.88, Blue Bird said the fuel savings of the ISB equates to $1,029.46 a year over the MaxxForce 7.

The study is the latest information to be released by school bus and engine manufacturers in response EPA diesel emission regulations in effect since 2010. Last summer, IC Bus released its own comparison of parent company Navistar’s MaxxForce 7 using EGR with the Cummins ISB that claimed a 4.5 percent advantage in fluid economy, a term coined by the IC Bus to describe the measurement of diesel fuel plus liquid urea, or Diesel Exhaust Fluid (DEF), used by a vehicle’s emissions reduction system. Navistar’s EGR technology treats oxides of nitrogen (NOx) in the engine where as Cummins’ SCR treats the emissions in the tailpipe with the use of DEF to meet EPA requirements.

In February, Thomas Built Buses partnered with Cummins to publish its own study that claimed SCR increased fuel efficiency by 27 percent over EGR when comparing the ISB 6.7 with the MaxxForce DT.