A Cummins project to reduce fuel costs for Bartholomew Consolidated School Corp. could reap benefits for school corporations around the country.
In BCSC alone, the recommended changes from Cummins research could save more than $45,000 per year, if the existing fleet is upgraded and new bus purchase specifications are modified.
If school corporations nationwide were to implement the modifications, there could be millions of dollars in fuel savings per year, Cummins researchers said.
BCSC has been looking at ways to reduce transportation costs as diesel fuel prices have increased.
Jeff Caldwell, BCSC school board president and executive director — pickups/SUVs for Cummins, saw an opportunity for the engine maker to help.
Caldwell said that by examining the buses, it was possible that a Cummins team could suggest modifications allowing buses to use less diesel fuel.
“We see that big number once a year, and we all ask ourselves what we can do to make that number smaller, and in this case the team did a terrific job,” Caldwell said. “When I put my other hat on as a school board president, if we can spend less dollars on fuel it lessens the tax burden and increases the number of dollars we can put back in the classroom.”
A community involvement project
Caldwell sponsored a Cummins Community Involvement Six Sigma project beginning in 2010 to explore options to improve BCSC bus fuel efficiency.
The school corporation negotiates a contract with a fuel supplier for what it will pay per gallon for a given period, which allows school officials to budget estimated fuel costs each year.
The school corporation has 94 routes and about 100 buses in regular service that use about 200,000 gallons of fuel annually.
With a negotiated rate of $3.22 per gallon, which is lower than the consumer rate, that amounts to $644,000 per year in fuel costs. At 7 percent in increased fuel efficiency, savings of $45,080 could be achieved. That jumps to $64,000 if efficiency is increased by 10 percent.
Those changes wouldn’t be realized right away, since it costs about $2,500 to upgrade each bus, and not all the buses are being upgraded at the same time.
BCSC has two modified buses in the fleet now, and a third is in the process of being converted.
The school corporation changes out about 10 buses per year, and the modifications can be requested in specifications for new buses as they are ordered.
At that rate, within 10 years, the entire BCSC fleet could be upgraded to include more fuel-efficient vehicles.
Finding fuel savings
Caldwell credits Cummins assistant chief engineer Steve Bellinger and environmental engineer Mark Slaton for bringing the fuel savings project to fruition.
Improving engine performance is part of the Cummins business model, Bellinger said. So opportunities to reduce fuel consumption in the engine were almost nonexistent — the engines were already efficient.
With that in mind, the project team focused on changes to other parts of the bus to achieve better fuel mileage.
The team’s goal was to increase fuel efficiency by at least 7 percent through optimization of the power train system.
Bellinger said it is a common misconception that the engine alone controls fuel efficiency.
“At the end of the day overall efficiency goes much deeper,” Bellinger said. “The design of the vehicle and the power train system has a significant effect on the overall efficiency of any vehicle and engines operated at lower speeds yield improved fuel efficiency.”
The powertrain system refers to the transmission, the rear axle and axle ratios.
Steve Forster, BCSC fleet services manager, said any upgrades had to be achieved without affecting performance.
“What we were trying to do, because we spend a lot of money on diesel fuel, is hit the sweet spot,” Forster said. “No matter what we are doing, however, the most important thing is the safe transport of the students and we will give up on optimization to make sure it is safe.”
The project team needed to ensure there was no dropoff in takeoff acceleration, which is the time the bus takes off from a stop until it reaches 20 miles per hour.
If the buses are too sluggish on takeoff, Bellinger said, the potential for accidents could increase.
Partners from Allison Transmission and Blue Bird Buses joined Cummins and BCSC team members on the project.
“After analyzing the data, we then asked what changes we could make ... that might allow us to reduce the fuel that is actually being consumed by this engine,” Bellinger said.
Focus on ‘controllable elements’
Potential changes to the vehicles focused on controllable elements, such as shift schedule, the number of forward gears used and the axle ratio.
The amount of time spent at each operating speed, called buckets, was uncontrollable. The fuel used in some buckets, however, such as when the bus was at idle at traffic lights, could be reduced.
After identifying the buckets that could be changed, the next step was to figure out how to achieve the desired result without affecting bus performance, Bellinger said.
“I started studying the amount of fuel consumed in drive and reverse when the vehicle is stationary,” Bellinger said. “Every time a bus pulls up to a traffic light or stop sign, there is significant load on the engine.”
The same is true for the many stops made to pick up or drop of students throughout the day.
School bus transmissions have a reduced engine load feature that can automatically place a vehicle in an almost neutral state when idling. A modification that allowed the vehicle to be placed in that state every time it came to a stop significantly reduced the fuel being consumed.
Engines also are more efficient when operated at lower speeds, and the school bus engines were running at a high RPM shift schedule.
RPMs are the number of times the crankshaft of an engine, or the shaft of a motor, rotates in one minute.
“Anything we can do to reduce the average engine RPMs per mile will result in improvements in efficiency,” Bellinger said. “As the engine operates at lower speeds, however, there is no free lunch in this world, so the average power output is also less.”
It was determined that if the rear axle ratio was increased, it would offset the loss of power and the buses would not be sluggish on takeoff.
Testing the upgrades
Tests were conducted in May 2012 using a control vehicle that was not modified and a test vehicle with the upgrades. The buses ran on the exact same drive cycle in an identical driving environment. The drivers and buses were switched to ensure the results remained consistent no matter who was driving the bus.
“That was the exciting part for me,” Forster said. “We finally got to get them out and see if they would perform as we thought they would.”
The results not only exceeded fuel efficiency expectations, but also achieved environmental benefits.
For the 10 days the buses were tested over more than 600 miles in city operation, the test vehicle averaged
6.97 miles per gallon, compared to 6.21 mpg for the control vehicle, a 12.27 percent increase in fuel efficiency.
The highway increases were not as large, since much of the efficiency is realized during frequent stops, but the overall efficiency increased about 10 percent.
Cummins officials anticipate the benefits will be realized far beyond BCSC.
They want to show their results to other school systems throughout Indiana and the United States, Bellinger said.
Cummins analyzed data based on converting 80 percent of new rear-engine school buses manufactured each year in the United States to the more efficient model.
The annual savings, based on a 10 percent increase in fuel efficiency at $3.25 per gallon, would amount to $842,000 and 259,237 fewer gallons of fuel used.
Bellinger said Cummins is confident similar reductions could be achieved on front-engine buses. Using the same 80 percent estimate on those buses, costs could be reduced by $6.7 million, with a decrease in fuel usage of more than 2 million gallons.
Forster said BCSC is proud to partner with Cummins on a project with such far-reaching implications.
“Cummins and BCSC have been working a long time to make things better, and this is just another example of that,” Forster said. “We’ve been using exclusively Cummins engines since 1972, so it’s been a long-term partnership and anytime we can help each other, we take advantage of that.”
The following modifications were suggested by a Cummins-led Six Sigma team to improve fuel efficiency in rear-engine buses for the Bartholomew Consolidated School Corp.:
Enable RELs: The transmissions used in the school buses have a feature called Reduced Engine Load (REL) that can automatically place a vehicle in an almost neutral state when idling. A modification that allows the vehicle to be placed in that state every time it came to a stop significantly reduced the amount of fuel consumed.
Reduce shift schedule and utilize all six forward shift ranges: The school bus engines were running at a high RPM shift schedule. When the schedule was lowered and all six forward shift ranges were utilized, it increased fuel efficiency.
Increase the rear axle ratio: Operating the engine at a lower RPM shift schedule also reduced the power output. Increasing the rear axle ratio offset the loss of power and protected the launch performance of the buses.