You see them on every highway: big, rounded semis with aerodynamic fairings and tails. Unfortunately, aerodynamics has little effect on trucks operating at less than 50 mph for most of their duty cycle. But there are other ways to cut fuel costs. Each by itself isn’t significant, but together they have a big impact.
A vehicle’s energy comes from just one place: fuel burned in the engine. Anything that lessens energy demand saves fuel. If, for example, a wheel-end seal starts to go bad and contaminants get into the bearings, they’ll put a drag on the bearing. The vehicle will then require more power to travel any particular distance. The following measures minimize power requirements:
Wide-base single tires. For years dual tires under loads increased carrying capacity; off-road tires had deep lug tread patterns and very hard tread rubber for traction and damage resistance. Using two tires instead of one requires twice the energy to flex the sidewalls; off-road tires need a great deal of energy to overcome their inherent stiffness.
Switching to wide-base single tires engineered for vocational and on-off highway use saves 3% to 4% on fuel use.
Changing from deep lug to shallow lug tires: another 2%.
claims its heavy-duty, full synthetic 5W-40 saved 8.2% in SAE/TMC tests conducted against conventional 15W-40.
Thinner oils cut internal engine drag. Savings in fuel use: about 1.5%.
Using synthetics in the gear box and drive axles: another 1%.
Engine fan usage. The fan consumes 50 to 60 hp. Using waterless coolant and adjusting the fan-on temperature saves up to 3% in over-the-road trucks. Using power take-off in stop-and-go operations could produce more or less.
Braking behavior. According to the Technology and Maintenance Council’s Recommended Practice RP1114, Driver’s Effect on Fuel Economy, “Driver performance accounts for as much as a 35% difference in fuel economy performance.” Variables include horsepower demand, vehicle speed, and brake use:
- Horsepower demand is directly related to speed and acceleration rates; the faster a driver goes and the faster he accelerates, the more fuel he burns.
- Every time the brakes are applied, kinetic energy is converted to heat. The heat in the brakes is then dissipated to the air from the brakes. The heat or kinetic energy is created from the engine burning fuel. Dissipate the heat and you’re wasting fuel. Drivers who look to the next traffic light and time their approach, coast to stop signs, and ease up near the top of a hill so they can use gravity on the downhill side rather than slowing with the brakes use the least fuel.
Progressive shifting. Not long ago, engines had relatively narrow power bands, sometimes as little as 14% of total available engine revolutions (from 1,800 to 2,100 rpm). Today, engines run much slower, with peak torque as low as 1,000 to 1,100 rpm and peak horsepower at 1,800 rpm. With a 45% power band, shifting can occur at lower engine speeds.
Drivers striving for fuel economy use progressive shifting. They take advantage of torque multiplication in lower gears to shift at lower rpm and to skip unneeded gears. To help them out, manufacturers developed a new breed of automated manual transmission for vocational applications. These transmissions help any driver with a light touch achieve even better fuel economy:
- Eaton Corp.’s UltraShift Plus has variations programmed to optimize shift points
- Volvo Trucks North America (I-Shift), Mack Trucks Inc. (mDRIVE), and Detroit Diesel Corp. (DT12) automated 12-speed transmissions provide optimal shifting for their engines’ proprietary fuel mapping
- For those who prefer the constant torque application from a full automatic, Allison Transmission’s TC10 10-speed transmission features load-based shift schedules. Current plans are to complement, not replace, Allison’s rugged on-off-highway 4000 RDS, but much of the technology will be shared in the near future
- Even pickup trucks are using more gears to better match engine efficiency to road speed. The new Ram 1500’s 8-speed automatic improves performance without sacrificing economy.
Technological advancements, however, occur in small increments, not big chunks. So the greatest opportunity for improvement will remain driver performance.
— Paul Abelson ([email protected]) is a former director of the Technology and Maintenance Council (TMC) of the American Trucking Associations, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.
The greatest opportunity for improving fuel economy is driver performance.
How to take the volatility out of fuel prices
If your operation buys at least 1 million gallons of fuel a year, a 12-year-old software-as-a-service could trim fuel prices by 4 cents to 6 cents/gallon. That adds up to $40,000 to $60,000 of savings a year.
Houston-based FuelQuest takes the volatility out of clients’ fuel buying. Rather than buy in bulk, the company monitors financial markets to build a supply portfolio.
“We can predict with reasonable certainty the direction of prices from day to day,” says Vice President and General Manager Ryan Mossman. “By timing purchases, we might save a customer 7 cents by buying today instead of tomorrow.”
The company can help any fleet that has its own fuel tanks.
“They tell us how big their tanks are, how much fuel they typically use, and their operating hours,” Mossman says. “Once we have those parameters, our network operations center monitors inventories via the Internet, places orders using our technology, and handles every aspect of when they get a load of fuel and where they get it from.”
The company buys 19 billion gallons a year for clients, which include Veolia Environmental Services, Carmuese, FirstGroup, and J.B. Hunt.
For more information, visit www.fuelquest.com.