Many fleets are concerned about the cost of fuel. Some are switching to various alternative fuels, such as natural gas or propane (autogas), while others have pursued technologies.
"These are all viable technologies that offer significant savings when utilized in the right application," says Bob Johnson, director of fleet relations for NTEA. "Unfortunately, not every fleet's drive and duty cycles are conducive to the use of these technologies.
"In addition, the fleet may not have the necessary funds to invest in alternative technologies. Fortunately, numerous other tactics can be employed to help conventionally-powered fleets achieve significant reductions in fuel consumption."
The Association for the Work Truck Industry, NTEA (www.ntea.com) represents companies that manufacture, distribute, install, sell and repair commercial trucks, truck bodies, truck equipment, trailers and accessories.
NO LARGE FINANCIAL INVESTMENT
Fleets ought not loose sight of common "conventional" fuel reduction technologies, Johnson says.
"Most of these technologies have the advantage of not requiring as great a financial investment as most of the alternative energy sources. In addition, if you are using an alternative energy source, you can still implement these technologies for an even greater savings."
The savings associated with many of these "conventional" technologies are still drive and/or duty cycle dependent, but their lower cost of entry results in a "wider threshold of effective utilization," he points out.
ENERGY EFFICIENCY
Alternative energy sources reduce overall operating costs by providing the required energy at a lower cost, says NTEA's Johnson. "Conventional energy cost reduction technologies achieve their gains by simply using less energy per unit of work done.
"The important factor here is the unit of work done. It does not matter if you do the same amount of work you have done in the past with less energy, or do more work with the same amount of energy used in the past. Either way, you are using less energy per unit of work accomplished."
Horsepower is a basic unit of work. One unit of horsepower is defined as 33,000 ft/lbs of work per minute. The critical factors with horsepower are weight, speed and distance.
"If you don't move anything, you have accomplished no measurable work," explains Johnson. "Therefore, in the case of your trucks, the energy used overcomes factors such as engine and driveline friction and pumping losses provides no measurable work.
"In addition, sometimes measurable work components, such as pumping water in a truck's cooling system, generating electricity or operating the vehicle's brake system, do not directly assist in moving the vehicle. Thus, they do not contribute to the accomplishment of the truck's primary function, which is to move goods or materials."
These energy losses keep the vehicle operating and provide for safe and comfortable operation, he notes. Since they are necessary, but not directly productive, they are often referred to as parasitic loads. Anything that can be done to reduce all forms of friction, air resistance and non-productive work will contribute to the increased operational efficiency trucks.
ENERGY USE
The overall energy utilization efficiency of an internal combustion engine varies depending on the type of engine – gasoline vs. diesel – and application of the engine – automotive vs. truck – being evaluated, Johnson explains. But on average, only about 20 percent of the energy generated by fuel combustion is actually available to power the vehicle (see Table 1). The balance of the energy is lost is shown in Table 2.
Table 1. Available Energy to Move a Vehicle
Wind Resistance (aerodynamic losses at highway speed)
Energy Use:
9 percent
Rolling Resistance
Energy Use:
6 percent
Braking Losses
Energy Use:
5 percent
Source: U.S. Department of Energy
Table 2. Balance of Energy Use
Thermal Losses (radiator, exhaust heat, etc.)
Energy Use: 60 percent
Engine Idling, Combustion, Pumping Losses
Energy Use: 7 percent
Parasitic Losses
Energy Use: 5 percent
Drivetrain Losses (friction)
Energy Use: 5 percent
Engine Friction
Energy Use: 3 percent
Source: U.S. Department of Energy
"Looking at just the energy actually available to move the vehicle, aerodynamic losses account for 45 percent of the net usable energy expenditure (at highway speed), rolling resistance equates to 30 percent and braking losses make up the remaining 25 percent," says Johnson. "Obviously, these percentages will vary depending on the drive and duty cycle of the vehicle, aero coefficient, etc."
THERMAL LOSSES
NTEA's Johnson says that excluding thermal losses, all of the other engine losses account for around 20 percent of the total energy balance associated with an internal combustion engine. There are a number of things that can be done to reduce engine and driveline losses, with many of them being maintenance issues. Among them:
Pumping Losses
- Maintain the exhaust system properly.
- Replace engine air filters on regular basis.
- Avoid making exhaust system modifications.
- Keep engine valves properly adjusted.
Engine Friction
- Use the proper grade of engine oil.
- Utilize a quality synthetic oil of the proper grade.
Parasitic Losses
- Maintain drive belts properly.
- Specify electrically-driven accessory components (fans, AC compressors, power steering pumps, etc.).
- Reduce lighting loads by spec'ing LED lighting components.
- Right-size components such as air compressors and maintain systems to avoid leaks.
Drivetrain Losses
- Spec the proper components for the vehicle application (avoid over- or under-sizing components).
- Utilize synthetic lubes in all gearboxes.
- Maintain transmission coolers properly.
- Maintain drivelines with particular attention to universal joints.
- Minimize driveline angles.
IDLE MANAGEMENT
Particular attention needs to be paid to idle management, stresses Johnson, because in a typical vehicle application, idling losses equate to around 3 percent of the total energy budget. "However, since only 20 percent of the budget actually reaches the ground, that 3 percent is equal to almost 15 percent of the productive energy component.
"Granted, you will never be able to totally eliminate engine idling, but if you can reduce it by 33 percent, you may possibly see a net increase of 5 percent in your overall fuel economy, which is significant."
He notes that many vocational applications have idle time factors far in excess of the norm, especially in PTO-equipped vehicles. In these applications, an active idle management system may provide even greater gains.
Johnson offers some approaches to idle management:
- Realistic idling limitations combined with effective driver education.
- Idle-time tracking (telematics) combined with productive drive feedback.
- Automatic idle shutdown systems.
- Idling alarms (alarm trigger time may vary by application).
- Auxiliary hotel load management systems.
- Use of auxiliary power units.
"This list is far from comprehensive, but it gives you a starting point," he says. "Be sure to take the time to evaluate your specific applications and look for opportunities to limit engine idle time.
"In addition to reducing fuel consumption, you will also be reducing emissions, environmental noise and engine wear."
