At one time, air-conditioning defined a luxury car, but today almost every car, regardless of model, makes cool air. The same fate may await commercial trucks with auxiliary power units intended to reduce main engine idle time — today relatively rare, tomorrow virtually standard equipment.
Fleet operators have all sorts of reasons for considering installation of auxiliary power units on tractors, Martin Duffy, vice-president, engineering, for Thermo King Corporation explained to a round table session of the Truckload Carriers Association Refrigerated Division annual meeting. The meeting was held on July 12 to 14, 2006, in Coeur d'Alene, Idaho. In addition to the obvious attempt to conserve fuel at a time when fuel prices are at historic highs, fleets may install APUs to enhance driver comfort or to maintain engine block temperature in cold weather climates, he said.
Route scheduling can have an important impact on which idle reduction technology to choose, Duffy said. For instance, repetitive routes in certain areas of the country offer the opportunity to use shore power systems such as those installed in many truckstops. Routes with predictable stops for a specified, limited time make the use of battery systems worthwhile. However, irregular routes with unpredictable or infrequent stops may make on-board, engine-powered systems the most useful power system, he said.
As more fleets look to APUs to reduce idling, managers want to know if the systems add to truck residual value, Duffy said. Some of that answer depends on trade cycles. For an APU to add to resale value, it must have a service life that exceeds normal tractor trade cycles.
Idle reduction technology can also be a factor in driver recruitment and retention, Duffy said. This is a two-part problem — first, finding new drivers and, second, keeping them with the company. Driver comfort and convenience appears to be a major concern when drivers choose to work for a company and, more importantly, when drivers choose to stay with a carrier for an extended period. Determining which idle control technology to adopt takes careful study, because trucking now has access to more than 40 different systems with a significant range between the least expensive to the most expensive, he said.
Purchase price for idle reduction technology depends on how the systems work, Duffy said. At the low end of the spectrum, engine idle controls and fuel-fired heaters offer the lowest price as well as the most basic performance. Price increases as more, such as fans and thermostat control, are asked from the systems. At the top of the price pyramid, systems with self-contained diesel engines and electric generating capacity, such as the APUs offered by Carrier Transicold and Thermo King, are the most complex and offer the widest variety of performance.
The decision needs to be made on individual fleet requirements, but it appears that high-performance APUs offer the best prospects for attracting and retaining quality drivers, Duffy said.
Understanding idle patterns
Obviously, the concepts behind purchasing high-performance APUs can be applied to other systems, but using the higher priced systems in an initial payback scenario seems to be most useful, Eduardo Andrade, business manager, special products for Carrier Transicold, said. The first step is to gain an understanding of fleet idling patterns. A good example might be a fleet that runs tractors 130,000 miles annually at an average speed of 50 mph and idles the main engine 48% of the time. That idle percentage need not be a guess, because the information can be extracted from the electronic control module on the engine, he said.
A tractor in this fleet example logs at least 5,000 hours of annual engine time, Andrade said. If the engine idles 48% of the total, that engine runs 2,400 hours without moving the tractor an inch; that equates to 120,000 miles of unused travel capacity. The next step is to calculate what that idle time costs. “The problem inherent in making this calculation is that the electronic control module on the main engine may underestimate the amount of fuel used,” he said. “For the most accurate calculation, a fleet is probably better off running an independent test rather than trusting data from the ECM.”
Determining fuel consumption at idle is relatively easy, but also fairly tedious, Andrade said. It requires use of a graduated container marked at least in one-tenth gallon increments as well as an accurate stopwatch. The engine must be started and allowed to reach normal operating conditions, which should include customary loads such as running the air-conditioner. “The most common reason for idling is running the climate control system, so measuring fuel consumption without turning the air-conditioner on won't provide an accurate number,” he said. “To figure fuel consumption at idle, measure the time needed to use exactly one gallon. From that information, an accurate calculation of gallons per hour is possible.”
Don't trust ECMs
The difference between an actual test and the engine ECM can be fairly large, Andrade said. For instance, one example shows an actual consumption rate of one gallon per hour compared to 0.7 gallon per hour based on data from the ECM. In that particular case, an investigation later showed that neither the air-conditioner nor the alternator was running. In a different test of a tractor with an older engine, the ECM indicated fuel consumption at idle of a little less than 0.7 per hour, while the actual performance test showed the engine using 1.2 gallons per hour. In a test performed at high ambient temperature ensuring that the air-conditioning was fully loaded, the engine used about 1.5 gallons per hour while the ECM indicated only 0.7 gallons per hour. “The point here is that cost calculations cannot be made using inaccurate fuel consumption data,” he said.
For most of the year, the national average price for diesel has hovered around $2.90 per gallon, Andrade said. Using that average price, a truck idling for 2,400 hours a year at 1.25 gallons per hour would burn $8,700 worth of fuel. Over a five-year service life, that comes to more than $40,000. In comparison, one of the high-performance auxiliary power units with a self-contained engine consumes about 0.2 gallon per hour for an immediate saving of more than $3 per hour.
That immediate saving doesn't move straight to the bottom line, Andrade cautioned, because no idle reduction technology will ever eliminate 100% of main engine idle time. High-performance APUs can come close by using automatic start/stop systems, but systems that start the APU when the main engine shuts down still will not eliminate the idling that takes place in traffic or other situations where the main engine has to run. However, actual fleet results have shown a drop in main engine idle to as low as 5% to 10% of total engine hours, he said.
High savings level
If fleets can reduce idle time to 10%, they can save almost $7,000 per tractor per year, Andrade said. That's just in fuel cost. Total saving won't be that high, because maintenance for the APU has to be subtracted.
Whatever the cost saving, APUs probably are worth the investment, because main engine idling is bad by definition, Andrade said. Many experts suggest that running a large bore engine at idle speed wears internal components twice as fast as running the engine at normal highway rpm. Some lubrication engineers think that idling causes lubricating oil to break down faster. If the main engine is used only to power the truck, fleets should be able to consider extended oil change intervals, he said.
Most fleets change oil at around 20,000 miles and do six to seven oil changes a year, Andrade said. That costs almost $1,200 a year in basic service plus oil and filters. If 48% idle time is factored into the service interval equation, the engine actually experiences 38,000 miles of wear between oil changes. Using that additional 18,000 miles per change interval for actually moving the truck, fleets have an opportunity to save about $500 a year on oil changes.
This line of thinking can help with resale value as well. “In some instances, we are seeing fleets get higher resale value for engines with fewer operating hours,” Andrade said. “The key to this change is to convince prospective buyers to look at hours instead of miles and to be able to document the number of hours claimed.”
