“A Bridge Formula truck will tend to be longer to spread the weight,” says Samantha Parlier, vocational marketing manager for Kenworth Truck Co. in Kirkland, Wash. “You may need to have lift axles, but there are different rules on how much load you can add with lift axles. And, some states don’t allow lift axles. Local dealers will know the rules and regulations.”
2010 ENGINES - SCR OR EGR
Also crucial is understanding how 2010 federal engine-emissions standards may require changes from a buyer’s current dump-truck specs when a new model is purchased. “The extent of these changes depends upon each dump truck operator’s choice between two available engine technologies, which may also affect truck performance and operating costs over its lifetime,” Parlier says.
Operators can choose an engine aftertreatment approach that utilizes selective catalytic reduction (SCR) technology in combination with exhaust gas recirculation (EGR), or an in-cylinder approach through increased EGR. Both technologies use EGR to circulate a portion of an engine’s exhaust gas back to the engine cylinders and a diesel particulate filter (DPF) to remove particulate matter from the exhaust. A critical difference is the amount of exhaust gas that is recirculated back to the engine; the enhanced EGR approach uses a significantly higher level of recirculated exhaust gases. SCR also mixes a reactant—most commonly a solution of urea and de-ionized water known as diesel exhaust fluid (DEF)—with the nitrogen oxides (NOx) in exhaust gases. The exhaust then passes through a catalyst, where the DEF reacts with the NOx to convert it into nitrogen and water.
Increased EGR reduces NOx by boosting the amount of exhaust gases in the engine cylinder, then slowing and cooling the combustion process and burning off pollutants. The increased heat created with the enhanced EGR approach requires greater engine cooling capacity. Increased EGR also requires more fuel to be injected into the DPF for active regenerations.
“SCR doesn’t rely on engine heat to treat emissions, so SCR-based engines offer the advantage of higher fuel economy,” Parlier says. “Since SCR doesn’t narrow the engine’s maximum speed range for optimum efficiency, or its ‘sweet spot,’ to attain emission reductions, fleets also can maintain fuel economy at lower or higher engine speeds.”
According to Parlier, it is important for operators choosing SCR to consider DEF tank capacity and placement. “To support SCR system integration, Kenworth has a range of exhaust and DEF tank sizes and locations designed for dump trucks. This helps dump operators to maintain their wheelbase and body configuration when spec’ing Kenworth trucks with 2010 engines,” she says.
Kenworth provides a 5.6-gal. tank with a clear back-of-cab option that especially suits dump trucks where frame space is often critical. The tank has a range of more than 1,500 miles between refillings. Combined with a Kenworth SCR and DPF package under the cab access step, its impact to the customer is negligible.
Not all SCR technology engines, however, are the same. “An aftertreatment catalyst using copper zeolite is much more efficient than one with iron zeolite at reducing NOx at normal engine operating temperatures,” Parlier says. “Engines using copper zeolite may enjoy up to an additional 2 percent fuel-economy improvement over engines using iron zeolite.” Paccar engines and Cummins engines both use copper zeolite.
A THIRD OPTION: NATURAL GAS
Natural gas-powered engines such as the Westport Innovations GX 15-liter engine and LNG system for heavy-duty Class 8 trucks offer a third option for operators looking for an alternative to a standard diesel engine. Based on the Cummins ISX diesel engine, the Westport GX is available in power ratings of 400 to 475 hp and torque ratings of 1,450 to 1,750 lb.-ft. for operators hauling particularly heavy bulk loads; plus, the LNG fuel tanks can be configured to suit the operators’ range requirements.
Where less horsepower or torque is needed, the Cummins ISL G engine—rated at 320 hp and 1,000 lb.-ft of torque—
operates on either LNG or compressed natural gas (CNG). It uses a maintenance-free, three-way catalyst and is 2010 EPA- and CARB-compliant without the use of SCR technology or a DPF.
“Deciding on whether to go with CNG- or LNG-powered trucks may be determined by the availability of the fuel in your area,” Parlier says. “With many local transit and government agencies using compressed natural gas to power buses and trucks, sources of CNG fuel may be easier to find in some areas than LNG.”
Operators should also consider that fueling CNG-powered trucks doesn’t require special training as is the case with LNG trucks, she adds. Because LNG fuel as a liquid has a higher energy density than CNG, however, an LNG-powered truck can go further on the same amount of fuel.
While neither LNG nor CNG has the high energy density of diesel fuel, both are cleaner fossil fuels, so they produce less carbon pollution than diesel. And, since both are domestically produced, they offer the potential of reduced reliance on foreign oil. The drawback can be a significantly higher-cost engine, Parlier says. But, some state and local air-quality control agencies may provide grants to help offset additional engine-technology costs. Additionally, by deleting the additional weight associated with the SCR or EGR emission control systems, a natural gas-powered truck may be able to carry more payload.
LOAD & HAULING
Load types, e.g., sand & gravel, asphalt or demolition debris, will have a bearing on the chassis spec, since hauling demolition debris or heavy rock will require a sturdier body and suspension. Also relevant is the environment or territory to be navigated.
“If you will be going off-road a lot into rough terrain, you’ll need a suspension that is heavier-duty and has more articulation,” Parlier advises. “But if you’re hauling longer distances, you’ll need to consider the trade-off between ease of dumping and the ability to haul more load per trip. For example, a transfer dump will allow you to haul more with one driver, but it will take longer to unload. Double bottom-trailers carry a lot of payload, too, but with those you’re limited on where you can drop the load—it’s a lot harder to dump gravel into a hole for a swimming pool, for instance, with bottom dumps.”
One of the big mistakes many people make with dump-truck engines is they spec too much power, says Parlier. “You should get just enough horsepower to do the job. Generally, 350 to 400 hp is plenty for most applications. Extra horsepower just uses more fuel, puts more strain on the rest of the drivetrain, and adds cost up front,” she says. “If you go with a smaller 13-liter block, you save around 700 lb. over the 15-liter option.”
A generous ratio range is critical for the transmission installed with the engine. A low gear is needed to exit hilly jobsites and a sufficiently high top gear is required to attain decent highway speeds. Although the Eaton Fuller 8LL is a common truck spec, Parlier recommends an 18-speed transmission for larger and heavier trucks: “If you are hauling over 90,000 lb., you should consider an 18-speed, because you get much closer splits from bottom to top.”
The typical dump truck uses 46,000-lb. rear axles. That spec covers most trucks, from 14/16-yd. solo dumps through combinations up to 110,000 GCW.
Air filtration is another factor to consider in off-road operation. Dual-polished external air cleaners are impressive in appearance and provide excellent filtration with low air restriction; but, they are quite expensive compared with under-hood air cleaners. A small up-front investment on a better air cleaner avoids the greater expense of a dusted engine. Moreover, better filtration usually will mean longer life for the filter elements, e.g., dual 15-in. air cleaners will last over seven times as long as a single 11-in. underhood air cleaner before needing replacement.
Cutting vehicle weight can be profitable when hauling many loads per day. Nonetheless, since many weight-saving strategies cost more up front, the customer will need to balance that expense against anticpated gains due to hauling more payload.
Spec’ing components, such as wheels, air tanks and clutch housings, in aluminum rather than steel can save significant weight. “Use the smallest fuel tank you can get away with,” Parlier adds. “Some operators can use a 56-gal. tank, but most will need at least 75 to 90 gallons to get through a day.”
Valuable pounds can also be spared by choosing the right suspension. “The difference can be as high as 400 lb.” Parlier says of the different suspension options.
To avoid hauling extra steel in the vehicle frame, the dealer can work with a Kenworth application engineer to provide enough frame only where its needed. A strong crossmember typically will be needed at the back of the cab to strengthen the hoist-mounting area. If lift axles are to be added later, the dealer must include that information in the order so that the frame can be prepared.
DRIVER PERFORMANCE ITEMS
Among driver performance-related items, Parlier recommends dual small gears rather than a large single steering gear to achieve best turn performance and road feel from steering. The dual system will also last longer than a single system.
Try to spec as much glass area as possible, Parlier adds, and plenty of mirrors. “Kenworth DayLite doors give a larger glass area in the main door window,” she affirms. Further, picking low-replacement cost windshields, when they’re available, offers sizeable long-term savings: “Most vocational fleets replace at least one windshield side per truck per year. Two-piece flat-glass windshields with roped-in seals can be replaced in half an hour for a total cost of under $100, saving thousands of dollars over the life of the truck.”
Also recommended are lift axles in a six-channel ABS system. “Lift axles, especially steerable ones, are normally over-braked for the load,” Parlier notes. “By including them in the ABS system, they’re less likely to lock up, and tire flat spotting is reduced.” Two additional Kenworth driver-performance items that Parlier touts are Extended Day Cab and QuietCab options, which can “dramatically reduce driver fatigue, and that helps keep them more productive.” The Extended Day Cab provides six inches more room fore-and-aft, plus five inches more headroom. The QuietCab option reduces in-cab noise by two decibels, equivalent to cutting perceived noise by almost 50 percent.