Image

Credit: Kenworth Truck Co.

If you're in the market for a dump truck, it's important to do your homework. Unlike some other vocations, dump truck specifications are very regionalized. What works in one area of the country will not work in another.

Your first piece of homework: Find out what the length and weight regulations are in your state. Try to take maximum advantage of the weight laws to maximize payload. Some states, mostly in the West, require compliance with the Federal Bridge Formula; others don't. This will have a big influence on how the axles are set up and spaced.

"A Bridge Formula truck will tend to be longer to spread the weight," says Samantha Parlier, vocational marketing manager for Kenworth Truck Company 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. Your local Kenworth dealer will know the rules and regulations."

In states where you don't need to comply with the Bridge Formula, you can spec trucks shorter and with higher axle ratings, making them more maneuverable on jobsites.

2010 ENGINES - SCR OR EGR

It's also important to understand how the 2010 federal engine emissions standards may require some changes to be made when spec'ing for new truck purchases compared to your current dump truck spec.

"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 still 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," Parlier says.

"For dump trucks where truck frame space is often critical, Kenworth provides a 5.6-gallon tank with a clear back of cab option unique to the industry. The tank has a range of more than 1,500 miles between refillings. When combined with a Kenworth SCR and DPF package under the cab access step, there is essentially no impact to the customer."

Not all SCR technology engines are the same, however. "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

For those operators looking for an alternative to a standard diesel engine, natural gas-powered engines such as the Westport Innovations GX 15-liter engine and LNG system for heavy duty Class 8 trucks can offer a third option. For those operators hauling particularly heavy bulk loads, the Westport GX, based on the Cummins ISX diesel engine, is available in power ratings of 400 to 475 hp and torque ratings of 1,450 to 1,750 lb-ft. Plus, the LNG fuel tanks can be configured to suit the operators' range requirements.

Operators who don't need that high of horsepower or torque can spec the Cummins ISL G engine, which is rated at 320-hp and 1,000 lb-ft of torque. The ISL G engine 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 it does with LNG trucks, she adds. However, LNG fuel has a higher energy density than CNG since it is a liquid, so an LNG-powered truck can go further on the same amount of fuel.

Neither LNG nor CNG has the high energy density of diesel fuel, but both are cleaner fossil fuels, so they produce less carbon pollution than diesel fuel. Also, both are domestically produced, so they have the potential to reduce 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 have limited programs with grants to help offset the additional cost of the engine technology. Plus, 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.