Dozers Display Diesel Improvements

By Georgia Krause, Contributing Editor | July 12, 2011
Caterpillar D8T crawler dozer

As crawler dozer manufacturers sweep the eraser crumbs off their drawing boards again to tailor their mid-size-model designs to meet EPA’s Tier 4-I emissions mandates, they are taking the opportunity to build in additional efficiency. Good air, good productivity, good business.

The EPA says that when the country’s entire inventory of older off-road engines has been replaced with Tier 4-compliant machines (by 2030), the country will enjoy an annual reduction of more than 738,000 tons of NOx and 129,000 tons of particulate matter.

Although earlier-Tier engines have made a significant dent in carbon monoxide, nitrous oxide and hydrocarbon emissions, Tier 4-I rules require almost nonexistent NOx and PM readings. And there’s the engineering design rub.

NOx is created at high combustion temperatures, while particulate matter forms at lower combustion temperatures. Balancing the yin-yang of engine operations and emissions means adding components and systems that can necessitate more maintenance, monitoring and modernizing the landscape in the engine compartment.

As part of Tier 3 compliance, manufacturers successfully integrated cooled exhaust gas recirculation systems (EGR) which take part of the machine’s exhaust, cools it, then sends it back to the combustion chamber where the reduced temperature inhibits NOx emissions. But while an EGR system knocks out the NOx, it doesn’t do much for PM emissions. To reach Tier 4-I compliance, manufacturers are incorporating diesel particulate filters (DPF) into the dozer’s exhaust system that can catch the minuscule soot particles that burned off either as part of the engine’s operations or on the operator’s demand with a fuel-injection method to incinerate the PMs.

Another route to meet EPA’s requirements is to allow the engine’s temperature to run high, which results in lower particulate matter emissions, and add a selective catalytic reduction system (SCR) to reduce NOx. SCR systems inject a water-based urea solution into the exhaust system, causing a chemical reaction that converts nitrogen oxides into harmless nitrogen and water within the catalytic converter. Although an SCR system can reduce NOx emissions up to 90 percent and help cut PM emissions by 30 to 50 percent, according to the Diesel Technology Forum, buyers should consider that the SCR method requires installation of an additional tank for the urea solution, likely adding another step to the machine’s daily service checklist.

Manufacturers are customizing emission-control systems to work with existing clean-air platforms.

Komatsu’s new D65-17 and D155AX-7 crawler dozers are powered by Tier 4-I Komatsu engines that use an advanced electronic control system to manage air flow rate, fuel injection, combustion parameters, and aftertreatment functions to optimize performance and reduce emissions. Komatsu’s hydraulically actuated variable geometry turbocharger and exhaust gas recirculation valve, combined with a diesel particulate filter, reduce particulate matter 90 percent and lower NOx emissions 45 percent.

Deere prefers to use a simpler emissions package. The Deere PowerTech 6.8-L IT4 Tier 4-I diesel engine in the 850K model dozer uses a cooled-EGR configuration coupled with a DPF. Deere says the filter self-cleans automatically during routine operations, keeping the operator’s focus on the job instead of idling down for maintenance.

Caterpillar’s D6T, D7E and D8T dozers carry house brand C9.3 and C15 ACERT engines with Cat’s clean emission modules (CEM). The CEM aftertreatment unit includes a diesel oxidation catalyst (DOC), a diesel particulate filter, and Cat’s NOx reduction system (CRS). The DOC uses a chemical process to convert emissions in the exhaust system, and the DPF traps particulate matter. NOx emissions are kept in check by continuously diverting and cooling small amounts of exhaust, which is routed back into the combustion chamber. Cat’s regeneration system runs in the background and monitors the dozer’s operating conditions. If the regeneration system detects excessive particulate build-up, it automatically increases exhaust gas temperatures to burn it off. Operators have the option to initiate a regeneration cycle on demand. 

Enhancements on the upgraded mid-size dozers are giving fleets more accuracy and increasing productivity. Bruce Boebel, product manager with Komatsu, says, “The slow economy has a lot of contractors these days looking for a dozer in the midrange 200-to-400-horsepower class that will do more. They want more versatility from their equipment. Contractors tend to think of their mid-size crawler dozer as a tool, and they want that tool to do as many different jobs as possible before they have to go out and buy another one that is specific to another job.” Komatsu offers an upgraded version of its Komtrax equipment-monitoring system and a new enhanced provision for easy installation of geopositioning and machine control systems. “Productivity from  a smaller dozer fitted with new control technology can be as efficient as a larger machine due to the greater accuracy available to the operator,” Boeble says.

Similarly, Cat’s crawler dozers come with factory-installed integrated wiring to add Cat’s grade control and telematics systems: AccuGrade and ProductLink.

As engineers wrestle with meeting Tier 4-F requirements, expect more improvements in dozer designs and systems, from onboard computers to tracks.

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