Cleaner engines for mobile machines

May 5, 2005
With record-level fuel prices and EPA Tier-3 diesel-engine exhaust emission standards taking effect, off-road equipment buyers are putting unprecedented emphasis on the powerplants in their new machines.

Caterpillar's C6.6 sixcylinder diesel is available in a broad power range from 119 to 250 hp. Maximum torque at 1,400 rpm is 728 lb-ft.

By midyear, Caterpillar, Peoria, Ill. (, will have nine offhighway engines that feature the company's proprietary Acert-technology, which precisely controls the combustion cycle to minimize emissions. All nine meet Tier-3 standards.

The C6.6 is the smallest of the new engines. It has 10% more displacement despite having the same overall envelope of its predecessor, the 3056E, yet does not need more cooling. The engine maintains a 500-hr recommended service interval and has the same mounting points.

Cross-flow heads on the C6.6 use four valves per cylinder and hydraulically actuated, electronically controlled injectors for combustion control, which reduce exhaust emissions and engine noise. A structural sump and new engine block and gear train enhance quieter operation.

The C6.6 communicates with other machine systems through a CANbus and industry-standard J1939 connector. This permits features such as enhanced diagnostics, cruise control, and throttle override by the hydraulic system or transmission.

The C6.6 will meet Tier-3 requirements and later be Tier-4 compliant with the addition of an aftertreatment exhaust system.

At the opposite end of the spectrum, Caterpillar released its new C32 engine boasting a 32-liter displacement. It weighs substantially less than the 3508B engine it replaces — 5,368 lb compared to the 3508B's 9,101 lb — but has more power — 1,300 hp compared to 1,100 for the 3508B. Low-end rating is 860 hp at 2,100 rpm, and a 1,500-hp version will be available for use below 700-m elevation.

The C32, like the other engines, uses Acert technology to precisely control combustion and minimize NOx and particulates. For instance, the fuel system injects small amounts of fuel several times during each combustion cycle to boost fuel economy and lower emissions. And an advanced air system provides more cool air in the combustion chamber. The system controls the air volume required at various loads and speeds, and automatically adjusts to engine requirements. Approximately 125 variables — in more than 10 million possible combustion combinations — are balanced for emissions, performance, fuel efficiency, and durability.

More than 185,000 engines using Acert technology have been built for onhighway use. And while off-road requirements are not exactly the same, the similarities permitted a smooth transition to the construction-equipment market, according to Cat officials.

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