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Off-highway engines must also fill a wider variety of applications. "Off-highway applications have such a broad range of installation, duty cycle and horsepower requirements," says Bruce Farrar, Cummins Inc.

Multiple solutions
Smaller off-road engines don't require the complex solutions developed for on-highway regulations.

"Because the emissions levels that each market must achieve are substantially different, on-highway and off-highway engine manufacturers use different technologies," says Doug Laudick, product manager, John Deere Power Systems.

In fact, manufacturers employ different strategies based on the engine size and application.

For example, John Deere Power Systems developed three different platforms for its Tier III engines. "There is no such thing as a one-size-fits-all solution to the Tier III challenge," says Laudick. "What differentiates the three platforms is the level of emissions control technology employed. PowerTech M engines (42 to 99 hp) feature economy of design, a fixed-geometry or wastegated turbocharger, mechanical controls, a mechanical unit pump fuel system or a mechanical rotary fuel system."