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Stringent on-road emissions regulations have led to the adoption of many emission control strategies, including common rail fuel injection, electronic engine controls, exhaust gas recirculation (EGR) and, most recently, diesel particulate filters (DPFs). Several solutions developed for on-highway engines have also been adopted for off-road use. But many technologies simply aren't practical for off-road application.

"The heavy-duty on-road engines are all big engines - you are talking about 200 to 400 hp," says Enrique

Sauerteig, director of compliance and certification, Deutz. Many of these technologies can be transferred to larger off-road engines. "The bigger engines that we have for off road have electronic controls, common rail technology - features that are very similar to what has been used in the on-road market."

However, Tier III regulations apply to off-road engines from 49 to 751 hp. Price becomes a real issue when it comes to adopting existing technologies for the smaller engines. "The cost issue is going to be greater on the smaller engines because of the ratio between the cost of the emissions control system and the cost of the engine," Sauerteig points out.

In addition, smaller engines do not have to meet the same standards as larger models.

"The standards for off-road engines are classified in power categories," says Sauerteig. The larger the engine, the more stringent the regulations. "We have managed to meet Tier III off-road requirements on the small engines simply with internal measures - like optimization of the combustion system and improvements to the injection system - without the need for electronic controls."