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."
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.
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."
Then you step up in horsepower. "PowerTech E engines (60 to 200 hp) are a simple emissions solution that feature a fixed-geometry turbocharger, full-authority electronic controls and a high-pressure common-rail fuel system or electronic unit pump fuel system," says Laudick.
At the top of the line is the more complex PowerTech Plus engines (149 to 600 hp) that feature cooled EGR, a variable-geometry turbocharger, state-of-the-art engine control unit and electronic unit injector system or high-pressure common-rail fuel system.
"These technologies overlap across displacement options, and the only engines that are available in just one platform are the PowerTech Plus 9.0L and 13.5L," says Laudick. "So it has more to do with offering customers multiple technology solutions than it does with letting the technology be dictated by the engine size."
Clearly, no one solution fits every application. "There are many ways to meet the new regulations. And given the range of engines to which the regulations apply, it's critical to match the right solution with the right application," says Farrar. "The industry's solutions range from controlling the byproducts of combustion in-cylinder to recirculation of exhaust gas back to the combustion chamber with cooled EGR."