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Cooling off-highway engines requires a different approach than what is used for on-highway models. "In on-highway applications, ram air is abundant and helps to cool an engine with the additional heat rejection requirements of highly advanced, emissions technology," says Farrar. "Lack of ram air becomes problematic for off-highway applications such as excavators, skid-steer loaders, pavers and other construction equipment."

Cooling the new engines is one of the greatest challenges. "Whatever we do to reduce emissions is going to put more heat into the cooling system," says Sauerteig. This will require bigger charge air coolers and larger radiators. "You need to move more cooling air through the coolers."

Differences between on- and off-highway fuels present another challenge. "The availability of low-sulfur fuels becomes important when looking at aftertreatment or cooled EGR solutions," says Farrar. "Off-highway fuel today can contain sulfur up to the 4,000- to 5,000-ppm ranges. Sulfur levels above 500 ppm can be problematic for some NOx reduction solutions such as cooled EGR, and aftertreatment methods such as NOx adsorber catalysts." Such low-sulfur fuels are not mandated until October of 2007 for off-highway markets, but are available through the on-highway market.

The environment experienced by on-highway engines is also much different than for off-road engines.

"Off-highway engines have to perform in harsh, rugged conditions - dusty construction sites, extreme hot or cold, etc. - so it's not simply a matter of adapting technologies from current on-highway engines," says Laudick. "It's more a question of what technologies are needed to specifically meet off-highway emissions regulations. Each engine technology carries a cost, and selecting the appropriate level of technology is critical to remaining competitive in the off-highway market segment. "