40 to 60% increase in cooling requirements. Improved lubricants will be needed to tolerate the
resulting higher temperatures.
Figure 5. Diesel Engine Emissions
Higher-temperature lubricants could have other advantages as well. For example, a higher-
temperature cooling fluid would increase the efficiency of the radiator by increasing the delta T.
That would enable better aerodynamic design, which would improve fuel efficiency.
The efficiency of the drivetrain transmission and axles also is of interest because 5% of total
engine horsepower typically is lost in the drivetrain as heat. Furthermore, the required cooling
components add weight and cost.
Off-road vehicles include equipment for construction, mining, agriculture, forestry, paving, and
waste-hauling. Because the fuel consumption of off-road vehicles is only about 18% of that of
heavy-duty trucks, one might argue that it would be difficult to justify R&D directed toward
increasing fuel efficiency of off-road vehicles. However, the issues related to off-road vehicles
are virtually identical to those for heavy-duty trucks, so any R&D directed toward diesel-
powered trucks would be equally applicable to off-road vehicles.
The main issues facing operators of off-road vehicles are up time (including reliability and
durability), owning and operating costs, and environmental compliance (see Figure 6). In
addition, there is an economic incentive to use ever-larger vehicles. This places increasing
demands on the materials of construction because the weight of the vehicle increases with the