thermo-acoustic refrigeration, and thermoelectric refrigeration. Natural refrigerants such as
carbon dioxide are already being evaluated.
Emissions Regulations and Engine Durability. Current and near-future exhaust-
emissions legislation for heavy-duty engines has been met by optimization of combustion
systems, widespread use of turbocharging, aftercoolers, high-pressure fuel-injection equipment,
and injection-timing retardation. Future legislation, including 2002 EPA regulations, will require
additional emissions reduction technology such as EGR and/or exhaust-gas aftertreatment.
Relative to thermal loading, retarded injection timing increases overall heat rejection to
coolant and oil by up to 10 %. Local thermal load at the top of the cylinder bore may increase by
30-80%. EGR raises inlet manifold temperatures, increases the thermal load on the cooling
system, and deprives the engine of coolant diverted to the EGR cooler.
Several approaches can be considered for improving thermal-management systems to
cope with increased heat rejection and thermal loads. These include precision cooling; new
and/or improved cooling strategies; reduced parasitic loads on the engine; optimized external
coolant circuits; electric water and oil pumps; electronic thermostats and valves; improved
radiators and fans; variable-speed fan drives; improved heat-transfer fluids; operation at higher
coolant temperatures; and electrically driven air-conditioning compressors. All have varying
influences across the ranges of vehicle speeds, engine speeds, and engine loads. As a
consequence, we must be able to evaluate the benefits of design changes on vehicle fuel economy
and emissions over the entire vehicle speed and load range; this requires a validated drive-cycle