Diesel powered systems such as, but not limited to, off-road vehicles, marine diesel powered propulsion plants, stationary diesel powered system and rail vehicle systems, or trains, are usually powered by a diesel power unit. With respect to rail vehicle systems, the diesel power unit is part of at least one locomotive and the train further includes a plurality of rail cars, such as freight cars. Locomotives are complex systems with numerous subsystems, with each subsystem being interdependent on other subsystems.
Diesel fueled power units typically require cooling systems to limit the temperatures of various engine components. Internal combustion engines have internal cooling passages for the circulation of coolant to remove heat energy from the engine components. Lubricating oil which is circulated throughout the engine to reduce friction will also absorb heat and, therefore, will also require cooling to avoid reaching temperatures that would detrimentally affect its lubricity. Diesel engines often utilize turbochargers to increase power by compressing the intake combustion air to a higher density. Such compression results in the heating of the combustion air, which must then be cooled prior to its use to enable the engine to have high volumetric efficiency and low emissions of exhaust pollutants. For mobile applications such as rail locomotives, the only readily available heat sink is the surrounding ambient air. It is known to utilize a pumped cooling medium, such as water, to transport heat to finned radiator tubes. The radiator tubes then transfer the heat to the ambient air, often using forced convection provided by fans.
It is often desirable to maintain an internal combustion engine and its associated intake combustion air at multiple different temperatures in order to optimize the performance of the engine. Consequently, coolant at one temperature may be provided to the cylinder jackets of a turbocharged diesel engine and coolant at a lower temperature may be provided to an intercooler for cooling the compressed combustion air. Such a system may use a single pump, heat exchanger, and temperature control valve to accomplish the dual cooling objectives.
Other turbocharged diesel engine cooling schemes may use a subcooler in addition to a radiator. The subcooler is typically located upstream of the radiator in a flow of cooling ambient air. For locomotive applications, ambient air flowing through the radiators is normally provided by a multi-speed fan, since the radiators are positioned on the roof of the locomotive. The use of a subcooler provides a greater temperature difference capability between the temperature of the engine and the temperature of the combustion air.
Diesel engines may also use cooled fluid and/or compressed fluid cooling systems to cool lubricant fluids, such as engine lubrication oil. For example, heated engine oil coming from the engine may be passed through an oil cooler having an oil/coolant heat exchanger supplied with a coolant at a lower temperature than the oil to transfer heat from the oil to the coolant. Typically, the coolant includes water and/or a water antifreeze mixture cooled in the radiator and/or one or more associated sub-coolers. Additional oil cooling may be provided using a compressed coolant cooling scheme.
Conventional turbocharged diesel powered locomotives may use a cooling circuit that selectively uses a sub-cooler radiator section to provide sub cooled water or an antifreeze/water mixture to an oil cooler and/or the turbocharger compressor intercooler. At lower ambient temperatures and or low load conditions, the conventional locomotive cooling circuit may provide coolant to both the oil cooler and the intercooler to maintain a desired engine oil temperature and a desired emission level produced by the engine. During operation in high ambient temperatures and/or at high engine loading, it may not be possible to provide sufficient cooling capacity from the coolant in the circuit to cool the engine oil without sacrificing cooling of another cooled component, such as the intercooler. Consequently, at higher ambient temperatures and/or higher loads, coolant supplied to the intercooler may be redirected to the oil cooler to preferentially cool the engine oil at the expense of higher pollutant emission. For example, U.S. Pat. No. 7,131,403 describes one such cooling system for maintaining sufficient coolant flows to the intercooler and oil cooler for providing lower NOx emissions at ambient temperatures up to about 80° Farenheit (F.). Above 80° F. ambient, the cooling system may be configured for routing coolant flows so as to protect the engine by not exceeding oil temperature limits, but at the expense of producing higher NOx emissions.
Owners and/or operators of locomotives, off-road vehicles, marine diesel powered propulsion plants, and/or stationary diesel powered systems desire to optimize cooling of diesel fueled power generation units used in these applications over a wide range of operating conditions and ambient environments.