Locomotive engine heat, left uncontrolled, can damage engine parts and shorten the life of the engine and its attached components. An effective radiator system keeps the engine and components at the optimum operating temperature, regardless of whether the locomotive is operating in mountains or flatlands or hot or cold. A locomotive radiator system primarily cools air, water, and oil. The air is used in the combustion process; the water for cooling the engine and turbo (if equipped); and oil for lubricating the engine components.
The radiator system is intended to keep the engine operating at nearly the same temperature, regardless of the ambient air outside the locomotive. This allows maximum horsepower to be available at all times and extends the life of the engine and its lubricants.
Electro-Motive Diesel and General Electric differ in radiator system design. EMD uses a “wet” radiator system in which fluid is cycled through the radiator system constantly while the engine is operating. GE on the other hand employs a “dry” system where fluids are routed through the radiator system only as conditions warrant. Each builder uses a system of valves to route fluids to banks of radiators to achieve the level of cooling needed at any given time. While both builders use fans on the main radiator banks to assist in cooling, EMD’s system also uses a shutter system to control the flow of air across the radiators.
Modern EMD and GE locomotives use a split cooling system with separate paths to reduce the coolant temperature to the levels required.
In split cooling on a GE locomotive, a majority of the fluid cooled in the radiator is sent back to the locomotive at one temperature while a portion of the coolant is routed through additional radiator banks called sub-coolers (or aftercoolers) for further temperature reductions. Once passed through these additional cooling banks, the fluid travels to various devices such as the air to water intercooler to assist in cooling the engine intake air. The combustion air is first drawn in and compressed in the turbocharger. Compression heats the air and must be cooled before being used for combustion. Cooler air is denser and is more oxygen-rich, making it a preferred manifold air temperature for increasing power, controlling emissions, and reducing fuel consumption. After passing though the intercooler, the intake air passes through a heat exchanger where additional cooling occurs if conditions warrant before going to the engine for combustion.
Another path from the sub-coolers is to the oil cooler, prior to the coolant returning it to the engine. Lubricating oil absorbs heat while inside the engine and needs to be cooled before returning. Subjecting lubricating oil to high heat shortens the life of the oil and would force more frequent oil changes to maintain the engine in good working order. Higher temperatures lower the viscosity (thickness) of oil, which increases the wear of internal components.
EMD utilizes a slightly different layout, with two separate loops from the engine, one for the radiator and oil cooler and another for the aftercooler. Various connections between the two loops allow the onboard computer to utilize excess cooling capacity in the aftercooler loop if needed.
The vast majority of locomotives on the road today utilize simple tap water for coolant in their radiator systems. Water is much more efficient at transferring heat than a mix of water and antifreeze that’s typically found in your car’s radiator system. Benefits of using water allow the overall size of the radiator system to be smaller due to its higher efficiency, the lower cost of water compared to antifreeze/water mixture, and water’s ubiquity. Any garden or water hose that can reach a locomotive can add fluid to the radiator system in a pinch. There are also environmental concerns with using antifreeze since the water system needs to be drained occasionally for maintenance. To keep the radiator system in top shape, a corrosion inhibitor is added to the water. This additive protects the system from developing rust, corrosion, and scaling.
With Tier 4 emissions regulations in effect as of Jan. 1, 2015, the radiator systems for both builders will change again. Further cooling will be necessary to achieve the new environmental standards. Trains will cover those changes after more Tier 4 locomotives are on the road.
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