Abstract:
A locomotive engine having an engine cooling system, a compressor for compressing engine intake air, and an aftercooler for cooling the compressed intake air prior to introduction into an intake manifold of the engine. The locomotive also has a dynamic brake system that includes a dynamic brake grid and one or more cooling fans. The engine cooling system includes an engine cooling circuit having coolant passages internally disposed in the engine, and a radiator and radiator fans configured to receive coolant exiting the engine and return cooled coolant to the engine. An enhanced aftercooler cooling circuit is disposed in fluid communication with the engine cooling circuit and includes a heat exchanger arranged to receive coolant exiting the engine coolant passages, cool the coolant passing therethrough, and return cooled coolant to the aftercooler. The heat exchanger is advantageously positioned in a manner whereby the dynamic brake grid cooling fan is operatively associated with both the dynamic brake grid and the heat exchanger.

Description:
This application claims the benefit of Ser. No. 60/551,258, filed Mar. 08, 2004. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates generally to a cooling system and method for cooling a locomotive engine, and more particularly to such a cooling system for a locomotive engine having an aftercooler incorporated therewith. 
     2. Background Art 
     On Apr. 16, 1998, the Environmental Protection Agency (EPA) enacted emissions standards for newly manufactured and re-manufactured locomotive engines. Ultimately, all locomotives manufactured on or after 1973 will be required to meet the enacted emissions standards at the time of manufacture or re-manufacture. Exceptions are made to the following locomotives: electric locomotives; historic/steam powered locomotives; locomotives originally manufactured before 1973; and locomotives owned and operated by small railroads. 
     Three different sets of emissions standards have been adopted, with applicability of the standards dependent on the date a locomotive was first manufactured, as identified in Table 1 below. Locomotives manufactured after 1973 and not identified in the exceptions noted above, must also meet the smoke opacity limits identified in Table 2 below. Although the limits provided in Tables 1 and 2 are relatively higher than the limits provided by on-highway truck engine emission standards, it is expected that a significant reduction in NOx emissions from the status quo will result from implementation of the new standards. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Emission Standards for Locomotives, (g/bhp · hr) 
               
             
          
           
               
                   
                 HC* 
                 CO 
                 NO x   
                 PM 
               
               
                   
                   
               
             
          
           
               
                   
                 Tier 0 (1973–2001) 
                   
                   
                   
                   
               
               
                   
                 Line-haul Duty Cycle 
                 1.0 
                 5.0 
                 9.5 
                 0.60 
               
               
                   
                 Switcher Duty Cycle 
                 2.1 
                 8.0 
                 14.0 
                 0.72 
               
               
                   
                 Tier 1 (2002–2004) 
               
               
                   
                 Line-haul Duty Cycle 
                 0.55 
                 2.2 
                 7.4 
                 0.45 
               
               
                   
                 Switcher Duty Cycle 
                 1.2 
                 2.5 
                 11.0 
                 0.54 
               
               
                   
                 Tier 2 (2005 and later) 
               
               
                   
                 Line-haul Duty Cycle 
                 0.3 
                 1.5 
                 5.5 
                 0.20 
               
               
                   
                 Switcher Duty Cycle 
                 0.6 
                 2.4 
                 8.1 
                 0.24 
               
               
                   
                   
               
               
                   
                 *HC standard is in the form of THC for diesel engines 
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Smoke Standards for Locomotives, % Opacity - Normalized 
               
             
          
           
               
                   
                 Steady-state 
                 30-sec peak 
                 3-sec peak 
               
               
                   
                   
               
             
          
           
               
                   
                 Tier 0 
                 30 
                 40 
                 50 
               
               
                   
                 Tier 1 
                 25 
                 40 
                 50 
               
               
                   
                 Tier 2 
                 20 
                 40 
                 50 
               
               
                   
                   
               
             
          
         
       
     
     An important technology employed to reduce NOx emissions on turbocharged engines, such as large Diesel engines used to drive a generator on Diesel-electric locomotives, is an aftercooler. An aftercooler is a heat exchanger, typically water-to-air, that is positioned between a compressed air discharge port of the compressor stage of a turbocharger and an intake manifold of the engine, and functions to reduce the temperature of the compressed intake, or boost, air discharged from the compressor section of the turbocharger. As a result of cooling the compressed intake air in the aftercooler prior to introduction into the intake manifold of the engine, the temperature of combustion, and consequently NOx formation, are advantageously reduced. 
     Heretofore, all turbocharged Diesel-electric locomotives are at least jacket-water aftercooled, and their radiators sized appropriately. Therefore, the same water that passes through the engine and the engine radiator also passes through the coolant passages of the aftercooler, resulting in the need for increased radiator and cooling fan size to dissipate the additional heat load attributed to the aftercooler. 
     U.S. Patent Application Publication No. 2002/0174653 published Nov. 28, 2002, for a LOCOMOTIVE ENGINE COOLING SYSTEM AND METHOD by Teoman Uzkan describes a separate circuit aftercooling system, which will provide lower charge air temperatures than provided by jacket-water cooled systems. However, the system proposed by Uzkan requires increased cooling capacity to cool the separate aftercooler cooling circuit. Such an arrangement could be integrated into new locomotives, but is impractical to retrofit into existing locomotives. Existing locomotive cooling systems have insufficient cooling capability to dissipate the increased heat load imposed by an additional aftercooler. 
     Another cooling arrangement, also found in newer Diesel locomotive engine designs, uses a dedicated aftercooler cooling system radiator separated from the engine cooling system radiator. In this arrangement, the aftercooler cooling circuit operates independently of the cooling circuit for the engine and uses a separate coolant, i.e., the aftercooler cooling circuit is not fluidly connected to the engine cooling system, and requires a radiator and electrically-driven fan system devoted solely to cooling fluid circulating in only the aftercooler cooling circuit. For example, U.S. Pat. No. 6,006,731 granted Dec. 28, 1999 to Teoman Uzkan for a LOCOMOTIVE ENGINE COOLING SYSTEM describes a locomotive engine cooling system having separate engine and aftercooler coolant loops with separate radiators and electrically-driven fans exclusively assigned to each of the loops. Such an arrangement can be readily incorporated in the design of a new locomotive, but, because of space limitations imposed when attempting to retrofit such a cooling system to existing locomotives, cannot be considered for application to existing locomotives. As noted above, when locomotives manufactured from 1973 through 2001 are overhauled, they must meet the Tier 0 emission requirements. 
     The present invention is directed to overcoming the problems set forth above with respect to providing enhanced aftercooler cooling circuits for existing turbocharged locomotives. It is desirable to have an aftercooler cooling circuit that does not require modification of an existing engine coolant radiator or enlargement of the cooling fan for the engine coolant radiator. It is also desirable to have an enhanced aftercooler cooling circuit that can be readily installed in the very limited space available in the car body of existing locomotives. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, an engine cooling system for a locomotive having an engine equipped with a compressor for compressing engine intake air, an aftercooler, and a dynamic braking system includes an engine cooling circuit and an aftercooler cooling circuit. The engine cooling circuit includes coolant passages in the engine and a radiator arranged to receive, cool and return coolant to the engine. The aftercooler cooling circuit has a coolant-to-air heat exchanger positioned in fluid-thermal communication with a dynamic brake grid cooling fan so that the brake grid cooling fan is operatively associated with both the dynamic brake grid and the aftercooler cooling circuit. The aftercooler cooling circuit also includes a heat exchanger inlet conduit providing fluid communication between the engine and the heat exchanger, a heat exchanger outlet conduit providing fluid communication between the heat exchanger and the aftercooler, and an aftercooler fluid conduit configured to pass coolant existing the aftercooler to the engine cooling circuit. 
     In another aspect of the present invention, a Diesel-electric locomotive includes a Diesel engine having a turbocharger, an aftercooler and a cooling system for cooling the engine and the aftercooler, and a dynamic brake system. The cooling system includes an engine cooling circuit and an aftercooler cooling circuit disposed in fluid communication with the engine cooling circuit, and has a coolant-to-air heat exchanger positioned upstream of the aftercooler in fluid-thermal communication with a dynamic brake grid cooling fan operatively associated with both the dynamic brake grid and the heat exchanger. 
     In still another aspect of the present invention, a method for cooling an engine of a locomotive having an engine and a dynamic brake system includes positioning a heat exchanger in fluid-thermal communication with a cooling fan of the dynamic brake system and providing an engine cooling circuit having a radiator. Coolant water is passed from the radiator into the inlet of the heat exchanger, then passed through the heat exchanger while the cooling fan of the dynamic brake system is operating and ambient air is drawn through the heat exchanger, thereby cooling the passing coolant water. The cooled coolant water is then passed from the heat exchanger into the aftercooler, then through the aftercooler into the engine cooling circuit and subsequently through the radiator of the engine cooling circuit. 
     In yet another aspect of the present invention, a method for retrofitting an existing locomotive to provide an enhanced aftercooler cooling circuit, in which the locomotive has an engine, an engine cooling system, a turbocharger, an aftercooler in fluid communication with the engine cooling circuit, and a dynamic brake system having a dynamic brake grid and at least one cooling fan, includes positioning a heat exchanger in fluid-thermal communication with the dynamic brake grid cooling fans in such a manner that the cooling fans draw ambient air past the dynamic brake grid and the heat exchanger. The method of retrofitting an existing locomotive also includes connecting an outlet of the engine coolant passages to an inlet of the heat exchanger and connecting an outlet of the heat exchanger to the aftercooler in such a manner as to pass cooled coolant water from the heat exchanger through the aftercooler and into the engine cooling system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the locomotive engine cooling system and method for cooling the engine, in accordance with the present invention, may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a simplified schematic of a prior art Diesel locomotive and cooling system; 
         FIG. 2 . is a simplified schematic of a retrofitted locomotive and cooling system in accordance with the present invention; 
         FIG. 3  is a side view of a portion of a locomotive retrofitted in accordance with the present invention; and 
         FIG. 4  is a partial sectional view of the locomotive illustrated in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a typical arrangement of certain components of a prior art locomotive having a Diesel engine  110  and a cooling system. In one aspect of the present invention, a method for retrofitting a Diesel locomotive, such as that represented in  FIG. 1 , to provide a cooling system having an improved aftercooler cooling circuit is illustrated in  FIGS. 2–4 . As described below in detail, the locomotive engine cooling system and method for cooling the engine in accordance with the present invention are particularly suited for use in retrofitting an existing locomotive engine. More particularly, the present invention is suited for retrofitting a Diesel-electric locomotive, such as GM EMD 40, 50, 60, and 70 Series locomotives manufactured by General Motors Corporation. The present invention is also applicable to other diesel-electric powered prime movers, such as large mining trucks, that have dynamic braking systems similar to those used on locomotives. 
     Although specifically directed retrofitting existing Diesel-electric locomotive engines, various aspects of the present invention are also applicable to other internal combustion engines and commercially manufactured locomotives and prime movers. Also, the present invention is equally applicable to new locomotives and locomotive engines. 
     In  FIG. 1 , a Diesel-electric locomotive representative of the prior art has a Diesel engine  110  equipped with a turbocharger  112 , or other intake air compression means, and a pair of aftercoolers  114 , both operatively associated with the engine  110 . The engine  110  includes an engine cooling system for circulating coolant water through each of two banks (left and right) of the engine  110  during engine operation.  FIG. 1  illustrates only one side of or bank of engine  110  and thus, shows only one bank or side of the engine cooling system. The engine cooling system employs one or more radiators  116 , each having an electrically-driven cooling fan  118  positioned in fluid communication with a centrifugal pump  120  that directs the coolant water through the engine  110  and subsequently circulated back to the radiator  116 . More specifically, hot water exits the engine  110  at a first engine coolant outlet port  150  and passes into the radiator  116  by way of a fluid conduit  152   a . Cooled water is drawn from the radiator  116 , by operation of the pump  120  and associated fluid conduits into a first engine coolant inlet port  122  of the engine  110 . The engine  110  is equipped with coolant passages  124   a ,  124   b , through which the water circulates and by which heat is transferred from the engine  110  into the circulating coolant water. 
     A second engine coolant outlet port  126  and a fluid conduit  156  fluidly connect the coolant passages  124   a  of the engine  110  with the coolant passages of the aftercooler  114 . The aftercooler  114  circulates the water to convectively communicate with hot compressed air discharged from the compressor stage of a turbocharger  112  before returning the coolant water to the cooling system of the engine  110  by way of a fluid conduit  130  and a second engine coolant inlet port  128 . From the engine coolant passages  124   b , the hot coolant water is then recirculated through the radiator  116 . 
     In a typical engine cooling system, a low point in the system is equipped with a water dump valve  158 , as shown in  FIG. 1 . The dump valve  158  is preferably temperature controlled to activate draining of the cooling system when the water temperature falls below a preselected temperature. For example, the dump valve  158  may be set to activate, i.e., open, when the water temperature falls below 40° F. to prevent freeze damage when the engine is not running. 
     The turbocharger  112  has a compressor stage that compresses intake air prior to introduction into the intake manifold of the engine  110 . The turbocharger  112  includes an ambient air intake port  112   a , a compressed intake air conduit  112   b  that passes the compressed intake air into the aftercooler  114 , and a cooled compressed intake compressed air conduit  112   c . More specifically, the aftercooler  114  cools the compressed intake air received from the turbocharger  112  and then passes the cooled compressed intake air into the intake manifold of the engine  110  through the cooled compressed air conduit  112   c . Typically, depending on the ambient air temperature and the amount of compression, the compressed intake air temperatures may be as high as about 350° F. (at rated power) when discharged from the compressor stage of the turbocharger  112 . The coolant water temperature entering the aftercooler  114  is generally maintained at a temperature of about 175° F. Through operation of the aftercooler  114 , the compressed intake air temperature may be reduced to about 190° F. (at rated power) before entering the intake manifold of the engine  110 . The reduction in temperature of the intake air also provides a reduction of the temperature in the cylinders and a further reduction in NO x  emissions. 
     The engine  110  also includes an exhaust conduit  112   d  that communicates exhaust gases discharged from the engine  110  into the turbocharger  112 , and the turbocharger has an exhaust discharge outlet  112   e.    
     In addition to the engine  110 , the locomotive has a dynamic brake electrical load dissipation system  140  that includes a dynamic brake grid  142  and one or more electrically-driven cooling fans  144 . The dynamic brake system  140  supplements operation of the locomotive air brake system. Briefly, during dynamic braking, the traction motors, not shown, of the locomotive are driven by the locomotive wheels and function as generators, thereby converting kinetic energy of the moving locomotive into electrical energy. The resulting electrical power is routed to the dynamic brake system  140  where it is dissipated as heat energy through electrically resistant grids in the dynamic brake grid  142 . The cooling fans, or blowers,  144  force cooler ambient air over the dynamic brake grid  142  thereby effecting convective heat transfer. The heated air is then exhausted through the roof of the locomotive. Typically the dynamic brake system is positioned in the car body above, or near, the engine  110 . 
       FIG. 2  illustrates a cooling system for the locomotive engine  110  in accordance with the present invention. As discussed below, the cooling system embodying the present invention may be referred to as having two cooling circuits: an engine cooling circuit similar to that provided by the system in  FIG. 1 , and an aftercooler cooling circuit. For purposes of the present description, the engine cooling circuit includes, among other components, the engine radiator  116 , the water pump  120 , the dump valve  158 , the engine coolant passages  124   a ,  124   b , and associated piping. In the illustrative preferred embodiment of the present invention, the cooling apparatus embodying the present invention is provided as a retrofit modification of the existing Diesel locomotive engine  110  illustrated in  FIG. 1 . 
     As used herein, the term “retrofit” refers to a new installation of an enhanced aftercooler cooling circuit on an existing engine cooling system as illustrated in  FIG. 1 . In  FIG. 2 , the retrofit installation on the engine  110  is indicated by solid lines, whereas the existing or original installation is indicated by dash lines. 
     Referring to  FIG. 2 , the aftercooler cooling circuit of the cooling system embodying the present invention includes an added, dedicated heat exchanger  210  that cools engine-heated coolant water before circulation through the aftercooler  114 . The aftercooler cooling circuit preferably includes a heat exchanger supply conduit  212  extending from the existing engine outlet  126  to an inlet port  210   a  of the heat exchanger  210 . The aftercooler cooling circuit embodying the present invention further includes a heat exchanger discharge conduit  214  extending from an outlet port  210   b  of the heat exchanger  210  to the aftercooler  114 . Thus, the aftercooler cooling circuit redirects coolant water from the engine  110 , typically having a temperature of about 170° to 175° F., into the air-water heat exchanger  210  for additional cooling, rather than directly to the aftercooler  214 . 
     In the preferred embodiment of the present invention, the engine cooling system uses the existing cooling fans  144  of the dynamic brake system  140  to operate in conjunction with the heat exchanger  210 . The coolant fans  144  draw ambient air through the heat exchanger  210 , thereby reducing the coolant temperature from about 175° F. to a temperature typically in the neighborhood of about 20° F. above ambient temperature. Preferably, the coolant water temperature is reduced to a temperature between about 90° F. and 125° F., prior to introduction into the aftercooler  14 . 
     An important feature of the present invention is that no additional cooling fans are required. When dynamic brake grid cooling is required during braking there is no requirement for enhanced charge air cooling by the aftercooler. Moreover, when enhanced charge air cooling is required there is no demand for dynamic brake grid cooling. Thus, the requirement for dynamic brake grid cooling and the requirement for enhanced charge air cooling are mutually exclusive and, accordingly, the existing dynamic brake grid cooling fans can advantageously be used when not needed for brake grid cooling to cool water passing through the aftercooler cooling circuit 
     The cooled coolant water passing through the aftercooler  114 , advantageously reduces the temperature of the compressed intake air entering the intake manifold to a temperature of, for example, about 150° F., as opposed to a low temperature of about 190° F. with the prior art. The cooler compressed intake air reduces the temperature inside the engine cylinders, including the peak temperature. As a result, the amount of NO x  generated during the combustion process is reduced. 
     As illustrated in  FIG. 2 , the retrofit cooling system embodying the present invention uses the existing engine cooling circuit as well as the new retrofit components of the aftercooler cooling circuit. The retrofit aftercooler cooling circuit uses the same coolant water as that circulated through the engine  110 . Moreover, the cooling system embodying the present invention uses the existing engine-driven pump  120  to direct coolant water through the engine  110 , the added heat exchanger  210 , the aftercooler  114 , and the engine radiator  116 . Typically, the engine-driven water pump  120  is sufficiently sized to handle fluid flow through the additional components and piping of the retrofit cooling system embodying the present invention. The piping configuration required by the retrofit installation is relatively small because, in existing locomotives, the dynamic brake system  140  is typically located in the car body above, or near, the existing engine and aftercooler  14 . Thus, the length of the fluid conduits  212 ,  214 , between the engine area and the added heat exchanger  210  is relatively short and, therefore, the pressure differential across the aftercooler cooling circuit is minimized. 
     Existing locomotive engine designs preclude the use of coolant other than water. Preventive means are, therefore, implemented to guard against freezing within the engine cooling system. Another advantage provided by the cooling system embodying the present invention is that it provides means for eliminating and/or otherwise reducing the possibility of the coolant water freezing in the aftercooler cooling circuit. First, the engine driven water pump  120  continuously provides coolant water flow in the aftercooler cooling circuit as well as the engine cooling circuit when the engine is running. Secondly, the coolant water that is pumped into the aftercooler cooling circuit comes from the engine  110 , and thus it is at or near engine temperature, which is always well above the freezing temperature of water. This is true even when the engine  110  is operating at light load or is idling. Thirdly, the aftercooler cooling circuit is fluidly connected to the engine water dump system and the water dump valve  158 . As discussed above, the dump valve  158  is designed to drain all of the engine&#39;s cooling water in the event that the water temperature drops below, for example, 40° F. Draining of the fluid conduits  212 ,  214  and the heat exchanger  210  is further facilitated because these components are positioned at or above the low point of the engine  110  and well above the dump valve  158 . Integration of the engine water dump system into the cooling apparatus therefore alleviates freeze protection concerns when the engine is not operating. 
     Another important aspect of the cooling system embodying the present invention is that the aftercooler cooling circuit, particularly the aftercooler fans  144 , do not add significant parasitic load on the engine  110  or the locomotive. Operation of the separate circuit aftercooler cooling circuit actually reduces the load on the existing cooling system and the engine&#39;s oil cooling system because the aftercooler cooling circuit provides for cooler compressed intake air introduced into the engine  110 . The cooler compressed intake air results in a reduction of heat generated in the engine, thereby resulting in a reduction in the heat dissipation requirements imposed on engine cooling circuit and engine lubricating oil. As a result, the existing radiator fans  118  for the existing engine cooling circuit will do less work. 
       FIG. 3  is a simplified illustration of an engine compartment  310  of the locomotive driven by the Diesel engine  110 . The engine compartment  310  has a front end  312 , a back end  314 , all-around walls (not shown), and a roof  316 . To facilitate the description of the present invention, only certain components of the engine  110  and the engine compartment  310  are shown. The retrofit installation of the aftercooler cooling circuit supply and return conduits  212 ,  214  in accordance with the present invention is indicated by dash lines in  FIG. 3  to distinguish the retrofit installation from the existing, or original, installation. 
     In typical locomotive designs, the turbocharger  112  and the aftercooler  114  are situated toward the front end  312  of the engine compartment  310 . Also, the dynamic brake grid  142  and the cooling fans  144  are typically positioned directly and conveniently above the engine  110 . The dynamic brake cooling fans  144  are supported within a shroud  318  on the roof  316 . As illustrated in  FIG. 3 , the existing engine coolant outlet port  126  and the fluid conduit  156  fluidly connects the coolant passages in the engine  110  with the aftercooler  214 . In the retrofit installation embodying the present invention, the original fluid conduit  156  is replaced by the heat exchanger supply conduit  212  which extends upwardly from the engine coolant outlet port  126  to the heat exchanger  210  positioned above the engine  110 , and the heat exchanger discharge, or coolant return, conduit  214 . The heat exchanger discharge conduit  214  extends downwardly from the heat exchanger  210  to the aftercooler  114 . Because the cooling fans  144  are located only a short distance from the engine coolant outlet port  126  and the aftercooler  114 , the fluid conduits  212 ,  214  are relatively short in length. 
     As mentioned above with respect to  FIGS. 1 and 2 ,  FIG. 3  also shows only a portion of the cooling system embodying the present invention. A second cooling circuit is provided on the opposite side of the engine, not shown, and includes a second aftercooler, a second heat exchanger, and connecting supply and return conduits. 
     In accordance with the present invention, the cross-sectional view shown in  FIG. 4  illustrates components of both aftercooler cooling circuits. Specifically,  FIG. 4  shows both heat exchangers  210 ,  210 ′, heat exchanger supply conduits  212 ,  212 ′, and heat exchanger return conduits  214 ,  214 ′ respectively positioned on left and right sides of the engine  210 . 
     Typically, the engine compartment  310  has upwardly extending walls  428  that meet with the roof  316  to enclose the engine  110 . Each wall  428  has a modified intake hatch with louvered covers  430 ,  430 ′ designed for the intake of ambient air  434  during operation of the dynamic brake grid cooling fans  144 . On existing installations, the wall  428  has louvered hatch covers that are situated inwardly from the position of the modified louvered hatch covers  430 ,  430 ′ and, therefore, do not extend outwardly as indicated by the modified louvered hatch covers. The existing, or original, louvered hatch covers are typically positioned where heat exchanger supports  432  are indicated. Thus, the modified louvered hatch covers  430 ,  430 ′ create an expanded areas in which the heat exchangers  210 ,  210 ′ may be conveniently mounted for optimum heat transfer between the heat exchangers  210 ,  210 ′ and the flow of ambient air  434 . 
     As illustrated in  FIG. 4 , the heat exchangers  210 ,  210 ′ are mounted in a vertical position between respective louvered hatch covers  430 ,  430 ′ and dynamic brake grids  142 ,  142 ′. Moreover, inclined duct walls  420 ,  420 ′ respectively direct the airflow  434  through the dynamic brake grids  142 ,  142 ′ and the heat exchangers  210 ,  210 ′. The duct wall  420 ,  420 ′ also deflect the hot air flow  436  through the fan  144  and the shroud  318 , and then outwardly into the atmosphere. The inclined duct walls  420 ,  420 ′ define, in cooperation with the louvered hatch covers  430 ,  430 ′, respective airflow paths for ambient air through the heat exchangers  210 . 210 ′ and associated dynamic brake grids  142 .  142 ′. 
     Operation of the existing dynamic brake grid cooling fans  144  is provided by an existing DC powered motor  444  centrally supported between the inclined walls  420 ,  420 ′ at a position directly above the engine  210 . It will be apparent to one skilled in the art that suitable controls may be implemented for operation of the motor  444  so as to control the speed of the cooling fans  144 , as required by load demands on the separate circuit aftercooler heat exchangers  142 ,  142 ′. For example, at relatively low ambient temperatures, the heat transfer required between the coolant water and the aftercooler  114  may not be as great as it would be at higher ambient temperatures. In such conditions, one or more cooling fans  144  may be shut down, or one or more fans  144  may be operated at less than full or normal speed, to provide a predetermined desirable intake manifold air temperature. 
     Various embodiments of the present invention have been described herein. It should be understood by those of ordinary skill in the relevant mechanical art that the above-described embodiments, such as the cooling system specifically designed for a Diesel locomotive engine, are set forth merely by way of example and should not be interpreted as limiting the scope of the invention, which is defined by the appended claims. For purposes of this invention, the term “locomotive” as used herein includes all vehicles, such as large mining trucks, that have similar dynamic braking systems. Other alternative embodiments, variations and modifications of the foregoing embodiments that embrace various aspects of the invention will be understood upon a reading of the detailed description, in light of the prior art. For example, it will be understood that application of the various aspects of the cooling system may be applied to different types of engines, or other types of Diesel locomotive engines with or without the turbocharger, for example, using other compressor means and the aftercooler system described herein. The various types of configurations described here may be combined with features or other embodiments or many other features may be omitted or replaced.