Patent Application
20080121136
The invention relates generally to locomotives and, more particularly, a locomotive using natural or similar gases as their main engine fuel.
Conventional stand-alone locomotives have output power ranging from approximately 300 horsepower (for example, locomotives used in mining and tunneling) to 6000 horsepower (for example, locomotives for long haul cross-country freight trains). In many locomotive applications, especially ones in which there are significant grades along a route, a plurality of conventional stand-alone locomotives may be used to haul a large train composed of from a few to over one hundred cars. Conventional propulsion systems include fully-electric locomotives typically fed from an overhead line or diesel-hydraulic locomotives where the mechanical power generated by a diesel engine is adapted to the driven variable axle speed by means of a hydraulic transmission, gearing and other mechanical arrangements.
Certain other conventional railroad locomotives are typically powered by mixed or hybrid systems, such as a diesel-electric system. Such conventional locomotives may be used to capture and store energy that is otherwise wasted by incorporating an energy storage system (for example, battery pack, capacitor bank, flywheel assemblies, fuel cells, or a combination thereof). As a result, locomotive energy source is “hybrid” in nature. The energy storage system may be charged by an on-board engine, or another conventional hybrid or stand-alone locomotive, a regenerative braking system, or an external power source. The stored energy may be used to power the traction motors of the locomotive, auxiliary loads, or other cars of the train. Auxiliary loads may be referred to as for example, alternator blower, power electronics blower, traction motor blowers, compressed air unit, radiator fans, and other cooling equipment as well as smaller loads for lightning, battery back up, electronics control or the like.
However, there are drawbacks associated with the usage of oil-derived products such as diesel as a fuel for hybrid locomotives. For example, burning of diesel is associated with high levels of exhaust emissions, such as sulphur, particulates, nitrogen oxides, or the like, leading to environmental contamination. Additional equipment such as particulate filters may be required for after treatment of the exhaust gases to reduce environmental contamination. Moreover, because oil derivatives have greater densities than certain other fuels, locomotives transporting such fuels become heavier. Moreover, conventional hybrid locomotives are not adaptable to different load cycles and customer scenarios, such as freight switchers, passenger transport, or the like.
Accordingly, there is a need for a system that reduces emissions associated with combustion in hybrid locomotives. Also, there is a need for a system that reduces weight of the hybrid locomotive and is adaptable to different load cycles and customer scenarios.
In accordance with one exemplary embodiment of the present invention, a hybrid locomotive includes at least one traction motor coupled to at least one of a plurality of axles and configured to drive at least one axle. An electrical power converter is coupled to an alternator which is coupled to a main engine and to the at least one traction motor and configured to supply electrical energy to the at least one traction motor. A fuel storage unit is coupled to the main engine and configured to supply a gaseous fuel to the main engine.
In accordance with another exemplary embodiment of the present invention, a hybrid locomotive includes at least one traction motor coupled to at least one of a plurality of axles and configured to drive at least one axle. A power converter is coupled to an alternator which is coupled to a lean-mixture internal combustion engine and to the at least one traction motor and configured to supply electrical energy to the at least one traction motor. A fuel storage unit is coupled to the lean-mixture internal combustion engine and configured to supply a gaseous fuel to the lean-mixture internal combustion engine.
In accordance with another exemplary embodiment of the present invention, a method for operating a hybrid locomotive includes supplying a gaseous fuel to a main engine. The main engine is operated to supply electrical energy via an alternator and a power converter to at least one traction motor. The at least one traction motor is operated to drive at least one of a plurality of axles.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As discussed in detail below, embodiments of the present invention provide a hybrid locomotive including at least one traction motor coupled to at least one of a plurality of axles and configured to drive at least one axle. A power converter is coupled to a alternator of a main engine (e.g. a lean-mixture internal combustion engine) and to the at least one traction motor and configured to supply electrical energy to the at least one traction motor. A fuel storage unit is coupled to the main engine and configured to supply a gaseous fuel mixture to the main engine. In certain exemplary embodiments, fuel may be stored in the form of compressed gas, or liquefied gas, or adsorbed gas, or gas generated as a result of a previous chemical, or electrical, or mechanical, or thermal conversion. At least one secondary energy storage unit is configured to store and supply energy (after suitable adaptation) to the at least one traction motor, or auxiliary loads. The locomotive in accordance with the exemplary embodiments of the present invention is adaptable to different load cycles and customer scenarios, e.g. freight switchers, passengers trains, or the like. Properly operated gas engines may meet these objectives but cannot alone be used in standard locomotive regime (involving several full load swings per hour) without redesign inevitably including higher volume and weights. The system in accordance with the exemplary embodiments of the present invention, overcomes these problems in the hybrid version at the system level with little or no redesign of the internal combustion engine. The narrow positive operating range of the internal combustion engine (where high efficiency and low emissions are achieved) is extended by decoupling from the internal combustion engine the inconveniencies that variable speed and variable load represent. The secondary energy storage unit is used to account for the limitations of the main engine and secondary engines, to boost tractive effort and not merely as a means for storing braking energy. In certain embodiments, the secondary energy storage unit may be recharged during night, or during periodic maintenance conditions, or during low load conditions. Gas burning is also associated with reduced emissions, such as of particulates, nitrogen oxides, carbon dioxide, sulphur, or the like. In certain embodiments, the electric power from the secondary energy storage unit may be used for tractive effort inside stations, switch yards, in cities, or the like for controlling exhaust emissions and to reduce noise. Specific embodiments of the present invention are discussed below referring generally to
Referring to
In the illustrated embodiment, a fuel storage unit 26 is coupled to the main engine 16 and configured to supply a gaseous fuel to the main engine 16. The gaseous fuel may include natural gas (compressed or liquefied), biogas, hydrogen, propane, or a combination thereof stored in gaseous, or liquid, or solid form. The fuel storage unit 26 may include an on-board locomotive fuel storage unit, or a separate energy tender vehicle for fuel storage. It is known that diesel fuel burning is associated with relatively higher levels of emissions requiring extensive after treatment of exhaust gases. In accordance with the exemplary embodiments of the present invention, burning of gaseous fuel (e.g. through the use of a lean mixture) results in reduced exhaust emissions.
Referring to
As discussed earlier, the fuel storage unit 26 is coupled to the main engine 16 and configured to supply a gaseous fuel mixture to the main engine 16. In one exemplary embodiment, the gaseous fuel may include liquid natural gas maintained at about −160 degrees Celsius. In another exemplary embodiment, the gaseous fuel includes a compressed natural gas maintained at ambient temperature and pressure range between 20 to 300 bars. In yet another exemplary embodiment, the gaseous fuel includes a liquefied petroleum gas such as butane or propane, and in particular embodiments the liquid petroleum gas is maintained at pressure of approximately 10 bars. In certain exemplary embodiments, the fuel storage unit 26 provided on board the locomotive is periodically refueled from fuel sources located on side of rail track. In certain other exemplary embodiments, the fuel storage unit is replaced in bulk, possibly with the help of truck lifters where the operator needs to connect the fuel storage unit to a gas pipeline system via a connection valve.
In certain exemplary embodiments, the main engine 16 is operated at variable speed and variable power load conditions. In certain other exemplary embodiments, the main engine 16 is operated at rated speed and rated power load conditions. The supply of electrical energy from the main engine 16 and the secondary energy storage unit 28 is varied depending on the load cycle. In one exemplary embodiment, for long distance applications, when the locomotive 10 is traveling at a speed less than or equal to a predetermined speed, electric power is fully supplied from the secondary energy storage unit 28 to the traction motors 20 to drive the wheels 12. The main engine 16 is shut off or in idling mode. When the locomotive is traveling at a speed greater than a predetermined speed, or, alternatively when the locomotive has reached a location along the way where emissions are of less concern (e.g. in the outskirts of a city, far away from urban train stations, or the like.), the electric power is fully supplied from the main engine 16 to the traction motors 20. Secondary storage recharging may occur during dynamic braking events or in advance if a path planner is available. In another exemplary embodiment, the main engine 16 supplies rated power (at rated speed) from the starting conditions of the locomotive, and the excess power (engine power minus traction power or auxiliary load power) from the main engine 16 may be used to recharge the secondary energy storage unit 28 during acceleration and deceleration conditions. The secondary energy storage unit 28 may be slowly charged during normal cruising conditions and may be charged faster during dynamic braking events. The secondary energy storage unit 28 may be fully recharged during dynamic braking conditions of the hybrid locomotive 10.
In certain other exemplary embodiments, the electric power from the secondary energy storage unit 28 is used to boost the tractive effort during starting conditions, high uphill gradients, and also heavy-haul conditions. In certain exemplary embodiments, for heavy-duty cycle applications such as in switchers, the main engine 16 is operated at full power conditions to drive traction motors 20 and recharge the secondary energy storage unit 28 continuously. The hybrid locomotive 10 in accordance with the embodiments of the present invention is adaptable to different load cycles and customer scenarios such as freight switchers, passenger trains, and heavy-haul applications.
Referring to
In the illustrated embodiment, the locomotive 10 includes a speed sensor 36 configured to detect speed of the main engine 16 and a power sensor 38 configured to detect power load of the main engine 16. A control unit 40 is configured to control speed and power load of the main engine 16 based on the output of the sensors 36, 38. The control unit 40 may also be used to control the power supply from the main engine 16 and the secondary energy storage unit 28 depending on the detected speed and power load. The control unit 40 may include a processor having hardware circuitry and/or software that facilitates the processing of signals from the sensors 36, 38. As will be appreciated by those skilled in the art, the processor may include a microprocessor, a programmable logic controller, a logic module or the like.
It should be noted herein that even though two sensors 36, 38 are illustrated, in certain other exemplary embodiments, the locomotive 10 may include a plurality of other sensors. For example, the locomotive 10 may include a variety of sensors to aid manage the power management in the system. The variety of sensors may include a locomotive track speed sensor employing velocity estimation from GPS position sensing and from averaging the traction motors or wheels speeds, one or gas flow sensors configured to detect the flow of gaseous fuel, a gas pressure gauge configured to detect pressure of gaseous fuel, a plurality of voltage sensors configured to detect DC-link voltage, secondary unit storage voltage, one or more current sensors configured to detect current through the alternator 22, the motors 20, and the secondary storage unit 28, one or more temperature sensors configured to detect temperature at the gas supply line, the main engine 16, the alternator 22, the power converter 24, the interface 30 to secondary storage unit, the secondary storage unit 28, and the motors 20. A state of charge estimator configured to detect the state of charge in the secondary storage unit 28 may also be employed.
In certain embodiments, the control unit 40 further includes a database, and an algorithm implemented as a computer program executed by the control unit computer or the processor. The database may be configured to store predefined information about the type of locomotive, speed and power conditions, type of gaseous fuel, type of engine, or the like. The database may also include instruction sets, maps, lookup tables, variables or the like. Such maps, lookup tables, and instruction sets, are operative to correlate characteristics of locomotive with the electric power requirements. The database may also be configured to store actual sensed or detected information pertaining to the speed and power load conditions. The algorithm may facilitate the processing of sensed information pertaining to the speed and power load conditions. Any of the above mentioned parameters may be selectively and/or dynamically adapted or altered relative to time. In one example, the control unit 42 is configured to update the above-mentioned predetermined speed threshold limit based on the load cycle and the customer scenarios. In another example, the control unit 42 is configured to update the proportioning of power from the main engine 16 and the secondary energy storage unit 28 based on the load cycle and the customer scenarios. Similarly any number of examples in which the parameters are altered are envisaged.
Referring to
In the illustrated embodiment, the locomotive includes a secondary engine 42 configured to drive a secondary power conversion unit 44. It should be noted herein that even though one secondary engine is illustrated, in certain other exemplary embodiments, more than one secondary engine may also be used. The secondary engine 42 may be of a different type than the main engine 16. A separate gas supply line may be provided for the secondary engine 42. The secondary power conversion unit 44 is configured to convert the mechanical energy provided by the secondary engine 42 into a form acceptable to one or more traction motors. The secondary power conversion unit 44 includes an alternator 46 and a power converter 48 (e.g. includes rectifier) configured to supply direct current or alternating current (depending on the requirement) to the traction motors and possibly “auxiliary loads”. The engines 16, 42 are adapted to generate power to meet the traction and auxiliary power demands, by switching the secondary engine 42 on or off, or by operating at idle or partially load conditions, according to the requirements. The embodiment illustrated
Referring to
In the illustrated exemplary embodiment, auxiliary power is ensured to the locomotive irrespective of the functioning of the main engine 16. The rating of the secondary energy storage unit 28 may be reduced (compared to the main engine rated power) to maintain auxiliary load during periods when the engine is not operated. For freight and long haul operations, the ratings of the main engine 16, secondary energy storage unit 28, and the interface 30 are increased to higher levels of power. For shunting operations, the ratings of the main engine 16, secondary energy storage unit 28, and the interface 30 are reduced to lower levels of power. As a result, the locomotive is adaptable to varying load conditions.
Referring to
Referring to
The method further includes storing electrical energy in a secondary energy storage unit as represented by the step 76. In certain exemplary embodiments, electrical energy is stored in the secondary energy storage unit during dynamic braking. The secondary energy storage unit supplies stored electrical energy to the traction motors to drive plurality of axles coupled to the wheels. The combination of the main engine and the secondary energy storage unit facilitates to address the varying traction power demands of the locomotive. The secondary energy storage is used to account for the power limitations of the main engine.
In accordance with certain exemplary embodiments of the present invention, the combination of the gas-fueled main engine and the secondary energy storage unit are configured to address the varying traction power demands. The secondary energy storage unit accounts for limitations of the main engine. In certain exemplary embodiments, where two or more engines such as two gas engines are used, the main engine may be operated in a thermodynamically “open-cycle” configuration in which gas (fed from fuel storage unit) is combusted inside the main engine and exhausted to the atmosphere, whereas the secondary engine(s) may be operated in a thermodynamically “closed-cycle” configuration in which work is generated based on a pressure gradient. In certain other embodiments, the secondary engine may be operated in a thermodynamically “open-cycle” on board the locomotive.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
