# Patent

## Title
Energy recovery system for a mobile machine

## Abstract

The disclosure is directed to an energy recovery system for a mobile machine. The system may have a tank configured to store a liquid fuel for combustion within a main engine located on the locomotive, and a fuel delivery circuit connecting the tank to the main engine. The system may also have an auxiliary engine, and a boil-off circuit connecting the tank to the auxiliary engine. The system may also have an accumulator fluidly connected to the boil-off circuit between the tank and the auxiliary engine and configured to store gaseous fuel formed in the tank, and a carbon adsorbent disposed within the accumulator and configured to adsorb the gaseous fuel. The auxiliary engine may be configured to selectively generate a suction force to withdraw gaseous fuel adsorbed onto the carbon adsorbent.

## Background
TECHNICAL FIELD
The present disclosure relates generally to a recovery system, and more particularly, to an energy recovery system for a mobile machine.
BACKGROUND
Natural gas has been used as an alternative fuel for internal combustion engines in mobile machines. Because natural gas has a lower volumetric energy density than traditional fuels, such as diesel and gasoline, mobile machines generally utilize liquefied natural gas (“LNG”). At atmospheric pressures, natural gas must be chilled to below about −160° C. to remain in liquid form. Mobile machines utilizing LNG as a fuel, store the LNG in insulated tanks. Because these tanks are not perfect insulators, heat enters the tanks, causing some of the LNG to boil (“boil-off”). The boil-off increases the pressure of the tanks, and can cause excessive stress to the tanks if not removed. Traditional LNG systems vent the boil-off (composed mostly of methane) directly to the atmosphere. However, because methane is a greenhouse gas, government regulations are soon expected to prohibit the direct venting of boil-off to the atmosphere.
One method of handling boil-off from an LNG tank is described in U.S. Patent Publication No. 2008/0053349 (“the '349 publication”) of O'Connor that published on Mar. 6, 2008. The '349 publication describes a marine vessel having a tank for storing LNG. The '349 publication delivers boil-off gas from the tank to a combustion section via a gas inlet. Combustion air is also directed to the combustion section and the resulting air-gas mixture is ignited. This system effectively converts the boil-off to carbon dioxide and water, which are less harmful to the environment.
Although the system of the '349 publication may be capable of preventing boil-off from directly venting to the atmosphere, it may be wasteful. Specifically, because the system of the '349 publication only combusts the boil-off, energy associated with the boil-off is lost from the system as heat and exhaust.
The energy recovery system of the present disclosure solve one or more of the problems set forth above and/or other problems with existing technologies.
SUMMARY
In one aspect, the disclosure is directed to an energy recovery system for a mobile machine. The system may include a tank configured to store a liquid fuel for combustion within a main engine located on the locomotive, and a fuel delivery circuit connecting the tank to the main engine. The system may also include an auxiliary engine, and a boil-off circuit connecting the tank to the auxiliary engine. The system may also include an accumulator fluidly connected to the boil-off circuit between the tank and the auxiliary engine and configured to store gaseous fuel formed in the tank, and a carbon adsorbent disposed within the accumulator and configured to adsorb the gaseous fuel. The auxiliary engine may be configured to selectively generate a suction force to withdraw gaseous fuel adsorbed onto the carbon adsorbent.
In another aspect, the disclosure is directed to a method of operating a mobile machine. The method may include directing liquid fuel from a tank toward a main engine, and directing gaseous fuel formed in the tank through an accumulator toward an auxiliary engine. The method may also include adsorbing gaseous fuel on a carbon adsorbent disposed in the accumulator, and withdrawing gaseous fuel adsorbed on the carbon adsorbent with a suction force generated by the auxiliary engine.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a pictorial illustration of an exemplary disclosed mobile machine;
FIG. 2 is a diagrammatic illustration of an exemplary disclosed energy recovery system that may be used in conjunction with the mobile machine of FIG. 1; and
FIG. 3 is a flowchart depicting an exemplary disclosed method of controlling the energy recovery system of FIG. 2.



DETAILED DESCRIPTION
FIG. 1 illustrates an exemplary embodiment of a mobile machine 6, such as a train consist having a locomotive 7 and a tender car 8. In some embodiments, mobile machine 6 may also include additional cars (not shown) towed by locomotive 7 and tender car 8, for example, a passenger car, a cargo container car, or another type of car. Locomotive 7 may include a body 12 supported at opposing ends by a plurality of trucks 14 (e.g., two trucks 14). Each truck 14 may be configured to engage a track 16 via a plurality of wheels 17, and support a frame 18 of body 12. Any number of engines may be mounted to frame 18 and configured to produce electricity that drives wheels 17 included within each truck 14. In the exemplary embodiment shown in FIG. 1, locomotive 7 includes a main engine 20 and an auxiliary engine 22.
Main engine 20 may be a large engine having sixteen cylinders and a rated power output of around 4,000 brake horsepower (bhp). It should be noted, however, that engines with other suitable number of cylinders or rated power outputs may alternatively be utilized. Main engine 20 may drive a traction generator (not shown) capable of outputting AC and/or DC electrical power. The electrical power may be used to generate the propulsive force of mobile machine 6 via traction motors (not shown). Main engine 20 may be an LNG engine or another type of fuel-powered engine.
Auxiliary engine 22 may have a smaller output than main engine 20, and be coupled to mechanically rotate a generator (not shown) to provide electrical power to an external load 24 (shown only in FIG. 2). For example, auxiliary engine 22 may have fewer cylinders (e.g., six to twelve) and a lower rated power output (e.g., 400-1400 bhp). It should be noted, however, that engines with other suitable number of cylinders or rated power outputs may alternatively be utilized. Similar to main engine 20, auxiliary engine 22 may be an LNG engine or another type of fuel-powered engine. External load 24 may include, for example, lights, motors, heating elements, electronic circuitry, refrigeration devices, air conditioning units, etc.
Tender car 8 may include a tank 25 configured to store a liquid fuel (e.g., LNG) for combustion within main engine 20. Tank 25 may be an insulated, single or multi-walled tank configured to store the liquid fuel at low temperatures, such as below about −160° C. Tank 25 may be mounted to a frame 26 configured to be pulled by locomotive 7. Frame 26 may be supported by a plurality of trucks 28 (e.g., two trucks 28). Similar to truck 14, each truck 28 may be configured to engage track 16 via a plurality of wheels 30.
As shown in FIG. 2, mobile machine 6 may be equipped with an energy recovery system (“system”) 200 that is configured to generate work by combusting boil-off gas formed in tank 25. System 200 may include, among other things, a fuel delivery circuit 202 and a boil-off circuit 204. Fuel flow may be regulated through fuel delivery circuit 202 and boil-off circuit 204 by a controller 210.
Fuel delivery circuit 202 may include components that cooperate to deliver liquid fuel stored in tank 25 toward main engine 20 and auxiliary engine 22. Fuel delivery circuit 202 may include, among other things, conventional pumps, conduits, heat exchangers, accumulators, and injectors (not shown) configured to condition and deliver low-temperature liquid fuel from tank 25 toward main engine 20 in gaseous form, as is known in the art. Fuel delivery circuit 202 may also include a control valve 203 that helps to regulate flow between tank 25 and engines 20 and 22.
Control valve 203 may be a proportional type valve having a valve element movable to regulate a flow of fuel. The valve element may be solenoid-operable to move between a flow-passing position and a flow-blocking position. In the flow-passing position, control valve 203 may permit a maximum rate of the fuel from delivery circuit 202 to flow toward main engine 20. In the flow-blocking position, control valve 203 may completely block fuel from flowing to main engine 20 by diverting substantially all the fuel from fuel delivery circuit 202 toward auxiliary engine 22. Control valve 203 may also include an intermediate position between the flow-passing position and the flow-blocking position. In the intermediate position, control valve 203 may permit a particular amount of the fuel to flow toward main engine 20, while diverting a remaining portion of the fuel toward auxiliary engine 22. Control valve 203 may also include an off position that blocks the flow of fuel to both main engine 20 and auxiliary engine 22.
During fuel conditioning and delivery, some fuel within tank 25 may evaporate into a gaseous fuel. Boil-off circuit 204 may include components that cooperate to process the gaseous fuel formed within tank 25. In particular, boil-off circuit 204 may include an inlet control valve 212, an accumulator 214, and an outlet control valve 216. Gaseous fuel may flow from tank 25 through inlet control valve 212 to accumulator 214. From accumulator 214, gaseous fuel may flow through outlet control valve 216 to auxiliary engine 22, where it may be mixed with inlet air and combusted.
Inlet control valve 212 may be a controllable pressure-relief valve configured to selectively allow fluid communication between tank 25 and accumulator 214. When inlet control valve 212 opens, it may allow gaseous fuel to escape tank 25 and enter accumulator 214. Inlet control valve 212 may include a spring-loaded mechanism (not shown) that opens at a predetermined pressure to avoid over-pressurization of tank 25. Additionally or alternatively, inlet control valve 212 may include one or more controllable actuators, such as one or more electric solenoids that are operable to open inlet control valve 212 based on a sensed pressure or other trigger parameter. Controller 210 may be operatively connected to the actuator(s) of inlet control valve 212, so that controller 210 may selectively trigger opening and closing of inlet control valve 212 to release gaseous fuel and pressure from tank 25.
Accumulator 214 may include an activated carbon adsorbent 215 configured to accumulate pressurized gaseous fuel and selectively release the fuel to auxiliary engine 22 via control valve 216 under particular conditions. Carbon adsorbent 215 may be physically or chemically activated, and may adsorb gaseous fuel from tank 25. Gaseous fuel may also be stored in the void spaces of carbon adsorbent 215 and in void spaces of accumulator 214 not filled with carbon adsorbent 215. Carbon adsorbent 215 may be disposed in powder or pellet form. Alternatively, carbon adsorbent 215 may be formed in a monolith, briquettes, or any other suitable form. Gaseous fuel from tank 25 may be directed into accumulator 214 via control valve 212.
Outlet control valve 216 may be substantially similar to control valve 203, but may be configured to selectively allow fluid communication between accumulator 214 and auxiliary engine 22. When outlet control valve 216 is in a flow-passing position, it may allow gaseous fuel to escape accumulator 214 and flow to auxiliary engine 22. That is, auxiliary engine 22 may generate a suction force that withdraws adsorbed gaseous fuel from accumulator 214 and carbon adsorbent 215 when outlet control valve 216 is open. Outlet control valve 216 may include one or more controllable actuators, such as one or more electric solenoids that are operable to open outlet control valve 216 when actuated. Controller 210 may be operatively connected to the actuator(s) of outlet control valve 216, so that controller 210 may selectively trigger opening and closing of outlet control valve 216 to release gaseous fuel from accumulator 214.
Controller 210 may be a single microprocessor or multiple microprocessors that include a mechanism for controlling an operation of recovery system 200. Numerous commercially available microprocessors can be configured to perform the functions of controller 210. It should be appreciated that controller 210 could readily be embodied in a general engine or machine microprocessor capable of controlling numerous engine and/or machine functions. Controller 210 may include a memory, a secondary storage device, a processor, and any other components for running an application. Various other circuits may be associated with controller 210 such as power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and other types of circuitry.
Controller 210 may rely on input from one or more sensors during regulation of recovery system 200. In the disclosed exemplary embodiment, controller 210 may rely on at least one sensor 234 located between accumulator 214 and auxiliary engine 22 and configured to measure a concentration of gaseous fuel downstream of accumulator 214, although any number and types of sensors may be utilized. Sensor 234 may direct a corresponding signal to controller 210 for further processing.
In one embodiment, a timer 240 may be associated with controller 210. In response to a command from controller 210, timer 240 may track an elapsed time. Signals indicative of this elapsed time may be directed from timer 240 to controller 210.
FIG. 3 illustrates an exemplary energy recovery process performed by controller 210. FIG. 3 will be discussed in more detail in the following section to better illustrate the disclosed concepts.
INDUSTRIAL APPLICABILITY
The disclosed energy recovery system may be applicable to any mobile machine utilizing a low-temperature liquid fuel. The disclosed energy recovery system may enhance fuel efficiency by using otherwise wasted gaseous fuel formed in a liquid fuel tank to generate useful electricity. Operation of recovery system 200 will now be described.
If, at any time during the operation of consist 6, an amount of stored gaseous fuel in accumulator 214 is higher than a high-capacity threshold (step 300: Yes), controller 210 may move outlet control valve 216 to the flow-passing position to direct gaseous fuel from accumulator 214 to auxiliary engine 22 regardless of a demand for electrical power from external load 24 (step 310). The high-capacity threshold may be associated with a capacity of accumulator 214 (i.e., carbon adsorbent 215) to store additional gaseous fuel. Controller 210 may determine that the stored amount of gaseous fuel in accumulator 214 is at the high-capacity threshold based on a cumulative opening time that inlet control valve 212 is in the flow-passing position since a last opening of outlet valve 216. The cumulative opening time of inlet control valve 212 may be indicative of the amount of gaseous fuel stored in accumulator 214, because gaseous fuel may exit tank 25 and flow to accumulator 214 at a known rate when inlet control valve 212 is opened. Controller 210 may then compare the amount of gaseous fuel stored in accumulator 214 with a known storage capacity of accumulator 214. Controller 210 may calibrate the storage capacity calculation of accumulator 214 based on a variety of factors including, but not limited to, ambient temperature and the usage of accumulator 214. If not yet operational, controller 210 may initiate operation of auxiliary engine 22 at this time. From step 310, controller 210 may proceed to step 320.
At step 320, controller 210 may determine if there is a demand for electricity from external load 24. This demand may be determined based on operator commands (e.g., via an operator input device (not shown) for controlling external load 24) indicating that external load 24 has an electrical demand or a mechanical demand (e.g., if external load 24 is a pump directly driven by auxiliary engine 22). It should be noted that any other suitable mechanism for determining an electrical demand of external load 24 may alternatively be utilized. If external load 24 has an electrical (or mechanical) demand at step 320, controller 210 may proceed to step 330.
At step 330, controller 210 may operate auxiliary engine 22 in a power generating mode to produce electrical power via a generator and distribute the generated electricity to external load 24 or a mechanical load. From step 330, controller 210 may proceed to step 340.
At step 340, controller 210 may determine if the amount of gaseous fuel stored in accumulator 214 is below a low-delivery threshold. The low-delivery threshold may substantially correspond to the low-capacity threshold, or may be another suitable threshold. The low-delivery threshold may be a capacity at which accumulator 214 is unable to deliver gaseous fuel to auxiliary engine 22. It should be noted that while accumulator 214 is at the low-delivery threshold (or zero delivery capacity), some gaseous fuel may still be adsorbed to carbon adsorbent 215. Controller 210 may determine the available amount of gaseous fuel within accumulator 214 based on a cumulative opening time that outlet control valve 216 has been in the flow-passing position since a last opening event of outlet control valve 216, similar to the determination made at step 300. Alternatively, controller 210 may receive a signal from sensor 234 that is indicative of a concentration of gaseous fuel leaving accumulator 214. Based on this signal, controller 210 may determine that accumulator 214 is below the low-delivery threshold when a measured concentration of gaseous fuel downstream of accumulator 214 is below a threshold level. If controller 210 determines that the amount of available gaseous fuel in accumulator 214 is below the low-delivery threshold, controller 210 may return to step 300. If controller 210 instead determines that the amount of available gaseous fuel in accumulator 214 is above the low-delivery threshold, controller 210 may return to step 320.
If at step 320, controller 210 instead determines that external load 24 has an electrical demand of about zero, controller 210 may proceed to step 350. At step 350, controller 210 may operate auxiliary engine 22 in a burn-off mode. In the burn-off mode, excess gaseous fuel may be burned away to relieve pressures in tank 25 and/or accumulator 214 without generating significant amounts of electricity. In one embodiment, controller 210 may operate auxiliary engine 22 in an idle state during the burn-off mode. Alternatively, controller 210 may operate auxiliary engine 22 to generate electricity in the burn off-mode, which may then be stored or dissipated in a resistive grid, if desired. From step 350, controller 210 may proceed to step 340.
If at step 300, controller 210 instead determines that the amount of stored gaseous fuel in accumulator 214 is lower than the high-capacity threshold, controller 210 may proceed to step 360. At step 360, controller 210 may determine if there is a demand for electricity from external load 24 in a similar manner as performed at step 320. If at step 360, controller 210 determines that external load 24 has an electrical demand of about zero, controller 210 may return to step 300. If at step 360, controller 210 instead determines that external load 24 has an electrical (or mechanical) demand, controller 210 may proceed to step 370.
At step 370, controller 210 may determine the amount of stored gaseous fuel in accumulator 214 in a manner similar to step 300. Controller 210 may then determine if the stored amount of gaseous fuel in accumulator 214 is higher than a low-capacity threshold. The low-capacity threshold may be associated with an amount of gaseous fuel stored in accumulator 214 sufficient to operate auxiliary engine 22. When the stored amount of gaseous fuel in accumulator 214 is higher than the low-capacity threshold, controller 210 may move outlet control valve 216 to the flow-passing position and direct gaseous fuel from accumulator 214 to auxiliary engine 22 (step 380), where auxiliary engine 22 may be operated in the power generating mode. If not yet operational, controller 210 may initiate operation of auxiliary engine 22 at this time. From step 380, controller 210 may proceed to step 390.
At step 390, controller 210 may determine if the amount of gaseous fuel stored in accumulator 214 is below a low-delivery threshold in a manner similar to step 340. If controller 210 determines that the amount of available gaseous fuel in accumulator 214 is below the low-delivery threshold, controller 210 may return to step 300. If controller 210 instead determines that the amount of available gaseous fuel in accumulator 214 is above the low-delivery threshold, controller 210 may return to step 360.
If at step 370, controller 210 instead determines that the amount of stored gaseous fuel in accumulator 214 is lower than the low-capacity threshold, controller 210 may proceed to step 395. At step 395, controller 210 may move control valve 203 to the flow-passing position or to the intermediate position, and direct liquid fuel from tank 25 through fuel delivery circuit 202 toward auxiliary engine 22, where auxiliary engine 22 may be operated in the power generating mode. If not yet operational, controller 210 may initiate operation of auxiliary engine 22 at this time. From step 395, controller 210 may return to step 300. It should be noted that liquid fuel may gasify through fuel delivery circuit 202 before being delivered to auxiliary engine 22.
The disclosed energy recovery system 200 may provide a mechanism for improving fuel efficiency of mobile machine 10. For example, the disclosed energy recovery system 200 may divert boil-off gas to be used as fuel by auxiliary engine 22. Energy recovery system 200 may thus utilize energy from boil-off gas that otherwise would be lost, and reduce liquid fuel consumption by auxiliary engine 22.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed energy recovery system without departing from the scope of the disclosure. Other embodiments of the energy recovery system will be apparent to those skilled in the art from consideration of the specification and practice of the energy recovery system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.

## Claims

1. An energy recovery system for a mobile machine, comprising:
a tank configured to store a liquid fuel for combustion within a main engine located on the locomotive;
a fuel delivery circuit connecting the tank to the main engine;
an auxiliary engine;
a boil-off circuit connecting the tank to the auxiliary engine;
an accumulator fluidly connected to the boil-off circuit between the tank and the auxiliary engine and configured to store gaseous fuel formed in the tank; and
a carbon adsorbent disposed within the accumulator and configured to adsorb the gaseous fuel,
wherein the auxiliary engine is configured to selectively generate a suction force to withdraw gaseous fuel adsorbed onto the carbon adsorbent.

2. The energy recovery system of claim 1, further including an inlet valve configured to selectively pass gaseous fuel from the tank to the accumulator when a pressure of the tank exceeds a tank pressure threshold.

3. The energy recovery system of claim 2, further including an outlet valve configured to selectively pass gaseous fuel from the accumulator toward the auxiliary engine when an amount of gaseous fuel stored in the accumulator exceeds a high capacity threshold.

4. The energy recovery system of claim 3, further including a controller configured to:
determine the amount of gaseous fuel stored in the accumulator based on a cumulative opening time of the inlet valve since a last opening event of the outlet valve; and
activate the outlet valve based on the determined amount.

5. The energy recovery system of claim 4, further including a control valve selectively movable by the controller to direct fuel from the tank toward only the main engine, toward only the auxiliary engine, or toward both the main engine and the auxiliary engine.

6. The energy recovery system of claim 5, wherein the controller is further configured to move the control valve to direct fuel from the tank toward the auxiliary engine when the amount of gaseous fuel stored in the accumulator is below a low capacity threshold.

7. The energy recovery system of claim 4, wherein the outlet valve is movable by the controller to selectively pass gaseous fuel from the accumulator to the auxiliary engine when the amount of gaseous fuel stored in the accumulator exceeds a low capacity threshold.

8. The energy recovery system of claim 4, wherein the controller is configured to operate the auxiliary engine in a power generating mode when the amount of gaseous fuel stored in the accumulator the exceeds a high capacity threshold and an external load connected to the auxiliary engine has an electrical demand.

9. The energy recovery system of claim 4, wherein the controller is configured to operate the auxiliary engine in a burn-off mode when the amount of gaseous fuel stored in the accumulator exceeds the high capacity threshold and an external load connected to the auxiliary engine has an electrical demand of about zero.

10. The energy recovery system of claim 4, wherein the controller is configured to operate the auxiliary engine in an idle state during the burn-off mode.

11. The energy recovery system of claim 4, wherein the controller is further configured to move the outlet valve to a flow-blocking position when an amount of stored gaseous fuel in the accumulator is below a low delivery threshold.

12. The energy recovery system of claim 11, wherein the controller is further configured to move the outlet valve to the flow-blocking position based on a cumulative opening time of the outlet valve.

13. The energy recovery system of claim 11, further including a sensor located between the accumulator and the auxiliary engine and configured to measure a concentration of gaseous fuel exiting the accumulator, wherein the controller is configured to move the outlet valve to the flow-blocking position based on the measured concentration.

14. A method of operating a mobile machine, comprising:
directing liquid fuel from a tank toward a main engine;
directing gaseous fuel formed in the tank through an accumulator toward an auxiliary engine;
adsorbing gaseous fuel on a carbon adsorbent disposed in the accumulator; and
withdrawing gaseous fuel adsorbed on the carbon adsorbent with a suction force generated by the auxiliary engine.

15. The method of claim 14, further including operating the auxiliary engine in a power generating mode when an amount of adsorbed gaseous fuel exceeds a high capacity threshold and an external load connected to the auxiliary engine has an electrical demand.

16. The method of claim 14, further including operating the auxiliary engine in a burn-off mode when an amount of adsorbed gaseous fuel exceeds a high capacity threshold and an external load connected to the auxiliary engine has an electrical demand of about zero.

17. The method of claim 16, further including operating the auxiliary engine in an idle state during the burn-off mode.

18. The method of claim 14, further including directing liquid fuel from the tank toward the auxiliary engine when an amount of adsorbed gaseous fuel is below a low capacity threshold.

19. The method of claim 14, further including directing adsorbed gaseous fuel toward the auxiliary engine only when an amount of adsorbed gaseous fuel exceeds a low capacity threshold.

20. A train consist, comprising:
a locomotive having:
a frame;
a main engine mounted to the frame;
a plurality of wheels configured to support the frame and driven by the main engine; and
an auxiliary engine mounted to the frame;

a tender car having a tank configured to store a liquid fuel;
a boil-off circuit connecting the tank to the auxiliary engine;
an accumulator fluidly connected to the boil-off circuit between the tank and the auxiliary engine and configured to store gaseous fuel formed in the tank; and
a carbon adsorbent disposed within the accumulator and configured to adsorb the gaseous fuel, wherein the auxiliary engine is configured to selectively generate a suction force to withdraw gaseous fuel adsorbed onto the carbon adsorbent;
an inlet valve configured to selectively pass gaseous fuel from the tank to the accumulator when a pressure of the tank exceeds a tank pressure threshold; and
an outlet valve configured to selectively pass gaseous fuel from the accumulator toward the auxiliary engine when an amount of gaseous fuel stored in the accumulator exceeds a high capacity threshold.