System and method for control of exhaust gas recirculation (EGR) utilizing process temperatures

A system includes a reciprocating internal combustion engine with one or more reaction zones configured to receive a charge flow that is configured to react within the one or more reaction zones, thereby forming an exhaust gas flow, and a controller. The charge flow includes an oxidant flow, a fuel flow, and a recirculated portion of the exhaust gas flow. The controller is configured to control a ratio of the recirculated portion of the exhaust gas flow to a fuel mixture. The controller controls the ratio based at least in part on a first temperature, a second temperature of the charge flow, and a third temperature of the recirculated portion of the exhaust gas flow. The fuel mixture includes the oxidant flow and the fuel flow. The first temperature includes one or any combination of a sensed temperature of the oxidant flow, the fuel flow, or the fuel mixture.

BACKGROUND

The subject matter disclosed herein relates to reciprocating internal combustion engines, and more specifically, to recirculating exhaust gas with a fuel mixture through a reciprocating internal combustion engine.

A reciprocating engine utilizes pressure, such as from combustion of a mixture of fuel and air, to generate hot gases to drive a reciprocating piston. The reciprocating piston may drive a shaft and one or more loads (e.g., electrical generator, compressor) coupled to the shaft. In certain configurations, fuel and air are pre-mixed prior to ignition to reduce emissions and to improve combustion. In addition, the reciprocating engine may employ exhaust gas recirculation (EGR) to reduce formation of nitrogen oxides (NOx). Unfortunately, it may be difficult to control the amount of EGR suitable for the engine.

BRIEF DESCRIPTION

In a first embodiment, a system includes a reciprocating internal combustion engine with one or more reaction zones configured to receive a charge flow that is configured to react within the one or more reaction zones, thereby forming an exhaust gas flow, and a controller. The charge flow includes an oxidant flow, a fuel flow, and a recirculated portion of the exhaust gas flow. The controller is configured to control a ratio of the recirculated portion of the exhaust gas flow to a fuel mixture. The controller controls the ratio based at least in part on a first temperature, a second temperature of the charge flow, and a third temperature of the recirculated portion of the exhaust gas flow. The fuel mixture includes the oxidant flow and the fuel flow. The first temperature includes one or any combination of a sensed temperature of the oxidant flow, the fuel flow, or the fuel mixture.

In a second embodiment, a system includes a first temperature sensing system configured to determine a first temperature of a fuel mixture, a second temperature sensing system configured to determine a second temperature of a charge flow, a third temperature sensing system configured to determine a third temperature of a recirculated portion of an exhaust gas flow, at least one flow control valve, and a reciprocating internal combustion engine. The fuel mixture includes an oxidant flow and a fuel flow, and the charge flow includes the fuel mixture and the recirculated portion of the exhaust gas flow. The at least one control valve is configured to control a ratio of the recirculated portion of the exhaust gas flow to the fuel mixture based at least in part on the first temperature of the fuel mixture, the second temperature of the charge flow, and the third temperature of the recirculated portion of the exhaust gas flow. The reaction zone is configured to react the charge flow to form the exhaust gas flow.

In a third embodiment, a method of operating a reciprocating internal combustion engine includes determining a first temperature of a fuel mixture, determining a second temperature of a charge flow, determining a third temperature of a recirculated portion of an exhaust gas flow, determining a ratio of the recirculated portion of the exhaust gas flow to the fuel mixture based at least in part on the first temperature, the second temperature, and the third temperature, and controlling the charge flow to the reciprocating internal combustion engine at least partially based on the ratio. The charge flow reacts within a reaction zone of the reciprocating internal combustion engine. The fuel mixture includes an oxidant flow and a fuel flow. The charge flow includes the fuel mixture and the recirculated portion.

DETAILED DESCRIPTION

An exhaust gas recirculation (EGR) system as described herein recirculates exhaust gases internally within a reciprocating internal combustion (IC) engine. Oxidant and fuel are premixed into a fuel mixture prior to injection into a reaction zone of the reciprocating IC engine. Substantially complete (e.g., stoichiometric) combustion without exhaust gas recirculation reacts approximately all the oxidant and fuel into combustion products (e.g., carbon dioxide, carbon monoxide, nitrogen oxides (NOx), and water). Reactions with approximately stoichiometric quantities or surplus oxidant may react at high temperatures (e.g., approximately 2800° F.), thereby increasing NOxemissions. A portion of the exhaust gas may be recirculated to dilute the oxidant in the fuel mixture, to lower the combustion temperature, and to reduce NOxemissions. The fuel mixture and the recirculated portion of the exhaust gas may be referred to as the charge mixture. The quantity of the recirculated portion may be increased to control (e.g., reduce) the combustion temperature and the NOxemissions, and the recirculated portion may be decreased to control (e.g., increase) the stability (e.g., flame stability) of the reciprocating IC engine.

A controller and/or a valve control system may control flow rates of the oxidant, the fuel, and the recirculated portion of the exhaust gas, thereby enabling a desired composition of the charge mixture to react within the reciprocating IC engine. As discussed herein, the composition of the charge mixture may be determined by the controller based at least in part on a determined temperature of the fuel mixture, a determined temperature of the charge mixture, and a determined temperature of the recirculated portion of the exhaust gas. In some embodiments, the enthalpies of the fuel mixture, the charge mixture, and the recirculated portion of the exhaust gas are determined by the controller. In some embodiments, the determination of the composition of the charge mixture may be augmented based at least in part on a determined pressure of the fuel mixture, a determined pressure of the charge mixture, or a determined pressure of the recirculated portion of the exhaust gas, or any combination thereof. However, flow rates determined by the controller based on temperatures as described herein may be more accurate and/or robust than flow rates determined based on pressure measurements alone. For example, oxidant flow rates greater than approximately 10 pounds per minute through the flow control system may have pressure fluctuations due to turbulence. Moreover, flow determination via temperature measurements may have lower costs and/or lower system complexity than flow determination via flow meters (e.g., Venturi-type, orifice-type) and direct measurement of NOxin the exhaust gas flow.

FIG. 1is a diagram of an embodiment of a reciprocating internal combustion (IC) engine system10having a reciprocating IC engine12, a flow control system14, and a load16driven by the reciprocating IC engine12. The load16may include, but is not limited to, a vehicle or a stationary load. In some embodiments, the load16may include a compressor, a pump, an electric generator, a transmission, a propeller on an aircraft or boat, a fan, or any suitable device capable of being powered by the reciprocating IC engine12. The flow control system14includes an oxidant supply system18, a fuel supply system20, and a controller22(e.g., an electronic control unit). The oxidant supply system18intakes an oxidant stream23(e.g., oxygen, air, oxidant-reduced air, or oxidant-enriched air) and supplies the oxidant flow24. In some embodiments, the oxidant supply system18intakes the oxidant stream23from an external environment26. The fuel supply system20may include a fuel reservoir28configured to supply a fuel flow30to the reciprocating IC engine12. The fuel of the fuel flow30may include, but is not limited to, one or more of the following fuels: methane, ethane, ethene, propane, propylene, isobutane, butane, isopentane, pentane, hexane, heptanes, hydrogen, or gasoline. The fuel supply system20may supply a liquid fuel flow30or a gaseous fuel flow30.

The oxidant flow24and the fuel flow30mix within a premix conduit32to form a fuel mixture34that flows to a reaction zone36(e.g., combustion chamber) of the reciprocating IC engine12. As may be appreciated, the reciprocating IC engine12may have one or more reaction zones36, and each reaction zone36is adjacent to a reciprocating piston38that moves within a respective cylinder40. For example, some reciprocating IC engines12may include 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, or more reaction zones36(e.g., combustion chambers) and respective reciprocating pistons38. The fuel mixture34may be injected into the reaction zone36via an intake valve42and compressed via the reciprocating piston38moving in a first direction44. The fuel mixture34reacts (e.g., combusts) within the reaction zone36, thereby driving the reciprocating piston38in a second direction46as combustion products from the reaction expand. In some embodiments, one or more spark plugs48induce the reaction (e.g., ignite the fuel mixture34) in the reaction zone36. The one or more reciprocating pistons38are coupled to a drive shaft50(e.g., crank shaft) that is drivingly coupled to the load16, thereby rotating the drive shaft50in a third direction52to drive the load16. An exhaust valve54releases the reacted combustion products from the reaction zone36through an exhaust conduit57as an exhaust gas flow56.

The flow control system14may recirculate a portion58of the exhaust gas flow56through a recirculation conduit59to the premix conduit32to form the charge flow60. In some embodiments, the controller22may control one or more of the oxidant flow24, the fuel flow30, and the recirculated portion58of the exhaust gas flow56via flow control valves62. The controller22may control a flow rate of the fuel mixture34by controlling the oxidant flow24and the fuel flow30. The controller22controls the composition and flow rate of the charge flow60based at least in part on a first temperature of the fuel mixture34, a second temperature of the charge flow60, and a third temperature of the recirculated portion58of the exhaust gas flow56.

Multiple temperature sensors64may transmit feedback signals to the controller22based at least in part on a temperature of a flow proximate to the respective temperature sensor64. The temperatures sensors64may transmit intermittently, at regular intervals, or substantially continuously, feedback signals indicative of directly or indirectly sensed temperatures, or may provide the actual temperature values of the respective flows. Each temperature sensor64may include, but is not limited to, a thermocouple, a resistor temperature detector (RTD), a thermistor, a pyrometer (e.g., a radiation and/or optical pyrometer), or a thermometer, or any combination thereof. The temperatures sensors64may be arranged on an exterior wall66of the premix conduit32, on an interior wall68of the premix conduit32, or through the interior wall68and within the respective flow (e.g., oxidant flow24, fuel flow30, fuel mixture34, recirculated portion58, charge flow60). In some embodiments, a temperature sensor64may be arranged at a position that enables the temperature sensor64to transmit a feedback signal representative of a sufficiently mixed flow. For example, a first temperature sensor70may be arranged at a position72downstream of the introduction of the fuel flow30to the oxidant flow24where the fuel mixture34is a substantially homogenous mixture based on testing, calibration, or fluid dynamic calculations. In some embodiments, the temperature of a substantially homogenous mixture may vary less than approximately 1 degree C. across a cross-section of the mixture.

The controller22may determine an exhaust gas recirculation (EGR) ratio between the mass flow rate of the recirculated portion58of the exhaust gas flow56and the mass flow rate of the fuel mixture34based at least in part on transmitted signals from the temperature sensors64. The equations presented herein describe relationships between the respective flows and the respective temperatures. The mass flow of the fuel mixture34after junction74prior to mixing with the recirculated portion58may be determined from Equation (1), and the mass flow of the charge flow60at junction76may be determined from Equation (2):
Mmixture=Moxidant+Mfuel(1)
Mcharge=Mmixture+Megr(2)
where Mmixtureis the mass flow rate of the fuel mixture34, Moxidantis the mass flow rate of the oxidant flow24, Mfuelis the mass flow rate of the fuel flow30, Mchargeis the mass flow rate of the charge flow60, and Megris the mass flow rate of the recirculated portion58. In some embodiments, Moxidantmay be between approximately 0.45 to 433 kgs/minute (e.g., approximately 1 to 955 lbs/minute), approximately 4.5 to 300 kgs/minute (e.g., approximately 10 to 660 lbs/minute), or approximately 45 to 136 kgs/minute (e.g., approximately 100 to 300 lbs/minute). Mfuelmay be between approximately 0.02 to 30 kgs/minute (e.g., approximately 0.04 to 66 lbs/minute), approximately 0.2 to 20 kgs/minute (e.g., approximately 0.4 to 44 lbs/minute), or approximately 2 to 10 kgs/minute (e.g., approximately 4.4 to 22 lbs/minute). As may be appreciated, Equations (1) and (2) describe a mass balance of the respective flows that enter the reaction zone36. The controller22controls one or more of the respective flows to control the EGR ratio determined from Equation (3):

%⁢⁢EGR=MegrMmixture(3)
where % EGR is the EGR ratio. Increasing the EGR ratio over a lower threshold may decrease the combustion temperature and the NOxemissions from the reciprocating IC engine12; however, EGR ratios over an upper threshold of approximately 40 percent may increase misfiring of the one or more reciprocating pistons34, thereby decreasing the stability (e.g., flame or combustion stability) of the reciprocating IC engine12. Accordingly, Megrmay be between approximately 1 and 40 percent, approximately 5 to 35 percent, or approximately 10 to 25 percent of Mmixture.

The enthalpy of a flow may be determined based at least in part on the mass flow rate, a specific heat of the flow, and a temperature of the flow. Equation (4) describes the specific heat of the charge flow60(Mcharge):
Mcharge*Cpcharge=Mmixture*Cpmixture+Megr*Cpegr(4)
where Cpchargeis the specific heat of the charge flow60, Cpmixtureis the specific heat of recirculated the fuel mixture34, and Cpegris the specific heat of the recirculated portion58of the exhaust gas flow56. Equation (4) may be rewritten with Equation (2) to define Cpchargein terms of Cpmixtureand Cpegr, as shown in Equation (5):

Cpcharge=Megr*Cpegr+Mmixture*CpmixtureMegr+Mmixture(5)
According to the first law of thermodynamics, the enthalpy (Qcharge) of the charge flow60leaving junction76is equal to the sum of the enthalpy (Qmixture) of the fuel mixture34and the enthalpy (Qegr) of the recirculated portion58entering the junction76, as shown in Equation (6):
Qcharge=Qmixture+Qegr(6)
Qcharge, Qmixture, and Qegrare defined respectively by Equations (7)-(9):
Qcharge=Mcharge*Cpcharge*(Tcharge−Tref)  (7)
Qmixture=Mmixture*Cpmixture*(Tmixture−Tref)  (8)
Qegr=Megr*Cpegr*(Tegr−Tref)  (9)
where Tchargeis the temperature of the charge flow60, Tmixtureis the temperature of the fuel mixture34, Tegris the temperature of the recirculated portion58, and Trefis a reference temperature. In some embodiments, Tmixturemay be approximated as the temperature of the oxidant flow24(Toxidant), the temperature of the fuel flow30(Tfuel), or any combination thereof. Additionally, or in the alternative, Tmixturemay be sensed directly by a temperature sensor64configured to sense the temperature of the fuel mixture34, or indirectly utilizing one or more of Toxidantand Tfuel.

The enthalpy of the charge flow60may be determined through substitution of Equations (7)-(9) into Equation (6) and setting Trefequal to zero, forming Equation (10):
Mcharge*Cpcharge*Tcharge=Mmixture*Cpmixture*Tmixture+Megr*Cpegr*Tegr(10)

Further substitution of Equations (2) and (5) into Equation (10) and algebraic manipulations result in Equation (11):
Megr*Cpegr*(Tcharge−Tegr)=Mmixture*Cpmixture*(Tmixture−Tcharge)  (11)
From Equation (11), the EGR ratio may be determined as shown by Equation (12):

%⁢⁢EGR=MegrMmixture=Cpmixture*(Tmixture-Tcharge)Cpegr*(Tcharge-Tegr)(12)
In some embodiments, the specific heat of the fuel mixture34may be approximately equal to the specific heat of the recirculated portion58, thereby further simplifying Equation (12) into Equation (13):

Utilizing Equation 12 or Equation 13, a processor78of the controller22may determine the EGR ratio of the recirculated portion58to the fuel mixture34based at least in part on the sensed temperature of the fuel mixture34, the sensed temperature of the charge flow60, and the sensed temperature of the recirculated portion58of the exhaust gas flow56. In some embodiments, the controller22may determine the EGR ratio of the recirculated portion58to the fuel mixture34based at least in part on the above equations, computer models, historical data, trend data, current sensor data, fleet data, look-up tables, graphs, or any combination thereof. The desired EGR ratio may be based at least in part on an operating mode of the reciprocating IC engine12. For example, the desired EGR ratio may be different for a startup sequence and/or a shut down sequence relative to a steady-state sequence. In some embodiments, the desired EGR ratio may be based at least in part on the load16, such that the desired EGR ratio for a relatively small load (1000 hp) is lower than the desired EGR ratio for a relatively large load (5000 hp). The controller22may store instructions and/or temperature signals to determine % EGR in a memory80. The memory80may include, but is not limited to, a volatile and/or non-volatile memory. For example, the memory80may include one or more hard drives, flash memory, read-only memory, random access memory, or any combination thereof.

Using the controller22, the temperature of the fuel mixture34may be determined directly via the first temperature sensor70, or indirectly via a second temperature sensor82configured to transmit a second temperature signal based on the temperature of the oxidant flow24and a third temperature sensor84configured to transmit a third temperature signal based on the temperature of the fuel flow30. In some embodiments, the controller22may determine a fuel-air ratio (% F/A) of the fuel flow30to the oxidant flow24in the fuel mixture34in a similar manner to determining the EGR ratio. For example, the controller22may utilize Equation 14:

%⁢⁢F/A=MfuelMoxidant=Toxidant-TmixtureTmixture-Tfuel(14)
where Toxidantis the temperature of the oxidant flow24and Tfuelis the temperature of the fuel flow30. The controller22may control the fuel-air ratio by adjusting at least one of the oxidant flow24and the fuel flow30.

Additionally, or in the alternative, an oxygen sensor85(e.g., lambda sensor) coupled to the controller22may sense the oxygen concentration in the recirculated portion58of the exhaust gas flow56. The controller22may determine the fuel-air ratio based on the oxygen concentration in the recirculated portion58sensed by the oxygen sensor85. In some embodiments, the controller22may compare the fuel-air ratio determined from the oxygen sensor85feedback to the fuel-air ratio determined via Equation 14. Accordingly, the controller22may utilize the oxygen sensor85to verify the fuel-air ratio determined from Equation 14, the controller22may utilize the fuel-air ratio determined from Equation 14 to verify the oxygen concentration sensed by the oxygen sensor85, or the controller22may utilize the fuel-air ratio determined from Equation 14 and the oxygen concentration sensed by the oxygen sensor85to determine and control the fuel-air ratio of the fuel flow30to the oxidant flow24in the fuel mixture34.

The controller22may be coupled to an operator interface86(e.g., display with a graphical user interface) configured to receive an operator input88or to provide an operator output90to the operator. For example, the operator may input specific heat values for the oxidant flow24, the fuel flow30, or the recirculated portion58, upper or lower EGR ratio thresholds, a desired EGR ratio, a desired threshold flow rate for the oxidant flow24, the fuel flow30, or the recirculated portion58, or any combination thereof. In some embodiments, the operator may input identification information for equipment, such as serial numbers or model numbers. The operator interface86may facilitate operator control of the speed and/or loading of the reciprocating IC system10. In some embodiments, the operator interface86may display operational information on the status of the reciprocating IC system10, such as the speed, the load16, the fuel efficiency, the fuel consumption, the operating temperature, the EGR ratio, the fuel level, trends, emissions levels (e.g., NOx, CO, CO2, SOx), and so forth.

In some embodiments, one or more pressure sensors92may transmit pressure signals to the controller22based at least in part on a measured pressure of the oxidant flow24, the fuel flow30, the fuel mixture34, the recirculated portion58, or the charge flow60, or any combination thereof. The controller22may utilize the pressure signals to augment the determination of the % EGR. For example, the controller22may utilize one or more pressure sensors92, orifice plates, or flow meters to determine the flow rate of one or more flows.

FIG. 1further illustrates a schematic view of an embodiment of the flow control system14configured to supply the charge flow60to the reaction zone36of the reciprocating IC engine12and to recirculate a portion58of the exhaust gas flow56from the reciprocating IC engine12. The reciprocating IC engine system10may include multiple reciprocating pistons38and multiple reaction zones36. In some embodiments, the system14may supply the charge flow60to each reaction zone36via a respective premix conduit32. In other embodiments, the premix conduit32may couple with a charge manifold94configured to supply the charge flow60to each of the reaction zones36.

Upon determination of the EGR ratio between the recirculated portion58and the fuel mixture34, the controller22may adjust the flow rate of at least one of the fuel mixture34and the recirculated portion58that are mixed to form the charge flow60. In some embodiments, the controller22adjusts the flow rate of the fuel mixture34by adjusting the flow rate of the oxidant flow24. Additionally, or in the alternative, the controller22adjusts the flow rate of the fuel mixture34by adjusting the flow rate of the fuel flow30. For example, the controller22may adjust the respective flow control valves62of the oxidant supply system62and/or the fuel supply system20. The controller22may adjust the flow control valve62coupled to the recirculation conduit59to control the recirculated portion58of the exhaust gas flow56. In summary, the controller22may adjust the flow rate of the oxidant flow24, the flow rate of the fuel flow30, the flow rate of the fuel mixture34, or the flow rate of the recirculated portion58of the exhaust gas flow56, or any combination thereof.

FIG. 2illustrates a method100of an embodiment for controlling the EGR ratio between the recirculated portion58of the exhaust gas flow56and the fuel mixture34supplied to the reciprocating IC engine12ofFIG. 1. Optionally, the controller22may receive (block102) specific heat properties related to the respective flows (e.g., oxidant flow24, fuel flow30, fuel mixture34, recirculated portion58of the exhaust gas flow56). The controller22may determine (block104) the temperature (Tmixture) of the fuel mixture34via one or more temperature sensors64. For example, a temperature sensor64may transmit a signal based at least in part on the temperature of the fuel mixture34. Additionally, or in the alternative, the controller22may determine the temperature of the fuel mixture34via a relationship between a temperature of the oxidant flow24and a temperature of the fuel flow30. For example, the controller22may determine the temperature of the fuel mixture34based at least in part on the flow rates of the oxidant flow24and the fuel flow30, and the temperatures of the oxidant flow24and the fuel flow30. The controller22also determines (block106) the temperature (Tegr) of the recirculated portion58of the exhaust gas flow56via one or more temperature sensors64. In some embodiments, Tegrmay be between approximately 40 to 80 degrees C. (e.g., approximately 104 to 176 degrees F.), between approximately 50 to 75 degrees C. (e.g., approximately 122 to 167 degrees F.), or between approximately 55 to 70 degrees C. (e.g., approximately 131 to 158 degrees F.) or more. The controller22further determines (block108) the temperature (Tcharge) of the charge flow via one or more temperature sensors64, where the charge flow includes the oxidant flow24, the fuel flow30, and the recirculated portion58of the exhaust gas flow56. The one or more temperature sensors64may be arranged at a point to enable the signal transmitted to the controller22to correspond to a substantially homogenous mixture within the charge flow.

Utilizing one of Equations (12) or (13), the controller22determines (block110) the EGR ratio between the recirculated portion58of the exhaust gas flow56and the fuel mixture34supplied to the reciprocating IC engine. Based at least in part on the EGR ratio, the controller22may control (block112) the charge flow inputs, such as the oxidant flow24, the fuel flow30, and/or the recirculated portion58of the exhaust gas flow56. The controller22may control one or more of the charge flow inputs in a feedback loop to adjust the EGR ratio to a desired value, such as between approximately 15 to 40%.

In some embodiments, the controller22may control the charge flow input and adjust the EGR ratio in order to reduce the NOxemissions below a desired level (e.g., approximately 500 to 1000 ppm), to control the combustion temperature between a desired range (e.g., approximately 650 to 980 degrees C. or 1200 to 1800 degrees F.), or to increase the stability of the reciprocating IC engine. For example, the memory of the controller22may store one or more look-up tables that relate NOxemissions, combustion temperature, and/or engine stability to various values for the EGR ratio between the recirculated portion of the exhaust gas flow and the fuel mixture, various to fuels, and/or to various oxidant flows.

Technical effects of the invention include the determination and control of the EGR ratio between the recirculated portion of the exhaust gas flow and the fuel mixture provided to a reciprocating IC engine based at least in part on the temperature of the fuel mixture, the temperature of the charge flow supplied to the reciprocating IC engine, and the temperature of the recirculated portion. The controller may determine the EGR ratio utilizing temperature sensors with or without pressure sensors. The controller may determine the enthalpies of the respective flows and may control one or more of the fuel mixture or the recirculated portion to control the EGR ratio. In some embodiments, the controller may control the oxidant flow or the fuel flow to adjust the fuel mixture. The controller may control the EGR ratio in order to affect the NOxemissions from the reciprocating IC engine, to reduce the combustion temperature of the reciprocating IC engine, and/or to increase the stability of operation of the reciprocating IC engine.