Split-cycle engine

Abstract

To provide a split-cycle internal combustion engine and a method of operating the split-cycle internal combustion engine.SOLUTION: A split-cycle internal combustion engine 100 comprises: a compression cylinder 10 receiving a compression piston 12; a combustion cylinder 20 receiving a combustion piston 22; a crossover passage 30 arranged between the compression cylinder 10 and the combustion cylinder 20 to supply working fluid to the combustion cylinder 20; a reactivity regulator 85 capable of operating to regulate the reactivity of fuel used in a combustion process; and a controller 60 arranged to receive at least one indication of (i) the pressure of the working fluid, (ii) the temperature of the working fluid, (iii) the generation of NOx caused by combustion, and (iv) the degree of engine knocking in the combustion cylinder. The controller 60 is configured to operate the reactivity regulator 85 so as to regulate the reactivity of fuel on the basis of the received indication.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to split-cycle internal combustion engines and methods of operating split-cycle internal combustion engines. [Background technology]

[0002] Conventional internal combustion engines operate based on the Otto or Diesel cycle. In these cycles, improving efficiency (i.e., performance) is generally accompanied by increased emissions of NOx, particulates, and carbon dioxide. In recent years, with growing concerns about air pollution and global warming, exhaust gas regulations have become increasingly strict. Considering the aforementioned engine cycles from this perspective, improving cycle efficiency leads to increased temperatures, which leads to the formation of more NOx. Therefore, performance is severely limited relative to efficiency. Exhaust aftertreatment has been proposed to suppress NOx formation, but this inevitably increases the complexity of the manufacturing process.

[0003] For both the Otto and Diesel cycles, efficiency is based on the pressure at the end of compression. Diesel cycle efficiency is also based on the combustion ratio, since rpm and combustion ratio affect the volume ratio at the beginning and end of combustion. Therefore, improving the efficiency of conventional engines is substantially limited because the peak temperatures and pressures associated with the engine can reach very high levels.

[0004] The formation of NOx compounds occurs in regions where the temperature of the air-fuel mixture rises above 2100 K. This can occur, for example, in localized "hot spots" or on a larger scale, such as throughout an engine cylinder. NOx compounds are associated with respiratory health problems in humans, and the formation of these compounds and their atmospheric emissions pose significant health risks. Furthermore, the formation of these compounds is endothermic, making them inherently useless for maximizing the conversion of chemical energy to power.

[0005] UK Patent Application Nos. 1622114.5, 1706792.7 and 1709012.7 disclose split-cycle internal combustion engines that use coolant injectors for cryogenic fluids (fluids that have been condensed to a liquid phase by a refrigeration process). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] UK Patent Application No. 1622114.5 [Patent Document 2] UK Patent Application No. 1706792.7 [Patent Document 3] UK Patent Application No. 1709012.7 Summary of the Invention

[0007] Aspects of the invention are set out in the independent claims, with optional features set out in the dependent claims. Aspects of the invention may be used in combination with each other and features of one aspect may be applied to other aspects.

[0008] Aspects of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings in which: [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an exemplary split-cycle internal combustion engine system; [Figure 2] 1 is a schematic diagram of an exemplary split-cycle internal combustion engine system; [Figure 3] FIG. 2 is a temperature entropy diagram of an exemplary split-cycle internal combustion engine operation. [Figure 4] This is the temperature entropy diagram of Figure 3 with isobars added to the graph. [Figure 5] 1 is a graph illustrating an example scenario of split-cycle internal combustion engine usage based on equivalence ratio, start temperature, and end temperature. [Figure 6]1 is a flow chart illustrating an exemplary method of operating a split-cycle internal combustion engine. [Figure 7] 1 is a flow chart illustrating an exemplary method of operating a split-cycle internal combustion engine. [Figure 8] 1 is a flow chart illustrating an exemplary method of operating a split-cycle internal combustion engine. [Figure 9] 1 is a flow chart illustrating an exemplary method of operating a split-cycle internal combustion engine. [Figure 10] 1 is a flow chart illustrating an exemplary method of operating a split-cycle internal combustion engine. [Figure 11] 1 is a flow chart illustrating an exemplary method of operating a split-cycle internal combustion engine. [Figure 12] 1 is a flow chart illustrating an exemplary method of operating a split-cycle internal combustion engine. DETAILED DESCRIPTION OF THE INVENTION

[0010] In one example, a split-cycle internal combustion engine is disclosed that includes a controller configured to control a cooling system so that the peak temperature of combustion in the combustion cylinder is below a selected threshold. The controller may control the peak temperature of combustion to reduce the production of NOx and particulates during combustion. This control has clear environmental advantages, as these chemicals are known to be harmful to humans.

[0011] In one example, a split-cycle internal combustion engine is disclosed that includes a controller configured to control the opening and closing of an intake valve that controls the flow of working fluid to a combustion cylinder. The controller may control the intake valve to open and close at selected times to control the peak temperature of combustion in order to reduce the production of NOx and particulates during combustion. This control has clear environmental advantages, as these chemicals are known to be harmful to humans.

[0012] In one example, a split-cycle internal combustion engine is disclosed that includes a controller configured to control a reactivity moderator that adjusts the reactivity of a fuel based on received indications of engine operating conditions. The controller may control the reactivity moderator to increase the reactivity of the fuel when the fuel reactivity is low. This allows for increased efficiency because a greater proportion of the fuel can be burned.

[0013] In one example, a split-cycle internal combustion engine is disclosed that includes a controller configured to control the injection timing of fuel injectors that inject fuel into combustion cylinders. The controller may control the timing of the injectors to control the peak temperature of combustion in the combustion cylinders. This allows for lower peak temperatures, enabling the controller to reduce the production of NOx and particulates during combustion, which has clear environmental benefits since these chemicals are known to be harmful to humans.

[0014] In one example, a split-cycle internal combustion engine is disclosed that includes a controller configured to control a cooling system based on an estimate of a peak combustion temperature to maintain the peak combustion temperature within a selected range. This may enable the controller to prevent the engine from operating at temperatures high enough to cause NOx and particulate emissions during combustion, and may also enable the controller to prevent the engine from operating at temperatures low enough to cause poor engine performance.

[0015] In one example, a split-cycle internal combustion engine is disclosed that includes a controller configured to control a cooling system so that the working fluid in the crossover passage flows into the combustion cylinder at a velocity above a velocity threshold. This allows for better mixing of the fuel and working fluid prior to combustion. This may reduce fuel richness, resulting in a leaner mixture that ensures complete fuel combustion and reduces the production of particulates such as soot. Furthermore, the occurrence of "hot spots" may be reduced, where combustion occurs at higher peak temperatures that produce undesirable pollutants such as NOx.

[0016] In one example, a split-cycle internal combustion engine is disclosed that includes a controller configured to control the cross-sectional area defined by an intake valve to a combustion cylinder so that the working fluid flows into the combustion cylinder at a velocity above a velocity threshold, thereby allowing for better mixing of the fuel and working fluid prior to combustion. This may reduce fuel richness and reduce the occurrence of "hot spots" where combustion produces NOx or particulates.

[0017] FIG. 1 illustrates a first example of a split-cycle internal combustion engine 100 configured to control a peak combustion temperature below a selected threshold. The engine 100 is configured to provide an indication of the peak combustion temperature to a controller 60. The controller 60 determines the peak combustion temperature based on the indication. The controller 60 controls a cooling system to regulate the temperature of a working fluid supplied to the combustion cylinders 20 of the engine 100 based on the determined peak combustion temperature. In particular, the cooling system may be configured to control the temperature of the working fluid in the crossover passage 30 between the compression cylinder 10 and the combustion cylinder 20 of the engine 100 so that the temperature is sufficiently cool when used in the combustion cylinders 20 as part of the combustion process, such that the peak combustion temperature does not exceed a selected threshold. The controller 60 may operate based on a feedback loop that controls operation of the cooling system so that the temperature of the working fluid supplied to the combustion cylinders 20 may be controlled within a selected range. This may enable control of the peak combustion temperature, for example, so that the production of NOx compounds may be suppressed. The feedback loop may be based on a cooling threshold, and in response to the controller determining that the peak temperature of combustion is below the cooling threshold, the controller controls the cooling system by adjusting the temperature of the working fluid to cause the peak temperature of combustion to exceed the cooling threshold, which may enable the controller to control the engine to operate within a selected peak temperature range.

[0018] As shown, FIG. 1 illustrates an arrangement of a split-cycle internal combustion engine 100 including a compression cylinder 10 and a combustion cylinder 20. The compression cylinder 10 houses a compression piston 12 connected to each crank on a portion of a crankshaft 70 via a connecting rod 52. The combustion cylinder 20 houses a combustion piston 22 connected to each crank on the portion of the crankshaft 70 via a connecting rod 54. The compression cylinder 10 is connected to the combustion cylinder 20 via a crossover passage 30. The crossover passage 30 may include a recuperator that may be used for heat transfer. The compression cylinder 10 includes an intake port 8 that receives fluid from outside the engine 100 and an exhaust port 9 that is connected to the crossover passage 30. The exhaust port 9 includes a valve, for example, a check valve, to prevent compressed fluid from flowing back into the compression cylinder 10. Combustion cylinder 20 includes an intake valve 18 connected to a crossover passage 30 and an exhaust valve 19 that passes exhaust from combustion cylinder 20 to an exhaust port. These connections define a fluid flow path between compression cylinder 10 and combustion cylinder 20 via crossover passage 30.

[0019] The engine 100 further includes a cooling system. The cooling system is shown to include a coolant reservoir 40 coupled to the compression cylinder 10 via a coolant injector 14 that defines a fluid flow path. The cooling system may further include an injector, not shown in FIG. 1 , that injects coolant into the crossover passage 30. The cooling system may include the use of heat transfer via a recuperator. For example, this may include utilizing heat at the exhaust from the combustion cylinder to heat the recuperator. This may include utilizing a recuperator to transfer heat escaping from the split-cycle internal combustion engine 100. The engine 100 may further include a fuel reservoir 80 coupled to the combustion cylinder 20 via a fuel injector 82 such that a fluid flow path is defined between the fuel reservoir 80 and the combustion cylinder 20.

[0020] The engine 100 includes a controller 60 and multiple sensors, shown in black dotted lines, coupled to the controller 60. However, the illustrated sensors are merely exemplary, and it is understood that a different number of sensors may be provided and that the sensors may be located in different positions. For example, the intake 8 may further include a temperature sensor. The sensors may be coupled to the controller 60 via physical wiring or may be wirelessly connected. In the example shown in FIG. 1 , a compression sensor 11 is present in the compression cylinder 10. The compression sensor 11 may be mounted, for example, near the intake 8 or near the coolant injector 14. The compression sensor 11 may include a temperature sensor. The exemplary engine 100 shown in FIG. 1 further includes a combustion sensor 21 in the combustion cylinder 20. The compression sensor 21 may include a temperature sensor or a pressure sensor. Additionally, a crossover sensor 31 is illustrated in the crossover passage 30. The crossover sensor 31 may include a temperature sensor or a pressure sensor. Engine 100 further includes a crank sensor 71 mounted on crankshaft 70. The crank sensor may provide an indication of torque demand from the engine. Additionally, an exhaust sensor 91 is shown downstream of exhaust valve 19 of combustion cylinder 20. Exhaust sensor 91 may include a temperature sensor, a pressure sensor, or a lambda sensor configured to provide an indication of NOx concentration in the exhaust of the engine. In some examples, coolant liquid reservoir 40 may further include a sensor to measure a quantity, such as mass, of liquid contained in reservoir 40. Controller 60 is further coupled to coolant injector 14, fuel injector 82, and / or reservoir 80.

[0021] The plurality of sensors are configured to send at least one signal to the controller 60 to provide an indication of at least one parameter associated with the engine 100. The engine 100 parameters may include the temperature of the working fluid within the engine (e.g., at different locations, such as the exhaust, the compression cylinder 10, the crossover passage 30, etc.). This may include the pressure of the working fluid within the engine, the demand on the engine, the amount of NOx production within the engine, the timing of the opening and closing of the intake valve 18, and the timing of fuel injection into the combustion cylinder. The engine 100 parameters may include an indication of engine knock, which may be based, for example, on received audio signals of engine operation. Engine knock, which may occur when fuel does not ignite at the proper time during a piston's cycle, may be detected based on listening to engine noises, and the indication of engine knock may be considered an engine parameter.

[0022] 1 , the compression sensor 11 is configured to measure at least one parameter associated with the compression cylinder 10. The combustion sensor 21 is configured to measure at least one parameter associated with the combustion cylinder 20. The crossover sensor 31 is configured to measure at least one parameter associated with the crossover passage 30. Additionally, the crank sensor 71 is configured to measure the RPM of the engine 100, and the exhaust sensor 91 is configured to measure at least one parameter of the exhaust exiting the exhaust valve 19 of the combustion cylinder 20. In this manner, the measurement of the at least one parameter provides an indication of the peak temperature of combustion in the combustion cylinder 20. Each sensor may provide the indication of the peak temperature to the controller 60 so that the controller 60 can determine the peak temperature of combustion in the combustion cylinder 20.

[0023] Engine 100 is configured such that air is drawn into compression cylinder 10 through intake port 8 of compression cylinder 10. Compression piston 12 is positioned to compress the air, and coolant liquid may be added to compression cylinder 10 during the compression phase. Crossover passage 30 is positioned to receive working fluid via outlet 9 and deliver it to combustion cylinder 20 via intake valve 18. Engine 100 is further configured to add fuel from fuel reservoir 80 to the working fluid in combustion cylinder 20 via fuel injector 82, combust the fuel-working fluid mixture (e.g., by operation of an ignition source, not shown), and extract useful power through rotation of crankshaft 70.

[0024] The fuel reservoir 80 is connected to the controller 60 such that the controller 60 controls the supply of fuel to the combustion cylinder 20. In some examples, the controller 60 is configured to determine the amount of fuel to be injected based on a received indication of at least one engine parameter 100. For example, the controller 60 may be configured to obtain an indication of the at least one parameter from a signal indicative of a peak combustion temperature received from the exhaust sensor 91 or a signal indicative of engine demand received from the crank sensor 71.

[0025] During operation, controller 60 is configured to receive an indication of a peak combustion temperature. The signal is received from at least one of the sensors shown in FIG. 1 . For example, controller 60 may receive an indication of the temperature of the exhaust from exhaust sensor 91. If the controller receives an indication from a sensor that does not directly measure the peak combustion temperature, the controller determines an estimate of the peak combustion temperature in combustion cylinder 20 based on the received indication. For example, the received indication of the temperature in the exhaust may be used to infer the peak combustion temperature in the combustion cylinder. If the controller receives an indication from a sensor that directly measures the peak combustion temperature (e.g., combustion sensor 20), the controller may use the peak temperature indication rather than separately determining the peak temperature.

[0026] The peak temperature of combustion typically occurs toward the end of the piston 22's movement from top dead center (TDC) to bottom dead center (BDC). If the controller 60 receives an indication from a sensor that cannot directly measure this peak temperature (e.g., a sensor not located within the combustion cylinder 20), the controller 60 may be configured to determine an estimate of the peak temperature based on the received indication. This may include the use of a mathematical model capable of estimating the peak temperature of combustion based on values ​​of engine parameters (e.g., the temperature of the working fluid in the crossover passage). For example, such a model may include determining values ​​based on historical data for heat generation throughout the engine's cycle and / or for heat dissipation and resulting cooling after combustion occurs. The sensor may measure system and / or working fluid parameters (e.g., temperature, pressure), which may be the indication provided to the controller 60. Based on this indication, the controller 60 may use known thermodynamic relationships to determine an estimate of the peak temperature within the combustion cylinder 20. For example, based on received indications of pressure and temperature of the working fluid, the concentration of the working fluid may be determined (eg, based on an equation of state linking pressure, temperature, and concentration).

[0027] In one example, the controller 60 may receive an indication of the peak combustion temperature from a sensor that measures a parameter of the working fluid after combustion. For example, this measurement may be performed by the exhaust sensor 91. The exhaust sensor 91 may be configured to measure the temperature of the working fluid in the exhaust. The post-combustion temperature provides an indication of the peak combustion temperature. An estimate of the peak combustion temperature may be determined based on historical data, for example, the post-combustion temperature using a look-up table. It will be appreciated that this may provide a value that closely approximates the peak temperature of the working fluid during combustion because the time when the working fluid leaves the combustion cylinder 20 and passes through the exhaust valve 19 is shortly after the peak combustion temperature has been reached. Therefore, the exhaust sensor 91 may measure the post-combustion temperature and, based on this measurement, provide an indication of the peak combustion temperature to the controller 60. The controller 60 then measures the peak combustion temperature based on the post-combustion temperature. The peak combustion temperature is higher than the post-combustion temperature. The peak combustion temperature may be determined using a look-up table that includes a correlation between post-combustion temperature values ​​and corresponding peak combustion temperature values.

[0028] In another example, the controller 60 may receive an indication of the peak temperature of combustion from a sensor that measures a parameter of the working fluid prior to combustion. For example, this measurement may be performed by a supply sensor. Here, supply sensor may refer to any sensor that provides an indication of an engine parameter or working fluid prior to combustion. For example, the indication may be from the compression sensor 11 or the crossover sensor 31. The crossover sensor 31 may be configured to measure the temperature of the working fluid in the crossover passage 30 prior to flowing into the combustion cylinder 20. The crossover sensor 31 may therefore measure the temperature of the working fluid prior to combustion and provide an indication of this temperature to the controller 60. The controller 60 then determines an estimate of the peak temperature of combustion in the combustion cylinder 20 based on the pre-combustion temperature. The pre-combustion temperature is lower than the peak combustion temperature. The controller 60 may determine the estimate of the peak combustion temperature using a look-up table that includes a correlation between pre-combustion temperature values ​​and corresponding peak combustion temperature values. The correlation value may be determined using a mathematical model that models the thermodynamics of the system for temperature prediction. This value may include an empirically determined value.

[0029] It will be appreciated that the lookup table used in any of the examples may include other parameters. The lookup table may enable the controller 60 to determine an estimate of the peak temperature of combustion based on the current conditions of the engine 100 and the temperature of the working fluid (e.g., pre- or post-combustion temperature). For example, one of the other parameters may include an indication of demand on the engine 100, which may be determined based on a signal received from the crank sensor 71. One parameter may include a timer indicating the duration the engine 100 has been running. This may include an indication of the temperature of the engine; during engine start-up, the operating temperature is lower while the engine warms up. Thus, the duration the engine has been running may provide an indication of the expected temperature of the engine itself. One parameter may include an indication of the temperature of the entire engine 100. It will be appreciated that the other parameters may include any suitable parameter that may affect the determination of the peak temperature of combustion in the combustion cylinder 20. For example, during start-up of engine 100, combustion cylinder 20 may be cooler than during normal operation, and the increase in temperature of the working fluid between the pre-combustion temperature and the peak combustion temperature may be smaller than when combustion cylinder 20 heats up after extended use or during times of high demand. Based on an indication of the temperature of engine 100 (e.g., combustion cylinder 20), or, for example, based on a timer indicating how long engine 100 has been running, a correlation from pre-combustion temperature to peak combustion temperature may provide a more accurate estimate of the peak temperature of combustion in combustion cylinder 20.

[0030] Controller 60 is configured to control the cooling system to cool the working fluid in response to determining that the temperature of the working fluid exceeds a selected threshold. During start-up of engine 100, engine 100 operates at a lower temperature, and therefore controller 60 may determine that the estimated peak temperature of combustion is significantly lower than the selected threshold. In this case, controller 60 may control the cooling system so that little or no cooling is provided.

[0031] As the engine 100 progresses from a start-up state to a normal operating mode, the controller 60 is configured to determine the peak combustion temperature and control the cooling system to regulate the temperature of the working fluid. Control of the cooling system is based on a feedback loop that includes routine monitoring of the peak combustion temperature and controlling the cooling of the working fluid so that the peak combustion temperature does not exceed a selected threshold. In response to determining that the peak combustion temperature exceeds a selected threshold, the controller 60 is configured to operate the cooling system to increase cooling of the working fluid. In the example shown in FIG. 1 , this includes controlling the coolant injector 14 to inject more coolant into the compression cylinder 10. However, it will be appreciated that other methods of controlling the temperature of the working fluid (e.g., by heat conduction using a recuperator) may also be provided. As the working fluid in the compression cylinder 10 is compressed, a portion of the heat rise of the working fluid may be absorbed by the injected coolant. The coolant absorbs a certain amount of heat to exceed the latent heat of vaporization, which acts to reduce the temperature rise in the combustion cylinder 20. Thus, the controller 60 can control the heat of the working fluid by controlling the amount of coolant injected into the combustion cylinders 20. In particular, the controller 60 can affect the heat of the working fluid in the crossover passage 30 before it enters the combustion cylinders 20.

[0032] The selected threshold may include a criterion for peak combustion temperature. The controller may determine whether the criterion is met based on a comparison including the estimated peak combustion temperature and the criterion. The selected threshold may be a maximum temperature value above which peak combustion temperatures do not meet the criterion. The selected threshold value may be selected to suppress the formation of NOx compounds. The controller may compare the peak combustion temperature value to the selected threshold, where the comparison is based on an average value of peak combustion temperatures, i.e., a "global" value of peak temperatures across the cylinder. In another example, the controller may compare the peak combustion temperature value to the selected threshold, where the comparison is based on a local peak value of peak combustion temperature. The local peak value may include the highest peak combustion temperature value in any region of the combustion cylinder 20. In some examples, the selected threshold may include an indication of both values. The selected threshold may require a temperature of 2200 Kelvin or less, may require a temperature less than 2150 Kelvin, may require a temperature less than 2125 Kelvin, may require a temperature less than 2100 Kelvin, may require a temperature less than 2075 Kelvin, may require a temperature less than 2050 Kelvin, may require a temperature less than 2000 Kelvin, or may require a temperature less than 1900 Kelvin. It will be appreciated that this value may depend on the equivalence ratio of the working fluid and fuel mixture and may therefore vary.

[0033] The controller 60 controls the cooling system to adjust the temperature of the working fluid provided to the combustion cylinder 20 in response to determining that the peak temperature of combustion exceeds a selected threshold. As previously described, the temperature is adjusted using the cooling system. In one example, this may be done by increasing the amount of coolant injected into the compression cylinder 10, but may also or alternatively be done by controlling heat transfer away from the recuperator in the crossover passage. The controller 60 may be configured to determine the degree of cooling based on the determined indication of the peak temperature of combustion. The cooling system may be operated continuously such that the amount of coolant injected is proportional to the amount of cooling required to cool the working fluid temperature below the selected threshold. The cooling system may be operated individually such that a first amount of coolant is injected above a first selected threshold and a second amount of coolant is injected above a second selected threshold. There may be multiple such thresholds.

[0034] The controller 60 may control the split-cycle internal combustion engine 100 so that the combustion process is carried out at a lower temperature to reduce the production of NOx compounds by controlling the cooling system to adjust the peak temperature of combustion within the combustion cylinder 20.

[0035] Although the controller has been described as controlling the cooling system to inject more coolant, it will be appreciated that similar results can be achieved in other ways. For example, this could be achieved by injecting a different type of coolant or injecting coolant at a different temperature. It will further be appreciated that the sensor is configured to provide the controller 60 with an indication of the peak temperature of combustion. However, this indication does not necessarily have to include temperature, but may include a measurement of any suitable thermodynamic parameter from which the peak temperature of combustion can be determined. For example, a temperature value may be determined from a pressure value using known thermodynamic relationships.

[0036] In another aspect, the split-cycle internal combustion engine 100 of FIG. 1 may operate to regulate the temperature of the working fluid in the combustion cylinder 20 using the timing of the intake valve 18. The intake valve 18 is operable to move from a closed state in a first position during the piston's cycle to an open state in a second position during the piston's cycle. When the intake valve 18 is open, working fluid in the crossover passage 30 enters the combustion cylinder 20, and when the intake valve 18 is closed, no working fluid enters. In operation, the controller 60 may select between the first and second positions based on selected thresholds and / or cooling thresholds. The two positions may be selected to be separated by a selected time period, which may be fixed as a constant and / or variable. Combustion in the combustion cylinder 20 typically occurs at or near the piston's TDC position during the cycle. Therefore, the first position is selected to be before TDC so that the working fluid in the crossover passage 30 has time to enter the combustion cylinder 20 before combustion occurs. The second position may be selected to be at or before TDC so that combustion exerts a greater force on the piston. This is because combustion causes the working fluid to expand, moving the combustion piston 22 toward BDC. If the intake valve remains open during combustion, some of the working fluid may flow back into the crossover passage rather than exerting a greater force on the combustion piston 22. Therefore, if the second position is selected so that the intake valve closes before the expansion of the working fluid occurs, a greater force is applied to the combustion piston 22.

[0037] Because the first position is before TDC, the working fluid in the combustion cylinder 20 is compressed somewhat before combustion occurs. This increases the temperature of the working fluid. Because the temperature of the working fluid before combustion affects the peak temperature of combustion in the combustion cylinder 20, the controller 60 can adjust the peak temperature of combustion in the combustion cylinder 20 by controlling the temperature increase in the combustion cylinder 20 caused by this compression. The amount of temperature increase caused by compression in the combustion cylinder 20 is determined by the first position. The closer the first position is to BDC, the greater the amount of heating of the working fluid. Therefore, the controller 60 may select the first position based on a determined amount of heating required. This may be determined based on the determined peak temperature of combustion in the combustion cylinder 20, and the working fluid is then additionally heated a desired amount to achieve a selected temperature before combustion so that the peak temperature of combustion falls within a selected range.

[0038] For example, in response to determining that the estimated peak combustion temperature exceeds a selected threshold, the controller 60 selects the first position that is later in the piston's cycle. In response to determining that the peak combustion temperature is below a cooling threshold, the controller 60 selects the first position that is earlier in the piston's cycle so that the working fluid can receive more heat. Similarly, the controller 60 may control the second position based on the peak combustion temperature, the cooling threshold, and the selected threshold.

[0039] In another aspect, the split-cycle internal combustion engine 100 of FIG. 1 may operate using timing of fuel injection by the fuel injector 82 to regulate the temperature of the working fluid within the combustion cylinder 20. The injection of fuel may occur at an injection location in the piston's cycle. The injection may occur over a set period of time or a variable period of time, which may be based on the amount of fuel injected. The controller 60 is configured to select the injection location based on the determined peak combustion temperature estimate. For example, the controller 60 may control the fuel injector 82 to inject fuel at a late injection location in the piston's cycle in response to determining the peak combustion temperature estimate above a selected threshold. The late injection location may include a location in the piston's cycle that is later than the current injection location. The controller 60 may control the fuel injector 82 to inject fuel at an early injection location in the piston's cycle in response to determining the peak combustion temperature estimate below a cooling threshold. The early injection location may include a location in the piston's cycle that occurs earlier than the current injection location.

[0040] Typically, combustion occurs at or shortly after the TDC position of the combustion piston 22. By controlling combustion to occur at TDC, the combustion piston 22 is subjected to a longer-lasting expansion force as it returns to its BDC position. The volume of the combustion cylinder 20 defined by the position of the combustion piston 22 changes during the piston stroke and is smallest at the TDC position of the combustion piston 22. Combustion at this TDC position may result in greater working fluid expansion than combustion later in the piston's cycle. Combustion near TDC may result in a greater temperature change from the onset temperature than combustion after TDC. As a result, the peak temperature of combustion within the combustion cylinder 20 may be higher for combustion initiated earlier. Combustion cannot occur without fuel.

[0041] The controller 60 is configured to control the fuel injector 82 to inject fuel into the combustion cylinder 20 at an injection position in the piston's cycle. The controller may delay the injection of the fuel so that it is injected later in the piston's cycle (e.g., after TDC). Based on the determined estimate of the peak temperature of combustion in the combustion cylinder 20, the controller may determine that the estimate of the peak temperature is too high and that NOx may be produced. As a way of regulating the temperature in the combustion cylinder 20, the controller may delay the injection of fuel so that combustion occurs later in the piston's cycle. This may reduce the peak temperature of combustion and reduce NOx production.

[0042] In another embodiment, the split-cycle internal combustion engine 100 of FIG. 1 may operate using a controller 60 to control the cooling system to adjust the peak temperature of the working fluid supplied to the combustion cylinder 20 based on an estimate of the peak temperature of combustion in the combustion cylinder 20. The controller 60 may use the estimate to ensure that the peak temperature of combustion in the combustion cylinder 20 falls within a selected range. In particular, during normal operation of the engine 100, the controller may select the selected range such that the peak temperature of combustion in the combustion cylinder does not exceed a selected threshold and / or fall below a cooling threshold. The selected range may be selected to be a range of values ​​between the cooling threshold and the selected threshold. This allows the controller 60 to control the operation of the engine such that both efficiency and NOx production meet selected criteria.

[0043] The controller 60 may determine an estimate of the peak combustion temperature based on the received indication of the engine parameters. For example, the controller 60 may determine the estimate based on the received indication of the engine demand. In this case, the controller 60 may predict an estimate of the peak combustion temperature to be reached in the combustion cylinder 22 based on the engine demand indication (e.g., an indication of the temperature of the working fluid supplied to the combustion cylinder 22).

[0044] This prediction may be based on historical data associated with engine 100. For example, controller 60 may access a look-up table containing correlations between one or more values ​​for at least one engine parameter and corresponding peak temperature estimates. Controller 60 may include a machine learning component that provides a model for peak combustion temperature prediction based on input data about the engine (e.g., engine parameters or a log of engine measurements since engine start-up). This machine learning component may be "trained" on data with known peak combustion temperatures associated with the input data. This allows the machine learning component's predictive model to learn and update based on the training data, providing a more reliable and accurate system for predicting peak temperatures. Based on this estimate, the controller may control the cooling system to ensure that the peak combustion temperature in combustion cylinder 20 falls within a selected range.

[0045] The split-cycle internal combustion engine 100 of Figure 1 may regulate the temperature of the working fluid according to the examples described above. Temperature regulation may also be based on a combination of the examples described above.

[0046] Figure 2 illustrates a second example split-cycle internal combustion engine 100 configured to control peak combustion temperatures below a selected threshold. Because engine 100 of Figure 2 is similar to engine 100 of Figure 1, components that perform substantially the same functions are designated with the same reference numerals and will not be described again.

[0047] The split-cycle internal combustion engine 100 of FIG. 2 further includes a reactivity adjuster 85. The reactivity adjuster 85 is connected to the controller 60 such that the controller 60 may control the operation of the reactivity adjuster 85. The reactivity adjuster 85 is operable to adjust the reactivity of the fuel used during the combustion process. The reactivity adjuster 85 is illustrated as operable to affect the fuel (e.g., in the fuel reservoir 80) injected into the combustion cylinder 20. The reactivity adjuster 85 is further illustrated as operable to directly affect the fuel in the combustion cylinder 20. The reactivity adjuster 85 is operable to increase the ignition ability of the fuel. This may include at least one of increasing the reactivity of the fuel and / or providing additional means to ignite the fuel in the combustion cylinder 20. The controller 60 may further control the operation of the reactivity adjuster 85 in response to determining that the reactivity of the fuel is above an excess reactivity threshold. This may help reduce NOx formation because an over-reactive fuel may result in higher peak combustion temperatures.

[0048] In the illustrated example, the reactivity adjuster 85 includes a system for directing electromagnetic radiation (e.g., laser or microwave radiation) at the fuel to provide an additional ignition source for the fuel in the combustion cylinder 20. This may provide a more precise ignition mechanism and allow the fuel to ignite under undesirable ignition conditions, such as when the combustion cylinder 20 is below the ignition threshold temperature. The controller 60 may be configured to control the reactivity adjuster 85 to provide the additional ignition source for the fuel in response to determining that the temperature in the combustion cylinder 20 and / or the temperature of the working fluid is below the ignition threshold. The reactivity adjuster 85 may also include a selective energy transfer system. The selective energy transfer system may provide targeted radiation to certain compounds present in the fuel-working fluid mixture to enhance reaction rates. This may include targeted radiation to decompose compounds (e.g., CH4 (methane)) for improved combustion so that combustion occurs at a lower onset temperature and peak combustion temperatures, thereby reducing NOx production.

[0049] In some examples, reactivity moderator 85 may include a system for supplying an oxidizer or free radicals to the fuel. This supply may be provided within combustion cylinder 20 or within fuel reservoir 80 (e.g., prior to injection of the fuel into combustion cylinder 20). The provision of an oxidizer may allow a higher percentage of the fuel to ignite, improving the likelihood of initial ignition of the fuel. For example, suitable oxidizers include oxygen or ozone, although it will be understood that any suitable oxidizer may be added.

[0050] The controller 60 is configured to receive an indication of at least one of the pressure, concentration, and temperature of the working fluid and, based thereon, determine ignition parameters for the working fluid. The determined ignition parameters may provide an indication of the ignition ability of the fuel. For example, the ignition parameters may provide an indication of the intended proportion of the fuel to ignite. The controller 60 is configured to determine the ignition parameters based on the received indication. For example, this may include using a lookup table to identify values ​​for the ignition parameters based on one or more values ​​of thermodynamic properties of the working fluid. These values ​​may be determined theoretically and / or empirically. For example, the controller 60 may identify that when the fuel is cold, it is less likely to ignite, and therefore, in response to receiving an indication that the temperature of the working fluid is low, determine a low value for the ignition parameters.

[0051] The controller 60 is configured to operate the reactivity adjuster 85 in response to determining that the ignition parameter is below the ignition threshold. Operation of the reactivity adjuster 85 increases the value of the ignition parameter, thereby contributing to improving the likelihood that the fuel will ignite. The controller 60 may be configured to determine the degree of operation of the reactivity adjuster 85 based on the determined ignition parameter. For example, the degree of operation of the reactivity adjuster 85 may be determined based on the magnitude of the difference between the ignition parameter and the ignition threshold. There may be multiple ignition thresholds, and the controller 60 may determine the degree of operation of the reactivity adjuster 85 based on which threshold the ignition parameter meets. The reactivity adjuster 85 may be particularly beneficial during start-up of the engine 100 when the ignition parameter is below or significantly below the ignition threshold. For example, the temperature of the combustion cylinder 20 may be very low, and operation of the reactivity adjuster 85 allows the fuel to ignite and combustion to occur even at much lower temperatures.

[0052] FIG. 3 shows an exemplary temperature-entropy diagram for the operation of the split-cycle internal combustion engine shown in FIG. 1 or FIG. 2. The dotted line represents the engine's cycle without cooling, and the solid line represents the cycle with cooling. This diagram is based on an approximation of an engine using a nitrogen-only cycle. These cycles output the same amount of heat. For the cycle with added coolant, the bottom left point shows lower values ​​for both temperature and entropy compared to the cycle without cooling. This is due to the increased mass and decreased temperature resulting from the addition of coolant. Therefore, the top right point for the cycle with cooling shows lower temperature and entropy than the cycle without cooling. This point represents the peak combustion temperature. The amount of cooling may be controlled to keep this peak combustion temperature below a selected threshold. This reduces NOx production while avoiding a concomitant loss of engine efficiency due to the same amount of heat release. This is because the ratio between the initial and final pressures of the combustion cylinder may be the same for both the cycle with and without cooling, and engine cycle efficiency is determined based on this ratio. The slope of the line extending from the upper left point to the upper right point of each cycle indicates the efficiency of conversion from thermal energy to pressure. The shallower the slope, the higher the conversion efficiency. As shown in Figure 3, the cycle with cooling has a shallower slope, which may indicate a higher efficiency of conversion from thermal energy to pressure.

[0053] Figure 4 shows an example temperature-entropy diagram of the operation of the split-cycle internal combustion engine of Figure 3, with isobars added. The isobars indicate that the ratio of final pressure to initial pressure of combustion is the same for both the cooled and uncooled cycles. As a result, both cycles operate at the same level of engine efficiency. However, because the "cooled" cycle is controlled to have a lower temperature than the uncooled cycle, the maximum temperature of combustion may be lower. This, in turn, may reduce the production of NOx and / or particulates.

[0054] FIG. 5 is a graph showing example onset temperatures and corresponding end temperatures for the combustion of n-dodecane, methane (CH), and isooctane in a combustion relationship. The graph also indicates the equivalence ratio values ​​for each of these fuels at the onset temperature. The graph also shows the end temperature range above which NOx typically forms, with a line at a final temperature of approximately 2200 Kelvin. Typically, the temperature value for NOx formation is the same for each fuel listed herein. For example, the selected threshold may be chosen based on typical values ​​for the temperature at which NOx formation occurs. The graph also shows the onset temperature range above which complete combustion of the fuel typically occurs. As shown, this range extends from approximately 690 Kelvin to approximately 1600 Kelvin. For example, the cooling threshold may be selected based on the lower end of the range above which complete combustion occurs. This is because if the onset temperature of combustion falls below this lower value, the fuel may not completely ignite and burn, resulting in inefficient combustion.

[0055] The graph shows that when N-dodecane is the fuel and the onset temperature ranges from 690 Kelvin to 820 Kelvin, complete combustion can occur without the final temperature of combustion entering the NOx region. The graph shows this occurs over the equivalence ratio temperature range of 0.4-0.48. For equivalence ratios of 0.5 and 0.52, at low onset temperatures within this temperature range, the final temperature of combustion does not reach the NOx region. However, at high onset temperatures, the final temperature of combustion can reach the NOx region. As an example, at an equivalence ratio of 0.5 and an onset temperature of approximately 690 Kelvin, the final temperature of combustion is approximately 2100 Kelvin, which is not within the NOx region. As another example, at an equivalence ratio of 0.5 and an onset temperature of 820 Kelvin, the final temperature of combustion is approximately 2220 Kelvin, which is within the NOx region. This shows that by controlling the onset temperature within a certain range, the final temperature of combustion for a given equivalence ratio can be prevented from entering the NOx region, thereby suppressing NOx production.

[0056] As shown in the graph, the equivalence ratio is the fuel-to-air equivalence ratio (φ). For dodecane, when the fuel-to-air equivalence ratio is 0.4, the air-to-fuel equivalence ratio (λ) is 2. The fuel-to-air equivalence ratio may be selected based on a lean threshold. The lean ratio may be defined based on the fuel-to-air equivalence ratio. For example, the lean threshold may be selected based on a fuel-to-air equivalence ratio of 0.4, which may be 0.42, 0.44, 0.46, 0.48, or 0.5. If the fuel and working fluid mixture is leaner than a certain value, particulate generation may occur. The lean threshold may be selected based on this value. Particulate generation may include the generation of soot in the engine. The leanness of the working fluid and fuel mixture may be controlled so that the mixture is lean enough to avoid particulate generation. Particulate generation typically occurs as a result of a fuel "rich zone," where the fuel is not mixed with enough oxygen, resulting in incomplete combustion. Additionally, combustion can be controlled to avoid the production of compounds HC and CO, the presence of which typically leads to inefficient combustion. The equivalence ratio can be based on a local equivalence ratio, an average equivalence ratio for the combustion cylinder, or both.

[0057] In another aspect, the engine 100 of either FIG. 1 or FIG. 2 may be operative such that the controller 60 controls at least one thermodynamic property of the working fluid in the crossover passage 30 so that the flow of working fluid into the combustion cylinders 20 meets selected criteria. In particular, the controller 60 is configured to control at least one of the pressure and concentration of the working fluid in the crossover passage 30 so that the working fluid enters the combustion cylinders 20 at a velocity that exceeds a velocity threshold. The velocity threshold is selected so that the working fluid entering the combustion cylinders 20 achieves a lean mixture of fuel and the working fluid within the combustion cylinders 20. For example, the working fluid may enter through the intake valve 18 at a velocity that generates a large amount of turbulence and achieves a high flow of fluid over the fuel injectors 82. When fuel is injected into the combustion cylinders 20, the fuel may be favorably dispersed according to the flow velocity of the working fluid. This may reduce the number of “pockets of fuel” that burn at a higher temperature than ambient, and therefore reduce the amount of NOx and / or soot formed. This also allows the fuel to react completely, leaving no pyrolysis products, and therefore allows a higher proportion of the fuel to be consumed to produce useful power.

[0058] In operation, the controller 60 is configured to receive an indication of at least one of the pressure and concentration of the working fluid in the crossover passage 30. The indication may be received from the crossover sensor 31, which may be configured to measure a suitable thermodynamic parameter from which the pressure and / or concentration may be determined. The controller 60 may determine the pressure and / or concentration using a look-up table or mathematical model correlating the measured parameter with a corresponding value of the pressure and / or concentration. The controller 60 is configured to compare the determined value with an input threshold value. The input threshold value may be a value of the measured parameter in the crossover passage that is expected to cause the working fluid to enter the combustion cylinder 20 at a velocity greater than or equal to the velocity threshold value. The controller 60 is configured to control the pressure and / or concentration of the working fluid based on the comparison. The pressure and / or concentration of the working fluid is controlled so that the fluid enters the combustion cylinder 20 at a velocity greater than the velocity threshold value.

[0059] The velocity threshold is selected to be a velocity that induces turbulent flow of fluid into and within the combustion cylinder 20 to achieve a lean mixture of fuel with the working fluid. The velocity threshold value may be determined based on the pressure and / or concentration of the working fluid in the crossover passage 30, and may also be determined based on the dimensions of the combustion cylinder 20 and the intake valve 18, and may be used to model the flow of fluid into the combustion cylinder 20. Thus, the velocity threshold value is selected so that the flow of working fluid into the combustion cylinder 20 at the velocity threshold results in a lean mixture of fuel. The lean mixture of fuel is selected so that complete combustion occurs and particulate generation is suppressed. Optionally, the leanness may be selected so that fuel ignition is staggered over the duration of the combustion stroke, rather than all of the fuel igniting at once, which may result in a more consistent power output from the engine 100. For example, the velocity threshold may be greater than 350 meters per second (m / s), 345 m / s, 343 m / s, 340 m / s, 335 m / s, 330 m / s, 325 m / s, 320 m / s, 310 m / s, or 300 m / s, although it will be appreciated that this value may be significantly higher or lower depending on different engine parameters. For example, pressure or concentration may affect the velocity threshold value. Typically, at these velocities, the fluid flow entering the combustion cylinder 20 will experience choked flow, a supersonic phenomenon that interferes with the flow of working fluid entering the combustion cylinder 20.

[0060] The input threshold value may be selected based on a velocity threshold value and / or a selected level of turbulence within the combustion cylinder 20. For example, the input threshold value may be selected based on empirical data and / or a mathematical model that provides an indication of an associated level of turbulence within the combustion cylinder 20. The input threshold value may be selected such that a working fluid having a pressure and / or density at the input threshold value enters the combustion cylinder 20 at the velocity threshold value.

[0061] The controller 60 is configured to control the pressure and / or concentration of the working fluid in response to determining that the pressure and / or concentration of the working fluid exceeds the input threshold. The controller 60 may use a cooling system to control the pressure and / or concentration of the working fluid. The controller 60 is configured to control operation of the cooling system in response to determining that the pressure and / or concentration is below the input threshold. This may reduce the temperature of the working fluid, thereby achieving greater pressure and / or higher concentration in the crossover passage 30. For example, in an engine 100 at 973 K and 7 MPa, reducing the temperature to 700 K results in a 40% increase in concentration. The extent of operation of the cooling system may be determined based on the extent to which the pressure and / or concentration of the working fluid differs from the input threshold. In the example of FIGS. 1 and 2 , the cooling system includes a coolant injector 14 that injects coolant into the compression cylinder 10 of the engine 100. Operation of the cooling system may include increasing the amount of coolant injected into the compression cylinder 10. The controller 60 may further control the amount of coolant injected based on the determined fluid pressure and / or concentration.

[0062] The increased pressure in the crossover passage 30 increases the pressure differential between the crossover passage 30 and the combustion cylinder 20, thus increasing the velocity of the working fluid flowing into the combustion cylinder 20 as the intake valve 18 to the combustion cylinder 20 moves open. This increase in concentration increases the concentration of oxygen carrying gases within the combustion cylinder 20. This increase in concentration also reduces the initial temperature of the working fluid within the combustion cylinder 20, reducing the likelihood of NOx formation. This increase in concentration increases the mass of the gas, resulting in a higher pressure and a lower temperature rise during combustion. This reduces the peak temperature of combustion, thereby reducing NOx formation.

[0063] Alternatively, the split-cycle internal combustion engine 100 may operate based on selected valve timing, including a timing associated with a first position in the piston's cycle when the intake valve 18 moves from a closed position to an open position and a timing associated with a second position in the piston's cycle when the intake valve 18 moves from an open position to a closed position. The first and second positions may be fixed such that the intake valve 18 moves at the selected positions outside of the control of the controller 60. Accordingly, the controller 60 may determine an input threshold value based on the selected positions. This may include determining the value of the input threshold value based on the engine 100 conditions at each position such that, after the intake valve 18 moves open at the first position, working fluid in the crossover passage 30 at the input threshold value may enter the combustion cylinder 20 at a velocity greater than the velocity threshold value.

[0064] In another aspect, the split-cycle internal combustion engine 100 may operate based on controlling the movement of the intake valve 18 relative to the combustion cylinder 20. The intake valve 18 may move from a closed state to an open state. Movement to the open state includes movement of the valve to provide a cross-sectional area for working fluid in a crossover passage through which the fluid enters the combustion cylinder 20. The intake valve 18 may be configured to move between a closed state and a plurality of open states. The plurality of open states may include a series of discrete states each defining a different cross-sectional area or may include a continuum of states with a continuously changing cross-sectional area. The controller 60 is configured to control the movement of the intake valve 18 to define a selected cross-sectional area for working fluid to enter the combustion cylinder 20.

[0065] The controller 60 is configured to control movement of the intake valve to establish the selected cross-sectional area. The controller is configured to select the selected cross-sectional area such that the working fluid in the crossover passage 30 flows through the cross-sectional area into the combustion cylinder 20 at a velocity above the velocity threshold. The controller 60 may determine the selected cross-sectional area based on received engine parameter indications. For example, the controller 60 may be configured to use a mathematical model (e.g., based on Bernoulli flow) to determine an estimate of the velocity of the fluid flowing into the combustion cylinder 20. The controller 60 may determine, based on the mathematical model or a look-up table, for example, that the cross-sectional area must be limited to the selected cross-sectional area for the working fluid to flow into the combustion cylinder 20 at a velocity below the velocity threshold. Thus, the controller 60 may control the intake valve 18 to move to an open state, which includes opening the valve, but not necessarily to a fully open state. Rather, the valve may be opened to some portion of a fully open state, for example, the intake valve may be moved to a half-open state. The degree to which the intake valve 18 is moved may be based on the received indication of the pressure in the crossover passage 30. For example, if the pressure in the crossover passage 30 is very high, the controller 60 may control the intake valve 18 to open to a fully open condition because, even with a larger cross-sectional area, working fluid may still enter the combustion cylinder 20 at a velocity greater than the velocity threshold. In another example, the controller 60 may determine that the pressure in the crossover passage 30 is not very high and therefore may control the intake valve 18 to open to a slightly open condition where the defined cross-sectional area is very small and the flow of working fluid into the combustion cylinder 20 is much faster.

[0066] The controller 60 is configured to control the valve lift so that the working fluid enters the combustion cylinder at a velocity that exceeds a velocity threshold. The velocity at which the working fluid enters the combustion cylinder may typically be determined as the peak flow velocity that occurs when the intake valve 18 opens, or shortly thereafter. This velocity may be determined based on measurements from an exhaust sensor. For example, if the exhaust sensor determines that NOx and / or particulate production exceeds a threshold level, the flow velocity is too slow. Controlling the movement of the intake valve 18 so that the flow velocity of the working fluid entering the combustion cylinder 20 exceeds the velocity threshold may result in a lean ratio of the air-fuel mixture in the combustion cylinder that exceeds a lean threshold. The lean threshold may suppress particulate generation if the fuel and working fluid are sufficiently mixed to provide sufficient oxygen for each unit of fuel to cause complete combustion and suppress particulate generation. Controlling the flow velocity above the velocity threshold may reduce stress on the fuel injector 82 due to reduced requirements on the fuel-working fluid mixture, which may extend the life of the injector. Additionally, by continuing to open the intake valve 18 at a low lift, the reduced travel distance may reduce the time it takes for the intake valve 18 to move from a closed to an open state, thereby speeding up the process of delivering working fluid from the crossover passage 30 to the combustion cylinder 20. As a result, the intake valve 18 may be opened later in the piston cycle.

[0067] The controller 60 may determine the movement of the intake valve 18 based on data related to the design of the intake valve 18. For example, dimensions such as the valve shape or face friction level may be considered. It will be appreciated that the details (e.g., shape, length, diameter, etc.) of the fluid flow path from the crossover passage 30 to the combustion cylinder 20 may affect the flow rate. The controller 60 may access a look-up table specific to the intake valve 18 when determining the cross-sectional area defined by the intake valve 18 for fluid flow.

[0068] In another aspect, split-cycle internal combustion engine 100 may operate based on variable valve timing, which may include controller 60 selecting the first and second positions based on determined values ​​of pressure and / or concentration of the working fluid such that, after intake valve 18 moves to an open state in the selected first position, the working fluid enters combustion cylinder 20 at a velocity greater than a velocity threshold.

[0069] A method of operating a split-cycle internal combustion engine, such as the split-cycle internal combustion engine 100 of FIGS. 1 and 2, is described below with reference to FIG. 6. The method begins in step 600 and proceeds to step 610, where an indication of a peak temperature is received. As previously described, this indication may be received from one or more sensors and may provide information regarding a parameter of the engine. In step 620, the peak temperature of combustion in the combustion cylinder 20 is determined based on the indication received in step 610. The peak temperature may be determined as previously described. In step 630, the determined peak temperature is compared to a selected threshold. In response to a determination that the peak temperature is below the selected threshold, the method proceeds to step 640, where the peak temperature is compared to a cooling threshold. In step 640, if the determined peak temperature is above the cooling threshold, it is determined that the peak temperature of the engine is within a suitable range. The method then loops back to the beginning, where another peak temperature indication is received. This return may be performed on a variable time scale; for example, instructions may be received at selected time periods, or more frequently during start-up when there is greater variation in the values ​​of the engine parameters. In response to a determination in step 630 that the determined peak temperature exceeds a selected threshold, or in response to a determination in step 640 that the determined peak temperature is below a cooling threshold, the method proceeds to step 650. In step 650, a cooling system is controlled to adjust the temperature of the working fluid based on the determined peak temperature. This temperature may be adjusted to move the peak combustion temperature within a preferred range. The method then returns to step 610. The frequency of received instructions may be higher for the return from step 650 than for step 640.

[0070] A method of operating a split-cycle internal combustion engine, such as the split-cycle internal combustion engine 100 of FIGS. 1 and 2, is described below with reference to FIG. 7. Steps 700-740 of the method correspond to steps 600-640, respectively, of FIG. 6 described above, and therefore will not be described again. In step 750, first and second positions for opening and closing the intake valve are selected to adjust the temperature of the working fluid in response to the determined peak temperature exceeding a selected threshold or in response to the determined peak temperature falling below a cooling threshold. The temperature of the working fluid may be adjusted to move the peak temperature of combustion within a desired range (e.g., between the cooling threshold and the selected threshold).

[0071] A method of operating a split-cycle internal combustion engine, such as the split-cycle internal combustion engine 100 of FIGS. 1 and 2, is described below with reference to FIG. 8. The method begins in step 800 and proceeds to step 810, where an indication of an engine parameter is received. In step 820, an ignition parameter for the fuel is determined based on the indication received in step 810. The ignition parameter may be determined as described above. In step 830, the ignition parameter is compared to an ignition threshold. In response to a determination that the ignition parameter exceeds the ignition threshold, the method proceeds to step 840, where the ignition parameter is compared to an excess reactivity threshold. In response to the ignition parameter being below the excess reactivity threshold, the ignition parameter is deemed to be within a suitable range, and the method loops back to step 810, as described above. In response to either the ignition parameter being below the ignition threshold or above the excess reactivity threshold, the method proceeds to step 850, where a reactivity adjuster is operated, for example, to adjust the working fluid so that the reactivity is within a suitable range for engine operation.

[0072] A method of operating a split-cycle internal combustion engine, such as the split-cycle internal combustion engine 100 of Figures 1 and 2, is now described with reference to Figure 9. Steps 900-940 of the method correspond to steps 600-640, respectively, of Figure 6 described above, and therefore will not be described again. In step 950, an injection location for an injector is selected in response to the determined peak temperature exceeding a selected threshold or in response to the determined peak temperature falling below a cooling threshold. The injection location is selected to regulate the temperature of the working fluid, as described above.

[0073] A method of operating a split-cycle internal combustion engine, such as the split-cycle internal combustion engine 100 of FIGS. 1 and 2, is described below with reference to FIG. 10. The method begins in step 1000 and proceeds to step 1010, where an indication of a peak temperature is received. Based on the indication received in step 1010, an estimate of the peak combustion temperature may be determined, as described above. In step 1030, the cooling system is controlled to keep the peak combustion temperature within a selected range. This step may include increasing and / or decreasing cooling of the working fluid based on whether the peak combustion temperature is below or above the selected range.

[0074] A method of operating a split-cycle internal combustion engine, such as the split-cycle internal combustion engine 100 of FIGS. 1 and 2, is described below with reference to FIG. 11. The method begins at step 1100 and proceeds to step 1110, where an indication of an engine parameter is received. In step 1120, a value of the engine parameter (pressure and / or temperature, in the example of FIG. 11) may be determined based on the engine parameter indication. This determination depends on the content of the indication. This may include using a thermodynamic relationship to process the value of one engine parameter to determine the value of another parameter (pressure or temperature). In step 1130, the determined parameter (pressure and / or temperature) is compared to an input threshold. In response to the parameter being above the input threshold, the working fluid is deemed suitable for use in the combustion cylinders, and the method loops back to 1110. In response to the parameter being within the input threshold, the method proceeds to step 1140, where the parameter (pressure / temperature) of the working fluid is controlled to be within a range suitable for the working fluid to enter the combustion cylinders 20 at a velocity greater than the velocity threshold. The method then loops back to step 1110 .

[0075] A method of operating a split-cycle internal combustion engine, such as the split-cycle internal combustion engine 100 of Figures 1 and 2, is now described with reference to Figure 12. Steps 1200-1230 of the method correspond to steps 1100-1130, respectively, of Figure 11 described above, and therefore will not be described again. In step 1240, the movement of the intake valve is controlled to define the cross-sectional area of ​​the intake valve opening through which working fluid enters the combustion cylinder 20 from the crossover passage 30. The cross-sectional area is selected, as previously described, to allow the working fluid to enter the combustion cylinder 20 at a velocity above the velocity threshold.

[0076] Although NOx has been described, it will be understood that the term NOx may be considered to encompass any suitable nitrogen oxide compound, such as NO or any other combination of nitrogen and oxygen, and is not to be construed as being limited solely to compounds having one nitrogen atom.

[0077] It will be understood that a piston cycle is cyclical, and thus, an occurrence later in a piston cycle may refer to an occurrence later in time. Each piston cycle may be considered to begin with the combustion piston 22 at its bottom dead center ("BDC") position. During the piston cycle, the combustion piston 22 subsequently progresses, moving from the BDC position to the top dead center ("TDC") position, and then returning to the BDC position. Thus, for example, descriptions of an injector injecting fuel earlier / later in the piston cycle or an intake valve opening and closing earlier / later in the piston cycle are based on the piston cycle moving from BDC to BDC.

[0078] With reference to the drawings generally, it will be apparent that schematic functional block diagrams are used to illustrate the functionality of the systems and devices described herein. However, it will be apparent that this functionality need not be divided exactly as shown, and should not be taken to imply any particular structure of hardware other than that described or claimed below. The functionality of one or more components shown in the drawings may be further divided and / or distributed throughout the devices of the present disclosure. In some embodiments, the functionality of one or more components shown in the drawings may be combined into a single functional entity.

[0079] In some examples, one or more memory elements may store data and / or program instructions used to perform the operations described herein. Embodiments of the present disclosure provide a tangible, non-transitory storage medium including program instructions operable to program a processor to perform one or more of the methods described and / or claimed herein and / or to provide a data processing apparatus described and / or claimed herein.

[0080] The operations and apparatus generally described herein may be implemented using fixed logic, such as an assembly of logic gates, or programmable logic, such as software and / or computer program instructions executed by a processor. Other examples of programmable logic include a programmable processor, programmable digital logic (e.g., a field programmable gate array (FPGA), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM)), an application specific integrated circuit (ASIC), or any other type of digital logic, software, code, electronic instructions, flash memory, an optical disk, a CD-ROM, a DVD ROM, a magnetic or optical card, any other type of machine-readable medium suitable for storing electronic instructions, or any combination thereof.

[0081] It will be apparent from the foregoing description that the embodiments shown in the drawings are merely exemplary and encompass features that may be generalized, omitted, or substituted as described and claimed herein. Other examples and variations of the apparatus and methods described herein will be apparent to those skilled in the art in the context of this disclosure.

Claims

1. a compression cylinder containing a compression piston; a combustion cylinder containing a combustion piston; a crossover passage disposed between the compression cylinder and the combustion cylinder to supply working fluid to the combustion cylinder; a reactivity regulator operable to regulate the reactivity of the fuel used during the combustion process; a controller arranged to receive values ​​of at least one of (i) the pressure of the working fluid, (ii) the temperature of the working fluid, (iii) the production of NOx due to combustion, and (iv) the extent of engine knocking in the combustion cylinder; Equipped with the controller is configured to operate the reactivity adjuster to adjust the reactivity of the fuel based on the received value and to determine an ignition parameter associated with the fuel; The adjustment of the reactivity of the fuel includes: operating the reactivity modulator to enhance the reactivity of the fuel in response to determining that the ignition parameter is below an ignition threshold; operating the reactivity controller to reduce the reactivity of the fuel in response to determining that the ignition parameter exceeds an excess reactivity threshold; A split-cycle internal combustion engine comprising:

2. The ignition parameters are: a value for the ability of the fuel to ignite in the combustion cylinder; Including, 10. The split-cycle internal combustion engine of claim 1.

3. The ignition parameters are determined based on the fuel used for combustion.

3. A split-cycle internal combustion engine according to claim 1 or 2.

4. The ignition parameters are: (i) whether the fuel ignites in the combustion cylinder; and (ii) the fraction of the fuel that is to be ignited in the combustion cylinder; Including, A split-cycle internal combustion engine according to any one of claims 1 to 3.

5. the reactivity moderator is operable to improve the ability of the fuel to ignite. A split-cycle internal combustion engine according to any one of claims 1 to 4.

6. the reactivity adjuster is operable to adjust at least one chemical or physical property of the fuel and / or the working fluid supplied to the combustion cylinder to improve the ability of the fuel to ignite. A split-cycle internal combustion engine according to any one of claims 1 to 5.

7. the reactivity moderator is operable to direct electromagnetic radiation toward the fuel to provide an ignition source for the fuel. A split-cycle internal combustion engine according to any one of claims 1 to 6.

8. the reactivity moderator is operable to inject oxidizer into the combustion cylinder to improve the ability of the fuel to ignite. A split-cycle internal combustion engine according to any one of claims 1 to 7.

9. the reactivity moderator is operable to provide a stratified ignition process configured to improve the ability of the fuel to ignite. A split-cycle internal combustion engine according to any one of claims 1 to 8.

10. the reactivity moderator provides at least one of a source of free radicals and a source of ozone to improve the ability of the fuel to ignite; A split-cycle internal combustion engine according to any one of claims 1 to 9.

11. 1. A method of controlling a split-cycle internal combustion engine, the split-cycle internal combustion engine comprising: a compression cylinder containing a compression piston; a combustion cylinder containing a combustion piston; a crossover passage disposed between the compression cylinder and the combustion cylinder to supply working fluid to the combustion cylinder; a reactivity regulator operable to regulate the reactivity of the fuel used during the combustion process; Equipped with The control method includes: receiving values ​​for at least one of (i) the pressure of the working fluid, (ii) the temperature of the working fluid, (iii) NOx production from combustion, and (iv) the extent of engine knocking in the combustion cylinder; controlling the reactivity modulator to increase the reactivity of the fuel based on the received value and determining an ignition parameter associated with the fuel; and The adjustment of the reactivity of the fuel includes: operating the reactivity modulator to enhance the reactivity of the fuel in response to determining that the ignition parameter is below an ignition threshold; operating the reactivity controller to reduce the reactivity of the fuel in response to determining that the ignition parameter exceeds an excess reactivity threshold; Including, A method for controlling a split-cycle internal combustion engine, comprising:

12. 12. The method of claim 11, comprising program instructions configured to program a processor to implement the control method of claim 11.

1. A computer program product comprising:

Images