Patent Publication Number: US-9422902-B2

Title: Heat transfer systems for internal combustion engines and methods

Description:
If an Application Data Sheet (ADS) has been filed on the filing date of this application, it is incorporated by reference herein. Any applications claimed on the ADS for priority under 35 U.S.C. §§119, 120, 121, or 365(c), and any and all parent, grandparent, great-grandparent, etc. applications of such applications, are also incorporated by reference, including any priority claims made in those applications and any material incorporated by reference, to the extent such subject matter is not inconsistent herewith. 
     CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is related to and/or claims the benefit of the earliest available effective filing date(s) from the following listed application(s) (the “Priority Applications”), if any, listed below (e.g., claims earliest available priority dates for other than provisional patent applications or claims benefits under 35 USC §119(e) for provisional patent applications, for any and all parent, grandparent, great-grandparent, etc. applications of the Priority Application(s)). In addition, the present application is related to the “Related Applications,” if any, listed below. 
     Priority Applications 
     None 
     If the listings of applications provided above are inconsistent with the listings provided via an ADS, it is the intent of the Applicant to claim priority to each application that appears in the priority applications section of the ADS and to each application that appears in the Priority Applications section of this application. 
     All subject matter of the Priority Applications and the Related Applications and of any and all parent, grandparent, great-grandparent, etc. Applications of the Priority Applications and the Related Applications, including any priority claims, is incorporated herein by reference to the extent such subject matter is not inconsistent herewith. 
     TECHNICAL FIELD 
     The present disclosure relates generally to heat transfer systems configured to absorb and/or transfer heat from a combustion chamber of an internal combustion engine. The heat transfer systems may also be configured to reintroduce previously absorbed and/or transferred heat into the internal combustion engine via a fuel injector or another device. Heat transfer systems of the present disclosure may also be configured for retrofitting existing internal combustion engines. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments disclosed herein will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. These drawings depict only typical embodiments, which will be described with additional specificity and detail through use of the accompanying drawings in which: 
         FIG. 1  is a schematic illustration of a portion of an embodiment of a spark-ignition internal combustion engine comprising an embodiment of a heat transfer system. 
         FIG. 2A  is a schematic illustration of a portion of a cylinder during an intake stroke of the portion of the embodiment of the engine of  FIG. 1 . 
         FIG. 2B  is a schematic illustration of a portion of a cylinder during a compression stroke of the portion of the embodiment of the engine of  FIG. 1 . 
         FIG. 2C  is a schematic illustration of a portion of a cylinder during a power stroke of the portion of the embodiment of the engine of  FIG. 1 . 
         FIG. 2D  is a schematic illustration of a portion of a cylinder during an exhaust stroke of the portion of the embodiment of the engine of  FIG. 1 . 
         FIG. 3  is a schematic illustration of the portion of the embodiment of the engine of  FIG. 1  comprising another embodiment of a heat transfer system. 
         FIG. 4  is a schematic illustration of the portion of the embodiment of the engine of  FIG. 1  comprising another embodiment of a heat transfer system. 
         FIG. 5  is a schematic illustration of a portion of an embodiment of a rotary internal combustion engine comprising an embodiment of a heat transfer system. 
         FIG. 6A  is a schematic illustration of a portion of a cylinder during an intake stroke of the portion of the embodiment of the engine of  FIG. 5 . 
         FIG. 6B  is a schematic illustration of a portion of a cylinder during a compression stroke of the portion of the embodiment of the engine of  FIG. 5 . 
         FIG. 6C  is a schematic illustration of a portion of a cylinder during a power stroke of the portion of the embodiment of the engine of  FIG. 5 . 
         FIG. 6D  is a schematic illustration of a portion of a cylinder during an exhaust stroke of the portion of the embodiment of the engine of  FIG. 5 . 
         FIG. 7  is a schematic illustration of a portion of an embodiment of a compression-ignition internal combustion engine comprising an embodiment of a heat transfer system. 
         FIG. 8A  is a schematic illustration of a portion of a cylinder during an intake stroke of the portion of the embodiment of the engine of  FIG. 7 . 
         FIG. 8B  is a schematic illustration of a portion of a cylinder during a compression stroke of the portion of the embodiment of the engine of  FIG. 7 . 
         FIG. 8C  is a schematic illustration of a portion of a cylinder during a power stroke of the portion of the embodiment of the engine of  FIG. 7 . 
         FIG. 8D  is a schematic illustration of a portion of a cylinder during an exhaust stroke of the portion of the embodiment of the engine of  FIG. 7 . 
         FIG. 9  is a schematic illustration of the portion of the embodiment of the engine of  FIG. 7  comprising another embodiment of a heat transfer system. 
         FIG. 10  is a graph depicting a pressure volume diagram of an embodiment of the present disclosure. 
         FIG. 11  is a graph depicting a pressure volume diagram of another embodiment of the present disclosure. 
         FIG. 12  is a graph depicting a pressure volume diagram of yet another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     An internal combustion engine may comprise a heat transfer system disposed in thermal communication with a combustion chamber of the engine. The heat transfer system may be configured to absorb heat from the combustion chamber during a compression of a first combustion fluid. The heat transfer system may be further configured to transfer the absorbed heat to a first cooling fluid. Removal of the heat from the combustion chamber may reduce a quantity of energy or work required or used for compression and may enable increasing the charge density in the combustion chamber or increasing the compression ratio of the engine. Further, in some embodiments, the transferred heat may be reintroduced into the combustion chamber during a predetermined time period (i.e., without limitation, during at least a portion of a power stroke) such that at least a portion of the absorbed and/or transferred thermal energy is not discarded, lost, or wasted. In some other embodiments, the transferred heat may be used for another purpose (e.g., run through a thermoelectric power generator). In some additional embodiments, the heat transfer system may be designed such that it may be used to retrofit an existing internal combustion engine. 
     As used herein, the term “internal combustion engine” generally refers to an engine wherein combustion of a first combustion fluid, such as a fuel, occurs in a variable-volume combustion chamber that is an integral part of the engine&#39;s fluid flow circuit. There are many types of internal combustion engines, including, but not limited to, both reciprocating and rotary configurations. Common types of internal combustion engines include, but are not limited to, two-stroke engines, four-stroke engines, six-stroke engines, diesel engines, Atkinson cycle engines, Miller cycle engines, and Wankel engines. Any of the components, devices, and/or systems described herein may be configured to operate in any type of internal combustion engine. 
     It will be readily understood that the components of the embodiments as generally described and illustrated in the Figures herein could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the Figures, is not intended to limit the scope of the disclosure, but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated. 
     The phrases “connected to,” “coupled to,” and “in communication with” refer to any form of interaction between two or more entities, including mechanical, electrical, magnetic, electromagnetic, fluid, and thermal interaction. Two components may be coupled to each other even though they are not in direct contact with each other. For example, two components may be coupled to each other through an intermediate component. 
     The term “fluid” is used in its broadest sense to refer to any fluid, including both liquids and gasses as well as solutions, compounds, suspensions, etc., which generally behave as a fluid. 
       FIG. 1  is a schematic illustration of a portion of an embodiment of a spark-ignition internal combustion engine comprising an embodiment of a heat transfer system  100 . All the figures herein are schematic in nature. In other words, the figures show the functional and operational relationships of components of the system, but are not intended to indicate any particular structure or spatial disposition of any component or any group of components in the system. Additionally, the schematic views herein may be drawn to show internal working components of the engine without explicitly designating cross sections or cutaways of other components. For example, a cylinder may be schematically shown with a piston disposed therein without indicating a cross sectional portion or cutaway of the cylinder wall. 
     In the embodiment of  FIG. 1 , a portion of an embodiment of a combustion chamber  120  defining an interior volume  125  is depicted. The illustrated embodiment of a spark-ignition internal combustion engine can comprise the combustion chamber  120  and a heat absorption element  102 . As shown, the heat absorption element  102  is in communication, or thermal communication, with the interior volume  125  of the combustion chamber  120 . For example, the heat absorption element  102  may be fixedly positioned in the interior volume  125  of the combustion chamber  120 . In another example, the heat absorption element  102  may be configured to extend into the interior volume  125  of the combustion chamber  120  from a top portion, or head, of the combustion chamber  120 . Alternatively, the heat absorption element  102  may be configured to extend into the interior volume  125  of the combustion chamber  120  from a side portion of the combustion chamber  120  or the heat absorption element  102  may be configured to extend into the interior volume  125  of the combustion chamber  120  from a face of a piston  150  disposed within the interior volume  125  of the combustion chamber  120 . In some embodiments, the heat absorption element  102  may be configured to absorb at least a portion of an amount of heat generated by work done on a first combustion fluid disposed in the interior volume  125  of the combustion chamber  120 . The first combustion fluid may comprise air, an air-fuel mixture, oxygen, a recycled exhaust gas, an inert gas, and/or any other suitable fluid. The work done on the first combustion fluid may be compression of the first combustion fluid. For example, compression of a volume of the first combustion fluid in the interior volume  125  of the combustion chamber  120  may be effected or performed by movement of the piston  150 . In some embodiments, the transfer of heat absorbed by the heat absorption element  102  from the combustion chamber  120  to a position outside of the combustion chamber  120  may reduce, or be configured to reduce, the amount of work required or used to compress the volume of the first combustion fluid. Suppressing a peak temperature of the compressed first combustion fluid by heat transfer out of the interior volume  125  of the combustion chamber  120  may permit the use of higher compression ratios in some embodiments of internal combustion engines, and thus may enable higher internal combustion engine operating efficiencies. 
     The heat absorption element  102  may also be configured to transfer at least a portion of the absorbed heat to a first cooling fluid. The first cooling fluid may comprise a coolant, an engine coolant, a fuel, air, another suitable fluid, or any combination thereof. The heat absorption element  102  may be configured to comprise time-varying heat absorption properties. For example, the heat absorption element  102  may be configured such that the first cooling fluid flows at least substantially continuously through the heat absorption element  102  or through at least a portion of the heat absorption element  102 . Alternatively, the heat absorption element  102  may be configured such that the first cooling fluid flows at least substantially intermittently through the heat absorption element  102  or through at least a portion of the heat absorption element  102 . The first cooling fluid may flow, or be configured to flow, at least substantially intermittently through the heat absorption element  102  such that heat is absorbed from the combustion chamber  120  at one or more predetermined time periods when it may be advantageous, or more advantageous, to absorb heat from the combustion chamber  120  relative to other time periods. In some embodiments, at least a portion of the first cooling fluid may egress, or be configured to egress, from the heat absorption element  102 , or from at least a portion of the heat absorption element  102 , during at least a portion of a power stroke. In some other embodiments, a majority of the first cooling fluid may egress, or be configured to egress, from the heat absorption element  102 , or from at least a portion of the heat absorption element  102 , during at least a portion of the power stroke. Egress of the first cooling fluid from the heat absorption element  102  may also occur during other time periods. 
     In various embodiments, the heat absorption element  102  may be configured to transfer at least a portion of the absorbed heat to a heat sink  115 . As used herein, a heat sink is a device or material configured to absorb heat from a heat source without substantially increasing in temperature. At least a portion of the absorbed heat, or a majority of the absorbed heat, may be transferred to the heat sink  115  via the first cooling fluid, wherein the first cooling fluid may be disposed in a thermal transfer element  106  configured to couple each of the heat absorption element  102  and the heat sink  115 . The heat sink  115  may comprise a second cooling fluid, a fuel, air, a solid, another suitable substance, or any combination thereof. The second cooling fluid may comprise a coolant, an engine coolant, a fuel, air, another suitable fluid, or any combination thereof. In some embodiments, the second cooling fluid may comprise the first cooling fluid, or vice versa. Also, in some other embodiments, the second cooling fluid may be in communication (i.e., without limitation, thermal communication) with the first cooling fluid. For example, in some embodiments, the second cooling fluid can act as a thermodynamic sink. The second cooling fluid can act to transfer at least a portion of the heat from the first cooling fluid (i.e., via a heat exchanger) and carry or transfer at least a portion of the heat to a fuel tank or other device wherein the second cooling fluid can transfer at least a portion of the heat to a fuel or another suitable fluid (i.e., via a second heat exchanger). In certain embodiments, the second cooling fluid can act to transfer at least a portion of the heat from the first cooling fluid (i.e., via a heat exchanger) and carry or transfer at least a portion of the heat to a fuel tank or other device wherein the second cooling fluid can combine or mix with the fuel or other suitable fluid. As described herein, in some embodiments wherein the heat sink comprises a second cooling fluid, the absorbed heat may eventually be transferred to the surrounding air via a radiator, or another suitable device, such that the temperature of the second cooling fluid is maintained. 
     In some embodiments, the heat sink  115  may comprise a fuel immediately prior to the fuel&#39;s injection into the combustion chamber. In other embodiments, the heat sink  115  may comprise bulk fuel, wherein the bulk fuel is the fuel that supplies the engine (e.g., the fuel in the vehicle&#39;s fuel tank). 
     The heat sink  115  may also be configured to comprise two or more different substances, wherein the two or more different substances may be maintained substantially independently or separately from each other, and wherein the two or more substances may be in communication (i.e., without limitation, thermal communication) with each other. For example, the heat sink  115  may comprise both a cooling fluid and a fuel, wherein the cooling fluid and the fuel are not present in the heat sink  115  as a mixture, but wherein the cooling fluid and the fuel are in thermal communication with each other. In some embodiments, the heat sink  115  may be coupled, or operatively coupled, to a heat exchanger and/or a radiator. For example, the heat sink  115  may be coupled to a heat exchanger, wherein the heat exchanger is configured to transfer heat between a cooling fluid which is in communication with the heat absorption element  102  and fluid fuel configured for later use. In various embodiments, the heat sink  115  may be thermally coupled to a first cooling fluid via a heat exchanger. In various other embodiments, the heat sink  115  may comprise a radiator. 
     The heat sink  115  may comprise an intermediate fluid, such as a second cooling fluid, in communication with both a first cooling fluid and fuel. In embodiments wherein the heat sink  115  comprises both a second cooling fluid and a fuel, the heat absorption element  102  may be configured such that at least a first portion of the absorbed heat in the heat absorption element  102  is transferred, for example via a first cooling fluid, to the second cooling fluid and at least a second portion of the absorbed heat is transferred to the fuel. In yet other embodiments, a fuel injector (not shown) may be configured to introduce at least a portion of the heated fuel from the heat sink  115  into the interior volume  125  of the combustion chamber  120  during a predetermined time period. For example, the fuel injector may introduce the heated fuel into the combustion chamber  120  during at least a portion of a power stroke. The heat transfer system  100 , in combination with a fuel injector, a heat exchanger, and/or another device, can be configured to reintroduce the absorbed and/or transferred heat energy into the internal combustion engine to avoid, or at least partially avoid, removing the heat energy from the system. For example, introduction of the absorbed and/or transferred heat energy into the interior volume  125  of the combustion chamber  120  prior to and/or during the power stroke may necessarily increase the work done on the piston  150  during at least a portion of the power stroke. 
     In certain embodiments, the heat absorption element  102  may be configured to absorb more heat during a first time period in comparison to, or relative to, during a second time period. Stated another way, the heat absorption element  102  may be configured to comprise a greater heat absorption capacity during a first time period in comparison to, or relative to, during a second time period. For example, the first time period may comprise at least a portion of an intake stroke (i.e., prior to a compression stroke) and/or at least a portion of the compression stroke, and the second time period may comprise at least a portion of a power stroke. Other suitable time periods are also within the scope of this disclosure. In some embodiments, the second time period may comprise essentially all, or substantially all, of the power stroke. For example, a thermal conductance from the first combustion fluid and/or the interior volume  125  of the combustion chamber  120  to the first cooling fluid through or via the heat absorption element  102  may be configured to decrease during at least a portion, or during essentially all, of the power stroke. In other words, a heat conduction state of the heat absorption element  102  may be configured to change or oscillate over time. Further, the heat absorption element  102  may be configured to transition between a low thermal resistance state and a substantially non-heat-absorbing state. In some embodiments, the heat absorbing functions or properties of the heat absorption element  102  may be due to a mechanical and/or physical change of the heat absorption element  102 . In certain other embodiments, the heat absorbing functions or properties of the heat absorption element  102  may be due to a functional or non-physical change of the heat absorption element  102 . 
     In various embodiments, the heat absorption element  102  may comprise a phase change material. Heat absorption element  102  comprising a phase change material can be used to absorb heat within a fixed temperature range. Upon absorbing heat, the heat absorption element  102  comprising a phase change material can be cooled (i.e., via a circulating coolant, a heat pipe, etc.) such that at least a portion of the absorbed heat is drawn out of the phase change material. The transfer or drawing out of the heat from the phase change material can be configured to occur continuously or substantially continuously. 
     Absorption and/or transfer of heat energy from the interior volume  125  of the combustion chamber  120  during at least a portion of the compression stroke may decrease the amount of work required or used during the compression stroke. Whereas, absorption and/or transfer of heat energy from the interior volume  125  of the combustion chamber  120  during at least a portion of the power stroke may decrease the amount of work available to move the piston. In certain embodiments, the heat transfer system  100  and/or the heat absorption element  102  may be configured to cease or stop absorbing heat when a temperature in the combustion chamber  120  exceeds a specific or predetermined temperature or range of temperatures. For example, the transition of the heat absorption element  102  from the low thermal resistance state and the substantially non-heat-absorbing state may be due to decreasing or eliminating flow of a coolant through the heat absorption element  102 . In another configuration, the transition of the heat absorption element  102  from the low thermal resistance state and the substantially non-heat-absorbing state may be due to alternating the flow of the coolant through the heat absorption element  102  with the flow of a gas, wherein the gas absorbs less heat than the coolant or wherein the gas is configured to absorb less heat than the coolant. The heat absorption element  102  may absorb heat, or significant heat, while the heat absorption element  102  is undergoing a phase change and the heat absorption element  102  may absorb less heat, or much less heat, when the phase change is complete (i.e., when the phase change material has melted or vaporized). 
       FIGS. 2A-2D  are schematic depictions of various stages of a single thermodynamic cycle of the embodiment of the spark-ignition internal combustion engine of  FIG. 1 .  FIG. 2A  schematically illustrates an embodiment of a time point during an intake stroke. During the depicted intake stroke, the piston  150  moves downward, as shown by an arrow  152 . Directional terms, such as “downward,” “upward,” “top,” “bottom,” etc., are used herein with reference to the direction of compression in the illustrated embodiment of the combustion chamber. The terms are used for the sake of convenience and are not necessarily intended to be limiting. For example, a second embodiment of a spark-ignition internal combustion engine may be oriented substantially inverse to that of the embodiment illustrated in  FIGS. 2A-2D  such that in the second embodiment, movement of a piston during an intake stroke may be depicted as being “upward.” 
     Referring again to  FIG. 2A , the downward movement of the piston  150  may draw or introduce a fresh charge of, or a volume of, the first combustion fluid  130  into the interior volume  125  of the combustion chamber  120 , as shown by an arrow  154 . As illustrated, the heat absorption element  102  is disposed in a wall  122  of the combustion chamber  120 . As discussed above, other positions of the heat absorption element  102  are also within the scope of this disclosure. In some embodiments, the heat absorption element  102  may comprise a plurality of channels configured for flow or passage of the first cooling fluid. In certain embodiments, the channels may be microchannels, also referred to herein as microchannel heat transfer elements. As used herein, a microchannel is a channel comprising laminar flow at operating conditions and a height-to-width ratio of approximately 1 or greater. As such, at typical pressures and flow velocities for cooling, one dimension of a microchannel comprising a liquid may be between approximately 10 micrometers and approximately 100 micrometers, and one dimension of a microchannel comprising a gas may be between approximately 100 micrometers and approximately 1,000 micrometers. The aspect ratio of a microchannel heat exchanger may distinguish a microchannel heat exchanger from a simple film heat exchanger, wherein a heat-absorbing fluid may simply flow along one side of a plate. 
     In some embodiments, the first cooling fluid may be circulated, pumped, or transported by a pump or another suitable device. For example, the first cooling fluid and the heat absorption element  102  may be part of a closed-loop system coupled to a pump (not shown), wherein the pump may be configured to circulate, pump, or transport the first cooling fluid. Further, referring again to  FIG. 1 , the closed-loop system may comprise at least the heat absorption element  102 , the thermal transfer element  106 , the heat sink  115 , and the first cooling fluid. In another example, the first cooling fluid may be a component of a main engine cooling system, or preexisting engine cooling system, wherein the cooling fluid is pressurized by a pump. In some other embodiments, the first cooling fluid may be circulated, pumped, or transported by at least partial compression of the plurality of channels, or the plurality of microchannel heat transfer elements, as the charge is compressed by the piston  150 . 
       FIG. 2B  is a schematic illustration of a time point during a compression stroke of the embodiment of the engine of  FIG. 1 . During the compression stroke, the piston  150  moves upward, as shown by an arrow  153 . As the piston  150  moves upward the first combustion fluid  130  is compressed, which may generate heat. Compression of a constant mass of a fluid will raise the temperature of the fluid. During the intake stroke, high surface area structures (e.g., fins, pins, etc.) comprising a plurality of microchannel heat transfer elements  103  may be deployed from the heat absorption element  102 . Deployment of the plurality of microchannel heat transfer elements  103  can increase a surface area of the plurality of microchannel heat transfer elements  103  available for heat transfer and may aid in the transfer of heat from the first combustion fluid  130 . In the illustrated embodiment, the heat absorption element  102  comprises a plurality of microchannel heat transfer elements  103 , wherein the plurality of microchannel heat transfer elements  103  forms a plate comprising an array of pins, or a pin grid array. Other configurations of the channels and/or microchannel heat transfer elements are also contemplated. For example, a plurality of individual microchannel heat transfer elements that are only coupled to one another at the heat absorption element  102  may deploy into the interior volume  125  of the combustion chamber  120 , wherein the microchannel heat transfer elements may further comprise one or more one-way valves. In some embodiments, the plurality of microchannel heat transfer elements  103  may form a substantially net- or web-like lattice or structure. The plurality of microchannel heat transfer elements  103  may also comprise an open porous or mesh-like structure (e.g., a mesh-like plate). In some configurations, the plurality of microchannel heat transfer elements  103  may comprise an array of grid-like fins, or a series of fins. The plurality of microchannel heat transfer elements  103  may extend or spread out into the interior volume  125  of the combustion chamber  120  from a single entrance point to the interior volume  125  of the combustion chamber  120 . Additionally, the plurality of microchannel heat transfer elements  103  may extend into and retract out of the interior volume  125  of the combustion chamber  120  at multiple or various time points. The plurality of microchannel heat transfer elements  103  may also be valve-like or the plurality of microchannel heat transfer elements  103  may fold out from and back against a head or a wall of the combustion chamber  120 . 
     In various embodiments, the plurality of microchannel heat transfer elements  103  may be configured to transition between a low-profile configuration and a deployed configuration. During the compression stroke, the plurality of microchannel heat transfer elements  103 , as illustrated, can deploy into at least a portion of the interior volume  125  of the combustion chamber  120 . For example, the plurality of microchannel heat transfer elements  103  may be configured to transition from the low-profile configuration of  FIG. 2A  to the deployed configuration of  FIG. 2B . In some embodiments, the piston  150  may be configured such that it does not contact the heat absorption element  102  and/or the plurality of microchannel heat transfer elements  103 . Such a configuration may decrease or minimize the possibility of damaging, or increasing wear on, the heat absorption element  102  and/or the plurality of microchannel heat transfer elements  103 . When in the deployed configuration, the plurality of microchannel heat transfer elements  103  may be configured to transfer more heat from the combustion chamber  120  than when the plurality of microchannel heat transfer elements  103  is in the low-profile configuration. Other configurations, as discussed above, wherein the transition between a high heat-transfer state and a low heat-transfer state may not comprise mechanical and/or physical transformation of the heat absorption element  102  are also within the scope of this disclosure. As such, the other embodiments disclosed herein may be adapted to comprise a non-mechanical and/or non-physical transition of the heat absorption element  102 . The plurality of microchannel heat transfer elements  103  may also be configured to transfer heat from the interior volume  125  of the combustion chamber  120  to a heat sink (not shown) via a first cooling fluid. In some embodiments, the plurality of microchannel heat transfer elements  103  may be substantially flexible, while in some other embodiments, the plurality of microchannel heat transfer elements  103  may be substantially rigid. 
     In certain embodiments, heating of a fuel component of the first combustion fluid  130  prior to its introduction into the interior volume  125  of the combustion chamber  120  may increase the vapor pressure of the first combustion fluid  130  and thus may impact the vaporization intake quality upon injection of the first combustion fluid  130 . In certain embodiments, the heating of the first combustion fluid  130  may facilitate the use of “heavy” diesel fuel as the first combustion fluid  130  in spark-ignition internal combustion engines as it may permit increased vapor pressure upon introduction of the first combustion fluid  130  into the interior volume  125  of the combustion chamber  120 . 
     In other embodiments, at least a portion of the heat absorption element  102  may be configured to transition from the low-profile configuration to the deployed configuration for a first time period, and at least a portion of the heat absorption element  102  may be further configured to transition from the deployed configuration to the low-profile configuration for a second time period. The first time period may comprise at least a portion of the intake stroke (i.e., prior to the compression stroke) and/or at least a portion of the compression stroke, and the second time period may comprise a least a portion of a power stroke. In yet other embodiments, the second time period may comprise essentially all, or substantially all, of the power stroke. Transition of at least a portion of the heat absorption element  102  during other time periods is also contemplated. The transitions from the low-profile configuration to the deployed configuration, and vice versa, may be driven hydraulically, mechanically, pneumatically, etc. In some embodiments, the transitions from the low-profile configuration to the deployed configuration, and vice versa, may be driven at least partially by pressure in the cylinder. For example, attaining or exceeding a predetermined pressure within the cylinder and/or onset of combustion may at least partially activate or aid in the transition of the heat absorption element  102  from the deployed configuration to the low-profile configuration. 
       FIG. 2C  schematically illustrates a time point during a power stroke of the embodiment of the engine of  FIG. 1 . As the piston  150  approaches or reaches a top portion, or head, of the combustion chamber  120 , a spark plug  160  may fire or spark, igniting the compressed first combustion fluid  130 . The ignition and burning of the first combustion fluid  130  can cause the volume of the first combustion fluid  130  to expand, which is configured to force or push the piston  150  downward as indicated by the arrow  152 . As illustrated, the plurality of microchannel heat transfer elements  103  can transition from the deployed configuration to the low-profile configuration during at least a portion of the power stroke. Stated another way, at least a portion of the heat absorption element  102  may be configured to be at least partially withdrawn from the interior volume  125  of the combustion chamber  120  between at least a portion of the compression stroke and at least a portion of the power stroke. As stated above, such a configuration may limit heat loss, and therefore power loss, during at least a portion of the power stroke. In other embodiments, a shape of a heat absorption element, like heat absorption element  102 , may be configured to change between at least a portion of a compression stroke and at least a portion of a power stroke. A surface area of the heat absorption element may also be configured to change or decrease between at least a portion of the compression stroke and at least a portion of the power stroke. In still other embodiments, a position of the heat absorption element may be configured to change between at least a portion of the compression stroke and at least a portion of the power stroke. For example, the position of the heat absorption element may change such that the heat absorption element is no longer in communication, or thermal communication, with an interior volume of a combustion chamber. In some embodiments, the heat absorption element  102  may also be configured to make or undergo a functional transformation and not a mechanical and/or physical transformation. 
       FIG. 2D  is a schematic depiction of a time point during an exhaust stroke of the embodiment of the engine of  FIG. 1 . As illustrated, after the above-described power stroke an exhaust valve  155  may open, and upward movement of the piston  150 , as depicted by the arrow  153 , can force the burned or exhausted first combustion fluid  132  from the interior volume  125  of the combustion chamber  120 , as illustrated by arrow  156 . 
       FIGS. 3 and 4  are schematic illustrations of portions of other embodiments of spark-ignition internal combustion engines comprising two other embodiments of a heat transfer system  200 ,  300 . The embodiments of  FIGS. 3 and 4  may include components that resemble components of the embodiment of  FIGS. 1-2D  in some respects. For example, the embodiment of  FIG. 3  includes a schematic element designated as a heat absorption element  202  of the heat transfer system  200 , and the embodiment of  FIG. 4  includes a schematic element designated as a heat absorption element  302  of the heat transfer system  300 , which may resemble the schematic representation of the heat absorption element  102  of  FIG. 1 . Accordingly, like or analogous features are designated with like reference numerals, with the leading digits incremented to “2” and “3,” respectively. Relevant disclosure set forth above regarding similarly identified features thus may not be repeated hereafter. Moreover, specific features of the system and related components shown in  FIGS. 3 and 4  may not be shown or identified by a reference numeral in the drawings or specifically discussed in the written description that follows. However, such features may clearly be the same, or substantially the same, as features depicted in other embodiments and/or described with respect to such embodiments. Accordingly, the relevant descriptions of such features apply equally to the features of the system and related components of  FIGS. 3 and 4 . Any suitable combination of the features, and variations of the same, described with respect to the system and components illustrated in  FIGS. 1-2D , can be employed with the system and components of  FIGS. 3 and 4 , and vice versa. This pattern of disclosure applies equally to further embodiments depicted in subsequent figures and described hereafter. 
     It will be appreciated by one of skill in the art having the benefit of this disclosure that the heat transfer systems  200 ,  300  of  FIGS. 3 and 4  may function in an analogous manner to the heat transfer system  100  described in connection with  FIGS. 1-2D . Thus, while specific features and elements of the subsequent heat transfer systems  200 ,  300  will be described below, disclosure above regarding the relationship of components and the function of the heat transfer system  100  of  FIGS. 1-2D  may be applied to the heat transfer systems  200 ,  300  of  FIGS. 3 and 4 . Again, this pattern of disclosure applies to subsequent disclosure as well: disclosure relative to any embodiment may be analogously applied to any other embodiment herein. 
     In certain embodiments, the heat transfer systems  100 ,  200 ,  300  may be configured to be retrofitted into an embodiment of an existing spark-ignition internal combustion engine. With reference to  FIG. 3 , a heat transfer system  200  can comprise a heat absorption element  202  configured to be disposed within an interior volume  225  of a combustion chamber  220 . The heat absorption element  202  may be configured to absorb heat from the interior volume  225  of the combustion chamber  220 . The heat transfer system  200  can also comprise a thermal transfer element  206 , wherein the thermal transfer element  206  is in communication, or fluid communication, with the heat absorption element  202 . As shown, the thermal transfer element  206  can be configured to extend at least from a first position at or adjacent the heat absorption element  202  to a second position outside of the combustion chamber  220 . The thermal transfer element  206  may comprise a fluid flow path or a heat pipe. 
     In some embodiments, the thermal transfer element  206  may comprise a fluid flow path. The fluid flow path may be configured to transfer heat from the heat absorption element  202  to a heat sink  215 . For example, the fluid flow path may comprise a first cooling fluid wherein the first cooling fluid flows and/or circulates through the fluid flow path between at least the heat absorption element  202  and the heat sink  215 . As described above, a pump may be coupled to the thermal transfer element  206  and the pump may be configured to circulate the first cooling fluid between at least the heat absorption element  202  and the heat sink  215 . The heat sink  215 , as also described above, may comprise a second cooling fluid and/or any other suitable fluid or substance. In some embodiments, the heat sink  215  may be coupled, or operatively coupled, to a heat exchanger and/or a radiator. In various embodiments, the heat sink  215  may be thermally coupled to a first cooling fluid via a heat exchanger. In various other embodiments, the heat sink  215  may comprise a radiator. 
     In other embodiments, the thermal transfer element  206  may comprise a heat pipe. The heat pipe may be configured to transfer heat from the heat absorption element  202  to the heat sink  215 . In some embodiments, the heat pipe may be configured to discard or transfer all or at least a portion of the heat absorbed by the heat absorption element  202  to a position outside of the combustion chamber  220  (i.e., without limitation, the heat sink  215 ). As described above in connection with the fluid flow path, the heat sink  215  in communication with the heat pipe may also comprise a second cooling fluid and/or any other suitable fluid or substance. In some embodiments, a heat pipe may comprise a cooling fluid, wherein the cooling fluid may evaporate in the interior volume  225  of the combustion chamber  220 , or cylinder, condense in the heat sink  215 , and be pumped or transferred back to a head of the cylinder, or to another position at or adjacent the cylinder, via a capillary wick, wherein the capillary wick may be disposed within, or operatively coupled to, the heat pipe. 
     Referring again to  FIG. 3 , the interior volume  225  of the combustion chamber  220  of the embodiment of an existing spark-ignition internal combustion engine comprises a predetermined compression ratio. Upon retrofitting of the existing engine, the heat absorption element  202 , and/or the thermal transfer element  206 , may occupy at least a portion of the interior volume  225  of the combustion chamber  220 . In such an embodiment, the heat absorption element  202 , and/or the thermal transfer element  206 , can alter the predetermined compression ratio of the combustion chamber  220 . 
     As shown, the heat absorption element  202 , and/or the thermal transfer element  206 , is at least partially disposed through an existing aperture of the combustion chamber  220  (i.e., a spark plug  260  aperture  262 ). In some embodiments, the heat transfer system  200  configured for retrofitting an existing spark-ignition internal combustion engine may comprise a spark plug element. For example, the heat absorption element  202  may be configured to provide a spark similar to that provided by a spark plug. In other embodiments, the heat absorption element  202  may be coupled to, or disposed into a portion of, a spark plug. Thus, retrofitting an existing engine may comprise replacing an existing or stock spark plug with a device or an element configured to occupy the spark plug aperture, contain at least a portion of the heat transfer system, and provide a spark. 
     Referring to  FIG. 4 , the heat transfer system  300  may be at least partially disposed within, or coupled to, a piston  350 . As illustrated, the heat absorption element  302  may be at least partially disposed within the piston  350  such that the heat absorption element  302  is in communication, or thermal communication, with an interior volume  325  of a combustion chamber  320 . The heat transfer system  300  can also comprise a thermal transfer element  306 , wherein the thermal transfer element  306  is in communication with the heat absorption element  302 . As described above in connection with the embodiment of  FIG. 3 , the thermal transfer element  306  can be configured to extend at least from a first position at or adjacent the heat absorption element  302  to a second position outside of the combustion chamber  320 . Thus, retrofitting may comprise installation of a new piston so configured. Other locations or positions within an embodiment of an existing spark-ignition internal combustion engine may also be suitable for the disposition of another embodiment of a heat transfer system, similar to heat transfer systems  100 ,  200 ,  300 . 
     In some embodiments, a spark-ignition internal combustion engine system can comprise one or more variable-volume combustion chambers, similar to combustion chambers  120 ,  220 ,  320 . The spark-ignition internal combustion engine system may further comprise a heat transfer system, similar to heat transfer systems  100 ,  200 ,  300 , comprising one or more heat absorption elements, wherein each heat absorption element may be in communication with at least one of the variable-volume combustion chambers. Heat absorption elements, as disclosed, may also be configured to absorb heat from interior volumes of the variable-volume combustion chambers. 
       FIG. 5  depicts a schematic embodiment of a rotary, or Wankel, internal combustion engine comprising a plurality of variable-volume combustion chambers  420   a ,  420   b ,  420   c . As illustrated, a heat transfer system  400  comprising a heat absorption element  402  can be disposed in communication, or thermal communication, with an interior volume  425   b  of the variable-volume combustion chamber  420   b . In certain embodiments, the heat absorption element  402  may be configured to absorb heat from the interior volume  425   b  of the variable-volume combustion chamber  420   b.    
       FIGS. 6A-6D  schematically depict various stages of a single thermodynamic cycle of the embodiment of the rotary internal combustion engine of  FIG. 5 .  FIG. 6A  is a schematic illustration of a time point during an intake stroke of the embodiment of the engine of  FIG. 5 . During the depicted intake stroke, rotation of a rotor  465 , as indicated by an arrow  467 , can draw or introduce a fresh charge, or a volume, of a first combustion fluid  430  into the interior volume  425   a  of the variable-volume combustion chamber  420   a , as indicated by an arrow  454 . As illustrated, the heat absorption element  402  is disposed in a wall  422  of the variable-volume combustion chamber  420   b.    
       FIG. 6B  schematically illustrates a time point during a compression stroke of the embodiment of the engine of  FIG. 5 . During the depicted compression stroke, the rotor  465  continues its rotation, as shown by the arrow  467 , and the rotor  465  compresses the first combustion fluid  430 . The compression of the first combustion fluid  430  can generate heat. In the illustrated embodiment, the heat absorption element  402  comprises a plurality of microchannel heat transfer elements  403 , wherein the plurality of microchannel heat transfer elements  403  forms a plate comprising an array of pins. Other embodiments of the heat absorption element  402  are also contemplated. For example, as described above, a plurality of individual microchannel heat transfer elements that are only coupled to one another at the heat absorption element  402  may deploy into the interior volume  425   b  of the combustion chamber  420   b . In some embodiments, the plurality of microchannel heat transfer elements  403  may form a substantially net- or web-like lattice or structure. The plurality of microchannel heat transfer elements  403  may also comprise an open porous or mesh-like structure (e.g., a mesh-like plate). In some configurations, the plurality of microchannel heat transfer elements  403  may comprise an array of grid-like fins, or a series of fins. The plurality of microchannel heat transfer elements  403  may extend or spread out into the interior volume  425   b  of the combustion chamber  420   b  from a single entrance point to the interior volume  425   b  of the combustion chamber  420   b . Additionally, the plurality of microchannel heat transfer elements  403  may extend into and retract out of the interior volume  425   b  of the combustion chamber  420   b  at multiple or various time points. The plurality of microchannel heat transfer elements  403  may also be valve-like or the plurality of microchannel heat transfer elements  403  may fold out from and back against a head or a wall of the combustion chamber  420   b . In some embodiments, the plurality of microchannel heat transfer elements  403  may be substantially rigid. 
     During the compression stroke, the plurality of microchannel heat transfer elements  403  may deploy into at least a portion of the interior volume  425   b  of the variable-volume combustion chamber  420   b . For example, the plurality of microchannel heat transfer elements  403  may be configured to transition from a low-profile configuration, as shown in  FIG. 6A , to a deployed configuration, as shown in  FIG. 6B . When in the deployed configuration, the plurality of microchannel heat transfer elements  403  may be configured to transfer more heat from the variable-volume combustion chamber  420   b  than when the plurality of microchannel heat transfer elements  403  is in the low-profile configuration. The plurality of microchannel heat transfer elements  403  and/or heat transfer system  400  may be further configured to absorb and transfer heat from the interior volume  425   b  of the variable-volume combustion chamber  420   b  to a heat sink (not shown) via a first cooling fluid. The heat transfer system  400  may be configured to reduce an amount of work required or used to compress the first combustion fluid  430 . 
     Again, as described above, the heat absorption element  402  may be configured to transition from the low-profile configuration to the deployed configuration for a first time period, and the heat absorption element  402  may be further configured to transition from the deployed configuration to the low-profile configuration for a second time period. The first time period may comprise at least a portion of the intake stroke (i.e., prior to the compression stroke) and/or at least a portion of the compression stroke, and the second time period may comprise a least a portion of a power stroke. In yet other embodiments, the second time period may comprise essentially all, or substantially all, of the power stroke. Other suitable time periods are also contemplated. 
       FIG. 6C  is a schematic illustration of a time point during a power stroke of the embodiment of the engine of  FIG. 5 . A spark plug  460  can be configured to fire or spark, thus igniting and burning the compressed first combustion fluid  430 . Ignition and burning of the first combustion fluid  430  causes the volume of the first combustion fluid  430  to expand, which at least partially drives the continued rotation of the rotor  465 , as depicted by the arrow  467 . As illustrated, the plurality of microchannel heat transfer elements  403  can transition from the deployed configuration to the low-profile configuration. Stated another way, at least a portion of the heat absorption element  402  may be configured to be at least partially withdrawn from the interior volume  425   b  of the variable-volume combustion chamber  420   b  between at least a portion of the compression stroke and at least a portion of the power stroke. In other embodiments, a shape of a heat absorption element, like heat absorption element  402 , may be configured to change between at least a portion of the compression stroke and at least a portion of the power stroke. A surface area of the heat absorption element may also be configured to change or decrease between at least a portion of the compression stroke and at least a portion of the power stroke. In still other embodiments, a position of the heat absorption element may be configured to change between at least a portion of the compression stroke and at least a portion of the power stroke. For example, the position of the heat absorption element may change such that the heat absorption element is no longer in communication with an interior volume of a variable-volume combustion chamber. In some embodiments, the heat absorption element  402  may also be configured to make or undergo a functional transformation and not a mechanical and/or physical transformation. 
       FIG. 6D  schematically depicts a time point during an exhaust stroke of the embodiment of the engine of  FIG. 5 . As the rotor  465  continues to rotate, as indicated by the arrow  467 , a burned or an exhausted first combustion fluid  432  is expelled, or exits, from the interior volume  425   c  of the variable-volume combustion chamber  420   c , as illustrated by an arrow  456 . 
     In some embodiments, the heat transfer system  400  may be configured to transfer a greater portion of the total amount of heat absorbed from the variable-volume combustion chamber  420   b  during at least a portion of the compression stroke as compared to, or in relation to, during at least a portion of the power stroke. For example, the heat absorption element  402  may be configured to comprise better thermal coupling during at least a portion of the compression stroke as compared to during at least a portion of the power stroke. As described in connection with other embodiments of a heat transfer system, at least a portion of the heat transfer system  400  may be disposed, or positioned, at other locations within an embodiment of a rotary internal combustion engine. For example, at least a portion of an embodiment of a heat transfer system  400  may be disposed in a rotor  465 . 
       FIG. 7  is a schematic illustration of a portion of an embodiment of a compression-ignition internal combustion engine, or diesel engine, depicting another embodiment of a heat transfer system  500 . As compared to the embodiments described above, the illustrated embodiment does not comprise a spark plug. In the illustrated embodiment, a portion of a combustion chamber  520  defining an interior volume  525  is depicted. As depicted, a compression-ignition internal combustion engine can comprise a combustion chamber  520  and a heat absorption element  502 . The illustrated heat absorption element  502  is in communication, or thermal communication, with the interior volume  525  of the combustion chamber  520 . In some embodiments, the heat absorption element  502  may be configured to absorb heat from the combustion chamber  520  and/or the interior volume  525  of the combustion chamber  520 . Specifically, the heat absorption element  502  may be configured to absorb at least a portion of the heat during at least a portion of a compression stroke. In another example, the heat absorption element  502  may absorb at least a portion of an amount of heat generated by work done on a first combustion fluid disposed in the interior volume  525  of the combustion chamber  520 . The first combustion fluid may comprise air, an air-fuel mixture, oxygen, a recycled exhaust gas, an inert gas, and/or any other suitable fluid. For example, a volume of air may be disposed, or introduced, into the interior volume  525  of the combustion chamber  520 . The work done on the first combustion fluid may be compression of the first combustion fluid. The compression of the first combustion fluid can generate or produce heat. In certain embodiments, the absorption of heat from the combustion chamber  520  and/or transfer of the absorbed heat to a position outside of the combustion chamber  520  may reduce, or be configured to reduce, the amount of work required or used to compress the first combustion fluid. 
     Absorption of heat from the combustion chamber  520  at one or more predetermined time periods may further decrease the work required or used to compress the first combustion fluid. In some embodiments, the heat absorption element  502  may be configured to absorb more heat during a first time period in comparison to, or in relation to, during a second time period. The first time period may comprise at least a portion of an intake stroke (i.e., prior to a compression stroke) and/or at least a portion of the compression stroke, and the second time period may comprise at least a portion of a power stroke or, in some embodiments, essentially all of the power stroke. Specifically, the heat absorption element  502  may absorb more heat during at least a portion of the compression stroke than during at least a portion of the power stroke. Other suitable time periods are also contemplated. Stated another way, the heat absorption element  502  may be configured to comprise a greater heat absorption capacity during a first time period in comparison to, or relative to, during a second time period. 
     In some embodiments, the heat absorption element  502  may be further configured to transfer at least a portion of the absorbed heat to a first cooling fluid. The first cooling fluid may comprise a coolant, an engine coolant, air, a fuel, another suitable fluid, or any combination thereof. The first cooling fluid may flow, or be configured to flow, substantially continuously through the heat absorption element  502 . Alternatively, the first cooling fluid may flow, or be configured to flow, substantially intermittently through the heat absorption element  502 . For example, at least a portion, or a majority, of the first cooling fluid may egress, or be configured to egress, from the heat absorption element  502  during at least a portion of a power stroke. In certain embodiments, the first cooling fluid may egress from the heat absorption element  502  during another suitable time period. 
     A thermal conductance from the first combustion fluid to the first cooling fluid via the heat absorption element  502  may be configured to change during a predetermined time period. For example, the thermal conductance from the first combustion fluid to the first cooling fluid via the heat absorption element  502  may decrease during at least a portion of a power stroke. In some embodiments, a heat conduction state of the heat absorption element  502  may be configured to change during a predetermined time period. For example, the heat conduction state of the heat absorption element  502  may be configured to oscillate over time. In further embodiments, the heat absorption element  502  may be configured to transition between a low thermal resistance state and a substantially non-heat-absorbing state. For example, the heat absorption element  502  may be in a low thermal resistance state during at least a portion of a compression stroke, and, alternatively, the heat absorption element  502  may be in a substantially non-heat-absorbing state during at least a portion of a power stroke. 
     To effect the above-described functional changes of the heat absorption element  502 , the heat absorption element  502  may be configured to undergo a physical change. For example, a shape and/or a position of the heat absorption element  502  may be configured to change between at least a portion of the combustion stroke and at least a portion of the power stroke. The shape and/or position of the heat absorption element  502  may also be configured to change during other time periods. In another example, a surface area of the heat absorption element  502  may be configured to change or decrease between at least a portion of the combustion stroke and at least a portion of the power stroke. The surface area of the heat absorption element  502  may also be configured to change during other time periods. In certain embodiments, the heat absorption element  502  may be configured to be at least partially withdrawn from the interior volume  525  of the combustion chamber  520  between at least a portion of the combustion stroke and at least a portion of the power stroke. The heat absorption element  502  may also be configured to be at least partially withdrawn from the interior volume  525  of the combustion chamber  520  during other time periods. Withdrawal, or at least partial withdrawal, of the heat absorption element  502  from the interior volume  525  of the combustion chamber  520  may affect or decrease the amount of heat that the heat absorption element  502  is able to absorb. In some embodiments, the above-described functional changes of the heat absorption element  502  may be effected by a non-mechanical and/or non-physical change of the heat absorption element  502 . 
     With continued reference to  FIG. 7 , the heat absorption element  502  may be coupled to a heat sink  515  via a thermal transfer element  506 . In some embodiments, the heat absorption element  502  may be configured to transfer at least a portion of the absorbed heat to the heat sink  515 . In some other embodiments, the heat absorption element  502  may be configured to transfer a majority of the absorbed heat to the heat sink  515 . The absorbed heat may be transferred via the first cooling fluid. In some embodiments, as discussed above, the first cooling fluid may be circulated, pumped, or transported by a pump or another suitable device. The heat sink  515  may comprise a second cooling fluid, and the transferred heat may be further transferred from the first cooling fluid to the second cooling fluid. For example, the first cooling fluid and the second cooling fluid may be in communication, or fluid communication, with one another. In other embodiments, the heat sink  515  may comprise a fuel, or the heat sink  515  may comprise both a second cooling fluid and a fuel. At least a first portion of the absorbed heat may be transferred to the second cooling fluid and at least a second portion of the absorbed heat may be transferred to the fuel. For example, there may be an excess of absorbed heat and thus the first portion of the absorbed heat may be discarded or lost, and the second portion of the absorbed heat may be utilized. In other embodiments, the heat sink  515  may be coupled to, or operatively coupled to, a heat exchanger or a radiator. For example, the absorbed heat may be discarded or lost via transfer to the radiator. In contrast, the absorbed heat may be transferred to the heat exchanger and at least a portion of the heat energy may be further utilized. In various embodiments, the heat sink  515  may be thermally coupled to a first cooling fluid via a heat exchanger. In various other embodiments, the heat sink  515  may comprise a radiator. 
     In embodiments wherein the heat sink  515  comprises fuel, the fuel may be heated. For example, upon transfer of heat from the heat absorption element  502  to the heat sink  515  the fuel can be heated. A fuel injector, or another suitable device, may be configured to introduce at least a portion of the heated fuel into the interior volume  525  of the combustion chamber  520 . The fuel injector, or another device, may be further configured to introduce the heated fuel into the interior volume  525  of the combustion chamber  520  at a predetermined time. For example, the fuel injector may inject or introduce the heated fuel into the interior volume  525  of the combustion chamber  520  during at least a portion of a power stroke. Fuel injectors of multiple types, including, but not limited to, single-point, continuous, central port, multiport, or direct injection, may be used in both spark-ignition and compression-ignition internal combustion engines. A fuel injector may also be configured to inject or introduce the heated fuel at various positions in an internal combustion engine, including, but not limited to, a throttle body, an intake port, upstream of a cylinder&#39;s intake valve, and/or directly into the combustion chamber. 
     In some embodiments, the fuel injector, or another device, may be configured to introduce the heated fuel into an interior volume of a precombustion chamber (not shown). Various aspects and components of the embodiments described for coupling to, and/or integration with, the combustion chamber  520  may be adapted for use with a precombustion chamber or for embodiments of engines comprising a precombustion chamber. For example, a plurality of microchannel heat transfer elements, similar to the plurality of microchannel heat transfer elements  503 , may be disposed in communication with a precombustion chamber and/or deployed into the precombustion chamber to absorb heat from the precombustion chamber. 
       FIGS. 8A-8D  are schematic depictions of various stages during a single thermodynamic cycle of the embodiment of the compression-ignition internal combustion engine, or diesel engine, of  FIG. 7 .  FIG. 8A  schematically illustrates a time point during an intake stroke. During the illustrated intake stroke, a piston  550  moves downward, as shown by an arrow  552 . The downward movement of the piston  550  may draw or introduce a fresh charge, or a volume, of a first combustion fluid  530  into the interior volume  525  of the combustion chamber  520 , as shown by an arrow  554 . In some embodiments, the first combustion fluid  530  may comprise air, an air-fuel mixture, oxygen, a recycled exhaust gas, an inert gas, and/or another suitable fluid. As illustrated, the heat absorption element  502  can be disposed in a wall  522  of the combustion chamber  520 . As discussed above, other positions of the heat absorption element  502  are also within the scope of this disclosure. In some embodiments, the heat absorption element  502  may comprise a plurality of channels configured for flow or passage of a first cooling fluid. As disclosed elsewhere in the present disclosure, the first cooling fluid may comprise a coolant, an engine coolant, a fuel, air, and/or another suitable fluid. In certain embodiments, the disclosed channels may comprise microchannel heat transfer elements  503 , as defined above. 
       FIG. 8B  is a schematic illustration of a time point during a compression stroke of the embodiment of the engine of  FIG. 7 . During the compression stroke, the piston  550  moves upward, as shown by the arrow  553 . As the piston  550  moves upward the first combustion fluid  530  is compressed generating heat. During at least a portion of the compression stroke the compressed first combustion fluid  530  may comprise sufficient heat to ignite a second combustion fluid. In the illustrated embodiment, the heat absorption element  502  comprises a plurality of microchannel heat transfer elements  503 , wherein the plurality of microchannel heat transfer elements  503  forms a plate comprising an array of pins, or a pin grid array. Other configurations of the heat absorption element  502  are also contemplated. For example, as described above, a plurality of individual microchannel heat transfer elements  503  that are only coupled to one another at the heat absorption element  502  may deploy into the interior volume  525  of the combustion chamber  520 . In some embodiments, the plurality of microchannel heat transfer elements  503  may form a substantially net- or web-like lattice or structure. The plurality of microchannel heat transfer elements  503  may also comprise an open porous or mesh-like structure (e.g., a mesh-like plate). In some configurations, the plurality of microchannel heat transfer elements  503  may comprise an array of grid-like fins. The plurality of microchannel heat transfer elements  503  may extend or spread out into the interior volume  525  of the combustion chamber  520  from a single entrance point to the interior volume  525  of the combustion chamber  520 . Additionally, the plurality of microchannel heat transfer elements  503  may extend into and retract out of the interior volume  525  of the combustion chamber  520  at multiple or various time points. The plurality of microchannel heat transfer elements  503  may also be valve-like or the plurality of microchannel heat transfer elements  503  may fold out from and back against a head or a wall of the combustion chamber  520 . In some embodiments, the plurality of microchannel heat transfer elements  503  may be substantially rigid. 
     In one embodiment, the plurality of microchannel heat transfer elements may comprise at least two substantially parallel channels, wherein the at least two channels are positioned from approximately 1 millimeter to approximately 1 centimeter apart. The at least two channels may be coupled to an array of microchannel heat transfer elements, wherein the at least two channels and the array of microchannel heat transfer elements are configured to deploy into and out of the interior volume of the cylinder. A first of the at least two channels may be configured to carry or transfer a first cooling fluid into the array of microchannel heat transfer elements. Further, a second of the at least two channels may be configured to carry or transfer the first cooling fluid away from the array of microchannel heat transfer elements. The array of microchannel heat transfer elements may provide an area for transferring heat from the fuel charge and from the interior volume of the cylinder. 
     In various embodiments, the plurality of microchannel heat transfer elements  503  may be configured to transition between a low-profile configuration and a deployed configuration. During the compression stroke, the plurality of microchannel heat transfer elements  503 , as illustrated, can deploy into at least a portion of the interior volume  525  of the combustion chamber  520 . For example, the plurality of microchannel heat transfer elements  503  may be configured to transition from the low-profile configuration of  FIG. 8A  to the deployed configuration of  FIG. 8B . When in the deployed configuration, the plurality of microchannel heat transfer elements  503  may be configured to transfer more absorbed heat from the combustion chamber  520  than when the plurality of microchannel heat transfer elements  503  is in the low-profile configuration. The plurality of microchannel heat transfer elements  503  and/or the heat transfer system  500  may be configured to transfer heat from the interior volume  525  of the combustion chamber  520  to a heat sink (not shown) via a first cooling fluid. In some embodiments, the plurality of microchannel heat transfer elements  503  may be substantially rigid. In some other embodiments, the plurality of microchannel heat transfer elements  503  may be substantially flexible. 
     In other embodiments, at least a portion of the heat absorption element  502  may be configured to transition from the low-profile configuration to the deployed configuration for a first time period, and the heat absorption element  502  may be further configured to transition from the deployed configuration to the low-profile configuration for a second time period. The first time period may comprise at least a portion of the intake stroke (i.e., prior to the compression stroke) and/or at least a portion of the compression stroke, and the second time period may comprise a least a portion of a power stroke. In yet other embodiments, the second time period may comprise essentially, or substantially, all of the power stroke. Other suitable time periods are also contemplated. 
       FIG. 8C  schematically illustrates a time point during a power stroke of the embodiment of the engine of  FIG. 7 . As the piston  550  reaches a top portion of the combustion chamber  520 , a fuel injector  570  may inject or introduce a second combustion fluid  535  into the interior volume  525  of the combustion chamber  520 . The heat generated by the compression of the first combustion fluid  530  may ignite the introduced second combustion fluid  535 . The ignition and burning of the second combustion fluid  535  causes the volume of at least the second combustion fluid  535  to expand, which drives or pushes the piston  550  downward, as indicated by the arrow  552 . As illustrated, the plurality of microchannel heat transfer elements  503  can transition from the deployed configuration to the low-profile configuration. Stated another way, at least a portion of the heat absorption element  502  may be configured to be at least partially withdrawn from the interior volume  525  of the combustion chamber  520  between at least a portion of the compression stroke and at least a portion of the power stroke. In some embodiments, the piston  550  may be configured such that it does not contact the heat transfer system  500 , thus avoiding potential damage to and/or wear on the heat transfer system  500 . 
     In other embodiments, a shape of the heat absorption element, like heat absorption element  502 , may be configured to change between at least a portion of the compression stroke and at least a portion of the power stroke. A surface area of the heat absorption element may also be configured to decrease between at least a portion of the compression stroke and at least a portion of the power stroke. In still other embodiments, a position of the heat absorption element may be configured to change between at least a portion of the compression stroke and at least a portion of the power stroke. For example, the position of the heat absorption element may change such that the heat absorption element is no longer in communication with an interior volume of a combustion chamber. 
     With reference to  FIG. 8C , the heat transfer system  500  may be coupled to the fuel injector  570 . In some embodiments, the heat transfer system  500  may be configured to absorb heat into a fuel present in at least a portion of the heat transfer system  500 . The heat transfer system  500  may be further configured to transfer the heated fuel from the heat absorption element  502  to the fuel injector  570  such that the heated fuel may be injected into the combustion chamber  520  at a predetermined time. Such a configuration may enhance or increase the efficiency of the compression and/or power strokes of the compression-ignition internal combustion engine. 
     In certain embodiments, the fuel injector  570  may be coupled to both the combustion chamber  520  and the heat absorption element  502 . The fuel injector  570  may be configured to introduce or inject at least a portion of the heated fuel from the heat absorption element  502  into the interior volume  525  of the combustion chamber  520  at a predetermined time. Such an embodiment may also be adapted for use in an embodiment of a compression-ignition internal combustion engine comprising a precombustion chamber. In certain other embodiments, the heat absorption element  502  may be coupled to, or in communication with, a heat exchanger (not shown). The heat exchanger may be configured to transfer an amount of heat from a heated first cooling fluid to the first combustion fluid  530 , wherein the fuel injector  570  may be configured to introduce or inject the heated first combustion fluid  530  into the interior volume  525  of the combustion chamber  520  at a predetermined time. 
       FIG. 8D  is a schematic depiction of a time point during an exhaust stroke of the embodiment of the engine of  FIG. 7 . As illustrated, after the power stroke an exhaust valve  555  may open, and upward movement of the piston  550 , as depicted by the arrow  553 , can drive or force exhausted first and/or second combustion fluids  532 ,  537  from the interior volume  525  of the combustion chamber  520 , as illustrated by an arrow  556 . 
       FIG. 9  is a schematic illustration of a portion of another embodiment of a compression-ignition internal combustion engine depicting another embodiment of a heat transfer system  600 . As detailed above, in certain embodiments the heat transfer systems  100 ,  200 ,  300 ,  400 ,  500  may be configured to be retrofitted into an embodiment of an existing internal combustion engine. With reference to  FIG. 9 , the heat transfer system  600  may be at least partially disposed within or coupled to a piston  650 . As illustrated, the heat absorption element  602  may be at least partially disposed within the piston  650  such that the heat absorption element  602  is in communication, or thermal communication, with an interior volume  625  of a combustion chamber  620 . The heat transfer system  600  can also comprise a thermal transfer element  606 , wherein the thermal transfer element  606  is in communication with the heat absorption element  602 . As described above in connection with other embodiments, the thermal transfer element  606  can be configured to extend at least from a first position at or adjacent the heat absorption element  602  to a second position outside of the combustion chamber  620 . Other locations or positions within an embodiment of an existing compression-ignition internal combustion engine may also be suitable for the disposition of another embodiment of a heat transfer system, similar to heat transfer systems  100 ,  200 ,  300 ,  400 ,  500 ,  600 . 
     In some embodiments, a heat transfer system, similar to heat transfer systems  500 ,  600 , may be coupled to a glow plug and/or at least a portion of the heat transfer system may be at least partially disposed through a glow plug aperture. Alternatively, the heat transfer system may comprise a glow plug element. The heat absorption element may also be configured to extend from the glow plug aperture into at least a portion of an interior volume of a combustion chamber, or a precombustion chamber, at a predetermined time. For example, the heat absorption element may extend from the glow plug aperture into at least a portion of the interior volume of the combustion chamber, or the precombustion chamber, during at least a portion of the power stroke. The heat transfer system may further comprise a thermal transfer element that extends through at least a portion of the glow plug aperture. In some embodiments, the thermal transfer element may be configured for the passage of the first cooling fluid. For example, the thermal transfer element may comprise a lumen for disposition of the first cooling fluid. The thermal transfer element may be further configured to transfer heat from the interior volume of the combustion chamber to a heat sink. 
     As detailed above in connection with other embodiments, the heat transfer system  600  may be coupled to the fuel injector  670  and/or at least a portion of the heat transfer system  600  may be at least partially disposed through a fuel injector aperture. Likewise, the heat transfer system  600  may be at least partially disposed through an aperture of a removable and/or replaceable component. A heat transfer system may also be coupled to a fuel injector, and/or at least a portion of the heat transfer system may be at least partially disposed through a fuel injector aperture, a removable component aperture, and/or a replaceable component aperture in a spark-ignition internal combustion engine. 
     The above-described components and systems may also be utilized or incorporated into engines comprising variable-stroke capabilities or variable-compression-ratio capabilities. Various engines may leverage the cooling of a compressed combustion fluid to attain the combustion fluid-utilization efficiencies of some compression-ignition internal combustion engines or diesel engines. 
     Methods are also contemplated in connection with the systems and elements disclosed above. Disclosure recited in connection with any system herein may be analogously applied to any method. In other words, any of the processes, steps, cycles, or functions described in connection with the systems above may be analogously incorporated into methods within the scope of this disclosure. 
     An exemplary method relating to the systems discussed above may comprise a method of improving the performance of an internal combustion engine. The method may comprise absorbing heat from an interior volume of the combustion chamber during at least a portion of a compression stroke. In some embodiments, a greater portion of a total amount of heat may be absorbed from a compressed first combustion fluid than is absorbed from a total amount of heat from an ignited first combustion fluid. Stated another way, more heat may be removed from the combustion chamber when the first combustion fluid is being compressed than when the first combustion fluid is being ignited and burned. The improvement in the performance of the internal combustion engine may comprise reducing compression work. In some embodiments, the method of improving the performance of an internal combustion engine may comprise increasing a charge density in the combustion chamber at the start of the compression stroke. In certain embodiments, the method of improving the performance of an internal combustion engine may comprise increasing a compression ratio of the engine. 
     In some embodiments, the method may further comprise transferring at least a portion of the heat absorbed from the first combustion fluid and/or the combustion chamber to a position outside of the combustion chamber. As described above, the absorbed heat may be transferred to a heat sink. Alternatively, the heat transferred from the compressed first combustion fluid may be introduced or reintroduced into the interior volume of the combustion chamber during at least a portion of the ignition and/or burning of the first combustion fluid. 
     Another exemplary method relating to the systems discussed above may comprise increasing a maximum charge density in a combustion chamber of an internal combustion engine. In some embodiments, the method may further comprise maintaining a compression ratio of the engine and increasing an initial charge density in the combustion chamber. In other embodiments, the method may further comprise increasing a compression ratio of the engine and maintaining an initial charge density in the combustion chamber. 
     Yet another exemplary method relating to the systems discussed above may comprise a method of retrofitting an existing internal combustion engine by disposition of a heat transfer system, as described above, in communication with one or more combustion chambers of the existing internal combustion engine. In a retrofitted internal combustion engine the charge density in the combustion chamber may be increased, as the retrofitted engine may comprise an increased compression ratio and as such may tolerate increased compression. 
       FIG. 10  is a pressure volume (PV) diagram illustrating the effects of cooling (i.e., the absorption and/or transfer of heat from an interior volume of a combustion chamber, as described above) in an idealized internal combustion engine. Process  775 , or the process shown by the line extending from point A to point B, depicts a compression of contents of the interior volume of the combustion chamber (i.e., via movement of a piston). Process  775 ′, or the process shown by the line extending from point A to point B′, depicts the compression of contents in an interior volume of a combustion chamber wherein absorption and/or transfer of heat, as disclosed herein, has occurred. Process  780 , or the process shown by the line extending from point B to point C, indicates combustion or ignition of the contents of the interior volume of the combustion chamber and subsequent burning of the contents. Process  780 ′, or the process shown by the line extending from point B′ to point C, depicts the compression of contents in the interior volume of the combustion chamber wherein absorption and/or transfer of heat has occurred. Process  785 , or the process shown by the line extending from point C to point D, indicates expansion of the contents of the interior volume of the combustion chamber (i.e., the power stroke) and process  790 , or the process indicated by the line extending from point D to point A, indicates exhaust. As indicated by the area  777 , the cooling may reduce compression work in the engine. 
       FIG. 11  depicts pressure volume curves of a first internal combustion engine  792  and a second internal combustion engine  794 . The second engine  794  comprises an increased compression ratio  796  relative to the first engine  792 , while a temperature at ignition as indicated by the dotted line  778  is substantially the same in both engines  792 ,  794 . As discussed above, increasing the compression ratio  796  of an internal combustion engine may improve a performance of the engine. Also, an engine with an increased compression ratio  796  may tolerate increased compression. Further, methods of the present disclosure may comprise increasing the compression ratio  796  of the engine while maintaining an initial charge density in the interior volume of the combustion chamber. 
       FIG. 12  depicts another PV diagram illustrating the effects of an increased charge density  787 , and increased pressure rise, in an internal combustion engine. Improving the performance of an internal combustion engine may comprise increasing a charge density in the interior volume of the combustion chamber at or near the start of the compression at point A. In contrast to  FIG. 11 , methods of the present disclosure may alternatively comprise maintaining a compression ratio of the engine and increasing an initial charge density in the interior volume of the combustion chamber. 
     Without further elaboration, it is believed that one skilled in the art can use the preceding description to utilize the present disclosure to its fullest extent. The examples and embodiments disclosed herein are to be construed as merely illustrative and exemplary and not as a limitation of the scope of the present disclosure in any way. It will be apparent to those having skill in the art, having the benefit of this disclosure, that changes may be made to the details of the above-described embodiments without departing from the underlying principles of the disclosure herein.