Ducted combustion systems utilizing duct cooling

A ducted combustion system is disclosed. The ducted combustion system may include a combustion chamber and a fuel injector in fluid connection with the combustion chamber and including at least one orifice opening from an injector tip of the fuel injector, the at least one orifice injecting fuel into the combustion chamber as at least one fuel jet. The system may further include at least one duct disposed within the combustion chamber such that the at least one fuel jet, at least partially, enters the at least one duct upon being injected into the combustion chamber. The system may further include a duct cooling system configured to cool a mixture of fuel and air of the at least one fuel jet.

TECHNICAL FIELD

The present disclosure generally relates to internal combustion engines and, more particularly, relates to ducted combustion systems for internal combustion engines that utilize duct cooling systems.

BACKGROUND

Modern combustion engines may include one or more cylinders as part of the engine. The cylinder and an associated piston may define a combustion chamber therebetween. Within the combustion chamber, fuel for combustion is directly injected into the combustion chamber by, for example, a fuel injector, which is associated with the cylinder and has an orifice disposed such that it can directly inject fuel into the combustion chamber.

Different mixtures and/or equivalence ratios of the fuel/air mixture within the fuel jet may produce different results during combustion. The manners in which the injected fuel mixes and/or interacts with the air and other environmental elements of the combustion chamber may impact combustion processes and associated emissions. Further, if the fuel and air mixing is inadequate, then suboptimal or abnormally large amounts of soot may form within the combustion chamber.

To aid in preventing or reducing soot formation and to increase efficiency in such combustion engines, systems and methods for ducted combustion have been developed. For example, U.S. Patent Publication No. 2012/0186555 (“Ducted Combustion Chamber for Direct Injection Engines and Method”) discloses ducted combustion within a combustion engine. The ducts of the '555 application generally include fins disposed around a fuel jet injected by a fuel injector. Such ducts may form a passageway corresponding to an orifice of the fuel injector, into which fuel jets are injected. The fuel jets may be channeled into the ducts, which may improve fuel combustion because upstream regions of a direct-injected fuel jet may be affected by faster and more uniform mixing as well as by an inhibition or reduction of entrainment of combustion products from downstream regions of the same or neighboring jets.

While the teachings of the '555 application are advantageous in providing an improved fuel/air mixture, further improvements in both fuel/air mixtures and flame lift-off length in the ducts are always desired, as such improvements may further reduce emissions and soot formation. Therefore, systems and methods for ducted combustion that utilize duct cooling systems are desired.

SUMMARY

In accordance with one aspect of the disclosure, a ducted combustion system is disclosed. The ducted combustion system may include a combustion chamber, which is defined as an enclosure bound at a first end by a flame deck surface of a cylinder head of an internal combustion engine and bound at a second end by a piston top surface of a piston disposed within the internal combustion engine. The system may further include a fuel injector in fluid connection with the combustion chamber and including at least one orifice opening from an injector tip of the fuel injector, the at least one orifice injecting fuel into the combustion chamber as at least one fuel jet. The system may further include at least one duct disposed within the combustion chamber between the flame deck surface and the piston top surface, the at least one duct being disposed such that the at least one fuel jet, at least partially, enters the at least one duct upon being injected into the combustion chamber. The system may further include a duct cooling system configured to cool a mixture of fuel and air of the at least one fuel jet.

In accordance with another aspect of the disclosure, another ducted combustion system is disclosed. The ducted combustion system may include a combustion chamber, which is defined as an enclosure bound at a first end by a flame deck surface of a cylinder head of an internal combustion engine and bound at a second end by a piston top surface of a piston disposed within the internal combustion engine. The system may further include a fuel injector in fluid connection with the combustion chamber and including a plurality of orifices opening from an injector tip of the fuel injector, the plurality of orifices injecting fuel into the combustion chamber a plurality of fuel jets. The system may further include a duct structure defining a plurality of ducts and disposed within the combustion chamber between the flame deck surface and the piston top surface, the plurality of ducts being disposed such that each of the plurality of fuel jets at least partially enters one of the plurality of ducts upon being injected into the combustion chamber. The system may further include a duct cooling system configured to cool a mixture of fuel and air of the at least one fuel jet of the plurality of fuel jets.

In accordance with yet another aspect of the disclosure, a method for operating a combustion system is disclosed. The method may include injecting a fuel jet into a combustion chamber of an internal combustion engine, the combustion chamber defined as an enclosure bound at a first end by a flame deck of a cylinder of an internal combustion engine, and bound at a second end by a piston top surface of a piston disposed within the internal combustion engine. The method may further include directing the fuel jet, at least partially, into a duct to provide a substantially uniform mixture of fuel and air within the fuel jets. The method may further include cooling the substantially uniform mixture of fuel and air within the duct while the fuel jet is in the duct.

Other features and advantages of the disclosed systems and principles will become apparent from reading the following detailed disclosure in conjunction with the included drawing figures.

While the following detailed description will be given with respect to certain illustrative embodiments, it should be understood that the drawings are not necessarily to scale and the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In addition, in certain instances, details which are not necessary for an understanding of the disclosed subject matter or which render other details too difficult to perceive may have been omitted. It should therefore be understood that this disclosure is not limited to the particular embodiments disclosed and illustrated herein, but rather to a fair reading of the entire disclosure and claims, as well as any equivalents thereto.

DETAILED DESCRIPTION

Turning now to the drawings and with specific reference toFIG. 1, a combustion engine10is shown. The engine10may be an internal combustion engine having a plurality of cylinders12. For example, the cylinders12may be defined as cylinder bores within an engine block13of the engine10. Each of the plurality of cylinders12includes a combustion chamber14. Each combustion chamber14may have a generally cylindrical shape, in accordance with the general shape of the cylinder12.

The combustion chamber14is shown in greater detail in the front, cross-sectional view ofFIG. 2. As shown inFIG. 2, and with continued reference toFIG. 1, the combustion chamber14may be bound at one end by a flame deck surface16of a cylinder head18of each cylinder12. The combustion chamber14may be further bound at a second end by a piston top surface22of a piston24. The piston24is reciprocally disposed within the bore and, as shown inFIG. 1, is connected to a crankshaft26via a connecting rod28. A fuel injector30is in fluid connection with the combustion chamber14and may be mounted in the cylinder head18. The fuel injector30includes a tip32that protrudes into the combustion chamber14through the flame deck surface16. Therefore, the fuel injector30, via the tip32, can directly inject fuel into the combustion chamber14as, for example, one or more fuel jets.

During operation of the engine10, air enters the combustion chamber14via one or more intake valves34(shown inFIG. 2). Air is able to enter the combustion chamber14when the air intake valves34are open, generally, during an intake stroke and/or at the end of an exhaust stroke and/or at the beginning of a compression stroke. When air is present in the combustion chamber14, the fuel injector30, via the tip32, will inject high pressure fuel through orifices36of the tip32as fuel jets35. The fuel jets35may generally disperse within the combustion chamber14to create a fuel/air mixture within the combustion chamber14. Ignition produces combustion, which, in turn, provides work on the piston24to produce motion upon the crankshaft26to drive an output38. Following combustion, exhaust gas may be expelled from the combustion chamber14via one or more exhaust valves39, when said exhaust valves39are open during an exhaust stroke and/or at the end of a power stroke and/or at the beginning of an intake stroke of the engine10.

Within the combustion chamber14, uniformity of the fuel/air mixture may be relevant to the combustion efficiency and may be relevant to the amount and type of combustion byproducts that are formed. For example, if the fuel/air mixture is too rich in fuel due to insufficient mixing within the fuel jets35, then higher soot emissions may occur within the combustion chamber14and/or combustion efficiency may be affected. However, using one or more ducts40disposed within the combustion chamber14may provide for more uniform fuel/air mixing within the fuel jets35. By using one or more ducts40, a lift-off length of a flame associated with a fuel jet35may be altered (extended or reduced) to achieve an optimized lift-off length. The one or more ducts40may alter lift-off length due to energy exchange between the one or more ducts40and the fuel/air mixture of the fuel jet35, due to altering fluid dynamics of the fuel/air mixture of the fuel jet35, and/or due to prevention of lift-off length recession by acting as a flame arrester.

The one or more ducts40may be disposed within a flame region42of the combustion chamber14. The flame region42may be defined as a region of the combustion chamber14extending from the flame deck surface16to the piston top surface22, when the piston24is at or close to a maximum compression distance or top dead center (TDC) position.

To further illustrate the one or more ducts40and their interaction with one or more fuel jets35injected from the one or more orifices36of the tip32of the fuel injector30, the ducts40, within the combustion chamber14, are shown in greater detail inFIG. 3. The one or more ducts40may be duct structures45, as shown. Upon being injected out of the one or more orifices36, the fuel jets35may, at least partially, enter the ducts40at duct openings46and may flow through the ducts40to duct outlets47. In some examples, the ducts40may be positioned and/or supported within the combustion chamber14by a support structure49. The support structure49may be any mounting suitable for positioning the ducts40within the combustion chamber14.

Use of the ducts40may provide improved mixing of a fuel/air mixture within the fuel jets35. Further, by channeling the fuel jets35into the ducts40, entrainment of combustion products from downstream regions of the same or neighboring fuel jets35may be inhibited or reduced. By using such ducts40, levels of soot within the combustion chamber14may be reduced greatly. Additionally, the ducts40may direct combustion away from the fuel injector30, such that longer flame lift-off lengths may be achieved.

Flame lift-off lengths may further be altered by using a duct cooling system50, as illustrated inFIGS. 3 and 4. The duct cooling system50may include a coolant source52for providing a coolant54to the duct structures45via duct cooling passages55, which may be defined by the structure of the duct structure(s)45. Additionally, the duct cooling passages55may allow the coolant52to flow away from the duct structures45, for heat transfer purposes (e.g., transporting the coolant52to an optional heat sink). The duct cooling passages55, as best shown inFIG. 4, may be any void within the interior of the structure of the duct structure(s)45. While the duct cooling passages55are shown as extending, circumferentially, about the interior of the duct structure45, the duct cooling passages55may be defined as any passage within the duct structure45. The duct cooling passages55may be in fluid communication with connective cooling passages56, which may be defined by the structure the duct support structure49. In some examples, the coolant54and/or the coolant source52may be associated with a heat sink58.

For providing the coolant54, the coolant source52may be any reservoir, outside source, internal source, or the like, which may provide the coolant54to the ducts40. For example, the coolant source52may be a connection between the duct cooling system50and a larger cooling system for the engine10, as a whole. Alternatively, the coolant source52may be independent of a cooling system for the engine10and may be specific to one or more of the cylinders12. The coolant54may be any coolant, generally in a liquid form, which can be used to reduce the temperature of engine10components. The coolant54may include, but is certainly not limited to including, one or more of engine coolants, anti-freeze, ethylene glycol, water-based coolants, and the like. In some examples, the coolant54may transfer heat absorbed from the ducts40to the heat sink58, thereby allowing the coolant54to absorb more heat and properly cool the duct(s)40.

The coolant54may reach the duct cooling passages55of the duct structure(s)45via the connective cooling passages56. The connective cooling passages56may be any fluid connection between the coolant source52and the duct cooling passages55, such as, for example, any kind of void within the duct support structure49. Additionally, such a void defining the connective cooling passages56may include any form of piping, tubing, coating, or other structure for aiding in the flow of the coolant54in to and out of the duct cooling passages55.

Use of the duct cooling system50, and any other duct cooling system described below, may be useful in optimizing the flame-lift off lengths associated with the fuel jets35. The duct cooling system50may lower the temperatures of surfaces of the ducts40and/or any interior space defined within the ducts40and, thereby, cools the fuel/air mixture within the ducts40. Flame lift-off lengths may increase in response to decreases in ambient temperature; therefore, a decrease in temperature proximate to the duct40may cool the fuel jets35and, thereby, increase the flame lift-off length of the fuel jets35. Increases in flame lift-off lengths may be associated with decreases in soot within the combustion chamber14.

Turning now toFIG. 5, another duct cooling system60is shown, which shares many like elements of the duct cooling system50ofFIGS. 3 and 4. The duct cooling system60may include a fuel/oil source62for providing one or both of fuel and oil to the duct structures45as a fuel/oil coolant64. The fuel/oil coolant64may be delivered to the duct cooling passages55, for example, by connecting the fuel/oil source62to the connective cooling passages56. The fuel/oil source62may be any source of fuel and/or oil, such as a tap into a fuel source associated with the fuel injector30or a direct line to a fuel source for the engine10, as a whole. The fuel/oil source62may include any additional source of fuel and/or oil, such as, but not limited to engine oil sources, transmission oil sources, and the like.

The fuel/oil coolant64has a much lower temperature than that of ignited fuel within the combustion chamber14. Therefore, it can absorb heat produced proximate to the ducts40and aid in cooling the ducts40using the duct cooling system60. Because fuel and/or oil is readily available due to the ducts40and/or support structure49being in close proximity to the fuel injector30, using the fuel/oil coolant64may be advantageous.

Yet another example of a duct cooling system70is illustrated inFIG. 6. The duct cooling system70may include thermoelectric cooling elements72configured to electrically cool the ducts40. The thermoelectric cooling elements72may be any element which transfers heat by using electrical energy. Example thermoelectric cooling elements72include, but are not limited to including, a Peltier device, a Peltier heat pump, a solid state refrigerator, a thermoelectric cooler, and/or any other device known in the art for using electricity for cooling.

The thermoelectric cooling elements72may receive electricity from a power source74. The power source74may be any element for providing power to the thermoelectric cooling elements72, such as, but not limited to, a battery, a generator, a connection to a power source of the engine10, and the like. In some examples, the output of the power source and, therefore, the cooling levels of the thermoelectric cooling elements72may be controlled by a controller76, which may be any processor, microcontroller, computer, or other controlling element associated with the engine10.

Each thermoelectric cooling element72is associated with a duct structure45. In some examples, the thermoelectric cooling element72may be associated with the duct support structure49. In such examples, the thermoelectric cooling elements72may be embedded within or otherwise affixed to or attached to the duct support structure49. Additionally or alternatively, the thermoelectric cooling elements72may be in contact with and/or embedded within the duct structures45. For example, the thermoelectric cooling elements72could extend into a passage within the duct structures45(e.g., the duct cooling passages55ofFIGS. 3-5).

By utilizing thermoelectric cooling with the duct cooling system70, the ducts40may be cooled using preexisting power sources associated with the engine10. Thermoelectric cooling by the duct cooling system70may lower the temperatures within the ducts40, proximate to the ducts40, and within the fuel/air mixture of the fuel jets35. By utilizing the duct cooling system70, increased flame lift-off lengths for the fuel jets35may be achieved.

Further cooling of the ducts40may be achieved by using a duct cooling system80, as shown inFIG. 7. The duct cooling system80may utilize heat pipes82and a heat sink84associated with the heat pipes82to cool the ducts40and/or the air/fuel mixture within and/or proximate to the ducts40. The heat pipes82may be filled with fluid, in both a pure liquid form and a pure vapor form of said fluid. For example, the fluid may include a methanol-based fluid, which has a low boiling point, and/or the fluid may include a water-based fluid. Heat may be input to the heat pipes82(for example, proximate to the duct40) at a first end85of the heat pipes82. Input of the heat may evaporate part of the liquid portion of the internal fluid of the heat pipe82.

In a non-limiting example heat pipe82wherein heat enters the heat pipe82at the first end85, the heat pipe82may be, functionally, divided into condensation, adiabatic, and evaporation sections. When heat is input at the first end85, the heat that is input evaporates liquid stored in the wick into a vapor. To remove heat, the vapor travels down the adiabatic section to reach the condensation section. At the condensation section, the vapor condenses into liquid and recedes, or soaks into, the wick. Surface tension on the liquid in the wick pulls the liquid through the wick from the condensation section, through the adiabatic section, and to the evaporation section. There, the liquid can be evaporated into vapor to further transfer heat from the first end85to the second end87, which may be proximate to the heat sink86.

By utilizing heat pipes82in the duct cooling system80, heat can be transferred away from the duct structures45, thereby cooling the duct structures45and the proximate area. As such, the fuel air/mixture of the fuel jets35may be cooled, reducing the flame lift-off length.

Other systems for cooling the ducts40and/or the fuel jets35may be employed, such as a trip wire based duct cooling system90ofFIGS. 8 and 9. The duct cooling system90ofFIGS. 8 and 9may include one or more trip wires92, each trip wire92disposed proximate to the opening46of one of the duct structures45. The trip wire92may be any structure disposed at the openings46which may increase the cone angle of the fuel jet35within the duct structure45, as shown inFIG. 9. In some examples, the one or more wires92may be disposed as and/or configured as a mesh structure at the opening46of the duct structure45. By spreading the cone angle of the fuel jet35, the fuel/air mixture may be more evenly distributed throughout the duct structure45, and the fuel/air mixture may be better mixed. By cooling the ducts40and/or the fuel/air mixture, increased flame lift-off lengths may be achieved.

To similarly distribute the fuel jet35and, thereby, cool the ducts40, an alternative duct cooling system93may be used, as illustrated inFIGS. 10 and 11. In the embodiment ofFIGS. 9 and 10, the one or more ducts40may include one or more tilted duct structures95. By using tilted duct structures, as positioned by a tilting support structure99, a duct center axis97of the tilted duct structures95may be not co-axial with a jet center axis96of the fuel jets35. Because the duct center axis97and jet center axis96are not co-axial, the fuel jet35may contact a duct wall94within the tilted duct structure95and, therefore, disperse in a widening manner within the jet. As with the use of the trip wire92, this arrangement will spread the spray of the fuel jet35at an early point within the tilted duct structure95, thereby distributing the fuel jet35within the tilted duct structure95. This, in turn, may cool the air/fuel mixture within the tilted duct structure95, leading to increases in flame lift-off length.

Turning now toFIG. 12, an example embodiment of a duct structure140, which may be used in conjunction with the cylinder12and combustion chamber14of the engine10, is shown. The duct structure140defines a plurality of ducts145and may be disposed within a flame region42of the combustion chamber14. As shown, the ducts145are defined within the duct structure140as, for example, bores within the duct structure140. Upon being injected out of the one or more orifices36, the fuel jets35may enter the ducts145at duct openings146and may flow through the ducts145to duct outlets147.

Similar to the ducts40discussed above, the ducts145of the duct structure140may provide for more uniform fuel/air mixing within fuel jets35. Using such a duct structure140, which defines a plurality of ducts145, a lift-off length of a flame associated with a fuel jet35may be altered (extended or reduced) to achieve an optimized lift-off length.

Flame lift-off lengths may further be altered by using a duct cooling system150. The duct cooling system150may include a coolant source152for providing a coolant154to the duct structure140via duct cooling passages155, which may be defined by the structure of the duct structure(s)140. The duct cooling passages155may be configured such that they provide the coolant154to the duct structure140in locations proximate to the ducts145of the duct structure140, thereby cooling the ducts145and the areas proximate to the ducts145. The duct cooling passages155may be any void within the interior of the duct structure140. The duct cooling passages155may be defined as any passage within the duct structure140.

Additionally, the duct cooling passages155may be in fluid communication with connective cooling passages156, which may be defined by, for example, the cylinder head18, such that the connective cooling passages156connect the coolant source152to the duct cooling passages155. In some examples, the coolant154and/or the coolant source152may be associated with a heat sink158.

For providing the coolant154, the coolant source152may be any reservoir, outside source, internal source, or the like, which may provide a coolant to the duct structure140. For example, the coolant source152may be a connection between the duct cooling system150and a larger cooling system for the engine10, as a whole. Alternatively, the coolant source152may be independent of a cooling system for the engine10and may be specific to one or more of the cylinders12. The coolant154may be any coolant, generally in a liquid form, which can be used to reduce the temperature of components of the engine10. The coolant154may include, but is certainly not limited to including, one or more of engine coolants, anti-freeze, ethylene glycol, water-based coolants, and the like. In some examples, the coolant154may transfer heat absorbed from the duct structure140to the heat sink158, thereby allowing the coolant154to absorb more heat and properly cool the duct structure140.

Turning now toFIG. 13, another duct cooling system160is shown, which shares many like elements of the duct cooling system150ofFIG. 12. The duct cooling system160may include a fuel/oil source162for providing one or both of fuel and engine oil to the duct structure140as a fuel/oil coolant164. The fuel/oil coolant164may be delivered to the duct cooling passages155, for example, by connecting the fuel/oil source162to the connective cooling passages156. The fuel/oil source162may be any source of engine fuel and/or engine oil, such as a tap into a fuel source associated with the fuel injector30or a direct line to a fuel source for the engine10, as a whole. Because fuel and/or engine oil is readily available due to the duct structure140being in close proximity to the fuel injector30, using the fuel/oil coolant64may be advantageous.

Yet another example of a duct cooling system170is illustrated inFIG. 14. The duct cooling system170may include thermoelectric cooling elements172configured to electrically cool the duct structure140. The thermoelectric cooling elements172may be any element which transfers heat by using electrical energy. Example thermoelectric cooling elements172include, but are not limited to including, a Peltier device, a Peltier heat pump, a solid state refrigerator, a thermoelectric cooler, and/or any other device known in the art for using electricity for cooling.

The thermoelectric cooling elements172may receive electricity from a power source174. The power source174may be any element for providing power to the thermoelectric cooling elements172, such as, but not limited to, a battery, a generator, a connection to a power source of the engine10, and the like. In some examples, the output of the power source174and, therefore, the cooling levels of the thermoelectric cooling elements172may be controlled by a controller176, which may be any processor, microcontroller, computer, or other controlling element associated with the engine10.

Each thermoelectric cooling element172is associated with the duct structure140. In some examples, the thermoelectric cooling element172may be built into or otherwise embedded within the duct structure140. Additionally or alternatively, the thermoelectric element may be attached or otherwise affixed to the duct structure140. For example, the thermoelectric cooling elements172could extend into a passage within the duct structure140(e.g., the duct cooling passages155ofFIGS. 3-5).

Further cooling of the duct structure140may be achieved by using a cooling system180, as shown inFIG. 15. The cooling system180may utilize heat pipes182and a heat sink184associated with the heat pipes182to cool the duct structure140and/or the air/fuel mixture within and/or proximate to the ducts145. The heat pipes182may be filled with fluid, in both a pure liquid form and a pure vapor form of said fluid. For example, the fluid may include a methanol-based fluid, which has a low boiling point, and/or the fluid may include a water-based fluid. Heat may be input to the heat pipes182(for example, proximate to the duct40) at a first end185of the heat pipes182. Input of the heat may evaporate part of the liquid portion of the internal fluid of the heat pipe182. In some examples, the liquid that is evaporated may be contained in a wick, which lines the interior of the heat pipe182adjacent to an outer shell of the heat pipes182.

By utilizing heat pipes182in the duct cooling system180, heat can be transferred away from the duct structures145, thereby cooling the duct structures145and the proximate area. As such, the fuel air/mixture of the fuel jets35may be cooled, increasing the flame lift-off length.

Further, another embodiment of a duct cooling system190for use in conjunction with the duct structure140is illustrated inFIG. 16. The duct cooling system190includes a cooling reservoir192which may be defined by the duct structure140. The cooling reservoir192may be filled, in whole or in part, with a coolant194, which may be water or any other liquid that may transfer heat away from the ducts145of the duct structure140. The cooling reservoir192may be cast as part of one or both of the duct structure140and the cylinder head18. Further, the cooling reservoir192may include a plurality of basins196, each of the plurality of basins196being proximate to one of the ducts145. Similarly to the other cooling systems detailed above, the duct cooling system190may direct heat away from the ducts145, thereby cooling the fuel/air mixture within the ducts145and increasing the flame lift-off lengths.

INDUSTRIAL APPLICABILITY

The present disclosure relates generally to internal combustion engines and, more specifically, to ducted combustion systems. While the present disclosure shows the embodiments as related to internal combustion engines having reciprocating pistons, the teachings of the disclosure are certainly applicable to other combustion systems, which utilize diffusion or non-premixed flames, such as gas turbines, industrial burners, and the like. As discussed above, the various arrangements of ducts and their associated duct cooling systems are useful in promoting a substantially uniform fuel/air mixture within fuel jets and may inhibit or reduce entrainment of recirculated combustion products from downstream regions into upstream regions of fuel jets injected into combustion chambers. However, using such systems and methods for ducted combustion may also decrease fuel/air mixing, while reducing equivalence ratio at the lift-off length.

An example method utilizing the ducted combustion systems shown inFIGS. 1-16and described above is exemplified in the flowchart ofFIG. 17, which represents a method200for operating a combustion system. The method200begins at block210, by injecting a fuel jet35into the combustion chamber14of the engine10. The fuel jet35may be directed, at least partially, into a duct of the one or more ducts40, to provide a substantially uniform fuel/air mixture within the fuel jet35, as shown in block220. While the present description of block220refers to the one or more ducts40ofFIGS. 3-11, the block220and/or the method200may employ any of the ducts shown above inFIGS. 3-16, such as, but not limited to, the ducts145of the duct structure140.

The method200further includes cooling the fuel/air mixture of the fuel jet35within the one or more ducts40, as shown in block230. Cooling the fuel/air mixture can be achieved using a cooling system associated with the combustion chamber14of the engine10, such as, but not limited to, the duct cooling systems50,60,70,80,90,93,150,160,170,180,190as described above.

Use of the duct cooling systems50,60,70,80,90,93,150,160,170,180,190, or any other duct cooling system, may be useful in optimizing the flame-lift off lengths associated with the fuel jets35. The duct cooling systems50,60,70,80,90,93,150,160,170,180,190may lower the temperatures of surfaces of the ducts40,145and, thereby, cool the fuel/air mixture proximate to the ducts40,145. Flame lift-off lengths may increase in responses to decreases in ambient temperature; therefore, a decrease in temperature proximate to the duct(s)40,145may cool the fuel jets35and, thereby, increase the flame lift-off length of the fuel jets35. Increases in flame lift-off lengths may be associated with decreases in soot within the combustion chamber14.

As such, by using the duct cooling systems50,60,70,80,90,93,150,160,170,180,190, greater uniformity of equivalence ratio within the fuel jets35may be achieved. Achieving a reduced equivalence ratio at the lift-off length may be accomplished by altering the lift-off length, when employing any of the aspects of the present application. Alterations to the lift-off length may occur if heat is transferred from the fuel/air mixture of the fuel jets35. Additionally or alternatively, alterations to the lift-off length may be achieved by alteration of fuel jet fluid dynamics, which are resultant of characteristics of the ducts40. Substantially soot-free combustion may be achieved if the equivalence ratio at the flame lift-off length is less than two. Therefore, at block240, the method200may include maintaining an equivalence ratio less than two at the flame lift-off length.

FIGS. 18-20show a variety of flames produced during combustion and having different lift-off lengths and associated equivalence ratios. First, the exemplary drawing ofFIG. 18shows a fuel jet252with a lift-off length254, after which the fuel jet252ignites into a flame256. Such examples may have a high equivalence ratio (e.g., in a range of 4-5) at the flame lift-off length254. Such prior art examples may include unwanted soot production within a combustion chamber.

Turning toFIG. 19, a fuel jet262is shown with a lift-off length264, after which the fuel jet ignites into a flame266. Because of the use of a duct268(shown in a cross-sectional view) during combustion, the lift-off length264is greater and the equivalence ratio (e.g., around 2-3) at the lift-off length264may be lower than that ofFIG. 18. Having the lower equivalence ratio may lead to reduced soot production during combustion.

Lastly,FIG. 20shows a further improvement upon the prior art example ofFIG. 18, in that the length of a duct278(shown in a cross-sectional view) is configured to have a length configured to have a low enough equivalence ratio (less than two) such that soot formation is inhibited. A flame276of a fuel jet272may be sufficiently far enough from a fuel injector such that it has an equivalence ratio of less than two at a lift-off length274. It has been found that an equivalence ratio of less than two may produce great results in soot reduction. The lift-off length274which allows for the equivalence ratio to be less than two is enabled by using the duct278, which extends sufficiently far enough from the injector to enable such an equivalence ratio.

Returning now toFIG. 17and, more specifically, block250, the method200may reduce entrainment of recirculated combustion products from a downstream region of the fuel jet35to an upstream region of the fuel jet35by substantially containing a segment of the fuel jet35within a duct40,145. Reducing such entrainment may lead to an overall reduction in soot production within the combustion chamber14and may lead to greater overall efficiency of the engine10. Presence of ducts40,145may alter amount and position of entrainment of recirculated combustion products, within the fuel jets35.

It will be appreciated that the present disclosure provides ducted combustion systems, internal combustion engines utilizing ducted combustion, and methods for operating combustion systems utilizing ducted combustion. While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.