Patent Application
20130220245
The present disclosure is directed to an engine system and, more particularly, to an engine system having a dedicated connection between cylinders.
Combustion engines such as diesel engines, gasoline engines, and gaseous fuel-powered engines are supplied with a mixture of air and fuel for combustion within the engine that generates a mechanical power output and a flow of exhaust gases. The exhaust gases produced by the engine can contain a complex mixture of air pollutants generated as byproducts of the combustion process. For example, the exhaust gases can include a high concentration of NOx when the combustion process generates temperatures greater than about 1500° F.
Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of pollutants emitted to the atmosphere from an engine can be regulated depending on the type of engine, size of engine, and/or class of engine. For this reason, engine manufacturers have implemented a variety of different methods for reducing the type and/or amount of pollutants generated by the engine. One method used by some manufacturers includes reducing combustion temperatures of the engine below the threshold temperature at which NOx formation occurs.
An exemplary NOx-reducing system is disclosed in U.S. Pat. No. 7,028,648 that issued to Hasegawa et al. on Apr. 18, 2006 (“the '648 patent”). In particular, the '648 patent discloses a system for an engine having a plurality of cylinders sharing a single crankshaft. Combustion characteristics of the cylinders are improved by taking out gas from an expanding cylinder and directing the gas into a compressing cylinder. This flow of gas between cylinders is facilitated by way of a dedicated conduit and cam-operated valves associated with each cylinder. By taking out gas from the expanding cylinder at a time of highest temperature, the overall temperature of that cylinder is reduced, thereby also reducing an amount of NOx formed within the cylinder. In addition, by directing the removed gases into the compressing cylinder, a greater power output can be subsequently generated by the compressing cylinder.
Although the system in the '648 patent may help to lower NOx production, it may also be problematic. In particular, the gases being transferred between cylinders include burned or partially burned molecules (soot and particulate matter), which can clog the conduit and/or associated valves. In addition, the transferred gases are at an elevated temperature, which could result in excessive NOx production by the cylinder receiving the gases. Further, it may be difficult to precisely time opening of the gas-transferring valves at peak combustion such that pressures and/or temperatures in the donating cylinder are maintained at desired levels.
The disclosed engine system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.
In one aspect, the disclosure is directed toward an engine system. The engine system may include an intake manifold configured to direct air into combustion chambers of the engine, and an exhaust manifold configured to direct exhaust from the combustion chambers to the atmosphere. The engine system may also include at least one conduit extending from a first of the combustion chambers to a second of the combustion chambers, and at least one valve associated with the at least one conduit. The at least one valve is configured to pass fluid from the first of the combustion chamber to the second of the combustion chambers during a compression stroke of a first piston within the first of the combustion chambers and during an expansion stroke of a second piston within the second of the combustion chambers.
In another aspect, the disclosure is directed toward a method of operating an engine. The method may include compressing air, and directing compressed air through an intake manifold into a plurality of combustion chambers. The method may also include directing exhaust from the plurality of combustion chambers through an exhaust manifold to the atmosphere. The method may further include directing fluid from a first of the plurality of combustion chamber through at least one conduit to a second of the plurality of combustion chambers when a first piston associated with the first of the plurality of combustion chambers is moving through a compression stroke and a second piston associated with the second of the plurality of combustion chambers is moving through an expansion stroke.
An exemplary internal combustion engine 10 is illustrated in
Piston 20 may be configured to reciprocate between a bottom-dead-center (BDC) or lower-most position within liner 16, and a top-dead-center (TDC) or upper-most position. In particular, piston 20 may be pivotally connected to a crankshaft (not shown) and the crankshaft may be rotatably disposed within engine block 12 so that a sliding motion of each piston 20 within liner 16 results in a rotation of the crankshaft. Similarly, a rotation of the crankshaft may result in a sliding motion of piston 20. As the crankshaft rotates through about 180 degrees, piston 20 may move through one full stroke between BDC and TDC. Engine 10, as a two-stroke engine, may have a complete cycle that includes a power(expansion)/exhaust/intake stroke (TDC to BDC) and an intake/compression stroke (BDC to TDC).
During a final phase of the power(expansion)/exhaust/intake stroke described above, air may be drawn and/or forced into combustion chamber 22 via one or more gas exchange ports (e.g., intake ports) 30 located within an annular surface 32 of liner 16. In particular, as piston 20 moves downward within liner 16, a position will eventually be reached at which intake ports 30 are no longer blocked by piston 20 and instead are fluidly communicated with combustion chamber 22. When intake ports 30 are in fluid communication with combustion chamber 22 and a pressure of air at intake ports 30 is greater than a pressure within combustion chamber 22, air will pass from an intake manifold (or other intake duct) 34 through intake ports 30 into combustion chamber 22. The timing at which intake ports 30 are opened (i.e., unblocked by piston 20 and fluidly communicated with combustion chamber 22) may have an effect on a pressure gradient between intake ports 30 and combustion chamber 22 and/or an amount of air that passes into combustion chamber 22 before intake ports 30 are subsequently closed by the ensuing upward movement of piston 20. The opening and/or closing timings of intake ports 30 may also have an effect on a temperature of the air directed into combustion chamber 22. Fuel may be mixed with the air before, during, or after the air is drawn into combustion chamber 22.
During the beginning of the intake/compression stroke described above, air may still be entering combustion chamber 22 via intake port 30 and piston 20 may be starting its upward stroke to mix the fuel and air within combustion chamber 22. Eventually, intake port 30 may be blocked by piston 20 and further upward motion of piston 20 may compress the mixture. As the mixture within combustion chamber 22 is compressed, the pressure and temperature of the mixture will increase. Eventually, the pressure and temperature of the mixture will reach a point at which the mixture combusts, resulting in a release of chemical energy in the form of pressure and temperature spikes within combustion chamber 22. In fuel-injected engines, initiation of combustion may start at or after the start of fuel injection.
During a first phase of the power(expansion)/exhaust/intake stroke, the pressure spike within combustion chamber 22 may force piston 20 downward, thereby expanding the volume of combustion chambers 22 and imparting mechanical power to the crankshaft. At a particular point during this downward travel, one or more gas exchange ports (e.g., exhaust ports) 36 located within cylinder head 18 may open to allow pressurized exhaust within combustion chamber 22 to exit. In particular, as piston 20 moves downward within liner 16, a position will eventually be reached at which exhaust valves 38 move to fluidly communicate combustion chamber 22 with exhaust ports 36. When combustion chamber 22 is in fluid communication with exhaust ports 36 and a pressure of exhaust gas in combustion chamber 22 is greater than a pressure within exhaust ports 36, exhaust gas will pass from combustion chamber 22 through exhaust ports 36 into an exhaust manifold 40. The timing at which exhaust valves 38 move to open exhaust ports 36 may have an effect on a pressure gradient between combustion chamber 22 and exhaust ports 36 and/or an amount of exhaust that passes from combustion chamber 22 before exhaust ports 36 are subsequently closed by exhaust valves 38. The opening and/or closing timings of exhaust ports 36 may also have an effect on a gas temperature within combustion chamber 22. In the disclosed embodiment, movement of exhaust valves 38 may be cyclically controlled by way of a cam that is mechanically linked to the crankshaft. It is contemplated, however, that movement of exhaust valves 38 may be controlled in any other conventional manner, as desired. It is also contemplated that exhaust ports 36 could alternatively be located within cylinder liner 16 and exhaust valves 38 omitted, if desired, such as in a loop-scavenged two-cycle engine.
As shown in
After passing through turbines 46, the exhaust may first be treated before being released back to the atmosphere. In particular, one or more exhaust treatment devices (not shown) may be located to receive the exhaust from turbine 46. The exhaust treatment devices may include, for example, a particulate filter, one or more catalysts, or another treatment device known in the art. The exhaust treatment devices may be configured to remove, trap, reduce, or otherwise convert pollutants in the exhaust flow of engine 10 to innocuous substances.
Engine 10 may be equipped with a system 42 that is configured to selectively and fluidly communicate one combustion chamber 22 directly with another combustion chambers 22. Specifically, system 42 may include a conduit 54 that is connected between fewer than all of combustion chambers 22 in a manner separate from intake and exhaust manifolds 34, 40. In the disclosed embodiment, conduit 54 is connected between only two combustion chambers 22. It should be noted, however, that conduit 54 may alternatively be connected between three or more combustion chambers 22 and/or that multiple conduits 54 may separately connect different pairings and/or groupings of combustion chambers 22, if desired. At least one valve 56 may be associated with conduit 54 and configured to control fluid flow through conduit 54.
Returning to
Controller 60 may embody a single or multiple microprocessors, field programmable gate arrays (FPGAs), digital signal processors (DSPs), etc. that include a means for controlling an operation of system 42. Numerous commercially available microprocessors can be configured to perform the functions of controller 60. It should be appreciated that controller 60 could readily embody a microprocessor separate from that controlling other non-exhaust related functions, or that controller 60 could be integral with a general engine microprocessor and be capable of controlling numerous engine functions and modes of operation. If separate from a general engine microprocessor, controller 60 may communicate with the general engine microprocessor via data links or other methods. Various other known circuits may be associated with controller 60, including power supply circuitry, signal-conditioning circuitry, actuator driver circuitry (i.e., circuitry powering solenoids, motors, or piezo actuators), communication circuitry, and other appropriate circuitry.
Before, during, and/or after regulating exhaust flow through conduit 54 via valve(s) 56, controller 60 may receive data indicative of an operational condition of engine 10 and/or an actual flow rate, constituency, temperature, and/or pressure of fluid within conduit 54. Such data may be received from another controller or computer (not shown), from sensors strategically located throughout system 42, and/or from a user of engine 10. Controller 60 may then utilize stored algorithms, equations, subroutines, look-up maps and/or tables to analyze the operational condition data and determine a corresponding desired flow rate and/or constituency of fluid within conduit 54 that produces a desired performance of engine 10. Based on the desired flow rate and/or constituency, controller 60 may then cause valve 56 to open at the right timing relative to the strokes of the associated pistons 20 such that the desired flow rate and constituency of fluid is passed therebetween.
The disclosed system may be applicable to any engine where interconnection between combustion chambers of the engine can enhance operation of the engine. The disclosed system may enhance engine operation by selectively directing air from a compressing combustion chamber to an expanding combustion chamber, thereby reducing a peak temperature of the compressing combustion chamber. When the peak temperature is maintained at a sufficiently low level, for example below about 1500° F., the production of NOx may be reduced. Operation of system 42 will now be described with reference to
As shown in
In one embodiment, valve(s) 56 may be controlled to open when the first piston 20 is being propelled downward by expanding combustion gases (i.e., when the first piston 20 is undergoing an expansion stroke—curve 300) at a point A, and again controlled to close toward the end of the expansion stroke at a point B. At this same time, the second piston 20 may be pushing upward to compress air within the second combustion chamber 22 (i.e., the second piston 20 may be moving through a compression stroke—curve 310) and the pressure within the second combustion chamber 22 may be much greater than the pressure within the first combustion chamber 22. The pressure differential between the first and second combustion chambers 22, combined with the current operations of the first and second pistons 20 (i.e., expansion and compression strokes), may cause compressed air (or a compressed mixture of fuel and air) to be pushed from the second combustion chamber 22 into the first combustion chamber 22 via conduit 54. Point A may correspond with about 10 degrees of crank angle before the second piston 20 reaches its TDC position and about 35 degrees of crank angle after the first piston 20 passes through its TDC position. Point B may correspond with about TDC of the second piston 20 and about 55 degrees of crank angle after the first piston 20 passes through its TDC position.
This flow of fluid from the second combustion chamber 22 to the first combustion chamber 22 may reduce a quantity of air (or air and fuel) within the second combustion chamber 22 at the start of combustion. A reduced amount of air (or air and fuel) in the second combustion chamber 22 may result in a reduced combustion temperature and pressure during the following expansion stroke, and a corresponding reduction in the formation of particular pollutants (e.g., NOx). In addition, the flow of compressed air into the first combustion chamber 22 may help to scavenge exhaust from the first combustion chamber 22 as well as increase an exhaust pressure used to drive turbocharger 50.
Several advantages may be associated with the disclosed system 42. In particular, because conduit 54 may be dedicated to facilitating only inter-cylinder fluid communication, characteristics of conduit 54 (e.g., material properties, volume, flow area, etc.) may be selected for optimum performance. In addition, because valve(s) 56 may open during the end of a compression stroke and the end of an expansion stroke, the timing of the opening may be less critical than at other phases of the combustion process. Finally, because the fluid passed between combustion chambers 22 in the disclosed system may consist primarily of air (or air and fuel, but generally not combustion gases), contamination or fouling of system components (e.g., conduit 54, valves 56, etc.) may be unlikely and improved scavenging of the combustion chamber may be attained.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed engine system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed engine system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
