Abstract:
An ignition system for use with an engine is disclosed. The ignition system may have an igniter connected to selectively ignite a fuel mixture within the engine, an injector located to inject a non-combustible gas into the engine, and a controller in communication with the igniter and the injector. The controller may be configured to energize the igniter during a first mode of engine operation to ignite the fuel mixture, and cease energizing the igniter during a second mode of engine operation. The controller may also be configured to actuate the injector during the second mode of engine operation to promote auto-ignition of the fuel mixture.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to an ignition system and, more particularly, to an ignition system using an igniter and a gas injector to initiate combustion. 
       BACKGROUND 
       [0002]    Engines, including diesel engines, gasoline engines, gaseous fuel powered engines, and other engines known in the art ignite an air/fuel mixture to produce heat. In one example, fuel injected into a combustion chamber of the engine is ignited by way of a spark plug, a glow plug, or an AC/DC ignition source. The heat and expanding gases resulting from this combustion process are directed to displace a piston or move a turbine blade, both of which can be connected to a crankshaft of the engine. As the piston is displaced or the turbine blade is moved, the crankshaft is caused to rotate. This rotation is utilized to directly drive a device such as a transmission to propel a vehicle, or a generator to produce electrical power. 
         [0003]    During operation of the engine described above, a complex mixture of air pollutants can be produced as a by product of the combustion process. These air pollutants are composed of, among other things, the oxides of nitrogen (NO X ). Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of NO X  emitted to the atmosphere from an engine is regulated depending on the type of engine, size of engine, and/or class of engine. 
         [0004]    It has been established that a well-distributed combustion flame having a low flame temperature can reduce NO X  production to levels compliant with current emission regulations. One way to generate a well-distributed flame with a low flame temperature is to introduce a lean air/fuel mixture into the combustion chambers of the engine. This lean mixture, when ignited, burns at a relatively low temperature. The lowered combustion temperature slows the chemical reaction of the combustion process, thereby decreasing the formation of NO X . As emission regulations become stricter, leaner and leaner mixtures are being implemented. 
         [0005]    Although successful at reducing emissions, very lean air/fuel mixtures are difficult to ignite. That is, a conventional igniter (spark plug, glow plug, etc.) may be insufficient to initiate and/or maintain combustion of a mixture that has little fuel (compared to the amount of air present). As a result, the emission reduction available from a typical engine operated in a lean mode may be limited. In addition, conventional igniters suffer from low component life. 
         [0006]    One attempt at improving combustion initiation of a lean air/fuel mixture is disclosed in U.S. Pat. No. 7,171,924 ( the &#39;924 patent), issued to Robel et al. on Feb. 6, 2007. The &#39;924 patent discloses an internal combustion engine having a combustion chamber, and a piston slidably disposed within the combustion chamber. The piston is configured to reciprocate through a compression stroke to pressurize an air/fuel mixture within the combustion chamber. The internal combustion engine also has an air supply and a fuel supply in selective fluid communication with the combustion chamber. The internal combustion engine further has a supply of non-combustible gas, and an injector in fluid communication with the combustion chamber and the supply of non-combustible gas. The injector is configured to inject the non-combustible gas from the supply into the combustion chamber at a time during or just after completion of the compression stroke to cause auto-ignition of the pressurized air/fuel mixture within the combustion chamber. In one example, the non-combustible gas includes recirculated exhaust. In this manner, ignition of a lean air/fuel mixture may be possible without the use of a conventional igniter. 
         [0007]    Although the engine of the &#39;924 patent benefits from auto-ignition of a lean air/fuel mixture, improvements may still be possible. Specifically, in some situations such as during startup or cold operation, the injection of non-combustible gas may, alone, be insufficient to promote auto-ignition. 
         [0008]    The disclosed ignition control system is directed to overcoming one or more of the problems set forth above. 
       SUMMARY OF THE INVENTION  
       [0009]    In one aspect, the present disclosure is directed to an ignition system for an engine. The ignition system may include an igniter connected to selectively ignite a fuel mixture within the engine, an injector located to inject a non-combustible gas into the engine, and a controller in communication with the igniter and the injector. The controller may be configured to energize the igniter during a first mode of engine operation to ignite the fuel mixture, and cease energizing the igniter during a second mode of engine operation. The controller may also be configured to actuate the injector during the second mode of engine operation to promote auto-ignition of the fuel mixture. 
         [0010]    In another aspect, the present disclosure is directed to a method of initiating combustion within an engine. The method may include locally heating a fuel mixture within the engine to initiate combustion during a first mode of engine operation, and ceasing the local heating during a second mode of engine operation. The method may further include injecting a non-combustible gas into the engine during the second mode of engine operation to facilitate auto-ignition of the fuel mixture. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a diagrammatic and schematic illustration of an exemplary disclosed engine; and 
           [0012]      FIG. 2  is another diagrammatic and schematic illustration of another exemplary disclosed engine. 
       
    
    
     DETAILED DESCRIPTION   
       [0013]      FIG. 1  illustrates an exemplary combustion engine  10 . For the purposes of this disclosure, engine  10  is depicted and described as a four-stroke gaseous-fueled engine, for example a natural gas engine. One skilled in the art will recognize, however, that engine  10  may be any other type of combustion engine such as, for example, a gasoline or a diesel-fueled engine. Engine  10  may include an engine block  12  that at least partially defines one or more cylinders  14  (only one shown in  FIGS. 1 and 2 ). A piston  16  may be slidably disposed within each cylinder  14  to reciprocate between a top-dead-center (TDC) position and a bottom-dead-center (BDC) position, and a cylinder head  18  may be associated with each cylinder  14 . Cylinder  14 , piston  16 , and cylinder head  18  may together define a combustion chamber  20 . It is contemplated that engine  10  may include any number of combustion chambers  20  and that combustion chambers  20  may be disposed in an “in-line” configuration, a “V” configuration, or in any other suitable configuration. 
         [0014]    Engine  10  may also include a crankshaft  22  that is rotatably disposed within engine block  12 . A connecting rod  24  may connect each piston  16  to crankshaft  22  so that a sliding motion of piston  16  between the TDC and BDC positions within each respective cylinder  14  results in a rotation of crankshaft  22 . Similarly, a rotation of crankshaft  22  may result in a sliding motion of piston  16  between the TDC and BDC positions. In a four-stroke engine, piston  16  may reciprocate between the TDC and BDC positions through an intake stroke, a compression stroke, a combustion or power stroke, and an exhaust stroke. It is also contemplated that engine  10  may alternatively be a two-stroke engine, wherein a complete cycle includes a compression/exhaust stroke (BDC to TDC) and a power/exhaust/intake stroke (TDC to BDC). 
         [0015]    Cylinder head  18  may define an intake passageway  26  and an exhaust passageway  28 . Intake passageway  26  may direct compressed air or an air and fuel mixture from an intake manifold  30 , through an intake opening  32 , and into combustion chamber  20 . Exhaust passageway  28  may similarly direct exhaust gases from combustion chamber  20 , through an exhaust opening  34 , and into an exhaust manifold  36 . 
         [0016]    An intake valve  38  having a valve element  40  may be disposed within intake opening  32  and configured to selectively engage a seat  42 . Valve element  38  may be movable between a first position, at which valve element  40  engages seat  42  to inhibit a flow of fluid relative to intake opening  32 , and a second position, at which valve element  40  is removed from seat  42  to allow the flow of fluid. 
         [0017]    An exhaust valve  44  having a valve element  46  may be similarly disposed within exhaust opening  34  and configured to selectively engage a seat  48 . Valve element  46  may be movable between a first position, at which valve element  46  engages seat  48  to inhibit a flow of fluid relative to exhaust opening  34 , and a second position, at which valve element  46  is removed from seat  48  to allow the flow of fluid. 
         [0018]    A series of valve actuation assemblies (not shown) may be operatively associated with engine  10  to move valve elements  40  and  46  between the first and second positions. It should be noted that each cylinder head  18  could include multiple intake openings  32  and multiple exhaust openings  34 . Each such opening would be associated with either an intake valve element  40  or an exhaust valve element  46 . Engine  10  may include a valve actuation assembly for each cylinder head  18  that is configured to actuate all of the intake valves  38  or all of the exhaust valves  44  of that cylinder head  18 . It is also contemplated that a single valve actuation assembly could actuate the intake valves  38  or the exhaust valves  44  associated with multiple cylinder heads  18 , if desired. The valve actuation assemblies may embody, for example, a cam/push-rod/rocker arm arrangement, a solenoid actuator, a hydraulic actuator, or any other means for actuating known in the art. 
         [0019]    A fuel injection device  50  may be associated with engine  10  to direct pressurized fuel into combustion chamber  20 . Fuel injection device  50  may embody, for example, an electronic valve situated in communication with intake passageway  26 . It is contemplated that injection device  50  could alternatively embody a hydraulically, mechanically, or pneumatically actuated injection device that selectively pressurizes and/or allows pressurized fuel to pass into combustion chamber  20  via intake passageway  26  or in another manner (i.e., directly). The fuel may include a compressed gaseous fuel such as, for example, natural gas, propane, bio-gas, landfill gas, or hydrogen. It is also contemplated that the fuel may be liquefied, for example, gasoline, diesel, methanol, ethanol, or any other liquid fuel, and that an onboard pump (not shown) may be required to pressurize the fuel. 
         [0020]    The amount of fuel allowed into intake passageway  26  by injection device  50  may be associated with a ratio of fuel-to-air introduced into combustion chamber  20 . Specifically, if it is desired to introduce a lean mixture of fuel and air (mixture having a relatively low amount of fuel compared to the amount of air) into combustion chamber  20 , injection device  50  may remain in an injecting position for a shorter period of time (or otherwise be controlled to inject less fuel per given cycle) than if a rich mixture of fuel and air (mixture having a relatively large amount of fuel compared to the amount of air) is desired. Likewise, if a rich mixture of fuel and air is desired, injection device  50  may remain in the injecting position for a longer period of time (or otherwise be controlled to inject more fuel per given cycle) than if a lean mixture is desired. 
         [0021]    An ignition system  52  may be associated with engine  10  to help regulate the combustion of the fuel and air mixture within combustion chamber  20  during a first mode and a second mode of operation. Ignition system  52  may include an igniter  54 , an injector  56 , and an electronic control unit (ECU)  58 . ECU  58  may be configured to regulate operation of igniter  54  and injector  56  in response to input received from one or more sensors  60 . 
         [0022]    Igniter  54  may facilitate ignition of the fuel and air mixture within combustion chamber  20  during the first mode of operation. Specifically, during a startup event or during operation of engine  10  in cold conditions, the temperature of the fuel and air mixture within combustion chamber  20  may be too low for efficient auto-ignition of the mixture (even with the help of injector  56 ). To initiate combustion of the fuel and air mixture, igniter  54  may be energized to locally heat the mixture, thereby creating a flame that propagates throughout combustion chamber  20 . As the combustion process progresses, the temperature within combustion chamber  20  may continue to rise to a level that supports efficient auto-ignition of the mixture. In one embodiment, igniter  54  may be a spark plug. It is contemplated, however, that igniter  54  may alternatively embody a glow plug, an RF igniter, a laser igniter, or any other type of igniter known in the art. 
         [0023]    Injector  56  may be configured to selectively inject a quantity of pressurized non-combustible gas into combustion chamber  20  to facilitate auto-ignition of the fuel air mixture therein during the second mode of operation. In particular, during warm operation of engine  10  (i.e., operation after startup or after engine  10  has reached a minimum temperature that supports auto-ignition, or during a lean or another operation unsuitable for ignition by igniter  54 ) injector  56  may be moved between a first position, at which the pressurized gas is blocked from combustion chamber  20 , and a second position, at which the pressurized gas flows into combustion chamber  20 . The ingress of the pressurized gas when injector  56  is in the second position may cause the mixture of fuel and air within combustion chamber  20  to exceed a threshold pressure and/or a threshold temperature associated with ignition of the mixture. It is contemplated that injector  56  may be caused to pressurize the non-combustible gas during injection into combustion chamber  20 , for example, by way of a cam driven plunger, if desired. It is further contemplated that injector  56  may be also be used during the first mode of operation in conjunction with igniter  54  to enhance startability or cold operation of engine  10 , if desired. 
         [0024]    The non-combustible gas may be, for example, hot exhaust gas recirculated from manifold  36  by way of a passage  57  and pressurized to about 2000 psi prior to injection into combustion chamber  20 . Alternatively, the non-combustible gas could include air, oxygen or nitrogen enriched air, CO 2 , or any other suitable gas. Although described as a non-combustible gas, it is contemplated that the exhaust may, in some situations, contain species representative of complete or partially complete combustion (i.e., the non-combustible gas may contain residual amounts of combustible gas). It is contemplated that, if engine  10  includes a turbocharger, the exhaust may be directed from exhaust manifold  36  at a location upstream of the turbocharger, such that the heat from the combustion process is maintained within the exhaust. During the pressurizing process performed by injector  56 , the temperature of the non-combustible gas may rise even more, by an amount substantially proportional to the rise in pressure and may reach temperatures of, for example, about 1000° C. or higher. It is also contemplated that a means for heating the non-combustible gas may also be included, if desired. 
         [0025]    ECU  58  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 engine  10  in response to signals received from sensor  60 . Numerous commercially available microprocessors can be configured to perform the functions of ECU  58 . It should be appreciated that ECU  58  could readily embody a general engine microprocessor capable of controlling numerous system functions and modes of operation. Various other known circuits may be associated with ECU  58 , 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. 
         [0026]    Sensor  60  may be configured to generate a signal indicative of an engine performance parameter. In one example, the engine performance parameter may be associated with the two modes of engine operation described above. For example, sensor  60  may be disposed proximal to crankshaft  22 , and configured to measure and generate a signal indicative of an instantaneous angular position of crankshaft  22 . Based on this position, a speed of engine  10  may be derived and used to determine when the operation of engine  10  has transitioned from the first mode to the second mode (i.e., when the speed of engine  10  exceeds a starting speed). The position information may also be used to determine a timing at which igniter  54  is energized and/or when injector  56  is controlled to pass pressurized exhaust into combustion chamber  20 . In another example, sensor  60  may be a temperature sensor configured to measure and generate a signal indicative of a temperature of engine  10  used to determine when the operation of engine  10  has transitioned from the first mode to the second mode (i.e., when a temperature of engine  10  exceeds a threshold temperature signifying that operation engine  10  can efficiently support auto-ignition). It should be noted that other similar sensors are also contemplated. 
         [0027]      FIG. 2  illustrates an alternate embodiment of engine  10 . In contrast to  FIG. 1 , engine  10  of  FIG. 2  includes a pre-combustion chamber  100  having orifices  102 . Pre-combustion chamber  100  may be in fluid communication with combustion chamber  20  via orifices  102  and exposed to a mixture of fuel and air similar to that present in combustion chamber  20 . It is contemplated that any number of orifices  102  may be included within pre-combustion chamber  100 . In this embodiment, igniter  54  and/or injector  56  may be disposed to initiate combustion within pre-combustion chamber  100  instead of directly within combustion chamber  20 . After ignition within pre-combustion chamber  100 , one or more flame jets may pass from pre-combustion chamber  100  through orifices  102  into combustion chamber  20 , thereby igniting the remaining fuel and air mixture. In some embodiments, the use of a pre-combustion chamber may improve the combustion process within the main combustion chamber. 
       INDUSTRIAL APPLICABILITY 
       [0028]    The disclosed ignition system may be applicable to any combustion engine where precise control over combustion initiation is desired. Although particularly suited for use with lean-burn, low-NO X  producing engines, the disclosed ignition system may be used with any combustion engine during any type of operation. The disclosed ignition system may improve combustion initiation of a lean-burn engine by facilitating auto-ignition with injections of heated and pressurized non-combustible gas. And, during startup, cold conditions, or other operations that may not readily support auto-ignition, the disclosed system may utilize a conventional igniter alone or in conjunction with the gas injections. The operation of engine  10  will now be explained. 
         [0029]    During an intake stroke of engine  10 , as piston  16  is moving within combustion chamber  20  between the TDC position and the BDC position, intake valve  38  may be in the first position, as shown in  FIG. 1 . During the intake stroke, the downward movement of piston  16  towards the BDC position may create a low-pressure condition within combustion chamber  20 . The low-pressure condition may act to draw fuel and air from intake passageway  26  into combustion chamber  20  via intake opening  32 . As described above, a turbocharger may alternatively be used to force compressed air and fuel into combustion chamber  20 . The fuel may be introduced into the air stream either upstream or downstream of the turbo charger or, alternatively, may be injected directly into combustion chamber  20 . It is contemplated that the fuel may alternatively be introduced into combustion chamber  20  during a portion of the compression stroke, if desired. 
         [0030]    Following the intake stroke, both intake valve  38  and exhaust valve  44  may be in the second position at which the fuel and air mixture is blocked from exiting combustion chamber  20  during the ensuing upward compression stroke of piston  16 . As piston  16  moves upward, from the BDC position towards the TDC position during the compression stroke, the fuel and air within combustion chamber  20  may be mixed and compressed. At a time during the compression stroke or, alternatively, just after completion of the compression stroke, combustion of the compressed mixture may be initiated. 
         [0031]    As described above, combustion may be initiated in one of two different ways, depending on the current operation of engine  10 . For example, during the first mode of operation (i.e., during engine startup or cold operation), ECU  58  may energize igniter  54  to locally heat the now compressed fuel and air mixture. This local heating may result in a flame that propagates throughout combustion chamber  20 , thereby igniting the remaining fuel and air mixture. 
         [0032]    During the second mode of operation, injector  56  may introduce the pressurized exhaust gas into combustion chamber  20 , thereby increasing the pressure and/or temperature of the air and fuel mixture above its auto-ignition threshold. Injection may occur such that auto-ignition is established just after TDC when piston  16  is moving downward through the power stroke. It is contemplated that auto-ignition may alternatively occur just prior to TDC when piston  16  is completing the compression stroke. It is also contemplated that an additional injection of the exhaust gas may be directed into combustion chamber  20  during either the intake stroke or the exhaust stroke to increase swirling, thereby improving mixing of the fuel and air. It is further contemplated that injector  56  may be used together with igniter  54  during the first mode of operation to enhance ignition, if desired. 
         [0033]    In the alternate embodiment of  FIG. 2 , at the time during the compression stroke or just after completion of the compression stroke, igniter  54  and/or injector  56  may be controlled to initiate combustion first within pre-combustion chamber  100  rather than directly within combustion chamber  20 . Because pre-combustion chamber  100  may be fluidly communicated via orifices  102  with a fuel and air mixture similar to that within combustion chamber  20 , ignition of the mixture within pre-combustion chamber  100  may result in ignition within combustion chamber  20 . That is, as the mixture within pre-combustion chamber  100  ignites, the combustion process occurring within pre-combustion chamber  100  may extend into combustion chamber  20  via orifices  102  to raise the temperature and pressure of the mixture within combustion chamber  20  above the ignition threshold of the mixture within combustion chamber  20 . In this manner, injection within pre-combustion chamber  100  may cause ignition of the fuel and air mixture within combustion chamber  20 . Because the volume of pre-combustion chamber  100  may be smaller than the volume of combustion chamber  20 , the injection amount of exhaust gas into pre-combustion chamber  100  required to cause auto-ignition of the fuel and air mixture may be less than when injection occurs directly into combustion chamber  20 . 
         [0034]    Because engine  10  may utilize two different sources of ignition for different operating conditions, reliability and performance of engine  10  may be enhanced. In particular, the use of igniter  54  may enhance starting and operation of engine  10  under cold conditions, while the use of injector  56  may improve efficiency and lower emissions during normal operation. 
         [0035]    It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed ignition system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed ignition 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.