Patent Publication Number: US-9843165-B2

Title: Cap shielded ignition system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims the benefit of priority to U.S. patent application Ser. No. 14/664,431, filed on Mar. 20, 2015, the contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     Engines operating on gaseous fuels, such as natural gas, are commonly supplied with a lean fuel mixture, which is a mixture of air and fuel containing excess air beyond that which is stoichiometric for combustion. In some engines, multiple chambers within the igniter plug can allow more efficient combustion of lean fuel mixtures. However, bulk flow and turbulence in the vicinity of the flame kernel can tend to extinguish the flame kernel. Bulk flow and turbulence can increase the chance of misfires or failed ignition events. In some cases, electrode quenching can be a problem for combustion stability when using lean mixtures with a prechamber-type igniter plug. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side cross-sectional view of a portion of an internal combustion engine including a shielding cap. 
         FIG. 2A  illustrates a cross-sectional view of a portion of a first example ignition system including a shielding cap. 
         FIG. 2B  illustrates a cross-sectional view of a portion of the first example ignition system showing example flow. 
         FIG. 2C  illustrates a perspective view of a portion of the first example ignition system. 
         FIG. 2D  illustrates a cross-sectional view of a portion of a second example ignition system including a shielding cap. 
         FIG. 3  illustrates a cross-sectional view of a portion of a third example ignition system including a shielding cap and peripheral shields. 
         FIG. 4A  illustrates a cross-sectional view of a portion of a fourth example ignition system including a shielding cap. 
         FIG. 4B  illustrates a cross-sectional view of a portion of a fifth example ignition system including a shielding cap. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The concepts herein relate to igniting an air/fuel mixture in a combustion chamber of an engine using an igniter with a shielding cap. 
       FIG. 1  shows a cross-section of a portion of an example internal combustion engine  100 . The example internal combustion engine  100  is a reciprocating engine and includes a head  102 , a block  122 , and a piston  104 . The piston  104  is located inside a cylinder inside the block  122 . The piston  104  is able to reciprocate inside the cylinder during engine operation. The combustion chamber  106  is a volume located inside the cylinder between the head  102  and the piston  104 , and is bounded by the block  122 .  FIG. 1  shows a single piston  104 , but the internal combustion engine  100  may have multiple pistons  104  with associated components. 
     The example internal combustion engine  100  includes an intake passage  108  with intake valve  110  and an exhaust passage  112  with exhaust valve  114 . The passages  108 ,  112  are in the head  102  adjacent to the combustion chamber  106 , and the valves  110 ,  114  form part of the walls of the combustion chamber  106 . During engine operation, the intake valve  110  opens to let a fresh charge of air/fuel mixture flow from the intake passage  108  into the combustion chamber  106 . In other instances, the intake valve  110  admits only air and an in-combustion chamber fuel injector admits fuel to form the air/fuel mixture in the combustion chamber  106 . After combustion, the exhaust valve  114  opens to exhaust combustion residuals out of the combustion chamber  106  and into the exhaust passage  112 . Although the concepts herein are described herein with respect to a reciprocating internal combustion engine, the concepts could be applied to other internal combustion engine configurations. 
     The example internal combustion engine  100  includes an example carrier  116  and an igniter plug  123 . The carrier  116  is located in the head  102  and is threadingly and/or otherwise coupled to the head  102 . In some instances, the carrier  116  can extend into the combustion chamber  106 , be flush with a wall of combustion chamber  106 , or be recessed from a wall of combustion chamber  106 . The example igniter plug  123  is received inside the example carrier  116  and is coupled to the carrier  116  threadingly and/or otherwise. The carrier  116  thus defines an outer enclosure around the igniter plug  123 . 
     The igniter plug  123  is a device configured to initiate a flame kernel to ignite the charge in the combustion chamber  106 , such as a spark plug, laser igniter, and/or other type of igniter. The igniter plug  123  resides generally around a center longitudinal axis. The example igniter plug  123  includes a first ignition body and a second ignition body adjacent the first ignition body to define a flame kernel initiation gap. In some cases, the first ignition body and second ignition body are centered about the center longitudinal axis. The example igniter plug  123  includes a plug body  124  and an example shielding cap  130  at the end of the plug body  124 . The cap  130  is a body that shields the flame kernel initiation gap from air/fuel mixture flows directed generally in the direction of the center longitudinal axis that would otherwise impinge on the gap and tend to extinguish the flame kernel. 
     The example igniter plug  123  and carrier  116  of  FIG. 1  act as a “prechamber” type igniter in that an antechamber  120  encloses flame kernel initiation (i.e., the first and second ignition bodies and the flame kernel initiation gap). The antechamber  120  is an enclosed chamber or space defined inside the carrier  116 . The antechamber  120  is adjacent to but separate from the combustion chamber  106 . In some instances, the antechamber  120  can be formed in the head  102  itself and the carrier  116  can be omitted. The antechamber  120  is defined about an end of the igniter plug  123 . In other instances, rather than being in a separate carrier  116 , the antechamber  120  can be integrated with the igniter plug  123  (e.g., in a common or conjoined housing or enclosure). The antechamber  120  is shown having a symmetrical shape about the center longitudinal axis of the carrier  116  and igniter plug  123 , but in other instances it could be an asymmetrical shape. The antechamber  120  includes an internal nozzle portion  128 , which extends axially through the antechamber  120  from a central passage  126  toward the igniter plug  123 . The internal nozzle portion  128  operates as a jet passage to nozzle a consolidated stream of air/fuel mixture axially through the antechamber  120  and into the igniter plug  123 . In some cases, the antechamber  120  includes an internal enlarged portion axially between the internal nozzle portion  128  and the inner chamber, which has a larger transverse dimension than the internal nozzle portion  128 . The igniter plug  123 , while described in connection with the antechamber  120  in a prechamber configuration in  FIG. 1 , as will be discussed below, could alternatively be used without antechamber  120  and just extending into the main combustion chamber  106 . 
     The example carrier  116  includes diverging jet apertures  118 . The jet apertures  118  include external ends, which terminate at the exterior of the carrier  116  and are nominally located inside the combustion chamber  106 . The internal ends of the jet apertures  118  converge to a central passage  126  that opens into the antechamber  120  through the internal nozzle portion  128 . The jet apertures  118  can number one or more and can be located on the carrier  116  in a symmetric or asymmetric pattern, diverging from the central passage  126 . In some cases, at least one of the jet apertures  118  is parallel (precisely or substantially) to the center longitudinal axis or perpendicular (precisely or substantially) to the center longitudinal axis. In some cases, one of the jet apertures  118  coincides with the center longitudinal axis. In some cases, at least one of the jet apertures  118  are not parallel or perpendicular to the center longitudinal axis. The jet apertures  118  allow charge, flame, and residuals to flow between the antechamber  120  and the combustion chamber  106 . The jet apertures  118  and central passage  126  operate as jet passages to nozzle combusting air/fuel mixture from the antechamber  120  into divergent flame jets that reach into the combustion chamber  106  and ignite the charge in the combustion chamber  106 . The jet apertures  118  and central passage  126  also direct fresh air/fuel mixture from the combustion chamber  106  into the igniter plug body  124 . The central passage  126  directs the flow into a consolidated stream through the internal nozzle portion  128  along the center of the antechamber  120  toward the igniter plug  123 . 
     In operation of the engine  100 , the compressive action of the piston  104  forces a portion of the cool (relative to residual combustion gasses), fresh air/fuel mixture to flow from the combustion chamber  106  into the central passage  126  through the jet apertures  118 . The central passage  126  receives the incoming air/fuel mixture, converges air/fuel mixture into a consolidated stream, and directs the flow into the internal nozzle portion  128  of the antechamber  120 . The internal nozzle portion  128  nozzles the incoming cool, fresh charge into a central high-velocity consolidated stream primarily directed toward the cap  130  of the igniter plug  123 . The antechamber  120  receives all of its air/fuel mixture from the main combustion chamber  106 . In other instances, the antechamber  120  can have a fuel feed that supplies a portion of the received fuel or air/fuel mixture into the antechamber  120 . 
       FIG. 2A-B  illustrate cross-sectional views of portions of example ignition system  200 .  FIG. 2C  illustrates a perspective detail view of igniter plug  123  of example ignition system  200 . The example ignition system  200  can be used in an internal combustion engine such as engine  100 . Ignition system  200  shown in  FIG. 2A  includes an igniter plug  123  received within a carrier  116 . The ignition system  200  also includes a cap  130  at an end of the plug body  124  disposed within antechamber  120 . The cap  130  is longitudinally spaced from the plug body  124  by a support  137  that includes legs  138   a - b . The ignition system  200  also includes a first ignition body  136  and a second ignition body  134  adjacent the first ignition body  136  that define the flame kernel initiation gap  135 . In some implementations, the first ignition body  136  and the second ignition body  134  are disposed between the plug body  124  and the cap  130 . In some implementations, the first ignition body  136  is carried by the plug body  124 . In some implementations, the second ignition body  134  is carried by the cap  130 . In some implementations, both ignition bodies  134 ,  136  are carried by the plug body  124 . In some implementations, one or both of the ignition bodies  134 ,  136  are carried by the support  137 . In some implementations, the ignition system  200  includes more than two ignition bodies, e.g., three ignition bodies, four ignition bodies, etc. In some cases, the ignition bodies  134 ,  136  are in a J-gap configuration. In some implementations, one of the first ignition body  134  or the second ignition body  136  is a laser head. 
     The cap  130  is configured to shield the flame kernel initiation gap from incoming longitudinal flow.  FIG. 2B  illustrates ignition system  200 , with arrows  150   a - c  indicating portions of flow. For example, the incoming flow can be the incoming air/fuel mixture directed at the plug body  124  from the internal nozzle portion  128 , as described previously. The incoming longitudinal flow is shown in  FIG. 2B  with arrow  150   a . The cap  130  blocks or redirects the flow from impinging directly onto the flame kernel initiation gap  135 . The redirected flow is shown in  FIG. 2B  with arrow  150   b . By shielding the flame kernel initiation gap from incoming flow, the cap  130  is able to reduce turbulence behind the cap  130  and create a quiescent zone around the flame kernel initiation gap  135 . A first portion of the redirected flow recirculates into the antechamber  120 , shown by arrow  150   c . A second portion of the redirected flow recirculates into the region around the gap  135  with a relatively low flow velocity, shown by arrow  150   d . The quiescent zone around the flame kernel initiation gap can allow healthier flame kernel growth with less chance of quenching and provide fresh charge into and the removal of residuals from the flame kernel initiation gap region. In some implementations, the use of a cap  130  can allow ignition with less laser power and reduced chance of quenching. 
     The cap  130  provides a transverse shielding surface. The cap  130  has a radial  132  that extends radially from the center of the cap  130  to the perimeter of the cap  130 . In some implementations, the cap  130  has a frustoconical shape with a radial  132  perpendicular (precisely or substantially) to the center longitudinal axis. In some implementations, the radial  132  of cap  130  is at a non-zero, non-90 degree angle with respect to the center longitudinal axis. The cap  130  can also have a disc shape, dome shape, cylindrical shape, conical shape, prismatic shape, polyhedral shape, irregular shape, or another shape or combination of shapes. In some implementations, the cap  130  is not apertured. In some cases, the transverse diameter D 1  (an example shown in  FIG. 2D ) of the cap  130  is greater than the transverse diameter D 2  (c.f.,  FIG. 2D ) of the first ignition body  136  and less than the transverse diameter D 3  (c.f.,  FIG. 2D ) of the igniter plug  123 . In some cases, for a relatively small igniter plug  123 , the diameter D 3  of the igniter plug  123  is less than the diameter D 1  of the cap. Configured in this manner, the diameter D 1  of the cap  130  is large enough to protect the flame kernel initiation gap  135  from impinging flow, but small enough to allow the cap  130  to be inserted through carrier  116  and into a receiving chamber (e.g., antechamber  120 , combustion chamber  106 , or another chamber). 
     In some cases, the cap  130  is shaped to generate, re-enforce, or enhance the incoming flow of air/fuel mixture to be aerodynamically directed lateral to the center longitudinal axis. The incoming air/fuel mixture can be redirected from the cap  130  laterally into the antechamber  120 . A portion of the redirected air/fuel mixture enters the region around the flame kernel initiation gap  135  through peripheral opening  139  (described below), where it is ignited. Another portion of the redirected air/fuel mixture can circulate in a toroidal vortex around the outer perimeter of the antechamber  120 . For example, the antechamber  120  walls can guide the circulating flow to re-enter the flow from the internal nozzle portion  128  orthogonally (precisely and/or substantially) to the primary direction of flow or generally in the primary direction of the flow from the internal nozzle portion  128  (i.e., not counter to the primary direction of flow). Recombining the flow in this manner does not substantially counter the incoming flow, and thus substantially maintains the flow velocity from the internal nozzle portion  128  to the igniter plug  123  that sweeps residuals in front of the igniter plug  123 . The resulting circulation creates a toroidal vortex of flow in the antechamber  120  that provides a controlled degree of turbulence within the antechamber  120 . The turbulence from the circulating flow sweeps the flame out of the flame initiation region and into the antechamber  120  to mix in the antechamber  120  and ignite the air/fuel mixture in the antechamber  120 . Also, as the central flow and the vortex flow meet, the mixing of the flows creates turbulence which can accelerate combustion. Finally, the toroidal vortex confines residual combustion gasses within the circulation in the antechamber  120 , away from the flame kernel initiation gap  135 . 
     The example support  137  connecting the cap  130  to the plug body  124  includes two legs  138   a - b  extending between the cap  130  and the plug body  124 . The example legs  138   a - b  are radially offset from the center longitudinal axis. In other implementations, the support  137  can include another number of legs, e.g., one leg, three legs, six legs, or another number. In some implementations, the support  137  includes multiple radially offset legs. For example, the support  137  can include multiple legs which are circumferentially spaced apart. In some implementations, different legs can have different positions or shapes. For example, the legs can be spaced evenly apart or have different spacings between adjacent legs. Different legs can also be connected to the cap  130  and/or the plug body  124  at different radial positions. A leg can be curved, angled, straight, or have an irregular shape. A leg can be parallel (precisely or substantially) to the center longitudinal axis or angled with respect to the center longitudinal axis. 
     The support  137  defines a peripheral opening  139  around a perimeter of the cap  130 . For example, the support  137  shown in  FIG. 2A  defines a peripheral opening  139  that is interrupted by legs  138   a - b . The majority of the region surrounding the flame kernel initial gap is open to the surrounding chamber (e.g., antechamber  120  in  FIG. 2A , combustion chamber  106  in  FIG. 2D ). For example, the area of the outer surfaces of the legs  138   a - b  is less than the area of the peripheral opening  139  defined by the support  137 . Thus, charge, flame, and residuals can flow between the flame kernel initiation gap  135  and the surrounding chamber. The flame kernel is protected from impinging flow by the cap  130 , but is substantially unobstructed during flame kernel growth. The flame kernel can grow and expand into the antechamber  120 , where it can begin combustion of the air/fuel in the antechamber  120 . In some cases, a total radially-facing area of the support  135  is less than a total area of the peripheral opening  139 . In some cases, the peripheral opening  139  has a larger total area than the total area of outward-facing surfaces of the support  137 . 
     The example ignition system  250  shown in  FIG. 2B  is substantially similar to ignition system  200  of  FIGS. 2A-2C , except that the cap  130  is a disc-shaped body with a radial  132  perpendicular (precisely or substantially) to the center longitudinal axis and the end of the igniter plug  123  including the cap  130  and flame kernel initiation gap  135  is disposed within combustion chamber  106 . The ignition system  250  does not include an antechamber. In this manner, the cap  130  is open and does not create a second pressure chamber different from the main combustion chamber. The cap  130  in ignition system  250  shields the flame kernel initiation gap  135  from impinging flow from within the combustion chamber  106 . For example, the cap  130  can protect the flame kernel initiation gap  135  from bulk fluid flow in the combustion chamber  106 . 
       FIG. 3  shows a cross-sectional view of a portion of example ignition system  300 . Ignition system  300  is substantially similar to ignition systems shown in  FIGS. 1-2 , except that ignition system  300  also includes example peripheral shields  302   a - b . Ignition system  300  includes a cap  130  supported to plug body  124  by legs  304   a - b . The legs  304   a - b  are parallel (substantially or precisely) to the center longitudinal axis. The peripheral shields  302   a - b  are bodies spaced radially around the cap  130  that extend longitudinally from the cap  130  toward the plug body  124 . The peripheral shields  302   a - b  provide additional shielding for the flame kernel initiation gap from impinging flow. For example, the peripheral shields  302   a - b  can shield the flame kernel initiation gap from lateral flow. Example ignition system  300  shows two legs  304   a - b  and two shields  302   a - b , but other implementations can include more or fewer legs and/or shields. In some implementations, some or all of the peripheral shields extend longitudinally from the plug body  124  toward the cap  130 . The peripheral shields can be flat, curved, angled, irregular, or have another shape. In some implementations, the peripheral shields  302   a - b  are angled with respect to the center longitudinal axis. The peripheral shields  302   a - b  can be evenly spaced or unevenly spaced around the center longitudinal axis. The peripheral shields  302   a - b  can be positioned radially inward of the support and/or radially outward of the support. In some implementations, the peripheral shields  302   a - b  have different radial offsets. In some implementations, a single shield partially surrounds a portion of the center longitudinal axis or completely surrounds the center longitudinal axis. 
       FIGS. 4A-B  show a cross-sectional views of portions of example ignition systems  400 ,  450 , respectively. The ignition system  400  is substantially similar to ignition systems shown previously in this disclosure, except that the cap  130  has a conical shape and the legs  402   a - b  supporting the cap  130  have an angled shape with a relatively large radial offset at the plug body  124  and a relatively small radial offset at the cap  130 . The angled shape of the legs  402   a - b  and the conical shape of the cap  130  can facilitate redirection of oncoming longitudinal flow away from the flame kernel initiation gap in a lateral direction. The ignition system  450  is substantially similar to ignition systems shown previously in this disclosure, except that legs  452   a - b  are positioned adjacent to the flame kernel initiation gap. By positioning the legs  452   a - b  close to the flame kernel initiation gap, the legs  452   a - b  can provide additional shielding and containment of the quiescent zone. In this manner, the support and its legs can be configured, positioned, or shaped in different ways to provide different features, including those not shown. 
     A number of examples have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other examples are within the scope of the following claims.