Patent Publication Number: US-2018038270-A1

Title: Two-stage precombustion chamber for large bore gas engines

Description:
I. CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/020,770, entitled “Two-Stage Precombustion Chamber For Large Bore Gas Engines,” and filed Sep. 6, 2013, which claims priority of U.S. Patent Application No. 61/697,628, entitled “Two-Stage Precombustion Chamber For Large Bore Gas Engines,” and filed Sep. 6, 2012; which is related to U.S. patent application Ser. No. 13/602,148, entitled “Method and apparatus for achieving high power flame jets while reducing quenching and autoignition in prechamber spark plugs for gas engines,” and filed on Sep. 1, 2012 and International Patent Application Number PCT/US2012/53568, entitled “Method and apparatus for achieving high power flame jets while reducing quenching and autoignition in prechamber spark plugs for gas engines,” and filed on Sep. 1, 2012, both of which claim priority to U.S. Patent Application No. 61/573,290, entitled “Method and apparatus for achieving high power flame jets while reducing quenching and autoignition in prechamber spark plugs for gas engines,” and filed on Sep. 3, 2011. This application is also related to International Patent Application Number PCT/US2011/002012, entitled “Prechamber Ignition System,” and filed on Dec. 30, 2011, which claims priority to U.S. Patent Application No. 61/460,337, entitled “High efficiency ricochet effect passive chamber spark plug,” and filed on Dec. 31, 2010. The entirety of each of the foregoing patent applications is incorporated by reference herein in their entirety. 
    
    
     II. FIELD OF THE INVENTION 
     The disclosure generally relates to systems and methods for a two-stage precombustion chamber, and more particularly to a two-stage precombustion chamber that reduces NOx emissions in fueled, precombustion chamber gas engines. The two-stage precombustion chamber can be also achieved by simply replacing a conventional spark plug, used with conventional fueled prechamber, with a passive prechamber spark plug. 
     III. BACKGROUND OF THE INVENTION 
     Large gas engines with cylinder bore diameter greater than 200 mm typically use fuel-fed, rich precombustion chambers to enhance flame propagation rate with lean air/fuel mixtures in the main combustion chamber. A drawback of this type of system is that a fuel rich prechamber generates very high NOx and even though the main chamber generates very low NOx the combined amount remains higher than the legislated amount. 
     There is a need to address the foregoing deficiencies in the art. 
     IV. SUMMARY OF THE INVENTION 
     In certain embodiments, a two-stage precombustion chamber is disclosed comprising: a first prechamber stage enclosing a first prechamber volume, the first prechamber stage comprising: one or more first stage holes communicating between the first prechamber volume and a second prechamber volume; a primary electrode disposed within the first prechamber volume; and one or more ground electrodes disposed within the first prechamber volume and offset from the primary electrode to form one or more electrode gaps; and a second prechamber stage enclosing the second prechamber volume, the second prechamber stage comprising: one or more second stage holes communicating between the second prechamber volume and a combustion chamber volume; wherein the two-stage precombustion chamber further comprises at least one fuel admission point configured to admit fuel to the second prechamber volume; and wherein the first prechamber volume is smaller than the second prechamber volume and the first prechamber stage and the second prechamber stage are arranged in a selected relationship with respect to each other, such as to generate a first fuel concentration in the first prechamber volume that is higher than a second fuel concentration in the second prechamber volume. Each of the one or more first stage holes may comprise a penetration angle and a rotational offset and each of the one or more second stage holes comprise a hole angle that maintains proportionality of flow direction and flow momentum in each of the two stages. The one or more first stage holes and the one or more second stage holes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may have a first shape and the second prechamber stage may have a second shape and the first and second shapes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may be positioned relative to the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may be positioned symmetrically on a center hole axis of the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first fuel concentration may be at least about 5% higher than the second fuel concentration. The first prechamber volume may be smaller than the second prechamber volume. The first prechamber volume may be less than about 50% of the second prechamber volume. Each of the one or more first stage holes may define a first stage hole axis and each of the one or more second stage holes may define a second stage hole axis and each first stage hole axis and each second stage hole axis may define an index angle, a penetration angle and a rotational offset. The index angle, the penetration angle and the rotational offset of the first stage holes and the second stage holes may be selected to generate a first fuel concentration in the first prechamber volume that is higher than a second fuel concentration in the second prechamber volume. The first stage prechamber may comprise a passive prechamber spark plug with a heat range selected to maintain all surface temperatures of the passive prechamber spark plug below a thermal runaway point dictated by the air-fuel mixture composition and by the level of combustion mean effective pressure at which the engine operates. 
     In certain embodiments, a two-stage precombustion chamber is disclosed comprising: a first prechamber stage enclosing a first prechamber volume, the first prechamber stage comprising: one or more first stage holes communicating between the first prechamber volume and a second prechamber volume; a primary electrode disposed within the first prechamber volume; and one or more ground electrodes disposed within the first prechamber volume and offset from the primary electrode to form one or more electrode gaps; and a second prechamber stage comprising: an external surface and an internal surface enclosing the second prechamber volume; one or more second stage holes communicating between the internal surface and the external surface; and a fuel admission point configured to admit fuel into the second prechamber volume wherein the first prechamber stage and the second prechamber stage are flow-dynamically matched. Each of the one or more first stage holes may comprise a penetration angle and a rotational offset and each of the one or more second stage holes may comprise a hole angle that maintains proportionality of flow direction and flow momentum in each of the two stages. The one or more first stage holes and the one or more second stage holes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may have a first shape and the second prechamber stage may have a second shape and the first and second shapes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may be positioned relative to the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may be positioned symmetrically on a center hole axis of the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. A first fuel concentration in the first prechamber volume may be higher than a second fuel concentration in the second prechamber volume. The first fuel concentration may be higher than the second fuel concentration before a spark is introduced. The first fuel concentration may be at least about 5% higher than the second fuel concentration. The first prechamber volume may be smaller than the second prechamber volume. The first prechamber volume may be less than about 50% of the second prechamber volume. Each of the one or more first stage holes may define a first stage hole axis and each of the one or more second stage holes may define a second stage hole axis and wherein each first stage hole axis and each second stage hole axis may define an index angle, a penetration angle and a rotational offset. The index angle, the penetration angle and the rotational offset of the first stage holes and the second stage holes may be selected to generate a first fuel concentration in the first prechamber volume that is higher than a second fuel concentration in the second prechamber volume. 
     In certain embodiments, a method of reducing NOx levels in gas engines is disclosed, comprising: providing a two-stage precombustion chamber comprising: a first prechamber stage enclosing a first prechamber volume, the first prechamber stage comprising: one or more first stage holes communicating between the first prechamber volume and a second prechamber volume; a primary electrode disposed within the first prechamber volume; one or more ground electrodes disposed within the first prechamber volume and offset from the primary electrode to form one or more electrode gaps; and a second prechamber stage enclosing the second prechamber volume, the second prechamber stage comprising: one or more second stage holes communicating between the second prechamber volume and a combustion chamber volume; wherein the first prechamber stage and the second prechamber stage are flow-dynamically matched; introducing one or more fuel admission points to the second prechamber volume; and generating a spark across at least one of the one or more electrode gaps to ignite a fuel-air mixture in the first prechamber volume. Each of the one or more first stage holes may comprise a penetration angle and a rotational offset and each of the one or more second stage holes may comprise a hole angle that maintain proportionality of flow direction and flow momentum in each of the two stages. The one or more first stage holes and the one or more second stage holes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may have a first shape and the second prechamber stage may have a second shape and the first and second shapes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may be positioned relative to the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may be positioned symmetrically on a center hole axis of the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber volume may be smaller than the second prechamber volume. The first prechamber volume may be less than about 50% of the second prechamber volume. The first prechamber volume may contain a first fuel-air mixture with a first fuel concentration and the second prechamber volume may contain a second fuel-air mixture with a second fuel concentration and the first fuel concentration may be higher than the second fuel concentration. The first fuel concentration may be higher than the second fuel concentration before the spark is generated. The first fuel concentration may be at least about 5% higher than the second fuel concentration. Each of the one or more first stage holes may define a first stage hole axis and each of the one or more second stage holes may define a second stage hole axis and each first stage hole axis and each second stage hole axis may define an index angle, a penetration angle and a rotational offset. The index angle, the penetration angle and the rotational offset of the first stage holes and the second stage holes may be selected to generate a first fuel-air mixture in the first prechamber volume with a higher fuel concentration than a second fuel-air mixture in the second prechamber volume. The method may further comprise providing cooling to the first stage prechamber to maintain all surface temperatures of the first prechamber below a thermal runaway point dictated by the air-fuel mixture composition and by the level of combustion mean effective pressure at which the engine operates. The method may further comprise providing cooling to the second stage prechamber to maintain all surface temperatures of the second prechamber to prevent flame quenching and to promote flame propagation speed as dictated by the air-fuel mixture composition and flow dynamic. 
     In certain embodiments, a method of reducing NOx levels in gas engines is disclosed, comprising: providing a two-stage precombustion chamber comprising: a first prechamber stage enclosing a first prechamber volume, the first prechamber stage comprising: one or more first stage holes communicating between the first prechamber volume and a second prechamber volume; a primary electrode disposed within the first prechamber volume; one or more ground electrodes disposed within the first prechamber volume and offset from the primary electrode to form one or more electrode gaps; and a second prechamber stage comprising: an external surface and an internal surface enclosing the second prechamber volume; and one or more second stage holes communicating between the internal surface and the external surface; wherein the first prechamber stage and the second prechamber stage are flow-dynamically matched; introducing one or more fuel in-filling streams to the second prechamber volume; and generating a spark across at least one of the one or more electrodes gaps to ignite a fuel-air mixture in the first prechamber volume. Each of the one or more first stage holes may comprise a penetration angle and a rotational offset and each of the one or more second stage holes may comprise a hole angle that maintains proportionality of flow direction and flow momentum in each of the two stages. The one or more first stage holes and the one or more second stage holes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may have a first shape and the second prechamber stage may have a second shape and the first and second shapes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may be positioned relative to the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may be positioned symmetrically on a center hole axis of the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber volume may be smaller than the second prechamber volume. The first prechamber volume may be less than about 50% of the second prechamber volume. The first prechamber volume may contain a first fuel-air mixture with a first fuel concentration and the second prechamber volume may contain a second fuel-air mixture with a second fuel concentration and the first fuel concentration may be higher than the second fuel concentration. The first fuel concentration may be higher than the second fuel concentration before the spark is generated. The first fuel concentration may be at least about 5% higher than the second fuel concentration. Each of the one or more first stage holes may define a first stage hole axis and each of the one or more second stage holes may define a second stage hole axis and each first stage hole axis and each second stage hole axis may define an index angle, a penetration angle and a rotational offset. The index angle, the penetration angle and the rotational offset of the first stage holes and the second stage holes may be selected to generate a first fuel-air mixture in the first prechamber volume with a higher fuel concentration than a second fuel-air mixture in the second prechamber volume. 
     In certain embodiments, a method for controlling the admission of fuel to a two-stage precombustion chamber utilizing an electrically actuated valve is disclosed, comprising adjusting a quantity of fuel admitted and timing of admitting the quantity of fuel relative to engine position to achieve a desired fuel distribution in the two-stage precombustion chamber; wherein the two stages are flow-dynamically matched. At least one of the quantity of fuel and the timing of admitting the fuel may be adjusted utilizing a closed feedback loop based on one or more previous operating cycles and the feedback loop may include feedback generated from the two-stage precombustion chamber or the main combustion chamber. 
     In certain embodiments, a method for controlling and adjusting the characteristics of a spark discharge event within a two-stage precombustion chamber is disclosed, comprising utilizing an electronically controlled ignition stem to adjust the characteristics of a spark discharge event based on the fuel distribution present in a two-stage precombustion chamber; wherein the two stages are flow-dynamically matched. The characteristics of the spark discharge may be adjusted utilizing a closed feedback loop based on one or more previous operating cycles and the feedback loop may include feedback generated from the two-stage precombustion chamber or the main combustion chamber. 
     In certain embodiments, a two-stage precombustion chamber is disclosed comprising: a first prechamber stage enclosing a first prechamber volume, the first prechamber stage comprising: one or more first stage holes communicating between the first prechamber volume and a second prechamber volume; a primary electrode disposed within the first prechamber volume; and one or more ground electrodes disposed within the first prechamber volume and offset from the primary electrode to form one or more electrode gaps; and a second prechamber stage enclosing the second prechamber volume, the second prechamber stage comprising: one or more second stage holes communicating between the second prechamber volume and a combustion chamber volume; wherein the first prechamber stage and the second prechamber stage are flow-dynamically matched. Each of the one or more first stage holes may comprise a penetration angle and a rotational offset and each of the one or more second stage holes comprise a hole angle that maintain proportionality of flow direction and flow momentum in each of the two stages. The one or more first stage holes and the one or more second stage holes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage has a first shape and the second prechamber stage may have a second shape and the first and second shapes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first shape may be a first bullet shape and the second shape may be a second bullet shape. The first prechamber stage may be positioned relative to the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may be positioned symmetrically on a center hole axis of the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. A first fuel concentration in the first prechamber volume may be higher than a second fuel concentration in the second prechamber volume. The first fuel concentration may be higher than the second fuel concentration before a spark is introduced. The first fuel concentration may be at least about 5% higher than the second fuel concentration. The first prechamber volume may be smaller than the second prechamber volume. The first prechamber volume may be less than about 50% of the second prechamber volume. The two-stage precombustion chamber may further comprise a fuel admission point configured to admit fuel into the first prechamber volume. The two-stage precombustion chamber may further comprise a fuel admission point configured to admit fuel into the second prechamber volume. Each of the one or more first stage holes may define a first stage hole axis and each of the one or more second stage holes may define a second stage hole axis and each first stage hole axis and each second stage hole axis may define an index angle, a penetration angle and a rotational offset. The index angle, the penetration angle and the rotational offset of the first stage holes and the second stage holes may be selected to generate a first fuel concentration in the first prechamber volume that is higher than a second fuel concentration in the second prechamber volume. The first stage prechamber may comprise a passive prechamber spark plug with a heat range selected to maintain all surface temperatures of the passive prechamber spark plug below a thermal runaway point dictated by the air-fuel mixture composition and by the level of combustion mean effective pressure at which the engine operates. 
     In certain embodiments, a two-stage precombustion chamber is disclosed comprising: a first prechamber stage enclosing a first prechamber volume, the first prechamber stage comprising: one or more first stage holes communicating between the first prechamber volume and a second prechamber volume; a primary electrode disposed within the first prechamber volume; and one or more ground electrodes disposed within the first prechamber volume and offset from the primary electrode to form one or more electrode gaps; and a second prechamber stage comprising: an external surface and an internal surface enclosing the second prechamber volume; and one or more second stage holes communicating between the internal surface and the external surface; wherein the first prechamber stage and the second prechamber stage are flow-dynamically matched. Each of the one or more first stage holes may comprise a penetration angle and a rotational offset and each of the one or more second stage holes may comprise a hole angle that maintain proportionality of flow direction and flow momentum in each of the two stages. The one or more first stage holes and the one or more second stage holes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may have a first shape and the second prechamber stage may have a second shape and the first and second shapes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first shape may be a first bullet shape and the second shape may be a second bullet shape. The first prechamber stage may be positioned relative to the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may be positioned symmetrically on a center hole axis of the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. A first fuel concentration in the first prechamber volume may be higher than a second fuel concentration in the second prechamber volume. The first fuel concentration may be higher than the second fuel concentration before a spark is introduced. The first fuel concentration may be at least about 5% higher than the second fuel concentration. The first prechamber volume may be smaller than the second prechamber volume. The first prechamber volume may be less than about 50% of the second prechamber volume. The two-stage precombustion chamber may further comprise a fuel admission point configured to admit fuel into the first prechamber volume. The two-stage precombustion chamber may further comprise a fuel admission point configured to admit fuel into the second prechamber volume. Each of the one or more first stage holes may define a first stage hole axis and each of the one or more second stage holes may define a second stage hole axis and each first stage hole axis and each second stage hole axis may define an index angle, a penetration angle and a rotational offset. The index angle, the penetration angle and the rotational offset of the first stage holes and the second stage holes may be selected to generate a first fuel concentration in the first prechamber volume that is higher than a second fuel concentration in the second prechamber volume. 
     In certain embodiments, a method of reducing NOx levels in gas engines is disclosed, comprising: providing a two-stage precombustion chamber comprising: a first prechamber stage enclosing a first prechamber volume, the first prechamber stage comprising: one or more first stage holes communicating between the first prechamber volume and a second prechamber volume; a primary electrode disposed within the first prechamber volume; one or more ground electrodes disposed within the first prechamber volume and offset from the primary electrode to form one or more electrode gaps; and a second prechamber stage enclosing the second prechamber volume, the second prechamber stage comprising: one or more second stage holes communicating between the second prechamber volume and a combustion chamber volume; wherein the first prechamber stage and the second prechamber stage are flow-dynamically matched; introducing one or more fuel admission points to a selected one of the first prechamber volume and the second prechamber volume; and generating a spark across at least one of the one or more electrode gaps to ignite a fuel-air mixture in the first prechamber volume. Each of the one or more first stage holes may comprise a penetration angle and a rotational offset and each of the one or more second stage holes may comprise a hole angle that maintain proportionality of flow direction and flow momentum in each of the two stages. The one or more first stage holes and the one or more second stage holes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may have a first shape and the second prechamber stage may have a second shape and the first and second shapes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first shape may be a first bullet shape and the second shape may be a second bullet shape. The first prechamber stage may be positioned relative to the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may be positioned symmetrically on a center hole axis of the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber volume may be smaller than the second prechamber volume. The first prechamber volume may be less than about 50% of the second prechamber volume. The one or more fuel admission points may be introduced into the first prechamber volume. The one or more fuel admission points may be introduced into the second prechamber volume. The first prechamber volume may contain a first fuel-air mixture with a first fuel concentration and the second prechamber volume may contain a second fuel-air mixture with a second fuel concentration and the first fuel concentration may be higher than the second fuel concentration. The first fuel concentration may be higher than the second fuel concentration before the spark is generated. The first fuel concentration may be at least about 5% higher than the second fuel concentration. Each of the one or more first stage holes may define a first stage hole axis and each of the one or more second stage holes may define a second stage hole axis and each first stage hole axis and each second stage hole axis may define an index angle, a penetration angle and a rotational offset. The index angle, the penetration angle and the rotational offset of the first stage holes and the second stage holes may be selected to generate a first fuel-air mixture in the first prechamber volume with a higher fuel concentration than a second fuel-air mixture in the second prechamber volume. The method may further comprise: providing cooling to the first stage prechamber to maintain all surface temperatures of the first prechamber below a thermal runaway point dictated by the air-fuel mixture composition and by the level of combustion mean effective pressure at which the engine operates. The method may further comprise: providing cooling to the second stage prechamber to maintain all surface temperatures of the second prechamber to prevent flame quenching and to promote flame propagation speed as dictated by the air-fuel mixture composition and flow dynamic. 
     In certain embodiments, a method of reducing NOx levels in gas engines is disclosed, comprising: providing a two-stage precombustion chamber comprising: a first prechamber stage enclosing a first prechamber volume, the first prechamber stage comprising: one or more first stage holes communicating between the first prechamber volume and a second prechamber volume; a primary electrode disposed within the first prechamber volume; one or more ground electrodes disposed within the first prechamber volume and offset from the primary electrode to form one or more electrode gaps; and a second prechamber stage comprising: an external surface and an internal surface enclosing the second prechamber volume; and one or more second stage holes communicating between the internal surface and the external surface; wherein the first prechamber stage and the second prechamber stage are flow-dynamically matched; introducing one or more fuel in-filling streams to a selected one of the first prechamber volume and the second prechamber volume; and generating a spark across at least one of the one or more electrode gaps to ignite a fuel-air mixture in the first prechamber volume. Each of the one or more first stage holes may comprise a penetration angle and a rotational offset and each of the one or more second stage holes may comprise a hole angle that maintains proportionality of flow direction and flow momentum in each of the two stages. The one or more first stage holes and the one or more second stage holes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may have a first shape and the second prechamber stage may have a second shape and the first and second shapes may be arranged to maintain proportionality of flow direction and flow momentum in each of the two stages. The first shape may be a first bullet shape and the second shape may be a second bullet shape. The first prechamber stage may be positioned relative to the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber stage may be positioned symmetrically on a center hole axis of the second prechamber stage to maintain proportionality of flow direction and flow momentum in each of the two stages. The first prechamber volume may be smaller than the second prechamber volume. The first prechamber volume may be less than about 50% of the second prechamber volume. The one or more fuel admission points may be introduced into the first prechamber volume. The one or more fuel admission points may be introduced into the second prechamber volume. The first prechamber volume may contain a first fuel-air mixture with a first fuel concentration and the second prechamber volume may contain a second fuel-air mixture with a second fuel concentration and the first fuel concentration may be higher than the second fuel concentration. The first fuel concentration may be higher than the second fuel concentration before the spark is generated. The first fuel concentration may be at least about 5% higher than the second fuel concentration. Each of the one or more first stage holes may define a first stage hole axis and each of the one or more second stage holes may define a second stage hole axis and each first stage hole axis and each second stage hole axis may define an index angle, a penetration angle and a rotational offset. The index angle, the penetration angle and the rotational offset of the first stage holes and the second stage holes may be selected to generate a first fuel-air mixture in the first prechamber volume with a higher fuel concentration than a second fuel-air mixture in the second prechamber volume. 
     In certain embodiments, a method for controlling the admission of fuel to a two-stage precombustion chamber utilizing an electrically actuated valve is disclosed, comprising adjusting a quantity of fuel admitted and timing of admitting the quantity of fuel relative to engine position to achieve a desired fuel distribution in the two-stage precombustion chamber; wherein the two stages are flow-dynamically matched. At least one of the quantity of fuel and the timing of admitting the fuel may be adjusted utilizing a closed feedback loop based on one or more previous operating cycles and wherein the feedback loop includes feedback generated from the two-stage precombustion chamber or the main combustion chamber. 
     In certain embodiments, a method for controlling and adjusting the characteristics of a spark discharge event within a two-stage precombustion chamber is disclosed, comprising utilizing an electronically controlled ignition system to adjust the characteristics of a spark discharge event based on the fuel distribution present in a two-stage precombustion chamber; wherein the two stages are flow-dynamically matched. The characteristics of the spark discharge may be adjusted utilizing a closed feedback loop based on one or more previous operating cycles and wherein the feedback loop may include feedback generated from the two-stage precombustion chamber or the main combustion chamber. 
    
    
     
       V. BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts two variations of a two-stage precombustion chamber in accordance with certain embodiments. 
         FIG. 2  depicts an exemplary comparison of NOx output between a conventional precombustion chamber with a conventional spark plug and a two-stage precombustion chamber with a passive prechamber spark plug in accordance with certain embodiments. 
         FIG. 3  depicts the total volume of certain embodiments of a passive prechamber spark plug, which may be used as the first stage in a two-stage precombustion chamber in accordance with certain embodiments. 
         FIG. 4  depicts the volume ahead of the gap of certain embodiments of a passive prechamber spark plug, which may be used as the first stage in a two-stage precombustion chamber in accordance with certain embodiments. 
         FIG. 5  depicts the volume behind the gap of certain embodiments of a passive prechamber spark plug, which may be used as the first stage in a two-stage precombustion chamber in accordance with certain embodiments. 
         FIG. 6  depicts an exemplary penetration angle of a passive prechamber spark plug which may be used as the first stage in a two-stage precombustion chamber in accordance with certain embodiments. 
         FIG. 7  depicts an exemplary index angle of a passive prechamber spark plug, which may be used as the first stage in a two-stage precombustion chamber in accordance with certain embodiments. 
         FIG. 8  depicts an exemplary rotational offset of a passive prechamber spark plug, which may be used as the first stage in a two-stage precombustion chamber in accordance with certain embodiments. 
         FIG. 9  depicts an exemplary pattern radius of a passive prechamber spark plug, which may be used as the first stage in a two-stage precombustion chamber in accordance with certain embodiments. 
         FIG. 10  depicts an exemplary prechamber ceiling distance from center electrode of a passive prechamber spark plug, which may be used as the first stage in a two-stage precombustion chamber in accordance with certain embodiments. 
         FIG. 11  depicts an exemplary port length of a passive prechamber spark plug, which may be used as the first stage in a two-stage precombustion chamber in accordance with certain embodiments. 
         FIG. 12  depicts an exemplary port diameter of a passive prechamber spark plug, which may be used as the first stage in a two-stage precombustion chamber in accordance with certain embodiments. 
         FIG. 13  depicts an exemplary precombustion chamber insertion depth of a passive prechamber spark plug, which may be used as the first stage in a two-stage precombustion chamber in accordance with certain embodiments. 
     
    
    
     VI. DETAILED DESCRIPTION 
     In certain embodiments, the two-stage precombustion chamber  100  concept disclosed herein, may be used to reduce engine NOx levels, with fueled precombustion chambers, while maintaining comparable engine power output and thermal efficiency. 
     Certain embodiments provide a method and a structure to achieve more effective combustion with leaner mixtures resulting in lower NOx. In certain embodiments as shown in  FIG. 1 , conventional precombustion chambers may be modified so that a first stage of combustion  110  occurs in a relatively small volume, with a relatively fuel rich mixture  170 , and a second stage of combustion  120  occurs in a relatively larger volume with a relatively fuel lean mixture  150 . In certain embodiments, a more efficient overall combustion characterized by low levels of NOx formation can be achieved by the two-stage precombustion chamber  100  system while generating very high energy flame jets  140  emerging from the second prechamber stage  120  into the main combustion chamber. 
     In certain embodiments, the two-stage prechamber  100  system can be achieved by simply replacing a conventional spark plug, used in fueled prechamber, with a passive prechamber spark plug to provide for the first stage prechamber  110  in the two-stage precombustion chamber  100  system. 
     The amount of NOx produced in a prechamber may be mainly dictated by the air-fuel ratio and by the volume of reactants. As the volume of reactants at the lower air-fuel ratio is decreased, the amount of NOx formed may be proportionally reduced. In certain embodiments, with the 2-stage precombustion, the volume of the fuel rich  170  stage can be reduced by at least a factor of 2, thereby reducing NOx production by approximately a factor of 2. In certain embodiments, the flame jet energy also may be dictated by the air-fuel ratio and by the volume of reactants. As the volume of reactants at the lower air-fuel ratio is decreased, the flame jet energy also may be reduced. In certain embodiments with the two-stage precombustion  100 , the second prechamber stage  120 , characterized by a relatively leaner mixture  150 , is ignited by powerful flame jets  140  emerging from the relatively fuel rich  170  first prechamber  110  stage. The ignition by powerful flame jets  140  may result in a fast combustion of the leaner mixture  150  in the second prechamber stage  120 , which may generate high energy flame jets  140  from the second prechamber stage  120 . These high energy flame jets  140  may ignite the lean air fuel mixture  150  in the engine main combustion chamber  120  and achieve low overall NOx emissions, while maintaining comparable engine power output and thermal efficiency to a system employing a conventional precombustion chamber. 
     In certain embodiments as shown in  FIG. 1 , the volume of the first prechamber stage  110  may be substantially smaller than the volume of the second prechamber stage  120 . The volume of the first prechamber stage  110  may be less than about 50% of the volume of the second prechamber stage  120 . 
     In certain embodiments, either the first prechamber stage  110  or the second prechamber stage  120  can be fueled directly by a separate fuel line. In certain embodiments, if the first prechamber stage  110  is fueled directly by a separate fuel admission point  130  as shown in the top two figures of  FIG. 1 , a richer first fuel concentration in the first prechamber  110  stage may result than if the second prechamber  120  stage is fueled directly by a separate fuel admission point  130  as shown in the bottom two figures of  FIG. 1 . Conversely, a second fuel concentration in the second prechamber  120  stage may be leaner if the first prechamber  110  stage is fuel directly by a separate fuel admission point  130  as shown in the top two figures of  FIG. 1  than if the second prechamber  120  stage is fueled directly by a separate fuel admission point  130  than as shown in the bottom two figures of  FIG. 1 . Performance may be improved in comparison to conventional single stage precombustion chambers by either fueling the first prechamber  110  stage or the second prechamber  120  stage directly. In certain embodiments, a passive prechamber (PPC) spark plug may be used as the first prechamber  110  stage. In certain embodiments, a fuel-fed second prechamber  120  stage may be used in conjunction with a PPC spark plug as the first prechamber stage  110 . Exemplary non-limiting examples of PPC spark plugs are disclosed in related U.S. patent application Ser. No. 13/602,148 and International Patent Application Numbers PCT/US2012/53568 and PCT/US2011/002012, which are incorporated by reference herein. 
     In certain embodiments, the communication between the first prechamber  110  stage, the second prechamber  120  stage and the main combustion chamber may occur through one or more holes with a predetermined relative pattern and angles. In certain embodiments, the one or more holes may include one or more first stage holes  115  for communicating between the first prechamber  110  stage and the second prechamber  120  stage and one or more second stage holes  125  for communicating between the second prechamber  120  stage and the main combustion chamber. In certain embodiments, each of the one or more first stage holes  115  may define a first stage hole axis  160  and each of the one or more second stage holes  125  may define a second stage hole axis  160 . Each first stage hole axis  160  and each second stage hole axis  160  may define an index angle  610 , a penetration angle  600  and a rotational offset  620 . The index angle  610 , the penetration angle  600  and the rotational offset  620  of the first stage holes  115  and the second stage holes  125  may be selected to generate a first fuel concentration in the first prechamber  110  stage that is higher than a second fuel concentration in the second prechamber stage  120 . In certain embodiments, the volumes and aspect ratios of the two prechamber stages, along with the location of the electrodes within the first stage prechamber  110 , the hole patterns, angles and the separate fueling, may be selected to create a first fuel concentration in the first prechamber  110  stage that is substantially higher than a second fuel concentration in the second prechamber  120  stage. 
       FIG. 2  shows exemplary results for reduction of NOx output achieved with a two-stage precombustion chamber system  100  with a PPC spark plug as compared to a conventional precombustion chamber with a conventional spark plug. The results shown in the  FIG. 2  demonstrate that lower NOx emissions were achieved without penalty in engine thermal efficiency with this non-optimized system. Therefore, there is a great potential for an optimized two-stage precombustion chamber system  100  with a PPC spark plug, to achieve stable operation with leaner mixtures in the precombustion chamber resulting in very low NOx emissions, much below the 0.5 g/bhp-hr level. 
     In certain embodiments, the physical parameters shown in  FIGS. 3-13  may be varied alone or in combination to vary the first fuel concentration in the first prechamber  110  stage and the second fuel concentration in the second prechamber  120  stage to result in a higher first fuel concentration than the second fuel concentration. 
     As shown in  FIG. 3 , Total Volume  300  may be defined as the volume of air inside the prechamber spark plug not including the volume of the ports/holes. 
     As shown in  FIG. 4 , Volume Ahead of the Gap  400  may be defined as the volume of air inside the prechamber spark plug from the center of the gap to the endcap not including the volume of the ports/holes. 
     As shown in  FIG. 5 , Volume Behind the Gap  500  may be defined as the volume of air inside the prechamber spark plug between the center of the gap and the rear of the prechamber not including the volume of any ports/holes that may be at the rear of the prechamber. 
     As shown in  FIG. 6 , the Penetration Angle  600  may be defined as the angle between the plane perpendicular to the axis  160  of the prechamber spark plug and the centerline of the port/hole. 
     As shown in  FIG. 7 , the Index Angle  610  may be defined as the angle of rotation about the axis  160  of the prechamber spark plug and the location on the port where the centerline of the port meets the front plane of the prechamber spark plug. 
     As shown in  FIG. 8 , Rotational Offset  620  may be defined as the perpendicular distance between the axis  160  of the prechamber spark plug and the centerline of the port/hole (measured on the plane at the front of the prechamber spark plug). 
     As shown in  FIG. 9 , the Pattern Radius  630  may be defined as the perpendicular distance from the axis  160  of the prechamber spark plug to the centerline of the port/hole, measured at the front plane of the endcap. 
     As shown in  FIG. 10 , the Prechamber Ceiling Distance  640  from the Center Electrode may be defined as the distance along the axis  160  of the prechamber spark plug from the top of the center electrode to the inside of the endcap. 
     As shown in  FIG. 11 , the Port Length  650  may be defined as the length of the port/hole, measured along the centerline of the port/hole, from the inside of the endcap to the outside of the endcap. 
     As shown in  FIG. 12 , the Port Diameter  660  may be defined as the diameter of the port/hole. 
     As shown in  FIG. 13 , the Precombustion Chamber Insertion Depth  670  may be defined as the distance from the firing deck to the end of the prechamber spark plug. As shown,  FIG. 9  assumes that the firing deck is located at the end of the threads.