Abstract:
An igniter for ignition over a wide air/fuel ratio range. Igniter includes an igniter body including an internal cavity disposed substantially within the igniter body, an internal spark gap disposed substantially within the internal cavity, an external spark gap disposed substantially on an exposed surface of the igniter body, and a fuel charge delivery system for delivering a fuel charge to the internal cavity. A method for compression-igniting an air/fuel mixture in a cylinder of a internal combustion enigne, the method comprising introducing a substantially homogenous charge of a first air/fuel mixture into a cylinder of the internal combustion engine during an intake stroke, compressing the substantially homogenous charge of the first air/fuel mixture in the cylinder of the internal combustion engine during a compressin stoke, and combusting the substantially homogenous charge of the first air/fuel mixture in the cylinder of the internal combustion engine during a power stroke by injecting partially combusted products of a second air/fuel mixture into the cylinder, with the first air/fuel mixture having a substantially higher ratio, by weight, of air to fuel and the second air/fuel mixture.

Description:
[0001]     This application is being filed as a PCT International Patent Application in the name of Savage Enterprises, Inc., a U.S. national corporation and resident, (Applicant for all countries except US) and Harold E. Durling, a U.S. resident and citizen (Applicant for US only), on 7 Sep. 2001, designating all countries and claiming priority to U.S. Ser. No. 60/230,982 filed 7 Sep. 2000. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates generally to an igniter for use in internal combustion engines. More particularly, the invention relates to an internal combustion igniter, which permits the engine to be operated in a “spark-ignited” mode of operation (with a relatively rich fuel to air ratio) during periods of relatively heavy load and in a diesel mode of operation (with a relatively lean fuel to air ratio) during periods of relatively light load.  
       BACKGROUND  
       [0003]     Internal combustion engines (i.e., those having an intake stroke, a compression stroke, a power stroke, and an exhaust stroke, either as separate strokes (four-stroke) or combined (two-stroke) events) may be divided into two general types: spark-ignited and compression-ignited (e.g., diesel).  
         [0004]     Spark-ignited engines and compression-ignited engines each have distinct advantages and disadvantages. For example, as versus compression-ignited engines, spark-ignited engines are generally less expensive to produce, have a greater power density (i.e., horsepower produced per volume of cylinder displacement), and are usually supplied with stoichiometric air/fuel ratios that produce relatively low levels of pollutant emissions. The pollutants that are produced by spark-ignited engines run with stoichiometric air/fuel ratios can also be further reduced to currently acceptable levels by utilizing the post-combustion catalytic converter technology available today.  
         [0005]     However, the stoichiometric air/fuel ratios required by spark-ignited engines are generally much richer as compared to the air/fuel ratios utilized in compression-ignited (e.g., diesel) engines. Whereas a spark-ignited engine may run on an air/fuel ratio in the ratio of 20:1, a compression-ignited engine may utilize a much higher air/fuel ratio in the range of 40:1 or 50:1. Therefore, compression-ignited engines generally exhibit better fuel economy.  
         [0006]     Compression-ignited engines, which run on such lean air/fuel mixtures and do not operate nearly as close to stoichiometric conditions as spark-ignited engines, tend to produce a higher rate of undesirable emission pollutants. Moreover, the emission pollutants that are produced by compression-ignited engines are not nearly as amenable to treatment by the post-combustion catalytic technology currently available, as are the pollutants produced by spark-ignited engines. Chief among the pollutants produced by combustion-ignition engines are nitrogen-containing compounds (i.e., NOX). Such nitrogen-containing compounds result, at least in part, from the high temperatures produced during compression-ignition. Soot is another pollutant produced in greater quantities during combustion-ignition, and arises primarily from the manner in which fuel droplets sprayed into the hot compressed air burn.  
         [0007]     Additionally, as noted above, compression-ignition engines tend to have a significantly lower “power density” as compared to spark-ignited engines. For example, while a high performance spark-ignited engine may produce in the range of 60 horsepower per liter of engine displacement, a compression-ignited engine may produce only in the range of about 10 horsepower per liter of engine displacement. A need exists for improvements.  
       SUMMARY OF THE DISCLOSURE  
       [0008]     An igniter for an internal combustion engine operating over a substantially wide range of air/fuel ratios, the igniter including an igniter body. The igniter body further includes an internal cavity disposed within the igniter body, an internal spark gap disposed within the internal cavity and an external spark gap disposed substantially on an exposed surface of the igniter body. The igniter also includes a fuel charge delivery system for delivering a fuel charge to the internal cavity.  
         [0009]     A method for operating an internal combustion engine including determining a load threshold within a load range of the internal combustion engine, operating the internal combustion engine in a spark-ignited mode of operation when the determined load threshold is exceeded, operating the internal combustion engine in a homogeneous-charge compression-ignited mode of operation when the determined load threshold is not attained. The homogeneous-charge compression-ignited mode of operation further includes introducing a substantially homogenous charge of an air/fuel mixture into a cylinder of the internal combustion engine during an intake stroke, compressing the substantially homogeneous charge of the air/fuel mixture in the cylinder of the internal combustion engine during a compression stoke, and combusting the substantially homogeneous charge of the air/fuel mixture in the cylinder of the internal combustion engine during a power stroke by injecting active radicals of combustion in to the cylinder. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0010]      FIG. 1  is a cross-sectional view of an example embodiment of an igniter or spark plug of the present invention for a use in a combustion engine. 
     
    
     DETAILED DESCRIPTION  
       [0011]     Referring to  FIG. 1 , an example embodiment of an igniter  10 , or spark plug, of the present invention is shown. An advantage of the embodiment described is that it is functional in an internal combustion engine utilizing a wide range of air/fuel ratios. Igniter  10  includes, proceeding radially from its exterior surface inward, a cylindrical shell  12  (preferably formed of a metal, such as steel), a primary cylindrical insulator member  14 , a fuel or chemical charge delivery system  16  and a first gap electrode  18 , shown in this embodiment, axially aligned and disposed substantially along an elongated central axis  20  of igniter  10 .  
         [0012]     In the example embodiment shown, fuel or chemical charge delivery system  16  is a conventional liquid fuel injection nozzle (described more fully below), which is supplied with a fuel or chemical mixture through a delivery conduit  22  that also extends along central axis  20 . Delivery conduit  22  passes centrally through a secondary cylindrical insulator member  24 , which mates into and is positioned adjacent primary cylindrical insulator member  14 . A first jam nut  26  threadingly engages shell  12 , through threads  28 , and contacts a shoulder  102  of primary cylindrical insulator member  14  to retain it in place against member shell  12 . Second cylindrical insulator member  24  is retained through the provision of a second jam nut  30 , which threadingly engages first jam nut  26  through threads  32 .  
         [0013]     The above description of construction details relating to the first and second insulator members  14  and  24 , respectively, and the first and second jam nuts  26  and  30 , respectively, apply to a prototypical model of igniter  10  presently constructed. One of skill in the art will appreciate that for manufacturability purposes, a mass-produced igniter  10  could employ a single cylindrical insulator member and could also dispense with the jam nuts  26  and  30 , respectively, employing instead a crimping of the shell  12  to retain such single cylindrical insulator member in place.  
         [0014]     In the example embodiment shown, a lower end  104  of the fuel charge delivery system  16  is received within the interior diameter of a tapering cylinder portion  34  of first electrode member  18 , which has a wider upper end portion for seating the fuel charge delivery system  16 , and a narrower lower end portion from which rod-shaped central electrode  18  projects downward. Surrounding central electrode  18  and extending downward from tapering cylindrical portion  34  of member first electrode  18 , the interior of the igniter is provided with an internal cavity  36 , which terminates in an outwardly opening orifice  38 . Internal cavity  36  is bounded by primary cylindrical insulator  14 , which has an upper substantially cylindrical sidewall portion  40 , a lower substantially cylindrical sidewall portion  42 , and a tapering sidewall portion  44  extending therebetween.  
         [0015]     In the example embodiment shown, an intermediate electrode  46  including a conducting material extends upwardly from orifice  38  to a point proximate the tip of central electrode  18 . Preferably, intermediate electrode  46  conforms substantially to the shape of and closely contacts the sidewall portions  40 ,  42 , and  44 . More preferably, the intermediate electrode  46  is provided in the form of a coating which overlays the sidewall portions  40 ,  42 , and  44 . The coating preferably includes a catalyst to promote rapid combustion of a fuel charge delivered to and combusted within internal cavity  36 . Examples of catalysts are platinum and platinum-containing substances and compounds.  
         [0016]     Igniter  10  is mounted in a cylinder head  48  and projects through cylinder head  48  (shown in partial view) into a cylinder of an internal combustion engine  50 . Igniter  10  engages cylinder head  48  through the provision of interlocking threads  52 . In the example embodiment shown in  FIG. 1 , charge delivery system  16  is a liquid fuel injector system, including an outer housing  54 , a valve seat  56  disposed within the outer housing  54 , a ball-shaped valve  58  having a stem  60  projecting therefrom, and a biasing coil spring  62  surrounding stem  60 . Coil spring  62  connects to an upper portion of stem  60  and is in tension so as to urge ball-shaped valve  58  upward against valve seat  56 . A metered amount of a fuel charge is delivered, under pressure, through delivery conduit  22  and thence through interior of outer housing  54  of fuel charge delivery system  16 . Pressurized metered fuel charge forces ball-shaped valve  58  downward and away from valve seat  56  so as to enter the wider upper end portion of the tapering cylindrical portion of member first electrode  18  in which fuel charge delivery system  16  is seated. The tapering cylindrical member is provided with at least one throughgoing aperture  64 , which allows the delivered fuel charge to pass through the tapering cylindrical portion  34  of first electrode  18  and enter internal cavity  36  proximate the tip of first electrode  18 .  
         [0017]     To initiate combustion, a first voltage potential is applied to first electrode  18 , communicated to first electrode  18  from an ignition system (not shown) attachment point  80  on exposed portion of the delivery conduit  22 , while shell  12  of igniter  10  is maintained at a reference voltage potential. Preferably, the reference voltage at shell  12  is maintained at ground voltage, and an ignition voltage is applied to first electrode  18 . More preferably, delivery conduit  22 , outer housing  54  of fuel charge delivery system  16 , and tapering cylindrical portion  34  of member first electrode  18 , all connect electrically, in series with engine ignition system contact point  80  to the arcing tip of first electrode  18  and form, together, first terminal of the igniter  10 . With the first and reference terminals at differing voltage potentials, two separate spark gaps are formed: an internal spark gap  66  between the first electrode  18  and the intermediate electrode  46  and an external spark gap  68  formed between intermediate electrode  46  and the reference electrode shell  12 . Internal spark gap  66  is located within cavity  36 , while external spark gap  68  is disposed substantially adjacent external surface of the lower tip of cylindrical insulator  14  of igniter  10  and found within the volume of cylinder  50 . Internal spark gap  66  and external spark gap  68  are, in the embodiment shown, each of annular shape and are electrically disposed in series with one another.  
         [0018]     When, as shown in the example embodiment of  FIG. 1 , the intermediate electrode  46  is configured to extend substantially around the entire circumference of internal cavity  36 , an electrical capacitor is effectively formed. Intermediate electrode  46  forms one plate of the capacitor, shell  12  forms another plate of the capacitor, and cylindrical insulator member  14  forms a dielectric separator. Capacitor is connected electrically in series with internal spark gap  66  and external spark gap  68 . When the ignition voltage is applied to first electrode  18 , the capacitor so formed maintains intermediate electrode  46  at ground potential until internal spark gap  66  breaks down. At that point, the capacitor begins charging, with current flowing across internal spark gap  66 . Capacitor subsequently discharges when voltage potential between internal electrode  44  and reference electrode shell  12  is sufficiently elevated to break down external spark gap  68 . As a result of the capacitor so formed by intermediate electrode  46 , reference electrode shell  12 , and cylindrical insulator member  14 , internal spark gap  66  and external spark gap  68  fire in series (on the order of microseconds apart) rather than simultaneously. Since internal spark gap  66  and external spark gap  68  fire sequentially rather than simultaneously, peak voltage is reduced from that which would be required to fire the two spark gaps simultaneously. In the example embodiment shown, fuel charge delivery system  16  described above forms a fuel injection nozzle  58 , which delivers a metered fuel charge to a position proximate the internal spark gap  66 .  
         [0019]     An advantage of the example embodiment shown is that igniter  10  permits an internal combustion engine to be operated in a “spark-ignited” mode of operation (with a relatively rich fuel to air ratio) during periods of relatively heavy load and in a diesel mode of operation (with a relatively lean fuel to air ratio) during periods of relatively light load. When operating in a spark-ignited mode of operation, fuel charge delivery system  16  is not actuated and, therefore, the only combustible mixture delivered to the cylinder  50  is an air/fuel mixture delivered on the intake stoke in a conventional manner, e.g., through a fuel injection or carburetion system. For example, an example of a conventional intake port  70  and a conventional injection/carburetion system  72 , as shown in  FIG. 1 , with an intake valve  74  shown in an open position, e.g., during an intake stoke. As one of skill in the art would appreciate, during an intake stroke of the internal combustion engine, a substantially well-dispersed air/fuel charge will be delivered to cylinder  50 . Thereafter, intake valve  74  closes and, as cylinder  50  undergoes a compression charge, some of this charge will be forced through orifice  38 , into internal cavity  36  of igniter  10 . When ignition voltage is applied to central electrode  18 , internal spark gap  66  and external spark gap  68  fire in series, with internal spark gap  66  firing in the range of microseconds before the firing of external spark gap  68 . In this spark-ignited mode of operation, igniter  10  functions similarly to a torch jet spark plug, one example of which is disclosed in U.S. Pat. No. 5,421,300, to Durling et al. In the torch jet mode of operation, igniter  10  ignites the air/fuel mixture forced into internal cavity  36  during the compression stoke, such that a jet of partially combusted fuel emanates from orifice  38  and projects into cylinder  50 , so as to enhance the burning rate of the air/fuel mixture therein. Additionally, external spark gap  68 , which is disposed substantially within cylinder  50 , contributes to a rapid and full combustion of the air/fuel mixture contained within cylinder  50 .  
         [0020]     Preliminary results by the applicants have indicated that the upper limit of the air to fuel ratio (by weight) achievable by this spark-ignited mode of operation is on the order of about 20:1. Leaner mixtures than this approximate 20:1 ratio of air to fuel tend to not ignite sufficiently or not ignite at all. However, leaner mixtures (e.g., above 20:1 of air/fuel) offer the possibility of achieving more efficient fuel consumption. Accordingly, the inventive igniter  10  can additionally be operated in a compression-ignition mode of operation, which preliminary results have indicated permits achieving air/fuel ratios on the order of about 40:1 or even perhaps 50:1.  
         [0021]     In compression-ignition mode of operation, a well-dispersed and relatively lean air/fuel mixture (e.g., on the order of about 40:1 to about 50:1) is delivered to cylinder  50  during the intake stoke, and some of this relatively lean air/fuel mixture is forced into internal chamber  36  of igniter  10  during the compression stroke. At or just before ignition, a small charge of a relatively rich air/fuel mixture is delivered by fuel charge delivery system  16  to internal cavity  36  and adjacent internal spark gap  66 . When the elevated ignition voltage is applied to central electrode  18 , internal spark gap  66  and external spark gap  68  again fire in series, on the order of microseconds apart. The charge delivered by fuel charge delivery system  16  to internal cavity  36 , together with the relatively lean mixture forced into internal cavity  36 , combine into a relatively rich mixture and are ignited by the annular spark formed between central electrode  18  and internal electrode  44 . A torch jet is thereby created, which ejects partially combusted products through orifice  38 . Such partially combusted products are dispersed within cylinder  50  and ignite the already compressed and relatively lean main charge therein, resulting is a rapid and thorough combustion of the main charge. The resulting combustion of the main charge results primarily from compression but is triggered by the dispersion throughout the main charge of the partially combusted products emitted from internal cavity  36 . An advantage of this method is that an engine using igniter  10  under a light load accomplishes homogeneous compression ignition of lean air/fuel ratios by introducing charged radicals, not limited to the form of a flame, but also being heated above ambient operating conditions, into the cylinder. One of skill in the art will appreciate that, optimally, igniter  10  is timed to fire when the state of compression is optimum for lean, fuel-efficient, compression ignition, for example, by controlling the timing of compression ignition in a homogeneous air/fuel mixture by “seeding” cylinder  50  with active chemical radicals-produced on demand by igniter  10 . An advantage of this method of engine operation is that ignition is not limited to initiation only by a spark or only by compression, but rather by allowing the engine to choose spark and seeded compression ignition, depending on load at which the engine is operating.  
         [0022]     While the present invention has been disclosed by way of a detailed description of a number of particularly preferred embodiments, it will be clear to those of ordinary skill that the art that various substitutions of equivalents can be affected without departing from either the spirit or scope of the invention as set forth in the appended claims.