BACKGROUND OF THE INVENTION
This invention is directed to a surface gap spark plug and its use in an internal combustion engine or a related device.
Spark plugs having air gaps and surface gaps are known in the art. The air gap spark plug is the more conventional type; it is the common type of spark plug used in gasoline fueled internal combustion engines. It is characterized in that the spark is generated across an air gap between the primary electrode of the spark plug and the secondary or ground electrode. The surface gap spark plug is commonly used as a high energy jet fuel igniter; it is characterized in that the spark is generated across a solid, nonconductive or semiconductive surface running between the primary electrode and the ground electrode.
The spark characteristics of either type of plug are subject to change as deposits form on the electrodes during the course of their use in initiating the combustion of the fuel in an engine or other device. These deposits can build up to a point where the spark plug will not produce a spark as required; this tendency to build up a deposit on a spark plug is commonly referred to as fouling. Fouled spark plugs reduce efficiency of the combustion operation.
A surface gap spark plug has been discovered which is considerably more resistant to fouling than spark plugs currently available, especially those of the air gap type; use of this spark plug improves the efficiency of operation of internal combustion devices; and of internal combustion engines which uses a fuel containing organometallic additives.
SUMMARY OF THE INVENTION
A surface gap spark plug suitable for providing a spark to ignite fuel in a combustion chamber features a novel surface gap configuration which improves resistance to fouling; a method of improving the operation of an internal combustion engine which burns a fuel containing an organometallic additive, by using the aforesaid improved surface gap spark plug.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal partial section view of a surface gap spark plug of the present invention.
FIG. 2 is an enlarged section view of the portion of the spark plug of FIG. 1 below dotted line AA.
FIG. 3 is an end view of a section through said FIG. 1 spark plug at 1'-1'.
FIG. 4 is a longitudinal partial section view of a surface gap spark plug of the present invention which additionally has a series gap.
FIG. 5 illustrates another modification of the enlarged section view shown in FIG. 2.
FIG. 6 is an end view of a section through the spark plug tip of FIG. 5, at 2'-2'.
DESCRIPTION OF PREFERRED EMBODIMENTS
An embodiment of this invention is a surface gap spark plug featuring a recessed surface gap. A preferred embodiment is a surface gap spark plug suitable for supplying a spark to ignite fuel in a combustion chamber which comprises
A. a center electrode,
B. an insulator having a central passageway running longitudinally through said insulator to receive said center electrode,
C. a metal shell enclosing a portion of said insulator, said shell serving as a ground electrode, the lower end of said shell having an opening which corresponds substantially in size and shape to and is in substantial register with the distal end of said passageway,
d. said center electrode extending into said passageway to within 0.03 to 0.08 inches of said opening in said shell,
thus providing a surface gap ranging from 0.03 to 0.08 inches in length from said center electrode along said insulator to said outer shell for a spark to be generated.
The aforesaid spark plug having a cylindrical center electrode and passageway is more preferred; the diameter of this cylindrical electrode and passageway may be from about 0.050 to about 0.150 inches; in a most preferred embodiment the surface gap ranges from about 0.035 to about 0.055 inches in length and the diameter of the electrode and passageway is about 0.08 inches.
Another preferred embodiment is the spark plug described above wherein said metal shell has a thickness at said opening such that the ratio of said thickness to said surface gap length is from about 1:5 up to about 5:1, preferably from 2:1 to about 4:. It is still more preferable that said center electrode, said passageway, and said opening are cylindrical, substantially concentric and said opening has a diameter at least 0.01 inches greater than the diameter of said passageway.
These embodiments of the invention will be further elucidated by considering the illustrative examples presented in FIGS. 1--6.
FIG. 1 is a longitudinal partial section view of a surface gap spark plug of the present invention. The spark plug in FIGS. 1, 2, and 3 will be generally designated as 1. In FIG. 1, the spark plug 1 comprises a center electrode 2 which is positioned in the central passageway 3 which runs longitudinally through the insulator 4. A metal shell 5 encloses a portion of the insulator 4; the lower end of the metal shell 5 has an opening 6 which is in substantial register and of substantially the same size and shape as the passageway 3 at the lower end of the insulator 4. The metal shell 5 serves as the second or ground electrode.
The center electrode 2 terminates within the passageway 3 so as to define a surface 7 along the insulator 4, between the end 2a of the center electrode 2 and the lower end of said metal shell 5 at 5a. This surface 7 is referred to as the surface gap. It is along this surface 7 that the spark is generated when the center electrode 2 and the metal shell 5 are in circuit with an ignition source. Any suitable ignition source can be used.
The dimensions of the elements of the spark plug of FIG. 1 below the dotted line AA are of importance. The distance from the center electrode 2 at 2a to the outer shell at 5a (the surface gap) may be varied to fit the needs of the ignition system, fuel, combustion chamber shape, particular combustion device, and the like. When the spark plug of FIG. 1 is used in a liquid or gaseous hydrocarbon fueled, reciprocating, internal combustion engine, this distance (2a to 5a) or surface gap 7 can be varied from 0.03 inches to about 0.08 inches; a surface gap of 0.035 to about 0.055 is preferred. The center electrode 2 is substantially equal in diameter to the passageway 3 where the surface 7 is defined from the point 2a. This diameter can, of course, be varied.
Another dimension of importance is the thickness of the metal shell (or ground electrode) 5 between 5a and 5b. In FIG. 1 the distance between 5a and 5b is illustrated as being substantially smaller than the surface gap 7. This distance between 5a and 5b of metal shell 5 can also be increased to be equal or greater than the surface gap. Thus, for example if the surface gap 1 in FIG. 1 were 0.05 inches then the distance between 5a and 5b (or the thickness at this point) can be 0.01 inches, 0.04 inches, 0.08 inches or even greater.
In addition to the essential parts and dimensions discussed above, the FIG. 1 illustration also shows a conventional terminal 8 which extends through and outside the insulator 4 and is in contact with the center electrode 2; this terminal 8 provides a means of engaging a conventional wire conductor (not shown) from an ignition source (not shown). FIG. 1 also illustrates that the center electrode 2 is held in place in the passageway 3 in the insulator 4 by means of a pressed powder seal 9; the same means is used to hold the insulator 4 within the metal shell 5. The spacer 10 also illustrate a conventional means for holding the insulator 4 away from the outer shell 5. These means of mounting and holding the essential elements of the spark plug of FIG. 1 are used for illustrative purposes; any other conventional or art recognized means of accomplishing the same purpose in the spark plug assembly can be used.
The size, shape and configuration of the insulator 4, the center electrode 2, and the shell 3 are not critical except for the dimensions defining and limiting the surface gap 7 and the configuration of the spark plug below the broken line AA. It is understood of course that the insulator should always be of the proper thickness to permit spark generation by the high voltage pulse of the ignition source, to occur only across the surface gap and any series gap (see discussion of FIG. 4 below) in the spark plug.
FIG. 2 is an enlarged section view of the portion of the FIG. 1 spark plug below dotted line AA. All identifying numbers are the same as and designate the same parts as in FIG. 1. The enlarged section more clearly illustrates the dimension relationships of this section of the spark plug 1 as set forth above in the description of FIG. 1.
FIG. 3 is an end view of a section through said FIG. 1 spark plug at 1'-1'. It illustrates the substantial register of and correspondence in size and shape of the opening 6 in the outer shell 5 and the passageway 3 and the central electrode 2 at 2a. Although the electrode 2 and the opening 6 are circular and this is preferred, the electrode and the opening may be square, oblong, triangular, rectangular, etc., that is of any desired shape provided the critical dimension/register relationships pointed out above are maintained.
FIG. 5 illustrates a modification of that spark plug end or tip shown in FIG. 2. All identifying numbers designating the same parts are the same as in FIG. 2. FIG. 5 shows a spark plug tip in which the thickness of the metal shell 5 between 5a and 5b is greater than the surface gap 7 length. In other words, the ratio of the thickness (distance between 5a and 5b) and the surface gap 7 length is greater than 1. The center electrode 2, the passageway and the opening 6 are substantially concentric. By substantially concentric, I mean that the ground electrode 5 at 5a is so positioned that it does not protrude or extend past the insulator 4 into the passageway 3 at 11. It also shows that the diameter of the opening 6 is slightly larger than the diameter of the passageway 3 at 11. Keeping a finite difference, of e.g., 0.005 inches, 0.01 inches, 0.02 inches, etc. between these diameters, facilitates maintaining substantial concentricity in manufacturing or otherwise fabricating the spark plug of the present invention.
When the ration of the thickness (distance between 5a and 5b) of the ground electrode 5 and the spark gap length 7 is greater than 1 and preferably between 2:1 and 4:1, there is a substantial improvement in the operating characteristics of the spark plug of the present invention. The modification illustrated by FIG. 5 can be used with spark plugs having series gaps (as illustrated in FIG. 4) with equal effectiveness.
FIG. 6 is an end view of a section through FIG. 5 at 2'-2'. It shows the substantial concentricity of the center electrode 2, the passageway 3 and the opening 6 of the outer shell 5. Although the electrode 2, the passageway 3 and the opening 6 are cylindrical in FIG. 6, this is meant to illustrate and not limit the shape of these elements. Thus, the electrode 2, passageway 3, and opening 6 can all be square, rectangular, triangular, elliptical, etc. or a combination of any of these configurations provided that the substantial concentricity of these elements is maintained.
FIG. 4 is a longitudinal partial section view of a spark plug identical with that in FIG. 1 except that the center electrode 2 has an additional gap between 2b and 2c, said gap being in series with the surface gap 7. The center electrode 2 above 2b also has a central bore 11 which extends through the terminal 8; this bore 11 provides a means of ventilating the series gap between 2b and 2c. The presence of this series gap (2 b-2 c) permits more efficient spark generation at the surface gap 7. Although the series gap in FIG. 4 is internal, that is, enclosed by the insulator 5, this series gap can also be located outside the insulator 3. Any series gap means known in the art may be used in the present surface gap spark plug. The series gap between 2b and 2c can be varied from 0.05 to 0.250 inches.
The materials used in fabricating the insulator, center electrode, outer shell and other portions of the spark plug of the present invention are not of critical importance. Thus, these elements of the spark plug can be made of any material which has suitable physical and electrical properties.
The spark plug of the present invention is especially useful to provide a spark in a reciprocating, spark ignition, internal combustion engine which is fueled with a suitable hydrocarbon fuel containing a spark plug deposit-forming additive. Suitable hydrocarbon fuels include hydrocarbons boiling in the gasoline range, liquefied normally gaseous hydrocarbons such as propylene, propane, butane, methane and the like, and gaseous hydrocarbons such as methane, natural gas and the like; spark plug deposit-forming additives encompass organometallic additives in general and the so-called "antiknock" agents in particular. Thus, another embodiment of this invention is a method of operating a spark ignition internal combustion engine by providing each combustion chamber (cylinder) with a fuel containing an organometallic additive, sufficient air for combustion, and igniting the air/fuel charge with a spark provided by a surface gap spark plug of the present invention whereby time to misfire is substantially increased. An especially preferred embodiment of this method is accomplished by utilizing a fuel containing a tetrahydrocarbyllead, such as tetraethyllead, tetramethyllead, and the like, or a cyclopentadienyl compound of iron, manganese, nickel and the like in antiknock quantities. A most preferred embodiment of this method utilizes a fuel containing an antiknock quantity of (methylcyclopentadienyl) manganese tricarbonyl.
To demonstrate this dramatic improvement in spark plug life and efficiency, an engine test was used to compare the resistance to fouling of a conventional air gap spark plug and a surface gap spark plug illustrated by FIG. 1. The test involved operating an internal combustion engine using a gasoline fuel containing an organometallic antiknock additive and determining the number of hours to misfire; a misfire indicates that the spark plug has fouled and is either not sparking, or is sparking in such a manner that a suitable fuel/air mixture is not igniting. The test was conducted in a single cylinder engine; following is the data obtained in a series of tests of a conventional air gap spark plug and a surface gap spark plug of the type illustrated in FIG. 1. ##SPC1##
1. the test cycle was 30 minutes with throttle open 75--100 percent followed by 45 seconds at idle-- repeated until misfire occurred. The fuel used was isooctane containing 2.0 grams per gallon of manganese as (methylcyclopentadienyl) manganese tricarbony.
2. Discontinued without misfire shortly after 201 hours. ##SPC2##
A. the test cycle was 24 hours at throttle open 25 percent and 1,200 r.p.m. (revolutions per minute) followed by two minutes at throttle open 100 percent and 1,200 r.p.m.--repeated until misfire occurred. The fuel was a commercial gasoline containing 3.17 grams per gallon of lead as tetraethyllead, 1.24 grams per gallon of a bromohydrocarbon and 1.08 grams per gallon of a chlorohydrocarbon.
B. discontinued without misfire shortly after 305 hours.
The ignition system used in this engine test was one equivalent to induction coil/ 12-volt system used in regular production automobile engines.
It is readily apparent from the data in Tables I and II that the surface gap spark plug of the present invention has a significantly greater resistance to fouling compared to the conventional air gap spark plug in a gasoline engine using a gasoline containing either a manganese or lead containing additive. With the manganese containing fuel (Table I), the conventional spark plug misfired after only 48 hours; the surface gap plug of the FIG. 1 type operated without misfire for more than 201 hours. With the lead containing fuel (Table II) the conventional plug misfired at 55 hours while the surface gap plug of the FIG. 1 type misfired after 107 hours, an improvement of about 100 percent. Furthermore, when the surface gap plug's spark gap was increased to 0.056 inches, there was no misfire even after 305 hours.
The same type of evaluation was conducted using a regular production V-8 automobile engine. In this test, four cylinders were provided with conventional air gap spark plugs and four cylinders were provided with surface gap plugs of the present invention. Again, the tests were conducted with gasolines containing tetraethyllead or (methylcyclopentadienyl) manganese tricarbonyl. The data obtained for these tests are tabulated below. ##SPC3##
1. The fuel used was a commercial gasoline containing 2.0 grams per gallon manganese as (methylcyclopentadienyl) manganese tricarbonyl. The test cycle used was one hour operation at equivalent of 65 miles per hour (mph) followed by one hour operation at equivalent of 55 m.p.h.--the cycle was repeated; misfire was automatically recorded.
2. All four surface gap spark plugs performed without misfire for over 131 hours at which time the test was discontinued. ##SPC4##
A. The fuel used was a commercial gasoline containing 3.17 grams per gallon of lead as tetraethyllead, 1.24 grams per gallon of a bromohydrocarbon scavenger and 1.08 grams per gallon of a halohydrocarbon scavenger. The test cycle was 100 seconds operation at 35 m.p.h. equivalent followed by 40 seconds at idle, repeated for 100 hours.
B. The percentage of misfires for all four spark plugs of each type at throttle open 100 percent was then recorded.
By conventional air gap spark plug, I mean the standard type of spark plug used in current regular production automobile engines.
By increasing the time to misfire and reducing the rate of misfire, the efficiency of an internal combustion engine is greatly improved. In addition, the emission of unburned hydrocarbons into the atmosphere is also significantly reduced.
The data in Tables III and IV again shows how vastly superior the surface gap spark plugs are in their resistance to fouling in a standard 8-cylinder automobile engine using a lead or manganese containing gasoline fuel.
By increasing the time to misfire and reducing the rate of misfire, the efficiency of an internal combustion engine is greatly improved. In addition, proper ignition of the fuel/air mixture significantly reduces the emission of unburned hydrocarbons into the atmosphere.
The present invention is directed to (1) an improved surface gap spark plug which features a recessed surface gap, and (2) an improved method of operating an internal combustion engine using a fuel containing an organometallic additive and the improved surface gap spark plug.
Both embodiment have been described above. Claims to the invention follow.