US2672729A - Spark plug - Google Patents

Description

March 23, 1954 w. H. VAN RY 2,672,729

SPARK PLUG Filed 001;. 28, 1950 f T? if 26 JNVENTOR. Mu/AM H. l/AN RY BY WM 4% A TTORNLF'VS' Patented Mar. 23, 1954 -William H. Van Ry,

Boeing Airplane Compa corporation of Delaware Application OctobcriZS, 1950, Serial No.

Claims.

This invention relates to an improved spark plug and spark plug installation for internal combustion apparatus :of the liquid fuel burning type (and is herein illustratively described by reference to its application in a gas turbine engine of a type intended for use in airplanes. A general object of the invention is to enable such engines to be started reliably at low temperatures, below those at which previous types of spark plugs used in such engines can operate effectively.

A more specific :object is a low temperature ignition spark vplug installation in which the spark plug is very favorably located for receiving an ignition mixture of fuel injected into the engine combustion chamber to start the engine, and yet the electrodes are protected effectively against fouling and against shortening .heat resulting from continuous high operating temperature in the adjoining combustion chamber.

Still anothero'bject of-the invention is the application to best advantage in a gas turbine engine-or thelikeef a fuel preheating type spark plug, and additionally the provision of an imture enginelstar'ting operation.

"The preheating of liquid fuel in spark plugs has been proposed previously for use in internal combustion engines of the reciprocating type. However, "the problem of starting gas turbine engines or the like at very low temperatures has presented special diflicul'ties which are not-present'in the usual reciprocating engine. "For example, the unusually high temperatures devel oped in gas iturbine engines greatly shorten the life of spark plugs unless special protective measures are employed. Furthermore, any expected "location of the spark plug electrodes for protection from the high temperature ,gases in the combustion chamber to prolong their *life would seem only to aggravatethe alreadydiflicult prdblern of "starting the engine 'at low initial temperatures because of the resulting effective rem'oten'ess'oi the-electrodes from the 'moreactive zone of the combustion space.

In accordance with :the'present invention employin'g an improved fuel preheating type of sparkplug,installation of the spark plug is made atthe bottom of the combustion "liner at a'locaoffuelintheform of drainage from'the chamber excessive life- :Seattle, Wash, assignor to ny, Seattle, Wash, a

formlsaturates the spark gap region in sufilcient quantities for reliable starting'evenat the lowest engine starting temperatures expected.

In accordance with further features of the invention, the spark plug .shell, which opens into the :bottom of the combustion liner of the engine, crosses through the air jacket space by which such liner is cooledduring-operw tion of the engine. Within such jacket, an opening in the .side of the spark plug .shell admits air vfrom the jacket space into the spark plug interior and thereby causes agitation and circulation of the fuel droplets therein to insure contact thereof with .the heating coil. More specifically, the opening isso arranged and directed that this circulating air enters the spark plug interior generally tangentially. 'The resulting swirling motion of the fuel droplets inside the spark plug she'll carries them outward to the inside Wall of the spark plug shell by centrifugal force. The heating :coil is advantageousiy positioned immediately adjacent to such wall and thereby contacts and vaporizes the fuel particles in maximum degree.

Still another feature of the improved spark plug and installation thereof in gas turbine engines, for example, is the arrangement of electrodes protectively Within the interior of -the spark plug shell away from this intense "heat normally present in the engine combustion chamber. Moreover, electrode cooling is afforded by air ilow in the engine cooling jacket "and around'the spark plug shell, "and also more-directly by the effect of fuel-circulating *airentering the spark plug 'shell itself through *the tangential opening therein. In the preferred electrode arrangement, .as herein illustrated, the electrode elements are located centrally inside the shell and preferably along its axis to position the spark gap at a region of low'velocity of the fuel-circulating air whichenterstheshelL This arrangement'insuresa supply-of warm fuelladen air at the spark gap for ready "ignition thereof, because the heavier cool air and fuel particles within the shell swirl "outward under centrifugal force awayfrom the "centrally located spark gap, whereas thewarm vapors rise'through the gap region as 'dc-isired.

Preferablythe heating'coil is placed indirect physical contact with the interior "wall of the spark 'plug shell 'to provide mechanical "support to the coil against turbulence and vibrational forces present in the engine.

These and other features, objects "and .advantages of the improved spark plug "andlsparkplug installation will become morefully evident from the "following detailed description thereof "based upon the accompanying drawing, which illustrates the invention in its preferred form and setting.

'Figurel is alongitudinal vertical sectional view of the improved spark plug installation in a gas turbine engine combustion apparatus.

Figure 2 is an end view of the spark plug installation looking in the direction of the arrows 2, 2 in Figure l to show the tangential location of the side opening in the spark plug shell.

Figure 3 is a top view of the improved spark plug unit installed as in Figure 1.

In starting the usual gas turbine engine the engine rotor shaft is driven by an electric motor or other auxiliary power source to rotate the engine air compressor and operate the fuel pump. As a result fuel and air are forced into the engine combustion chamber in quantities conducive to starting of the engine. The combustion mixture is then ignited by a spark plug and the combustion rocess thereafter is self-perpetuating. As mentioned above, however, these engines, typical of a class of internal combustion devices, using heavy hydro-carbon fuels and for other reasons, are very difficult to start reliably at low temperatures. Also there is the attendant difiiculty of short electrode life due to the extremely high temperatures maintained in the combustion chamber during normal operation of the engine, to which the spark plug, although used primarily only in the starting operation, remains subject.

In Figure l the illustrated portion of the gas turbine engine comprises the forward end section of the annular combustion liner iii having an end Wall 12, in which the fuel injection nozzle i4 is mounted to direct a spray of liquid fuel into the combustion chamber defined by such liner. The broken lines It represent the conical pattern outline of the fuel sprayed into the chamber. A cooling jacket l8 surrounding thecombustion liner 10 "provides an annular space around such liner through which air is forced under pressure created by the engine compressor (not shown), the general flow of air being indicated by arrows. Some of this air enters the combustion chamber within the liner it through wall openings in the latter as indicated, to provide a supply of oxygen for combustion of the fuel. The details of the combustion chamber and cooling jacket and also the arrangement and construction of the fuel injection nozzle M and suitable supply conduits connected to the nozzle are in themselves no part of the present invention and are described at no greater length herein for that reason.

It will be observed in Figure 1 that some of the fuel sprayed into the combustion chamber by the nozzle Hi until combustion takes place will fall to the bottom of the combustion chamber. This is indicated symbolically by the fallingdroplets 20 represented in the figure. In accordance with one phase of the present invention, advantage is taken of the inherent tendency for some of the fuel to fall from the discharge stream of theinjection nozzle 14 and to collect in the bottom of the combustion chamber, as a means of priming a fuel preheating spark plug unit installed in a fuel receiving location in the bottom wall of such combustion chamber. For this purpose thespark plug unit 22 is mounted in depending position in the bottom wall of combustion liner iii in registry with a drainage aperture 24 in such wall, through which the fuel droplets fall into the interior of thespark plug shell 26. Such fuel particles entering the spark plug interior come into contact with theheating element 28 therein and are thereby converted into warm vaporous form conducive to ready ignition in thespark gap 38 betweenelectrodes 32 and 34. Because of the special location of the fuel preheatingspark plug unit 22 in the combustion liner below the discharge location of the fuel injection nozzle and in registry with the drainage hole 24, there is always ample assurance that an adequate supply of liquid fuel will drain or drop into the spark plug interior for engine starting purposes.

Additional features of the invention reside in the construction of the spark plug unit itself and also in its arrangement with relation to the fuel chamber and cooling jacket for obtaining most efficient low temperature starting of the engine and also maximum protection of the spark plug electrodes against extreme heat from the combustion chamber.

As shown, the spark plug unit depending from the bottom wall of the combustion liner It] extends across the lower portion of the cooling jacket space hence lies in the path of flow of cooling air passing through the jacket in the direction of the arrows. A side opening 36 facing against the cooling air stream is formed in thespark plug shell 26 to admit air from the jacket space into the spark plug interior. The air thus admitted not only facilitates cooling of thespark plug electrodes 32 and 34 mounted in theshell 26, but agitates and circulates fuel particles around inside the interior of the spark plug, so that in large degree they come into contact with theheating element 28, as desired. Preferably the side opening 36, facing against the air stream in the cooling jacket space is directed generally tangential with relation to the interior of theshell 26, as shown in Figures 2 and 3, so that the admitted air will move circumferentially within the spark bottom of the plug and create a swirl of airborne fuel particles therein. As these particles swirl around inside the spark plug shell, they spiral outward under centrifugal force and tend to concentrate in the annular region immediately adjacent to the in terior wall of the shell as they settle slowly by gravity toward the bottom of the spark plug interior.

By employing a spiralcoil heating element 28 or the like, which lies immediately adjacent to the inside wall of theshell 26 in and along the path of the swirling particles of fuel, the latter are converted with maximum efficiency into the desired warm vaporous form by contact or proximity with the heating element surfaces. Preferably, and as shown in Figures 1 and 3, theheating element 28 comprises an electric heating coil placed in direct physical contact with the inside wall of the shell 25, such coil extending over a substantial portion of the length of the spark plug shell and lying generally below the air inlet opening 36. The lower end of the coil is secured physically and electrically to the insulated binding post comprising themachine screw 38 passing through an opening in the lower side portion of theshell 26 and insulated therefrom by a nonmetallic grommet 4i and washer 42 in the manner shown. The upper end of theheating coil 28 is welded or otherwise permanently bonded to the groundedelectrode 32 fixed upon the upper end portion of the shell 25. lhe heating coil is suitably coated with baked enamel or other thin temperature-resistant insulating material permitting direct physical contact of the coil with the grounded shell of the spark plug without electrically shorting the coil turns. When the coil is installed inside theshell 26, it is expanded somewhat by twisting in order to insure firm engagement thereof with the wall of the shell so that maximum mechanical support to the coil is afforded against vibrational forces.

Ll Electric current to heat the coil 29 is supplied from a suitable source (not shown) connected to thebinding post screw 30 and to the grounded shell of the spark plug to complete a heating cuit.

In their preferred form as shown in the drawing, the spark plug electrodes are arranged to provide a spark gap located in the central region of the spark plug interior. places the spark gap til in a low velocity region of air moving around inside the spark plug cavity. As a result the warm iuel vapors conducive to ready ignition, being relatively light tend to gather in the central region occupied by the spark gap whereas the heavier liquid fuel particles borne by cooler air swirl outward and away from the spark gap under centrifugal force entailed by circulation of air admitted through the shell opening 35, as previously explained. As these liquid particles come into contact with the annular heating coil. 20, however, and are converted into warm vapor-cue form they are displaced generally inward toward the central portion of the spark plug and rise into and through the region of the spark gap in a continuous process.

In the illustrated case the lower electrode 34 extends straight upward along the axis of the spark plug and terminates just above the upper end of the heating coil body portion, while theupper electrode 32 extends downward along the same axis to its terminal spaced just above the electrode 54, to define thespark gap 30. The u per end portion of theelectrode 32 is turned at right angles to its axial portion for connection to the upper edge of the shell 25.

By locating the spark plug electrodes thus protectively within the shell 25 and removed from the more intense heat of the combustion chamber of the engine, greatly increased spark plug life is thereby achieved. The added cooling effect of air admitted throughopening 36 and also general cooling of the spark plug shell. 2i) by virtue of its location in the cooling jacket space further increase the life of such spark plugs.

Because other details of construction of the spark plug and the way in which the same is attached to the engine combustion structure may vary considerably, no detailed explanation of the remaining portions of the illustrated spark plug structure is made, the drawing generally illustrating a typical arrangement of the parts involved. It will be appreciated that these and the parts specifically described may vary somewhat as to form and arrangement without departing f the essentials of the invention in its Various aspects.

1' claim my invention:

1. In internal combustion apparatus having a combustion chamber and a fuel injection nozzle mounted in one wall thereof above it bottom, the spark plug installation comprising an openended spark plug shell depending from the bottom wall of the combustion chamber, such bottom on the bottom of said combustion chamber, and said open-ended spark plug shell being mounted, open end up, in fuel receiving position thereunder, coacting spark plug electrode elements carried by and within said shell substantially wholly below said drainage aperture, and fuel preheating means mounted within said shell and comprising a heating element arranged to heat ll i) fuel within said shell to a more readily ignitable condition for ready starting of the combustion apparatus.

In a gas turbine engine or the like having a combustion chamber, a fuel injection nozzle mounted in one wall thereof above its bottom and cooling duct means extending along the bottom outside wall of said combustion chamber to receive and guide a stream of cooling air therealong, the spark plug installation comprising an open-ended spark plug shell depending from the bottom wall of the combustion chamber and extending through the cooling duct thereunder, such bottom wall having a fuel drainage aperture therein so disposed in relation to said nozzle and to the contours of said bottom as to function as an outlet passage for liquid fuel dropping to or collecting on the bottom of said combustion chamber, and. said open-ended spark plug shell being mounted, open end up, in fuel receiving position thereunder, coasting spark plug electrode elements carried by and within said shell substantially wholly below said drainage aperture, and fuel preheating means mounted within said shell and comprising a heating element arranged to heat fuel within said shell to a more readily ignitable condition for ready starting of the gas turbine engine, said shell having a side opening therein admitting air from the cooling air stream into the shell interior for circulation of such air and fuel particles therein to effect maximum contact of such fuel with said heating element.

3. The spark plug installation defined in claim 2, wherein the spark plug shell is generally cylindrical and the side opening therein is generally tan ential with relation thereto causing circumferential flow of air around the interior of such shell.

4. The spark plug installation defined in claim 2, wherein the spark plug shell is generally cylindrical and the side opening therein is generally tangential with relation thereto causing circumferential flow of air around the interior of such shell, the heating element being of cylindrical form adjoining the inside wall of the shell and extending below such opening for maximum heating contact with such coil of circulating fuel particles falling in the shell and spiraling oute ward under centrifugal force.

5. The spark plug installation defined in claim 4, wherein the spark plug electrodes are mounted within the spark plug shell in relative positions defining a spark gap which is generally central and is thereby located in a region of relatively low velocity of circulating air, inside the spark plug shell.

WILLIAM H. VAN RY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,214,390 Towle Jan. 30, 1917 1,505,049 Mason Aug. 12, 1924 1,694,001 Dana Dec. 4, 1928 1,784,541 Rouillarcl Dec. 9, 1930 2,162,572 Bock June 13, 1939 2,385,833 Nahigyan Oct. 2, 1945 2,404,335 Whittle July 16, 1946 2,493,743 Benson Jan. 10, 1950 2,508,250 Holley May 16, 1950 2,526,159 Steeg Oct. 17, 1950 2,543,366 Haworth Feb. 27, 1951 2,578,501 Boosinger Dec. 11, 1951

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