US2590778A - Dual plug ignition system - Google Patents

Description

March 1952 E. w. LAUTENBERGER DUAL PLUG IGNITION SYSTEM Filed July 6, 1950 Inventor Elmer- W. Lautenber i er by M Y His Attorney Patented Mar. 23, 1952 DUAL PLUG IGNITION: SYSTEM Elmer W. Lantenberger, Schenectady, N. Y., as.-

si'gnor to General Electric Company, a corpo- Application Julyfi, 1950, Serial No. 172,337

tional ignition systemsv almost invariably fail to light their burners and, numerous attempts to overcome this res-tart difficulty-haverailed.

Indications have been. that-1a larger spark gap improves altitude starting performance; However,, there is" a practical limit to which a spark gapcan belengthened'and this depends upon the available output voltage of the ignition unit which units already' produce the maximum line to ground voltages that it is practical toimpress on high-tension ignition cables which are: also already stressed well. beyond their corona level. The lack of a practical ignition system due to the foregoing problem has. heretofore imposed'a serious limitation on the development and operationof jet engines otherwise capable of high altitude flying.

It is an object of. this inventionl to provide an ignition system which overcome the foregoing restart'difliculties at high altitudesand yet which is simple andipositive inoperation.

It is-a f'ur-ther object of this invention to provide' an ignition system which is particularly adapted for high altitude jetengine aircraft.

Still. another object of: this invention is top-rovide an ignition system which will operate at both lowand high altitudeswhileoat the same time providing thetype of electrical discharge required at. the higher altitudes to initiate combustion.

A still further objectof myinventionis toprovide an ignition. system. in. which two separate spark plugs are. used in the same combustion chamber, neither of which plugs have a ground electrode.

Astill further, object of this invention is topro vide an ignition system. whlchwill not stress the system insulation beyond present maximum practical levels and yet will. provide twice the usually available voltage to jump the. spark gap.

A still further object of this invention isto provide a system capable .of firing a. spark gap roughly twice as large as the maximum gap that it is practical to fire with a conventional system.

Still another object is to provide an. electrical discharge for initiating combustion which has greatly increasedcapacitive and inductive components and consequently provides greater power and energy.

According to my invention, I provide an ignition system which comprises two separate spark plugs, each of which plugs are oppositely disposed in the same combustion chamber and have a single ungroundedelectrode. Ahightension circuit is connected between the two. electrodes and the latter are energized simultaneously, the polarity of the voltage impulses. on one. electrode being positive andthepolarity of. the voltage impulses on the other electrode. being. negative '50 that the electrical discharges. take place in a wide gap betweenlthe twospark plugs.

The invention will be more. fully understood by referring now. to the accompanying. drawing of. a diagrammatic representation ofmy improved ignition system as applied to one of, the combustion chambers. of a. jet engine.

The drawing show-ea cross-sectional view of a combustion. chamber I which has an inner liner 2. This chamber represents. one of a plurality of combustion chambersrwhich are normally annularly disposed within the outer. periphery. of a conventional jet engine.

Projecting into the combustion chamber are two spark plugs 3 and 4 which. are of identical construction. Looking at spark plug 3 it, will be seen. to comprise an elongated high voltage electrode 5 which is. centrally disposedlin a ceramic insulator 5 within a metal housing I having a mounting flange 8 whereby the spark plug 3 may be keyed and secured to the combustionchambcr. It will be noted that my spark plug has a single extended high voltage electrode. but no ground electrode: .The upper portion above the mounting flange may be of any suitable conventional construction.

As mentioned above, sparkplug. 4 is similar in construction to spark plug, 3. and they. should be cooperatively located so that the inner extremities of their central-1y disposed. electrodesextend toward each other irrespective of the. axial disposition of their housing 1. in. the chamber.

Spark plugs 3 and 4. are energized by ignition coils ill and H. Coil it has a primary or.low tension winding l2 and, a secondary or high tension winding I 53 and one end of each of these windings are connected togethenthe opposite end of high tension winding 13 being connected by a cable 14. to the. single electrode 5 of spark plug 3.

Ignition coil H is similar to. the one just. described, it also comprising a low tension winding l5 and a high tension winding Hi, having, one end 3, of each connected together, the other end of the high tension winding l6 being connected via cable H to the single electrode 9 of spark plug 4. The two high tension windings l3 and iii are serially connected together at IS.

A source of sparking voltage for my system may be obtained in a number of different ways known to the art. For purposes of illustrating a completely operative system, I have shown a vibrator type battery operated system which uses a conventional electrical circuit except that an additional ignition coil, and a capacitor having twice the usual capacity, have been added to the circuit as will hereinafter be described.

As shown in the drawing, a battery [-9 is connected in series with a switch 20, ignition coil primaries l2 and I5, and with a circuit comprising the parallel arrangement of a capacitor 2| and a vibrator 22. The ignition coil primaries have approximately two-thirds the number of turns normally employed in a conventional single ignition coil circuit. One side of the battery i9 is connected to one end of ignition coil primary l5 and grounded at 24.

The vibrator 22 is seen to comprise a reed 23 at the top of which is mounted an armature 24. In addition, the reed 23 carries two pairs of contacts 25 and 26 which operate with the reed as will be explained. When the reed 23 is at rest, contacts 25 are closed, and a circuit may be traced through an electromagnet 21 to ground.

With the foregoing understanding of the elements and their organization, the operation of my invention will be readily understood from the following explanation. When the switch is closed, current will flow through closed contacts 25, electromagnet 21 and to ground thus causing the armature 24 to be drawn to the right thereby closing contacts 26. This will cause current to build up in the ignition coil primaries l2 and I5. After contact has been established at 25, the contacts at 25 will open and the electromagnet 21 will be de-energized and the reed 23 will return to the left position. This cycle will continue and current flow to the ignition coil primaries i2 and [5 will be alternately established and interrupted. With each interruption, the flux produced by current in the ignition coil primaries, collapses at a very rapid rate. Much of this flux links the ignition coil secondaries l3 and 16 as well as the primaries l2 and I5. The rapid rate of decay of flux in each of these ignition coils induces voltages in both the primary and secondary windings. Because the secondary windings have more than one hundred times as many turns as the primary windings their voltages are correspondingly very much higher. As shown in the drawing, the ignition coils are connected to produce voltages in coils l3 and I6 which are 180 out of phase so that spark plug 3 will be energized by a high voltage having a polarity opposite to that of the high voltage supplied to spark plug 4. This results in developing a voltage which is twice as great as the voltage developed in a conventional single ignition cell system yet withoutany increase in the line to ground voltage stress on ignition cables l4 and IT.

The opening of contacts 26 causes capacitor 2! to be switched into the primary circuit and this capacitor thereupon becomes charged by the voltage which was induced in primary coils l2 and I5. Due to the secondary capacitance of the cables and spark plugs, they also will be charged by the voltage induced in secondary coils l3 and 16. At the instant that the voltage between electrodes 5 and 9 reaches the breakdown potential of the gap a high frequency spark will jump the gap and dissipate the energy stored in the secondary capacitance of the system. It will be appreciated that the use of a second high tension cable and spark plug in my system has doubled this capacitance and energy in the spark compared to that obtainable from a conventional single spark plug system. Following the discharge of secondary capacitance, the energy of the primary capacitor is dissipated in the spark at a much lower frequency. This capacitive component is also greatly increased in my system since it will be recalled that the addition of a second ignition coil to the circuit permits the use of a primary capacitor having twice the electrical size. Finally, the inductive component or are which follows the spark is also greatly increased inasmuch as it is produced by the inductive energy of two ignition coils rather than one as in conventional systems.

Thus, the system herein described not only provides twice the output voltage usually available and thus makes it possible to substantially double the gap length between electrodes without causing any increase in the electrical stress on the system insulation, but, furthermore, the energy of each electrical discharge across the gap is greatly increased by virtue of the larger capacitive and inductive components of the spark and are. These advantages obtained when using my ignition system have been found by wind tunnel test of a full scale jet engine to result in greatly improved high altitude starting performance.

In Patent 2,447,782 to Welge, there is shown an ignition system directed to the elimination or suppression of radio frequency interference which results from their operation in internal combustion engines. The Welge patent discloses a system in which a single spark plug has two electrodes both of which are insulated from ground and fed by a balanced two wire system. It will be evident upon examination, however, that this system has only a superficial resemblance to my invention since it requires a close interrelation of leads to the spark plug and this would increase rather than improve the severe corona and insulation breakdown problems encountered at high altitudes. In my system the cables to the plugs are purposely widely separated which construction is just opposite to that of the Welge patent which teaches the balancing out of radio interference voltages. The present invention requires electrodes to be widely separated and, in fact, to be removed outside the bounds of the same spark plug in order to provide a greater capacitive component. It will be appreciated, therefore, that the above patentees system is not capable of producing as long and as hot a spark at high altitudes.

It should be understood that my system will operate at sea level as well as at high altitudes and this will depend partly upon the choice of the gap distance. For practical purposes, and to insure firing at sea level conditions, I prefer to set the gap between electrodes at about one-half inch to insure positive starting throughout the altitude range of the aircraft although my system will operate with gap settings several inches long at altitudes in the order of 50,000 feet provided adequate insulator flashover distance is built into the exposed end of the spark plug.

Although a particular embodiment of my invention has been illustrated and described, modifications thereof will readily occur to those skilled in the art. It should be understood, therefore, that the invention is not limited to the particular arrangement disclosed but that the appended claim is intended to cover all modifications which do not depart from the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is: 7

In an ignition circuit for a jet engine combustion chamber, a pair of separate single-electrode spark plugs adapted to project into said chamber in opposing relation to define a spark gap therebetween, each said plug including means insulating the plug electrode from said chamber and the external ends of said plug electrodes bein widely spaced apart, a pair of separate ignition transformers each having a low voltage primary winding and'iahigh voltage secondary winding, a common connection connecting, said primary windings and said secondary windings respectively in backtd-back series circuit relation thereby to provide'at opposite ends of said secondary windings instantaneous voltages of opposite polarity, means grounding said windings at a point electrically adjacent said common connection, and a pair of insulated high-voltage lead wires positioned remotely with respect to .each other and connecting said opposite ends of said secondary windings to said plug electrodes respectively, whereby said plug electrodes are supplied with voltages of opposite polarity with respect to ground and the voltage applied across said gap is substantially greater than the lineto-ground voltage at any part of saidcircuit.

ELMER W. LAUTEN'BERGER.

REFERENCES orrEn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 578,266 Rowbotham Mar. 2. 1897 604,241 Tuttle May 17, 1898 1,888,692 Powers Nov. 22, 1932 2,115,873 Powers May 3, 1938 2,447,782 Welge Aug. 24, 1948 2,470,568 MeCrumm May 17, 1949

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