US2557909A - Apparatus for aiding high altitude ignition in jet power plants - Google Patents

Description

June 19, 1951 J. CROSS ETAL APPARATUS FOR AIDING HIGH ALTITUDE IGNITION IN JET POWER PLANTS Filed Jan. 13, 1950 Time- INVENTORS James M Cross 1 BY Norman E W/rifc/wrcfi ATTORNEY Patented June 19, 1.951

APPARATUS FOR AIDIN G HIGH ALTITUDE IGNITION IN JET POWER PLANTS James W. Cross, Kent, and Norman E. Whitchurch, Akron, Ohio, assignors to Goodyear Aircraft Corporation tion' of Delaware Akron, Ohio, a corpora- Application January 13, 1950, Serial No. 138,304 4 Claims. (01. 315-441) This invention relates to an electric ignition apparatus and in particular to an apparatus for aiding high altitude burning and. ignition in jet power plants.

The advent of the jet power plant has necessitated a re-evaluation of the problem of igniting fuel-air mixtures. The low energy electric spark ignition systems used on reciprocating engines have been found to be unsatisfactory, particular,-v ly when used on jet power plants at high altitude. Tests have shown that at reduced pressures, a high energy spark is required. to ignite the fuelair mixtures. Under starting conditions the combustion chamber pressure in a jet power plant decreases with increasing altitude. Therefore, at, the reduced pressures encounteredat high altitudes, a low energy spark will not provide good ignition. One type of jet engine ignition system present.- ly 'in use consists of a high voltage transformer which fires one spark plug. One disadvantage of this system is a result of the reduced breakdown voltage of a sparkgap at reduced pressure. .Because of this reduced breakdown voltage, the peak energy in the spark'is reduced as the altitude is increased; consequently, thissystem is inadequate for high-altitude ignition.

Another type of system now inuse has a lowvoltage, high-energy ignition spark which is initiated by a high-voltage, low-energy trigger spark. This system does not make the most efficient use of the spark energy. Tests have shown that a high peak energy spark produces better ignition than a low peak energy spark of equal total energy. This high peak energy can best be supplied by a high voltage discharge. The system according to this invention provides just such a high-energy, high-voltage spark. In addition, it anticipates the possible future need for several spark sources to be positioned as desired in the combustion zone by firing any required number of spark plugs.

It is the general object of this invention to avoid and overcome the foregoing and other difl'lculties of and objections to prior art practices by theprovision for jet power engines of a triggered multiple ignition system which produces high peak energy sparks which positively ignite fuel-air mixtures at the low pressures occurring at high altitudes.

Another object of the invention is to control the firing of the engine spark plugs by an enclosed spark gap switch of high breakdown voltage.

, Another obj ct of the invention is to provide a high energy ignition system requiring no movable parts.

The aforesaid objects and other objects which will become apparent as the description proceeds are achieved by providing an ignition system which essentially consists of a high-voltage power. source furnishing direct current for the ignition circuit to which are connected in parallel one or more energy storage capacitors, each of which is connected in series with a spark plug, and of a fast acting low-loss switch connected across the ignition circuit which prevents the capacitors from discharging through the plugs until the desired amount of energy at proper voltage has been stored. These capacitors may be charged in various ways, described later on, and from any suitable source of high D. C. voltage which, according to the following description, is obtained by half-wave rectification of a high voltage.

source. In the following circuits a self-triggering, enclosed spark gap has been used as the switch, but other suitable fast acting, low-loss switches, e. g., a hydrogen thyratron, and external triggering may be used if desired.

For a better understanding of the invention, reference should now be had to the accompanying drawing, wherein:

Fig. 1 illustrates a basic circuit of the system, according to the invention.

Fig. 2 shows a voltage-time diagram of the circuit of Fig. 1. v

Fig. 3 shows an improved modification of the ignition system shown in Fig. 1.

Fig. 4 shows a voltage-time diagram of the circuit of Fig. 3.

With specific reference to the form of the invention illustrated in Fig. 1 of the drawing, the numeral l indicates an alternating current source, provided with a main switch 2 for closignition ing the current into the high voltage transformer 3 from where it passes through a rectifier 4 as direct current which flows in the main circuit 5, 6 to charge a charging capacitor 1 connected across the circuit 5, 6. The charging capacitor 1 0per-' ates upon storage capacitors 8a., 8b 8n, each connected in series with ignitor gaps, or spark plugs 9a, 9b .Bn, respectively, and upon a self-triggering, enclosed spark gap or switch l0 requiring a much higher voltage for firing.

The operation of the system is as follows:

Upon closing the main switch 2, the alternating voltage source I is applied to the transformer 3."

Charging capacitor 1 charges through the rectifier 4 to a voltage large enough to fire one of the ignitor gaps, say 9a. Thisallows chargingca-.

pacitor l to discharge into storage capacitor 8a and the discharge will cease when the voltage on charging capacitor 1 is approximately equal to the voltage on storage capacitor 8a. When the discharge across capacitor i ceases capacitor 1 will recharge, but, because of the opposing voltage stored in capacitor 8a during the previous discharge, ignitor gap 80', will not fire again until each of the other ignitor gaps has fired in turn. After all of the ignitor gaps have fired, charging. capacitor 1 must charge to a higher voltage before the ignitor gaps will fire again because of the charges left in the storage capacitors.- Thus the ignitor gaps will continue to fire and the voltage on the charging capacitor 7 will rise in steps to a voltage high enough to eventually fire the switch gap In. The charging process is nowcomplete,

and upon firing of gap Hi all of the energy storage capacitors will discharge simultaneously through their associated ignitor gaps and the trigger or switch gap i0. This-discharge will provide high energy sparks as contrastedwith the previous low energy charging sparks. This process, which repeats itself, is diagrammatically illustrated-in- Fig. 2 in which the voltages across the charging capacitor and across the storage capacitors are indicated against time. It clearly shows how the voltage across the storage capacitors rises in steps until the voltage across 1 reaches the breakdown voltage of the switch gap and the firing of which simultaneously fires all spark gaps at high energy.

For example, if it be assumed. that the D. C. supply voltage is 14,000 volts, that the spark plugs are set-to fire atabout 5560 volts and the gap switch at 10,009 volts, and that the charging and storage capacitors are identical, then the charging capacitor .7 will charge up to about 5500' volts and fire the spark plugs 9a, 9b 9n, oneaafter another. Then, because of the opposing voltage left onthe storage capacitors 8a, 8b 8n, the charging capacitor will charge to about 8250 volts-before the spark plugs fire again. However, duringthe next'step the storage capacitor! will' reach a voltage of 10,000 volts, at which voltage the spark gap switch in and all spark plugs will fire at one and the same time at high energy.

The energy represented by this discharge is a function of the capacity of the energy storage capacitors, the breakdown voltage of the trigger gap, and the breakdown voltage of the'ignitor gaps. The voltage'at which the high energy discharge takes place can be shown to be approximately equal to the breakdown Voltage of the trigger gap minus the breakdown voltage of a single ignitor gap. Thus, decreasing the breakdown voltage" of the ignitor gap results in increasing energy in the discharge. For this reason the above system is particularly applicable to'jet aircraft engines. Under starting conditions, at high altitudes, the greatly reduced combustion chamber-pressure results in a lower breakdown voltage; This isaccompanied by an increase in park energy. which is desirable for improved ignition at high altitudes.

Since-the breakdown of the trigger gap results in rapid discharge of energy across the ignitor gaps, any carbon deposit which would normally result in' fouling 'of the-gaps will be burned. away by the high: temperature of the spark. This will result in longer, more reliable ignitor operation. Similarly, becauseof the nature-of the system, a single damaged plug will not result ina failureof the balance of the'system. Thi'ssys tem is relatively insensitive to fluctuations in voltage. Lowering the supply voltage results in a lowered spark repetition rate, but does not change the energy per spark. The system operation is not afiected by the use of long cables to the ignitor-gaps or spark plugs, since a relatively high capacity and a relatively'low shunt resistance across the ignitor gaps can be tolerated.

The most important features of the system can be summarized asfollows:

1;. Energy increases with increasing altitude.

2. Fires any number of plugs.

3. Will fire fouled plugs.

4. A damaged plug does not materially affect the operation. of other plugs.

5. No moving parts.

6. Canbe madeinsensitive to large supply voltage fluctuations.

'7. Highvoltage spark makes the most eflicient use of spark energy.

8 Unaffected bylong ignition cables.

By a slight modification of the circuit of-Figpl, as shown'Fig. 3, a system with somewhat different characteristics can be obtained,

It is-apparen-t that this circuit has been obtained from the circuit of Fig. 1 by removing the charging capacitor 'l and inserting a suitableresistance in: the .main circuit branch 5, G leading from the rectifier 4-, and resistances [2a, l2b I212; inv parallel with each spark plug. The operation of the circuit is the same as that' of the first circuit, with the important exception that the energy storage-capacitors 9a, 9b 912 now charge'throu'ghthe resistances shunting the plugs instead of through the plugs as before. (3onsequently, the breakdown voltage ofthe plugs no longer influences the voltage built up on the capacitors. The energy per spark is, therefore, constant and independent' of altitude. It is cletermined only by the size of the capacitors; the peak: D. 0. supply voltage, the breakdown-voltage of the gap H1, and the ratio ofthe plug shunt resistorsto the charging resistor H. In addition, since" the capacitors are charged directly from the source of D.-C;-voltage,- the efficiency of the circuitlissomewhat-higher than that of Fig. 1 It is interesting to note that the plugshunt re'-' sistances: I 2a-,..l2b We may be reduced to resistance values well below ohms without afiecting'thafiring of the plug. This is anin dication of the: ability of the-system to fire fouled plugs.

The most important features of the system are the same asthose of the previous system, except that. the: energy per spark is constantand in'-' dependent of altitude, andthe eflici'ency i -greater.

In the voltage -timediagram, Fig. 4, it is seen thatthe storage: capacitors are allcharged sim ultaneously to. a; voltage nearly equalto that necessary tob'reakzdownz the enclosedztrigger gap 16,. which thereby causes to fireall spark plugs by discharging allstorage; capacitors simultaneously, and to-thereby obtain'high energy-sparks which. will positively ignite fuel-air mixtures in starting ajet engine at high altitude.

From the aforesaid it will be recognized that the objects of the invention have been fully achieved; and that with this system'of relatively low weight'without any moving parts, high spark.

energy at high voltage can be producedto. posi-. tively igniteair-fuel mixtures at high altitudes forstarti'ng a .jet" engine.

While certain representative embodiments and details'have been shownforthe purpose of illus- 7'5 tratingtheinvention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

What we claim:

1. A high voltage discharge apparatus for jet aircraft ignition or the like including a high direct current voltage source, a plurality of spark plugs, a storage condenser in series with each plug, means for charging said condensers from the direct current voltage source, and a self-triggered switch in parallel with the spark plugs and associated charging condenser.

2. A high voltage discharge apparatus for jet aircraft ignition or the like including a high direct current voltage source, a plurality of spark plugs, a storage condenser in series with each plug, means for charging said condensers from the direct current voltage source, and an enclosed self-triggered spark gap switch having a breakdown voltage higher than that of the spark plugs in parallel with the spark plugs and associated charging condenser.

3. Apparatus comprising an electric ignition circuit for turbo jet and ram jet engines in an aircraft operating at high altitudes, a high voltage direct current source supplying said circuit, a charging capacitor connected in parallel with said circuit, at least one energy storage capacitor connected in parallel with said charging capacitor, a spark plug connected in series with each of said storage capacitors, and an enclosed selftriggering spark gap switch of predetermined but substantially higher breakdown voltage than that of the spark plugs and connected across said circuit, said charging capacitor being charged to a voltage substantially equal to that of the breakdown voltage of the spark plugs for firing one spark plug, whereby the charging capacitor charges the corresponding storage capacitor until the voltage of the charging capacitor about equals that of the storage capacitor, this spark plug, because of the opposing voltage of its storage capacitor will not fire again until each of the plugs has fired in turn, after all of the spark plugs have fired the charging capacitor must charge to a higher voltage before the spark plugs will fire again because of the charges left in the storage capacitors, thus, the gaps will continue to fire and the voltage on the charging capacitor will eventually fire said spark gap switch, the charging process is now complete and upon firing of said gap switch all of the energy storage capacitors will discharge simultaneously through their associated spark plugs and said switch gap providing high energy sparks in contrast to the previous low energy charging sparks.

4. Apparatus comprising an electric ignition circuit for turbo jet and ram jet engines in an aircraft operating at high altitudes, a high voltage direct current source supplying said circuit, a charging resistor in said circuit, at least one energy storage capacitor connected in parallel therewith, a spark plug connected in series with each of said storage capacitors, a shunting resistor in parallel with each spark plug for simultaneously charging all storage capacitors through said shunting resistors, and an enclosed spark gap switch of predetermined high breakdown voltage substantially higher than that of said spark plugs and connected across said circuit being adapted to fire simultaneously and periodically all spark plugs at high energy.

JAMES W. CROSS. NORMAN E. WHITCHURCH.

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

UNITED STATES PATENTS Number Name Date 2,040,439 Langer May 12, 1936 2,125,035 Smits July 26, 1938 2,297,006 Lohman Sept. 29, 1942

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