US2643511A - Engine starter having combustion chamber supplied with fuel and combustion supporting medium for constant ratio by weight - Google Patents

Description

June 30, 1953 A. T. BRIGGS 2,643,511

ENGINE STARTER HAVING COMBUSTION CHAMBER SUPPLIED WITH FUEL AND COMBUSTION SUPPORTING MEDIUM FOR CONSTANT RATIO BY WEIGHT Filed Oct. 7, 1949 INVENTOR. ARTHUR r. amass ATTORNE Y Patented June 30, 19 53 ENGINE STARTER HAVING COMBUSTION CHAMBER SUPPLIED WITH FUEL AND COMBUSTION SUPPORTING MEDIUM FOR CONSTANT RATIO BY WEIGHT Arthur 1. Briggs, South Williamsport, Pa., as-

signor to Avco Manufacturing Corporation, Cincinnati, Ohio, a corporation of Delaware Application October 7, 194:9,Serial No. 120,101

I 4 Claims. (Cl. Gil-39.14)

This invention relates to prime movers and particularly to engine starter mechanisms which are capable of producing a high starting torque under a wide variety of ambient atmospheric conditions. The present invention is particularly useful in starting aircraft propulsion units, such as turbo-jet engines, and for this reason the preferred embodiment herein disclosed is described with reference to such an aircraft engine.

An object of the present invention is the provision of an engine starter device which is substantially instantaneously available when required to start an associated engine. This is obviously a highly desirable feature, particularly when an aircraft engine must be started under flight conditions.

Inasmuch as aircraft propulsion units are required to operate under a wide variety of altitude conditions, it is an object of the present invention to provide an engine starter device that is capable of producing a high starting torque at high altitudes as well as at sea level and that is capable of starting an engine regardless of the variations of atmospheric temperature and pressure to which the starter is subjected.

Another object of the present invention is the provision of an engine starter which is compact and very light in weight but nevertheless capable of producing a high starting torque with safety and reliability. A further object of the invention is the provision of an engine starter which is practically independent of heavy batteries and consumes very little electrical energy in its operation, contrary to the requirements of certain electrical type engine starters that are in comrnon use today.

The present invention embraces a starter mechanism, the starting cycle of which is electrically initiated by the pilot or attendant of the engine to be started. The mechanism comprises a combustion chamber to which is supplied oxygen and liquid fuel in a predetermined ratio, the fluids being mixed and ignited within the combustion chamber thus producing highly heated and compressed gaseous combustion products for energizing a starter motor associated with the engine.

A desirable feature of a prime mover'mechanism is inherently stable operation and also automatic regulation. It istherefore an. important object of the present invention to provide a mechanism that is inherently stable and autmatically regulated in its production ofpower gases of a substantially constant temperature and pressure for energizing a starter motor to accelerate an engine to be started.

A still further object of the present invention is the provision in an engine starter mechanism of a simple, cheap and effective mechanical device which is constructed and arranged to deliver fuel and a combustion supporting medium to a combustion chamber in a fixed ratio, regardless of the rate of consumption of the mixture and demand to which the combustion chamber is subjected by the associated starter motor.

The starter motor incorporated in the present invention is supplied with highly heated and compressed fluid from the combustion chamber at all times during the starting cycle. Depending upon the type of starter motor used, the rate of flow of power gas to the motor may vary with the speed of the starter motor correspondingly as the associated engine, driven thereby, is accelerated and increases in speed. It is desirable to have the pressure of the gas, supplied to the starter motor, regulated to a constant value at all times regardless of the rate of consumption of the fluid and for this reason a particular advantage and object of thepresent invention is that the preferred embodiment is constructed and arranged to provide automatic pressure regulation of the power gas under all operating con ditions, such regulation being accomplished by means controlling the flow or" fluids to the combustion chamber, thus eliminating the need for regulating the pressure of the extremely hot and highly compressed gas itself.

A still further object of the present invention is the provision of an engine starter mechanism incorporating a speed sensitive element which automatically shuts off the mechanism after the associated engine has been started. Another object of the present invention is to provide an aircraft engine starter which operates with in-- creasing eficiency as the ambient atmospheric pressure decreases with increases of altitude.

Another object of the herein disclosed inve12- tion is its inherent efficiency of operation and relative simplicity. An advantage of this invention is that a wide variety of fuels may be used by the starter mechanism for starting an associated engine, thus making it possible to use the same fuel supply that the engine itself uses.

The novel features that are considered characteristic of the invention are set forth in the ap pended claims; the invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodi ment when read in conjunction with the accompanying drawing which shows diagrammatically 3 the construction and arrangement of the engine starter mechanism in operative relation to a turbo-jet aircraft engine.

With reference to the drawing, the preferred embodiment of my engine starter is shown in conjunction with a turbo-jet aircraft engine generally designated l, comprising a rotor 2 rota-. tively secured in bearings 3, the forward end of the rotor constituting a part of a compressor section 4 and the rear portion of the rotor constituting a part of a turbine section 5. Disposed intermediate the compressor and turbine sections is a fuel burner 6 to which liquid: fuel. is conveyed by a fuel pipe 1 from a fuel tank 8, which may be one of the main fuel tanks ofthe aircraft. Ignition plug 9 is provided in the fuel burner 6 to ignite the mixture of fuel and the compressed air supplied thereto by the com.- pressor section. The highly heated resulting products of combustion undergo a partial expansion in. the turbine section and completetheir expansion in nozzle section l0, provided; in the after part of the turbo-jet engine, the power developed by the turbine driving the compressor, thus making operation of the engine continuous.

Turbo-jet engines of the type herein disclosed cannot be started by merely supplying fuel to the combustion chamber, while energizing thev ignition plug, because initially there is no pressure, head available to force air through the fuel burnerv to support combustion and provide compressed gases for expansion through the turbine. For this reason, supplementaiymeans must be provided for initially accelerating the rotor. to a predetermined rotational speed in order, to render the compressor section operative and assure a continuous supply of compressed air to the fuel burner. When such a supply of compressed air is provided, continuous combustion is established in the burner by the ignition plug, and the energy subsequently developed. by the expansion of the hot gases in the turbine section supplies. the energy necessary forcontinuing the rotation of the rotor and compression ofair in the compressor section.

The supplementary starting means which. constitutes a preferred embodiment. of the present invention comprises a starter motor. ll which is arranged todrive rotor 2 through associated gearing, generally designated l2. A clutch l3 inter.- connects the gearing and the starter motor and transmits the energy of the motor-to a drive gear I4 which delivers power. through. intermittent idler gear [5 to a driven gear 16 which isjoined to and rotates with engine rotor 2.

During the starting cycle power gas. is supplied to the starter motor which is thereby rotated and delivers energy through clutch l3 and the associated gearing to the engineproper. The application of energy in this manner is continued until the rotor has attained a self-sustaining operating speed at which time the clutch is disengaged and the starter system isrendered inoperative.

It is contemplated that-various types-of conventional clutches, well known in the art, may be used; and it is recognized-that-disengagement of the clutch may be made dependentupoiithe speed attained by the engine relative to that of the starter motor, such as effected by a conventional over-running clutch when the speed of the normally driven member exceeds that of the driving member. 7

Many designs of starter motors may be used in a. practical application of this invention, either reference tosuch a starter motor.

a turbine type or direct displacement type of motor being suitable for the purpose. The present invention has particular utility and advantage when used in conjunction with a direct displacement type motor, such as a conventional piston and cylinder type motor, in which the flow power gas actuating the motor varies more or less linearly with its rotational speed; and for this reason, the invention will be described with As will be recogni'z ed by a person skilled in the art, it is important to the proper operation and durability of a direct displacement motor that the temperature of the; power gas. supplied thereto be regulated so as not to exceed and preferably to be held constantat a given value lest the oil film on the running surfaces of the motor be destroyed and general deterioration instigated.

A unique system is provided by the present invention to supply highly compressedand heated power gas to the. starter motorv at a substantially constant temperature and pressure. This system comprises'a high pressure source of oxygen gas H suchas acommercially available flask of oxygen, connected to aconduit l8 inwhichis operatively disposed a normally closed solenoid valve l9 which', when energized andopened, admits a, flow of the highly compressed oxygen to a; pressure reducing valve 20 Afterbeing; reduced to a predetermined pressure, the oxygen is directed to a rotary oxygenmotor 2|, which is directly coupled by a shaft 22. to a gear pump 23. The gear pump increases the pressure of and meters liquid fuel, supplied thereto by a conduit 24, which communicates with the main engine fueltank 8. Disposed in conduit 24' is a normally closedsolenoi'd valve- 2 5; whichis. energized and opened to permitaflow of fuel simultaneously with the opening of solenoidvalve 19.

It is desirable, although not necessary, to-maintain' the oxygen gas. atv constant temperature, variations of temperature causing the mixture ratio to depart slightly. from a constant value. However, for practicalpurposes, the mixture ratio is maintained substantiallyconstant by the herein disclosed device. Any temperature variation is. of minor importance, particularly during any starting cycle, which is usually less than aminute in duration.

It will be obvious from the description and the associated drawing that of necessity a pressure drop mustv occur. across, the? motor 21; in, order to-develop energytherein for. the rotation of shaft 22-. Preferably the rotary motor 2.], should have a very small clearance volume to make the metering characteristic. of the motor per. revolution relatively independent ofthe down streampressure of the oxygen. The rotary oxygenmotor. 21 may in practice bev merely agear pump of conventional design used as a motor, the: gears of the gearv pump being driven bythepassage, of oxygen, thus rotating .the associated shaft 22'.

When the engine. starting cycle is initiated, the normally closedsolenoid valvesareopened, permitting theflow of oxygen and liquid fuel'to rotary motor 21 and gear pump 23, respectively. The flow of oxygen through the motor-drives shaft 22 andgear pump 23'; Inasmuch as. the motor is supplied with oxygen ata substantially constant density because of its essentially constant pressure and temperature, each rotation of themotor represents the passage therethrough of a definite weight of oxygen. Similarly each ro. tation of ganpump' 23 compress'esand passes a fixed quantity of-liquidfuel: In order" to establish the proportion in which the oxygen and liquid fuel are to be metered, it is merely necessary to choose a motor 2| and a gear pump 23 having the desired volumetric displacements per revolution. Another very simple way of changing the mixture ratio established by the oxygen motor and fuel pump is by varying the pressure setting of oxygen pressure regulator 2!]. A variation of the pressure regulator whereby it establishes a higher down stream pressure increases the density of the oxygen at the inlet of rotary motor 2|. In a similar manner a decrease of pressure setting of the oxygen pressure regulator decreases the pressure of the oxygen at the inlet of the rotary motor and correspondingly decreases the density. It will be apparent that inasmuch as the displacement of liquid fuel per revolution of shaft 22 is constant at all times a change in the weight of oxygen passed per revolution of the rotary motor directly changes the resulting mixture ratio.

From experiments that have been completed with devices similar to the preferred embodiment herein disclosed it is apparent that a fuel to oxygen ratio of 2 to l by Weight is satisfactory for producing power gas to start associated engines. It will be apparent from a later part of this desciption that the actual mixture ratio used may be varied over a wide range, the ratio of 2 to 1 being merely illustrative of what has been actually used satisfactorily in practice. I

In order to initiate the starting cycle, an electrical switch 26 is closed by the pilot or attendant and is held in its closed position by an associated spring-urged latch member 21. The closing of switch 25 completes an electrical circuit through battery 28 and ignition coil 29, as well as through solenoid valves l9 and 25, which. are energized and admit fluid flow to the rotary motor and gear pump. Energization of the ignition coil 29 supplies a high potential current to a spark plug 39 which is provided ina side wall of a combustion chamber 3 I.

The oxygen flowing through and being metered by motor ii is conveyed by conduit 32 to the combustion chamber where it joins and is intimately mixed with metered fuel conveyed to the combustion chamber by a conduit 33 in which a flow regulator, generally designated 34, is provided. This flow reguator may be any conventional type and may include a needle valve 35, which is normally forced open by an associated spring and which is arranged for closing movements in response to fluid pressure acting on a piston member the compressed fluid being conveyed to the piston member from the combustion chamber by a conduit 31. The regulated fuel is atomized in the combustion chamberby a fuel nozzle 38.

The intimate mixture of fuel and oxygen within the combustion chamber is ignited by spark plug 3d, the ensuing combustion rapidly producing a high temperature within the chamber.

The highly heated and compressed products ofv combustion flow from the chamber to starter motor ll through conduit Ha and provide the energy for driving the starter motor which, through clutch is and the associated gearing, drives the engine to be started.

The starter mechanism disclosed can be made very light and compact. It is noteworthy that a combustion chamber approximately one inch in diameter and less than a foot long maybe used to supply power gas for starting a fullsize, commercial turbo-jet engine.

As the engine being started is acceleratedand increases in rotational speed, the direct displacement starter motor increases in speed and requires an increased rate of flow of power gas, placing an increased demand on the combustion chamber and causing a decrease of pressure therein. The pressure reduction is communicated to piston 36 of the fuel flow regulator permitting needle valve 35 to open and admit an increased fuel flow to the combustion chamber. The increased fuel flow permitted by needle valve 35 allows a greater rotational speed of shaft 22 resulting in a simultaneous increase of oxygen flow until the flow of fuel and oxygen have increased sufficiently to reestablish the original pressure. It will be apparent that inasmuch as a constant amount of oxygen and fuel is passed to the combustion chamber per revolution of shaft 22, the mixture ratio of the fuel and oxygen remains substantially constant whereby temperatures within the combustion chamber will remain within predetermined limits.

If for any reason the pressure tends to rise within the combustion chamber, the pressure increase is transmitted to piston 36 which moves needle valve35 towards the closed position, thus restricting the fiow of fuel to the combustion chamber. The restriction of the fuel flow reduces the rotational speed of shaft 22 and correspondingly the flow of oxygen through motor 2!. In this manner the rate of flow of oxygen and fuel to the combustion chamber is decreased until the original pressure is reestablished.

If a slight variation in the combustion chamber pressure is allowable, the fuel flow regulator 34 may be omitted entirely. The pressure within the combustion chamber will then be deter mined by that pressure which is established by the oxygen pressure regulator less the loss of pressure resulting from the flow of oxygen through the oxygen motor. In the event that the fuel fiow regulator is omitted, the pressure drop in the oxygen, as it flows through the motor, will be greater at high flows than at low flows in order to compensate for the increased resistance of the fuel lines and fuel nozzle 38 at the higher flows. For example, it has been calculated that with a fuel to oxygen ratio of 2 to l by weight the chamber pressure will vary from approximately 200 p. s. i. a. at flow to 211 p. s. i. a. at no flow.

For safety, a pressure relief valve 39 has been provided in a conduit 40 to relieve any excess pressures, generated within the combustion chamber during the establishment of combustion therein, to exhaust pipe 4! through which the spent gases are vented from the starter motor to the atmosphere.

A fly ball governor 42 of conventional design is directly driven by the starter motor and is constructed and arranged to close an electrical switch 43 when the starter motor has attained a rotary speed in excess of that required for the continuous operation of the turbo-jet engine. Closing of electrical switch @3 completes an electrical circuit through battery 28 and a solenoid M, the solenoid being cooperatively disposed to latch member 2'! for disengaging it from switch 28 upon its energization. Release of switch renders the starter system inoperative by permitting the closing of solenoid valves it and 25 and deenergizing spark plug 3d. As described hereinbefore, at this point clutch member is will be disengaged thereby disconnecting the starter motor from the engine while the engine continues its operation.

M in

It will be obvious to those skilled in the art that a combustion supporting medium different from oxygen can be used in conjunction with the herein disclosed device and that, furthermore, by simply varying the volumetric displacements of motor 2! and pump 23 the proportions of fuel and oxygen combined in the combustion chamber may be varied to limit the final temperature of the mixture of combustion products to a value acceptable for use in the starter motor. lhe temperature may be limited by the provision of either an excess of fuel or oxygen in the combustion chamber, the deviation of the mixture from the chemically correct mixture in each case tending to decreas the temperature of the. final products of combustion.

In analyzing the operation of my system it should be remembered that the combustion of hydro-carbon fuels in either air or oxygen in chemically correct mixtures results in. tempera.- tures much too high to be utilized in a conventional starter motor even if the motor be of the turbine type. It is to-be noted that, as a result of the addition of fuel in excess of that required for combustion, the volume of power gas isaugmented not only by the vaporization of the excess fuel but also by the formation ofintermediate combustion products rather than the final products of combustion which would be formed were sufiicient oxygen. available for complete combustion of the fuel.

From the nature of my invention it will be apparent that the successful operation of my mechanism is relatively'independent of the type of fuel used. The fuel may be the same as that used by the engine being started, thereby eliminating the need for any special starting. fuel or tanks. Inasmuch as an ample supply-of fuel is available in most aircraft installations, it maybe considered desirable, to operate the combustion chamber of my mechanism with a very rich mixture, thus conserving the oxygen and limiting-the temperature of the combustionv products. Since my mechanism provides a high torque by virtue of the high power gas temperature and pressure produced, the starting cycle is of relatively short duration and the actual consumption of fuel is negligible.

From a consideration of the disclosed device it will be evident that the operation of; starter mechanism is instantaneous for practical purposes. The thermal mass of the combustion chamber and motor is relatively small, enabling the system to rapidly attain thermal equilibrium and stable operating conditions.

In the event that a direct displacement motor is used, the efiiciency of the motoriwill-increase with an increase of altitude; since the accompanying decrease in ambient pressure will increase the available pressure differential which the motor can utilize in developing its'poweigthe oxygen pressure atthe inlet f:rotary motor-being completely independent of ambient" conditions.

The-herein disclosed device has been described with reference to any electrical ignition means. It is recognized, however, that any'means capable of initiating combustion of the mixture within the combustion chamber is suitable for the-pur poses-of my invention. In fact, iffa self-igniting mixture of fuel and combustion supporting medium be used, no ignition means isnecessary.

The principles herein disclosed are described and claimed in their broader'aspects; in myxapplication, Serial No.. 82,223, filedxMarch' 18;. 1949-, now Patent No. 2,611,239.

Having described a preferred embodiment of my invention, I. claim:

1. In an engine starter system; a source of oxygen under pressure; a source of liquid fuel; normally closed electrically actuated valves to permit a. flow of oxygen and fuel upon simultaneous energiza-tion; a pressure reducing valve supplied with oxygen under pressure upon energizationof said valves; a constant displacement rotary oxygen actuated motor supplied with oxygen at constant pressure by said reducing valve; a constant displacement gear pump driven by saidrotary oxygen actuated motor for compressing: fuel supplied thereto upon the energ-ization of said valves; a connection between said motor and. said gear pump to insure corresponding rotational speeds thereof a combustion chamber, said combustion chamber being connected with: said rotary motor and gear pump whereby it issupplied with fuel and oxygen in a. ratio. determined by the Volumetric capacity of said motor and pump; flow regulating means responsive to the pressure within said combustion chamber for regulating. the flow of fuelsupplied thereto; ignition means for initiating combustion within-said combustion chamber; a starter motor driven by combustion products from said combustion chamber; and means for energizing said electrically actuated valves.

2. In an enginestarter system; a source of oxygen-underipressure; a source of liquid fuel; normally closed electrically actuated valves: to permit a-flow of oxygen-and fueluponsimultaneous energization; a pressure reducing valve supplied with oxygen under pressure upon energization of said valves; a constant displacement rotary oxygen actuatedmotor'supplied with oxygen at constant pressureby said reducing valve; a constant displacement gear pump driven bysaid rotary oxygenzactuated motor for compressing fuel supplied thereto upon the energization ofsaid valves; a connection between said motor and said gear pump toinsure: corresponding rotational speeds thereof ;:a combustion chamber, said'combustion chamber being connected with said-r0tary motor and; gear-pump whereby it issupplied' with fuel andioxygenin aratio-determined'by the volumetric capacity-of:saidrmotor'and pump; flow regulating means responsive to the pressure within said combustion chamberz'for regulating the flow offuel supplied-thereto; ignition means for'initiating combustion within said combustion chamber: a: starter motor: drivenby combustion. products fromsaid combustion chamber; means. for energizing: said electrically actuated valves; and governor means responsive. to. the speed of the engine" beingstarted', whereby said: valves are deenergized when a predetermined speed has been attained.

3; In an engine starter system; asource of combustion supporting medium under pressure; a source of'fuel; normally closed' valves to permit a flowof combustion supporting medium andfuel when opened; a pressure reducing: valve supplied with combustion supporting "medium under-pressure upon opening 'of said valves; a constantidisplacement rotary fluid' actuated motor supplied with combustion supporting medium at constant pressure bysaid nreducing valve; a constant displacementpump driven bysaid'rotary fluid actuated motorv fOITCOHlDIGSSlIlgifUBI Isupplied thereto uporrthe-opening ofrsaidvalves; a connection between said-:motor-a-nd said'pump to insure corresponding rotational-speedsthereof; a combustion. 2 chamber, said combustion chamber being connected with said rotary motor and pump whereby it is supplied with fuel and combustion sup-porting medium in a ratio determined by the volumetric capacity of said motor and pump; fiow' regulating means responsive to the pressure within said combustion chamber for regulating the flow of fuel supplied thereto; ignition means for initiatin combustion within said combustion chamber; a starter motor driven by combustion products from said combustion chamber; and means for opening and closing said valves.

4. Apparatus as defined in claim 3 and, in addition, governor means responsive to the speed of the engine being started, said governor means being connected with said valve opening and closing means whereby said valves are closed when a predetermined speed has been attained 'by theengine.

ARTHUR T. BRIGGS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,040,350 Keys Oct. 8, 1912 1,052,588 Janicki Feb. 11, 1913 v 10 Number Name Date 1,528,902 Williams Mar. 10, 1925 1,815,097 Davidson July 21, 1931 2,154,572 Lansing Apr. 18, 1939 5 2,197,904 Terry Apr. 23, 1940 2,347,843 Rayfield May 2, 1944 2,351,750 Fawkes 1 June 20, 1944 2,390,959 Pfenninger Dec. 11, 1945 2,397,659 Goddard Apr. 2, 1946 10 2,406,926 Summerfield Sept. 3, 1946 2,450,950 Goddard Oct. 12, 1948 2,503,289 Nettel Apr. 11, 1950 2,505,798 Skinner May 2, 1950 2,550,678 Deacon May 1, 1951 15 FOREIGN PATENTS Number Country Date 606,613 France Mar. 12, 1926 616,695 Great Britain Jan. 26, 1949 OTHER REFERENCES Starter-Generator Control System for a Multijet Airplane, paper 48 239, presented at the 25 AIEE Middle Eastern District meeting, Washington, D. C., October 5-7, 1948.

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