US3903692A

US3903692A - Hot gas generator

Info

Publication number: US3903692A
Application number: US430959A
Authority: US
Inventors: David M Croker
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1972-07-24
Filing date: 1974-01-04
Publication date: 1975-09-09
Anticipated expiration: 1992-09-09

Abstract

A hot gas generator wherein liquid fuel is supplied to an annular heated reservoir surrounding the burner, whereby the heated fuel heats the walls of the combustion chamber, thereby enabling the generator to attain relatively high output temperatures in very short periods of time. The generator is useful in starting gas turbine engines, i.e. by discharging high temperature, high pressure gas through a nozzle into the blades of the turbine to initiate turbine rotation.

Description

United States Patent [1 1 Croker [63] Continuation-impart of Ser. No. 274,786, July 24,

I972, abandoned.

[52] U.S. C1 60/39.71; 60/3974 R; 431/173; 431/242; 43l/243 [51] Int. Cl. F23D 11/24; F23D 11/44 [58] Field of Search 60/3969, 39.71, 260, 267, 60/3914, 39.48, 39.7, 39.13, 39.74 R; 431/173, 242, 243

[56] References Cited UNITED STATES PATENTS 929.077 7/1909 Calkins 431/243 1,686.213 10/1923 Koudritsky 431/173 1,821,752 9/1931 Fisher 431/243 2.503.702 4/1950 Beggs...... 431/243 2589215 3/1952 Atwood 60/267 451 Sept. 9, 1975 2,729,060 1/1956 Allen ct a1. 60/3914 2,872,782 2/1959 Johnson et al 60/3969 2.881844 5/1959 Coty 60/3971 2,922,279 1/1960 Roberson et al... 60/39.71 1099,910 9/1963 Schirmer et a1... 60/3974 R 3.431.743 3/1969 Green 60/3948 3,533,233 10/1970 Fiedler et 31.... 60/3914 3,703.259 11/1972 Sturgess ct al. 60/3974 R 3.739576 6/1973 Chamberlain 60/3974 R 3.847534 11/1974 Nomaguchi et a1... 431/243 3,857,672 12/1974 Reed et a1 431/173 Primary ExaminerWilliam L. Freeh Assistant ExaminerR0bert E. Garrett Attorney, Agent, or Firm-Peter A. Taucher; John E. McRae', Robert P. Gibson [57] ABSTRACT A hot gas generator wherein liquid fuel is supplied to an annular heated reservoir surrounding the burner, whereby the heated fuel heats the walls of the combustion chamber. thereby enabling the generator to attain relatively high output temperatures in very short periods of time. The generator is useful in starting gas turbine engines. i.e. by discharging high temperature, high pressure gas through a nozzle into the blades of the turbine to initiate turbine rotation.

5 Claims, 2 Drawing Figures HOT GAS GENERATOR RELATION TO OTHER PATENT APPLICATION This is a continuation-in-part of an earlier filed Pat. application, Ser. No. 274,786 filed on July 24, 15172, now abandoned in the name of the present inventor, and assigned to the United States Government.

BACKGROUND OF THE INVENTION Previously it has been proposed to use hot gas generators for initiating rotation of turbine engines. For example, see US. Pat. 2,775,866 issued to K. B. Randall; US. Pat. 2,921,431 issued to A. C. Sampietro; US. Pat. 2,925,713 issued to R. M. Stevens; US. Pat. 2,968,152 issued to E. K. Moore; US. Pat. 3,004,387 issued to M. P. Woodward; and US. Pat. 3,707,074 issued to M. 1. Meyer et al.

THE PRESENT INVENTION The present invention proposes a hot gas generator especially designed to include a small burner capable of rapidly heating high pressure air or other gas to a relatively high temperature on the order of 1500 F. The heated gas can be discharged from the burner through a high pressure nozzle to impinge on the blades of a turbine engine, thereby initiating engine start-up. The burner is located to extend through an annular fuel supply reservoir that is maintained in a heated condition, e.g. at 100 F, whereby the fuel in the reservoir heats the burner surfaces; the aim is to enable the burner to rapidly heat the supply air to a high temperature, even when the apparatus is located in artic atmosphere. The annular fuel reservoir is pressurized prior to burner ignition; at burner ignition the pressurized fuel is injected into a stream of high pressure oxidizer gas (compressed air) to form a combustible mixture. This mixture passes through a narrow annular passage that is radially interposed between the combustion chamber and the heated fuel reservoir. The mixture is therefore heated when it enters the combustion chamber. The chamber arrangement promotes the rapid attainment of a high temperature, high pressure condition at the burner outlet without flame flashback or useless back pressure effects.

THE DRAWINGS FIG. 1 is a sectional view through one embodiment of the invention, taken generally on line 1-1 in FIG. 2.

FIG. 2 is a sectional view taken on line 22 in FIG.

FIGS. 1 and 2 illustrate a hot gas generator comprising an annular fuel reservoir 12 having an inner wall 14 and an outer wall 16. Liquid fuel is initially supplied to reservoir 12 by means of a fuel pump 18 located in a line 19 containing a solenoid valve 20 and check valve 22. The liquid fuel enters chamber 12 through a port 24.

After chamber 12 is completely filled with liquid fuel the fuel space may be pressurized by means of a high pressure air line 26 containing an electrically operated valve 28. The line connects with reservoir 12 through a port 30. Valve 28 is opened to pressurize the fuel only during periods when the burner is in operation; during non-operating periods valve 28 is closed.

Pressurized fuel is delivered upwardly through a vertical tube 32 to a pressure-responsive control valve 34 that has a spring operating force sufficient to keep the valve closed against the pressure developed by fuel pump 18. The pump pressure is effective to fill reservoir l2 and the space to the right of ball valve 34 when the reservoir is depressurized.

When reservoir 12 is filled and pressurized (by opening valve 28) fuel flows leftwardly past valve 34 through a nozzle opening 36 and into an air supply passage 38 for the burner; nozzle opening 36 forms a fuel intake connection to air supply passage 38. The supply air is initially taken from a high pressure source through a line 40 containing an electricallyoperated valve 42. During nonoperating periods valve 42 is closed. During burner-operating periods the air-fuel mixture flows downwardly through passage 38 into an annular passage 44 formed by a peripheral groove in a combustion cup element 46. Some of the airfuel mixture is forced through a number of ports 48 into the cup interior space 50 near the sparking end of spark plug igniter 52. Some of the mixture flows in a spinning fashion through a narrow annular inlet space 54 formed by the inner surface of reservoir wall 14 and the outer surface of combustion cup side wall 56; space 54 forms a peripheral inlet for the combustion chamber. Circumferential spin is imparted to the incoming gaseous mixture because passage 38 has a tangential connection to annular passage 44 (as seen in FIG. 2).

The combustion chamber is defined in part by a spherical wall 58 leading to a discharge nozzle wall 60. A nozzle (not shown) connects wall 60 to the vanes of a gas turbine engine, whereby hot combustion gases are discharged at high pressure against the turbine vanes to initiate turbine start-up in the manner described in the previously mentioned patents.

Burner start-up is initiated by switch energization of an immersion heater 62 located in the lower portion of reservoir 12. When the liquid fuel has reached an elevated temperature, e. g. F, a thermostatic operator 64 in the upper portion of the reservoir operates a snap switch 66 to start the burner operation. Operator 64 and switch 66 can be standard shelf items. As shown in FIG. 1 operator 64 is a tube-rod device wherein the tube has a low coefficient of thermal expansion, and the rod has a high coefficient of thermal expansion; switch actuation results from differential expansion.

Switch 66 is preferably arranged to control heater 62, pump 18, spark plug 52 and the three

valves

20, 28 and 42. At the actuation temperature of 100 F the switch deenergizes heater 62 and pump 18, closes valve 20, opens

valves

28 and 42, and energizes spark plug 52. Suitable relays and transformers may be employed to accomplish the program.

Valve 28 opens to pressurize the fuel in reservoir 12. The fuel is thereby forced past valve 34 into passage 38 where it mixes with the combustion air flowing from the now-opened line 40. Fuel-air mixtures flowing through ports 48 are ignited by spark plug 52. The rightwardly advancing flame front in chamber 50 ignites the mixture flowing from annular space 54 into the combustion zone 51. The hot combustion gases are exhausted at high pressure through a nozzle connected to wall 60.

The combustion process may be continued until the fuel level in reservoir 12 drops below the lower end of tube 32; i.e. below imaginary line 33. After that time the continued pressurization of reservoir 12 by air line 26 is ineffective to deliver fuel to passage 38. By that time the turbine should be operating.

The illustrated structure is believed to be advantageous in that the preheated fuel in reservoir 12 heats the fuel and also inner wall 14; the result is believed to be improved fuel volatilization, better fuelair homogenity, and improved combustion, even when the apparatus is located in sub-zero temperatures.

The spin given to the mixture in groove 44 and space 54 is believed to be advantageous in converting flow energy to pressure energy, in a fashion somewhat similar to that taking place in centrifugal fans. Space 54 is relatively narrow in the radial direction; e.g. about 0.06 inch, so that pressures generated by the combustion process presumably have minimum tendency to exert shock forces backwardly through space 54. Combustion pressures would presumably have to completely disrupt the spin imparted to the entering gases before such pressures could generate a useless backward shock force; the spin energy presumably acts to preclude such action. The narrowness of space 54 would appear to offer a restriction to flame flashback while still permitting large fuel entry into the combustion zone.

Sperherical combustion surfaces 58 probably reflects combustion pressures to establish a high pressure condition in space 51. Surface 58 also acts as a throat to accelerate the gases as they are discharged through the opening at 60.

Peripheral inlet space 54 is offset slightly from space 51 by reason of the inwardly extending surface 61; hopefully this will partially shield the inlet passage from shock so that high pressures are usefully directed through opening 60 rather than backwardly into the peripheral inlet.

1 claim:

1. A hot gas generator comprising an annular liquid fuel storage reservoir defined partly by a first imperforate inner annular wall and a second imperforate outer annular wall; means for heating the fuel in the fuel storage reservoir to thereby preheat the inner annular wall;

the inner surface of said inner wall serving to define a combustion chamber; a hollow combustion cup extending into the combustion chamber, said cup including an end wall and a third annular side wall spaced inwardly from the first inner annular wall to cooperate therewith in defining an annular fuel-air inlet space for the combustion cup interior; an air supply passage having a tangential connection with the annular inlet space at a point near the cup end wall; means for injecting preheated liquid fuel from the reservoir into the air supply passage; said fuel injecting means being connected to the air supply passage at a point upstream from the aforementioned tangential connection, whereby fuel and air are mixed during movement thereof through the passage and annular inlet space, said tangential connection serving to impart a circumferential spin to the fuel-air mixture as it flows through the annular inlet space; and an igniter extending through the end wall of the cup to ignite the fuel-air mixture therewithin.

2. The generator of claim 1: said fuel injection means comprising a pressure-responsive control valve effective to admit fuel to the air supply passage only when the reservoir is pressurized.

3. The generator of claim 2: said fuel reservoir being pressurized by a gas pressure means having a pressure connection in the ceiling area of the reservoir; said reservoir being connected to the pressure-responsive control valve through reservoir outlet opening located between the ceiling and floor areas of the reservoir, whereby pressurized fuel flow is discontinued upon the delivery of a predetermined quantity of fuel.

4. The generator of claim 1: said cup side wall and the inner annular wall of the reservoir being sufiiciently close to one another as to prevent flame flashback from the combustion space.

5. The generator of claim 1: the combustion cup having ports therethrough for conveying fuel air-mixtures from the annular inlet space into the cup space immediately adjacent to the ignitor ignition point.

Claims

1. A hot gas generator comprising an annular liquid fuel storage reservoir defined partly by a first imperforate inner annular wall and a second imperforate outer annular wall; means for heating the fuel in the fuel storage reservoir to thereby preheat the inner annular wall; the inner surface of said inner wall serving to define a combustion chamber; a hollow combustion cup extending into the combustion chamber, said cup including an end wall and a third annular side wall spaced inwardly from the first inner annular wall to cooperate therewith in defining an annular fuel-air inlet space for the combustion cup interior; an air supply passage having a tangential connection with the annular inlet space at a point near the cup end wall; means for injecting preheated liquid fuel from the reservoir into the air supply passage; said fuel injecting means being connected to the air supply passage at a point upstream from the aforementioned tangential connection, whereby fuel and air are mixed during movement thereof through the passage and annular inlet space, said tangential connection serving to impart a circumferential spin to the fuel-air mixture as it flows through the annular inlet space; and an igniter extending through the end wall of the cup to ignite the fuel-air mixture therewithin.

4. The generator of claim 1: said cup side wall and the inner annular wall of the reservoir being sufficiently close to one another as to prevent flame flashback from the combustion space.