US2626655A - Jet engine fuel supply system - Google Patents

Description

Jan. 27, 1953 w. c. TRAUTMAN ETAL 2,626,655

JET ENGINE FUEL SUPPLY SYSTEM Filed July 25, 1945 E? 35 Z': FZ-E-?: 39 43 4240 INVENTOR.

W. O. TRAUTMAN BY A. A. MEDDOCK ATTORNEY Patented Jan. 27, 1953 JET ENGINE FUEL SUPPLY SYSTEM Walter C. Trautman, Los Angeles, and Alvin A. Meddock, North Hollywood, Calif., assignors to Bendix Aviation Corporation, South Bend, 11111., a corporation of Delaware Application July 25, 1945, Serial No. 607,030

11 Claims. 1

This invention relates to fuel supply systems in which a liquid fuel is sprayed from atomizing jets into an air stream to create a combustible mixture and has particular application to the fuel system of a jet engine in which the fuel pump is driven by the engine.

A broad object of the invention is to insure delivery of fuel at high pressure to the jets at the time of starting to produce thorough atomization and prompt ignition of the mixture.

Another object of the invention is to provide more positive starting of jet engines.

Another object is to facilitate restarting of jet engines after a shutdown.

Still another object is to prevent flooding of jet engines at the time of starting.

Other more specific objects and features will become apparent from the detailed description to follow of a particular embodiment of the invention.

As now developed, a common form of jet engine burns kerosene or other fuel of low volatility by discharging the fuel at high pressure through atomizing jets into an air stream to form a comhustible mixture which is ignited by a spark plug or other known type of igniter. Furthermore, the fuel pressure is developed by a pump which is driven from the jet engine, and the engine is started by an electric starter capable of accelerating the rotor of the engine to a speed at which it is operative.

Difficulty has been encountered in starting such engines because of the fact that fuel was frequently admitted to the jets before the enginedriven pump was rotating fast enough to develop an atomizing pressure. As a result, fuel was discharged through the jets without being atomized sufficiently to produce an ignitible mixture with the air, which fuel accumulated in liquid form within the engine until such time as the fuel pressure rose to the point where sufficient atomization was obtained to permit ignition. Thereafter, the excess fuel that had accumulated in the engine burned rapidly and abnormally, with objectionable results both with respect to the engine structure and to objects in the path of the flame discharged from the engine. Furthermore, sometimes the flooding of the engine prevented startproduce thorough atomization of the first fuel.

discharged, and thereby promote prompt ignition. This result is accomplished by the use of an accumulator which stores the fuel discharged by the pump during initial operation thereof at slow speed, in combination with an automatic valve that releases the stored fuel from the accumulator at high pressure to the atomizing jets when the throttle valve is opened.

In the drawing:

Fig. 1 is a schematic diagram of a jet engine in combination with a fuel supply system in accordance with the invention; and

Fig. 2 is a detailed view partly in section of the accumulator and automatic valve structure em ployed in the system of Fig. 1.

Referring first to Fig. 1, there is disclosed schematically a conventional form of jet engine 10 which comprises a rotor shaft ll having an impeller 12 on one end for compressing air for com bustion and having a gas turbine 13 on the other end which is driven by the discharge gases. Air enters the forward end of the engine through an opening [4, is compressed by the impeller 12, and delivered to an annular manifold l5 from which it is discharged through a plurality of orifices it into the forward end of an annular combustion chamber '1. As the air enters the combustion chamber through the orifices I6, it is mixed with atomized liquid fuel discharged from a plurality of jets 18, which are supplied with fuel under pressure through a pipe l8, which in turn is normally supplied with fuel under pressure from a reservoir 20, through a suction pipe H, a pump 22, a check valve 23, and a throttle valve 24. The mixture of air and atomized fuel may be initially ignited by sparks from spark plugs 25 energized from a standard ignition circuit (not shown). The burning fuel is then discharged through the combustion chamber ll past the gas turbine l3 and out through a discharge passage 26. For purposes of illustration, the rotor shaft H is shown coupled by spur gears 21 and 28 to the fuel pump 22 and is also coupled through the spur gear 21, a spur gear 29, and a clutch 30 to an electric starting motor 3i.

It has been the practice to drain all fuel from the line I9 and the jets I8 when the engine is shut down. To this end, a drain line H containing a drain valve 10 is extended from the line is back to the reservoir 20. As shown, the valve 10 contains a poppet '12 which is normally lifted off its seatl3 by a light compression spring It, so that whenever the pressure in the line I9 drops to a low value following the closure of the throttle 24, the spring 14 lifts the poppet oil the seat 13 aeaaesc escape of fuel through the drain line when the,

engine is operating. 7

The structure so far described is conventional and its normal operation has been outlined. At the time of starting, a switch 32 in the starting circuit of the motor Si is closed, causing the latter to engage the clutchciio and accelerate the rotor shaft it and the pump 22. Initially, it has been the practice to slightly open the throttle valve 24 to permit the minimum. flow from the jets it necessary to sustain operation of the engine, and theoretically the mixture should be ignited and the engine should start to operate as soon as the starting motor 3! has accelerated the impeller E2 to a speed at which it will deliver sumcient air for operation. Often, however, it has been found that during the initial period of operation, the pump 22 was running too slowly to build up any substantial pressure in the pipe iii, with the result that fuel was discharged at low pressure from the jets l8 for a considerable interval of time before ignition took place, this fuel accumulating in the en ine so that if and when ignition did finally take place, there was sufiicient accumulated fuel to cause abnormal combustion of a very rich m xture that produced excessive heat within the tail portion of the jet engine itself and caused pro ection of flame to a substantial distance beyond the en ine. until the excess accumulated fuel had been consumed. Furthermore, the flow of fuel from the jets 58 while the pump 22 was coming u to speed prevented the fuel pressure from r sing as rapidly as it would if such initial flow from the jets were prevente and sometimes the pump was su plying insufficient pressure to roduce atomization at the time the im eller i2 has reached a sneed at which the engine would normally be operative. This prolonged the starting period and sometimes exhausted the starting battery 33 which drives the start n motor 3 i In accordance with the present invention the foregoing ob ectionable start ng characteristics have been eliminated or greatl m tigated y the provision of a valve and accumulator unit 35 having an inlet connection 36 connected to the fuel line ahead of the throttle valve 245 and having an outlet connection Si connected to the fuel line on the outlet side of the throttle valve.

Referring to Fig. 2, the unit 35 consists of an accumulator 35c and an automatic valve 35b for controlling flow between the accumulator 35a and the connections 36 and 3?. The accumulator 35c comprises a shell 38 containing a bladder 8d, the neck dd of which is in sea-ling relation to the shell at the bottom thereof. Thus, the lower end of the shell 38 may be closed by a screw plug it which compresses an annular flanged member 512 against the neck d8 of the bladder. The flanged member 412 contains holes 33 through which liquid can pass into and out of the bladder through an thereabove except when iiquid is forced into the bladder under pressure.

The valve mecha 35b n incorporated in the screw plug M, the latter. being shaped to provide a cylindrical bore t?! therein, opposit ends of which are closed by end plates 58 and (it, respectively, which have threaded ports for the reception of the connections and 3.7., respec tively.

There is slidably mounted within the bore til r a piston member 58, which is sealed with respect escapes through the jets i8.

to the bore 45? by a pair of sealing rings 55 and 52. At its right end, the piston 58 is sealed about a tubular neck 53, which extends into the piston from the closure member 39, by a sealing ring 55. The closure member to is sealed with respect to the bore G'd by a sealing ring 55.

A pair of puppets 56 and 51* are slidably mounted in a longitudinal bore 58 within the piston 5d, the two poppets being urged apart by a light helical compression spring 59. Poppet 56 is adapted to seal against a seat 66 at the inner end of a neck bl projecting inwardly from the closure member 58. The poppet 5? has two sealing surfaces, one adapted to seal against a seat 62 on the inner end of the necl: 5t, and another one adapted to seat on a seat 63 in the piston 5%.

At its left end, the piston 59 is provided with a bushing 56 which seals with the neck (it. The piston is normally urged into its right end position, as shown, by a helical spring 65 compressed between the piston and the left closure member it.

The complete system, including the unit 35, operates as follows, when the engine is to be started:

To start the engine, the starter switch 32 is actuated while the throttle valve 2&- is ,closed. The rotor shaft it gradually accelerates, and the pump 22 is, of course, simultaneously accelerated, but during this initial operation, no fuel flows to the jets it because the throttle valve 2 is closed.

However, the pump 22 delivers a gradually increasing flow of fuel, which flows through the connection 36 and into the bore 58 of the piston 56, past the poppet 58, the latter being closed only by its light spring 59 so that it functions as a check valve. The fuel entering the bore 58 escapes therefrom past the valve seat es and flows through a passage 66 into the bore "2-? and thence through the aperture id and the holes it into the bladder 39, distending the latter against the pressure of the air thereabove. As the air is compressed, the pressure of the fuel within the bladder increases. Escape of fuel into the connection 3? is prevented at this stage of operation because the poppet 5? is seated against the seat 62.

By the time the starting motor M has accelerated the rotor shaft it of the jet engine to a starting speed, considerable fuel pressure has been built up in the bladder 3d, and the operator then opens the throttle valve 2%, whereupon fuel flows through the line it to the jets E8. The line it is initially filled with air, and at first the fuel flows through the line without building up much pressure because the air in the line readily However, as soon as the linei is filled, and the fuel starts flowin through the jets E8, the pressure in line it is suddenly increased because of the resistance to flow of the liquid fuel oflered by the jets. This sudden rise in pressure in the line is is applied through the connection at, and through a passage 67 in the end closure member 69, to the right end of the piston 50, moving it to the left. The leftward movement or the piston first closes the seat 63 against the poppet 51 thereby preventing further flow of fuel through the bore 58 past the seat 63. The final movement of the piston 50 to the left carries the poppet 51 with it, thereby opening the poppet away from the seat 62 and permitting fuel to flow from the interior of the bladder 39 through the aperture 44, the bore 41, and the passage 66 to the connection 31 and thence to the line l9.

Following initial opening of the-poppet 51 off the seat 62, fuel may be supplied to the line I9 from the accumulator at a pressure higher than that delivered by the pump 22, but any reverse flow of fluid from the accumulator through line 31 and valve 24 back into the pump 22 is prevented by the check valve 23. A small vent 80 is provided between the bore 58 of the piston 50 and the annular recess 41 to permit escape of fuel displaced from the bore'58 by the neck Bl as the piston 56 moves to the left. A small leakage of fuel may occur through the vent 80 when the poppet 51 is off its seat 62 but on seat 63, and thc pump is developing high pressure, but the vent 80 is so small that such leakage is inconsequential.

The net result of the operations described is that following filling of the line 19 the fuel stored under the pressure in the accumulator 35c is delivered to the line 19 at high pressure even though the pump 22 may not yet be running fast enough to maintain high pressure in the line i9. Fuel is, therefore, discharged from the jets H3 at a pressure suflicient to eilect proper atomization, insuring immediate ignition of the fuel and starting of the jet engine. The latter thereupon accelerates to its normal speed, after which the fuel pump 22 is capable of maintaining full fuel pressure on the jets without the aid of the accumulator.

During the normal operation of the jet engine, the piston 59 of the unit 35 remains in its leftmost position because. the full pressure of the fuel in the connection 31 is applied to the right end of the piston, whereas the left end of the piston is exposed to atmospheric pressure by a vent 68 in the end closure member 48. Hence, open communication is maintained between the connection 3?! and the bladder 39, past the seat 62, through the passage 66 and the aperture 44.

In effect, the accumulator is therefore maintained floating on the line 19. The pressure of the pump 22 in the inlet connection 35 is applied to the left endof the poppet 51 and to the right end wall of the bore 58 in the piston 59, urging the poppet 51 against the seat 63 and tending to move the piston 50 to theright, but as long as the throttle valve 24 is open, this pressure is unable to overcome the pressure acting against the right end of the piston 50, which has a substantially larger area than does the bore 58 in the piston.

When the engine is to shut down, the operator closes the throttle valve 26, which quickly reduces the pressure in the line H! and the connection 31 to a low value, permitting the spring 65 to move the piston 56 into its right end position, in which the poppet 51 closes on the seat 62 and opens off the seat 63. This prevents further escape of fuel from the bladder 39 out through the connection 31. However, the jet engine and'the pump 22 will continue to coast for a period following closure of the throttle valve 21, and as long as the pump delivers fuel, it will continue to flow through the connection 36 and into the bladder 39, where it will be stored to facilitate the next start.

I It will be apparent from the foregoing description that the use of the unit 35 in the system of Fig. 1 provides for the immediate supply of fluid at high pressure to the jets I 8 following filling of the line IS in response to the opening of the throttle valve 24, so that immediate atomization and ignition of the fuel results. In addition to insuring positive starting, the unit prevents the accumulation of unburned fuel in the engine prior to ignition.

Although the apparatus can be designed to function at various pressures, in an actual embodiment of the invention tested the pressures had the following values: The normal air pressure in the accumulator shell 38 when the bladder 39 was completely collapsed was between 60 and p. s. i.; the pump 22 was capable of developing between and 200 p. s. i. at the starting speed of the jet engine; and was capable of developing approximately 500 p. s. i. at full running speed. The spring 65 was so proportioned relative to the pressure areas of the piston 50 as to cause the piston to open the poppet 51 off the seat 62 at a pressure in the connection 31 of between 15 and 26 p. s. i.

Although during normal operation of the engine the pressure in the line l9 and in the accumulator 35a may be as high as 500 p. s. i. this pressure drops quickly to zero value following closure of the throttle valve 24, and the piston 50 is moved to the right by its spring 55 when the pressure in the connection 31 drops to about 10 p. s. i. Since the air pressure in the accumulator 35a is always at least 60 p. s. i., the bladder 39 will always be completely collapsed when the piston 50 is returned to normal position by its spring 65. However, as previously described,- the engine continues to coast for some time following closure of the throttle valve 24, so that there is ample time to accumulate substantial fuel in the bladder 39, following return of the piston 50 to the right, and before the pump pressure drops appreciably.

Various departures from the exact construction described can be made without departing from the invention which is to be limited .only to the extent set forth in the appended claims.

We claim:

1. A valve device of the type described comprising: a body having an inlet port, an outlet port, and an accumulator port; first, normally open, valve means for communicating said inlet port with said accumulator port, second, normally closed, valve means for communicating said accumulator port with said outlet port; and means responsive to a rise in pressure in said outlet port above a predetermined value relative to the ambient pressure for opening said second valve.

2. A valve device of the type described comprising: a body having an inlet port, an outlet port, and an accumulator port; first. normally open valve means for communicating said inlet port with said accumulator port, second normally closed valve means for communicating said accumulator port with said outlet port; and means responsive to an increase of the pressure in said outlet port above a predetermined value for closing said first valve means and opening said second valve means.

3. A valve device of the type described comprising: a body having a cylinder, an inlet port, an outlet port, and an accumulator port; piston aeeaess imeansreciprocal in said cylinder and exposed to ambient pressure at one end and to pressure in said outlet port at the other end; passage means in said body including a first valve seat for intercommunicating said outlet and accumulator ports; a poppet valve normally closing said first seat; a second valve seat in said piston means; means defining a passage from said inlet portthrough said second seat to said accumulator port; the arrangement of said piston means and poppet being .such that movement of said piston means in response to pressure in said outlet port closes said second seat on said poppet and carries the poppet clear of said first seat.

4. A valve device as described in claim 3 including a second poppet valve seating against said inlet port, and spring means urging said second poppet against said inlet port for permitting fiuid flow from said inlet port into said body while preventing return flow through said inlet port.

5. A valve device of the type described comprising: a body defining a cylinder having an inlet port in one end thereof, an outlet port in the other end thereof, and an accumulator port in the side wall thereof; a hollow piston reciprocal in said cylinder and sealing with said inlet and outlet ports, and with the side wall of said cylinder on opposite sides of said accumulator port, passage means communicating one end of said piston with said outlet port; passage means communicating the other end of said piston with the atmosphere; a valve seat within said piston, a poppet valve within said piston, spring means urging said piston into one end position against the force of the pressure existent in the outlet port; a poppet valve within said piston and spring means urging it into sealing relation with said outlet port when said piston is in said one end position; a valve seat in said piston in spaced relation to said poppet valve when said piston is in said one end position and said poppet is seated against said outlet port, said piston and outlet port defining a chamber between said outlet port and said seat in said piston normally communicated through said seat in said piston with said inlet port; said outlet port and said seat in said piston being so positioned relative to said poppet valve that movement of said piston out of said one end position by pressure in said outlet port first engages the seat in said piston against said poppet to prevent flow of fluid from said inlet port through said seat in the piston, and thereafter carries said poppet clear of said outlet port to communicate said outlet port with said accumulator port.

6. A valve device as described in claim 5 includ ing an additional poppet within said hollow piston positioned back to back with respect'to said one poppet and adapted to seat against said inlet port, said spring means being interposed be.- tween said two poppets for urging them apart.

7. In a fuel system for a combustion engine including a fuel-atomizing jet, a fuel pump driven by the engine, a fuel line connecting the pump to the jet, a throttle valve in the fuel line, and

means for normally draining fuel from that portion of the fuel line between the throttle valve and said 'jets when substantially no pressure exists in the fuel line on the jet side of the throttle valve; an accumulator; means normally connecting said accumulator to said line on the pump side of said throttle valve; and means responsive to a rise in pressure in said fuel line on the jet side of said throttle valve above a predetermined value for connecting said accumulator to said fuel line on the jet side of said throttle valve.

8. A system as described in claim 7 including means responsive to said rise in pressure in said,

fuel line on the jet side of said throttle valve above said predetermined value for substantially I preventing flow of fuel from that portion of the fuel line on the pump side of said throttle valve into said accumulator.

9. A system as described in claim 7 including check valve means-for permitting flow of fluid from that portion of said fuel line on the pump side of said throttle valve into said accumulator while preventing reverse flow.

10. A system as described in claim 7 including means responsive to said rise in pressure in said fuel line on the jet side of said throttle valve above said predetermined value for substantially preventing fiow'of fuel from that portion of the fuel line on the pump side of said throttle valve into said accumulator, and check valve means for at all times preventing reverse flow from said accumulator into said fuel line on the pump side of said throttle valve. 7

11. A system as described in claim 7 including means responsive to said rise in pressure in said fuel line on the jet side of said throttle valve above said predetermined value for substantially preventing flow of fuel from that portion of the fuel line on the pump side of said throttle valve into said accumulator, check valve means for at all times preventing reverse flow from said accumulator into said fuel line on the pump side of said throttle valve, and check valve means in said fuel line adjacent said pump permitting fluid flow from the pump into the line while preventing reverse flow from said line back into the pump.

WALTER. C. 'IRAU'I'MAN. ALVIN A. MEDDOCK.

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

UNITED STATES PATENTS Taylor Dec. 5, 1944

Images