US3551073A

US3551073A - Pumping system with improved jet inducer

Info

Publication number: US3551073A
Application number: US783830A
Authority: US
Inventors: Paul F Petrovits
Original assignee: Chandler Evans Inc
Current assignee: Colt Industries Operating Corp; Colt Industries Inc
Priority date: 1968-12-16
Filing date: 1968-12-16
Publication date: 1970-12-29
Anticipated expiration: 1987-12-29

Description

' Dec. 29, 1970 PPPPPPPPPPP Ts 3,551,073

72W am United States Patent() U.S. Cl. 417-76 4 Claims ABSTRACT OF THE DISCLOSURE transfer supply fuel at vapor to liquid ratios greater than 0.30, thus providing for sustained system pumping operations in the event of failure of the system boost pump.

BACKGROUND OF THE INVENTION (1) Field of invention This invention relates to pumping systems. Particularly the present invention is directed to fuel pumping systems for gas turbine engines, especially aircraft gas turbine engines. More particularly, this invention relates to a fuel pumping system incorporating improved apparatus for transferring supply fuel having a high gas to liquid ratio at increased pressure to the inlet of a positive displacei ment fuel pump.

(2) Description of the prior art Positive displacement pumps, especially gear-type positive displacement pumps, have been employed for some time to meet the dry lift and high pressure starting requirements of aircraft gas turbine engine fuel pumping systems. The pressure drop encountered as the fuel traverses a length of fuel line reduces the total pressure applied to the fuel and permits free gas to come out of solution. Fluids having a high vapor to liquid ratio are generally diillcult to pump ellciently due to the formation of pockets of free gas which inhibit flow.

The problem of controlling the gases liberated in liquids transported in conduits, particularly in fuel lines carrying aviation fuels, utilized either the overboard release, the compression or the through pumping method. The overboard release method is to collect the free gas and release it overboard. The alternative compression method is to install a compressor in the fuel line to increase the line pressure, thereby redissolving the free gases. The overboard release of free gases involves the venting of the gases to atmosphere which permits the release of volatile vapors, and in the case of flammable vapor creates a safety hazard. The compression method utilizes an external compressor in which the size, weight and power consumption of the compressor make this method undesirable from the standpoint of large power losses and increased weight. The through pumping method utilizing jet inducers have proven successful, in certain applications, as a method of increasing the pressure of the supply fluid at the inlet of positive displacement fuel pumps, thereby preventing cavitation. Prior pumping system approaches utilizing a jet inducer had been found suitable for handling supply fluids with a vapor to liquid ratio up to 0.3, i.e., up to 0.30 part of vapor for each part of liquid. However, it was found prior art jet inducers would not transfer 3,551,073 Patented Dec. 29, 1970 supply fuel having a vapor to liquid ratio of 0.30 or greater unless the recirculated llow comprised a minimum of 68% of the total flow. Fuel pumping systems which formerly utilized the through pumping approach of the jet inducer as the most desirable method of increasing the fuel line pressure to thereby redissolve liberated free gases were found to be no longer operationally or economically adequate to deal with the fuel pumping problems presented by the increased vapor to liquid ratio.

(3) Summary of the invention The liquid fluids utilized in all iluid pumping systems contain partially dissolved gases in their normal state. The amount of gas contained for the saturation level is a function of temperature and pressure. In the case of aviation fuels utilized in aviation gas turbine engine fuel pumping systems, the solubility of air in the aviation fuel is proportional to the difference between the total pressure applied to the fuel and the vapor pressure of the fuel. In the case of aviation gas turbine fuel pumping systems, the fuel line pressure drops reduce the total pressure applied to the fuel and permit free gas to come out of solution. The formation of pockets of free gas inhibits the flow of the tluid in the fuel line and thereby reduces the efllciency of the pumping system. Jet inducers have proven useful t0 increase the pressure above the supply pressure and thereby transmit fuel at an increased pressure to the inlet of the main fuel pump such that the formation of free gas pockets is inhibited and pump cavitation is prevented. The jet inducer receives fuel from the fuel supply, mixes the supply fuel with recirculated high pressure fuel flowing from the jet nozzle to supply an increased volume of fuel at increased pressure to the inlet of the positive displacement pump.

Prior art jet inducers will not transfer supply fuel having a vapor to liquid ratio of 0.30 or greater unless the high pressure recirculated jet nozzle ilow is an uneconomical and inetllciently high percentage of the total output flow. The present invention utilizes a jet inducer having a mixing chamber so constructed that supply lfuels having a vapor to liquid ratio greatly in excess of 0.30 can be efficiently transferred through the jet inducer to the inlet of a positive displacement pump.

The use of this novel improved jet inducer pump is of particular significance in that it permits the more economical and reliable through pumping compression method to be utilized as the means of increasing fuel line pressure to thereby redissolve liberated free gases. Additionally, the inclusion of the jet inducer in the fuel pumping system between the discharge of the fuel supply boost pump and the inlet to the positive displacement pump provides a means whereby a fuel supply having a high vapor to liquid ratio can be transferred to the inlet of the positive displacement pump without causing cavitation, even in the event of a boost pump failure.

Accordingly, one object of the present invention is to provide a novel compression method of increasing the fuel line pressure of a fuel pumping system to thereby redissolve liberated gases.

Another object of the present invention is to provide a novel liquid pumping system including a jet inducer capa-ble of economically handling supply fluids on the order of 0.50 vapor to liquid ratio.

Still another object of the present invention is to provide a lluid pumping system including a novel mixing chamber wherein a supply fluid having a vapor to liquid ratio on the order of 0.50 is capable, in the event of a fuel boost pump failure, of being transferred through the jet inducer to the positive displacement pump.

Still another object of the present invention is to provide a fuel pumping system capable of supplying fuel under pressure to a positive displacement pump such that the positive displacement pump will not experiencecavitation in the event of a failure of the fuel supply system boost pump.

Other objects and advantages will be apparent and understood from the following detailed description of the drawings wherein like elements are numbered alike in the several figures.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of a fuel pumping system incorporating the present invention.

FIG. 2 is an isometric view illustrating the manner in which the novel mixing cham-ber is incorporated in the jet inducer component of the fluid pumping system.

FIG. 3 is a graphic presentation of the comparative performance of a prior art jet inducer with one including7 the novel features of the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Even though described herein for utilization in an aircraft fuel pumping system, it is to be understood that the present invention is applicable to any liquid pump system incorporating a jet inducer in which the presence of liberated gas resulting from reduced total pressure reduces the operating efficiency of the pumping system.

Referring now to FIG. 1, fuel from a tank 10 enters a submerged rst stage boost pump 14, usually a centrifugal pump, wherein the fuel is conveyed through pump 14 to conduit 16 and thence to jet inducer 18. The flow of fluid from tank 10 to inducer 18 is indicated by the arrow in conduit 16, and it will be understood that such arrows in any of the conduits of FIG. 1 indicate the direction of fuel flow therein when fuel is flowing in that conduit. The fuel entering jet inducer 18 from conduit 16 is joined with the fluid entering inducer 18 via conduit 20 to provide a total outlet flow that is delivered via conduit 22 to the inlet of positive displacement pump 24. The details of jet inducer 18 will be described hereinafter with reference to FIG. 2, but, for the purposes of the immediate description, it is sufficient to state that fuel is transferred from the fuel tank 10 to the jet inducer 18 and combined with the recirculation flow of conduit 20 to provide a total fiow in conduit 22 at an increased pressure such that a fluid flow of an increased volume and pressure is delivered to the inlet of positive displacement pump 24 to thereby prevent cavitation. The fuel enters boost pump 14 at pump inlet pressure, and exits pump 14 into conduit 16 at a higher pressure, referred to as yboost pump pressure. Fuel enters jet inducer 18 at a pressure, referred to as recirculation or drive pressure, and combines with fiuid in conduit 16 at boost pump pressure, and exits in conduit 22 at an increased pressure and flow, referred to as positive displacement pump inlet pressure. Conduit 22 delivers fuel at inlet pressure to the positive displacement pump 24 where the pressure is increased to a level referred to as pump discharge pressure, and the fuel at pump discharge pressure, as indicated by the arrow in conduit 26, is delivered to fuel control 28 where the fuel flow is divided with a portion proceeding, as indicated by the arrow in conduit 30, to the prime mover 32. A second portion, representing the unused fuel from the fuel control, is recirculated via conduit 20 to the jet inducer 18. It can be seen that the capacity of pump 22 must be greater than the maximuml fuel utilization of fuel control 28 such that a by-pass fuel flow will always be available as the recirculation flow in conduit 20 to jet inducer 18. As stated, all liquids contain partially dissolved gases in their normal state. In the particular instance illustrated herein, the solubility of air in aviation fuels is proportional to the difference between the total pressure applied to the fuel and the vapor pressure of the fuel. It can be seen that as fuel flows in conduit 16, due to fluid friction, the fuel line pressure drop reduces the total pressure applied to the fuel. This reduction in total pressure permits free gas to come out of solution. It is obvious that the quantity of free gas that comes out of solution is a function of the magnitude of the reduction in total pressure. The vapor to liquid ratio, that is the number of parts of vapor for each part of liquid, is a term utilized to dene the operational limitations and pumping capabilities of a particular fuel pumping system.

Utilizing aviation fuels in combination with the apparatus shown in FIG. l, with the boost pump 14 inoperative, thereby simulating a boost pump failure, the Vapor to liquid ratio of the fluid in conduit 16 is approximately 0.30. At a vapor to liquid ratio of 0.30, it was found that prior art jet inducers would not transfer fuel from conduit 16 unless the recirculation ow comprised a minimum of 68% of the total discharge flow in conduit 22. A recirculation flow representing 68% of the total flow renders the pumping efficiency of such a jet inducer system economically unacceptable. Thus, the presence of a vapor to liquid ratio of 0.30 at the induction inlet 16 of the jet inducer presents a pumping system operational and efficiency problem which must be solved.

Referring now to FIG. 2, a jet inducer is shown generally at 18. Recirculation fuel at high pressure enters inducer 18 via conduit 20 and passes through nozzle 34. Nozzle 34 is mounted in a mixing chamber 36 having a longitudinally extending interior peripheral wall. The fuel passing through nozzle 34 is accelerated such that a local reduced pressure is established at the mixing chamber 36 adjacent the throat area of nozzle 34. This local low pressure increases the pressure gradient between fuel tank 10 and chamber 36, thus providing an increased motive force to cause fluid to ow from tank 10 via pump 14 and conduit 16 such that an additive force is supplied to that generated by boostpump 14 and additionally furnishes a source of motive force in the event of a failure of boost pump 14. The local point of low pressure established in chamber 36 permits dissolved gas to escape from solution and form vapor pockets which hinder the flow of fluid through chamber 36 to exit port 38 and thence to conduit 22.

It has been found that by increasing the roughness of the surface of mixing chamber 36, the characteristics of the flow in the area of chamber 36 for the same range of Reynolds numbers can be changed from a laminar/ turbulent transition flow to a completely turbulent ow with attendant improvements in the pumping performance of the jet inducer.

An increase in the relative roughness of the periphery of mixing chamber 36 can be accomplished by several methods, such as rough grinding the periphery of -the walls of chamber 36, or inserting a Wire mesh screen in contact with the periphery of the mixing chamber wall thereby defining a wall having a knurled surface. It has been found that an increase in the relative roughness of the .surface of the mixing chamber could be most expeditiously accomplished by the inclusion of a wire mesh screen 40 placed in contact with the wall of mixing chamber 36, as shown in FIG. 2. To illustrate, by completely covering the cylindrical wall of mixing chamber 36 -with a 20 x 20 x .016 wire mesh screen 40, as shown in FIG. 2, the relative roughness was raised from about .0015 to about .0100, on a Moody diagram well known to those skilled in the art.

It has been found that increasing the relative roughness of the surface of mixing chamber 36 causes the flow in mixing chamber 36, represented by the intersection of conduit 16 and nozzle 34, to be transformed from a laminar/turbulent transition flow to an unstratified turbulent fiow such that the gas liberated from solution in the mixing chamber area is uniformly disbursed in the fluid, thereby completely preventing the formation of flow hindering vapor pockets and markedly improving the performance characteristics of the jet inducer.

To better appreciate the increases or improvements realized from this novel construction of a jet inducer mixing chamber, it is to be noted in FIG. 3 that in a prior art jet inducer for a vapor to liquid ratio of .3, a 68% recirculation flow is required; whereas, with the improved r jet inducer, represented by the instant invention, only 34% recirculation flow is required for the same total output oW, at the same Reynolds numbers, thus more than doubling the induced flow capability of this tluid pumping system. This increased pumping performance permits a through ow jet inducer to be utilized in a fuel pumping system including a centrifugal boost pump, wherein the requirements of the system are such that the system pumping operation must be sustained in the event of a boost pump failure.

While a preferred embodiment has been shown and described, various modilications and substitutions may be made Without departing from the spirit and scope of this invention. Accordingly, it is to be understood that this invention has been described by Way of illustration rather than limitation.

What I claim is:

1. A jet inducer comprising:

a housing defining a chamber therein with a longitudinally extending interior peripheral wall;

a first inlet conduit for receiving a ow of fluid;

a nozzle mounted in the chamber in fluid communication with the first inlet conduit for accelerating a flow of uid therefrom and establishing a local reduced pressure adjacent the throat area of the nozzle;

an outlet conduit in uid communication with the chamber and the nozzle for receiving a ow of uid from the chamber;

a second inlet conduit in fluid communication with the chamber and extending through the wall thereof for receiving a flow of fluid from a tank, the ilow therefrom being induced by the local reduced pressure adjacent the throat area of the nozzle;

said interior peripheral wall having a knurled surface which provides a relative wall roughness substantially above .0015 on a Moody diagram, said knurled surface covering a major portion of the wall and being at least partially located in the circumferential region of the second inlet conduit; and whereby, the formation of vapor pockets in the chamber is prevented by turbulence generated by the projections. 2. A jet inducer, as defined in claim 1, wherein the knurled surface is formed by:

a mesh screen secured to the Wall of the chamber, 3. A fuel pumping system incorporating a jet inducer, as defined in claim 1, including:

a boost pump iiuidly connected to the second inlet conduit; and a positive displacement pump tluidly connected to the outlet conduit. 4. A fuel pumping system incorporating a jet inducer as defined in claim 1, including:

a tank in fluid communication with the second inlet conduit for supply fuel thereto.

References Cited UNITED STATES PATENTS 683,005 9/ 1901 Sewall 103-277X 826,355 7/ 1906 Pollard 103-278 972,441 l0/ 1910 Durdin, Ir l03-260 973,351 10/1910 Hoffman 103-277 1,692,916 11/1928 Woodruff 103-262 2,479,783 8/ 1949 Sawyer et al. 103-262X 2,690,717 10/ 1954 Goodrie 10S-262 3,010,232 11/1961 Skakel et al. 103-262X 3,387,644 6/1968 Heinecke et al. 103-5(J)UX CARLTON R. CROYLE, Primary Examiner W. I. KRAUSS, Assistant Examiner U.S. Cl. X.R.