US3159349A

US3159349A - Liquid injection system with damper means

Info

Publication number: US3159349A
Application number: US249489A
Authority: US
Inventors: Richard A Crocco; Carey Colwell
Original assignee: Curtiss Wright Corp
Current assignee: Curtiss Wright Corp
Priority date: 1963-01-04
Filing date: 1963-01-04
Publication date: 1964-12-01
Anticipated expiration: 1981-12-01

Description

Dec. 1, 1964 R. A. cRocco ETAL 3,159,349

LIQUID INJECTION SYSTEM WITH DAMPER MEANS Filed Jan. 4, 1963 2 Sheets-Sheet 2 INVENTORS RICHARD A. ERUEEEI EULWELL CAREY ATTEIRNEY United States Patent 3,159,349 LEQUED lNSECTlON SYSTEM Wl'lll DAMPER li IEANS Richard A. Qrocco and Coiwell Carey, Glen Rock, N..l.,

assignors to urtiss-Wright Corporation, a corporation of Delaware Filed Jan. 4, 1%3, Ser. No. 249,489 Claims. (31. 239-453) This invention relates to high pressure liquid injection systems and more particularly to a pressurizing damping device for such high pressure liquid injection systems.

The invention is particularly useful in connection with a liquid injection system of the type comprising a discharge nozzle and a positive displacement pump with a passage therebetween for intermittently supplying liquid to the nozzle. It has been found that in the operation of a fuel injection system for an internal combustion engine that pressure waves travel back and forth in the supply passage with the result that pressures below the liquid vapor pressure may exist in the passage whereupon cavitation bubbles are created in the passage, which collapse against the passage walls, exerting very high pinpoint pressures and causing serious cavitation erosion of the passage walls.

Particularly in a fuel injection system for an internal combustion engine where the liquid passage is a fuel tube made of metallic material subject to such erosion, the tube may fail after a period of use.

In one app-roach to assure against rapid tube erosion, the tubes are made of expensive cobalt and manganese alloys instead of such materials as stainless or carbon steel, and this reduces the rate of erosion and extends the life of the tube.

In another approach to reduce such erosion, a flexible rubber-lined tube is placed in the fuel line between the nozzle and the end of the steel fuel tube. This minimizes bubble formation and collapse by damping the pressure oscillations in the tube fluid so that cavitation erosion is minimized. However, a less desirable type of nozzle spray results, causing a higher engine fuel consumption.

Where a tube failure is not critical and a tube replacement is simple, as in some industrial diesel engines, carbon steel tubes are used having an extra heavy wall.

it is an object of the invention to provide a new and improved means for preventing cavitation erosion in a high pressure liquid injection system. Specifically, the invention comprises a plurality of pressurizing damper plates spaced along the passage between the pump and injection nozzle in the portion of the passage near the discharge nozzle.

Another ob'ect is to provide novel means to increase the average pressure of each pressure wave produced by a pump discharge stroke and to decrease the amplitude of oscillations of such pressure waves in both the fuel line and nozzle of a high pressure fuel injection system. 2 Other objects of the invention will become apparent upon reading the annexed detail description in connection with the drawings in which:

FIG. 1 is a schematic diagram of'a combustion engine fuel injection system supplying an engine-cylinder fuel injection nozzle;

3,159,349 Patented Dec. 1, 1964 As illustrated in the schematic diagram of a conventional fuel injection system in FIG. 1, a typical combustion engine cylinder 1t) has a fuel injection nozzle 12 disposed in the head of the cylinder 1th for spraying fuel into the engine cylinder. The nozzle 12 is supplied with fuel through a fuel tube 14 connected to a fuel pump 16.

The pump 16 is a positive displacement type and comprises a plurality of piston 13 and cylinder 19 pump units only one of which is illustrated. Each piston and

cylinder pump unit

18, 19 supplies a predetermined quantity of fuel on each discharge stroke of its pistons to an individual fuel nozzle 12 through a fuel line 14. Each piston-cylinder pump unit automatically is recharged with fuel on its return stroke from a supply line 22. Such plunger 18 is a positive-displacement type which auto matically opens and closes an inlet connection from its supply line 22 on its intake and discharge strokes. A spring 20 returns the plunger on its intake stroke, opening the supply inlet.

Each rotation of the cam 24 pushes the plunger 18 through its discharge stroke forcing a quantity of fuel through the fuel line 14 from which it discharges from the fuel nozzle 12 into the associated engine cylinderlll. The cam 24- is operatively connected to the engine drive shaft as by means schematically indicated at 25 for actuating the plunger 18 in proper timed relation with the engine shaft rotation.

The fuel tube 14 preferably has a check valve 28 10- located next to the discharge end of the pump 16 to prevent fuel returning to the pump 16 and to keep the fuel tube 14 filled.

The nozzle 12 preferably has a check valve type of fuel discharge valve 3d at its outlet end which opens when the fuel pressure at the nozzle reaches a predetermined value whereupon fuel discharges into the engine cylinder. Hence, the valve 30 opens and closes substantially at the same time as the pump check valve 28 so that the fuel tube 14 remains full and the quantity entering the fuel tube on each stroke of the pump piston 18 is equal to the quantity discharging from the fuel nozzle 12. The nozzle check valve 3t also controls the nozzle discharge and type of spray.

As illustrated in FIG. 1, the portion of a fuel injection system supplying one cylinder is identical to the portions supplying the remaining cylinders of a combustion engine. A typical cylinder 10 has a piston 32 which is connected to the engine crankshaft 26 by a connecting rod 34, and its combustion chamber is supplied with air through an intake valve 36 and exhausted of waste gases through an exhaust valve 38.

The high pressure liquid injection system so far described is a conventional fuel injection system for an internal combustion engine.

In accordance with the invention, as illustrated in FIG. 2 by the enlarged cross-sectional view of the injection nozzle internals, the fuel passage 49 in the fuel tube 14 between the pump and nozzle outlet contains a pressurizing damping device 42 preferably located in the fluid pas sage through the nozzle.

The nozzle 12 embodiment shown in FIG. 2 is similar to a modified commercially-available nozzle. Before such modification, the nozzle has two parts: a barrel 44 with a passage 46 therethrough, and a hollow pinSll which is threaded into one end of the barrel passage 46. A check valve 36 is preferably disposed in the discharge end of the barrel 4- 5 and to communicate with one end of the hollow interior of the pin 56. The valve is urged ina 'the hollow barrel adjacent to the check valve 3t? so that a continuous passage extends through the nozzle 12 from the fuel tube 14 to the check valve 30 at the nozzle discharge.

. In accordance with the invention a pressurizing damper 42 is inserted in the fuel passage preferably in that portion 54 in the hollow pin 50. In order to modify an available nozzle, a hole is drilled and tapped in the pin 56 through its cap 56 and extending to its stem passage 54, and a screw 62 having a hollow stem 64 carrying the damper device 42 isthreaded into the hollow pin 50. Thus, .the'addition of such damper device 42 to a new or existing nozzle is easily done.

The damper 42 in the embodiment in FIG. 2 has a plu- .rality of batfie plates 58 joined together by a centered stem or spacing bar 60 to form a spool-like element. The spool-like damper device 42 is secured by soldering or brazing at the perimeters of the plates 53 to the inside surface of the hollow screw stem 64. The damper plates 58 are positioned in the flow path of the fuel within the hollow stem 64 of the screw 62, which in turn is positioned inside the hollow pin so that the screw 62 has a tight and sealed lit with the hollow pin 50, whereby all of the fuel flows through the hollow stem 64 of the screw 62 and around the bafile plates 58. The hollow stem 64 of the screw 62 has a cross passage adjacent to its head end for communicating with the fuel tube passage 4%. The

. 1 other end of such hollow stem 64 opens into the interior of the nozzle adjacent to the check valve 30. The hollow "stem 64 of the screw 62 thus forms a passage for thefuel flow through the nozzle.

As already stated, the damper device 42 comprises a preferably housed in its own removable sleeve 64.

since the damping action increases as the number of such plates 58 increases. However, the pump pressure and 7 tube pressure also increase as the number of plates increases.

. i is disposed radially inwardly of the wall of the passage 66a. Similar parts in FIG. 4 to those in FIG. 3 are identified by the same numerals but with a subscript a v added thereto for ease of illustration. Since the openings 74 in adjacent plates 58a are diametrically closer together, as is apparent in the projected details shown in the embodiment illustrated in FIG. 4 relative to that in FIG. 3, the damping action is lessened. Generally, the

greater the diametrical spacing between adjacent openings 74, the greater the damping action.

As already stated, the hollow stem 64 of the screw 62 forms a housing sleeve for the baffle plates 58 of the damper. Since the screw 62 is threaded into the nozzle 12 as illustrated in FIG. 2, its stem 64 is removably fitted into the fuel passage 54 so that the damper 42 is easily made and assembled in new or existing fuel injection systems. An existing nozzle can be easily assembled with the damper device, 42 by modifyingthe nozzle pin 5t? as illustrated. More-over, the damper device 42 is compact and lightweight so that itis not subject to the usual inertia loads and Vibration loads in the other parts of the fuel injection system, and it does not require a special supporting structure for attachment to a fuel injection system;

There are various theories for explaining cavitation erosion in a high pressure liquid injection system. The effects of erosion can be observed inside the nozzle 12 and particularly at various locations along the inner surface of the tube passage 40. It is known that bubbles or cavities occur when the fluid pressure drops below its vapor pressure, and the bubbles collapse when the fluid The plates 58 are spaced apart, with the length of the 7 space 70 between adjacent plates preferably equalling 15% to 25% of the inside. diameter or width of their ad jacent passage or tube; The damping action increases as the space 70 between adjacent plates 58 decreases, and the pump load and fuel pressure required also increases.

Each plate 58 also has an opening 68 therethrough of small cross-section relative to the cross-section of the adjacent portion of the fuel passage. Thus, each opening 68 preferably is 4% to 10% of the effective cross-sectional area of the adjacent fuel passage. The damping action,

' and the pump load and fuel pressure required, increase as this ratio of the opening area to passage area decreases. The openings 63 in adjacent plates 58 are rotatively displaced preferably 180 about the axis of the fuel passage so that the openings in every other plate are aligned.

In FIG. 3, the angle 72 of misalignment is illustrated,

angle of misalignment of 180.

As illustrated in FIG. 3, the openings 68 are preferably adjacent to the inner surface of the tube passage and are I disposed alternately adjacent to opposite sidewall portions of the passage 66 through the hollow screw 625 1 01 a passage 66 with a circular cross-section, the opening 68 through the plate 58 is preferably a segment of a circle so that manufacture isfacilitated. V a

As illustrated in FIG. 4, an alternate type of opening 74 through the plate 58a has a circular cross-section and pressure again rises above its vapor pressure. The characteristic vapor pressure of liquids varies for each liquid, for example, the vapor pressure for gasoline is slightly above atmospheric pressure; l

Laboratory and field tests on prior engine fuel injection systems lacking the benefits of the damper device 42 of the invention appear to reveal that: i V

(l) The extent of'bubbleformation and cavitation erosion has a correlation, and is approximately proportional, with the number of times the fluid pressure drops below the vapor pressure of the fluid.

(2) Upon each plunger discharge stroke, a single pressure surge travels through the tube from the plunger to the nozzle. Although this nozzle discharge appears to occur simultaneously with its pump plunger stroke due to the high speed of travel of the front of the surge actually the nozzle dischargeoccurs a short time later. Each plunger stroke and its surge is separated from its preceding stroke and surge by a time interval-which in the case of an engine fuel system is a small fraction of'a second, in the order of one-thirtieth of a second for normal, internal-combustion, gasoline-engine operation. The

duration of each plunger strokeand its surge is only a fraction of such time interval, or about one-fifth of such time interval.

(3) Test recordings of pressure at selected points along the tube indicate the type of fuel pressure waves at such points caused by the single pressure surge from a pump plunger stroke. As the surge passes a selected point, the fuel pressure rises from about atmospheric pressure to a higher average pressure as designed for the fuel injection system. Between plunger strokes, the residual pressure inthe fuel injection line remains at about atmospheric pressure. a V

(4) Moreover, such test recordings show that the pressure inthe fuel injection line oscillates during this surge,

' dropping to atmospheric pressure and below the vapor pressure of the fuel, in certain portions of the fuel passage particularlyin the intermediate portion of the fuel tube; ,It appears that as the front end of the surge from: a

the plunger stroke reaches the nozzle check valve, the

formation of a family of reflected or backward-moving waves begins. As the remainder of the surge moves toward and through the discharge valve, this family of backward-moving waves continues to increase and move back through the fuel tube. In the installations tested, a few of the first backward-moving waves reach the pump outlet before the end of the surge leaves the pump. Furthermore, as a result of these Waves, the fuel pressure oscillates with such a large amplitude in some portions of the fuel injection line, particularly at the intermediate portion of the fuel tube, that it intermittently rises and falls above and below the fuel vapor pressure, and thereby causes cavitation and erosion in such portions of the fuel line.

(5) It appears that this family of backward-moving waves emanating from the nozzle during its discharge is caused by the chattering of the nozzle check valve. It is believed that much of the cavitation would be avoided if the nozzle did not have a check valve, or were of a plain barrel design. However, the check valve type of nozzle is preferred to obtain good spray characteristics and to avoid high fuel consumption, particularly in the case of an intermittently operable fuel injection system.

After the damper device 42 of the invention is installed in the fuel passage, preferably in the nozzle 12, the following advantageous changes result:

All of the fuel pressures in the fuel tube 14 and in the nozzle 12, that is on both sides of the damper device 42, are raised substantially so that the minimum pressures do not fall below the vapor pressure of the fue In a particular installation, the pressure waves act in the following manner at such locations:

(1) The residual pressure between the plunger surges is raised substantially, or from about atmospheric pressure to about one-third of the average pressure of the surge which would exist in the absence of the damping device;

(2) The amplitude of the oscillations of the pressure during the plunger surge, as affected by the nozzle waves, is substantially decreased to about one-fifth of the amplitude which would exist in the absence of the damping device;

(3) The average pressure of the plunger surge as affected by the nozzle Waves, is raised substantially to about one and a half times its value which would exist in the absence of the damping device.

Thus, by placing the damper device 42 within or adjacent to the nozzle 12, cavitation erosion is prevented in the fuel passages up to the damper, and particularly within the passage 40 in the fuel tube 14. In addition, the cavitation erosion within the nozzle is also minimized.

As already indicated, with the type of nozzle illustrated in the drawings, the fuel spray from the nozzle 12 during each stroke of its pump is a pulsating, well-atomized type of spray. This type of spray is considered beneficial in an engine for good combustion efi'iciency. This beneiicial pulsating spray still exists with the damper 42 of the invention.

In FIG. 5 an alternate embodiment of the damper 42b is illustrated, disposed in the fuel tube 14]) and comprising a plurality of baffle plates 58b, preferably in the form of a spool-like element centered on a spacing bar 6%, longitudinally spaced along a portion or length of the fuel line passage 4% adjacent to the nozzle 12!). For ease of manufacture, the plates 58b are housed in a separate sleeve preferably in the form of a piece of tube 76 which is removably connected at each end to the adjacent part of the fuel tube 14 forming a continuous fluid passage 40b through the fuel line. The damper device 42b with its separate piece of tube or sleeve 76 and its plates 58b, is preferably in the form of a sub-assembly having each plate 58b copper brazed around its perimeter to the inner surface of the sleeve. The sub-assembly is joined at each end to the adjacent fuel tube 14 by silver solder at a temperature relatively lower than that for copper brazing so that existing fuel injection lines can be easily modified by the addition of such a damper device 421).

If the damper 42b is disposed in the fuel tube 1415 as illustrated in FIG. 5, it should be located in that portion of the tube 14b adjacent to the nozzle 12b preferably within the portion of its length not greater than thirty tube inside diameters away from the nozzle 12b in order to prevent bubble formation and cavitation erosion.

The exact position can be varied in such range from zero to thirty diameters to obtain an optimum pulsation and atomization of the fuel spray from the nozzle 1212. In one installation, it was found that locating the damper 42b at twenty diameters from the nozzle gave such wellatomized fuel spray. 7

While I have described my invention in detail in its present preferred embodiment it will be obvious to those skilled in the art after understanding my invention that various changes and modifications may be made therein without departing rom the spirit or scope thereof. It is intended by the appended claims to cover all such modifications.

What isclaimed is:

1. A high-pressure liquid-fuel injection system, comprising in combination positive-displacement pump means receiving liquid fuel and having an outlet and being operable to provide intermittent discharge of said fuel at high pressure from said outlet; a nozzle having valve means responding in an opening direction to high pres sure of predetermined level; passage means receiving said intermittent fuel discharge from said pump and delivering said fuel to said nozzle and being continuously full of fuel with air being excluded therefrom; and pressure-wave damping means disposed in said passage means in the region of said nozzle upstream from said valve and comprising a plurality of battle plates disposed transversely to said passage and spaced therealong and fixed to a central spacing bar to form an integral spool-like element immovable within said passage, each of said plates occluding said passage except for an open area of small cross-section relative to the cross-section of said passage, with adjacent open areas being misaligned to provide a tortuous flow path therethrough to damp reflected pres sure waves in said passage.

2. A high-pressure liquid-injection nozzle having an inlet at one end for receiving liquid fuel at high pressure in intermittent pulses from which air is excluded, valve means at the other end responding in an opening direction to high pressure of predetermined level and having passage means communicating with said inlet and said valve, and pressure-wave damping means disposed in said passage upstream from said valve means and comprising a plurality of baffie plates disposed transversely to said passage and spaced therealong and fixed to a central spacing bar to form an integral spool-like element immovable within said passage, each of said plates occluding said passage except for an open area of small cross-section relative to the crosssection of said passage, with adjacent open areas being misaligned to provide a tortuous flow path therethrough to damp reflected pressure waves in said passage.

3. A high pressure liquid injection system as claimed in claim 1 and in which the spacing between said plates is 15% to 25% of the approximate width of said passage.

4. A high pressure liquid injection system as claimed in claim 1 land in which the cross-sectional area of each opening is 4% to 10% of the effective area of the adjacent cross-section of the passage.

5. A high pressure liquid injection system as claimed in claim 1 and in which openings in adjacent plates are rotatively displaced approximately about the pas sage axis. 7

6. A high pressure liquid injection system as claimed in claim 1 and in which said damper means is located within the nozzle means.

7. A high pressure liquid injection system as claimed in claim 1 and in which the damper comprises at least four spaced plates.

8. A high pressure liquid injection system as claimed in claim 7 and in which said damper plates have a sepa- 7 rate housing sleeve removably connected into the pas- Silgfi.

9. A high pressure liquid injection system as claimed in claim 8 and in which said passage means is a metal tube and in which said housing sleeve for the damper plates is a portion of said metal tube.

10. A high pressure liquid injection system as claimed in claim 8 and in which said housing sleeve for the dampor plates is a hollow screw element which is fitted into the nozzle passage. 7

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS France Mar. 10, 1911 7 Great Britain May 29, 1919

Claims

2. A HIGH-PRESSURE LIQUID-INJECTION NOZZLE HAVING AN INLET AT ONE END FOR RECEIVING FUEL AT HIGH PRESSURE IN INTERMITTENT PULSES FROM WHICH AIR IS EXCLUDED, VALVE MEANS AT THE OTHER END RESPONDING IN AN OPENING DIRECTION TO HIGH PRESSURE OF PREDETERMINED LEVEL AND HAVING PASSAGE MEANS COMMUNICATING WITH SAID INLET AND SAID VALVE, AND PRESSURE-WAVE DAMPING MEANS DISPOSED IN SAID PASSAGE UPSTREAM FROM SAID VALVE MEANS AND COMPRISING A PLURALITY OF BAFFLE PLATES DISPOSED TRANSVERSLY TO SAID PASSAGE AND SPACED THEREALONG AND FIXED TO A CENTRAL SPACING BAR TO FORM AN INTEGRAL SPOOL-LIKE ELEMENT IMMOVABLE WITHIN SAID PASSAGE, EACH OF SAID PLATES OCCLUDING SAID PASSAGE EXCEPT FOR AN OPEN AREA OF SMALL CROSS-SECTION RELATIVE TO THE CROSS-SECTION OF SAID PASSAGE, WITH ADJACENT OPEN AREAS BEING MISALIGNED TO PROVIDE A TORTUOUS FLOW PATH THERETHROUGH TO DAMP REFLECTED PRESSURE WAVES IN SAID PASSAGE.