US 3808803 A
An anticarbon device for a scroll-type carburetor consists of a frustro-conical plug mounted on the upstream wall of the spin chamber at a location along the axis of the core outlet and the primary vortex. A plurality of passageways formed therethrough permit air to be introduced into the scroll and directed against those wall locations where carbon deposits usually form because of the reverse high temperature gas flow. The plug also retains the high air/fuel velocities through the swirl vanes for flashback prevention.
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Description (OCR text may contain errors)
United States Patent [191 Salvi ANTICARBON DEVICE FOR THE SCROLL FUEL CARBURETOR  Inventor: Enrico Salvi, Salem, Mass.
 Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.
 Filed: Mar. 15, 1973  Appl. No.: 341,440
 Cl 60/39.74 R, 239/400, 239/404,
 Int. Cl. F02c 7/22 [58-] Field of Search 60/39.74 R, 39.74 B; 239/400, 403-406; 261/79; 431/185, 183
 References Cited UNITED STATES PATENTS 3,605,405 Dubell et al. 60/39.74 R
m1 3,808,803 May 7,1974
Primary Examiner-Carlton R. Croyle Assistarit ExaminerR0bert E. .Garrett Attorney, Agent, or Firm-R. S. Sciascia; L. l. Shrago 7] ABSTRACT An anticarbon device for a scroll-type carburetor consists of a frustro-conical plug mounted on the upstream wall of the spin chamber at a location along the axis of the core outlet and the primary vortex. A plurality of passageways formed therethrough permit air to be introduced into the scroll and directed against those wall locations where carbon deposits usually form because of the reverse high temperature gas flow. The plug also retains the high air/fuel velocities through the swirl varies for flashback prevention.
8 Claims, 4 Drawing Figures ANTICARBON DEVICE FOR THE SCROLL FUEL CARBURETOR The present invention relates generally to scroll fuel carburetors and, more particularly, to an anticarbon device for such carburetors which eliminates smoke without reducing the required flashback margin.
One of the proposed solutions for minimizing air pollution caused by visible smoke emission from gas turbine engines involves carbureting the inlet air and delivering the combustible fuel/air mixture into the primary zone of the combustor as a vortical flow. The apparatus which achieves thi mode of operation generally comprises a housing defining a spin chamber that is centrally disposed about a core outlet. Fuel and air introduced into this chamber circulate through an array of swirl vanes and emerge as a vortical discharge flow of air and highly dispersed fuel. A skirt at the core outlet collects any non-varporized or atomized fuel that might otheerwise be expelled from the system, and a secondary array of swirl vanes disposed about this collector develops a secondary vortical flow into the combustion chamber about the primary vortex.
Such apparatus has been found to produce an extremely well vaporized fuel/air mixture which may be efficiently burned in the combustion chamber with reduced smoke emission. However, under certain operating conditions, the reduced pressure of the vortex core causes a reverse or recirculation flow to take place from the combustion chamber back to the central portion of the spin chamber. Although this recirculation does contribute to further vaporization of any liquid fuel from the spin chamber surfaces, this high temperature gas movement can have undesirable effects on the performance of the apparatus if it is not counteracted. For example, carbon deposits may accumulate on the upstream wall surface of the spin chamber and cause unstable burning conditions within the combustion chamber. Additionally, the high temperature gas impinging on this upstream wall may produce premature structural damage.
One technique that has been proposed to avoid these conditions involves perforating the upstream wall and sending large amounts of high velocity air ito the spin chamber to oppose the hot recirculating gases. 1 order not to upset the primary vortex and destroy the basic zero-dynamics of the system, this purge air has a swirl imparted to it that is in the same direction as the primary vortex flow. I
It has been found that there is still a tendency for a stagnation zone to occur at the center of the back face of the scroll. Carbon, consequently, may continue to accumulate on this portion of the upstream wall.
With the scroll type combustors, flashback maybe experienced when the fluid velocities through the vanes are not sufficiently high. These velocities have been increased by reducing the scroll-vane height. But when this is done by, for example, inserting a plug at the back of the scroll, the richness of the fuel mixture in the scroll increases and produces smoke.
It is, accordingly, a primary object of the present invention to provide an anticarbon device for a scroll fuel vaporizer.
Another object of the present invention is to provide an anticarbon device for a scroll fuel carburetor which minimizes smoking and retains high vane velocities for flashback prevention.
Briefly, and in somewhat general terms, the above objects are accomplished according to the present invention by positioning a plug at the upstream or back face of the scroll at a location which is along the central axis of the spin chamber so as to be co-axial with the core outlet and the primary vortex. This member, which has the general shape of a frustrated cone, extends across the spin chamber and projects a short distance into theinterior of the skirt. A plurality of circumferential apertures and a central aperture are provided in the cone thus permitting controllable amounts of air to be introduced into the scroll and directed against preselected back wall areas. This air prevents the build up of carbon deposits on these surfaces and also leans out the very rich mixture which otherwise oc curs in this general region of the scroll and causes smoking.
The plug also retains the presentsmall scroll-vane height associated with high fluid velocities throughthe vanes. This, as is known in the art, eliminates the possibility of flashback. Additionally, the surface of the anticarbon device is continuously scrubbed with the fuel- /air mixture, and this constant cleaning discourages any carbon accumulation on this device.
Other objects, advantages'and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:
FIG. 1 is a fragmentary axial cross-sectional view of an exemplary gas turbine engine combustion apparatus which may utilize the improved scroll. carburetor of the present invention;
FIG. 2 is a cross-sectional view of a scroll showing one modification of the anticarbon device mounted in place;
FIG. 3 is a front-view showing the locations of the various apertures; and
FIG. 4 schematically illustrates another configuration of the anticarbon plug.
Referring now to the drawings, FIG. 1 schematically illustrates the general cooperation between a gas turbine engine and a scroll fuel carburetor of the type which may utilize the present invention. The details of this system are shown in U. S. Pat. No. 3,605,405. of Sept. 20, I971 and reference may be had to this patent for a complete description of the operation and performance of the particular scroll carburetor shown. It
would be pointed out, however, that carburetor34 produces both a primary vortical flow 40 and a secondary vortical flow 67. However, the secondary flow need not be present as far as the operating principle of the present invention is concerned.
Referring now to FIG. 2, it will be seen that housing 35 of carburetor 34 is formed by an involute outer wall 48 and a pair of planar spaced upstream and downstream end walls 50 and 52, respectively. The air/fuel mixture introduced into end opening 55 thus experiences a circular motion of ever-decreasing radius in spin chamber 46, and, this, together with the action of swirl vanes such as 31, 32 within this chamber, produces the primary vortical flow 40.
The reduced pressure condition at the vortex core 56 causes the reverse flow, previously mentioned, to be established from combustion chamber 14 back into spin chamber 46, as shown by arrow 82. While this recirculation is beneficial in that it enhances vaporization of the liquid fuel from the spin chamber surfaces and any atomized fuel droplets carried by the air intake, it does, unfortunately, have detrimental effects if it is allowed to impinge upon the upstream end wall 50 of the spin chamber. For example, this high temperature may overheat this wall surface and cause structural deformation or damage. Additionally, it may cause the accumulation of carbon deposits on the interior wall surfaces and produces unpredictable burning conditions in the combustion chamber 14.
To eliminate this problem, as shown in FIG. 2, an anticarbon device 80 is mounted or otherwise secured to end wall 50 at a location which lies along the central axis of the core outlet and the primary vortex. This apparatus has the general shape of a truncated cone with, in this particular case, its outer surface 51 concave.
A plurality of apertures such as 90 and 91, better shown in FIG. 3, are cut through this member at a circle of locations adjacent its rim portion. Also, a central aperture 92 of progressingly greater diameter is formed therein was to provide a circular edge 93 at the apex.
The dimensions of plug 80 are such that its conical body portion extends completely across the spin chamber, with its apex portion projecting a short distance into the interior of skirt 89.
Cooperating with plug 80 is a spaced deflector 94 which has a central opening 96 formed therein to accommodate the anticarbon plug in a concentric manner. Deflector 94 includes a ring portion disposed within the spin chamber so as to confrontthe circle of air inlet apertures. A plurality of integrally formsupporting tabs project from this ring portion and are secured to the outside surface of the back wall. Alternatively, these tabs may be directly attached near the outer rim portion of the conical plug 80 so as to permit the insertion of the complete apparatus, that is, the plug and the deflector into the scroll as a unitary device. In this case, any suitable mounting arrangement may be employed to position this device in place on the back wall of the scroll.
In any event, the purpose of this deflector is to direct the air, which is injected into the interior of the scroll via the circle of apertures, such as 90 and 91, upstream against end wall 50 of the scroll. This air flow prevents the accumulation of any carbon on the swept surrounding wall surface. Some of this air is also admitted as a film around the concave surface of the truncated cone, and, when it leaves the apex, it does not interfere with the aero-dynamics of the primary vortical flow.
The circular trailing edge 93 serves as a means from which any fuel can shear off uniformly and concentrically to the scroll exit. Central aperture 92 is included to insure that all possible stagnation zones are eliminated.
In the operation of the apertures of FIG. 2, the fuel and air mixture passes through the various swirl vanes, such as 31 and 32, and the primary vortical flow is established in the usual manner. The additional air introduced through the circle of apertures in the anticarbon device, as mentioned hereinbefore, splashes onto the upstream surface of this scroll and prevents carbon formation thereon. Some of this air is also admitted as a film around the downstream surface of the truncated cone, and, when it is discharged therefrom, counteracts the recirculation flow. Further contributing to the counteraction of this flow is the air introducedat the central opening 92.
The fuel/air mixture emanating from the swirl vanes sstrikes the concave surface 81 of plug 80 and, thus,
this portion of the apparatus is continuously scrubbed. This constant cleaning prevents any carbon accumulation at this site.
It will also be pointed out that the additional air introduced into this system via the various apertures in plug 80 leans out the otherwise very rich mixture which sometimes is present in this region and is responsible for some of the smoking.
FIG. 4 shows an alternative anticarbon configuration. Here the surface is convex rather than concave and the central aperture has a constant diameterl What is claimed is:
1. For use in a scroll-type carburetor of the type having a spin chamber that includes spaced upstream and downstream planar walls interconnected by an involute wall, with said downstream wall having a circular opening that serves as a discharge exit for the vortical fuellair mixture, the combination of,
an anticarbon member secured to said upstream wall at a location corresponding to the central axis of said cirular opening,
said member having a generally frustro-conical body portion which extends across said spin chamber with the apex thereof terminating at a point beyond said circular opening,
said member also having a plurality of passageways formed therethrough which permit air to be injected into said spin chamber; and means for deflecting some of said injected air backwardly against surrounding exterior portions of said upstream wall which are adjacent said anticarbon member. 2. In an arrangement as defined in claim I, wherein said anticarbon member has a central aperture formed therein whose diameter increases to a maximum at said apex, and forms a circular edge thereat. 3. In an arrangement as defined in claim 1, wherein said frustro-conical body portion has a convex surface. 4. For use in a scroll-type carburetor. having a spin chamber that is formed by spaced upstream and downstream planar walls that are interconnected by an involute wall, with a circular opening formed in said downstream wall for discharging the vortical fuel/air mixture into the combustion chamber, the combination of,
a generally frustro-conical member secured to said upstream wall at a location such that the longitudinal axis of symmetry of said member coincides with the central axis of said circular opening, said member extending across said spin chamber with the apex thereof terminating at a point beyond said circular opening,
said member also having formed therein a plurality of passageways which permit air to be injected from outside said spin chamber into the interior thereof; and
means for deflecting some of said injected air against surrounding exterior portions of said upstream wall and forwardly along the surface of said member so as to counteract any recirculainto said spin chamber.
apex of said member. 7. In an arrangement as defined in claim 4, wherein some of said passageways of said plurality are arranged in a circle. 8. In an arrangement as defined in claim 4,
wherein the outer surface of said member'is curyed.