US 2578272 A
Description (OCR text may contain errors)
1951 A. c. R. THOMPSON LIQUID FUEL BURNER Filed Nov. 26, 1948 0 mm mi. m 0 Q m 16 NW m m mm N W C 4X 7 R Q ow O.\ 0 ii l QN I Q Q m ifwww mm 8 m v m Patented Dec. 11, 1951 LIQUID FUEL BURNER Arthur Charles Runciman Thompson, Cheltenham, England, assignor to Power Jets (Research and Development) Limited, London, England, a
British company Application November 26, 1948, Serial No. 62,016 In Great Britain December 13, 1947 6 Claims.
This invention relates to improvements in liquid fuel burners of the kind termed herein "spill-controlled," such burners comprising a swirl chamber of circular section having tangential ports through which liquid fuel under pressure is led into the chamber and is swirled about the axis of the chamber, part of the fuel being spilled back to the supply source through a spillway communicating with one end of the 'swirl chamber while the remainder of the fuel is discharged as a spray through a delivery orifice located at the opposite end of the said chamber.
The object of the present invention is to provide a construction which enables improved atomisation to be obtained and for this purpose according to the invention, means are provided whereby the fuel leaving the swirl chamber through a spillway is allowed to do so only after it has progressed for some distance within the swirl chamber towards the delivery orifice, thus reducing the energy lost through the spillway. Preferably the fuel is obliged to leave at a locality such that the maximum amount of energy is taken from the fuel entering the chamber.
In one form of the invention the desired effect is obtained by providing the spillway, in the locallty where it communicates with one end of the swirl chamber, with a tubular extension extending towards the delivery orifice and protruding into the swirl chamber whereby all the fuel spilled back to the supply source is obliged to flow through this extension. In this way liquid fuel leaving the swirl chamber through this tubular extension must first pass from the tangential ports through a substantial axial length of the swirl chamber towards the delivery orifice, so that the maximum amount of kinetic energy can be withdrawn from the liquid before it flows back to supply. For that purpose the tubular extension should protrude into the swirl chamber to an extent such that thearea of the annular section of the swirl chamber contained between the open end of the tubular extension and the radially adjacent part of the wall of the swirl chamber is substantially equal to the area of section of the tubular extension.
The said extension may be pivotally mounted so as to be free to pivot in all directions, thus permitting the extension to be self-aligning with the axis of the vortex and so to compensate for any slight offsetting in the position of the delivery orifice relative to the axis of the swirl chamber.
By way of example, three forms of the invention are described below with reference to the accompanying drawings in which Figure 1 is an axial section of one form of the invention, Figure 2 is a part of Figure 1 on an enlarged scale, Figure 3 is a similar view to Figure 2 showing a second form of the invention, and Figure 4 is a similar view of a third form.
Referring to Figure 1, a liquid fuel burner comprises a body of generally cylindrical form consisting of a casing I screw threaded to a casting 23, and provided with a banjo and lateral union 2 for liquid entry. As shown by the arrows, the liquid enters an annular space 3 and passes through a filter 4 into an annular space 5 and a further annular chamber 6 around the wall of a swirl chamber I into which the liquid passes through staggered tangential swirl ports 8.
One end of the chamber I is partly closed by an orifice plate 9 having a central delivery orifice I0 and the other end of the swirl chamber I communicates through a bore II in a bush I4 (the bore II being of greater diameter than that of orifice 10) with a central duct I2 which communicates with a second union l3 to which is connected a return pipe (not shown) leading back to supply through a manually operable throttle valve, the operation of which is used to vary the amount of liquid discharged through the orifice Ill.
The end portion 24 of bush I4 fits over one end of the duct I2 and the bush I4 is provided with a flange I5 against which bears one end of a spring IS. The other end of said spring I6 bears against a shoulder I'l formed in the casing I between the annular space -5 and the space 6 which is of greater diameter. A sleeve 25 fits around the bush I4 and registers with the nozzle plate 9.
Fluid tightness is ensured by metal washers I9, 20, 2| for example of aluminium, a resilient washer 22 for example of rubber, and a semiresilient washer I8 for example of fibre.
Liquid fuel swirling around the axis of chamber I forms a vortex and under suitable conditions some of the liquid fuel is discharged through the orifice Ill. If the above-mentioned throttle valve is opened to a greater extent, a larger quantity of fuel returns back through spillway II to the supply and a smaller quantity of fuel is discharged through the orifice Ill.
As so far described, the construction and mode of operation of the spill-controlled burner is already known: in applying the present invention to a burner of such known construction, the bush I4 is provided with a tubular extension 26 protruding into chamber I. Fuel flows from the ports 8 into chamber I towards orifice ID for a substantial axial length of chamber I, so that the maximum amount of kinetic energy is withdrawn from the liquid before it enters the open end 21 of extension 26 to flow back to supply.
Preferably the tubular extension 28 extends as shown in Figure 2 through the whole of the cylindrical portion Ia of the chamber I and through part of the frusto-conical portion of said chamber, the open end 21 of said extension being situated at a locality such that the area of the annular section of chamber I contained between the end of 21 and the radially adjacent part 28 of the wall of chamber 1 is substantially equal to the area of section of the extension 26.
asvsma In a modified form of the invention shown in Figure 3, the bush M is provided with a separate tubular extension 29 which protrudes into the chamber 1, this extension being pivotally attached to the bush M, for example by a ball joint or other universal joint, so that it is free to pivot in all directions. In the construction shown in Figure 3, the inner wall'of the bush i4 is provided at one end with a threaded bush 30 having a spherical or partly spherical seating 3i and the extension 29 is provided with a bulbous end 32 of similar form to enable it to pivot against the seating 3!. Such an arrangement permits the extension 29 to be self aligning with the axis of the vortex and so to com pensate for any slight ofi-setting in the position of the orifice l relative to the axis of the chamber 7.
In Figure 4 the tube I2 is itself provided with a separate tubular extension 33 having a bulbous end 34 adapted to seat against a spherical seating on a threaded part 35 at the end of tube l2.
Tests have shown that the invention enables a spill-controlled burner to have a good atomisation performance at low fuel fiow rates which is most important at high altitude, particularly in the case of a gas turbine aero-engine. In a particular case tests with such an engine have shown that with the known construction of spillcontrolled burner, stable conditions could not be obtained below a rotational speed of 3,000 revolutions per minute with a burner pressure of 45 lbs. sq. in. whereas with spill-controlled burners modified according to the present invention, stable conditions were obtained at a speed of 2,500 revolutions per minute with a burner pressure of 40 lbs. per sq. in. and in some cases it was found possible to reduce the speed to 2,100 revolutions per minute while maintaining stable conditions.
1. A liquid fuel burner comprising a swirl chamber of circular section, means defining tangential swirl ports for the admission of liquid fuel into said chamber, means defining a discharge orifice communicating with one end of said chamber, a duct communicating with the opposite end of said chamber but serving as a spill-way to spill back that part of'the fuel which enters the chamber and is not discharged through said discharge orifice, and a tubular extension for said spill-way in the locality where said spill-way communicates with said swirl chamber, said extension protruding into the swirl chamber whereby all the fuel spilled back is obliged to fiow through said extension, the outside diameter of said extension in the region of said tangential ports being a minor part of the internal diameter of the swirl chamber in said region, and the internal cross-sectional area of the extension being not greater than the minimum cross-sectional area of the annular space between the extension and the walls of said chamber.
2. A liquid fuel burner according to claim 1 wherein the spill-way comprises a tube and a detachable extension provided at one end of said tube, said detachable extension protruding into the swirl chamber and forming the said tubular extension.
3. A liquid fuel burner according to claim 1 wherein the said extension is pivotally mounted so as to be free to pivot in all directions.
4. A liquid fuel burner comprising a cylindrical sleeve, a nozzle plate, a flanged bush between the flange of which and said plate said cylindrical sleeve is supported to form a swirl chamber of circular section with a discharge orifice in said plate, means defining tangential swirl ports for the admission of liquid fuel into said chamber, a duct in contact with said flanged bush to serve with said bush as a spillway in spilling back that part of the fuel which enters the chamber and is not discharged through said discharge orifice in said plate and a tubular extension, the outside diameter of which, in the region of said tangential ports, is a minor part of the internal diameter of the swirl chamber in said region and the internal cross-sectional area of which is not greater than the minimum cross-sectional area of me annular space between said extension and the walls of said chamber.
5. A liquid fuel burner comprising a swirl chamber of circular section having a cylindrical portion and a conical portion tapering towards a discharge orifice, means defining tangential swirl ports for the admission of liquid fuel into said chamber at said cylindrical portion, a duct communicating with said chamber and serving as a spill-way to spill back that part of the fuel which enters the chamber and is not discharged through said discharge orifice, and a tubular extension for said spill-way in the locality where said spill-way communicates with said swirl chamber, said extension protruding into the swirl chamber, whereby all the fuel spilled back is obliged to flow through said extension, and having an outside diameter which is a minor part of the internal diameter of said cylindrical portion of said swirl chamber and an internal cross-sectional area which is not greater than the area of the annular section of the swirl chamber between the open end of the extension and the conical part of the wall of the swirl chamber in the plane of said open end.
6. A liquid fuel burner comprising an elongated swirl chamber of circular cross-section having a discharge orifice at the front end of the chamber and tangential swirl ports for the admission of liquid fuel in the region of the rear end of the chamber in combination with a spill pipe protruding axially into the interior of said chamber from the rear and extending along the greater part of the length of the chamber to define with the interior wall of the chamber an annular space the end of said spill pipe lying nearer to said discharge orifice than to said ports whereby fuel entering by said swirl ports can progress, with a swirling motion around the axis of the chamber, along the greater part of the length of the chamber before reaching the entrance to the spill pipe and the discharge orifice.
ARTHUR CHARLES RUNCIMAN THOMPSON.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,079,430 Bargeboer May 4, 1937 2,177,781 Haynes et al. Oct. 31, 1939 2,308,909 Blanchard Jan. 19, 1943 2,315,172 Voorheis Mar. 30, 1943 2,345,402 Lubbock et a1 Mar. 28, 1944 2,379,161 Kraps June 26, 1945