US2404335A - Liquid fuel burner, vaporizer, and combustion engine - Google Patents

Description

F. WHITTLE 2,404,335

LIQUID FUEL BURNER, VAPORIZER, AND COMBUSTION ENGINE Juli 16, 1946.

Filed Feb. 19, 194].

Pate'nted July 16, 1946' LIQUID FUEL BURNER, VAPORIZER, AND COMBUSTION ENGINE Frank Whittle, Rugby, England, assignor to Power Jets (Research London, England Application 2 Claims.

This invention relates to liquid fuel burners and vaporizers and to combustion engines or systems employing the same. In particular, although not exclusively, it is applicable to power units of aircraft propulsion systems of the previously known or proposed type in which the output of an air compressor takes part in combustion and then drives a gas turbine which in turn drives the compressor, the eilluent gases forming a propulsive reaction jet. The invention in some of its aspects is, however, applicable to liquid fuel burners and Vaporizers used in quite different connections, for example, in water heating apparatus, steam raising boilers or otherwise, wherever a plurality of combustion chambers and burners are to be operated in parallel and it is especially desired to equalize the performance of all.

The primary object of the invention is to provide highly efficient and uniform fuel combustion and air heating by a plurality of burners in different combustion chambers. A further object is to provide a burner and vaporizer arrangement which will be effective in an airstream of extremely high velocity; another object is to improve on igniting arrangements where a plurality of burners are in separate combustion chambers, and yet another object is to provide structurally simple yet efficient liquid fuel supply, Vaporizers, and burner arrangements in a power unit of the above mentioned type, wherein the compressor output is divided among a plurality of combustion chambers before being led into the turbine,

According to one feature of the invention, a

plurality of fuel jets are supplied from a common source, in parallel, and in each individual connectiona pressure-difference creating device such as a constriction, is provided, and is preferably so selected as to ensure the creation of a substantial pressure difference between the source and the jet in all ordinary running conditions. These constrictions are provided primarily to ensure that any disturbances of the resistance to flow occurring in one jet or associated vaporizer does not produce a surge of pressure or other inequality in a pipeline which is connected to another jet or jets and which may result in instability and fluctuation of fuel supply. According to another feature of the invention, each jet assembly preferably comprises a number of orifices arranged in spider or star fashion and directed substantially in an up-stream direction in a tubular combustion chamber through which an airstream of high velocity is created. Each jet is supplied by a vaporizer in the form of a pipe immediately Development) Limited,

February 19, 1941, Serial No. 379,735 Great Britain December 9, 1939 behind it in the airstream around which the combustion products pass. The combustion chamber surrounding the jets and vaporizers is preferably a tube which converges to the down-stream side of the jet and such tube is preferably co-axlally surrounded by a duct which leads the air into the combustion chamber, the sense of direction of flow of the air being reversed as it passes from the outer to the inner passage. Preferably in the air-flow immediately before the jet, means are provided for establishing a high degree of turbulence in the air, and such means may take the form of concentric rings of vanes arranged with opposite or different pitch. Each combustion chamber may be provided with a pilot or starter jet for the purpose of providing the initial heat for the Vaporizers, and each combustion chamber, or as is preferred, one chamber of a plurality, may be provided with igniting means comprising an electrical ignition plug. A feature of the invention resides in the interconnection of a plurality of combustion chambers by pipes for flame propagation as between one combustion chamber and its neighbor, and by this means only one chamber in a plurality need be equipped with igniting arrangements.

The invention as applied in a power unit as described in my co-pending application Serial No. 379,734, filed February 19, 1941, will now. be described more fully with the aid of the accompanying drawings, in which:

Figure 1 is a sectional view of a combustion chamber and its ignition arrangements and fuel distributor, whilst Figure 2 is an end view of the same, with the dome part removed, and

Fig. 3 is a diagrammatic view illustrating the interconnection of a plurality of combustion chambers.

For convenience, in Figure 1, the interconnecting stub pipes intended to be employed when a plurality of chambers are used in parallel are illustrated in rotationally displaced positions.

The combustion chamber is constituted by a cylindrical air casing I, to which at one end is attached a dome end 2, and at the other end a suitable closure including a connection for compressed air supply, such as a dome 3 with a circular part 3A for the connection of an air trunk. Within the casing I is mounted co-axially a flame tube 4 comprising a frusto-conical tube with a cylindrical portion 4A at its larger end. The smaller end of the flame tube 4, fits into anelbow part 5, which leads combustion products through a right angle for exit through the wall of the casthe flame tube.

' 3 ing I. The casing I, if it is one of a plurality required to operate in parallel (as in the power unit above mentioned), has air stub pipes IA leading radially from it, to connect with neighboring casings. Within these air stubs IA are, substantially co-axially, connecting the flame tube of one combustion chamber, to the flame tubes of its neighbors.

The dome 2 has passing through it a central, coaxial, bushing 2A into which fits apilot jet 5, which is an atomising spray jet, supplied with being fitted to any convenient adjacent parts.

Parts which would otherwise interfere with the electrode BA are cut away to such clearance as is necessary to avoid sparks jumping in undesired places.

In the otherwise open end of the flame tube portion 4A, a bafiie system is provided, the object of which is to produce a high degree of turbulence in air entering the flame tube at this end. This baiile system comprises a conical rim I, an outer co-axial cylindrical sleeve 8, and an inner. coaxial cylindrical sleeve 9. Between sleeves 8 and 9 is a series of swirl vanes 8A pitched one awaysay, clockwise looking downstream, and between sleeve 9 and the bush 2A is an inner series of swirl vanes 9A, oppositely pitched. Air coming from the casing I flows through these two series of vanes as shown diagrammatically by the arrow I0, and the result is a highly turbulent, high velocity, flow of air in the flame region within Some reversal of flow in the the axis is to be found with this arrangement, and this appears to be beneflcial in sustaining combustion.

Through the dome 2 andrim 1 there project eight fuel pipes II, which continue susbtantially parallel with (and symmetrical about) the flame tube axis, for about half the length of the flame tube, and then bend back upon themselves to point upstream. They terminate in jets at I IA. Th parts of these pipes which are exposed to the flame act as Vaporizers, so that whilst liquid fuel is fed into the pipes II, vaporized fuel'is projected upstream from the jets IIA. Such an arrangement by itself has the defect that it surges if a common source. It is obvious, for example, that slight inequalitiesof heat exchange as between the pipes of the vaporizer, can result in one tube starving of liquid fuel momentarily, whilst another gains. The starved pipe becomes hotter and the gaining pipe cooler, so the condition is self-aggravating, resulting in an unstable condition, cracking of fuel, and the building up of carbon in'the pipes. Since one of the objects of the invention is to produce uniform distribution of heat in the delivered gases (as well as uniformity in a plurality of combustion chambers), the following means are adopted to overcome this diflicul y.

The pipes I I come from a common equalizing chamber I2, which is fed with liquid fuel under messure by a fuel pipe I3, and which may contain a strainer such as a gauze I2A. Where each pipe II opens into the chamber I2, there is a small orifice IIB, which, conveniently, is a screwed-on nipple. 'I'he orifices of the nipples form restrictions, and they areselected so as to produce such pressure-drop across them, as will prevent surg in the vaporizers as a whole.

neighborhood of flame stubs 4B similarly fuel under pressure by a pipe 5A. The pilot jet the pipes I I are simply fed in parallel from secondary scribed,

It is not possible readily to lay down any proportions or dimensions for the restriction oriflces IIB; these depend on the nature, dimensions, running temperature, etc., of the pipes, the nature of the fuel, and the range of flow-rates t: Ible used, and the character of the jet orifices a A.

The flame tubes 4 are perforated as at 4C for the admission of air from the casing I. The air passing through these holes 40, is regarded as air, i. e. air not necessary to complete combustion. Th primary air is that which passes through the battle system. However, in practice it is found that with the high velocities and high rates of combustion for which the invention is intended to be used, the secondary air if properly admitted, speeds up combustion and shortens the flame.

tion is common to all, and ignition gnition in all, the flame stubs in one causes 43 communicatpressures in I claim: 1. In a combustion engine of 'coaxially within each oi said one open end and additional openingsin its side ,flame tube being that thereof. a circular-sectioned flame tube located air casings having wall for the entry of air, the open end or each or. the associated air casing through which air is supplied 'to the latter, means for supplying fuel to said flame tubes uniformly adjacent the open ends of said tubes, means interconnecting the interiors of all of said air casing to balance the pressures therein, and means interconnecting the interiors of said flame tubes, said means interconnecting the air casings comprising air stub pipes extending between adjacent casings, and said means interconnecting the flame tubes comprising additional stub pipes of less diameter than and passing through said air stub pipes.

2., In a combustion engine which is opposite the end l of the character described, a plurality of combustion units each I connecting said flame tubes arranged within the comprising a circular-sectioned air casing, means for delivering compressed. air to the interior or amass 6 said casing, a circular-sectioned flame tube mounted coaxially within said casing and having one end open whereby compressed air from said casing enters and traverses said tube, means adiacent said open end for creating turbulence in the air entering said tube, means for supplying uniformly distributed fuel into the turbulent air within said tube, the wall of said tilbe being periorated at both axially and peripherally spaced points for the passage of secondary air thereinto from said casing, and an outlet conduit for conducting products of combustion from the other end of said ilame tube to the exteriors! saidcaslng, means for interconnecting the air casings of said units, and 'means for interconnecting the flame tubes 'of said units, said. interconnecting means comprising concentric pipes with the pipes pipes connecting said air casings.

FRANK WHI'I'ILE;

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