Turbomachine combustion chamber injection system with optimized purge holes

Abstract

A turbomachine combustion chamber injection system comprises a sleeve (52), a bowl (60), and an air intake auger (56) delimited by an upstream internal surface (62B) of a downstream end wall (62) of the sleeve. The downstream end wall has purge holes (64), each having an inlet (64A) opening through an upstream external surface (62A) of the downstream end wall (62), and an outlet (64B) opening through the upstream internal surface (62B). The inlet (64A) has an inlet axis (A1) oriented along an inlet direction (D1), and the outlet (64B) has an outlet axis (A2) oriented along an outlet direction (D2). The outlet direction (D2) has a circumferential inclination (θ2), defined with reference to a cylindrical coordinate system centered on an injection axis (44), and in the same direction as the air intake twist (56). Figure for the abbreviation: Figure 13

Description

Title of the invention: Injection system for a turbomachine combustion chamber having optimized purge holes Technical field

[0001] The present invention relates to the field of injection systems intended for the injection of air and fuel mixtures into the combustion chambers of turbomachines, in particular turbojets intended for the propulsion of aircraft. State of the prior art

[0002] A turbomachine, such as a turbojet, comprises one or more compressor(s) delivering pressurized air to a combustion chamber where the air mixed with fuel is ignited to generate hot combustion gases. These gases flow downstream of the chamber to one or more turbine(s) which transform(s) the energy thus received to drive the compressor(s) in rotation and provide the work necessary, for example, to propel an aircraft. Typically, an annular combustion chamber comprises an inner annular wall and an outer annular wall, connected together at their upstream end by an annular chamber end wall. The chamber end wall has, circumferentially spaced apart, a plurality of passages each receiving an injection system in the middle of which is positioned a fuel injector nozzle, the assembly allowing the supply of a mixture of air and fuel into the combustion chamber.

[0003] The fuel, initially in liquid form, is brought to the chamber by each injector, the nose of which causes the fuel to be sprayed into fine droplets. The process of spraying and then evaporating the fuel is initiated at the injector's nose and continues within the injection system, in particular at a convergent-divergent internal wall, or venturi, and a divergent outlet wall, or bowl, by a driving effect of the pressurized air coming from the compressor. This pressurized air passes through, on the one hand, one or more swirlers of the injection system, for example of the radial or axial-radial type, to set the fuel sprayed by the injector into rotation, and, on the other hand, orifices provided in different parts of the injection system.

[0004] Such orifices, called purge holes, are sometimes formed in a wall defining, on an upstream side, an upstream external surface of the injection system, and delimiting, on a downstream side, such a swirler. Such purge holes are provided to avoid or limit the risks of flame rising within the swirler and the risks of coking along the walls delimiting the swirler.

[0005] The presence or absence of such purge holes on a given injection system, and, where applicable, the sizing of the purge holes are key parameters for sizing the re-ignition ceiling of a combustion chamber. The choice of the dimensions of such purge holes also appears to be a compromise between re-ignition performance and combustion stability on the one hand, and a risk of fuel stagnation in the injection systems on the other.

[0006] Under difficult ignition conditions such as in-flight re-ignition conditions, it may happen that the flame kernel initiated in front of the spark plug struggles to reach the recirculation region defined at the outlet of an injection system relatively close to the spark plug. It may also be that the flame stagnates in front of such an injection system without propagating to the neighboring injection systems, leading to a failure of ignition of the combustion chamber and requiring a new ignition attempt to be made. Statement of the invention

[0007] The present invention aims to optimize the purge holes in order to reduce the influence of the latter on ignition performance, particularly in difficult conditions.

[0008] The invention proposes for this purpose an injection system for injecting a mixture of air and fuel into a turbomachine combustion chamber, comprising a sleeve for receiving a fuel injector nozzle, a bowl, and at least one air intake swirler arranged axially between the sleeve and the bowl for injecting air into the injection system having a rotating movement in a circumferential swirling direction, around an injection axis of the injection system.

[0009] The sleeve comprises a downstream end wall defining, on an upstream side of the injection system, an upstream external surface of the latter, and on an opposite side, an upstream internal surface delimiting said air intake swirler upstream.

[0010] The downstream end wall comprises purge holes each having an inlet opening through said upstream external surface and an outlet opening through said upstream internal surface.

[0011] The inlet has an inlet axis oriented in an inlet direction, and the outlet has an outlet axis oriented in an outlet direction.

[0012] According to the invention, at least the outlet direction has a circumferential inclination, defined by reference to a cylindrical coordinate system centered on the injection axis, and in the same direction as the circumferential twist direction.

[0013] The purge holes are thus configured for co-rotating air injection with the air from the air intake swirler adjacent to the downstream end wall of the sleeve. The impact of the air from the purge holes on the swirl flow from the aforementioned swirler is thus reduced. In this way, the purge function, i.e. protection against coking and flame rise, can be maintained. without this being to the detriment of the stability of the flame and the ignition performance of the combustion chamber.

[0014] It should be noted that, because the air intake swirler is delimited upstream by the downstream end wall of the sleeve, this swirler is not of a purely axial type but can be of a radial type or of an axial-radial type, that is to say that the swirler has a pure radial orientation or with an inclination in the downstream direction.

[0015] In embodiments, the outlet direction has a radial inclination towards the injection axis.

[0016] In other embodiments, the output direction is orthogonal to the radial direction of said cylindrical coordinate system.

[0017] In embodiments, each purge hole is cylindrical in shape, whereby the inlet axis and the outlet axis of each purge hole coincide.

[0018] In other embodiments, each purge hole is curved in shape, such that the inlet direction has a circumferential inclination, defined with reference to said cylindrical coordinate system, less than the circumferential inclination of the outlet direction, for each purge hole.

[0019] In such embodiments, the circumferential inclination of the entry direction may be zero.

[0020] In such embodiments, the inlet direction may have a radial inclination, defined with reference to said cylindrical coordinate system, less than or equal to the radial inclination of the outlet direction, for each purge hole.

[0021] In such embodiments, the radial inclination of the input direction may be zero.

[0022] The invention also relates to a turbomachine for an aircraft, comprising a combustion chamber and at least one injection system of the type defined above for supplying the combustion chamber with a mixture of air and fuel. Brief description of the drawings

[0023] The invention will be better understood, and other details, advantages and characteristics thereof will appear on reading the following description given by way of non-limiting example and with reference to the appended drawings in which:

[0024] [Fig-1] is a schematic axial sectional view of a turbomachine intended for the aircraft propulsion;

[0025] [Fig.2] is a schematic half-view in axial section of a combustion chamber within the turbomachine of [Fig.l];

[0026] [Fig.3] is a schematic axial sectional view of an injection system of a type known, suitable for equipping the combustion chamber of [Fig.2];

[0027] [Fig.3A] is an enlarged schematic view of a portion of [Fig.3];

[0028] [Fig.4] is a schematic perspective view, substantially from upstream, of an injection system according to a first embodiment of the invention, also capable of equipping the combustion chamber of [Fig.2];

[0029] [Fig.5] is a schematic perspective view, substantially from downstream, of an upstream part of the injection system of [Fig.4];

[0030] [Fig.6] is a schematic perspective view of an inlet section of a purge hole belonging to the injection system of [Fig.4];

[0031] [Fig.6A] is a view of the inlet section of the purge hole in projection in a plane (R'C');

[0032] [Fig.6B] is a view of the inlet section of the purge hole in projection in a plane (R'X');

[0033] [Fig.6C] is a view of the inlet section of the purge hole in projection in a plane (X'C');

[0034] [Fig.7] is a schematic perspective view of an outlet section of the purge hole;

[0035] [Fig.7A] is a view of the outlet section of the purge hole in projection in a plane (R'C');

[0036] [Fig.7B] is a view of the outlet section of the purge hole in projection in a plane (R'X');

[0037] [Fig.7C] is a view of the outlet section of the purge hole in projection in a plane (X'C');

[0038] [Fig.8] is a view similar to [Fig.4], of an injection system according to a second embodiment of the invention, also capable of equipping the combustion chamber of [Fig.2];

[0039] [Fig.9] is a view similar to [Fig.5], of the injection system according to the second embodiment of the invention;

[0040] [Fig. 10] is a schematic perspective view of an inlet section of a purge hole belonging to the injection system of [Fig.8];

[0041] [Fig. 10A] is a view of the inlet section of the purge hole in projection in a plane (R'C');

[0042] [Fig. 10B] is a view of the inlet section of the purge hole in projection in a plane (R'X');

[0043] [Fig. 10C] is a view of the inlet section of the purge hole in projection in a plane (X'C');

[0044] [Fig. 11] is a schematic perspective view of an outlet section of the purge hole;

[0045] [Fig. 11 A] is a view of the outlet section of the purge hole projecting into a plan (R'C');

[0046] [Fig. 1 IB] is a view of the outlet section of the purge hole in projection in a plane (R'X');

[0047] [Fig. 1 IC] is a view of the outlet section of the purge hole in projection in a plane (X'C');

[0048] [Fig. 12] is a view similar to [Fig.4], of an injection system according to a third embodiment of the invention, also suitable for equipping the combustion chamber of [Fig.2];

[0049] [Fig. 13] is a view similar to [Fig.5], of the injection system according to the third embodiment of the invention;

[0050] [Fig. 14] is a schematic perspective view of an inlet section of a purge hole of a variant of the injection system of [Fig. 12];

[0051] [Fig. 14A] is a view of the inlet section of the purge hole in projection in a plane (R'C');

[0052] [Fig. 14B] is a view of the inlet section of the purge hole in projection in a plane (R'X');

[0053] [Fig. 14C] is a view of the inlet section of the purge hole in projection in a plane (X'C');

[0054] [Fig. 15] is a schematic perspective view of an outlet section of the purge hole;

[0055] [Fig. 15A] is a view of the outlet section of the purge hole in projection in a plane (R'C');

[0056] [Fig. 15B] is a view of the outlet section of the purge hole in projection in a plane (R'X');

[0057] [Fig. 15C] is a view of the outlet section of the purge hole in projection in a plane (X'C').

[0058] Throughout these figures, identical references may designate identical or similar elements. Detailed disclosure of preferred embodiments

[0059] [Fig.l] illustrates a turbomachine 10, for example a twin-spool, dual-flow turbojet for aircraft, generally comprising a fan 12 intended for the suction of an air flow F1 dividing downstream of the fan into a primary flow F2 circulating in a primary flow channel, hereinafter referred to as the primary flow path PV, and a secondary flow F3 circulating in a secondary flow channel, hereinafter referred to as the secondary flow path SV, arranged around the primary flow path PV.

[0060] By way of illustration, the turbomachine generally comprises a low pressure compressor 14, a high pressure compressor 16, a combustion chamber 18, a high pressure turbine 20 and a low pressure turbine 22 which jointly define the primary vein PV. The respective rotors of the high pressure compressor and the high pressure turbine are connected by a shaft called the "high pressure shaft", while the respective rotors of the low pressure compressor and the low pressure turbine are connected by a shaft called the "low pressure shaft", in a well-known manner. These rotors are rotatably mounted around an axis 28 of the turbomachine.

[0061] Throughout this description, the axial direction X is the direction of the axis 28. We also consider a first cylindrical coordinate system centered on the axis 28, in which a radial direction R is at all points orthogonal to the axis 28 and passes through the latter, while an ortho-radial or circumferential direction C is at all points orthogonal to the radial direction R and to the axis 28. A transverse plane is a plane orthogonal to the axis 28. The terms “internal” and “external” refer respectively to a relative proximity, and a relative distance, of an element with respect to the axis 28. Finally, the “upstream” and “downstream” directions are defined with reference to the general direction FD of the flow of gases in the primary PV and secondary SV veins of the turbomachine, in the axial direction X.

[0062] [Fig. 2] illustrates the combustion chamber 18 and its immediate surroundings, in a known configuration. Conventionally, this combustion chamber, which is of the annular type, comprises two coaxial annular walls, respectively radially internal 32 and radially external 34, which extend from upstream to downstream, in the aforementioned direction FD, around the axis of the combustion chamber which merges with the longitudinal axis 28 of the turbomachine. These radially internal 32 and radially external 34 annular walls are connected to each other at their upstream end by an annular chamber bottom wall 40, so that these walls externally delimit an interior volume V of the combustion chamber 18.

[0063] The annular chamber bottom wall 40 comprises passages distributed around the longitudinal axis 28 and through which are respectively mounted injection systems 42 configured to each deliver a layer of a mixture of air and fuel centered along a respective injection axis 44.

[0064] In addition, the combustion chamber is generally equipped with one or more spark plugs 45 mounted through the outer annular wall 34.

[0065] In operation, a portion 46 of an air flow 48 coming from a compressor such as the high-pressure compressor 16 supplies the injection systems 42 while another portion 50 of this air flow bypasses the combustion chamber by flowing downstream along the coaxial walls 32 and 34 of this chamber and allows, in certain cases, the supply of air inlet orifices provided within these walls 32 and 34.

[0066] As shown in [Fig. 3], each injection system 42 generally comprises, from upstream to downstream, a sleeve 52, sometimes called a “sliding feedthrough”, intended to receive a fuel injector nozzle 54 (visible in [Fig. 2] but not in [Fig. 3]), as well as one or more air intake swirlers 56, 58 (sometimes called “swirlers”), possibly separated from each other by a wall 59 with a radially internal end of convergent-divergent shape, commonly called a “venturi”, for injecting air into the injection system having a gyratory movement in a circumferential swirl direction SCI around the injection axis 44, and finally a bowl 60, sometimes called a “mixing bowl”, which essentially takes the form of a wall of revolution having a shape which diverges downstream. These elements are centered relative to the injection axis 44.

[0067] The present description refers to a second cylindrical coordinate system in which an axial direction X' is parallel to the injection axis 44 of an injection system considered, a radial direction R' is at all points orthogonal to the injection axis 44 and passes through the latter, while an ortho-radial or circumferential direction C' is at all points orthogonal to the radial direction R' and to the injection axis 44. In this context, a transverse plane is a plane orthogonal to the injection axis 44, and the terms "internal" and "external" respectively refer to a relative proximity, and a relative distance, of an element with respect to the injection axis 44.

[0068] Each of the swirlers 56, 58 comprises, in a well-known manner, fins 56A, 58A which delimit between them air channels, with respective axes oriented in directions each having a radial component and a circumferential component so as to give a swirling character to the air flow passing through the swirler.

[0069] The injection system illustrated in [Fig. 3] comprises two successive swirlers 56 and 58, both of the radial type, i.e. oriented transversely to the injection axis 44. In other words, the respective axes of the air channels defined between the fins of such swirlers are included in a plane transverse to the injection axis 44. The present disclosure is however also applicable to injection systems comprising one or more swirlers of the axial-radial type, i.e. in which the respective axes of the air channels extend in respective directions having an axial component and a radial component. Injection systems comprising both an axial-radial type swirler and a radial type swirler are also possible, as are injection systems comprising only a single swirler of the radial or axial-radial type.

[0070] In a manner known per se, the sleeve 52 comprises a downstream end wall 62 defining, on an upstream side of the injection system, an upstream external surface 62A of the latter, and on an opposite side, an upstream internal surface 62B delimiting upstream the air intake swirler 56 (at least a radially internal portion thereof). In addition, the downstream end wall 62 of the sleeve comprises purge holes 64 each having an inlet 64A opening through the upstream external surface 62A and an outlet 64B opening through the upstream internal surface 62B.

[0071] Such purge holes 64 are provided, in a known manner, to avoid or limit the risks of flame rising within the spiral 56 and the risks of coking along the walls delimiting the spiral.

[0072] As explained above, the present invention aims to optimize the purge holes in order to reduce the influence of the latter on the ignition performance, in particular in difficult conditions.

[0073] To describe such a purge hole 64, the present description refers to an inlet axis A1 of the purge hole as being an axis passing through a center CA of the inlet 64A of the purge hole, and having as its direction a direction tangent to the inner surface of the purge hole at the inlet 64A, averaged over the circumference of the inlet 64A. Similarly, an outlet axis A2 of the purge hole is an axis passing through a center CB of the outlet 64B of the purge hole, and having as its direction a direction tangent to the inner surface of the purge hole at the outlet 64B, averaged over the circumference of the outlet 64B. Furthermore, for the purposes of the present description, the inlet direction DI of such a purge hole is a Euclidean vector oriented from upstream to downstream having as its direction the direction of the inlet axis A1 of the purge hole and having an arbitrarily chosen norm.Similarly, the outlet direction D2 of such a purge hole is a Euclidean vector oriented from upstream to downstream having as its direction the direction of the outlet axis A2 of the purge hole and having an arbitrarily chosen norm.

[0074] Generally, the axial, circumferential and radial components of the inlet direction DI are defined by reference to the second cylindrical coordinate system taken at the center CA of the inlet 64A of a purge hole considered. Similarly, the axial, circumferential and radial components of the outlet direction D2 are defined by reference to the second cylindrical coordinate system, taken at the center CB of the outlet 64B of the purge hole considered.

[0075] Furthermore, the possible circumferential inclination of the inlet direction DI is the angle 0 or 01 between the axial direction X', defined at the center CA of the inlet 64A of the purge hole considered, and the orthogonal projection of the inlet direction DI in a local plane (X',C') passing through the center CA, as illustrated in FIGS. 6 and 6C, 10 and 10C, 14 and 14C. Similarly, the circumferential inclination of the outlet direction D2 is the angle 0 or 02 between the axial direction X', defined at the center CB of the outlet 64B of the purge hole considered, and the orthogonal projection of the exit direction D2 in a local plane (X',C') passing through the center CB, as illustrated in Figures 7 and 7C, 11 and 11C, 15 and 15C. A circumferential inclination 0 between 0 and 90 degrees thus results in a circumferentially inclined direction in the same direction as the circumferential spin direction SCI.

[0076] Finally, the possible radial inclination of the inlet direction DI is the angle [3 or [31 between the axial direction X', defined at the center CA of the inlet 64A of the purge hole considered, and the orthogonal projection of the inlet direction DI in a local plane (R',X') passing through the center CA, as illustrated in Figures 10 and 10B, 14 and 14B. Similarly, the possible radial inclination of the outlet direction D2 is the angle [3 or [32 between the axial direction X', defined at the center CB of the outlet 64B of the purge hole considered, and the orthogonal projection of the outlet direction D2 in a local plane (R',X') passing through the center CB, as illustrated in Figures 11 and 11B, 15 and 15B. A radial inclination [3 between 0 and 90 degrees thus results in an orientation inclined radially inwards, that is to say in the direction of the injection axis 44.

[0077] In the prior art corresponding to the injection system visible in [Fig. 3], such purge holes 64 are oriented purely axially in the second cylindrical coordinate system. Such purge holes known from the prior art are thus cylindrical in shape and have inlet axes A1 and outlet axes A2 which are coincident, parallel to the injection axis 44.

[0078] The invention provides, in general, that at least the outlet direction D2 of the purge holes 64 has a circumferential inclination in the same direction as the circumferential swirl direction SCI. The purge holes 64 are thus configured for co-rotating air injection with the air from the air intake swirl 56 adjacent to the downstream end wall 62 of the sleeve 52. The purge holes thus contribute to the “swirl number” within the injection system, the “swirl number” being, as a person skilled in the art knows, a parameter representative of the ratio of the quantities of movement of the air, respectively in the circumferential direction C', and in the direction X' of the injection axis 44. The reduction in the swirl number due to the air from the purge holes 64 is thus limited.In this way, the purge function, i.e. protection against coking and flame rise, can be achieved without this being to the detriment of the flame stability and the ignition performance of the combustion chamber.

[0079] Of course, the purge holes 64 being defined through the downstream end wall 62, their inlet DI and outlet D2 directions necessarily have a non-zero axial component.

[0080] In the first and second embodiments described with reference to FIGS. 4 to 1 IC, the purge holes 64 are each cylindrical in shape, whereby the axis inlet axis Al and outlet axis A2 of each purge hole are the same. The same is obviously true for the inlet directions DI and outlet directions D2.

[0081] More precisely, in the first embodiment (Figures 4 to 7C), the output direction D2 has a zero radial component.

[0082] The circumferential inclination 0 of the outlet direction D2 is preferably between 5 and 80 degrees. In other words, the ratio between the tangential component and the axial component of the outlet direction D2 is preferably between 0.1 and 6. In preferred embodiments, the circumferential inclination 0 of the outlet direction D2 is between 5 and 60 degrees.

[0083] The second embodiment (figures 8 to 1 IC) differs from the first embodiment in that the outlet direction D2 has a negative (non-zero) radial component, whereby the purge holes 64 are inclined radially inwards in the downstream direction.

[0084] The radial inclination [3 of the output direction D2 is preferably less than 80 degrees. In other words, the ratio between the radial component and the axial component of the output direction D2 is preferably less than 6.

[0085] In this second embodiment, the circumferential inclination of the outlet direction D2 is preferably still between 5 and 80 degrees, for example between 5 and 60 degrees. As in the first embodiment, the ratio between the tangential component and the axial component of the outlet direction D2 is thus also between 0.1 and 6.

[0086] Finally, in the third embodiment (FIGS. 12 to 15C), each purge hole 64 is of curved shape, so that the circumferential component of the inlet direction DI has an absolute value lower than the absolute value of the circumferential component of the outlet direction D2, for each purge hole 64. In other words, the inlet axis A1 is less inclined in the circumferential direction than the outlet axis A2, and the circumferential inclination 01 of the inlet direction DI is thus less than the circumferential inclination 02 of the outlet direction D2.

[0087] Such a geometric property of the purge holes 64 makes it possible to maximize the pressure of the air ingested by the purge holes by making the best use of the dynamic pressure of the air flow which circulates downstream and feeds the purge holes, and to minimize the pressure losses, while producing an effect similar to that of the other embodiments in terms of rotating the air ejected by the purge holes.

[0088] Thus, in the example illustrated by figures 12 and 13, the circumferential inclination of the entry direction DI is zero.

[0089] In embodiments, the input direction DI further has a radial component of absolute value less than the absolute value of the component radial of the outlet direction D2, for each purge hole 64. Thus, the inlet axis A1 is also less inclined radially inwards than is the outlet axis A2, and the radial inclination [31 of the inlet direction DI is thus less than the radial inclination [32 of the outlet direction D2.

[0090] Thus, in the example illustrated by figures 12 and 13, the radial inclination of the entry direction DI is zero.

[0091] Figures 14 to 15C relate to a variant of the third embodiment, in which the radial inclination [31 of the input direction DI is non-zero, for illustration purposes.

Claims

Claims

1. Injection system for injecting a mixture of air and fuel into a turbomachine combustion chamber, comprising a sleeve (52) for receiving a fuel injector nozzle, a bowl (60), and at least one air intake swirler (56) arranged axially between the sleeve (52) and the bowl (60) for injecting air into the injection system having a rotating movement in a circumferential swirl direction (SCI) around an injection axis (44) of the injection system, wherein the sleeve comprises a downstream end wall (62) defining, on an upstream side of the injection system, an upstream external surface (62A) thereof, and on an opposite side, an upstream internal surface (62B) delimiting upstream said air intake swirler (56),and wherein said downstream end wall (62) comprises purge holes (64) each having an inlet (64A) opening through said upstream external surface (62A) and an outlet (64B) opening through said upstream internal surface (62B), wherein said inlet (64A) has an inlet axis (A1) oriented in an inlet direction (D1), and said outlet (64B) has an outlet axis (A2) oriented in an outlet direction (D2), characterized in that at least the outlet direction (D2) has a circumferential inclination (0.02), defined by reference to a cylindrical coordinate system centered on the injection axis (44), and in the same direction as said circumferential spin direction (SCI).,

2. Injection system according to claim 1, wherein the outlet direction (D2) has a radial inclination (|3, [32) towards the injection axis (44).

3. Injection system according to claim 1, wherein the outlet direction (D2) is orthogonal to the radial direction (R') of said cylindrical coordinate system.

4. An injection system according to any one of claims 1 to 3, wherein each purge hole (64) is cylindrical in shape, whereby the inlet axis (A1) and the outlet axis (A2) of each purge hole (64) coincide.

5. An injection system according to any one of claims 1 to 3, wherein each purge hole (64) is curved in shape, such that the inlet direction (D1) has a circumferential inclination (01), defined by reference to said cylindrical coordinate system, less than the circumferential inclination (02) of the outlet direction (D2), for each purge hole (64).

6. An injection system according to claim 5, wherein the circumferential inclination (01) of the inlet direction (Dl) is zero.

7. Injection system according to claim 5 or 6, in which the inlet direction (D1) has a radial inclination ([31), defined by reference to said cylindrical coordinate system, less than or equal to the radial inclination ([32) of the outlet direction (D2), for each purge hole (64).

8. Injection system according to claim 7, wherein the radial inclination ([31) of the inlet direction (Dl) is zero.

9. Turbomachine for aircraft, comprising a combustion chamber (16) and at least one injection system (42) according to any one of claims 1 to 8 for supplying the combustion chamber with a mixture of air and fuel.

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