Abstract: A fuel-air mixer includes an annular shroud, inner and outer counter-rotating swirlers, a hub separating the inner and outer swirlers, a center body extending axially along the annular shroud, a fuel shroud disposed radially outwardly from the outer swirler circumferentially around the annular shroud, and a radial swirler disposed downstream of the inner and outer swirlers, the radial swirler being configured to allow an independent radial rotation of a second gas stream entering the annular shroud from a region outside a wall of the annular shroud separately from a stream flowing through the inner and outer swirlers, the radially rotating second gas stream entering the annular shroud at a region adjacent an outer wall of the annular shroud.

Abstract: A combustor for a gas turbine engine is disclosed which is able to operate with high combustion efficiency, and low nitrous oxide emissions during gas turbine operations. The combustor consists of a can-type configuration which combusts fuel premixed with air and delivers the hot gases to a turbine. Fuel is premixed with air through a swirler and is delivered to the combustor with a high degree of swirl motion about a central axis. This swirling mixture of reactants is conveyed downstream through a flow path that expands; the mixture reacts, and establishes an upstream central recirculation flow along the central axis. A cooling assembly is located on the swirler co-linear with the central axis in which cooler air is conveyed into the prechamber between the recirculation flow and the swirler surface.

Abstract: An air blast fuel injector for a gas turbine engine includes an elongate feed arm having an inlet fitting for receiving fuel and for distributing the fuel to first and second fuel delivery conduits extending through the feed arm. A nozzle body is operatively connected to the feed arm. The nozzle body includes an on-axis inner air circuit and fuel circuitry radially outboard of the inner air circuit for delivering fuel to a fuel swirler outboard of the inner air circuit. The fuel circuitry includes a first fuel circuit configured and adapted to deliver fuel to the fuel swirler from the first fuel conduit of the feed arm and a second fuel circuit configured and adapted to deliver fuel to the fuel swirler from the second fuel conduit of the feed arm.

Abstract: A combustor (10) including: a first premix main burner (14) comprising a first swirler airfoil section (38); a second premix main burner (15) comprising a second swirler airfoil section (40); and a supply air reversing region upstream of the premix burners (14), (15). The first swirler airfoil section (38) and the second swirler airfoil section (40) are effective to impart swirl to a first airflow and a second airflow characterized by a same swirl number as the airflows exit respective burners (14), (15). The combustor (10) is effective to generate a first airflow volume through the first premix main burner (14) that is different than a second airflow volume through the second premix main burner (15).

Abstract: Embodiments for an apparatus and associated method for reducing the residence time in a gas turbine combustor are disclosed. The embodiments of the present invention comprise a fuel nozzle that extends to a downstream plane of an end cap for a combustion liner where the axial distance of the premixer is reduced, however the swirl for mixing the fuel and air, is increased. As a result, the mixing of the fuel and air is essentially unchanged, thereby allowing higher air pressures and operating temperatures within the premixer without inducing auto-ignition.

Abstract: A fuel mixture is fed to a gas turbine combustor by an injection assembly, which has an outer body with combustion-supporting air inlets; a conical tubular portion housed inside the outer body and partly defining an inner conduit and an outer annular conduit; and a first and second feed circuit for feeding liquid fuel to the inner conduit and outer annular conduit respectively; the first circuit having a ring of conduits with respective axes parallel to a generating line of an outer surface of the conical tubular portion.

Abstract: A dual fuel nozzle for a gas turbine combustor includes a hub defining a fuel inlet and a plurality of liquid fuel jets disposed at a downstream end of the hub. The fuel jets are oriented to eject liquid fuel radially outward from the hub. An annular air passage includes a swirler that imparts swirl to air flowing in the annular air passage, and a splitter ring is disposed in the annular air passage and surrounds the plurality of liquid fuel jets. The nozzle allows liquid fuels to be injected into a swirling annular airstream and then atomized, dispersed and vaporized inside a lean premixing dual fuel nozzle for a gas turbine combustor.

Abstract: A premixed combustion burner for a gas turbine can efficiently premix fuel and air to produce fuel gas having a uniform concentration, while reliably achieving prevention of flash back by making the flow rate of fuel gas substantially uniform. The premixed combustion burner for a gas turbine has a fuel nozzle, a burner cylinder arranged so as to surround the fuel nozzle and form an air passageway between itself and the fuel nozzle, and swirler vanes that are arranged along an axial direction of the fuel nozzle in a plurality of positions around the circumferential direction of an outer circumference surface of the fuel nozzle. The swirler vanes gradually curve from an upstream side to a downstream side to spin the air traveling within the air passageway from the upstream side to the downstream side. A cutaway section is provided in a rear edge section on an inner circumference side of the swirler vanes.

Abstract: A mixer having a unitary construction is disclosed comprising an annular housing having an axis and at least a first swirler having a plurality of vanes arranged circumferentially around the axis such that circumferentially adjacent vanes form at least one flow passage that is oriented at least partially in an axial direction with respect to the axis. In another exemplary embodiment, a mixer having a unitary construction is disclosed comprising a swirler having a plurality of radial vanes arranged circumferentially around the axis and oriented at least partially in a radial direction.

Abstract: A turbomachine includes a compressor, a turbine, a combustor operatively coupled to the compressor and the turbine, and an injection nozzle assembly mounted in the combustor. The injection nozzle assembly includes a swirler member for conditioning a fluid flow passing through the injection nozzle assembly. The swirler member includes a hub portion, a plurality of vanes that extend from the hub portion, and at least one flow conditioning band. The at least one flow conditioning band extends about the hub portion and between the plurality of vanes to provide a localized flow impediment within the injection nozzle assembly.

Abstract: A combustor comprises a liquid fuel nozzle for injecting liquid fuel to a combustion chamber, and an air supply nozzle disposed around the liquid fuel nozzle and injecting air. The air supply nozzle is disposed such that air is injected from the air supply nozzle in a direction toward an axis of the liquid fuel nozzle. A space is formed around an outlet of the liquid fuel nozzle, through which the liquid fuel is injected from the liquid fuel nozzle to the combustion chamber, upstream of a distal end of the outlet in a direction in which the liquid fuel is injected. Carbonaceous deposits on surrounding surfaces of the outlet of the liquid fuel nozzle can be suppressed regardless of the operating conditions of a combustor.

Abstract: A fuel nozzle for a turbine is disclosed. The fuel nozzle includes a housing, a plurality of fuel passages disposed within the housing, and a plurality of air passages disposed within the housing. A total flow area of the plurality of fuel passages is substantially equal to a total flow area of the plurality of air passages.

Abstract: A fuel injector including a peripheral atomisation system having a plurality of fuel ejection orifices distributed at regular intervals along the circumference and an annular air eddy deflector. The deflector includes air ejection channels such that, for each fuel ejection axis defined by an ejection orifice, there is a corresponding air ejection channel of which at least the radially most internal part has a median substantially intersecting this fuel ejection axis.

Abstract: A fuel nozzle including a nozzle tube and a nozzle outlet opening is provided. The nozzle tube is connected to a fuel feed line for feeding a fuel to the nozzle tube, wherein the fuel is fed from the nozzle outlet opening to an annular air stream surrounding the fuel nozzle, wherein a first nozzle tube section that extends up to the nozzle outlet opening is designed in a floral pattern in such a way that the fuel may be fed substantially coaxially into the air stream.

Abstract: A nozzle includes a center body and a shroud circumferentially surrounding at least a portion of the center body to define an annular passage between the center body and the shroud. The nozzle further includes a bimetallic guide between the center body and the shroud. A method for supplying fuel to a combustor includes flowing a working fluid through a nozzle, injecting the fuel into the nozzle, and mixing the fuel with the working fluid to create a fuel and working fluid mixture. The method further includes swirling the fuel and working fluid mixture, sensing flame holding in the nozzle, and reducing the swirl in the fuel and working fluid mixture.

Abstract: A method of operating a combustor includes delivering a primary fuel flow through a plurality of primary fuel nozzles toward a primary combustion zone and combusting the primary fuel flow in the primary combustion zone. A secondary fuel flow is delivered through a secondary fuel nozzle toward a secondary combustion zone and combusted therein. The secondary fuel is located such that the plurality of primary fuel nozzles are arrayed around the secondary fuel nozzle. An outer swirler is located between the plurality of primary fuel nozzles and the secondary fuel nozzle and includes a plurality of outer swirler channels extending therethrough. A flow of swirler fuel is delivered through the plurality of outer swirler channels into the combustor substantially between the primary combustion zone and the secondary combustion zone to stabilize combustion in the primary combustion zone and/or the secondary combustion zone.

Abstract: A combustor includes a first combustion chamber, a pre-mixing primary fuel-nozzle assembly associated with the first combustion chamber, a second combustion chamber, and a secondary fuel-nozzle assembly associated with the second combustion chamber. The pre-mixing primary fuel-nozzle assembly includes a number of vanes configured to swirl airflow, each vane comprising a number of fuel injection holes configured to inject fuel into the airflow.

Abstract: A fuel injector nozzle for dispensing fuel in the combustion chamber of a gas turbine engine, comprises a fluid feed conduit having at least one internal channel for the passage of fluid from an inlet end to an outlet end of the fluid feed conduit. The fluid feed conduit has a first annular segment receiving fluid from the inlet end and a second annular segment fluidly connected to receive fluid from the first annular segment at a junction having a circumferential length less than the circumferential lengths of the first and second annular segments. The second annular segment includes fluid dispensing openings to dispense fluid from the conduit, and the first and second annular segments are coaxial and axially separated for relative movement over a major portion of the second segment to accommodate differential thermal expansion.

Abstract: A fuel injector for injecting fuel into a turbomachine combustion chamber, the injector presenting an injector nose for connection to an injection system fastened to the end wall of said combustion chamber, the injector nose comprising: a first channel for passing a flow of an air/fuel pre-mixture towards the combustion chamber, the first channel opening out into the center of the injector nose via an outlet opening for the air/fuel pre-mixture; an electrical insulator surrounding said outlet opening for the air/fuel pre-mixture; a plasma generator system disposed inside said electrical insulation and downstream from said outlet opening for the air/fuel pre-mixture in order to control ignition and combustion of the air/fuel pre-mixture; a second channel for passing a flow of fuel towards the combustion chamber, the second channel opening out outside said electrical insulation; and a third channel for passing a flow of fuel towards the combustion chamber, this third channel opening out outside the second ch

Abstract: A gas turbine fuel injector includes a nozzle body having a radially inner wall proximate to an internal air path and a radially outer wall. An insulative gap is defined between the radially inner and outer walls. The inner and outer walls are adapted and configured for relative axial movement at a first interface. An inhibitor ring is disposed proximate a downstream end of the inner wall for discouraging fuel from entering the insulative gap. A second interface is formed between the downstream end of the inner wall and an upstream end of the inhibitor ring to accommodate relative axial movement of the inner and outer walls.

Abstract: A fuel injector for a gas turbine engine of an aircraft, and more particularly a novel and unique heatshield structure for a fuel nozzle wherein a labyrinth seal is uniquely provided in the nozzle to isolate a portion of an insulating gap from an interface whereat fuel may enter the insulating gap, and the insulating gap is provided with a positive purge flow for forcing vapors out of the insulating gap.

Abstract: A burner and a method for operating a burner are provided. The burner includes a channel having a mixing zone and having a feed for an oxidation means, particularly an air feed, and at least one fuel feed for injecting fuel, wherein a separating means which divides the channel over a wide range of the channel into at least two separated channels, namely a first channel and a second channel, is provided in the channel. The method for operating a burner having a channel includes a mixing zone into which an oxidation mass flow and fuel are injected, wherein two substantially separate flow paths are formed by means of a separating means in the channel and the at least two separated first and second channels, formed by the separating means.

Abstract: A turbomachine includes a compressor, a turbine, a combustor operatively coupled to the compressor and the turbine, and an injection nozzle assembly mounted in the combustor. The injection nozzle assembly includes a swirler member provided with a hub portion having an internal surface. The injection nozzle assembly also includes a nozzle section, and a nozzle tip member fluidly coupled to the nozzle section and the swirler member. The nozzle tip member includes a body having a first end section that extends from the nozzle section to a second end section arranged in the hub portion of the swirler member. The nozzle tip member includes an external surface, and a discharge port. At least one of the external surface of the nozzle tip member and the internal surface of the swirler member hub portion is provided with a plurality of grooves.

Abstract: A combustor with a burner maintains combustion stability. The burner includes an air hole member 31 with a plurality of air holes 34, 35 provided at an upstream side of the combustion gases generated by a combustion chamber 1. A first fueling nozzle 33 jets fuel in a direction crossing a central axis of the burner towards at least two of air holes 35. A plurality of second fueling nozzles 32, one for each of the remaining air holes 34, are provided to jet the fuel in a direction routed along the burner axis towards the corresponding air hole 34. A fuel header 30 distributes the fuel to the first fueling nozzle 33 and each of the second fueling nozzles 32. A fuel header storage unit 70 shrouds the fuel header 30, fueling nozzles 32, 33, and has an air inflow hole 71.

Abstract: Embodiments of the present invention include a unique gas turbine engine and a unique dome panel assembly for a gas turbine engine combustor. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for gas turbine engines, gas turbine engine combustor systems and dome panel assemblies for gas turbine engine combustion system. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith.

Abstract: A gas turbine engine combustor includes a plurality of main fuel injector assemblies, and a plurality of pilot fuel injector assemblies, that are arranged and configured to reduce exhaust gas emissions during engine operation. The plurality of main fuel injector assemblies are arranged in a substantially circular pattern of a first radius, and each includes an outlet port having a first divergence angle. The plurality of pilot fuel injector assemblies are arranged in a substantially circular pattern of a second radius. Each pilot fuel injector assembly is disposed between at least two main fuel injector assemblies, and each includes an outlet port having a second divergence angle.

Abstract: A nozzle for channeling a fluid into a combustor assembly. The nozzle includes a body including a centerline, a first passageway extending through the body along the centerline, and a nozzle tip coupled to a downstream end of the first passageway. The nozzle tip has a radius extending from a center of the nozzle tip to an outer surface of the nozzle tip. The nozzle tip includes a downstream face, and a plurality of outlet passageways that each include an opening defined in the downstream face. Each opening includes respective X-, Y-, and Z-axes defined with respect to a tangent line, the radius, and the centerline. Each of the plurality of outlet passageways is at discharge angle of greater than 30° measured with respect to the respective Z-axis in a respective X-Z plane.

Abstract: A swirler for mixing fuel and air is provided. The swirler includes a plurality of vanes arranged on a reference circle diameter which, together with a first longitudinal end face of the vanes disposed on a first wall and a second wall disposed on an opposing second longitudinal end face of the vanes, form a flow channel. In this arrangement at least one injection orifice in the first wall and at least one further injection orifice in the second wall open into a flow channel. The arrangement of the at least two mutually opposing injection orifices in the wall of the swirler makes for a homogeneous distribution of the fuel in the flow channel and ensures a uniform mixing of the air with the fuel. This results in uniform and low-NOx combustion of the fuel/air mixture in a burner.

Abstract: Electric fields control an electric combustion. Plasmas are created by a dielectrically impeded discharge. At least one part of the fuel is mixed with water vapor in the supply line and is subjected to a plasma discharge in a compact reactor that is in close contact with the burner in terms of reaction kinetics. In the associated device, a plasma reactor for creating a reactive plasma gas with at least one supply line for the fuel gas-water vapor mixture and an electric energy supply is integrated into the burner. The device provides suitable flow guidance of the fuel gas-air mixture, of the fuel gas-water vapor mixture, and of the reactive plasma gas.

Abstract: A pilot combustor particularly for use in a burner of a gas turbine engine is provided. A method for burning a fuel in a pilot combustor zone of a pilot combustor is also provided. The pilot combustor includes rotationally symmetric walls defining a combustion room with an exit having a rich concentration of fuel in air for burning the fuel for the creation of a flow of an non equilibrium unquenched concentration of radicals elevated to a temperature above 2000 K in the combustion room and directed along a centre line of the pilot combustor through a throat at the exit of the pilot combustor, wherein a quarl is located downstream of the throat of the pilot combustor. According to the method the pilot combustor is arranged upstream of a burner for providing a main lean partially premixed combustion process.

Abstract: A fuel injector system for injecting fuel into a turbomachine combustion chamber, the system comprising first and second fuel injectors wherein the first injector (22) is positioned in the center of the injector system (20) so as to inject a first fuel spray (42), and wherein the second injector (28) surrounds the first injector in such a manner as to inject a second fuel spray (48) of generally annular shape around the first fuel spray. The injector system further comprises an air admission duct (22) with outlet orifices (62) opening out between the first and second injectors so as to create a separator air film (f1) between the respective combustion zones of the first and second fuel sprays.

Abstract: A method of assembling a fuel nozzle assembly for a gas turbine engine having a natural operating frequency includes providing a flange and providing a premix tube. The flange is fabricated from a first alloy such that the flange is configured to exhibit a first frequency that is different than the natural operating frequency of the gas turbine engine. The premix tube is fabricated from a second alloy such that the premix tube is configured to exhibit a second frequency that is different from the natural operating frequency of the gas turbine engine. The premix tube is coupled to the flange.

Abstract: A combustion device includes: a combustion liner in which a combustion chamber is formed; a main burner provided at a top portion of the combustion liner and including a premix passage configured to annularly inject a pre-mixed gas of a fuel and air into the combustion chamber and a radial swirler configured to introduce the fuel and the air to the premix passage in a radially inward direction; and a fuel injection pipe configured to inject the fuel to the radial swirler from an entrance side of the radial swirler, and the radial swirler is divided into a plurality of swirler stages by dividing plates in an axial direction.

Abstract: A swirl generator for injecting fuel into a gas turbine by injection of the fuel into a channel of the swirl generator of the gas turbine. The fuel injection is predetermined by the arrangement of a fuel injecting insert in a swirl generator segment.

Abstract: An air-blast fuel injector is disclosed which includes an outer air circuit having an exit portion, an inner air circuit having an outlet configured to direct air toward the exit portion of the outer air circuit, and a fuel circuit radially outboard of the inner air circuit and having an exit communicating with the outer air circuit upstream from the exit portion of the outer air circuit.

Abstract: A device for injecting an air/fuel mixture into a combustion chamber mounted within a restricted space is disclosed. This injection device includes a bowl having an external cylindrical wall continued at its downstream end by a divergent section provided, downstream, with a collar having the form of a ring extending radially outward. The divergent section of the bowl is connected, immediately upstream of the flange, by a connecting wall to a cylindrical ring. The cylindrical ring and the connecting wall form a connection rim oriented in the upstream direction. At least one row of vortex holes is formed in the external cylindrical wall, close to its upstream end, and the connecting wall of the connection rim of the bowl is provided with a row of cooling orifices inclined axially at an angle ? to the axis of symmetry of the injection device.

Abstract: A fuel injector for a gas turbine includes an outer air path having a converging exit portion, and a fuel path inboard of the outer air path. An inner air path inboard of the fuel path includes an outer wall having a converging exit region and surrounds an axial core duct defining an axial air path having a diverging exit region. The inner air path creates a pressure drop near a fuel injection opening to promote mixing and atomization of fuel over a range of power levels, including low power operation.

Abstract: A fuel spraying apparatus of a gas turbine engine includes a first fuel spraying section configured to spray fuel for diffusion combustion and a second fuel spraying section configured to spray fuel for premixed combustion. The second fuel spraying section is disposed so as to surround the first fuel spraying section. The apparatus further includes an air curtain generating section disposed between the first fuel spraying section and the second fuel spraying section. The air curtain generating section is configured to generate an air curtain which defines an outer edge of a diffusion combustion area in a combustion chamber.

Abstract: A burner arrangement includes a tubular mixing tube extending along an axis and configured to mix fuel and air, the mixing tube opening into a combustion chamber in a direction of flow; and a film air ring disposed in the mixing tube and arranged concentrically to the axis, the film air ring configured to prevent a backfiring of the fuel disposed in the mixing tube and to generate or reinforce an air film near the wall, wherein the film air ring has at least one annular gap concentric to the axis and configured to inject air.

Abstract: An airblast fuel injector for the combustor of a gas turbine engine has, in order from radially inner to outer, a coaxial arrangement of an inner swirler passage, an annular fuel passage, an annular mid swirler passage, and an annular outer swirler passage. The fuel passage extends to a prefilming lip, and the inner and mid swirler passages swirl air past the prefilming lip so that fuel fed from the fuel passage to the prefilming lip is entrained by the swirling air into a fuel spray stream. The outer swirler passage has a convergent portion. The radially inward wall of said convergent portion is defined by a frustoconical separator element which separates the outer swirler passage from the mid swirler passage, the separator element converging in the direction of air flow to terminate in a lip at the mouths of the mid swirler passage and the outer swirler passage.

Abstract: A burner 1 for combustion chamber is provided with a cylindrical mixing portion 3 that mixes air for combustion (oxidizing agent) and fuel in the interior thereof and has one end 3a that opens to a combustion portion 2; a spray nozzle (fuel spraying portion) 5 that sprays fuel in the mixing portion 3, being disposed on another end 3b of the mixing portion 3; first blowing ports 6 that introduce the air for combustion to the mixing portion 3 to form a swirling flow with the fuel, being disposed to open to the inner wall of the mixing portion 3; and second blowing ports 7 that additionally introduce the air for combustion to the mixing portion 3, opening in a direction different from the first blowing ports 6 and being disposed further to the other end 3b side of the mixing portion 3 than the swirling flow.

Abstract: A fuel injector for a gas turbine engine includes a nozzle body defining a central axis and having a main fuel circuit. An air circuit is formed within the nozzle body inboard of the main fuel circuit. A primary pilot fuel circuit is formed within the nozzle body inboard of the air circuit. A secondary pilot fuel circuit is formed within the nozzle body inboard of the air circuit and outboard of the primary pilot fuel circuit.

Abstract: A device for injecting a mixture of air and fuel into a combustion chamber of a turbomachine is disclosed. The injection device includes a novel sliding bushing and a novel annular cup for retaining the sliding bushing, making it possible to improve the air feed of the injection device.

Abstract: A combustor nozzle is provided. The combustor nozzle includes a first fuel system configured to introduce a syngas fuel into a combustion chamber to enable lean premixed combustion within the combustion chamber and a second fuel system configured to introduce the syngas fuel, or a hydrocarbon fuel, or diluents, or combinations thereof into the combustion chamber to enable diffusion combustion within the combustion chamber.

Abstract: The present application thus provides a combustor. The combustor may include an interior flow path therethrough, a number of nozzles in communication with the interior flow path, and an inlet guide vane system positioned about the interior flow path to create a swirled flow therein.

Abstract: A method for operating a gas turbine engine including a compressor and a combustor is provided. The method comprises channeling between about 0% to about 8% of the total airflow discharged from a compressor towards a pilot swirler coupled within the burner, wherein the burner includes a main swirler and an annular centerbody extending between the pilot and main swirlers, injecting a portion of the total fuel flow supplied to the burner through a plurality of apertures defined in a hollow pilot centerbody coupled within the pilot swirler, channeling the remaining airflow discharged from the compressor towards the main swirler, and injecting the remaining fuel flow supplied to the burner through at least one main swirler vane coupled within the main swirler, such that the portion of fuel is pre-mixed with a portion of the total airflow.

Abstract: A fuel nozzle air swirler assembly has a slotted cap to provide stress-relief. The stress-relief slits in the cap have an axial and a tangential component to impart a swirl to the air leaking therethrough in the same direction as that of the air exiting the swirler body.

Abstract: In a multimode fuel injector for combustion chambers, in particular a jet engine, a secondary circuit is connected to a distribution chamber perforated by a plurality of fuel ejection orifices and the primary circuit comprises at least one passage section adjacent the distribution chamber, for its cooling.

Abstract: A combustor comprises a liquid fuel nozzle for injecting liquid fuel to a combustion chamber, and an air supply nozzle disposed around the liquid fuel nozzle and injecting air. The air supply nozzle is disposed such that air is injected from the air supply nozzle in a direction toward an axis of the liquid fuel nozzle. A space is formed around an outlet of the liquid fuel nozzle, through which the liquid fuel is injected from the liquid fuel nozzle to the combustion chamber, upstream of a distal end of the outlet in a direction in which the liquid fuel is injected. Carbonaceous deposits on surrounding surfaces of the outlet of the liquid fuel nozzle can be suppressed regardless of the operating conditions of a combustor.

Abstract: A combustion chamber of a turbomachine is disclosed. The combustion chamber includes at least one bowl with a substantially frustoconical wall that is formed with an annular row of air injection orifices and a fuel injector arranged upstream of the bowl. The annular row of air injection orifices includes smaller-diameter orifices and larger-diameter orifices which are arranged in alternating fashion and with a uniform distribution around the axis of the bowl to produce two annular air/fuel mixture layers.