US3498055A - Smoke reduction combustion chamber - Google Patents

Description

March 1970 J. J. FAITANI ETA!- SMOKE REDUCTION COMBUSTION CHAMBER 2 Sheets-Sheet 1 Filed Oct. 16, 1968 INVENTORS JOSEPH J. FAITANI WILLIAM w. mn-zczxowsm, BY Q AGENT March 3, 1970 J.- J. FAITAN! ETAL 3,498,055

suoim REDUGTION couabsziron I CHAMBER Filed on. 16, 1968 r 2 Sheets-Sheet 2 FIG. 2

United States Patent US. Cl. 6039.06 14 Claims ABSTRACT OF THE DISCLOSURE A combustion chamber either an annular or can-annular type, which substantially elimnates the production of smoke while maintaining all other performance parameters of the combustion chamber. The combustion chamber is provided with a front end configuration which sub stantially eliminates local fuel rich regions and which provides a means for mixing the incoming fuel and air.

BACKGROUND OF THE INVENTION The present invention relates to combustion chambers and more particularly to any type combustion chamber for a gas turbine engine, the construction of the combustion chamber being such that the fuel-air mixture is combusted in such a manner that the formation of carbon, and hence visible smoke emission is markedly reduced. This smoke reduction is accomplished while maintaining all other combustion chamber performance parameters, such as combustion efficiency, combustion stability, altitude ignition, and durability.

As background, it is well known that a combustion chamber for use in a gas turbine must possess certain characteristics in order to satisfactorily perform its function, and this is particularly true of a gas turbine engine employed in a jet aircraft. The combustion chamber must be capable of easy start-up at ground level through a range of ambient air temperatures representing cold and hot weather conditions, that is, low fuel flows and short ignition delay time so as not to result in an explosive or hot start. In the case of a can-annular type burner which will be the type burner primarily discussed herein, after ignition of the fuel-air mixture in the burners that are equiped with spark igniters or some other ignition source, the flame must propagate to adjacent burners for a full light off and then accelerate to idle speed. The combustor must also have the capability of good stability limits, that is, operate satisfactorily at fuel-air ratios below and above the normal idle and rated thrust fuelair ratios in order to insure that during transient conditions, such as acceleration and deceleration operational modes which can result in off-design fuel-air ratio levels, the burners will not flame out. An additional characteristic that the combustion chamber must have is that it must be capable of altitude ignition over a wide flight speed and altitude range without causing compressor stall or other penalties which would prevent the engine from being brought up to idle speed. Additionally, the combustion chamber, after reaching idle speed, must have the capability of being accelerated to higher power settings, and this must be accomplished in a relatively short time, normally within seconds. The combustion chamber must also have the capability of producing a satisfactory discharge temperature pattern or be capable of alteration to result in such a pattern without detrimental effect on the previously mentioned performance parameters, in order to achieve long life of parts receiving the hot discharge gases from the burner. Finally, the combustion chamber must provide an atmosphere of combustion Patented Mar. 3, 1970 wherein the fuel-air mixture when combusted does not result in the emission of visible smoke from the engine. Whlle many of the elements employed in the present Invention are described in the prior art, for example, the Johnson patent, US. Patent No. 3,134,229, the Schiefer patent, US. Patent No. 2,974,485, the Pianko patent, US. Patent No. 3,352,106 and the Bachle patent US. Patent No. 3,018,625, it is pointed out that none of these particular references or the prior art in general solves the particular problem as the present invention does. As hereinbefore noted, in order to provide an acceptable combustion chamber for use in a gas turbine engine, it s necessary to maintain the performance parameters herembefore mentioned. Smoke emission has been a problem which the prior atr combustion chamber constructions have accepted so as not to penalize or adversely affect these performance parameters. The present invention does not accept smoke emission and substantially eliminates smoke emission without any penalty to the performance parameters hereinbefore mentioned.

SUMMARY OF THE INVENTION It is a primary object of the present invention to pro vide a combustion chamber which substantially eliminates smoke emission therefrom and which provides a combustion chamber which maintains the overall performance parameters which are acceptable for use in a gas turbine engine.

In general, the present day prior art gas turbine combustion chambers operate at lean overall fuel-air ratios, which are below the flammability limits of most normally used fuels. Therefore, in order to burn the incoming fuel and air, a region in the burner must be provided in which the fuel is mixed with the correct portion of air in order to initiate and sustain combustion over a wide range of operating conditions. This is normally done by controllng the airflow distribution into the burner as a function of burner length. Incoming air is therefore divided into primary air and secondary air, and the manner of injection, location and amount of primary air used, in large part, controls the smoke formation characteristics of a combustion chamber and is the main object of this invention. It is a main objective of this invention to control this effect.

As hereinbefore stated, a combustion chamber for a jet engine used in aircraft propulsion must possess acceptable stability and altitude ignition characteristics. Normally, in prior art combustion chambers, this is accomplished by setting up a Zone of recirculation in the front end of the burner in which all of the fuel is mixed with only a portion of the total airflow. This zone is one of low axial velocity, and the large stable recirculation eddies formed in this region result in excellent burner performance in the aforementioned parameters, except that it is prone to producing excessive carbon and hence results in a highly visible exhaust. It is equally well known that carbon is formed in rich fuel mixtures; hence, the problem is one of lack of oxygen and intimate mixing of fuel and air in the front end and other local regions. It has been determined that to obtain a satisfactory reduction in smoke, increasing the air flow proportion in the front end is effective but that the amount required invariably severely compromises the stability and altitude relight capability. The present invention determines and provides a construction and/or method to reduce smoke while at the same time maintaining the necessary performance parameters which are acceptable for use in a gas turbine engine.

The present invention accomplishes the foregoing by a unique combustion chamber configuration. Initially, in the combustion chamber of the present invention, a plurality of plunged holes are positioned at the front end of the combustion chamber. The size and location of these plunged holes are optimized so as to provide a critical airflow into the combustion zone of the combustion chamber. It has been determined that the critical airflow through these holes is in the range of 6 to 8 percent of the total airflow, a preferred amount of air being 7 percent. Additionally, the present invention positions an annular ram scoop around the plunged holes, the opening of the ram scoop facing upstream and the scoop wall being radially spaced from but covering the inlet opening of the plunged holes. The purpose of the ram scoop is to increase the pressure of the air flowing through the plunged holes, and since the plunged holes are directed radially, the pressurized air flowing through the plunged holes is capable of penetrating deeper or almost into the centerline of the combustion liner. In addition, the ram scoop provides for a more uniform flow through the passage leading to the plunged holes, and hence the airflow through each of the plunged holes is nearly the same. The present invention makes one other change to the conventional combustion chamber configuration in that it provides a unique air shroud around the fuel nozzle. This fuel nozzle air shroud contains a plurality of pas sageways for the entrance of primary air into the fuel nozzle supply means and the holes are angled so as to induce or impart a swirling motion to this incoming air. The incoming air is caused to flow around the fuel nozzle and is discharged in a plane substantially parallel to the axis of the fuel nozzle. The effect of this swirling air, produced by the angularity of the holes in the shroud, is twofold. It (1) provides an increase in the fuel spray angle, and (2) it locally aerates the fuel directly downstream of the fuel nozzle along the burner can centerline. It has been found that the angle of the passageways with respect to the centerline of the fuel nozzle is critical and should be in the range of between 18 to 35 degrees, a preferred angle being 28 degrees. Additionally, it has been determined that the amount of air flowing through these passageways and the nozzle shroud discharge face is critical and should be in the range of 1 to 3 percent, 2 percent being a preferred amount.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a cross sectional view of the liner within a combustion section envelope showing the device of the invention.

FIGURE 2 is a cross sectional view of a fuel nozzle supply means showing the nozzle and shroud.

FIGURE 3 is a view taken substantially along line 3-3 of FIGURE 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is shown in a diffuser case 1 which is intended to be located between the compressor and turbine of a gas turbine powerplant. A powerplant to which this type of combustion chamber is applicable is disclosed, for example, in the Savin patent, U.S. Patent No. 2,747,367.

As best shown in FIGURE 1, the combustion chamber is of a can-annular type, only one can being illustrated. It is to be understood that any type combustion chamber may be employed whether it be a can-annular type or an annular type. Again referring to FIGURE 1, the combustion chamber 4 consists of wall 5, wall 6, fuel nozzle 40 and combustion liner(s) 9. Walls 5 and 6 along with dome-shaped member 8 are the closure parts of combustion liner 9 of combustion chamber 4. The combustion liner 9 includes an upstream end where the primary combustion occurs, this being combustion zone 10 and an open end 12 wherein the exhaust gases are discharged to a turbine not shown herein.

As shown, high pressure compressor discharge air 12 enters the diffuser case 1 and flows toward the head end of the combustion chamber 4. As illustrated, combustion chamber 4 is supported from the combustion case 2 by any conventional means. The compressor discharge air divides itself around combustion chamber 4, entering each burner through holes or openings 20, nozzle shroud 22, burner can swirlers 24 and a series of openings 26, 28 and 30 which are distributed along the axial length of the liner. These latter reference characters and members will be described hereinafter in greater detail. As hereinbefore discussed, the apparent cause of smoke in a combustion chamber is primarily due to fuel rich regions in the front end of the combustion chamber. The fuel rich regions are caused by the inability to mix the fuel and available air uniformly and the inability to provide suflicient air to the primary zone, especially at the burner can center near the fuel injector. Attempts to provide the necessary mixing, by increasing the pressure drop and/or opening the air access holes, do not produce satisfactory results. By a large increase in air admission through the air access holes and/or large increases in burner pressure drop, a low smoke level may be achieved but at the expense of other performance parameters which make the combustion chamber unacceptable for engine use. If more moderate amounts of air and/or increase in pressure loss are used in order to retain the required level in all other performance parameters, it is found that the smoke reduction achieved is marginal and not satisfactory. It has therefore, been determined that the location, size and design of the front end air admission ports is a critical factor in a combustion chamber where it is desired to reduce the smoke level and maintain satisfactory performance parameters for use in a gas turbine engine.

In the configuration shown in FIGURE 1, air to improve mixing and thereby eliminate the local fuel regions to reduce carbon formation is added through a number of holes further upstream that is, slightly downstream of or immediately adjacent the fuel injector 30. These holes 20 may be located either in the dome-shaped member 8 of combustion chamber 4 or adjacent thereto and generally positioned circumferentially of linera 9. In the configuration of the present invention the holes are plunged, that is, extending radially inward to provide a positive direction towards the burner centerline 34 which would not otherwise occur. Plunged holes 20 provide the means for counteracting the effect of the air entering through swirler 24 which would tend to deflect any air entering liner 9 in an axial direction. Plunged holes 20, by directing the flow radially inward because of their shape, protect the air jet issuing therefrom from being dispersed by the air entering through swirler 24. This enables the air entering through plunged holes 20 to penetrate past swirler 2-4 and cooling air entering therethrough, hence permitting this air from plunged holes 20 to move toward the front end of the burner liner 9 and combine with the swirler air to form recirculation zone 36, as shown. In the configuration shown, the recirculation zone 36, which is formed by the combination of this radially inward air and the swirler air, is to locate a recirculation zone at a point much closer to the head or closed end 8 of the combustion chamber 4 than in the prior art constructions, hence permitting this air to be available to mix with the incoming fuel from the fuel injector 30 sooner than is the case with any of the prior art constructions.

It has also been determined that the amount of air injected into the combustion zone 10 of the linear 9 is critical, the amount of air being in the range of 6 to 8 percent of the total airflow being required, air in the amount of 7 percent being the preferred amount. One method of controlling the amount of this critical airflow is to provide a plunged hole which has an inlet opening which is in the range of from 0.35 inch to 0.50 inch. Additionally, to insure that the air entering through plunged holes 20 reaches recirculation zone 36, it has been found that plunged holes 20 should have a radial or depth dimension of from 0.1 inch to 0.25 inch. By so controlling the structural dimensions of plunged holes 20, the amount of airflow which is also critical may be controlled. It has been determined that the critical flow through plunged holes is from 6 to 8 percent of the total airflow, 7 percent being a preferred amount. The fuel rich regions and hence smoke can be almost entirely eliminated by merely increasing the size of the plunged holes, but this has a detrimental effect on burner stability and ignition. It should, therefore, be clear that the use of plunged holes 20 alone is not suflicient to achieve the desired overall results, it being necessary, in order to overcome the stability and ignition penalty associated with excessive air in the front end, to supply additional air through another feature of the present invention which will be hereinafter described.

This latter feature just mentioned is the introduction of additional air through the fuel nozzle supply means 40. The fuel nozzle supply means refers to and encompasses not only the fuel injector 30 but also the nozzle air shroud 22. This construction of the fuel nozzle supply means 40 additionally refers to the necessary piping and support members herein not shown. For a more explicit showing of the portion of the fuel supply means 40 pertinent to the present invention, reference is hereby made to FIGURE 2. As shown there, air enters the passage between shroud 22 and fuel nozzle 30' through holes 46 which are positioned in shroud 22 at an angle with respect to the centerline 49 of the fuel nozzle 30. More specifically, referring to FIGURE 3, it can be seen that the centerline 47 of passageway 46 forms an angle 0 with the vertical centerline 49 of fuel nozzle 30 and similarly with horizontal centerline 48 of fuel nozzle 30. It is this angle 0 which is critical as hereinafter described. The air entering through holes or passageways 46 is discharged in the same plane as the fuel is discharged from the fuel injector 30, this being substantially parallel thereto.

The angular nature of these holes is a critical factor in contributing to the performance of the present invention as it relates to maintaining the overall performance parameters and the reduction in smoke level. The amount of air permitted to enter and the swirling action imparted thereto are produced by the angularity of the holes 46 and have two primary effects: (1) an increase in fuelspray angle, and (2) the local aeration of the fuel directly downstream of the fuel nozzle along the burner can centerline. It should be noted that if the holes were drilled perpendicular to the shroud wall 22 rather than at an angle, the fuel-spray angle would decrease thereby concentrating fuel at the burners centerline, where it is difficult to mix with suflicient air because of the difliculty of penetrating into this region. This results in local rich fuel-air mixtures and hence carbon formation. The present invention avoids this problem by positioning the holes 46 at an angle 0, thereby actually increasing the fuelspray cone angle and spreading the fuel more uniformly over the front end cross section. Additionally, the air entering through the fuel nozzle shroud 22 is admitted to the critical region just downstream of the fuel nozzle providing the necessary air for the fuel that is still present in this region. It should be clear that control of the required amount of air is determined by the size of the holes 46 and the shroud opening 50, there being a particular flow relationship therebetween.

It is this combination of swirling air entering through holes 46 and the increasing of the nozzle shroud diameter opening 50 to accommodate the flow through the angular holes 46 and the further combination with plunged holes 20 which results in a combustion chamber burner performance that is satisfactory both from a smoke reduction level and a performance parameter aspect.

More specifically, an incremental smoke reduction is achieved by air admitted through plunged holes 20 and a further increment in smoke reduction is achieved by adding air through shroud 22 in the manner hereinbefore described. A further effect of the shroud configuration is to preserve the stability limits of the burner. The air admitted through plunged holes 20 is in the direction of increasing the blow-out limits of the combustion chamber. This is counteracted or compensated for by the construction of the fuel nozzle shroud 22. It is again reiterated that the angularity of the passageways 46 is critical, the angle with respect to the fuel nozzle centerline 49 being from 18 to 35 degrees, and angle of 28 degrees being preferred. It has additionally been noted that there is a very definite flow relationship between angular holes 46 and nozzle shroud opening 50, these two latter elements being controlled structurally so that they permit an airflow therethrough in the range of from 1 to 3 percent of the total airflow. The net eflfect then is that suflicient air can be injected through plunged holes 20 to produce the main reduction in smoke level, and by the use of the shroud air, a further reduction is achieved and the blow-out limits of the burner are preserved.

An additional feature, as shown in FIGURE 1, is the incorporation of a ram scoop 60. This ram scoop 60 may be an annular ram scoop extending completely around the individual burner cans, or it may be a scoop which is provided for each individual plunged hole 20, hence not necessarily a continuous annular member. The ram scoop consists of an outer wall 62 which is attached at its downstream end to liner 9 and extends forwardly upstream a sufficient distance so that wall 62 covers the opening or inlet of plunged holes 20. The incorporation of the ram scoop is primarily to provide a uniform flow field around plunged holes 20 so that each tube is flowing the same amount of air. Additionally, the incorporation of a ram scoop tends to increase the pressure or pressure head on the air flowing through the plunged holes and hence to increase the penetration of this air. The use of a ram scoop is particularly advantageous in a system which incorporates a wide angle dump diffuser wherein the airflow profile approaching the burner or combustion chamber may be non-uniform and that each of the admission ports is in the forward part of the burner, since normally a variation in pressure drop may occur resulting in a vari- .ation of flow through the holes. In fact, it has been determined that aspiration may occur at some locations, and the use of the ram scoop has been found to prevent this and additionally allow each plunged hole to flow full and in a more uniform manner. Additionally, the ram scoop 60 picks up air in a region of peak pressure and so for the same size hole allows more air to flow through the holes than would be the case without the ram scoop, and, as previously noted, increases the penetration capability of the air jet. It has been determined that to accomplish the foregoing, the upstream end of scoop 60 has a critical opening and must be in the range of from 0.1 inch to 0.3 inch, 0.2 inch being a preferred opening.

Additionally, the present invention, by controlling and matching various elements to obtain a desired flow relationship, provides a method of eliminating smoke. More specifically, it provides a flow through the plunged holes in the range of 6 to 8 percent which flows radially inward almost penetrating the liner centerline. By combining this flow with the flow through swirler 24, this latter flow, also being critical and being in the range of from 6 to 10 percent of the total flow, preferably 8 percent, and establishing recirculation zone 36 substantially adjacent fuel nozzle 30 with a lean-fuel-air ratio, the smoke production is substantially eliminated. The method of the present invention further maintains the stability and relight characteristics by providing a swirling flow in the range of 1 to 3 percent, thus providing a combustion chamber with more than acceptable performance parameters.

By employing the teaching and maintaining the critical flows hereinbefore mentioned, a combustion chamber of the type herein described has demonstrated the capability of full starts to idle over a flight Mach number range of 0.3 to 0.7 up to 40,000 feet without the production of smoke.

What is claimed is:

1. A combustion chamber comprising a housing, a liner supported by the housing and spaced radially therefrom, the liner having a plurality of openings along its axial length, the liner having a substantially closed end and an open end spaced axially therefrom, the liner providing a zone for combustion of a fuel-air mixture, thecombustion products being discharged through the open end, fuel nozzle means positioned at the closed end of the liner for supplying fuel to the combustion zone, and swirl vanes surrounding the fuel nozzle means, wherein the improvement comprises:

the liner having a plurality of plunged holes positioned at its closed end, the plunged holes extending substantially radially inward from the liner walls,

a ram scoop attached to the liner wall, the openings of the scoop facing upstream and the scoop wall being positioned over the in et opening of the plunged hole, and

the fuel nozzle means having a shroud, the shroud having at least one passageway for permitting the passage of air, the passageway being at an angle with respect to the centerline of the fuel nozzle, and the shroud including means for discharging the air in substantially the same plane as the fuel.

2. A combustion chamber construction as in claim 1 wherein;

the combined openings in the plunged holes and the fuel nozzle shroud permit primary combustion air to enter the liner combustion zone in the range of approximately 6 to 11 percent of the total airflow.

3. A combustion chamber construction as in claim 2 wherein;

the passageways within the fuel nozzle shroud are angled with respect to the fuel nozzle shroud in the range of 18 degrees to 35 degrees.

4. A combustion chamber construction as in claim 2 wherein; v I

the radially plunged holes permit primary combustion air in the range of about 6 to 8 percent of the total airflow to enter the liner combustion zone.

5. A combustion chamber construction as in claim 4 wherein;

the swirler vanes permit primary combustion air in the range of 6 to 10 percent to enter the liner combustion zone.

6. A combustion chamber construction as in claim 2 wherein;

the airflow through the fuel nozzle shroud is in the range of 1 to 3 percent of the total primary airflow.

7. A combustion chamber comprising a plurality of can-type burners, each burner having a liner perforated with openings over its axial length, the liner having an upstream end which is substantially a sealed dome-shaped member and a downstream end spaced axially therefrom, the liner providing a combustion zone therebetween of a fuel-air mixture, the combustion products'being exhausted through the open downstream end,-fuel-supply means positioned at the upstream end of the liner for supplying fuel to the liner combustion zone and swirler vanes surrounding the fuel nozzle means wherein the improvement comprises:

each of the liners having a plurality of plunged holes positioned in its dome-shaped portion, the plunged 1 the liner with respect to the plunged hole so as to extend over the inlet of the plunged hole, and

the fuel nozzle means including a shroud, the shroud having at least one passageway for permitting the flow of air therethrough, the passageways being angular with respect to the centerline of the fuel nozzle, and the shroud including means for discharging the air in substantially the same plane as the fuel. 8. A combustion chamber construction as in claim 7 wherein;

the combined openings in the plunged holes and the fuel nozzle shroud permit primary combustion air to enter each liner combustion zone in the range of approximately 6 to 11 percent of the total primary airflow.

9. A combustion chamber construction as in claim 8 wherein;

the plunged holes have a diameter in the range of from 0.35 inch to 0.50 inch and the nozzle shroud face opening diameter is in the range of 0.5 inch to 0.6 inch.

10. A combustion chamber construction as in claim 8 wherein;

the passageways within the fuel nozzle shroud make an angle with respect to the fuel nozzle shroud in the range of 18 degrees to 35 degrees.

11. A combustion chamber construction as in claim 9 wherein;

the radially extending plunged hole depth is in the range of 0.1 inch to 0.25 inch.

12. A combustion chamber construction as in claim 9 wherein;

the upstream opening of the ram scoop is in the range of 0.1 inch to 0.3 inch.

13. In a combustion chamber having at least one combustion zone, the method of reducing smoke and maintaining overall performance parameters therein comprising:

providing a first flow of primary combustion air to the upstream end of the combustion zone in the range of 6 to 8 percent of the total airflow;

affecting a pressure increase on the first flow, the pressurized fluid being directed radially inward,

providing a second flow of primary combustion air to the upstream end of the combustion zone in the range of 1 to 3 percent of the total airflow through a fuel nozzle supply means;

imparting a swirling motion to the second flow and discharging the second flow in a plane substantially parallel to the axis of the fuel nozzle supply means; supplying fuel to the first and second flows; and combusting the fuel air mixture.

14. The process of reducing smoke and maintaining overall performance parameters as in claim 13 including:

providing a third flow of combustion air thtrough a swirler means in the range of 6 to 10 percent of the total airflow;and

mixing the first flow and third flow to provide a recirculation zone substantially adjacent the fuel nozzle.

References Cited I UNITED STATES PATENTS 2,560,207 7/1951 Berggren et al --39.65 2,700,416 I 1/1955 Johnson et al. 2,982,099 5/1961 Carlisle et a1. 6039.65 XR 3,134,229 5/1964 Johnson 60-3965 CARLTON R. CROYLE, Primary Examiner US. Cl. X.R, 6039.6 39.74

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