Film Evaporation Combustion Chamber

The present invention relates to a film-evaporating combustion chamber with an evaporator pipe whose inner surfaces are wetted with a fuel film from a fuel supply installation and in which the evaporating fuel is seized by a swirling or rotating combustion-air flow sweeping along the inner diameter of the evaporator pipe and is mixed with the same, especially for vehicle gas turbines.

Film-evaporating combustion chambers of this type are known in the prior art (Motortechnische Zeitschrift 1959, pages 283 et seq.) On the one hand, the formation of the swirl flow and of the recirculation flow are of great significance for a good efficiency of such film-evaporating combustion chambers and on the other hand, also the manner how the fuel film to be evaporated forms at the inner wall of the evaporator pipe. It is essential that the fuel film be applied onto the inner wall of the evaporator pipe as rapidly and as uniformly as possible because only in that case a rapid evaporation and a mixing with the combustion air which takes place rapidly, are assured.

In the prior art types of construction, provision is made that the fuel enters from the outside of the evaporator pipe through a large number of radial bores or also through a ring of porous material. These types of prior art constructions entail the disadvantage that in the first case the radially inwardly directed fuel jets adhere directly at the evaporator pipe wall only under certain aerodynamic conditions and distribute themselves on the evaporator pipe in the form of a film only under these conditions. This distribution operation thereby depends decisively on the type and on the strength of the combustion air stream having a swirl or rotary movement. This entails the disadvantage that with a change of the supplied combustion air quantity, under certain circumstances also the intensity of the swirling flow may change so that the assurance no longer exists for the fact that the entire fuel supplied through the feedline is distributed also completely satisfactorily in the form of a film at the inner wall of the evaporator pipe. This is true in particular in case of use of film-evaporating combustion chamber in vehicle gas turbines where different driving conditions must exist.

In the other type of prior art construction, in which the fuel enters through a ring of porous material, the danger is not very great that the fuel reaches too far into the interior of the evaporator pipe; however, this type of prior art construction entails the disadvantage that the passing-through fuel is cracked and partly coked in the capillaries of the sintered material and that non-volatile residues clog up the capillaries.

The present invention is therefore concerned with the task to provide a fuel feed system which assures also under different driving conditions the formation of a fuel film and which nonetheless does not entail the danger that the fuel is cracked or coked in the feed means.

The present invention essentially consists in a film-evaporating combustion chamber of the aforementioned type in that the fuel feed installation is provided with at least one feedline which leads from the inside thereof to the inner wall of the evaporator pipe and whose discharge orifice is located directly in front of the inner wall. Appropriately, several feedlines which discharge distributed over the circumference are provided thereby in the form of relatively thin, small pipes so that the advantage is achieved in this manner that the fuel is thrown against the inner wall of the evaporator pipe already by its own inherent momentum and distributes itself thereat as film far-reachingly without influence of the swirling flow. In this type of construction, the fuel has to be deflected thereby at least in part by the rotating combustion air flow and has to be accelerated in the direction toward the evaporator pipe discharge and as a result thereof a portion of the area available for the evaporation is lost, even if the corresponding small feed pipes are provided at the inlet of the evaporator pipe.

It is therefore of advantage if in a construction of the film-evaporating combustion chamber in which a radial guide cascade is connected as guide wheel in the input ahead of the evaporator pipe and in which the evaporator pipe therefore possesses at the inlet an essentially radially extending inlet part, provision is made to apply the fuel through radially and axially directed small pipe portions onto this deflection area at the inlet of the evaporator pipe so that the distribution of the fuel takes place ahead of the beginning of the axially directed evaporator pipe, properly speaking, and an endless uniform film is present already at the beginning of the evaporator section.

Accordingly, it is an object of the present invention to provide a film-evaporator combustion chamber which avoids by simple means the aforementioned shortcomings and drawbacks encountered in the prior art.

Another object of the present invention resides in a film-evaporating combustion chamber in which the fuel is distributed film-like under all operating conditions.

A further object of the present invention resides in a film-evaporating combustion chamber which assures reliable operation under all operating conditions while preventing coking or cracking of the fuel in the feed system.

These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, two embodiments in accordance with the present invention, and wherein:

FIG. 1 is a longitudinal cross-sectional view through one embodiment of the inlet area of a film-evaporating combustion chamber in accordance with the present invention equipped with a radial guide cascade as feed device to a conically enlarged evaporating pipe;

FIG. 2 is a transverse cross-sectional view taken along line II--II of FIG. 1;

FIG. 3 is a longitudinal cross-sectional view through a modified embodiment of a film-evaporating combustion chamber in accordance with the present invention equipped with a modified fuel feed system; and

FIG. 4 is a transverse cross-sectional view taken along line IV--IV of FIG. 3.

Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like parts, and more particularly to FIGS. 1 and 2, the inlet area of a film-evaporating combustion chamber of a gas turbine engine generally designated by the reference character T is illustrated in FIG. 1 which essentially consists of a pipe-shaped or tubularly shaped air guide housing 1, into which the air flows in the direction of the arrow 2. A hood 3 which is closed in the inflow direction is inserted into the air guide housing 1 which, on the one hand, is retained by several radially extending bolts 4 and on the other, is connected by way of a radial guide cascade 7 with the connecting portion 13 of an evaporator pipe generally designated by the reference numeral 10 by means of bolts 8a and bushes 8b. The member 5 is mounted at the closed end of the hood 3 on a portion 9 of the hood 3 by way of the flanged cover 6 connected with the member 5 in one piece therewith, whereby the member 5 is constructed on its side directed toward the inside of the hood 3 as deflection hub for the air discharged out of the blade channels 7a (FIG. 2) of the radial cascade 7. The evaporator pipe 10 includes thereby an inlet area 11 which opens essentially as inlet funnel in the direction toward the blade channels 7a and continues in an initially cylindrical portion 12 that is subsequently enlarged conically shaped. Toward the outside the evaporator pipe portion includes an essentially cylindrical connecting portion 13 which is adjoined by the wall 14 of a reaction chamber 15 which does not adjoin the free end of the evaporator pipe 10. An installation 16 is arranged in the annular space formed between the wall 14 of the reaction chamber 15 and the evaporator pipe 10, which in the manner of an ejector permits to the combustion air supplied through the space 17 in the direction of the arrows 18 which enters through the openings 19, to leave through an annular slot 20 and therewith produces a back-flow moving in the direction of the arrows 21 which, however, forms no part of the present invention.

The fuel to be applied onto the inner wall 10a of the evaporator pipe 10 is fed through a supply channel 22 extending in the center of the member 5 and is conducted radially outwardly approximately within the area of the cylindrical portion 12 of the evaporator pipe 10 through several thin, small pipes 23 having a diameter of about 0.5 to about 1 mm. The discharge orifices of the small pipes 23 are thereby located directly in front of the inner wall of the cylindrical portion 12 so that the fuel which is under pressure in the feed channel 22 is thrown against the wall of the portion 12 with a certain inherent momentum. The fuel thereby distributes itself already to a certain extent film-shaped on the inner wall, which is further enhanced by the combustion air flow which by reason of the radial guide cascade 7 has a swirling or rotating motion, insofar as a fuel film will form starting from the area 12 on the wider inner wall 10a of the evaporator pipe 10. The fuel film then evaporates and the evaporating fuel is taken along by the swirling flow, mixes with the combustion air and reacts in the reaction space 15 while developing heat, whereby the return-conveyance of the heat into the inlet area of the evaporator pipe 10 takes place, on the one hand, essentially by convective heat-exchange by a back-flow in the center of the swirling or rotating hollow jet approximately in the direction of the arrow 24 and, on the other, however, also in the direction of the arrow 21 on the outside of the evaporator pipe 10 where the back-flow proceeds controlled by the installation 16.

The feed channel 22 may be provided in a conventional manner not illustrated in detail at the end face of the member 5, with connections for the main fuel and for the ignition fuel and additionally also with a compressed air connection which assures in the case of shutting-down the film-evaporating combustion chamber, that the fuel which is still present in the fuel feed channel 22 and above all in the small pipes 23 is blown out so that a cracking or coking of fuel residues in this area is precluded.

A modification of the embodiment described in connection with FIGS. 1 and 2 is illustrated in FIG. 3 insofar as in that case initially a radial portion 25 of fuel feedlines extending from the feed channel 12 is embedded in the material of the member 5 and in that this radial portion 25 of the small feed pipes then passes over again into an axially directed portion 26 whose discharge orifice is located again directly in front of the inner wall 10a of the evaporator pipe 10, however, in this embodiment still ahead of the deflection area 11 and ahead of the cylindrical portion 12. In this manner the fuel wets the surface of the evaporator pipe 10 already ahead of the beginning of the evaporator section, properly speaking, so that a uniform fuel film is formed already ahead of the beginning of the available evaporator section, especially also because the fuel can be pressed well against the walls at this deflection place by the flow, so that the assurance exists for a good evaporation and a rapid mixing. As can also be seen from FIG. 3, the member 5 may be provided with two connections 27 and 28 for the main fuel and the ignition fuel whereby one of the two connections may also be selectively connected by way of a conventional valve 37 with a compressed air connection 36. The ignition fuel may thereby enter in this embodiment, not through the small feed pipes 25 and 26, but instead through an atomizing nozzle 29 so that only after the starting of the combustion chamber one switches over to the main fuel which is then applied by way of the small pipes 25 and 26. The feed channel 22 which in this embodiment terminates in an annular space 30 that is located still on the inside of the member 5, then has to be fed with compressed air after turning-off the combustion chamber, so that the small pipes 25 and 26 are cleaned of any residual fuel.

While I have shown and described only two embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art and I, therefore, do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.