Catalytic Relight Coating for Gas Turbine Combustion Chamber and Method of Application

The invention relates to gas turbines, and more particularly to the combustion chambers (combustors) of gas turbines in which flame-out may occur. By "flame-out" is meant the quenching of the flame in the combustor which may occasionally occur due to transient disturbances in the flow of working fluid or due to perturbations, for example a blast in the vicinity such as could occur to a missile-borne gas turbine engine.

A number of different suggestions have been made for facilitating the reignition of fuel in a combustion chamber after flame-out. Ignition devices such as spark plugs and flares sometimes lack the durability and heat exchange characteristics necessary to effect proper reignition and are unreliable for relighting under all conditions.

Berl U.S. Pat. No. 2,970,439 and Toone U.S. Pat. No. 3,355,885 show catalytic ignitors in the form of containers or cylinders of catalytic material, used in combination with separate fuel supply means. British Pat. No. 843,780, published July 27, 1960 shows a fuel reignition device involving the insertion of a noble metal protrusion into the combustion chamber. In these known devices, parts are submerged in the gas flow path, increasing the possibility of damage. These prior devices fail to offer the advantages of the present invention which are described below.

Methods of applying a catalyst to a surface, which are useful in the present invention have been developed for the automotive chemical and petrochemical industries and are disclosed in various patents, including Leak U.S. Pat. No. 3,362,783; Hindin U.S. Pat. No. 3,615,166; Sergeys U.S. Pat. No. 3,903,020; and in Pfefferle application Ser. No. 06/139,340, filed Apr. 11, 1980. The latter discloses a method for applying catalyst to nonporous surfaces, a method which is also applicable to porous surfaces.

It is an object of the present invention to provide a novel and improved construction for a gas turbine combustion chamber, and method of reignition, which facilitates relighting in a reliable yet economical manner, and minimizes the risk of failure.

It is another object to provide an improved construction and method of this character which may be utilized with presently existing designs of combustion chambers.

Other objects, features and advantages of the present invention will become apparent from the following description, the appended claims and the accompanying drawings.

Briefly, the invention comprises a gas turbine combustion chamber having a wall with an inner surface exposed to the combustion chamber flame, and a coating of a catalytic material on said surface over a large enough area thereof to cause reignition of the fuel-air mixture after flame-out.

In another aspect, the reignition method of this invention comprises the step of applying a catalytic coating to the inner surface of a gas turbine combustion chamber over a sufficient area to facilitate reignition of the fuel-air mixture in the event of a flame-out.

FIG. 1 is a cross sectional view in elevation showing a portion of a combustion chamber constructed according to the present invention taken along the line 1--1 of FIG. 2;

FIG. 2 is a portion of the inner surface of the chamber showing the areas with and without coatings;

FIG. 3 is a fragmentary view taken along the line 3--3 of FIG. 1 and showing an uncoated area, and

FIG. 4 is an enlarged fragmentary cross-sectional view showing how the catalytic coating is bonded to the thermal barrier coating.

A combustion chamber for a gas turbine is generally indicated at 11 and comprises a forward segment generally indicated at 12 and a rear segment generally indicated at 13. An annular combustion chamber is shown having a central member 14 surrounding the turbine shaft, inlet passages at 15 in the form of a rotating fuel slinger, and inner and outer rows of compressed air inlet passages 16. Air deflector rings 17 are provided inside the chamber which generate a film of air for wall cooling. Optional cooling air slits 18 may also be provided. The bulk flow path of gases through the combustion chamber extends in the direction of the arrow 19. The inner surface of the combustion chamber wall is generally indicated at 20, this wall facing the fuel-air mixture within the combustion chamber. Conventionally, wall 20 is coated with a thermal barrier coating 21 seen in FIG. 4. Typically, this thermal barrier coating is composed of zirconium oxide with 6% yttrium oxide for stabilization of the crystal structure.

According to the invention, a catalytic coating generally indicated at 22 is bonded to the thermal barrier coating. The catalytic coating, which preferably comprises a noble metal catalyst such as platinum, chemically bonded to the thermal barrier coating, will have the function of reigniting the fuel-air mixture in the event of a flame-out. Reignition will result as a consequence of the combined effects of fuel, catalyst, air and sufficiently high temperatures.

Preferably, the catalytic coating is applied over most but not all of the interior surface 20 of forward segment 12 of the combustion chamber. For extreme conditions, it may be required to coat both segments 12 and 13. In order to facilitate relighting, certain areas of surface 20 are preferably left uncoated. In the illustrated embodiment, the uncoated areas are indicated in FIGS. 1, 2 and 3 as being two annular areas 23 and 24 plus a circumferentially spaced series of four triangular areas 25 inside outermost wall portion 26. These areas are partially shaded for emphasis in the figures. Area 23 extends radially inwardly from the inner row of air inlet passages 16, with the narrower uncoated band 24 outside the outer row of air inlet passages.

A suitable method of applying the catalytic relight coating to the gas turbine combustion chamber is shown by the following example: The inner surface 20 of the combustion chamber is previously coated with a zirconium oxide, yttrium oxide thermal barrier 21. The surface to be coated with the catalytic coating is cleaned if necessary by vapor degreasing to assure freedom from dirt, oil or grease. If necessary, suitable masks are employed on surface areas 23, 24 and 25 where no catalytic coating is desired.

A base coat is first applied comprising chloroplatinic acid, zirconyl nitrate and aluminum nitrate, with instruments of such design that no metallic parts come in contact with the coating. This material is applied in light even coats to prevent running. After each coat is applied it is dried in a forced circulating air oven at approximately 200.degree. F. for fifteen minutes at heat and then at approximately 300.degree. F. for twenty minutes at heat.

After a premeasured quantity of base coat has been applied in the aforesaid manner, a top coat is applied in one coat to the specified areas. The part is then dried in the aforesaid manner and any mask material carefully removed.

The coated part is then cured in an air circulating furnace by heating to approximately 250.degree. F. and holding for twenty minutes, raising the temperature to approximately 1300.degree. F., and holding at that temperature for one hour. The part is then furnace cooled to below 1000.degree. F. and then air cooled to room temperature. During this calcination process the noble metal compounds convert to pure metals and the zirconium and aluminum oxides convert to ceramic oxides. The noble metal is bonded to the thermal barrier coating by a matrix of ceramic material similar in composition to the thermal barrier itself. Care is taken to avoid accumulation of fumes in the furnace. The part is then enclosed in a sealed container. Preferred proportions of the base and top coats are as follows:

a. 1.1 gm platinum metal in the form of chloroplatinic acid

b. 0.5 gm aluminum nitrate

c. 3.0 cc zirconyl nitrate;

a. 0.5 gm palladium chloride

b. 1.0 cc water

c. 3.0 cc zirconyl nitrate

Duriang operation of a gas turbine engine having a combustion chamber constructed according to the present invention, in the event of flame-out the presence of the fuel-air mixture at the heated catalytic coating will cause reignition. Flames travelling along the catalytic coating will reach the uncoated areas at which point they will lift away from surface 20 and into the main body of the fuel-air mixture within the combustion chamber. This will facilitate relighting of the mixture within the entire combustion chamber.

While it will be apparent that the preferred embodiment of the invention disclosed is well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.