Combustion chamber

• See an internal combustion engine combustion chamber
• A furnace (heating) see firebox
• A steam locomotive see combustion chamber
• A steam generator, see there
• Of tobacco in a tobacco pipe qv

A combustion chamber is a container in which, by supplying an oxidizer (oxygen carrier, usually air), and one or more fuel is an exothermic reaction ( " burning " ) occurs, usually continuously. This reaction can optionally be accelerated by a catalyst.

A combustion chamber has a plurality of apertures for the removal of heat from the reaction gases, an opening for the introduction of the reactants. In this case, the fuel, and optionally of a catalyst in controlled amounts is introduced via nozzles into the combustion chamber. In rocket engines and the oxidant is introduced in controlled amounts into the combustion chamber. Essential feature of a combustion chamber is that this is not closed cyclically during operation. You do not use hypergolic reaction components, an igniter is needed to start the reaction still.

The fuel can be gaseous, liquid or even solid. When the fuel is solid, it can be finely ground is introduced into the combustion chamber.

A combustion chamber is used in rocket motors, gas turbines or in heating systems. Combustion chambers can be controlled quickly in their performance. Due to the use subject to high mechanical and thermal loads combustors. Depending on the application, the pressure in the combustion chamber of a rocket to be about 200 bar, the temperature of the reaction products of up to 3300 ° C. There are also forces of acceleration and vibration.

For the combustion chamber inner wall, especially super alloys or stainless steels with melting temperatures above 1350 degrees Celsius to 2623 degrees Celsius ( molybdenum) are used, which are designed in accordance with additions of tungsten, titanium and molybdenum the heat and pressure requirements.

At very high thermal load, the combustion chamber wall must be cooled. This is done either by the fuel which is transported prior to injection into the combustion chamber only in the tubes of the combustion chamber wall and thereby appropriately heated, or may be for short-term use also by a suitable heat shield, for example made ​​of graphite, tungsten or molybdenum, to happen. In combustion chambers of gas turbines typically used for cooling air, this occurs through small holes in the combustor wall so as to form a cooling film. There are also increasingly performed combustion chambers, where, on the hot gas side of the ceramic layer is applied. This material can withstand much higher temperatures and performs its good insulation effect to a strong temperature gradient to the actual combustion chamber wall. From outside the combustion chamber must be cooled by air also in this case (often by impingement cooling ), but is compared with the film cooling in the advantage that the cooling air does not enter the combustion chamber where it influences the incineration process.

Of the reaction space of a solid-fuel rocket is also referred to as a combustion chamber. Here, the fuel and oxidizer are in a solid mass inside the chamber. The mass first forms the combustion chamber wall. These combustors are not adjustable.

Combustion chamber designs for gas turbines

In addition to the outer shape combustion chambers also differ in the gas supply and the fuel supply.

Classification by types

Individual combustion chamber

Also combustor or English called "can- type combustion chamber". For single combustion chamber design more cylindrical combustion chambers are usually arranged in a network. Each combustion chamber has its own injector. Advantages of the individual combustion chambers are lower development costs and a fairly simple design of the items. Disadvantages are the higher weight and the increased space requirements compared to other construction methods. The entering the turbine gases also have a very non-uniform temperature distribution in the circumferential direction, which greatly shortens the life of the turbine and control system. This design was used exclusively in the early days of jet engines because of the development effort was the lowest. Today, this design is used only for smaller gas turbines.

Pipe - annular combustion chamber

Engl. "Can -annular combustion chamber" This is a hybrid design from the classic single combustion chamber and the modern annular combustion chamber. The individual combustion chamber is designed in a ring shape and has a plurality of injection nozzles arranged in a ring. This design offers several advantages of the annular combustion chamber ( higher energy density, improved combustion ), but all of the disadvantages of the individual combustion chamber design. This compromise of performance, weight, size and development effort has been rarely used in the past, since the development of the annular combustion chamber made ​​rapid progress.

Annular combustion chamber

Engl. " Annularly combustion chamber" Wherein the annular combustion chamber only one combustion chamber having an annular combustion chamber for a jet engine is necessary in place of a plurality of individual combustion chambers, which space and weight can be saved. In addition, the achievable energy density is much higher than other designs ( on the CF6 -80 engine to be burned in a combustion chamber volume of about 20 liters up to 12,000 liters of fuel per hour). There are several distributed (up to 30 ) individual injectors evenly, so that the escaping gases have a very uniform temperature distribution in circumference. This design was further developed until late, as it correspondingly powerful combustion chamber test facilities are needed to test the combustion chamber completely or segmentally.

Classification according to fuel supply

DC injection

The fuel is supplied in the same flow direction as the combustion air. Advantage: Technically easy to master, nowadays mostly used. Disadvantage: The mixing of fuel / air is not optimal, it must be aided by vortex formation, which increases the pressure drop.

Counter-current injection

The fuel is fed in opposition to the combustion air. It is hoped that thus an improved mixture formation, but the nozzle coking strong, which is why this type of construction " in development " for over 30 years and still found no significant use.

Fuel evaporation

In this construction, the fuel is " injected " under low pressure in a heated from the flame tube. The fuel vaporized in the pipe, at the same time, air is also passed through the. The mixture formation is the best of all three processes, the combustion occurs to very clean. Similarly, the injection can be made simple by the low pressure. This design was used quite early, when the injectors were still difficult to manufacture, but was then almost entirely supplanted by the rapid development of this technology. Nowadays, this technique we almost exclusively only used in modeling.

Fliehkraftzerstäubung

The fuel is fed through the hollow engine shaft and very finely atomized by the centrifugal force. The mixture formation is relatively good, the injection system can be held simply by the low pressure, however, the combustion occurs necessarily radially, whereby a special combustion chamber to be used by the multiple deflection of the gas flow has a higher pressure drop.

Classification according to gas guide

DC combustor

The combustion chamber is traversed linearly without significant changes in direction. Simple, compact construction with low pressure losses. This design is the most widely used in jet engines.

Reverse combustion chamber

The gas stream (but not in the combustion zone! ) Changes its direction as a rule two times by 180 °, whereby a good mixing and a uniform temperature is obtained at the outlet. This also allows the overall length to be reduced, which is why this design is frequently used in Kleingastubinen. The main disadvantage is the higher pressure drops that come through redirecting the gases into existence.

Radial combustor

This design is used exclusively in Fliehkraftzerstäubung, is very complex in design ( cooling air flow ) and is only used for smaller gas turbines. By the multiple change of direction of the gas flow also occurs here an increased pressure loss.

Many combustors used are multi-material design, developed the exact requirements of the engine accordingly. Therefore, this list is not exhaustive, there are constantly tested new designs to exhaust emissions, performance, weight, etc. to improve.