Since the company was founded, we have tackled a diverse range of problems associated with thermoacoustics.

Active instability control of land-based gas turbines

On the basis of many years of university research work by Dr.-Ing. Jakob Hermann (one of the company's founders) in this field, IfTA GmbH was the first company, back in 1997, to apply this technology to large-scale land-based Siemens AG gas turbines with a power rating of up to 240 MW and to establish it as an industry standard. Since 1997, almost 50 of these systems have been implemented successfully around the globe on land-based gas turbines. Their outstanding features include high efficiency in the suppression of combustion oscillations as well as high levels of system availability and reliability. This combination has enabled them to achieve unrestricted acceptance on the market and high levels of customer satisfaction.

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Small-scale furnaces

In particular, heating devices used in apartments and other residential dwellings can have a major and adverse impact on the quality of life if they prove to be subject to thermoacoustic oscillations. We develop cost-effective and easy-to-install methods to help prevent problems of this kind.

We define small-scale furnaces as combustion systems used at the lower end of the kW range, e.g. various kinds of gas thermal value equipment, oil burners etc. in apartments, detached homes and multiple occupancy homes. We also include in this category gas ovens, e.g. gas heaters used for camping and similar systems with a defined combustion chamber geometry in which acoustic oscillations can become established, and which also contain a burning flame.

Especially in the heating device sector, efficient low-pollution operation and smooth combustion are all important features because direct or indirect noise originating from the combustion system can, to a greater or lesser extent, have a profound and adverse impact on the quality of home life, and therefore on general quality of life.

Large-scale systems share common features with small-scale systems. For example, combustion oscillations can be caused by apparently minor changes in ambient conditions (gas composition, installation conditions, operating point, ambient temperature etc.). The impact of these changes can cover a very wide range: low-frequency buzzing with fixed or variable frequency when starting, sudden brief occurrence of instabilities caused by, e.g. the closing of a door (and its associated pressure impulse), high-frequency whistling (approx. 800Hz, 120dB) when operating at a defined operating point, etc.

It is understandable that this kind of behaviour in combustion systems is not acceptable for the manufacturer. In most cases, during the planning and development phase, little attention is paid to the optimisation of the thermoacoustic properties of a device and this can mean that any inherent tendency towards combustion instabilities may remain undetected until the prototype stage, or even until the test stage prior to market launch. It is then necessary to develop passive measures rapidly which can be installed quickly and cost-effectively without modifying the overall concept of the burner.

In several projects, IfTA GmbH has developed successful solutions for various renowned manufacturers and these solutions have proven capable of damping the combustion instabilities in these various devices. Following an experimental and numerical investigation of the system in our laboratory and/or on the computer during which we gained a detailed understanding of the causes of instability problems, passive measures were developed which x91detuned' the acoustics in such a way that it was no longer possible for combustion and acoustics to establish a feedback loop. In most cases, various different measures were devised (dampers, resonators etc.) which equipped manufacturers with a range of different options to prevent unstable system characteristics.

As well as developing efficient "quick solutions", we do of course also offer expert consultancy and guidance support during the planning and development stage, thus ensuring that problems of this kind will not occur in the test phase.

Given the sensitivity of this topic, it goes without saying that we treat all such investigations and information as absolutely confidential. We therefore quite deliberately avoid quoting any specific examples, or naming our customers at this stage. We are sure that you will understand our position.

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Large-Scale Furnaces

The power of these burners lies at the upper end of the kW to lower MW range and these units are employed in large offices or department stores, stadiums or airports. They no longer have their own combustion chamber and are instead operated in conjunction with an extremely wide and diverse range of boilers made by other manufacturers. This means that the burners need to deliver stable operating characteristics in the context of different geometries and varying conditions. It is therefore important to have a detailed knowledge of the oscillation tendency of these burners in order to estimate the risk of instability when they are used in different geometries. IfTA GmbH has carried out corresponding investigations.

In contrast to small-scale furnaces, e.g. gas thermal value equipment, heating devices etc. intended primarily for residential use, and offered as complete units, e.g. in conjunction with burners, boilers, heat exchangers and exhaust systems, large-scale furnaces are assembled individually from components sourced from various manufacturers. Products manufactured by burner manufacturers might for example be used in conjunction with boilers from another manufacturer. While it is true to say that combustion instabilities are always dependent on the overall system, i.e. burner, combustion chamber, exhaust and air intake system, certain tendencies favouring unstable characteristics can be detected at an early stage directly on the burner. For example, certain phenomena arising from mechanical flow properties might give rise to certain frequency components occurring on a larger scale than others during the combustion process. If these areas are close to the acoustic eigenfrequency of a boiler, and if other unfavourable conditions are also in place, there is a high probability of a link between combustion and acoustics, i.e. instabilities can be excited.

IfTA GmbH offers a wide and diverse range of investigations into the aforementioned causes of combustion instabilities. These investigations include measurements conducted directly on the affected system or on our customers' test rigs. To support these experimental investigations of the phenomenon, it is also advisable to conduct numerical simulation of the acoustic characteristics of boiler geometries.

As a customer, you can rely here, as in other sectors, on prompt expert and cost-effective support with your problems. It goes without saying that we will always treat your problem in complete confidentiality.

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Active Stall Controll

Thanks to a project supported by the German federal state of Bavaria, we were able to run a successful program of interdisciplinary research and development at a high level. By the completion of the 3 year project all the objectives defined at the outset were achieved: Project partners ISA from the German Armed Forces University (Universitaet der Bundeswehr) in Munich, MTU and IfTA GmbH were able, with the controller developed by IfTA GmbH to substantially increase the stable operating range of ISA"s own turbofan engine Larzac unit with the help of active compressor control.

This project was carried out in the context of an aerospace research project funded by the Bavaria federal government. Project partners included IfTA GmbH, MTU and the Jet Propulsion Institute ISA (Institut fuer Strahlantriebe) at the German Armed Forces University (Universitaet der Bundeswehr) in Munich who initiated the project. In this context, the scope for active control of compressor instabilities on an aerospace gas turbine was investigated. The aim of this research project was to displace the surge line of the compressor in the LARZAC 04 C5 turbofan engine unit at ISA (Institut fuer Strahlantriebe) with the help of active measures, i.e. the use of a controller, in such a way as to increase the size of the stable operating range and to improve the efficiency of the compressor. Following initial successful control tests with other research groups, using only dedicated test compressors, this work constitutes the first application involving a real and complete aircraft engine.

In this project, IfTA GmbH supplied all the controller hardware and software and supported the university with signal recording (metrology, recording) and evaluation (analysis, algorithms). Moreover, in the course of this project, further development and new development took place on hardware and software with a view to optimising the control function.

The application range of a compressor is restricted by what is known as the surge line, expressed during the phenomenon known as "surging" by a reversed flow across the entire cross section of the compressor. As a weaker and therefore less hazardous "preliminary stage" of this phenomenon, partial flow problems can move around the circumference of the compressor, also known as rotating stall.

The basic concept underlying active control of a compressor is to detect surge precursors or rotating stall problems and then to use a controller and an actuator to influence the system in such a way that the compressor does not encounter these undesirable operating conditions. A favourable solution has proven to be modulated air injection in the tip area of the blades on the first compressor stage, because this is where instabilities first occur.

Based on a modified form of the AIC system applied for active instability control of combustion oscillations on land-based gas turbines, various control strategies were devised during this project which were optimized for different compressor problems. With the help of these strategies and a specially adapted set of actuators, the research project, which lasted for three years, was able to deliver successful verification for the functional capability of active compressor stabilization. In overall terms, it worked to actively displace the surge line over the complete compressor speed range, and thus the feasibility of an industrial application of this innovative technology was proven. In comparison to constant air injection, active stabilization proved to be more effective, i.e. the same stabilization effect was achieved with less air and, at the same level of air consumption, the stable operating range was extended to the range achievable with constant air injection.

The innovative and research-related content of this collaboration was reflected by joint publications at international symposia.

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