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|The design of efficient cooling systems plays a decisive role in the development of modern gas turbine combustion chambers. Guaranteed adherence to the maximum permissible material temperatures is required while at the same time using as little cooling air as possible. The required mass flows of cooling air therefore need to be known as already at the development stage, since they directly influence the available combustion air and hence pollutant emissions from the combustion chambers.|
By developing a suitable model, the goal is to determine the wall temperature of a combustion chamber taking into account the radiant gases in the combustion region, the radiation interaction with particles (such as soot) suspended in the flame and the radiation of the combustion chamber walls. The temperature distribution determined in this way can then be used to optimise different cooling concepts.
The so-called Monte Carlo method is used for the numerical simulation of the radiation processes in the combustion chamber. The principle of this simulation method rests on tracking a large number of randomly distributed photons through the combustion space. The distribution of the absorbed photons ascertained in this way can ultimately be interpreted as the radiant heat transferred.
Within this research focus the following research projects are associated:
Coil coating is a continuous process for providing coating to a metal strip. In 2017, a total area of 1.37 billion m² of aluminium and steel was coated with 219 kt of paint in Europe, representing one third of the worldwide production. The coil coated products are mainly used in the construction market as building envelope. Consumers encounter coil coated products in everyday life for example as casing in a variety of size from fridges, washing machines to toasters and wireless speakers. In the coil coating process, a paint, mainly consisting of pigments, chemical crosslinkers and solvents, is applied to a metal strip. In a following step the paint is dried while the solvents evaporate. Afterwards, the paint is cured up to a certain temperature where the crosslinkers increase the adhesion between pigments and metal strip. In the conventional process the required heat is provided through convective heat transfer using hot air. In order to prevent the creation of an explosive atmosphere in the process, operation at a solvent concentration below the lower explosion limit by using an excess amount of air is inevitable. Prevention of VOC emission entails either recovery or thermal decomposition of the solvents, which can be stated as being technically complex and expensive due to the high dilution of the solvents.
In the ECCO project the proof of concept of a novel curing oven will be performed in a pilot scale coil coating line. In ECCO, the curing oven is operated at elevated solvent concentration which allows the direct utilization of solvents as a fuel for heat generation. Therefore, the oven system is separated in two sections: The radiant burner section, where intense radiation in the IR-spectrum is emitted at high temperatures resulting from combustion inside of a ceramic porous structure, and the curing oven section which is operated over the upper explosion limit or, in other words, below a critical oxygen concentration. The prevention of a thermal decomposition of the solvent loaded atmosphere at high temperatures is ensured through separation of the two oven sections by an IR-transmissive material. Starting from previous activities at TRL 4, an interdisciplinary approach is foreseen, based on advanced-materials, combustion technology and prediction tools for system design/optimization, with active participation of key industrial stakeholders, to bring this technology to TRL 6 and realize a prototype curing oven at industrially relevant size and environment. ECCO proposes an oven concept which leads to a drastically reduced size and increased energy efficiency as we as well a higher production flexibility due to a fuel-flexible, modular and potentially energetically self-sustainable process. In comparison to existing conventional convective curing systems, ECCO presents a less energy demanding, environment-friendly and economical technical curing oven concept.
Within this research focus in the past the following research projects were associated:
It has been shown that the commonly used surface radiation models without consideration of chemical reaction (combustion models) and without turbulence and soot formation models have to be re-considered. Instead, fluid dynamically driven coherent structures and CFD simulations of interacting fires have to be considered using the above mentioned sub models which partly have to be developed.
In particular, the knowledge about the interaction phenomena between two or even more pool fires will be investigated both, experimentally and numerically using CFD simulations. Additionally the knowledge about the length of the so-called clear combustion zone, which is not covered by black sooting regions, has to be deepened. Also the knowledge on the specific radiation (SEP) of single and interacting black sooting fires needs to be extended.
Of high importance and a pre-requisite for success of the above mentioned goals the knowledge on the elementary chemical reactions in peroxide pool flames has to be deepened, especially with respect to soot formation in such hydro-carbon pool flames. For this, mechanisms of soot formation will be improved and reaction mechanisms for the combustion of organic peroxides will be developed and integrated into CFD tools. Such tools can be flamelet models, which will be used int the present research work.
The SOPRANO project’s main scientific objective is to make a breakthrough in the overall investigation efforts in the field of soot particles chemistry, particles size distribution (PSD), and their radiative effect on combustors typical of aero-engines. SOPRANO aims at a qualitative shift in the knowledge and experimental and numerical approaches related to the characterization and prediction of soot emission and interaction with radiative Low NOx combustor environment.
The main industrial objective of SOPRANO is to carry out an in-depth characterization of soot particles emitted by a modern combustor at engine relevant operating conditions and at increased pressures to pave the way for the future design of high-performance combustors: a more accurate evaluation of the radiation effect and, therefore, a more reliable liner temperature prediction, will drive a review of the design criteria in terms of combustor air distribution and will improve durability of some key modules, e.g. the combustor’s liners.