A networked energy system that integrates the electricity, heat and transport sectors requires various energy converters. Using gas turbines, electricity can be obtained in a highly efficiently way from gaseous or liquid fuels. Natural gas is used almost exclusively today in gas power plants; in future they will be operated in an increasingly climate-neutral manner using fuels from renewable sources. Because of their flexibility regarding performance and fuels, gas turbines can take on a balancing and supplementary role in an energy system that is increasingly based on fluctuating renewable sources. Thanks to fuel cells, hydrogen can be used demand oriented and with a high degree of efficiency to generate electricity and heat. To obtain hydrogen, electrolysis and various solar-based high temperature procedures are being investigated.
This work is being undertaken at the DLR Institute of Combustion Technology, the DLR Institute of Propulsion Technology, the DLR Institute of Materials Research and the DLR Institute of Engineering Thermodynamics.
The overall gas turbine system consists of three main components – namely the compressor, combustion chamber and turbine. The system must be designed with pinpoint accuracy and optimised for the requirements of future energy systems that will be operated on a flexible basis. To develop gas turbines, investigations into flow fields, the chemical reactions that occur during combustion, and the resulting modelling of components are essential. Detailed measurements using optical and laser-based procedures are carried out on optically accessible combustion chambers under realistic conditions on atmospheric test stands and high pressure test rigs. Aerodynamic investigations take place on special compressor or turbine test rigs. DLR has developed extensive numerical simulation tools for modelling: the THETA flow-solver to simulate flows in the combustion chamber, TRACE for high-precision simulation of multi-stage compressors and turbo engines of all types under stationary and unsteady conditions, AutoOpti for an automated design optimisation, and GTLab to simulate the entire gas turbine system.
In developing new types of combustion chamber systems, the focus is on stationary gas turbines in the performance classes of 1 kWel to a few hundred MWel. In addition to the swirl burner concepts currently most frequently used, new types of FLOX® combustion chambers in particular are being investigated; these have high fuel flexibility, a broad operating range and low susceptibility to thermoacoustics.
The reduction in pollutant gas emissions is an important driver in the development of new combustion chambers for gas turbines and the design of future synthetic fuels. The relevant pollutants are nitrogen oxides, carbon monoxide, residual unburnt hydrocarbons and, for liquid fuels, soot. At the same time, emissions of the greenhouse gas carbon dioxide should also be reduced. One particular challenge lies in developing combustion concepts with low emissions that at the same time guarantee fuel and load flexibility, and allow an increase in efficiency and reliable operation.
An improvement in physical-chemical models and their incorporation in computing codes are required in order to design combustion sequences that result in lower emissions. Models are constructed on the basis of research into reaction kinetics using shock wave tubes and spectroscopic laser measurements on both generic combustion systems and test rigs to simulate technically-relevant flame conditions.
Unsteady combustion processes
Unsteady combustion processes, such as ignition (spontaneous and external ignition), quenching and unstable flames, are highly significant in gas turbine combustion chambers. These generally unwanted processes are heavily characterised by the interaction between the flow field and combustion reactions. Both numerical simulations and experimental investigations of this highly dynamic phenomena are very challenging. In order to analyse the chronological sequence of unsteady processes, high-speed laser measuring techniques are used on generic and realistic combustion chambers. These findings are then again integrated in complex combustion models in order to be able to simulate real systems as accurately as possible.
Power plant concepts based on micro gas turbines
Micro gas turbines with power capacities from 1 kW to several hundreds kW are used for the local supply of power and heat (combined heat and power generation, CHP) in buildings, businesses, commerce, services and in small and medium-sized industrial enterprises. Compared to large power stations, the benefit of generating energy through small, local CHP units is that there are no major losses due to transportation or conversion besides fuel transport, and the end user is provided with heat in addition to the generated electricity.
The focus of our research activities is on the development and design of power plant concepts based on micro gas turbines. Conventional systems are examined in addition to innovative concepts, such as the combination of a micro gas turbine with a solid oxide fuel cell (SOFC).
Fuel cells and electrolysis
As they are technically closely related, we are using our comprehensive electrochemical expertise to develop both fuel cells (PEFC) and SOFC) and electrolysers. Efficient, robust and economical solutions must be developed for both components for use in practical applications. In situ diagnostic techniques, as well as coating technologies, which are used to develop highly effective reactive surfaces, play an important role in identifying weaknesses during operation. The work on fuel cells also includes, in particular, their incorporation in stationary systems as well as mobile systems for motor vehicles and aircraft.