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Engler-Bunte-Institute Combustion Technology (EBI-vbt)

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76131 Karlsruhe

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Spray formation and combustion of liquid fuels

Sprays are used in a large number of engineering processes (spray-drying, colour sprays, combustion etc.). As appropriate to the actual case, the spray needs to have different properties regarding droplet size and distribution thereof. These parameters are significantly influenced by the design of the nozzle. In combustion engineering it has become an important goal to optimise the widely-used combustion systems for liquid fuels with regard to their energy consumption and pollutant emissions. Since the combustion of liquid fuels proceeds via the process steps of atomisation, vaporisation, mixing with combustion air and reaction, optimising the respective burners calls for a precise knowledge of the separate steps and the key influencing parameters. The infrastructure available within the institute allows sprays to be characterised with regard to flow field, droplet sizes and the associated distribution densities. An atomisation test bench is available for this purpose on which investigations can be carried out with the Particle Dynamics Analyser, the Laser Light Slice Method and Ultra Short Exposure Photography. A combustion chamber with a thermal power of up to 300 kW is available for investigating the combustion of liquid fuels in highly turbulent technical flames. The measuring equipment used for this ranges from conventional cooled probes through to optical non-contact measuring methods for determining velocity, temperature and mix composition.
Detailed description

Within this research focus the following research projects are associated:

Machine learning for Advanced Gas turbine Injection SysTems to Enhance combustoR performance
(MAGISTER)
The project is funded in the framework of Marie Skłodowska-Curie Actions as Innovative Training Network (ITN). Air transportation is expected to grow persistently over the next decades. Clean combustion technology for aircraft engines is a key enabler to reduce the impact of this growth on ecosystems and humans’ health. The vision for European aviation is shaped by the Advisory Council for Aviation Research and Innovation in Europe in the Flight Path 2050 goals, which define stringent regulations on pollutant emissions. To meet these goals, the major engine manufacturers develop lean premixed combustors operated at very high pressure. This development introduces a large risk for reduced reliability and lifetime of engines: pressure oscillations in the combustor called thermoacoustics. Aviation industry encounters currently the fourth industrial revolution: cyber-physical systems analyze and monitor technical systems and take automated decisions. This industrial revolution is known as “Industry 4.0” in Germany and “Industrial Internet” in the USA. An essential enabler of the fourth industrial revolution is Machine Learning. The ITN MAGISTER will utilize Machine Learning to predict and understand thermoacoustics in aircraft engine combustors, and to lead combustion research to a revolutionary new approach in this area.

Within this research focus in the past the following research projects were associated:

Low Emissions Core-Engine Technologies
(LEMCOTEC)
Improvement and optimisation of PERM system (together with AVIO, UNI FI, CIAM) Obtain the 65% NOx reduction at Injection System level, according to ACARE target, technology evolution of AVIO‟s PERM Injection System from NEWAC Verify injection system operability at critical engine cycle points, to fulfil specific requirements like ignition and lean blow out behaviour at idle conditions and combustion instabilities control at high power. Extend the performance of the PERM_EV injection system at real regional engine conditions for high OPR cycle points. The work will be organised as follows: An optimised PERM injection system (PERM_EV) will be developed and validated; baseline is the promising PERM2 IS injector, already tested at max 22 bars. Define the PERM_EV and test up to 20 bars in a tubular rig by the HP rig of KIT Develop an improved liner system to be coupled with the PERM_EV injector within the annular combustor configuration. Cold test will be performed by UNI FI. Test in a combustor rig (CIAM) with PERM injection systems and with advanced liner cooling system. Supported by detailed CFD modelling and extend the results to all the critical engine conditions. Test of a second iterated and optimised injection system configuration at KIT Investigate up TRL 4 the performance of a flame monitoring system, to be developed by KIT, and a plasma ignition system, to be developed by CIAM. Depending on the TRL of the components, all developed technologies will be integrated in the annular combustor configuration at M24. Research investigations will continue to M48 estimating their impact on the final combustor configuration.

Renewable Power Generation by Solar Particle Receiver Driven Sulphur Storage Cycle
(PEGASUS)
PEGASUS will investigate a novel power cycle for renewable electricity production combining a solar centrifugal particle receiver with a sulphur storage system for baseload operation. The proposed process combines streams of solid particles as heat transfer fluid that can also be used for direct thermal energy storage, with indirect thermochemical storage of solar energy in solid sulphur, rendering thus a solar power plant capable of round-the-clock renewable electricity production. Process scheme of the solar sulphur cycle / Image source: DLR The overall objective of PEGASUS is the development and demonstration of an innovative solar tower system based on solid particles combined with a novel thermochemical solar energy storage technology based on elemental sulphur, to achieve dispatchable and firm renewable electricity generation with a significant cost reduction with respect to current state-of-the-art concepts. The technology will be validated under real on- sun concentrated solar irradiation in the Solar Tower Jülich (STJ) thermal plant in Germany owned by the Project Coordinator, DLR. In this perspective, the project’s specific Technical Objectives of KIT are: To develop and realize a novel lab-scale sulphur burner able to modulate in a range of 10-50 kW with quantitative targets: sulphur combustion with >99 % combustion efficiency at power densities > 1,5 MW/m³ under atmospheric conditions (3 times higher than conventional sulphur combustion chambers) and flame temperatures > 1400 °C. To demonstrate the feasibility of the over-all proposed process, draft the complete flowsheet and analysis of optimized integrated process scaled-up to the 5MW_th power level, assess the technology vs. the targets set. More information is published in a press-release of KIT and on the public website of the project (link below)

Modellierung des Verbrennungsverlaufs bei der Verbrennung von flüssigen Brennstoffen und Flüssigbrennstoff/Wasser-Emulsionen.
(CEC_1F)
In the context of the objective of the German government and the European Union's energy policy, it is crucial to increase the share of renewable energy. However, due to the fect that renewable engergy production due fluctuating wind and sun energy does not correlate with the customer demand, it is neccesary to compensate this energy generation gap with flexible power plants. Such plants need to be operated in a flexible load range. In this context, gas power plants play an important role because they allow rapid load changes and provide energy at high efficiencies. Goal of the current project is the development of combustion technologies for climate-friendly energy conversion. The research that is to be done in subproject 1F serves to fulfill the subgoal "operational flexibility and fuel flexibility." The operational flexibility is critically dependent on the stability limits of the combustion, but their prediction is not adequately possible up-to-now. The fuel flexibility requires the safe design of burners that can be operated with both gaseous and liquid fuel. One important way to foster climate-friendly power generation is the increase in the efficiency of gas turbines. Since the increase in the efficiency is related with the increase of the pressure and temperature levels of the process, the main objective is based on the optimization of the cooling of the highly stressed parts. Such an optimization can not be done without the knowledge of the temperature distribution in the combustion chamber and the combustion chamber outlet, which is also a primary goal of the project. The calculation of the temperature distribution or the distribution of heat release depends on the following sub-processes: Detection of the droplet dispersion, which is dominated by the turbulent fluctuation movements Calculation of evaporation, which depends on the evaporation characteristics and the turbulent heat transfer from the gaseous to the liquid phase Analysis of the interaction between the turbulence and heat release The true representation of the realistic subprocesses represent the scientific part of the project goals 1F Calculated (LES) average temperature in the vicinity of an airblast nozzle using hexadecane as fuel (left: with - right without water addition).

Modular extension of an overall model for improved prediction of combustion process in liquid fuel/water emulsions
(CEC3H)
The research carried out withing the subproject 3H contributes to the fulfillment of the projects' goal "operation flexibility and fuel flexibility". Operation stability is mainly depending on the the stability limit of combustion, which is still difficult to predict. Fuel flexibility requires the thorough design of a combustor which is able to operate on gaseous and liquid fuels. The goals of the subproject 3H, which continues the successful work of the subproject 1F stem from these requirements and challenges. The liquid fuel and liquid fuel/water emulsion combustion model developed within in the framework of subproject 1F is able to predict the heat release during the combustion of liquid fuels with a given droplet diameter and velocity distribution. Hence, different important aspects which are important for the application of the model have not been accounted for. The first aspect concerns the specification of the droplet properties which is currently derived from experimental data. The second aspect is the neglect of heat losses which have a major impact on the calculation of flame stability and emissions. Furthermore, the model has only been validated for kerosene until now but not for diesel or diesel water emulsions. The subproject 3H addresses these questions and aims to the development of a tool which can be used in the design process of a gas turbine combustion chamber. To this end, the atomization of the liquid fuel shall be described by an empirical model. Moreover, the influence of heat losses on the heat release rate shall be captured. Further aspects, e.g. the droplet wall interaction and the role of the fuel-to-water ratio distribution which have a significant impact on the gas turbine combustion process are investigated.