Exploitable results
In relation to expected tripling of global aircraft traffic until 2015, the corresponding pollutant emission must not be neglected. Aeroengine development is highly supported by computational fluid dynamics (CFD) code calculations to evaluate construction details with regard to their impact on combustion related parameters and emissions. Therefore, a reliable and validated soot model implemented in CFD codes offers means not only to reduce expensive rig tests, but as well to open the possibility for new combustor design concepts with the potential of reducing pollutant emissions, in particular soot. The Sia-Team project delivered an 'enhanced and validated mechanistic soot model' (ESM) for kerosene like fuels. The improved predictive capability of CFD codes using the reduced ESM combined with radiative heat transfer models have been demonstrated under aero engine combustor conditions. The influence of the liquid phase on soot formation shall be tested on its significance.
The process from research to industrial application has been the main driver for the Sia-Team project and can be seen as a threefold process. First, the soot model has to be developed or improved according to the objectives of research. Second, this detailed model has to be reduced in complexity according to the objectives of (scientific) CFD code integration and handling and third, the CFD code itself has to be tuned according to the objectives of industrial development and design. The Sia-Team project has been designed to concentrate on the first step of this process with regard to soot modelling and influence of the liquid phase on soot formation in aeroengine combustion. Therefore the main objectives of this project have been:
1. The improvement and validation of the state-of-the-art mechanistic soot model, improving its predictive capability with respect to soot formation and oxidation in kerosene fuelled combustion.
2. Reduction of the ESM and implementation into scientific CFD codes, which use different methods of chemistry-turbulence interaction and are supported by radiative heat transfer models. Demonstration of applicability, performed by comparison with experimental data at semi-technical and technical scale burners, relevant to aeroengine combustor conditions.
3. Proving the existence and quantifying the possible extent of the influence of a liquid phase on soot formation.
The approach chosen by the Sia-Team project consisted of the detailed investigation on the influence of some kerosene fuel compounds and blends on soot formation. Extended knowledge on the relation of fuel compounds or blends to growth species (PAHs - polycyclic aromatic hydrocarbons) leading to soot nuclei have improved prediction of soot formation. This has given rise to the first process step, the reduction of complexity according to the objectives of scientific CFD codes. This has been established by the implementation into four different CFD codes, three codes describing the turbulence-chemistry interaction with different methods of probability density functions (PDFs) and two by a flamelet approach with post-processing. Some of the CFD codes have coupled the information on soot to radiative heat transfer models, thus predicting temperature loads of combustors. They have demonstrated their applicability to aeroengine combustor modelling by comparing calculations with validation data obtained through experiments at two technical scales, replicating special conditions of aeroengine combustion.
To support this first step of the transformation process, information had to be provided on the influence of the liquid phase on soot formation, the latter being described solely as a gas phase process. Therefore one part of this project has been dedicated to experiments, which have gained information through comparison of soot formation from a combustor fuelled with liquid or gaseous kerosene n alternatively at relevant aeroengine conditions. Another part deals with the soot formation by combustion of mono-disperse droplets in a group diffusion flame tying to couple liquid phase parameters like droplet diameter, fuel, etc. to soot formation and studying their influence.
The main output of this project has been a validated and reduced reaction mechanism for a kerosene model fuel, an improved mechanistic soot model with enhanced predictive capabilities for soot formation and oxidation, the implementation or use of its essential improvements by scientific and industrial CFD codes, coupled to radiative heat transfer models and the demonstration of its applicability simulating aeroengine combustor experiments at semi-technical and technical scales. Moreover, a new model approach, different from the mechanistic one the project has started with, has been investigated and implemented into CFD code. This bisectional model approach is especially suitable for CFD applications and reduces the complexity of the soot model itself as well as the computational efforts.
Due to its scientific approach to applied research this project has contributed to a better prospect of European combustion research.
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