The doctoral program is based on the work of highly experienced research laboratories. The four Academic Partners have developed considerable experience and skills in the natural gas combustion domain. One of the originalities is to link the different teams together with four additional industrial partners in order to suggest and develop new complementary perspectives combining mathematics and physics, chemistry and fluid mechanics, computation and experiments, all these different approaches aiming at a final real scale application for industrial use by companies.
The Scientific Programme is organized in 8 main Work Packages, as reported below.
Development of a comprehensive detailed kinetic mechanism to model the pyrolysis, oxidation and combustion of natural gas with predictive capabilities in a wide range of operating conditions. Special attention devoted to the chemistry of pollutant species like nitrogen oxides (NOx) and carbonaceous particles (soot).
The kinetic characterization of natural gas represents an important and crucial point to analyze and describe, especially considering the wide range of operating conditions in which it will be applied (conventional combustion, high-pressure, flameless combustion, oxy-fuel conditions, highly-diluted mixtures, lean conditions, etc.).
Task 1.1: A detailed kinetic mechanism for oxidation and combustion of natural gas will be developed. The kinetic scheme will be primarily validated using experimental data available in the literature. Additional data from the experimental campaign in WP6 will be exploited to further validate the mechanism in operating conditions closer to those of interest.
Task 1.3: A specific sub-mechanism of NOx (nitrogen oxides) formation and its interactions with the natural gas oxidation environment will be coupled to the mechanism developed above.
Task 1.3: The kinetic mechanism will be then extended to describe also the formation of large aromatic hydrocarbons (PAHs) and carbonaceous particles (soot). Particular attention will be focused on pollutants like aldehydes and aromatics. The model will simulate the morphology and chemical nature of the particulate matter generated during the natural gas combustion.
The primary purpose of WP2 will be that of revisiting existing chemistry and radiation literature sub-models in the perspective of the non-conventional combustion regimes investigated in the project. In particular, systematic reduction of chemical mechanisms will be carried out by means of “canonical reactors” sharing similarities with flameless combustion operations. Optimally reduced mechanism will be derived using techniques such as Sensitivity Analysis, theory of Directed Relation Graph (DRG), Computation Singular Perturbation (CSP) and Principal Component Analysis (PCA).
Task 2.1: The systematic validation of chemical mechanisms will be carried out using local and global sensitivity analysis. Local sensitivity analysis will be first used to emphasize what are the main input parameters affecting the predicted results in the investigated conditions. The parameters included in this study will be the rates of reaction and the thermodynamic data, which have both a dramatic impact on the results. The first order sensitivity of the predicted results to all input parameters will give a first approximation of the uncertainty of the simulation results based on the uncertainty of the input parameters.
Task 2.2: Global sensitivity analysis will be then used to determine the uncertainties on the predicted value. This analysis will involve a large number of simulations for each variation of the input parameters and will then requires sampling techniques such as Monte Carlo or structured sampling. The optimization of the kinetic mechanisms will rely on the simulation of simple idealized reactors (e.g. PSR, batch, PFR) for species, temperatures and ignition delay times. Laminar premixed and counter diffusion flames will be then employed to validate the mechanisms for the prediction of minor species and pollutants.
Task 2.3: Development of proper numerical techniques to reduce the detailed kinetic mechanisms developed in WP1, in order to make possible the numerical simulation of industrial-scale devices
The main objective is to study the formation of pollutant species such as NOx, polycyclic aromatic hydrocarbons (PAH) and solid particles (soot) in laminar flames fed with natural gas in operating conditions close to those of interest.
Task 3.1: Laminar flames will be numerical investigated using the detailed kinetic mechanism developed in WP1. The attention will be focused on the formation of pollutant species and the ultimate goal to be achieved is a more in-depth understanding of the mechanisms and reaction pathways that lead to their formation. This knowledge can then be used for improving the design of equipment for combustion of natural gas, characterized by low emissions of pollutants. Simplified geometrical configurations will be taken into account, in order to have the possibility to exploit the detailed kinetic mechanisms developed in WP1 without any reduction, i.e. without any simplification on the chemical side. This gives the possibility to describe the reactions occurring in the flame with an extremely high level of detail (which is impossible in terms of computational cost for complex geometries, to because of the large number of chemical species to be treated). In particular, the simulations will be devoted to counter-flow diffusion flames, premixed flat flames and axisymmetric coflow (diffusion and partially premixed) flames.
Task 3.2: Part of the activity will be devoted to the numerical simulation of laminar flames experimentally investigated in WP6, in order to further validate the kinetic mechanisms developed in WP1 in operating conditions which are closer to the real applications of natural gas combustion.
Understanding of interactions between chemistry and turbulence for natural gas combustion in conditions of typical applications of natural gas
Different strategies will be investigated to model the turbulence/chemistry interactions for the combustion technologies investigated within the present project.
Task 4.1: Established turbulent combustion models as well as new modeling strategies will be investigated in the project, in the framework of RANS and LES simulations. These turbulent combustion models will include flamelet/progress variable model (FPV) [15, 44], flame-generated manifolds (FGM)  and flame prolongation of ILDM (FPI) , the Eddy Dissipation Concept (EDC)  and the Partially Stirred Reactor (PaSR) approaches .
Task 4.2: Validation data sets for the present WP will be generated from ad-hoc DNS simulations as well as from the literature (Adelaide- and Delft-JHC burners and Cabra flame). For large-scale systems, data will be obtained under the International Flame research Foundation (IFRF) Research Programme on MILD combustion (http://www.research.ifrf.net/research/programmes.html).
Application of reduced kinetic mechanisms or equivalent approaches in the simulation of turbulent flames using different numerical techniques (RANS, LES, DNS). Assessment of the proposed methodology and analysis of the predictive capabilities with the experimental data collected in WP7.
Task 5.1. Initial benchmarking activity of the different LES codes and subgrid models to be used in this WP against two carefully selected non-reacting data sets of relevance for this project. For this activity, reference data should already be available, and as long as possible the same grid and open inflow/outflow conditions should be used.
Task 5.2. Comparative study of different existing LES combustion models (such as filtered and propagation based flamelet models and various finite rate chemistry models already used by the participants) on one or two selected combustion test cases. For this Task, reference data should already be available, Candidates for test problems in this WP are the ORACLES rig developed under the FP6 project MOLECULES (Bruel et al.) and the low-swirl stabilized premixed flame of Cheng type (Johanson et al.) jointly investigated by LTH, FOI and TU Darmstadt (Nogenmyr et al.).
Task 5.3. Development of improved LES combustion models for using reduced mechanisms developed in WP2. Several candidate approaches should here be considered. Just to mention a few: Filtered Tabulated Chemistry for LES, thickened flame models, transported and presumed PDF models, flamelet models with tabulated chemistry, PaSR type finite rate chemistry LES, homogenization-based finite rate chemistry LES. The modeling should be focusing on methodologies that can be used, in the near future to investigate practical combustion systems.
Task 5.4. Address additional modeling issues pertinent to the accurate predictions of real combustion systems. These issues have often been overshadowed by the more apparent problems of turbulence and turbulence chemistry interactions that have attracted considerable research interest over a long time, but needs to be addressed if we are striving towards a truly predictive simulation capability.
Task 5.5. Synthesis of the LES modeling activity leading to (i) a better understanding of the predictive capabilities of the different LES models used, (ii) improved LES models for turbulent combustion, (iii) guidelines for using LES in turbulent combustion of practical combustion systems, (iv) improved knowledge about the importance of different processes and their interactions.
Laminar flames will be experimentally investigated with two objectives: 1) Measurements of main combustion products and pollutant emissions from flames burning natural gas in steady laminar conditions as validation tool for detailed kinetic mechanisms developed in WP1 and applied in WP2; 2) Characterization of the dynamic of laminar or low Reynolds number flames submitted to flow or acoustic pulsations to support the development of LES models in WP5 to be applied in WP8.
Task 6.1: Experimental investigation of main combustion products and pollutant emissions in steady-state laminar flame burning natural gas.
Task 6.2: Mean statistics are generally not sufficiently discriminating to compare LES models predicting yet different unsteady behaviors. This task aims to characterize the dynamic of flame submitted to controlled flow or acoustic pulsations to assess the required ability of LES models to behave correctly in the limit of unsteady laminar flows, a situation that may be encountered when using fine grid meshes.
The experimental investigations serve (i) for a better understanding of unsteady processes and pollutant emissions especially in stratified combustion and (ii) to allocate reliable data for validation of numerical simulations. This approach is based on a comprehensive investigation of different turbulent flames at different levels of complexity. The turbulent flames of increasing complexity vary in their nozzle design, fuel and pressure conditions. These flames need to be characterized in view of their flow and scalar field in a comprehensive way. This is most accurately performed using non-intrusive high temporal and spatial resolution diagnostics.
Task 7.1: Experimental campaign on Rig A to allow complex geometry of injectors and different fuels.
Task 7.2: Experimental campaign on Rig B to operate at different pressure ratios.
Task 7.3: Experimental campaign on Rig C to run at different thermal efficiencies and allow practical engineering conditions
Objectives: Application of the numerical tools mainly developed in WP2, WP4 and WP5 for simulation of industrial-scale combustion devices with the aim to improve the combustion process and reduce the formation of pollutant species
Task 8.1 (lead FR-ECP): large eddy simulations (LES) of conventional swirling turbulent flames as encountered in gas turbines or industrial furnaces. The objective is to assess the ability of numerical simulations to reliably predict turbulent flame dynamics as well as pollutant emissions. Numerical simulations will be validated against data obtained in WP7.
Task 8.2 (lead BE-ULB, with IT-POLIMI): Numerical simulations of “flameless burners” for industrial burners (RANS). The objective is to assess the ability of models to predict highly diluted combustion regimes (flame stabilization, pollutant emissions) and to investigate optimized configurations.