| 1. |
- Feuk, Henrik, et al.
(författare)
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Impact of Methane and Hydrogen-Enriched Methane Pilot Injection on the Surface Temperature of a Scaled-Down Burner Nozzle Measured Using Phosphor Thermometry
- 2022
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Ingår i: International Journal of Turbomachinery, Propulsion and Power. - : MDPI AG. - 2504-186X. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- The surface temperature of a burner nozzle using three different pilot hardware configurations was measured using lifetime phosphor thermometry with the ZnS:Ag phosphor in a gas turbine model combustor designed to mimic the Siemens DLE (Dry Low Emission) burner. The three pilot hardware configurations included a non-premixed pilot injection setup and two partially premixed pilot injections where one had a relatively higher degree of premixing. For each pilot hardware configuration, the combustor was operated with either methane or hydrogen-enriched methane (H2/CH4: 50/50 in volume %). The local heating from pilot flames was much more significant for hydrogen-enriched methane compared with pure methane due to the pilot flames being in general more closely attached to the pilot nozzles with hydrogen-enriched methane. For the methane fuel, the average surface temperature of the burner nozzle was approximately 40 K higher for the partially premixed pilot injection configuration with a lower degree of mixing as compared to the non-premixed pilot injection configuration. In contrast, with the hydrogen-enriched methane fuel, the differences in surface temperature between the different pilot injection hardware configurations were much smaller due to the close-to-nozzle frame structure.
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| 2. |
- Papafilippou, Nikolaos, et al.
(författare)
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LES of Biomass Syngas Combustion in a Swirl Stabilised Burner: Model Validation and Predictions
- 2024
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Ingår i: Flow Turbulence and Combustion. - : Springer Nature. - 1386-6184 .- 1573-1987.
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Tidskriftsartikel (refereegranskat)abstract
- In this work, numerical investigations were performed using large eddy simulations and validated against detailed measurements in the CeCOST swirl stabilised burner. Both cold and reactive flow have been studied and the model has shown a good agreement with experiments. The verification of the model was done using the LES index of quality and a single grid estimator. The cold flow simulations predicted results closely to experiments setting baseline for the reactive simulations. Coherent structures like the vortex rope above the swirler and a precessing vortex core in the combustion chamber were identified. The reactive conditions were modelled with the Flamelet generated manifold and artificially thickened flame models. Simulations were performed for an experimental syngas composition from black liquor gasification at three different CO2 dilution levels. Three different Reynolds numbers were investigated with the model matching closely to experimentally detected 2D flow field and OH for the most CO2 diluted mixture. It was found that the opening angles of the flames differ by a maximum of 13% between experiments and simulations. The most diluted fuel investigated experienced a liftoff distance of 23.5 mm at the Re 25 k. This was also the highest liftoff distance experienced in this cohort of fuels. The same fuel also proved to have the thickest flame annulus at 78.5 mm. Overall, in cases with no experimental data available the predictions made by the model follow the same trends which hints its applicability to higher Re cases.
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| 3. |
- Pignatelli, Francesco, et al.
(författare)
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Displacement speed analysis of surface propagation in moderately turbulent premixed reacting waves
- 2021
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Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 33:3
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Tidskriftsartikel (refereegranskat)abstract
- The propagation of premixed reacting waves can be characterized by a displacement speed Sd at which the local surface of the reaction progress scalar moves respective to flow. Often, Sd is considered through decomposition into three parts of contribution due to the tangential diffusion of curvature, normal diffusion, and reaction. A set of recently derived transport equations for Sd and three of its decomposed parts provides new diagnostics for better understanding reaction wave propagation in a turbulent environment. In this work, those diagnostics are applied on four similarly setup direct numerical simulation cases studying the propagation of moderately perturbed planar reaction waves into homogeneous turbulence, and the reaction waves differ by the density ratio between fresh and burned gases. The data analysis reveals four self-acceleration behaviors: (i) surfaces propagating at large positive (negative) Sd tend to advance (retreat) faster, (ii) surfaces having large positive (negative) curvature tend to become more curved positively (negatively), (iii) thicken wave zones tend to become thicker, and (iv) surface elements accelerate toward their destruction. The extent of the above accelerations all reduces in the reaction wave having a high density ratio. This can be attributed to the turbulence inhibition due to the flow dilatation and viscosity increase across a thermal-expansion enabled reaction wave. The distribution of curvature for the reaction-zone surface skews toward a negative value, i.e., the curvature center pointing to the burned product.
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| 4. |
- Pignatelli, Francesco, et al.
(författare)
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Effect of CO2 dilution on structures of premixed syngas/air flames in a gas turbine model combustor
- 2023
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Ingår i: Combustion and Flame. - : Elsevier Inc.. - 0010-2180 .- 1556-2921. ; 255
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Tidskriftsartikel (refereegranskat)abstract
- The impact of CO2 dilution on combustion of syngas (a mixture of H2, CO, and CH4) was investigated in a lab-scale gas turbine model combustor at atmospheric pressure conditions. Two mild dilution levels of CO2, corresponding to 15% and 34% of CO2 mole fraction in the syngas/CO2 mixtures, were experimentally investigated to evaluate the effects of CO2 dilution on the flame structures and the emissions of CO and NOx. All experiments were performed at a constant Reynolds number (Re = 10000). High-speed flame luminescence, simultaneous planar laser-induced fluorescence (PLIF) measurements of the OH radicals and particle image velocimetry (PIV) were employed for qualitative and quantitative assessment of the resulting flame and flow structures. The main findings are: (a) the operability range of the syngas flames is significantly affected by the CO2 dilution, with both the lean blowoff (LBO) limit and the flashback limit shifting towards fuel-richer conditions as the CO2 dilution increases; (b) syngas flames exhibit flame-pocket structures with chemical reactions taking place in isolated pockets surrounded by non-reacting fuel/air mixture; (c) the inner recirculation zone tends to move closer to the burner axis at high CO2 dilution, and (d) the NOx emission becomes significantly lower with increasing CO2 dilution while the CO emission exhibits the opposite trend. The flame-pocket structure is more significant with increased CO2 dilution level. The low NOx emissions and high CO emissions are the results of the flame-pocket structures. © 2023 The Author(s)
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| 5. |
- Pignatelli, Francesco, et al.
(författare)
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Predictions of Spray Combustion using Conventional Category A Fuels and Exploratory Category C Fuels
- 2023
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Ingår i: AIAA SCITECH 2023 Forum. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624106996
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Konferensbidrag (refereegranskat)abstract
- Aviation currently contributes about 3% of the world’s CO2 emissions, 5% of the global warming, and 35% of the trade. Reducing the emissions and the global warming from aviation is thus essential. Many approaches to achieve this goal are underway, including H2, fuel cells, and batteries, but also by replacing the fossil jet fuel with sustainable jet fuel from non-fossil feedstocks. This involves many challenges, and among them we have the issue of current jet engines being developed for existing fossil jet fuels. To facilitate the change towards sustainable jet fuel, typically having different thermophysical and combustion properties compared to fossil jet fuels, we need to analyze the sensitivity of combustion to other fuels, having a wider range of thermophysical specifications. Here, we examine combustion of n-heptane, n-dodecane, Jet A, and two test fuels, C1 and C5 in three different combustors. The first and second cases are axisymmetric and rectilinear pre-vaporized premixed bluff-body stabilized flames, whereas the third is a single sector helicopter combustor for liquid fuel. A Finite Rate Chemistry (FRC) Large Eddy Simulation (LES) model is used together with small comprehensive reaction mechanisms of ~300 reactions. Comparison with experimental data is performed for the pre-vaporized combustor configurations. Good agreement is generally observed, and small to marginal differences in combustion behavior is observed between the different fuels.
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| 6. |
- Pignatelli, Francesco
(författare)
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Turbulent premixed flames in a model gas turbine combustor: fuel sensitivity and flame dynamics
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The demand for energy security and reduction of greenhouse gas emissions has led to a surge of interest in the development of high-efficiency and low-emission gas turbine engines that can run on alternative low carbon content fuels, such as hydrogen-enriched fuel and syngas. However, the combustion characteristics of these fuels can significantly alter the flame characteristics and operability range of existing combustors. Therefore, it is crucial to gain a better understanding of the turbulent combustion characteristics of these fuels from both fundamental and practical perspectives. In this thesis, a combination of numerical and experimental diagnostic methodologies has been employed to investigate how the fuel characteristics can affect the fundamental properties of flames and their structure in gas turbine-like combustors. The aimis to provide a comprehensive understanding of the complex combustion processes associated with these alternative fuels. The propagation of turbulent premixed flames under different density ratio conditions is investigatedusing direct numerical simulation (DNS). The displacement speed, which characterizes the self-propagation of an isosurface defined based on a reaction progress variable in a turbulent premixed flame, has gained significant interest in the scientific community for flame modeling purposes. In this thesis, a set of new transport equations for dilation and curvature-induced flame stretch rate is derived. Based on the set of evolution equations for displacement speed that takes into account the effects of curvature, normal diffusion, and reactions, this thesis analyzes the thermal expansion effect on the correlation between these quantities. The results reveal four scenarios of flame self-acceleration. The findings provide valuable insights into the understanding of the complex dynamics of turbulent premixed flames. A newly improved gas turbine model combustor, known as CeCOST burner, is the focus of an experimentalcampaign that involves laser-based diagnostics techniques, including simultaneous OH-/CH2O planar laser induced fluorescence (PLIF), simultaneous OH-PLIF, particle imaging velocimetry (PIV), and phosphor thermometry for surface temperature measurements. High-speed OH* chemiluminescence and exhaust gas measurements are also utilized. The results of the study reveal that hydrogen-enrichment can significantly extend the operation of methane/air to ultra-lean mixtures, resulting in low NOx emissions. The structures of the flame and the flow show significant variations with hydrogen-enrichment. Isolated flame pockets are identified in lean hydrogen-enriched methane/air flames, as well as in syngas flames where a substantial amount of hydrogen is present. The vortex breakdown structure is found to be strongly coupled with the location of the reaction zones. Furthermore, it is observed that pilot flames can enhance flame stabilization by producing hot gas and radicals that aid in anchoring the flames in the outer recirculation zone of the combustor. The findings of this study provide valuable insights into the combustion characteristics of methane/air, hydrogen-enriched methane/air, and syngas/air flames in the CeCOST burner, as well as the influence of pilot flames on flame and flow structures. These insights contribute to the development of more efficient and environmentally friendly gas turbine combustor designs.
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| 7. |
- Åkerblom, Arvid, et al.
(författare)
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Numerical Simulations of Spray Combustion in Jet Engines
- 2022
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Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 9:12
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Tidskriftsartikel (refereegranskat)abstract
- The aviation sector is facing a massive change in terms of replacing the currently used fossil jet fuels (Jet A, JP5, etc.) with non-fossil jet fuels from sustainable feedstocks. This involves several challenges and, among them, we have the fundamental issue of current jet engines being developed for the existing fossil jet fuels. To facilitate such a transformation, we need to investigate the sensitivity of jet engines to other fuels, having a wider range of thermophysical specifications. The combustion process is particularly important and difficult to characterize with respect to fuel characteristics. In this study, we examine premixed and pre-vaporized combustion of dodecane, Jet A, and a synthetic test fuel, C1, based on the alcohol-to-jet (ATJ) certified pathway behind an equilateral bluff-body flameholder, spray combustion of Jet A and C1 in a laboratory combustor, and spray combustion of Jet A and C1 in a single-sector model of a helicopter engine by means of numerical simulations. A finite rate chemistry (FRC) large eddy simulation (LES) approach is adopted and used together with small comprehensive reaction mechanisms of around 300 reversible reactions. Comparison with experimental data is performed for the bluff-body flameholder and laboratory combustor configurations. Good agreement is generally observed, and small to marginal differences in combustion behavior are observed between the different fuels.
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