| 1. |
- Ibron, Christian, et al.
(author)
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Numerical simulation of a mixed-mode reaction front in a PPC engine
- 2021. - 4
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In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38, s. 5703-5711
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Conference paper (peer-reviewed)abstract
- The ignition process, mode of combustion and reaction front propagation in a partially premixed combustion (PPC) engine running with a primary reference fuel (87 vol% iso-octane, 13 vol% n-heptane) were investigated numerically in a large eddy simulation (LES). A one-equation sub-grid scale model coupled to the partially stirred reactor model and a finite rate chemical model were used in LES. Different combustion modes, ignition front propagation, premixed flame and non-premixed flame, were observed simultaneously. Displacement speed of CO iso-surface propagation described the transition of premixed auto-ignition to non-premixed flame. High temporal resolution optical data of CH2O and chemiluminescence were compared with simulated results. A high-speed ignition front was found to expand through fuel-rich mixture and stabilize around stoichiometry in a non-premixed flame while lean premixed combustion occurs in the spray wake at a much slower pace. A good qualitative agreement of the distribution of chemiluminescence and CH2O formation and destruction indicated that the simulation approach sufficiently captures the driving physics of mixed-mode combustion in PPC engines. The transition from auto-ignition to flame occurs over a period of several crank angles and the reaction front propagation can be captured using the described model.
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| 2. |
- Yang, Miao, et al.
(author)
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CFD modeling of biomass combustion and gasification in fluidized bed reactors using a distribution kernel method
- 2022
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In: Combustion and Flame. - : Elsevier Inc.. - 0010-2180 .- 1556-2921. ; 236
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Journal article (peer-reviewed)abstract
- A three-dimensional reactive multi-phase particle-in-cell (MP-PIC) model is employed to investigate biomass combustion and gasification in fluidized bed furnaces. The MP-PIC model considered here is based on a coarse grain method (CGM) which clusters fuel and sand particles into parcels. CGM is computationally efficient, however, it can cause numerical instability if the clustered parcels are passing through small computational cells, resulting in over-loading of solid particles in the cells. To overcome this problem, in this study, a distribution kernel method (DKM) is proposed and implemented in an open-source CFD code, OpenFOAM. In DKM, a redistribution procedure is employed to spread the solid volume and source terms of the particles in the parcel to the domain in which the particles are clustered. The numerical stiffness problem caused by the CGM clustering can be remedied by this method. Validation of the model was performed using data from different lab-scale reactors. The model was shown to be able to capture the transient heat transfer process in a lab-scale bubbling fluidized bed reactor under varying fluidization velocities and loads of sand. Then, the model was used to study the combustion/gasification process in a bubbling fluidized bed reactor under varying ambient temperatures, equivalent air ratios, and steam-to-biomass ratios. The performance of DKM was shown to improve the accuracy and the robustness of the model. © 2021 The Author(s)
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| 3. |
- Yang, Miao, et al.
(author)
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Numerical simulation of biomass gasification in fluidized bed gasifiers
- 2023
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In: Fuel. - : Elsevier BV. - 0016-2361. ; 337
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Journal article (peer-reviewed)abstract
- Numerical simulation of biomass gasification in fluidized bed reactors faces several challenges including proper modeling of the physical and chemical processes involved in the gasification and numerical stiffness of the two-phase dense particle flow problem. In this paper, the multi-phase particle-in-cell (MP-PIC) model coupled with a recently developed distribution kernel method (DKM) and a new one-step pyrolysis model are employed to investigate biomass gasification in two lab-scale fluidized bed gasifiers (FBGs). The results are evaluated by comparing with the results from the Particle Centroid Method (PCM) and experimental measurements. The performance of DKM is shown to improve the robustness of the model and the new pyrolysis model is shown to improve the sensitivity of the yields of gasification products to operating temperature. The simulation results using the new pyrolysis model agree well with the experimental data under different gasification conditions. The model is shown to be able to capture the trend of gas products with respect to variations of steam/biomass ratio (SR) and operating temperature (Tr). The mechanisms of the formation of gas products are analyzed based on the numerical results. By increasing the SR and Tr, the production of H2 and CO2 is shown to increase while the production of CO and CH4 to decrease. It is shown that varying the steam/biomass ratio in the range of 0.8∼2.0 has a minor effect on the pyrolysis process and heterogeneous reactions, while homogeneous reactions are significantly affected, leading to changes in the final composition of the gas products. Varying the gasifier temperature Tr has on the other hand a crucial effect on the pyrolysis process and as such a significant impact on the gasification products and carbon conversion.
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