Kyushu University Academic Staff Educational and Research Activities Database
List of Presentations
Hiroaki Watanabe Last modified date:2018.10.18

Associate Professor / Combustion / Department of Mechanical Engineering / Faculty of Engineering


Presentations
1. Chiharu Aoyama, Hiroshi Fukuoka, Hiroaki Watanabe, A novel method to explore submarine gas resources from plumes originating from seafloor surface and/or shallow subsurface methane hydrates, 9th International Conference on Gas Hydrate, 2017.06.
2. Hazim Shehab, Ryoichi Kurose, Hiroaki Watanabe, Toshiaki Kitagawa, Numerical study on the effects of turbulence scale on spherically propagating hydrogen flames, 自動車技術会2018年春季大会, 2018.05.
3. Hazim Shehab, Hiroaki Watanabe, Masaya Muto, Ryoichi Kurose, Toshiaki Kitagawa, Numerical study on the effects of turbulence intensity and scale on spherically propagating flames, 第28回内燃機関シンポジウム, 2017.12.
4. Masaya Muto, Hiroaki Watanabe, Ryoichi Kurose, Large eddy simulation of pulverized coal combustion in multi-burner system -Effect of in-furnace blending method on NOx emission-, The First Asian Conference on Thermal Science, ACTS2017, 2017.03, In the field of pulverized coal combustion, the development of the combustion technology meeting the demands such as reducing environmental pollutants has been conducted by many researchers and developers. To make a further improvement, an understanding of the flow field and pulverized coal particle behaviors in the combustion furnace is necessary. However, it is difficult to obtain such information solely on the basis of experiments. In this study, large-eddy simulation (LES) is applied to the multi-burner pulverized coal combustion furnace and the effects of an in-furnace blending method, in which different kinds of coal (high volatile coal and low volatile coal) are injected at each burner stage, on NOx emission and unburned carbon concentration in fly ash are investigated. The blending ratio of high volatile coal is fixed at 33%. The variable density, low-Mach number, reacting flow equations with two-way coupling between gas phase and pulverized coal particles are solved using an unstructured LES solver, FrontFlow/Red extended by Kyoto University, Central Research Institute of Electric Power Industry and Numerical Flow Designing, Ltd. Result shows that oxygen is rapidly consumed near the burner, from which the low volatile coal is injected, and NOx decreases because the reducing atmosphere becomes dominant due to the lack of oxygen. These information on the effects of in-furnace blending method on the flow field that are considered to be essential for prediction of the product gases in the furnace, can only be captured in large scale unsteady simulation like present study..
5. Kenji Tanno, Seongyool Ahn, Hisao Makino, Hiroaki Watanabe, Numerical study of effect of operation condition for coal gasifier in oxo-fuel IGCC, The First Austrian-Japan Symposium on Carbon Resource Utilization, 2016.11.
6. Hiroaki Watanabe, Akihiro Yamashita, Nozomu Hashimoto, Isao Yuri, Hiroyuki Hishida, Numerical simulation of atmospheric combustion of gasified fuel from oxy-fuel IGCC system, 36th International Symposium on Combustion, 2016.08, CO-rich gasified fuel and oxygen with CO2-rich diluent is assumed to be burned at near stoichiometric condition in a gas turbine combustor of an oxy-fuel IGCC system. To investigate the fundamental combustion characteristics of such the CO-rich gasified fuel at near stoichiometric condition, large eddy simulations of a combustion on an atmospheric test combustor were performed. The test combustor operated by Central Research Institute of Electric Power Industry (CRIEPI), in which a small diffusion burner with separate fuel, oxidizer and diluent supply nozzles was employed. The combustor is a water-cooled combustor made of steel with refractory materials placed inside wall. The computational domain was designed to match the actual configuration of the burner. Numerical simulations employing one-step global reaction mechanism and employing two step reaction mechanism that considers CO2 dissociation reaction were performed. Both numerical simulation results were compared with the experimental results. The comparison reveals that the numerical simulation employing two-step reaction mechanism can reproduce the tendency of CO mole fraction distribution inside the combustor. On the other hand, the numerical simulation employing one-step global reaction mechanism could not predict the tendency of CO mole fraction distribution very much. Consideration of CO2 dissociation reaction is essential to predict the CO mole fraction in the CO-rich gasified fuel combustion field..
7. Seongyool Ahn, Hiroaki Watanabe, Kenji Tanno, Numerical analysis of formation and decomposition behavior of PAH species in a pulverized coal jet flame with an elementary kinetic mechanism, 36th International Symposium on Combustion, 2016.08, A numerical simulation was performed to investigate formation and decomposition behavior of polycyclic aromatic hydrocarbon (PAH) species in a pulverized coal jet flame by means of large eddy simulation (LES). For a gas phase kinetic, a skeletal mechanism derived from a detailed mechanism that includes a kinetic mechanism high carbonaceous species, up to C30, is employed in this study. In the devolatilization process, kinetic parameters for the release rate equation and the gas composition are determined by the FLASHCAHIN model. For a solid phase, a two-step simple reaction is implemented. The governing equations for the continuous phase are solved by means of LES. Coal particles are traced in the Lagrangian method individually with the parcel model. Heat, mass and momentum interactions between the continuous and dispersed phases are calculated based on the Particle-Source-In Cell model. The numerical simulation is performed by FrontFlowRed-Comb.
Particle distribution and velocities are compared to the experiment according to the axial distance and the radial distance at specific heights to see the flow field, and the simulation results show good agreement. Particles are more dispersed in the non-combustion case comparing to the combustion case because the pilot flame and volatile matter combustion make the flow stream fast and it becomes laminar flow shape. The calculated temperature chemical reactions is compared to flame temperature measured by two-color pyrometer. The simulation result is much lower than the measured one at the upstream flow region, but they are similar at the flame region. From this result, it is found that chemical reactions implemented in this calculation describe coal flame reactions well. In the result of mole fraction profiles of PAH species, it is found that devolatilized matters are located following an intersection of inner air flow and a hot reaction zone and their position is a little outside of lite volatiles. This is exactly same result of the previous research presented by Hayashi. This means that the large devolatilized species move to outside of inner-cold flow and put in high temperature and low oxygen concentration. This is a favorable environment for polymerization of species and it is easy to promote soot growth..
8. Wei Zhang, Hiroaki Watanabe, Toshiaki Kitagawa, Direct numerical simulation of ignition of a single particle freely moving in a uniform flow, 36th International Symposium on Combustion, 2016.08, In a numerical simulation of a diluted gas-particle two-phase reacting flow such as spray and coal combustion or gasification, the Eulerian-Lagrangian manner with the PSI-CELL method is generally employed to capture the motions of a number of particles with reducing the computational cost. However how this assumption affects the accuracy on the particle’s motion and ignition are rarely discussed. In this study, a direct numerical simulation (DNS) of the ignition of a single particle freely moving in a uniform flow to investigate the particle's motion and ignition behavior in detail. The Arbitrary Lagrangian-Eulerian (ALE) method is employed to compute the six-degree freedom computation of the particle's motion. The computational setting follows the experiment by Lee and Choi. The volatiles gas that is composed of CH4 and CO blows out at the particle surface and its velocity is set to 1.0 m/s and its direction is set perpendicular to particle surface. The ignition behavior is compared with that observed in the experiment. The effect of the particle's shape is also discussed. Results show that the long tail flame is formed after the particle released and as the particle accelerating, the tail flame becomes shorter and burning velocity becomes gently larger. This behavior is in good agreement with that in the experiment. While the slip velocity between the particle and the uniform flow becomes smaller than a certain threshold value, the burning velocity of the volatiles suddenly becomes large and finally a spherical flame is formed around the particle. After the spherical flame is formed, the burning velocity decreases again and then the flame becomes stable. It is found that this behavior can be understood by considering the variation of a strain rate (or scalar dissipation rate) between the volatiles jet and the surrounding gas flows. It is also revealed that the particles' shape dose not affect the ignition behavior very much..
9. Hiroaki Watanabe, Kenji Tanno, Ryoichi Kurose, Large-eddy simulation of coal gasification on a two-stage entrained flow coal gasifier, European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS Congress 2016), 2016.06, Large-eddy simulation of coal gasification on a two-stage entrained flow coal gasi- fier was performed to demonstrate the applicability of LES to coal gasification field. The La- grangian method is used to compute particle motions and dynamic SGS model is used as a turbulent model. The CRIEPI 2 tons/day research gasifier “FRONTIA” is targeted in this study and the results are compared to validate the numerical procedure. Results show that the gasification performance such as temperature, major chemical species were qualitatively in agreement with the experiment. It is also found that the strong swirl flow formed in the bottom part of gasifier plays an important role for mixing of dispersed particles with oxidizers to promote the endothermic gasification reactions. The LES is well demonstrated to capture the general feature of the coal gasification field in the two-stage entrained flow coal gasifier..
10. Masaya Muto, Hiroaki Watanabe, Ryoichi Kurose, Satoru Komori, Effect of fuel ratio of bituminous coals on pulverized coal combustion in multi-burner system using large-eddy simulation, European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS Congress 2016), 2016.06, In the field of pulverized coal combustion, the development of the combustion technol- ogy meeting the demands such as reducing environmental pollutants has been conducted by many researchers and developers. To make a further improvement, an understanding of the flow field and pulverized coal particle behaviors in the combustion furnace is necessary. However, it is difficult to obtain such information solely on the ba- sis of experiments. Therefore numerical simulations has been applied to pulverized coal combustion fields in a single-burner furnace and recently, an effect of fuel ratio of coal is also investigated by blending different type of coal in the furnace. While utility multi-burner furnaces have been investigated mainly using Reynolds-Averaged Navier- Stokes Simulation, recent development of computational resources and techniques gradually enable us to conduct large-eddy simulation (LES) of unsteady combustion phe- nomena in such furnaces. In this study, LES is applied to the multi-burner pulverized coal combustion furnace shown in left side of the figure and an effect of fuel ratio of coal is investigated. The computational domain is divided in about 102 million cells and about 22 million vertexes. The variable density, low-Mach number, reacting flow equations with two-way coupling between gas phase and pulverized coal particles are solved using an un- structured LES solver, FrontFlow/Red extended by Kyoto University, Central Research Institute of Electric Power Industry and Numerical Flow Designing, Ltd. Results show that the effect of fuel ratio of coal on the flow field that are considered to be essential for prediction of the product gases such as nitrogen oxide in the furnace, can only be captured in large scale unsteady simulation like present study..
11. Nagano Yukihide, Yosuke Fukuda, Akira Noomo, Taiki Tsukamoto, Hiroaki Watanabe, Toshiaki Kitagawa, Study on Spherically Propagating i-C8H18 Turbulent Flames using lean and EGR Conditions using Constant Volume Vessel, The First Pacific Rim Thermal Engineering Conference, PRTEC, 2016.03.
12. Nozomu Hashimoto, Jun Hayashi, Noriaki Nakatsuka, Kazuki Tainaka, Satoshi Umemoto, Hirofumi Tsuji, Fumiteru Akamatsu, Hiroaki Watanabe, Hisao Makino, Primary soot particle diameter distributions in a combustion field formed by 4kW pulverized coal jet burner measured by TIRE-LII, The First Pacific Rim Thermal Engineering Conference, PRTEC, 2016.03.
13. Hiroaki Watanabe, Masaya Muto, Ryoichi Kurose, Large-eddy simulation of pulverized coal combustion and gasification on semi-industrial furnaces, 11th Korea-Japan CFD Workshop (KJCFD2015), 2015.12.
14. Wei Zhang, Hiroaki Watanabe, Masaya Muto, Kotaro Hori, Toshiaki Kitagawa, Investigation of the motion of a particle with irregular shapes in a uniform flow by direct numerical simulation, 5th International Conference on the Characteristics and Control of Interfaces for High Quality Advanced Materials and 51st Summer Symposium on Powder Technology, 2015.07, This paper reports a numerical investigation of the motion of spherical and non-spherical particles with/without gas blowing-out in a vertical uniform flow. The shape of non-spherical particle is adjusted basing on scanning of a coal particle using CT scanner. The aim of this work is to clarify the motion of non-spherical particle. As a first stage of the research, the Arbitrary Lagrangian-Eulerian (ALE) method is employed and validated by comparing with the experiment in which the motion of a sphere settling under gravity in water at rest is studied. Secondly simulations of particles with or without gas blowing-out in a vertical uniform flow are performed. Six kinds of particles - spherical or spheroidal particle with equivalent surface area, equivalent volume or equivalent sphericity to that of coal particle - are used. The result shows that the spheroidal particle with equivalent volume has a more similar accelerating motion to that of coal particle than spherical particle. For spheroidal particle, its distribution of Probability Density Function (PDF) of Drag coefficient (CD) value shows a possibility to make a CD equation with Re and particle’s Min-Max CD value. With gas blowing-out, the CD values of spherical and spheroidal particle decrease obviously because of the sharply decrease of CD value contributed by friction. It is also revealed that the motion of coal particle with irregular shape is significantly dependent on its shape, especially with gas blowing-out. New parameters can describe particle shape need to be developed..
15. Seongyool Ahn, Kenji Tanno, Hiroaki Watanabe, Generation of a reduced chemical kinetic mechanism for coal combustion, 40th International Technical Conference on Clean Coal & Fuel Systems, 2015.06, A reduced mechanism is derived from the detailed coal combustion kinetic mechanism proposed by Richter and Howard[1] for large scale calculations. The detailed mechanism includes fundamental reaction kinetics of light hydrocarbons and the kinetic mechanism of poly aromatic hydrocarbons (PAH). Therefore, we should consider the PAH reaction part when we try to regenerate a reduced mechanism. The detailed mechanism consists of 257 species and 1107 elemental reactions. In order to reduce the mechanism, firstly, a skeletal mechanism is developed from the detailed mechanism using a combination method of DRGEPSA and CSP method[2-4]. Many temporary mechanisms are tested in various combustion conditions of temperature, equivalent ratios, and pressures. About 30% of maximum error is allowed for a skeletal mechanism and most reasonable one is selected through a comparison of the error of each mechanism. Through this process, 64 species and 150 reactions are remained in the skeletal mechanism. And then, the reduced mechanism is generated from the skeletal version via quasi-steady state approximate (QSSA) method [5,6]. Now we are testing the temporary versions using the homogeneous reactor of CHEMKIN PRO. under various conditions of coal combustion, and we can get the reasonable result in a soon time. This mechanism will be installed in the LES of coal jet flame and we expect it can give detailed information at the chemical reaction part and reduce the computing time dramatically.
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16. H. Watanabe, T. Kawai, S.-Y. Ahn, Numerical simulation of NOx formation in syngas combustion, 15th International Conference on Numerical Combustion, 2015.04, Characteristics of NOx formation in syngas combustion under O2/CO2 combustion condition is numerically investigated by means of homogeneous reactor model of CHEMKIN, a direct numerical simulation (DNS) with Arrhenius formulation (ARF) and DNS with the flamelet/progress variable approach (FPV) in comparison to air combustion condition. Results show that the major pathways for NO formation drastically change with O2/CO2 combustion condition in the zero-dimensional computation. The characteristics shown in the zero-dimensional computation is also confirmed in ARF. It is also revealed that the general feature of syngas combustion and the characteristics of NO formation can be precisely captured by FPV..
17. S.-Y. Ahn, H. Watanabe, K. Tanno, N. Hashimoto, Application of a skeletal kinetic mechanism of LES of a pulverized coal jet flame, 15th International Conference on Numerical Combustion, 2015.04.
18. S.-Y. Ahn, K. Tanno, N. Hashimoto, H. Watanabe, Large eddy simulation of a pulverized coal jet flame with a skeletal kinetic mechanism, 第28回数値流体力学シンポジウム, 2014.12.