Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Hiroaki Watanabe Last modified date:2018.06.11

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

1. Panlong Yu, Koyo Norinaga, Hiroaki Watanabe, Toshiaki Kitagawa, Prediction of hot coke oven gas reforming by LES coupled with the extended flamelet/progress variable approach, Fuel, 231, 234-243, 2018.05.
2. Wei Zhang, Hiroaki Watanabe, Toshiaki Kitagawa, Direct numerical simulation of ignition of a single particle freely moving in a uniform flow, Advanced Powder Technology, 28, 2893-2902, 2017.09.
3. Seongyool Ahn, Kenji Tanno, Hiroaki Watanabe, Numerical analysis of particle dispersion and combustion characteristics on a piloted coaxial pulverized coal jet flame, Applied Thermal Engineering, 124, 1194-1202, 2017.07.
4. Satoshi Umemoto, Shiro Kajitani, Koichi Miura, Hiroaki Watanabe, Motoaki Kawase, Extension of the chemical percolation devolatilization model for predicting formation of tar compounds as soot precursor in coal gasification, Fuel Processing Technology, 159, 256-265, 2017.02.
5. Hiroaki Watanabe, Seongyool Ahn, Kenji Tanno, Numerical investigation of effects of CO2 recirculation in an oxy-fuel IGCC on gasification characteristics of a two-stage entrained flow coal gasifier, Energy, 118, 181-189, 2016.12, Effects of CO2 recirculation within an oxy-fuel IGCC plant on a gasification characteristics of a two-stage entrained flow coal gasifier was numerically investigated by means of a three-dimensional unsteady Reynolds-averaged Navier-Stokes(RANS) simulation. The RNG k ε model and the Eulerian-Lagrangian manner were used to consider the effect of turbulence and the particles' motions, respectively. A char gasification model in which the Langmuir-Hinshelwood formulation was coupled with the random pore model was employed to estimate gasification reaction rate. Results showed that the gasification per- formance such as the per pass carbon conversion efficiency for the oxy-fuel condition in which CO2 replaced N2 in the primary and secondary gas flows was in the same level for the air-blown condition in which O2 flowed into the gasifier with N2, while the gaseous temperature drastically decreased for the former case. It was also found that the gaseous temperature was recovered to the same level for the air- blown condition with at least more than 35% of oxygen concentration in the gasifying agent and simultaneously the highly gasification performance was observed. It is essential to control O2 and CO2 concentrations in the gasifying agent to turn the CO2 recirculation to advantage in utilization of the O2- CO2 blown gasifier in the oxy-fuel IGCC system..
6. Nozomu Hashimoto, Hiroaki Watanabe, Ryoichi Kurose, Hiromi Shirai, Effect of different fuel NO models on the prediction of NO formation/reduction characteristics in a pulverized coal combustion field, Energy, 118, 47-59, 2016.12, To investigate the effects of fuel NO formation models on the prediction of NO concentrations in a coal combustion field, numerical simulations for a coal combustion field in a 760 kW test furnace were performed. Three models, those proposed by De Soete, Chen et al. and Mitchell et al. were employed to calculate fuel NO formation originating from volatile matter. The results show that the model proposed by Mitchell et al. reproduces the tendency of the experimental data better than the other two models. In addition, the difference between the NO conversion ratios of bituminous coal and sub-bituminous coal that contains a high level of moisture was examined in detail using simulation results from the model of Mitchell et al. It was found that the formation of a region with a low oxygen mole fraction immediately downstream of a region with a high NO production rate is essential to realize a low NO conversion ratio..
7. Nozomu Hashimoto, Jun Hayashi, Noriaki Nakatsuka, Kazuki Tainaka, Satoshi Umemoto, Hirofumi Tsuji, Fumiteru Akamatsu, Hiroaki Watanabe, Hisao Makino, Primary soot particle distributions in a combustion field of 4kW pulverized coal jet burner measured by time resolved laser induced incandescene (Tire-LII), Journal of Thermal Science and Technology, 10.1299/jtst.2016jtst0049, 1-11, 2016.12, To develop accurate models for the numerical simulation of coal combustion field, detailed experimental data using laser techniques, which can figure out the basic phenomena in a coal flame, are necessary. In particular, soot is one of the important intermediate substances in a coal flame. This paper is the first paper in the world reporting soot particle size distributions in a coal flame. The spatial distribution of the primary soot particle diameter were measured by the combination of the time-resolved laser induced incandescence (TiRe-LII) method and the thermophoretic sampling (TS) method. The primary soot particle diameter distribution was expressed by the log normal function based on the particle diameter measurement using SEM images obtained from the TS samples. The relative function between the signal decay ratio obtained by TiRe-LII and the primary soot particle diameter was defined based on the log normal function. Using the relative function, the spatial distributions of the primary soot particle diameter with the soot volume fraction were obtained. The results show that the small isolated soot regions instantaneously exist in the entire combustion field. This characteristics is different from spray combustion field. From the ensemble-averaged TiRe-LII images, it was found that the soot volume fraction and the primary soot particle diameter increases with increasing the height above the burner in any radial distance. It was also found that the volumetric ratio of small particles decreases with increasing radial distance at the region close to the burner exit. However, the variation of the soot particle diameter distribution along the radial direction becomes small in the downstream region. This tendency is caused by the turbulent mixing effect. It is expected that the accurate soot formation model will be developed in the near future by using the data reported in this paper..
8. Seongyool Ahn, Hiroaki Watanabe, Tetsuya Shoji, Satoshi Umemoto, Numerical investigation of reaction kinetics of coal volatiles with a detailed chemistry and its simplification, Journal of Thermal Science and Technology, DOI: 10.1299/jtst.2016jtst0014, 1-11, 2016.05, Reaction kinetics of coal volatile were numerically investigated based on analyses during reaction mechanism reduction procedure in detail in this paper. Computation on a closed homogeneous reactor model was performed to clarify important chemical species and their reaction pathways with evaluating the capability of prediction of ignition delay time and chemical species concentration under a wide range of equivalence ratios and temperatures. The kinetics of large hydrocarbons such as polycyclic aromatic hydrocarbons (PAH) that comprise a large portion of combustion features for complex hydrocarbon materials was focused on in a coal flame. The data computed here was analyzed through the combined process of the directed relation graph with error propagation and sensitivity analysis (DRGEPSA) and the computational singular perturbation (CSP) that can evaluate the roles of each species and reaction pathway respectively in the chemical system. Results show that hydrocarbons such as aromatics, methyl and ethyl groups play important role in the ignition and flame propagation processes. Finally, the skeletal mechanism including 64 species and 150 reactions was derived from the detailed mechanism that consists of 257 species and 1107 reactions within 30% error in the prediction of the ignition delay time and the mole fractions of major species in the propagating flame..
9. Nozomu Hashimoto, Hiroaki Watanabe, Numerical analysis of effect of furnace scale on heat transfer mechanism of coal particles in pulverized coal combustion field, Fuel Processing Technology, 145, 20-30, 2016.01, To investigate the effect of the furnace scale on the heat transfer mechanism of coal particles, numerical simula- tions of coal combustion fields in three different scale furnaces (915 MWth actual large scale boiler, 2.4 MWth and 0.76 MWth test furnaces) were conducted. High accuracy of simulation methods was validated with the mea- sured data. From the comparison of numerical simulations between three different scale furnaces, it was clarified that the particle residence time with high particle temperature for a small scale furnace is shorter than that for a large scale furnace even if the particle residence time passing the high temperature gas is the same. This is caused by the insufficient heat gain of particles for a small scale furnace due to the lower radiation heat transfer because of the thinner flame thickness in the small furnace. The sphericity of ash particles from small scale furnaces is lower than that for large scale furnaces due to the shorter particle residence time with high particle temperature. These findings should be considered when the usability of coal brands for actual large scale boilers is evaluated by the fly ash properties from a small scale experimental furnace..
10. Zhenzhen Wang, Yoshihiro Deguchi, Shunpei Katsumori, Akihiro Ikutomo, Junjie Yan, Jiping Liu, Kazuki Tainaka, Kenji Tanno, Hiroaki Watanabe, Ryoichi Kurose, Improved measurement characteristics of elemental compositions using laser-induced breakdown spectroscopy, Spectroscopy, 31, 1, 1-7, 2016.01, Rapid detection of coal and fly ash is significant to improve the efficiency of thermal power plants and reduce environmental pollution. Given its fast response, high sensitivity, real-time, and non- contact features, laser-induced breakdown spectroscopy (LIBS) has a great potential for on-line measurement in these applications. The direct measurement of particles and gases using LIBS was studied, and the method was shown to be effective for this application..
11. Hiroaki Watanabe, Daisuke Uesugi, Masaya Muto, Effects of parcel modeling on particle dispersion and interphase transfers in a turbulent mixing layer, Advanced Powder Technology, 26, 1719-1728, 2015.11, A three-dimensional particle-laden two-phase direct numerical simulation by employing the Eulerian–Lagrangian method is performed to investigate effects of parcel modeling on characteristics of particles’ spatial dispersion, interphase mass and momentum transfers in a turbulent mixing layer. As the parcel models, two typical models such as the volume fixed model, VFM, in which each parcel has the same vol- ume and the number fixed model, NFM, in which each parcel represents the same number of particles are examined. The case without the parcel model is also performed to compare with the models as a refer- ence, RC. Results show that the parcel models significantly affect the particle dispersion, interphase mass and momentum transfers. It is found that NFM can qualitatively capture the trend of RC with small dis- crepancies, while VFM cannot reproduce it very much. The discrepancies become marked with increasing the number of particles represented by one parcel. The results suggest that the parcel models should be carefully treated with confirming the number of particles represented by one parcel in the entire range of particle size distribution..
12. Chengyi Li, Srinivas Appari, Ryota Tanaka, Kyoko Hanao, Yeonkyung Lee, Kudo Shinji, Hayashi Jun-ichiro, Vinod M. Janardhanan, Hiroaki Watanabe, Koyo Norinaga, A CFD study on the reacting flow of partially combusting hot coke oven gas in a bench-scale reformer, Fuel, 159, 590-598, 2015.07, A computational fluid dynamics (CFD) approach to simulate reacting flow in a hot coke oven gas (HCOG) reformer is presented. The HCOG was reformed by non-catalytic partial oxidation in a tubular reactor (0.6 m i.d. and .
13. Srinivas Appari, Ryota Tanaka, Chengyi Li, Kudo Shinji, Hayashi Jun-ichiro, Vinod M. Janardhanan, Hiroaki Watanabe, Koyo Norinaga, Predicting the temperature and reactant concentration profiles of reacting flow in the partial oxidation of hot oven gas using detailed chemistry and a one-dimensional flow model, Chemical Engineering Journal, 10.1016/j.cej.2014.12.041, 266, 82-90, 2014.12, A numerical approach is presented for predicting the species concentrations and temperature profiles of chemically reacting flow in the non-catalytic partial oxidation of hot coke oven gas (HCOG) in a pilot- scale reformer installed on an operating coke oven. A detailed chemical kinetic model consisting of 2216 reactions with 257 species ranging in size from the hydrogen radical to coronene was used to pre- dict the chemistries of HCOG reforming and was coupled with a plug model and one-dimensional (1D) flow with axial diffusion model. The HCOG was a multi-component gas mixture derived from coal dry distillation, and was approximated with more than 40 compounds: H2, CO, CO2, CH4, C2 hydrocarbons, H2O, aromatic hydrocarbons such as benzene and toluene, and polycyclic aromatic hydrocarbons up to coronene. The measured gas temperature profiles were reproduced successfully by solving the energy balance equation accounting for the heat change induced by chemical reactions and heat losses to the surroundings. The approach was evaluated critically by comparing the computed results with experimen- tal data for exit products such as H2, CO, CO2, and CH4, in addition to the total exit gas flow rate. The axial diffusion model slightly improves the predictions of H2, CO, and CO2, but significantly improves those of CH4 and total exit flow rate. The improvements in the model predictions were due primarily to the improved temperature predictions by accounting for axial diffusion in the flow model..
14. H. Umetsu, H. Watanabe, S. Kajitani, S. Umemoto, Modeling and simulation of pulverized coal char combustion, SPEIC 2014: Towards Sustainable Combustion, 2014.11, The char combustion/gasification reaction is one of the most important keys for obtaining an accurate prediction because the reaction is often the rate-limiting reaction in a system. However, it is often difficult to obtain a good agreement with measured conversion without making an adjustment of the model parameters for each intended furnace because of its great simplicity, although the original model parameters which are determined by fundamental experiments (e.g. thermogravimetric analysis and drop tube furnace) should be used for any furnace. In this paper, the char combustion model (H. Umetsu, et al. Combustion and Flame, 2014) was examined for two kinds of numerical simulation: (i) one-dimensional simulation in which the flow field is assumed to be a plug flow and (ii) three-dimensional simulation using LES for fluid and Lagrangian particle tracking. The char combustion model was validated using the char oxidation data obtained by a drop tube furnace. For 1D simulation, it was demonstrated that the model can precisely capture characteristics in the wide range of temperatures and stages of carbon conversion. For 3D simulation, the same values of the model parameters were used and it was found that a plug flow assumption was relatively valid for the rear section of the furnace but a non-negligible disturbance in flow field was observed around the injector owing to a large difference in velocity between that from the injector and bulk flow. Because of the disturbance, a high conversion was observed for the region near the injector compared with 1D simulation. However, lower conversions were observed for the rear section. This is obviously because of lower temperature of the gas on the central axis..
15. Hiroaki Watanabe, Kenji Tanno, Hiroki Umetsu, Satoshi Umemoto, Modeling and simulation of coal gasification on an entrained flow coal gasifier with a recycled CO2 injection, Fuel, 10.1016/j.fuel.2014.11.012, 142, 250-259, 2014.11, Partially sharing of active sites on char particle by multicomponent gasifying agent and detailed chemistry of water–gas-shift reaction are modeled and implemented. A three-dimensional RANS-based simulation with these models is also performed to investigate effects of a CO2 injection on gasification characteristics within an entrained flow coal gasifier. Results show that the gasification performance such as carbon conversion, product gas composition and gaseous temperature distribution is precisely cap- tured by the present simulation. The reaction inhibition by the product gas and the reaction suppression by the multicomponent gasifying agent’s partially sharing active sites are reasonably predicted. The effects of the CO2 injection on the gasification characteristics are also discussed in detail with considering contributions of reaction pathways to the gasification performance. It is revealed that it is essential to locally control exothermic gaseous reactions and endothermic heterogeneous reactions in order to take advantage of the CO2 injection..
16. Masaya Muto, Hiroaki Watanabe, Ryoichi Kurose, Satoru Komori, Saravanan Balusamy, Simone Hochgreb, Large-eddy simulation of pulverized coal jet flame –Effect of oxygen concentration on NOx formation-, Fuel, 10.1016/j.fuel.2014.10.069, 142, 152-163, 2014.11, Large-eddy simulation is applied to a laboratory-scale open-type pulverized coal flame generated by a triple stream burner, and the NO production and reduction in oxy-fuel condition are investigated for the first time. Pulverized Cerrejon coal which is classified as bituminous coal is used as a fuel. The results show that regardless of the equivalence ratio, as the O2 concentration increases from 21% to 40%, O2 consumption becomes marked because gas temperature rises and oxidation reaction is enhanced by the higher concentration of O2. Also, NO is formed rapidly due to the oxidation reaction of nitrogen from volatile matter of coal, and its concentration reaches a few hundred ppm further downstream. After the rapid formation, in the case of equivalence ratio larger than unity, NO decreases, because the reducing atmosphere becomes dominant due to the lack of O2. The trend becomes significant as the O2 concentra- tion in the carrier gas increases from 21% to 40%. In the case of equivalence ratio less than unity, on the other hand, NO does not decrease clearly, because the oxidizing atmosphere contributes to the further formation of NO. Present study shows the usefulness of the large-eddy simulations for predicting the characteristics of pulverized coal flames..
17. M. Muto, H. Watanabe, R. Kurose, S. Komori, Large-eddy simulation of a pulverized coal multi-burner system, 11th World Congress on Computational Mechanics (WCCM XI), 2014.07.
18. Y. Deguchi, T. Kamimoto, Z. Z. Wang, J. J. Yan, J. P. Liu, H. Watanabe, R. Kurose, Application of laser diagnostics to thermal power plants and engines, Applied Thermal Engineering, 10.1016/j.applthermaleng.2014.05.063, 73, 1453-1464, 2014.06, The demands for lowering the burdens on the environment will continue to grow steadily. It is important to monitor controlling factors in order to improve the operation of industrial thermal systems. In engines, exhaust gas temperature and concentration distributions are important factors in nitrogen oxides (NOx), total hydrocarbon (THC) and particulate matter (PM) emissions. Coal and fly ash contents are parameters which can be used for the control of coal-fired thermal power plants. Monitoring of heavy metals such as Hg is also important for pollution control. In this study, the improved laser measurement techniques using computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS), low pressure laser-induced breakdown spectroscopy (LIBS), and laser breakdown time-of-flight mass spectrometry (LB-TOFMS) have been developed and applied to measure 2D temperature and species concentrations in engine exhausts, coal and fly ash contents, and trace species measurement. The 2D temperature and NH3 concentration distributions in engine exhausts were successfully measured using CT-TDLAS. The elemental contents of size-segregated particles were measured and the signal stability increased using LIBS with the temperature correction method. The detection limit of trace species measurement was enhanced using low pressure LIBS and LB-TOFMS. The detection limit of Hg can be enhanced to 3.5 ppb when employing N2 as the buffer gas using low pressure LIBS. Hg detection limit was about 0.82 ppb using 35 ps LB-TOFMS. Compared to conventional measurement methods laser diagnostics has high sensitivity, high response and non-contact features for actual industrial systems. With these engineering developments, transient phenomena such as start-ups in thermal systems can be evaluated to improve the efficiency of these thermal processes..
19. H. Watanabe, R. Kurose, M. Hayashi, T. Kitano, S. Komori, Effects of ambient pressure and precursors on soot formation in spray flames, Advanced Powder Technology, 10.1016/j.apt.2014.03.022, 25, 1376-1387, 2014.04, The effects of ambient pressure on soot formation in spray jet flames are investigated by means of a two- dimensional direct numerical simulation (DNS). In addition, the effects of precursors on soot formation are also discussed. The inception models considering acetylene and polycyclic aromatic hydrocarbon (PAH) precursors are employed and compared in this study. The extended flamelet/progress-variable approach (EFPV) in which heat transfer between a droplet and the surrounding fluid can be considered is employed as a combustion model. Jet A is used as a liquid fuel with considering the detailed chemistry including 274 chemical species and 1537 elemental reactions by the flamelet library. The evaporating droplets’ motions are tracked by the Lagrangian method and the non-equilibrium Langmuir–Knudsen model is used as an evaporation model. Results show that the spray jet flame structure and the soot for- mation characteristics are considerably affected by the ambient pressure condition. The soot volume frac- tion increases with increasing the ambient pressure. It is also revealed that the dominant process to promote the soot formation is different between the acetylene and PAH precursor models. It is essential to model a soot inception process with appropriate precursors in order to understand a detail mechanism of soot formation, since the precursor which plays the important role depends on the type of fuel and the combustion conditions..
20. H. Umetsu, H. Watanabe, S. Kajitani, S. Umemoto, Analysis and modeling of char particle combustion with heat and multicomponent mass transfer, Combustion and Flame, 161, 2177-2191, 2014.03, A char combustion model suitable for a large-scale boiler/gasifier simulation, which considers the variation of physical quantities in the radial direction of char particles, is developed and examined. The structural evolution within particles is formulated using the basic concept of the random pore model while simultaneously considering particle shrinkage. To reduce the computational cost, a new approximate analytical boundary condition is applied to the particle surface, which is approximately derived from the Stefan–Maxwell equations. The boundary condition showed reasonably good agreement with direct numerical integration with a fine grid resolution by the finite difference method under arbitrary conditions. The model was applied to combustion in a drop tube furnace and showed qualitatively good agreement with experiments, including for the burnout behavior in the late stages. It is revealed that the profiles of the oxygen mole fraction, conversion, and combustion rate have considerably different characteristics in small and large particles. This means that a model that considers one total conversion for each particle is insufficient to describe the state of particles. Since our char combustion model requires only one fitting parameter, which is determined from information on the internal geometry of char particles, it is useful for performing numerical simulations..
21. E. Sakai, T. Takahashi, H. Watanabe, Large-eddy simulation of an inclined round jet issuing into a crossflow, International Journal of Heat and Mass Transfer, 69, 300-311, 2014.03, For understanding of film cooling flow fields on gas turbine blades, this paper reports on a series of large- eddy simulations of an inclined round jet issuing into a crossflow. Simulations were performed at four blowing ratios, BR = 0.1, 0.5, 0.7 and 1.0, and the Reynolds number, Re = 15,300, based on the crossflow velocity and film cooling hole diameter. Results showed that the cooling jet flow structure drastically changed with the blowing ratio. A pair of rear vortices and hairpin vortices were observed for BR = 0.1. A horseshoe vortex periodically ejected, a pair of hanging vortices, a pair of rear vortices and hairpin vor- tices were observed for BR = 0.5. Similar vortical structures to BR = 0.5 were observed for BR = 0.7 although horseshoe vortex was not ejected periodically and stayed at a leading edge of the hole exit. For BR = 1.0, in addition to the former mentioned vortices, shear layer vortices and vertical streaks were observed on an upstream edge of the jet. It was consequently understood that the ubiquitous counter- rotating vortex pair which can be observed in the time-averaged flow field was actually originated in the different vortical structures with varying BR conditions. Temperature fields were also investigated to clarify how these different vortical structures affect the film cooling effectiveness..
22. H. Moriai, R. Kurose, H. Watanabe, Y. Yano, F. Akamatsu, S. Komori, Large-eddy simulation of turbulent spray combustion in a subscale aircraft jet engine combustor –Predictions of NO and soot concentrations-, Transaction of the ASME, Journal of Gas Turbine and Power, 10.1115/1.4024868, 135, 091503, 2013.09, Large-eddy simulation (LES) is applied to turbulent spray combustion fields in a subscale (1/2) aircraft jet engine combustor with an air-blast type swirl fuel nozzle and validity is examined by comparing with measurements. In the LES, Jet-A is used as liquid fuel, and individual droplet motion is tracked in a Lagrangian manner with a parcel model. As a turbulent combustion model, the extended flamelet/progress-variable approach, in which heat transfer between droplets and ambient gas including radiation and heat loss from walls can be taken into account, is employed. A detailed chemistry mechanism of Jet-A with 1537 reactions and 274 chemical species is used. The radiative heat transfer is com- puted by the discrete ordinate (DO) method. The equivalence ratio ranges from 0.91 to 1.29. The comparisons of the predicted droplet velocity and size, gaseous temperature, NO, and soot emissions with the measurements show that the present LES is capable of capturing the general features of the turbulent spray combustion fields in the subscale (1/2) aircraft jet engine combustor. .
23. Z. Z. Wang, Y. Deguchi, M. Kuwahara, T. Taira, X. B. Zhang, J. J. Yan, J. P. Liu, H. Watanabe, R. Kurose, Quantitative elemental detection of size-segregated particles using laser-induced breakdown spectroscopy, Spectrochimica Acta Part B, 10.1016/j.sab.2013.05.034, 87, 130-138, 2013.06, In order to simulate coal combustion and develop optimal and stable boiler control systems in real power plants, it is imperative to obtain the detailed information in coal combustion processes as well as to measure species contents in fly ash, which should be controlled and analyzed for enhancing boiler efficiency and reducing envi- ronmental pollution. The fly ash consists of oxides (SiO2, Al2O3, Fe2O3, CaO, and so on), unburned carbon, and other minor elements. Recently laser-induced breakdown spectroscopy (LIBS) technique has been applied to coal combustion and other industrial fields because of the fast response, high sensitivity, real-time and non-contact features. In these applications it is important to measure controlling factors without any sample preparation to maintain the real-time measurement feature. The relation between particle content and particle diameter is also one of the vital researches, because compositions of particles are dependent on their diameter. In this study, we have detected the contents of size-segregated particles using LIBS. Particles were classified by an Anderson cascade impactor and their contents were measured using the output of 1064 nm YAG laser, a spectro- graph and an ICCD camera. The plasma conditions such as plasma temperature are dependent on the size of particles and these effects must be corrected to obtain quantitative information. The plasma temperature was corrected by the emission intensity ratio from the same atom. Using this correction method, the contents of particles can be measured quantitatively in fixed experimental parameters. This method was applied to coal and fly ash from a coal-fired burner to measure unburned carbon and other contents according to the particle diameter. The acquired results demonstrate that the LIBS technique is applicable to measure size-segregated particle contents in real time and this method is useful for the analysis of coal combustion and its control because of its sensitive and fast analysis features..
24. J. Hayashi, N. Hashimoto, N. Nakatsuka, H. Tsuji, H. Watanabe, H. Makino, F. Akamatsu, Soot formation characteristics in a lab-scale turbulent pulverized coal flame with simultaneous planar measurements of Laser induced incandescence of soot and Mie scattering of pulverized coal, Proceedings of the Combustion Institute, 10.1016/j.proci.2012.10.002, 34, 2435-2443, 2012.10, Soot formation characteristics of a lab-scale pulverized coal flame were investigated by performing care- fully controlled laser diagnostics. The spatial distributions of soot volume fraction and the pulverized coal particles were measured simultaneously by laser induced incandescence (LII) and Mie scattering imaging, respectively. In addition, the radial distributions of the soot volume fraction were compared with the OH radical fluorescence, gas temperature and oxygen concentration obtained in our previous studies [1,2]. The results indicated that the laser pulse fluence used for LII measurement should be carefully controlled to measure the soot volume fraction in pulverized coal flames. To precisely measure the soot volume fraction in pulverized coal flames using LII, it is necessary to adjust the laser pulse fluence so that it is sufficiently high to heat up all the soot particles to the sublimation temperature but also sufficiently low to avoid including a too large of a change in the morphology of the soot particles and the superposition of the LII signal from the pulverized coal particles on that from the soot particles. It was also found that the radial position of the peak LII signal intensity was located between the positions of the peak Mie scattering signal intensity and peak OH radical signal intensity. The region, in which LII signal, OH radical fluores- cence and Mie scattering coexisted, expanded with increasing height above the burner port. It was also found that the soot formation in pulverized coal flames was enhanced at locations where the conditions of high temperature, low oxygen concentration and the existence of pulverized coal particles were satisfied simultaneously..
25. A. Fujita, H. Watanabe, R. Kurose, S. Komori, Two-dimensional direct numerical simulation of spray flames. Part 1: Effects of equivalence ratio, fuel droplet size and radiation, and validity of flamelet model, Fuel, 10.1016/j.fuel.2012.08.044, 104, 515-525, 2012.09, The effects of equivalence ratio, fuel droplet size, and radiation on jet spray flame are investigated by means of two-dimensional direct numerical simulation (DNS). In addition, the validity of an extended flamelet/progress-variable approach (EFPV), in which heat transfer between droplets and ambient fluid including radiation is exactly taken into account, is examined. n-decane (C10H22) is used as liquid spray fuel, and the evaporating droplets’ motions are tracked by the Lagrangian method. The radiative heat transfer is calculated using the discrete ordinate method with S8 quadrature approximation. The results show that the behavior of jet spray flame is strongly affected by equivalence ratio and fuel droplet size. The general behavior of the jet spray flames including the heat transfer between droplets and ambient fluid with radiation effect can be captured by EFPV..
26. J. Hayashi, H. Watanabe, R. Kurose, F. Akamatsu, Effects of fuel droplet size on soot formation in spray flames formed in a laminar counterflow, Combustion and Flame, 10.1016/j.combustflame.2011.05.015, 158, 2559-2568, 2011.06, The effects of fuel droplet size on soot formation in spray flames formed in a laminar counterflow are investigated experimentally and numerically. Sauter mean diameter (SMD) of quasi-monodispersed fuel spray (n-decane) is carefully controlled independently from the other spray characteristics using a fre- quency-tunable vibratory orifice atomizer, and the two-dimensional spatial distributions of soot volume fraction and soot particle size are measured by laser induced incandescence (LII) and time resolved LII (TIRE-LII), respectively. In addition, the soot formation processes are examined in detail by a two-dimen- sional direct numerical simulation (DNS) employing a kinetically based soot model with flamelet model. The results show that the soot formation area and location are strongly affected by the SMD of the fuel spray. As the SMD of the fuel spray increases, the average soot formation area expands, whereas local suppression of soot formation is instantaneously observed in the spray flames because of the appearance of groups of unburned droplets. The size of soot particles tend to be larger in the outer part of the soot formation area compared to soot in the inner part. This is because the surface growth of soot particles markedly proceeds compared to the coagulation and oxidation..
27. Y. Oki, J. Inumaru, S. Hara, M. Kobayashi, H. Watanabe, S. Umemoto, H. Makino, Development of oxy-fuel IGCC system with CO2 recirculation for CO2 capture, Energy Procedia, 10.1016/j.egypro.2011.01.156, 4, 1066-1073, 2011.04.
28. M. Muto, H. Watanabe, M. Tsubokura, N. Oshima, Negative Magnus effect on a rotating sphere at around the critical Reynolds number, Journal of Physics, 10.1088/1742-6596/318/3/032021, 318, 032021, 2011.03, Negative Magnus lift acting on a sphere rotating about the axis perpendicular to an incoming flow is investigated using large-eddy simulation at three Reynolds numbers of 1.0×104, 2.0 × 105, and 1.14 × 106. The numerical methods adopted are first validated on a non-rotating sphere and the spatial resolution around the sphere is determined so as to reproduce the laminar separation, reattachment, and turbulent transition of the boundary layer observed at around the critical Reynolds number. In the rotating sphere, positive or negative Magnus effect is observed depending on the Reynolds number and the rotating speed imposed. At the Reynolds number in the subcritical or supercritical region, the direction of the lift force follows the Magnus effect to be independent of the rotational speed tested here. In contrast, negative lift is observed at the Reynolds number at the critical region when particular rotating speeds are imposed. The negative Magnus effect is discussed in the context of the suppression or promotion of boundary layer transition around the separation point..
29. J. Inumaru, M. Otaka, H. Watanabe, Study on droplet entrainment of high-viscosity falling liquid film, Journal of Fluid Science and Technology, 5, 169-179, 2010.03, An experimental study of counter-current annular two-phase flow of high-viscosity liquid and air in a large diameter pipe was carried out to investigate the inception criterion for entrainment of molten slag droplet in an entrained flow coal gasifier. Liquid film thickness was measured using a high-speed camera for 4 types of liquid with various viscosities and surface tensions. It was clearly shown that the measured average wave amplitude had a good correlation with the gas Reynolds number, and that the predicted critical gas velocity for droplet inception using new formula of wave amplitude had a good agreement with the experimental results under the condition of very low fluid Reynolds number( Ref ≤10). The critical Weber number Wec =1.73 was obtained as inception criterion of droplet entrainment..
30. R. Kurose, H. Watanabe, H. Makino, Numerical simulations of pulverized coal combustion, KONA Powder and Particle Journal, 27, 144-156, 2009.10, Coal is an important energy resource for meeting the further demand for electricity, as coal reserves are much more abundant than those of other fossil fuels. In pulverized coal fired power plants, it is very important to improve the technology for the control of environmental pollutants such as NOx, SOx and ash particles including unburned carbon. With the remarkable progress in the performance of computers, it is strongly expected that the computational fluid dynamics (CFD) would be a tool for the development and design of such suitable combustion furnaces and burners for the pulverized coal combustion. The focus of this review is to highlight our recent progress of CFD of the pulverized coal combustion in terms of Reynolds-Averaged Navier-Stokes (RANS) simulation and Large-Eddy Simulation (LES) together with some of future perspectives..
31. H. Watanabe, R. Kurose, S. Komori, Large-eddy simulation of swirling flows in a pulverized coal combustion furnace with a complex burner, Journal of Environment and Engineering, 10.1299/jee.4.1, 4, 1-11, 2009.02, LES (Large-eddy simulation) of swirling cold-flows in a pulverized coal combustion furnace is performed and validated by comparing with experiment and RANS (Reynolds-Averaged Navier-Stokes) simulation with the standard k-ε model. Unstructured grids and energy-conserving scheme are employed to obtain robust and accurate solutions at high swirl numbers. The results show that the LES is in good agreement with the experiment in terms of the recirculation flow, though the RANS simulation overestimates it. This is considered due to the capability of prediction of turbulent mixing. The effect of secondary and tertiary swirler vanes' angles on the behavior of the recirculation flow are also well predicted by the LES. The recirculation flow affects the flame stabilization and combustion efficiency related to the particle residence time in the furnace. It can be said, therefore, that the LES is strongly recommended for the accurate prediction of the strong swirling flows in such furnaces..
32. H. Watanabe, R. Kurose, S. Komori, H. Pitsch, Effect of radiation on spray flame characteristics and soot formation, Combustion and Flame, 10.1016/j.combustflame.2007.07.021, 152, 2-13, 2007.10, Two-dimensional numerical simulations are applied to spray flames formed in a laminar counterflow and the effects of radiation on spray flame characteristics and soot formation are studied. N-Decane (C10H22) is used as the liquid fuel, and the droplet motion is calculated by the Lagrangian method. A single-step global reaction is employed for the combustion reaction model. A kinetically based soot model with a flamelet model is used to predict soot formation. Radiation is taken into account using the discrete ordinate method. The results show that radiation strongly affects the spray flame behavior and soot formation. Without the radiation model, flame temperature and soot volume fraction are greatly overestimated. The soot is formed in the diffusion flame regime, and its radiation emission increases with the increase in the equivalence ratio of the droplet fuel. This trend is in good agreement with that of the luminous flame behavior observed in the experiments..
33. H. Watanabe, R. Kurose, S.-M. Hwang, F. Akamatsu, Characteristics of flamelet in spray flames formed in a laminar counterflow, Combustion and Flame, 10.1016/j.combustflame.2006.09.006, 148, 234-248, 2007.01, A two-dimensional numerical simulation of a spray flame formed in a laminar counterflow is presented, and the flamelet characteristics are studied in detail. The effects of strain rate, equivalence ratio, and droplet size are examined in terms of mixture fraction and scalar dissipation rate. n-Decane (C10H22) is used as a liquid spray fuel, and the droplet motion is calculated by the Lagrangian method without the parcel model. A one-step global reaction is employed for the combustion reaction model. The results show that there appear large differences in the trends of gaseous temperature and mass fractions of chemical species in the mixture fraction space between the spray flame and the gaseous diffusion flame. The gas temperature in the spray flame is much higher than that in the gaseous diffusion flame. This is due to the much lower scalar dissipation rate and the coexistence of premixed and diffusion-limited combustion in the spray flame. For the spray flames, gas temperature and mass fractions of chemical species are not unique functions of the mixture fraction scalar dissipation rate. This is because the production rate of the mixture fraction, namely evaporation rate of the droplets, in the upstream region is not in proportion to its transport-diffusion rate in the downstream region. The behavior shows marked differences as the strain rate decreases, the equivalence ratio increases, or the droplet size decreases..
34. H. Watanabe, M. Otaka, Numerical simulation of coal gasification in entrained flow coal gasifier, Fuel, 10.1016/j.fuel.2006.02.002, 85, 1935-1943, 2006.03, This paper presents modeling of a coal gasification reaction, and prediction of gasification performance for an entrained flow coal gasifier. The purposes of this study are to develop an evaluation technique for design and performance optimization of coal gasifiers using a numerical simulation technique, and to confirm the validity of the model. The coal gasification model suggested in this paper is composed of a pyrolysis model, char gasification model, and gas phase reaction model. A numerical simulation with the coal gasification model is performed on the CRIEPI 2 tons/day (T/D) research scale coal gasifier. Influence of the air ratio on gasification performance, such as a per pass carbon conversion efficiency, amount of product char, a heating value of the product gas, and cold gas efficiency is presented with regard to the 2 T/D gasifier. Gas temperature distribution and product gas composition are also presented. A comparison between the calculation and experimental data shows that most features of the gasification performance were identified accurately by the numerical simulation, confirming the validity of the current model..