zhedian zhang - Academia.edu (original) (raw)

Papers by zhedian zhang

Electronics

Gas turbines are widely used in industry, and the combustion chamber, compressor, and turbine are... more Gas turbines are widely used in industry, and the combustion chamber, compressor, and turbine are known as their three important components. In the design process of the combustion chamber, computational fluid dynamics simulation takes up a lot of time. In order to accelerate the design speed of the combustion chamber, this article proposes a combustion chamber design method that combines an artificial neural network (ANN) and computational fluid dynamics (CFD). CFD results are used as raw data to establish a fast prediction model using ANN and eXtreme Gradient Boosting (XGBoost). The results show that the mean squared error (MSE) of the ANN is 0.0019, and the MSE of XGBoost is 0.0021, so the ANN’s prediction performance is slightly better. This fast prediction method combines CFD and the ANN, which can greatly shorten CFD calculation time, improve the efficiency of gas turbine combustion chamber design, and provide the possibility of achieving digital twins of gas turbine combustio...

推进技术, May 25, 2018

为了获得燃料分级比例与烟气排放之间的变化规律，基于燃料分级概念，结合数值模拟和实验研究的手段对以CH4为燃料的轴向燃料分级燃烧中NOx排放特性进行了研究。建立燃料分级化学反应器网络模型，研究了停... more 为了获得燃料分级比例与烟气排放之间的变化规律，基于燃料分级概念，结合数值模拟和实验研究的手段对以CH4为燃料的轴向燃料分级燃烧中NOx排放特性进行了研究。建立燃料分级化学反应器网络模型，研究了停留时间和燃料分级比例对NOx排放的影响，对燃料分级燃烧中的NOx反应途径进行了分析，并通过调节参与再燃的烟气比例分析了二级燃料与烟气的掺混性能对NOx排放的影响。针对燃料分级模型燃烧器，实验测量了不同燃料分级比例和不同二级燃料流量下的NOx排放。结果表明，燃料分级缩短了烟气在高温区的停留时间，抑制了热力型NO的生成；在再燃区燃烧反应初始阶段二级燃料与高温烟气形成还原性气氛，通过NO再燃还原了主燃烟气中的NO；在一定的总当量比工况下，燃料分级比例的增加降低了出口的NOx排放，提高了NOx排放中NO2的比例。与二级燃料进行掺混反应的烟气量过少会形成再燃区的局部高温，导致NOx排放增加。

In order to investigate the effects of fuel dilution on flame stability characteristics, open syn... more In order to investigate the effects of fuel dilution on flame stability characteristics, open syngas diffusion flames are established and H2O, N2 and CO2 are employed respectively as diluents. The burner configuration used in this study consists of a bluff body with a central jet flow of the fuel and a surrounding coflow of the air. The syngas is composed of 50% of H2 and 50% of CO (by volume). The experiments are conducted at 1 atmospheric pressure, and the temperatures of the fuel and the air are kept constant at about 400 K. The results show that the flame tapers inward and becomes more cylindrical in the shape as after the dilution, the flame becomes unstable due to dilution effects. It has been found that there is a maximum flow rate of diluents responsible for the flame extinction. Among these three dilutions, H2O diluted flames exhibit a highest stability, while CO2 diluted flames have the lowest one due to its large specific heat. Planar Laser-Induced Fluorescence (PLIF) measurements of the OH radical are applied to study the behavior of the OH radical in the flames. The results show that as the diluents introduced into the flame increases, the overall OH mole fraction significantly decreases, and the flame width also decreases. The structures of flame bases are also studied to obtain a better understanding of fuel dilution effects on the flame stability. The radial stabilization distance is decreased and the local flame extinctions in the reaction zones are found as dilution increases. For operating conditions close to the flame extinction limit, the flame reaction zones in the flame bases take on a more intermittent, shredded appearance.

Journal of engineering for gas turbines and power, Jan 17, 2020

Axial-fuel-staged combustion is a promising technology to reduce NOx emission at high turbine inl... more Axial-fuel-staged combustion is a promising technology to reduce NOx emission at high turbine inlet temperatures and provide extended gas turbine operational flexibility. To investigate the emissions characteristics of the axial-fuel-staged combustion, a staged model combustor was constructed and a parametric study was performed at atmospheric pressure. Fuel distribution, equivalence ratio, and jet velocity effects on the emissions characteristics have been studied in the present research. Results show that the influence of fuel distribution on emissions is depending on the combustor outlet temperature. The NOx emissions increase with secondary fuel fraction when the combustor outlet temperature is low but decrease when the combustor outlet temperature is high. Investigation of the equivalence ratio on each stage shows that a lower relative NOx increase in secondary combustion zone is achieved at higher first-stage equivalence ratio. Moreover, the secondary stage jet velocity was varied to study the jet mixing influence on the emissions. The results show that a higher jet velocity will enhance the mixing between the secondary jet and the upstream first-stage burnt gases, producing lower NOx emissions. Finally, a simplified axial-fuel-staged combustion chemical reactors network (CRN) model was established to study the mixing of the secondary fresh fuel/air mixture and the first-stage burnt gases. The CRN modeling results show that a poor mixing in the secondary stage will significantly increase the NOx emission, which means that the mixing enhancement at the secondary stage is important for the axial-fuel-staged combustor design.

Applied Thermal Engineering, Aug 1, 2015

The effect of air/fuel nozzle arrangement on MILD (Moderate or Intense Low-oxygen Dilution) combu... more The effect of air/fuel nozzle arrangement on MILD (Moderate or Intense Low-oxygen Dilution) combustion of coal-derived syngas under lean operating condition was evaluated in a parallel jet combustor. The results were presented on flow field using non-reactive numerical calculation and on OH* chemiluminescence images and exhaust emissions using experiments. The increase in equivalence ratio aids in the reduction of peak flame temperature and in the distribution of reaction volume. The critical equivalence ratios above which MILD combustion occurred were identified for four MILD configurations. The MILD configuration with both air and fuel injected from the opposite side of the combustor exit was observed to achieve MILD combustion at leaner condition than other three configurations. The MILD scheme was established for syngas fuel under highly lean condition with low NO x and CO emissions.

International Journal of Hydrogen Energy, May 1, 2023

This work presents an experimental study of the combustion characteristics of micron-sized alumin... more This work presents an experimental study of the combustion characteristics of micron-sized aluminum and magnesium powders under constant volume combustion experiments. Burning velocities were estimated from the measured pressure traces using both a simplified model for combustion on closed spherical bombs and a semi-empirical correlation for dust explosions, and compared to previous literature. Flame temperatures were measured by bi-color pyrometry and indicate that, for aluminum powders with a mean particle diameter smaller than 12 μm, the flame moves closer to the particle's surface. However, emission spectra obtained during combustion indicate that vapor-phase oxidation exists for all studied powders. Analysis of the combustion products further supported the presence of a vapor-phase reaction. For aluminum, the residue is composed by partially crystallized nanometric spheres as fine as 200 nm. MgO was found in crystallized cubic structures of different sizes, the finest ones also about 200 nm.

Social Science Research Network, 2022

Numerical optimization of nitrogen oxides (NOx) formation is an essential factor during developin... more Numerical optimization of nitrogen oxides (NOx) formation is an essential factor during developing low pollution combustor of gas turbine. The Computational Fluid Dynamics-Chemical Reactor Network (CFD-CRN) hybrid method has a great advantage in fast and accurate prediction of combustor NOx emissions. In this work, a hybrid CFD-CRN approach is established to predict pollutant emissions of a lean premixed model burner for gas turbine applications. Several criteria are compared for separating the combustor into chemically and physically homogeneous zones, and the crucial parameters such as residence time and flue gas recirculation ratio are calculated. The CRN model is preliminarily verified with experimental data. The effects of pressure and fuel-air unmixedness on NOx formation are subsequently investigated. In addition, the effects of changes in fuel/air flow distribution and crucial parameters of CRN model on NOx emissions are also estimated under different pressures and fuel-air unmixedness. The combustor is divided into several zones including reaction preheating region, flame front region, flame transition region, post flame region, main recirculation region and corner recirculation region based on CFD results of fuel-air mixing characteristics, velocity field, temperature field, distribution of OH mass fraction and Damkohler number. The complex CRN model has the advantage of predicting NOx emission characteristics under higher Tad conditions compared with the simple model, and its prediction of NOx emission shows good agreement with experimental data under various equivalence ratio conditions. The structure and distribution of several regions of CRN model are analogous but not significant when Reynolds number exceeds 105 under high pressure. The pathway analysis shows that the NOx emission gradually decreases through N2O and NNH mechanisms, resulted from the decreasing concentration of O radical under low Tad and high pressure. However, the pressure could significantly promote thermal NOx formation resulting form increase of temperature. The fuel-air unmixedness results in the increase of maximum flame temperature, which has significant effect on change of the CRN regions-separating. The fuel-air unmixedness causes the significant increasing of thermal NOx formation.

The Moderate or Intense Low-oxygen Dilution (MILD) combustion is characterized by low emission, s... more The Moderate or Intense Low-oxygen Dilution (MILD) combustion is characterized by low emission, stable combustion and low noise for various kinds of fuel. MILD combustion is a promising combustion technology for gas turbine. The model combustor composed of an optical quartz combustor liner, four jet nozzles and one pilot nozzle has been designed in this study. The four jet nozzles are equidistantly arranged in the combustor concentric circle and the high-speed jet flows from the nozzles will entrain amount of exhaust gas to make MILD combustion occur. The combustion characteristics of the model combustor under atmosphere pressure have been investigated through experiments and numerical simulations. The influence of equivalence ratio and jet velocity on flow pattern, combustion characteristics and exhaust emissions were investigated in detail, respectively. Laser Doppler velocity (LDV) was utilized to measure the speed of a series of points in the model combustor. The measurement results show that a central recirculation existed in the combustion chamber. As the jet velocity of the nozzles increases, the amount of entrained mass by the jet increases simultaneously, however, the central recirculation zone is similar in shape and size. The recirculation of the model combustor will remain self-similar when the jet velocity varies in the range. The calculation model and method were verified through comparing with experimentally LDV data and be used to optimize the model combustor. Planar laser-induced fluorescence of hydroxyl radical (OH-PLIF) approaches were adopted to investigate the flame structure, the reaction zone and the OH distribution. OH distribution of the paralleled and crossed sections in the model combustor were measured, the whole reaction zone have been analyzed. The results show that the OH distribution was uniform in whole combustor. The exhaust gas composition of the combustor was measured by the “TESTO 350” Exhaust Gas Analyzer. All measurements emission results were corrected to 15% O2 in volume. Experimental results showed that NOx and CO emissions were less than 10 ppm@15%O2 when the equivalence ratio ranges from 0.63 to 0.8.

Combustion with diluted syngas is important for integrated gasification combined cycle (IGCC) sys... more Combustion with diluted syngas is important for integrated gasification combined cycle (IGCC) system that attains high efficiency and low pollutant emissions. In syngas diffusion flames, peak flame temperature is higher than that in nature gas flames, so NOx emission is more significant. To achieve low NOx emission, fuel dilution is an effective way. In the present study, Flame structure and emission characteristics were experimentally and numerically studied in various fuel diluted syngas diffusion flames, and H2O, N2 and CO2 were employed as diluents respectively. The purpose of this paper is to better understand the behavior and mechanism of fuel diluted combustion and to provide fundamental data base for the development of syngas combustion techniques. Experiments were conducted by using jet diffusion flames in a model combustor. Flame size, exhaust temperature and emission concentration were measured. It was found that by introducing diluents into fuel stream, the stoichiometric surface was brought inward, namely the flame envelope shrunk due to a relatively low fuel concentration. The exhaust temperature was decreased. The results also indicated that with diluted fuel stream, there was an increase of CO emission and an apparent decrease of NO emission. For the same exhaust temperature, H2O had the most significant influence on NO emission among the three diluents, while CO2 affected CO emission most by inhibiting its oxidation thermally and chemically. Numerical simulations were performed in counterflow diffusion flames by applying Chemkin software. To reveal the mechanisms of various diluents in flames, the detailed chemistry of H2-CO-N2 system was employed. It was found that the concentration of OH radical is important for both NO and CO emissions. The OH concentration is affected not only by the type of diluents but also by the flame temperature, therefore it is determined by the coupling and competition of diluents’ chemical and thermal effects.

Combustion of syngas with humid air is important for integrated coal gasification humid air turbi... more Combustion of syngas with humid air is important for integrated coal gasification humid air turbine cycle for power generation. In contrast to hydrocarbon fuels, CO exists in bulky content in syngas. Thus the influence of air humidity on the oxidation of CO in syngas flames should be well understood. In the present study, the influence of air humidity on CO oxidation in syngas diffusion flames was investigated both experimentally and numerically. In the experiment, CO, CO2, O2 and temperature profiles in a model combustor of a syngas turbulent jet diffusion flame were measured. It was found that as the mass flow rate of dry air and the exhaust temperature kept constant, the profile of CO was influenced by air humidity, but CO exhaust did not exhibit a monotone increase over humidity. There exist an inflexion at the case of absolute humidity of the air X = 6.0. In addition, CO emission decreases with the increase of the thermal load. And the influence of the humidity on CO oxidation was not obviously when the thermal load is high. In the numerical simulation, flow field in the combustor was calculated by applying the composition PDF transport model and Flamelet model respectively. The numerical results were compared with the experiment and the PDF model was verified that it is more suited to simulate the CO oxidation. From the numerical analysis, it was found that the concentration of OH wasn’t monotonously increased with the added H2O and this directly affect the oxidation of CO via CO + OH → CO2 + H. In general, the influence of air humidity on the oxidation of CO in syngas diffusion flames depends on the coupling and competition of chemistry and fluid mechanics aspects. This helps to interpret the discrepancy of the results of gas turbine combustor test.

ABSTRACT MILD combustion is a promising combustion technology for the future gas turbine combusto... more ABSTRACT MILD combustion is a promising combustion technology for the future gas turbine combustor due to its high combustion efficiency, low exhaust emissions and enhanced combustion stability. It utilizes the concept of exhaust gas recirculation to achieve combustion at reduced temperature and flat thermal field. To examine the role of gas recirculation level on MILD combustion performance, a laboratory-scale axially staged combustor constituted of gas generation zone, mixing zone and MILD combustion zone is presented. To realize ultra-low NOx emissions for syngas characterized by high flame temperature, it is necessary to select an appropriate combustion mode for the gas generation zone. This study compared combustion performance and gas/fuel/air mixing feature between two configurations, gas generation zone of which are based on swirl diffusion combustion and coflow diffusion combustion, respectively. The results are compared on flow field with numerical simulation, and global flame signatures and exhaust emissions with experiment. Both numerical simulation and experiment are performed at equivalence ratio of 0.4, heat load of 24.4 kW, using 10 MJ/Nm3 syngas as the fuel at atmospheric pressure and normal temperature fuel and air. More uniform oxidizer, lower flame temperature and less NOx production are observed in coflow diffusion staged combustion. MILD combustion zone is beneficial for the reduction of NOx and oxidation of CO exit from the gas generation zone.

ABSTRACT Gas turbine is one of the key components for integrated gasification combined cycle (IGC... more ABSTRACT Gas turbine is one of the key components for integrated gasification combined cycle (IGCC) system. Combustor of the gas turbine needs to burn medium/low heating value syngas produced by coal gasification. In order to save time and cost during the design and development of a gas turbine combustor for medium/low heating value syngas, computational fluid dynamics (CFD) offers a good mean. In this paper, 3D numerical simulations were carried out on a full scale multi-nozzle gas turbine combustor using commercial CFD software FLUENT. A 72 degrees sector was modeled to minimize the number of cells of the grid. For the fluid flow part, viscous Navier-Stokes equations were solved. The realizable k-ε turbulence model was adopted. Steady laminar flamelet model was used for the reacting system. The interaction between fluid turbulence and combustion chemistry was taken into account by the PDF (probability density function) model. The simulation was performed with two design schemes which are head cooling using film-cooling and impingement cooling. The details of the flow field and temperature distribution inside the two gas turbine combustors obtained could be cited as references for design and retrofit. Similarities were found between the predicted and experimental data of the transition duct exit temperature profile. There is much work yet to be done on modeling validation in the future.

International Journal of Hydrogen Energy, 2021

h i g h l i g h t s The flow field of a novel Micromix burner was investigated. Compared with mul... more h i g h l i g h t s The flow field of a novel Micromix burner was investigated. Compared with multiple round jets, the merging point of the burner moves upstream. No recirculation region was found near the burner outlet. The simulation results can match the experimental results in a good trend.

Applied Thermal Engineering, 2023

Experimental Thermal and Fluid Science, Sep 1, 2021

The combustion of an oxygen/paraffin hybrid rocket motor was experimentally characterized. Firing... more The combustion of an oxygen/paraffin hybrid rocket motor was experimentally characterized. Firing tests were conducted for different oxidizer mass fluxes ranging from 2.47 to 3.40 g/ (cm 2 ⋅s). Variations in temperature and H 2 O partial pressure at the nozzle exit were diagnosed using mid-infrared tunable diode laser absorption spectroscopy (TDLAS) based on H 2 O absorption near 2.5 μm. Three H 2 O absorption lines were simultaneously covered by only one distributed feedback (DFB) laser using scanned-wavelength direct absorption (DA) mode with 2.0 kHz repetition rate. Measurement uncertainty was analyzed in detail considering line-strength uncertainty and Voigt fitting residuals. A two-dimensional (2D) model of the nozzle was constructed using the ANSYS FLUENT CFD software package. The combustion efficiency of the hybrid rocket motor was evaluated from the perspectives of chemical reaction and heat release, respectively, based on TDLAS results and CFD simulations. The effectiveness of the evaluation was validated by comparing its results with characteristic velocity (C*)-based combustion efficiency. Finally, comparisons of combustion efficiencies among different cases show that increasing the oxidizer mass flux or oxidizer-to-fuel ratio improves the combustion efficiency of the hybrid rocket motor under our experimental conditions.

The temperature and humidity of the combustion chamber inlet air under the humid air turbine cycl... more The temperature and humidity of the combustion chamber inlet air under the humid air turbine cycle (HAT) vary dramatically, with the highest air temperature of approximately 900 K and high humidity of about 0.3 kg/kg. Compared with conventional lean premixed combustion, which may cause risks such as flashback and autoignition under high-temperature conditions, micromix combustion has the characteristics of small mixing scale, compact flame, flashback resistance, and low emissions, and has been implemented in HAT cycle combustion chambers. In this work, a 9-nozzle micromix model burner with a 3 × 3 array arrangement was designed based on the flow field organization of multiple micromix round jets. The effects of heat load (30∼55 kW), air temperature (300∼630 K), and steam ratio (0∼0.143 kg/kg) variation on the combustion and pollutant emission characteristics of methane-humid air micromix flame at atmospheric pressure conditions were experimentally investigated. Intensified Charge-Coupled Device (ICCD) is adopted to detect OH* chemiluminescence distribution thus investigating the turbulence-reaction interactions and the characteristics of the reaction field. And the effect of humidity on NOx emission was qualitatively analyzed by combining it with a reactor network model. Results indicated that compact flames were achieved for different cases with flame heights of about 85∼185 mm. The steam ratio has a significant influence on the flame structure and NOx emission. Compared with the dry air condition, the flame length increased by nearly 50% while the steam ratio reached 0.143 kg/kg, and the NOx emission was kept at a relatively low level of about 5 ppm (@15% O2) under the designed operating condition. The in-depth understanding of humid air micromix combustion technology is a significant step toward the design of future stability combustors for the HAT cycle.

Frontiers of Energy and Power Engineering in China, May 1, 2007

The influence of grid turbulence on the shear layer of a jet and the premixed flames embedded in ... more The influence of grid turbulence on the shear layer of a jet and the premixed flames embedded in it was investigated in the present study. The velocity field of the jet was measured by using hot-wire anemometry. It was found that grid turbulence reduced turbulence intensities in the shear layer and suppressed low frequency fluctuation. Moreover, the energy contained in

For high-hydrogen-content fuel, the Micromix Combustion Technology has been developed as a potent... more For high-hydrogen-content fuel, the Micromix Combustion Technology has been developed as a potential low NOx emission solution for gas turbine combustors, especially for advanced gas turbines with high turbine inlet temperature. Compared with conventional lean premixed flames, multiple distributed slim and micro flames could lead to a lower NOx emission performance for shortening residence time of high temperature flue gas and generally a more uniform temperature distribution. This work aims at micromix flame characteristics of a model burner fueled with hydrogen blending with methane under atmosphere pressure conditions. The model burner assembly was designed to have six concentrically millimeter-sized premixed units around a same unit centrally. Numerical and experimental studies were conducted on mixing performance, flame stability, flame structure and CO/NOx emissions of the model burner. OH radical distribution by OH-PLIF and OH chemiluminescence (OH*) imaging were employed to analyze the turbulence-reaction interactions and characters of the reaction zone at the burner exit. Micromix flames fueled with five different hydrogen content H2-CH4 (60/40, 50/50, 40/60, 30/70, 0/100 Vol.%) were investigated, along with the effects of equivalence ratio and heat load. Results indicated that low NOx emissions of less than 10 ppm (@15% O2) below the exhaust temperature of 1920 K were obtained for all the different fuels. Combustion oscillation didn’t occur for all the conditions. It was found that at a constant flame temperature, the higher the hydrogen content of the fuel, the higher the turbulent flame speed and the weaker the flame lift effect. Combustion noise and NOx emissions also increase with increasing hydrogen content. The OH/OH* signal distribution indicated that a pure methane micromix flame showed a lifted and weaken distributed feature.

Electronics

Gas turbines are widely used in industry, and the combustion chamber, compressor, and turbine are... more Gas turbines are widely used in industry, and the combustion chamber, compressor, and turbine are known as their three important components. In the design process of the combustion chamber, computational fluid dynamics simulation takes up a lot of time. In order to accelerate the design speed of the combustion chamber, this article proposes a combustion chamber design method that combines an artificial neural network (ANN) and computational fluid dynamics (CFD). CFD results are used as raw data to establish a fast prediction model using ANN and eXtreme Gradient Boosting (XGBoost). The results show that the mean squared error (MSE) of the ANN is 0.0019, and the MSE of XGBoost is 0.0021, so the ANN’s prediction performance is slightly better. This fast prediction method combines CFD and the ANN, which can greatly shorten CFD calculation time, improve the efficiency of gas turbine combustion chamber design, and provide the possibility of achieving digital twins of gas turbine combustio...

推进技术, May 25, 2018

为了获得燃料分级比例与烟气排放之间的变化规律，基于燃料分级概念，结合数值模拟和实验研究的手段对以CH4为燃料的轴向燃料分级燃烧中NOx排放特性进行了研究。建立燃料分级化学反应器网络模型，研究了停... more 为了获得燃料分级比例与烟气排放之间的变化规律，基于燃料分级概念，结合数值模拟和实验研究的手段对以CH4为燃料的轴向燃料分级燃烧中NOx排放特性进行了研究。建立燃料分级化学反应器网络模型，研究了停留时间和燃料分级比例对NOx排放的影响，对燃料分级燃烧中的NOx反应途径进行了分析，并通过调节参与再燃的烟气比例分析了二级燃料与烟气的掺混性能对NOx排放的影响。针对燃料分级模型燃烧器，实验测量了不同燃料分级比例和不同二级燃料流量下的NOx排放。结果表明，燃料分级缩短了烟气在高温区的停留时间，抑制了热力型NO的生成；在再燃区燃烧反应初始阶段二级燃料与高温烟气形成还原性气氛，通过NO再燃还原了主燃烟气中的NO；在一定的总当量比工况下，燃料分级比例的增加降低了出口的NOx排放，提高了NOx排放中NO2的比例。与二级燃料进行掺混反应的烟气量过少会形成再燃区的局部高温，导致NOx排放增加。

In order to investigate the effects of fuel dilution on flame stability characteristics, open syn... more In order to investigate the effects of fuel dilution on flame stability characteristics, open syngas diffusion flames are established and H2O, N2 and CO2 are employed respectively as diluents. The burner configuration used in this study consists of a bluff body with a central jet flow of the fuel and a surrounding coflow of the air. The syngas is composed of 50% of H2 and 50% of CO (by volume). The experiments are conducted at 1 atmospheric pressure, and the temperatures of the fuel and the air are kept constant at about 400 K. The results show that the flame tapers inward and becomes more cylindrical in the shape as after the dilution, the flame becomes unstable due to dilution effects. It has been found that there is a maximum flow rate of diluents responsible for the flame extinction. Among these three dilutions, H2O diluted flames exhibit a highest stability, while CO2 diluted flames have the lowest one due to its large specific heat. Planar Laser-Induced Fluorescence (PLIF) measurements of the OH radical are applied to study the behavior of the OH radical in the flames. The results show that as the diluents introduced into the flame increases, the overall OH mole fraction significantly decreases, and the flame width also decreases. The structures of flame bases are also studied to obtain a better understanding of fuel dilution effects on the flame stability. The radial stabilization distance is decreased and the local flame extinctions in the reaction zones are found as dilution increases. For operating conditions close to the flame extinction limit, the flame reaction zones in the flame bases take on a more intermittent, shredded appearance.

Journal of engineering for gas turbines and power, Jan 17, 2020

Axial-fuel-staged combustion is a promising technology to reduce NOx emission at high turbine inl... more Axial-fuel-staged combustion is a promising technology to reduce NOx emission at high turbine inlet temperatures and provide extended gas turbine operational flexibility. To investigate the emissions characteristics of the axial-fuel-staged combustion, a staged model combustor was constructed and a parametric study was performed at atmospheric pressure. Fuel distribution, equivalence ratio, and jet velocity effects on the emissions characteristics have been studied in the present research. Results show that the influence of fuel distribution on emissions is depending on the combustor outlet temperature. The NOx emissions increase with secondary fuel fraction when the combustor outlet temperature is low but decrease when the combustor outlet temperature is high. Investigation of the equivalence ratio on each stage shows that a lower relative NOx increase in secondary combustion zone is achieved at higher first-stage equivalence ratio. Moreover, the secondary stage jet velocity was varied to study the jet mixing influence on the emissions. The results show that a higher jet velocity will enhance the mixing between the secondary jet and the upstream first-stage burnt gases, producing lower NOx emissions. Finally, a simplified axial-fuel-staged combustion chemical reactors network (CRN) model was established to study the mixing of the secondary fresh fuel/air mixture and the first-stage burnt gases. The CRN modeling results show that a poor mixing in the secondary stage will significantly increase the NOx emission, which means that the mixing enhancement at the secondary stage is important for the axial-fuel-staged combustor design.

Applied Thermal Engineering, Aug 1, 2015

The effect of air/fuel nozzle arrangement on MILD (Moderate or Intense Low-oxygen Dilution) combu... more The effect of air/fuel nozzle arrangement on MILD (Moderate or Intense Low-oxygen Dilution) combustion of coal-derived syngas under lean operating condition was evaluated in a parallel jet combustor. The results were presented on flow field using non-reactive numerical calculation and on OH* chemiluminescence images and exhaust emissions using experiments. The increase in equivalence ratio aids in the reduction of peak flame temperature and in the distribution of reaction volume. The critical equivalence ratios above which MILD combustion occurred were identified for four MILD configurations. The MILD configuration with both air and fuel injected from the opposite side of the combustor exit was observed to achieve MILD combustion at leaner condition than other three configurations. The MILD scheme was established for syngas fuel under highly lean condition with low NO x and CO emissions.

International Journal of Hydrogen Energy, May 1, 2023

This work presents an experimental study of the combustion characteristics of micron-sized alumin... more This work presents an experimental study of the combustion characteristics of micron-sized aluminum and magnesium powders under constant volume combustion experiments. Burning velocities were estimated from the measured pressure traces using both a simplified model for combustion on closed spherical bombs and a semi-empirical correlation for dust explosions, and compared to previous literature. Flame temperatures were measured by bi-color pyrometry and indicate that, for aluminum powders with a mean particle diameter smaller than 12 μm, the flame moves closer to the particle's surface. However, emission spectra obtained during combustion indicate that vapor-phase oxidation exists for all studied powders. Analysis of the combustion products further supported the presence of a vapor-phase reaction. For aluminum, the residue is composed by partially crystallized nanometric spheres as fine as 200 nm. MgO was found in crystallized cubic structures of different sizes, the finest ones also about 200 nm.

Social Science Research Network, 2022

Numerical optimization of nitrogen oxides (NOx) formation is an essential factor during developin... more Numerical optimization of nitrogen oxides (NOx) formation is an essential factor during developing low pollution combustor of gas turbine. The Computational Fluid Dynamics-Chemical Reactor Network (CFD-CRN) hybrid method has a great advantage in fast and accurate prediction of combustor NOx emissions. In this work, a hybrid CFD-CRN approach is established to predict pollutant emissions of a lean premixed model burner for gas turbine applications. Several criteria are compared for separating the combustor into chemically and physically homogeneous zones, and the crucial parameters such as residence time and flue gas recirculation ratio are calculated. The CRN model is preliminarily verified with experimental data. The effects of pressure and fuel-air unmixedness on NOx formation are subsequently investigated. In addition, the effects of changes in fuel/air flow distribution and crucial parameters of CRN model on NOx emissions are also estimated under different pressures and fuel-air unmixedness. The combustor is divided into several zones including reaction preheating region, flame front region, flame transition region, post flame region, main recirculation region and corner recirculation region based on CFD results of fuel-air mixing characteristics, velocity field, temperature field, distribution of OH mass fraction and Damkohler number. The complex CRN model has the advantage of predicting NOx emission characteristics under higher Tad conditions compared with the simple model, and its prediction of NOx emission shows good agreement with experimental data under various equivalence ratio conditions. The structure and distribution of several regions of CRN model are analogous but not significant when Reynolds number exceeds 105 under high pressure. The pathway analysis shows that the NOx emission gradually decreases through N2O and NNH mechanisms, resulted from the decreasing concentration of O radical under low Tad and high pressure. However, the pressure could significantly promote thermal NOx formation resulting form increase of temperature. The fuel-air unmixedness results in the increase of maximum flame temperature, which has significant effect on change of the CRN regions-separating. The fuel-air unmixedness causes the significant increasing of thermal NOx formation.

The Moderate or Intense Low-oxygen Dilution (MILD) combustion is characterized by low emission, s... more The Moderate or Intense Low-oxygen Dilution (MILD) combustion is characterized by low emission, stable combustion and low noise for various kinds of fuel. MILD combustion is a promising combustion technology for gas turbine. The model combustor composed of an optical quartz combustor liner, four jet nozzles and one pilot nozzle has been designed in this study. The four jet nozzles are equidistantly arranged in the combustor concentric circle and the high-speed jet flows from the nozzles will entrain amount of exhaust gas to make MILD combustion occur. The combustion characteristics of the model combustor under atmosphere pressure have been investigated through experiments and numerical simulations. The influence of equivalence ratio and jet velocity on flow pattern, combustion characteristics and exhaust emissions were investigated in detail, respectively. Laser Doppler velocity (LDV) was utilized to measure the speed of a series of points in the model combustor. The measurement results show that a central recirculation existed in the combustion chamber. As the jet velocity of the nozzles increases, the amount of entrained mass by the jet increases simultaneously, however, the central recirculation zone is similar in shape and size. The recirculation of the model combustor will remain self-similar when the jet velocity varies in the range. The calculation model and method were verified through comparing with experimentally LDV data and be used to optimize the model combustor. Planar laser-induced fluorescence of hydroxyl radical (OH-PLIF) approaches were adopted to investigate the flame structure, the reaction zone and the OH distribution. OH distribution of the paralleled and crossed sections in the model combustor were measured, the whole reaction zone have been analyzed. The results show that the OH distribution was uniform in whole combustor. The exhaust gas composition of the combustor was measured by the “TESTO 350” Exhaust Gas Analyzer. All measurements emission results were corrected to 15% O2 in volume. Experimental results showed that NOx and CO emissions were less than 10 ppm@15%O2 when the equivalence ratio ranges from 0.63 to 0.8.

Combustion with diluted syngas is important for integrated gasification combined cycle (IGCC) sys... more Combustion with diluted syngas is important for integrated gasification combined cycle (IGCC) system that attains high efficiency and low pollutant emissions. In syngas diffusion flames, peak flame temperature is higher than that in nature gas flames, so NOx emission is more significant. To achieve low NOx emission, fuel dilution is an effective way. In the present study, Flame structure and emission characteristics were experimentally and numerically studied in various fuel diluted syngas diffusion flames, and H2O, N2 and CO2 were employed as diluents respectively. The purpose of this paper is to better understand the behavior and mechanism of fuel diluted combustion and to provide fundamental data base for the development of syngas combustion techniques. Experiments were conducted by using jet diffusion flames in a model combustor. Flame size, exhaust temperature and emission concentration were measured. It was found that by introducing diluents into fuel stream, the stoichiometric surface was brought inward, namely the flame envelope shrunk due to a relatively low fuel concentration. The exhaust temperature was decreased. The results also indicated that with diluted fuel stream, there was an increase of CO emission and an apparent decrease of NO emission. For the same exhaust temperature, H2O had the most significant influence on NO emission among the three diluents, while CO2 affected CO emission most by inhibiting its oxidation thermally and chemically. Numerical simulations were performed in counterflow diffusion flames by applying Chemkin software. To reveal the mechanisms of various diluents in flames, the detailed chemistry of H2-CO-N2 system was employed. It was found that the concentration of OH radical is important for both NO and CO emissions. The OH concentration is affected not only by the type of diluents but also by the flame temperature, therefore it is determined by the coupling and competition of diluents’ chemical and thermal effects.

Combustion of syngas with humid air is important for integrated coal gasification humid air turbi... more Combustion of syngas with humid air is important for integrated coal gasification humid air turbine cycle for power generation. In contrast to hydrocarbon fuels, CO exists in bulky content in syngas. Thus the influence of air humidity on the oxidation of CO in syngas flames should be well understood. In the present study, the influence of air humidity on CO oxidation in syngas diffusion flames was investigated both experimentally and numerically. In the experiment, CO, CO2, O2 and temperature profiles in a model combustor of a syngas turbulent jet diffusion flame were measured. It was found that as the mass flow rate of dry air and the exhaust temperature kept constant, the profile of CO was influenced by air humidity, but CO exhaust did not exhibit a monotone increase over humidity. There exist an inflexion at the case of absolute humidity of the air X = 6.0. In addition, CO emission decreases with the increase of the thermal load. And the influence of the humidity on CO oxidation was not obviously when the thermal load is high. In the numerical simulation, flow field in the combustor was calculated by applying the composition PDF transport model and Flamelet model respectively. The numerical results were compared with the experiment and the PDF model was verified that it is more suited to simulate the CO oxidation. From the numerical analysis, it was found that the concentration of OH wasn’t monotonously increased with the added H2O and this directly affect the oxidation of CO via CO + OH → CO2 + H. In general, the influence of air humidity on the oxidation of CO in syngas diffusion flames depends on the coupling and competition of chemistry and fluid mechanics aspects. This helps to interpret the discrepancy of the results of gas turbine combustor test.

ABSTRACT MILD combustion is a promising combustion technology for the future gas turbine combusto... more ABSTRACT MILD combustion is a promising combustion technology for the future gas turbine combustor due to its high combustion efficiency, low exhaust emissions and enhanced combustion stability. It utilizes the concept of exhaust gas recirculation to achieve combustion at reduced temperature and flat thermal field. To examine the role of gas recirculation level on MILD combustion performance, a laboratory-scale axially staged combustor constituted of gas generation zone, mixing zone and MILD combustion zone is presented. To realize ultra-low NOx emissions for syngas characterized by high flame temperature, it is necessary to select an appropriate combustion mode for the gas generation zone. This study compared combustion performance and gas/fuel/air mixing feature between two configurations, gas generation zone of which are based on swirl diffusion combustion and coflow diffusion combustion, respectively. The results are compared on flow field with numerical simulation, and global flame signatures and exhaust emissions with experiment. Both numerical simulation and experiment are performed at equivalence ratio of 0.4, heat load of 24.4 kW, using 10 MJ/Nm3 syngas as the fuel at atmospheric pressure and normal temperature fuel and air. More uniform oxidizer, lower flame temperature and less NOx production are observed in coflow diffusion staged combustion. MILD combustion zone is beneficial for the reduction of NOx and oxidation of CO exit from the gas generation zone.

ABSTRACT Gas turbine is one of the key components for integrated gasification combined cycle (IGC... more ABSTRACT Gas turbine is one of the key components for integrated gasification combined cycle (IGCC) system. Combustor of the gas turbine needs to burn medium/low heating value syngas produced by coal gasification. In order to save time and cost during the design and development of a gas turbine combustor for medium/low heating value syngas, computational fluid dynamics (CFD) offers a good mean. In this paper, 3D numerical simulations were carried out on a full scale multi-nozzle gas turbine combustor using commercial CFD software FLUENT. A 72 degrees sector was modeled to minimize the number of cells of the grid. For the fluid flow part, viscous Navier-Stokes equations were solved. The realizable k-ε turbulence model was adopted. Steady laminar flamelet model was used for the reacting system. The interaction between fluid turbulence and combustion chemistry was taken into account by the PDF (probability density function) model. The simulation was performed with two design schemes which are head cooling using film-cooling and impingement cooling. The details of the flow field and temperature distribution inside the two gas turbine combustors obtained could be cited as references for design and retrofit. Similarities were found between the predicted and experimental data of the transition duct exit temperature profile. There is much work yet to be done on modeling validation in the future.

International Journal of Hydrogen Energy, 2021

h i g h l i g h t s The flow field of a novel Micromix burner was investigated. Compared with mul... more h i g h l i g h t s The flow field of a novel Micromix burner was investigated. Compared with multiple round jets, the merging point of the burner moves upstream. No recirculation region was found near the burner outlet. The simulation results can match the experimental results in a good trend.

Applied Thermal Engineering, 2023

Experimental Thermal and Fluid Science, Sep 1, 2021

The combustion of an oxygen/paraffin hybrid rocket motor was experimentally characterized. Firing... more The combustion of an oxygen/paraffin hybrid rocket motor was experimentally characterized. Firing tests were conducted for different oxidizer mass fluxes ranging from 2.47 to 3.40 g/ (cm 2 ⋅s). Variations in temperature and H 2 O partial pressure at the nozzle exit were diagnosed using mid-infrared tunable diode laser absorption spectroscopy (TDLAS) based on H 2 O absorption near 2.5 μm. Three H 2 O absorption lines were simultaneously covered by only one distributed feedback (DFB) laser using scanned-wavelength direct absorption (DA) mode with 2.0 kHz repetition rate. Measurement uncertainty was analyzed in detail considering line-strength uncertainty and Voigt fitting residuals. A two-dimensional (2D) model of the nozzle was constructed using the ANSYS FLUENT CFD software package. The combustion efficiency of the hybrid rocket motor was evaluated from the perspectives of chemical reaction and heat release, respectively, based on TDLAS results and CFD simulations. The effectiveness of the evaluation was validated by comparing its results with characteristic velocity (C*)-based combustion efficiency. Finally, comparisons of combustion efficiencies among different cases show that increasing the oxidizer mass flux or oxidizer-to-fuel ratio improves the combustion efficiency of the hybrid rocket motor under our experimental conditions.

The temperature and humidity of the combustion chamber inlet air under the humid air turbine cycl... more The temperature and humidity of the combustion chamber inlet air under the humid air turbine cycle (HAT) vary dramatically, with the highest air temperature of approximately 900 K and high humidity of about 0.3 kg/kg. Compared with conventional lean premixed combustion, which may cause risks such as flashback and autoignition under high-temperature conditions, micromix combustion has the characteristics of small mixing scale, compact flame, flashback resistance, and low emissions, and has been implemented in HAT cycle combustion chambers. In this work, a 9-nozzle micromix model burner with a 3 × 3 array arrangement was designed based on the flow field organization of multiple micromix round jets. The effects of heat load (30∼55 kW), air temperature (300∼630 K), and steam ratio (0∼0.143 kg/kg) variation on the combustion and pollutant emission characteristics of methane-humid air micromix flame at atmospheric pressure conditions were experimentally investigated. Intensified Charge-Coupled Device (ICCD) is adopted to detect OH* chemiluminescence distribution thus investigating the turbulence-reaction interactions and the characteristics of the reaction field. And the effect of humidity on NOx emission was qualitatively analyzed by combining it with a reactor network model. Results indicated that compact flames were achieved for different cases with flame heights of about 85∼185 mm. The steam ratio has a significant influence on the flame structure and NOx emission. Compared with the dry air condition, the flame length increased by nearly 50% while the steam ratio reached 0.143 kg/kg, and the NOx emission was kept at a relatively low level of about 5 ppm (@15% O2) under the designed operating condition. The in-depth understanding of humid air micromix combustion technology is a significant step toward the design of future stability combustors for the HAT cycle.

Frontiers of Energy and Power Engineering in China, May 1, 2007

The influence of grid turbulence on the shear layer of a jet and the premixed flames embedded in ... more The influence of grid turbulence on the shear layer of a jet and the premixed flames embedded in it was investigated in the present study. The velocity field of the jet was measured by using hot-wire anemometry. It was found that grid turbulence reduced turbulence intensities in the shear layer and suppressed low frequency fluctuation. Moreover, the energy contained in

For high-hydrogen-content fuel, the Micromix Combustion Technology has been developed as a potent... more For high-hydrogen-content fuel, the Micromix Combustion Technology has been developed as a potential low NOx emission solution for gas turbine combustors, especially for advanced gas turbines with high turbine inlet temperature. Compared with conventional lean premixed flames, multiple distributed slim and micro flames could lead to a lower NOx emission performance for shortening residence time of high temperature flue gas and generally a more uniform temperature distribution. This work aims at micromix flame characteristics of a model burner fueled with hydrogen blending with methane under atmosphere pressure conditions. The model burner assembly was designed to have six concentrically millimeter-sized premixed units around a same unit centrally. Numerical and experimental studies were conducted on mixing performance, flame stability, flame structure and CO/NOx emissions of the model burner. OH radical distribution by OH-PLIF and OH chemiluminescence (OH*) imaging were employed to analyze the turbulence-reaction interactions and characters of the reaction zone at the burner exit. Micromix flames fueled with five different hydrogen content H2-CH4 (60/40, 50/50, 40/60, 30/70, 0/100 Vol.%) were investigated, along with the effects of equivalence ratio and heat load. Results indicated that low NOx emissions of less than 10 ppm (@15% O2) below the exhaust temperature of 1920 K were obtained for all the different fuels. Combustion oscillation didn’t occur for all the conditions. It was found that at a constant flame temperature, the higher the hydrogen content of the fuel, the higher the turbulent flame speed and the weaker the flame lift effect. Combustion noise and NOx emissions also increase with increasing hydrogen content. The OH/OH* signal distribution indicated that a pure methane micromix flame showed a lifted and weaken distributed feature.