CFD modeling of heat transfer and fluid flow inside a pent-roof type combustion chamber using dynamic model

A numerical work has been performed to analyze the heat transfer and fluid flow in a pent-roof type combustion chamber. Dynamic mesh model was used to simulation piston intake stroke. Revolution of piston (1000 ≤ n ≤ 5000) is the main governing parameter on heat and fluid flow. k–ε turbulence model was used to predict the flow in the cylinder of a non-compressing fluid. They were solved with finite volume method and FLUENT 12.0 commercial code. Velocity profiles, temperature distribution, pressure distribution and velocity vectors are presented. It is found that the inclined surface of pent-roof type of combustion chamber reduces the swirl effect and it can be a control parameter for heat and fluid flow.     

Numerical and experimental investigation of a mild combustion burner

An industrial burner operating in the MILD combustion regime through internal recirculation of exhaust gases has been characterized numerically. To develop a self-sufficient numerical model of the burner, two subroutines are coupled to the CFD solver to model the air preheater section and heat losses from the burner through radiation. The resulting model is validated against experimental data on species concentration and temperature. A 3-dimensional CFD model of the burner is compared to an axisymmetric model, which allows considerable computational saving, but neglects some important burner features such as the presence of recirculation windows. Errors associated with the axisymmetric model are evaluated and discussed, as well as possible simplified procedures for engineering purposes. Modifications of the burner geometry are investigated numerically and suggested in order to enhance its performances. Such modifications are aimed at improving exhaust gases recirculation which is driven by the inlet air jet momentum. The burner is found to produce only 30 ppm_v of NO when operating in MILD combustion mode. For the same air preheating the NO emissions would be of approximately 1000 ppm_v in flame combustion mode. It is also shown that the burner ensures more homogeneous temperature distribution in the outer surfaces with respect to flame operation, and this is attractive for burners used in furnaces devoted to materials' thermal treatment processes. The effect of air excess on the combustion regime is also discussed.     

锅炉与炉窑燃料油使用中的常见问题及解决方法

对燃油锅炉与炉窑使用中的常见问题以及燃料油主要质量指标的优劣对燃烧工况的关联影响进行分析，并提出一种经济实用简便的解决方法，达到改善燃油锅炉与炉窑燃烧工况与抑制硫、钒的腐蚀，灰分积焦、积炭、油泥生成等，又达到降低能耗、减少烟气排放的目的。     

Numerical analysis of the thermo-fluid-dynamic field in the combustion chamber of an incinerator plant

As the interest for energy recovery from waste incineration has increased over the years, concern for the impact such processes have on the environment has also grown. To reduce such an impact, the legislation enforced in Italy and Europe imposes important restrictions on the temperature of the exhausts in the combustion chamber, which must be kept above certain values depending on the type of waste that is being incinerated, for a given period of time. Such conditions can be rather difficult and certainly very expensive to monitor with acceptable accuracy. In this work, a numerical approach is presented for modelling waste combustion in a full scale incineration plant. Both solid and gas phase reactions are considered. Various modes of heat and mass transfer between the waste bed, the air and the combustion products are taken into account, as well as radiation from the combustion chamber walls and the combustion products. The temperature distribution in the combustion chamber is obtained considering either forced or mixed convection. It is therefore shown that neglecting buoyancy effects may lead to appreciable errors. Verification of the code performance is based on comparison with the results of an experimental campaign at a full scale plant in Italy.     

Numerical modelling of a three-zone combustion for heavy fuel oil in inert porous media reactor

Numerical model for heavy fuel oil and air mixtures combustion is presented to simulate the behavior of the fuel in an inert porous medium reactor for hydrogen production. Three-zone combustion of oil and petroleum cokes separated by temperature ranges starting from ambient temperature to 560 K, from 560 K to 673 K, and above 673 K, is presented. Hydrogen production is achieved using water gas shift equilibrium reaction on the combustion products at different temperatures. Results show a high enthalpy contribution due to coke combustion formed in the low temperature oxidation reaction, being the most important reaction in relation to its zone size. Simulations increasing filtration velocity (from 0.05 to 0.9 m/s) has a favorable effect on the maximum temperature and the combustion front velocity. The effect of the simplified combustion model lowers computational time, with acceptable results for temperature as well as hydrogen production in contrast to laboratory tests and other software simulation such as COMSOL Multiphysics.     

Analysis of different combustion chamber geometries using hydrogen / diesel fuel in a diesel engine

ABSTRACT

In this study, the effects on combustion characteristics and emission were investigated in a direct injection diesel engine. In experimental and numerical studies, the engine was operated at 2000 rpm. The analyzes were made in the AVL-FIRE ESE Diesel part with Computational Fluid Dynamics (CFD) software. Standard combustion chamber (SCC) and Modified combustion chamber (MCC) geometry were compared in the modeling. By means of the designed MCC combustion chamber geometry, the fuel released from the injector was directed to the piston bowl area. Therefore, the mixture was homogenized and the combustion had been improved. In addition, the evaporation rate of the mixture increased with the MCC geometry. Also, lower NO and CO emissions were obtained with the MCC model compared to the SCC model. On the other hand, diesel fuel and mass 5% hydrogen fuel was used into diesel fuel as fuel in the study. The combustion process was investigated using hydrogen in different combustion chambers. The use of hydrogen as additional fuel resulted in higher combustion pressure, temperature and NO emissions. Compared to SCC type combustion chamber in the MCC type combustion chamber used diesel fuel, CO emission decreased of 6% and 3% for hydrogen-added mixture fuel. Also, compared to SCC type combustion chamber in the MCC type combustion chamber used diesel fuel, NO emission decreased of 11% and 32% for hydrogen-added mixture fuel. Moreover, flame velocity, heat release rate and flame propagation increased with the addition of hydrogen fuel.     

废轮胎热解油特性及其燃烧应用

随着石油资源的日益枯竭及废轮胎数量的日益增多,利用废轮胎热解制取燃料油对缓解能源供应紧张局面,充分利用废弃资源都具有重要意义.废轮胎热解油具有热值高、灰分低、粘度低和残炭值低等优点,但也存在整体性能较柴油差的缺陷.与柴油混合作为发动机燃料使用的结果表明,废轮胎热解油可以作为重柴油使用;炉内燃烧试验表明.废轮胎热解油污染物排放量较柴油高.探索合适的废轮胎热解工艺,提高废轮胎热解油的品质,是将废轮胎热解油直接作为燃料油使用须研究的主要课题之一.     

Experimental investigation concerning the influence of fuel type and properties on the injection and atomization of liquid biofuels in an optical combustion chamber

Due to the scarcity of fossil fuels and the future stringent emission limits, there is an increasing interest for the use of renewable biofuels in compression ignition engines. However, these fuels have different physical, chemical and thermodynamic properties affecting atomization, spray development and combustion processes. The results reported in this paper have been obtained by experimentation with a constant volume combustion chamber. The influences of physical fuel properties on injections under non-evaporating conditions are studied, using a pump-line-nozzle system from a medium speed diesel engine with injection pressures up to 1200 bar, by changing the fuel type and temperature. Experiments were conducted for diesel, biodiesel, straight vegetable oils and animal fats. Injection pressure and needle lift measurements were analyzed. A high speed camera was used to visualize the spray, which enabled us to study the spray penetration and spray angle. Our results show that the fuel temperature is an important parameter to control because it significantly affects the fuel properties. Both the injection timing and injection duration are affected by the fuel properties. The influences of these properties on the spray development were less pronounced. At low temperatures, a strongly deteriorated atomization of oils and fats was observed.     

Numerical investigation into the structural characteristics of a hydrogen dual-swirl combustor with slight temperature rise combustion

For decades, hydrogen has been identified as the most promising potential fuel to replace fossil fuels. In order to fully implement it and to promote the rationality of the design of hydrogen combustion chamber structure, it is very essential to understand the hydrogen/air combustion mechanism based on structural variations. The structural characteristics of a novel dual-swirl burner for hydrogen-air non-premixed combustion was studied numerically in this study. The influences of air distributions, swirling directions and nozzle configurations of the dual-swirl burner were studied, and the combustion performance was evaluated from various aspects. The numerical results showed that there was a trade-off between lower total pressure loss and the risk of fusing when considering air distribution strategies. The co-rotating swirl burner exhibited better uniformity of temperature distribution at the downstream of the combustor. The multi jet orifices showed superior penetration depth than the circular seam. Efficient and stable combustion could be achieved, which was beneficial to improve gas turbine efficiency and stable operation.     

微型燃气轮机燃烧室性能影响因素的探讨

针对微型燃气轮机燃烧室性能的各种影响因素(进气条件、燃料热值、燃烧室结构等)对燃烧稳定性和燃烧效率的影响,介绍了国内外相关实验和数值模拟研究现状,分析了燃烧室主要污染物的生成机理和影响因素,以及降低氮氧化物排放浓度的技术措施。     

Experimental study of the diesel spray combustion and soot characteristics for different double-injection strategies in a constant volume combustion chamber

In this work, broadband luminosity was used to detect ignition delay and diffused back-illumination extinction imaging was employed to measure soot property with different double-injection strategies in a constant volume combustion chamber under different ambient conditions. The interaction between the two-stage injections have been studied experimentally with two key parameters, dwell time and first injection duration. Results show that in two-stage injection cases, a faster flame propagation speed and a more homogeneous soot concentration distribution were observed in the second injection. Besides, averaged KL value in soot regions of the second injection is slightly less than that of the first one. The first injection has a better effect on the ignition delay of the second injection under low ambient pressure. Meanwhile, the soot onset time of the second injection is advanced more obviously. However, compared with the first injection, the advance amount of the ignition delay and the soot onset time of the second injection shows no particular sensitivity with ambient temperature. With longer pilot injection duration, the initial sooting location of the main injection shows a slight reduction but the total soot mass seems to be constant with the variation of the pilot injection duration.     

Thermodynamic and economic investigation of an innovative multigeneration plant integrated with the solar collector and combustion chamber

Today, effective and low-emission energy systems have been needed to combat environmental problems and to satisfy the growing energy requirement in a sustainable way. In this case, it has gained importance to the production of different useful commodities with the multigeneration plant that is obtained by integrating different systems. With this viewpoint, the key objective of this work is to design and analyze the solar collector and combustion chamber-assisted multigeneration model for power, heating, hydrogen, ammonia and freshwater generation. A newly designed plant comprises a gas turbine cycle, which includes a parabolic dish solar collector and combustion chamber, a Rankine power plant, a multi-effect desalination part, a hydrogen generation part, an ammonia generation part, and a solid oxide fuel cell unit. Comprehensive thermodynamic modeling, economic analysis and multiobjective optimization are executed to observe the performance of the whole plant and sub-system by employing energetic and exergetic approaches. Moreover, a parametric investigation is addressed to review the impacts of some important point changes on the modeled plant's efficiency. Analyses consequences display that the power and hydrogen generation amounts are 12,835 kW and 0.0607 kgs^?1. Also, freshwater generation capacity with desalination unit is computed as 4.89 kgs^?1. Moreover, total cost rate of the modeled plant is computed as 1074 $/h. Finally, the evaluated plant's energetic and exergetic efficiency is 58.38% and 54.21%, respectively.     

Numerical investigation of influence of homogeneous/heterogeneous ignition/combustion mechanisms on ignition point position during pulverized coal combustion in oxygen enriched and recycled flue gases atmosphere

It is expected that pulverized coal combustion will continue to play a major role in electricity generation for the foreseeable future. Oxy-fuel coal combustion is actively being investigated, as alternative to conventional pulverized-coal combustion, due to its potential to easier carbon dioxide sequestration. This paper presents experimental and numerical analysis of ignition phenomena in oxy-fuel conditions. A modification of standard sequential coal combustion model is proposed. The new model is developed following the criteria for the particle ignition mechanism as the function of surrounding conditions. The implemented model was validated based on ignition point position obtained from the drop tube facility experiments in various O₂-N₂ and O₂-CO₂ conditions. The obtained numerical results showed a much better agreement with the experimental results when compared with the simulations performed with the default FLUENT sub-models for coal particle ignition/combustion, thus enabling a quantitative determination of pulverized coal flame ignition point position using numerical analysis.     

Effect of strut angle on performance of hydrogen multi-jets inside the cavity at combustion chamber

Cavity flameholder is known as a promising technique to improve fuel mixing within the combustion chamber. This article studied the influences of the strut angle on the mixing performance of multi jets released inside the cavity flameholder. Finding the optimum jet configuration is done to promote the mixing performance of fuel through chamber when strut is applied in the upstream of the cavity flameholder. The impact of strut angle, fuel jet direction, and free-stream Mach number on the performance of three multi jets inside the chamber is disclosed in our research. For the simulation of our model, turbulent SST model is employed to obtain fuel distribution through the cavity. Our findings indicate that the counter jet is more operative in mixing of the fuel than co-jet since the main circulation is close to counter-jet, and fuel could efficiently distribute by the main circulation.     

Effect of altering combustion air flow on a steam power plant: energy and exergy analysis

Energy and exergy analyses were previously performed by the authors of a coal-fired steam power plant. These analyses suggest that the steam generator (and its combustion and heat-transfer processes) is the most inefficient plant device and that significant increases in overall plant efficiency are possible by reducing steam-generator irreversibilities. Here, a possible plant alteration is examined to increase the efficiency of the plant by reducing the irreversibility rate in the steam generator. The modification involves decreasing the fraction of excess combustion air from 0.40 to 0.15. The results show that overall-plant energy and exergy efficiencies both increase by 1.4% when the fraction of excess combustion air decreases from 0.4 to 0.15.Copyright © 2006 John Wiley & Sons, Ltd.     

A comprehensive study on performance,emission and combustion behavior of a compression ignition engine fuelled with WCO (waste cooking oil) emulsion as fuel

This work aims at evaluating the performance, emission and combustion of a diesel engine fuelled with WCO (waste cooking oil obtained from palm oil) and its emulsion as fuel. A single cylinder water-cooled diesel engine was used. Base data was generated with diesel and neat WCO as fuels. Subsequently, WCO oil was converted into its emulsion and tested. Neat WCO resulted in higher smoke, hydrocarbon and carbon monoxide emissions as compared to neat diesel. Significant reduction in all emission was achieved with the WCO emulsion. Cylinder peak pressure and maximum rate of pressure rise were found to be higher with WCO emulsion as compared to neat WCO mainly at high power outputs. Ignition delay was found as higher with neat WCO and its emulsion. It is concluded that WCO emulsion can be used in diesel engines without any modifications in the engine with superior performance and reduced emissions at high power outputs.     

Control of methane flame properties by hydrogen fuel addition: Application to power plant combustion chamber

This study presents a numerical investigation of the effects of mixing methane/hydrogen on turbulent combustion processes taking place in a burner similar to that integrated in gas turbine power plants. Thereby, in comparison to the reference case where the burner is fuelled by 100% of methane, the variations of the axial velocity field, temperature field and mass fraction of carbon monoxide field are examined for different percentages of hydrogen fuel injection. The computed results, obtained by using the software Fluent-CFD, are compared and validated against experimental reference data. Results show that the hydrogen addition to the methane has an impact on all physical and chemical parameters of the reactive system.     

Numerical investigation of drop dynamics in presence of wettability gradient inside a serpentine channel of proton exchange membrane fuel cell

Water management significantly affects the performance of a proton exchange membrane fuel cell (PEMFC). Therefore, interest is felt to numerically investigate water droplet movement and slug formation inside the microchannel (gas) of PEMFC. Two important parameters—water coverage ratio and pressure drop have been studied in detail. A U-shaped geometry with a round corner is used for this purpose. 3D unsteady-state models are used to study the drop dynamics using commercial CFD software ANSYS FLUENT 18. For tracking of water drop dynamics, the volume of fluid model is used. Two different situations are simulated. In the first case, the investigation of hydrodynamics of the 0.4 mm drop adhered to the surface of the gas diffusion layer (GDL) has been done. In the second case, simulation of air-water slug flow has been done. GDL surfaces at upstream and downstream of bend are modified using user-defined functions, such that the GDL surface has a dynamic contact angle with respect to the direction of flow. This makes it a continuously hydrophilic surface at upstream and continuously hydrophobic surface at downstream with respect to the direction of flow. The impact of GDL wettability on water retention and removal has been discussed. It is noted that the presence of a gradient facilitates the removal of water drop adhered to the GDL surface. For the case of a suspended drop with an increase of 1°/mm in the magnitude of the gradient, a decrease of 30% is observed in water coverage ratio and pressure drop observed in the channel. Such modified surfaces aids in the conversion of slugs to film at the downstream of bend that reduces maldistribution. The pressure fluctuations and average pressure drop are reduced by 66% when subjected to the aforementioned hybrid gradient.     

小型卧式燃煤热风炉内流动与传热过程的数值模拟及实验

为了研究第三挡板长度对热风炉燃烧性能的影响,以热风炉燃烧室为研究对象,利用FLUENT软件对其进行了数值模拟,模拟分析了燃烧室内的温度分布、速度分布及颗粒物浓度分布等情况,最后搭建了试验台对数值模型进行了验证。结果表明：燃烧室温度模拟值与实验值的相对误差在10%以内;燃烧高温区位于第一挡板和第二挡板顶部之间的区域;大部分颗粒物集中在炉排底部附近,随着烟气绕挡板流动,颗粒物浓度逐渐降低;热风炉燃烧室内第三挡板长度为270mm时,可以减少炉膛出口处颗粒物的排放,使燃烧更充分。     

Numerical investigation of flow field configuration and contact resistance for PEM fuel cell performance

A steady-state three-dimensional non-isothermal computational fluid dynamics (CFD) model of a proton exchange membrane fuel cell is presented. Conservation of mass, momentum, species, energy, and charge, as well as electrochemical kinetics are considered. In this model, the effect of interfacial contact resistance is also included. The numerical solution is based on a finite-volume method. In this study the effects of flow channel dimensions on the cell performance are investigated. Simulation results indicate that increasing the channel width will improve the limiting current density. However, it is observed that an optimum shoulder size of the flow channels exists for which the cell performance is the highest. Polarization curves are obtained for different operating conditions which, in general, compare favorably with the corresponding experimental data. Such a CFD model can be used as a tool in the development and optimization of PEM fuel cells.