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.     

Experimental investigation of dynamic and emission characteristics of a DLE gas turbine combustor

The DLE (dry low emission) technology has already been used on industrial gas turbine combustor and the NO X emission can be limited to 25 ppmv (@15% O 2 ), but one of the destructive effects is combustion instability. In this paper, the dynamic and emission characteristics of a DLE gas turbine combustor have been researched in the authors’ laboratory, and the results show that the key source of combustion instability is the non-uniformity of fuel in the flame zone. Two main fuel supply methods have been used to form different fuel distribution types; it is shown that in the perfectly premixed case the emission level is low and combustion process is stable. The PPF also has an obvious effect on the combustor’s emission and dynamic characteristics.     

Effects of spray characteristics on combustion performance of a liquid fuel spray in a gas turbine combustor

Spray characteristics like mean drop diameter and spray cone angle play an important role in the process of combustion within a gas turbine combustor. In order to study their effects on wall and exit temperature distributions and combustion efficiency in the combustor, a numerical model of a typical diffusion controlled spray combustion in a can‐type gas turbine combustion chamber has been made. A simple k–ϵ model with wall function treatment for near‐wall region has been adopted for the solution of conservation equations in carrier phase. The initial spray parameters are specified by a suitable PDF for size distribution and a given spray cone angle. A radiation model for the gas phase, based on modified first order moment method, and in consideration of the gas phase as a grey absorbing–emitting medium, has been adopted in the analysis. It has been recognized that an increase in mean drop diameter improves the pattern factor. However, the combustion efficiency attains its maximum at an optimum value of the mean diameter. Higher spray cone angle increases the combustion efficiency and improves the pattern factor, but at the same time, increases the wall temperature. Copyright © 1999 John Wiley & Sons, Ltd.     

Fast Ignition and Stable Combustion of Coarse Coal Particles in a Nonslagging Cyclone Combustor

A combustion set-up of an innovative nonalagging cyclone combustor called “Spouting-Cyclone Combustor(SCC)”，,with two-stage combustion,organized in orthogonal vortex flows,was established and the experimental studies on the fast ignition and stable combustion of coarse coal particles in this combustor were carried out.The flame temperature versus ignition time and the practical fast ignition the temperature fields in SCC were obtained.These results whow that it is possible to obtain highly efficient and clean combustion of unground coal particles by using this technology.     

Hydrogen injection as additional fuel in gas turbine combustor. Evaluation of effects

Industrial gas turbines fuelled by fossil fuels have been used widely in power generation and combined heat and power for many years. However they have to meet severe _NOx${\mathrm{NO}}_x$, CO and _CO2${\mathrm{CO}}_2$ (greenhouse effect) emissions legislation in many countries. This paper reports a study on injection of small quantities of hydrogen in a hydrocarbon fuelled burner like additionally fuel to reduce the pollutants emissions. Hydrogen is injected in the primary zone, premixed with the air. Using this injection together lean primary zone, it is possible to reduce the _NOx${\mathrm{NO}}_x$ level while CO an HC levels remains approximately constant.     

Thermo-acoustic velocity coupling in a swirl stabilized gas turbine model combustor

Limit-cycle thermo-acoustic velocity coupling mechanisms are studied in a perfectly-premixed swirl-stabilized combustor using data from 10 kHz repetition-rate stereoscopic particle image velocimetry (S-PIV) and OH planar laser induced fluorescence (PLIF). Five cases over a range of thermal powers and equivalence ratios were investigated, each of which underwent different amplitude limit-cycle oscillations. Proper orthogonal decomposition (POD) of the velocity data showed that each case contained a dynamic helical vortex core (HVC) that rotated around the combustor and greatly affected the flame behavior. Flow and flame statistics were compiled as a function of both the phase in the thermo-acoustic cycle and a phase representing the azimuthal position of the HVC relative to the measurement plane. These data were used to determine the thermo-acoustic energy transfer field at each HVC azimuthal angle, as described by the Rayleigh integral. It was found that periodic deformations of the HVC caused large-scale flame motions, resulting in regions of positive and negative energy transfer. The deformation of the HVC was linked to a swirl number wave that propagated from the burner nozzle. While the mechanism of thermo-acoustic coupling was the same for all cases, the phase between heat release and pressure oscillations varied significantly. This phase relationship was determined by the interaction of the pressure field, swirl wave, HVC deformation, and flame response. It was shown that these can be described by the combination of a Helmholtz resonator and a convective disturbance.     

旋流预混燃烧室燃烧特性及排放特性的数值模拟研究

为了综合考察燃气轮机燃烧室在高稳定性、低排放以及燃料适应性等方面的新要求,基于旋流预混燃烧技术,通过三维数值模拟方法开展了甲烷/空气、丙烷/空气预混燃烧特性及排放特性研究。结果表明：在一定的预混气进气质量流量条件下,当量比增大易引发回火,燃烧温度更高,同时NO_x排放指数增大,增加预混气质量流量,可在一定程度上提高回/熄火极限;当量比固定,增加预混气进气质量流量可避免潜在的回火现象,且NO_x排放指数线性降低;旋流器的旋流数增大能形成强旋流,稳定火焰,降低NO_x排放指数,但过大的旋流强度会引发回火现象;相比于甲烷/空气预混燃烧,丙烷/空气预混燃烧温度偏高,NO_x排放指数较大,但回熄火边界更宽,对应更广阔的稳定燃烧区间。     

Combustion behavior and stability map of hydrogen-enriched oxy-methane premixed flames in a model gas turbine combustor

The article describes an experimental study and comparison of the combustion behavior and determines the stability map of turbulent premixed H₂-enriched oxy-methane flames in a model gas turbine combustor. Static stability limits, in terms of flashback and blow-out limits, are recorded over a range of hydrogen fraction (HF) at a fixed oxygen fraction (OF) of 30% and a particular inlet bulk velocity, and the results are compared with the non-enriched case (HF = 0%). The static stability limits are also recorded for different inlet bulk velocity (4.4, 5.2, and 6 m/s) and the results are compared to explore the effect of flow dynamics on operability limits of H₂-enriched flames. The stability maps are presented as a function of equivalence ratio (0.3–1.0) and HF (0%–75%) plotted on the contours of adiabatic flame temperature (AFT), power density (PD), inlet Reynolds number (Re) and reacting mixture mass flow rate ($\dot{m}$) to understand the physics behind flashback and blow-out phenomena. The results indicated that both the flashback and blow-out limits tend to move towards the leaner side with increasing HF due to the improved chemical kinetics. The stability limits are observed to follow the Reynolds number indicating its key role in controlling flame static stability limits. The results showed that H₂ enrichment is effective in the zone from HF = 20% up to HF = 50%, and O₂ enrichment is also effective in a similar zone from OF = 20% up to 50%, with wider stability boundaries for H₂ enrichment. Axial and radial temperature profiles are presented to explore the effect of HF on the progress of chemical reactions within the combustor and to serve as the basis for validation of numerical models. Flame shapes are recorded using a high-speed camera and compared for different inlet velocities to explore the effects of H₂-enrichment and equivalence ratio on flame stability. The equivalence ratio at which a transition of flame stabilization from the inner shear layer (ISL) to the outer recirculation zone (ORZ) occurs is determined for different inlet bulk velocities. The value of the transition equivalence ratio is found to decrease while increasing the inlet bulk velocity. Flame shapes near flashback limit, as well as near blow-out limit, are compared to explore the mechanisms of flame extinctions. Flame shapes are compared at fixed adiabatic flame temperature, fixed inlet velocity and fixed flow swirl to isolate their effects and investigate the effect of kinetic rates on flame stability. The results showed that the adiabatic flame temperature does not govern the flame static stability limits.     

Modelling of the process of coal dust combustion in a cyclone furnace

This study presents the concept of a cyclone furnace for coal dust oxy-fuel combustion and gasification.The results of numerical calculations for the combustion and gasification processes were also presented.     

石煤燃烧的汞排放特性研究

我国南方煤炭资源相对贫乏,而石煤的资源相当丰富,为了综合利用石煤资源,利用1MW循环流化床试验台进行了石煤和烟煤的混燃试验,对底渣、烟气和飞灰中的Hg的含量进行了详细的分析,得出了石煤和烟煤混燃的底渣、烟气和飞灰中汞的分布特性,为石煤的进一步推广应用提供依据。     

Numerical investigation of combustion characteristics for hydrogen mixed fuel in a can-type model of the gas turbine combustor

Numerical simulations are performed to analyze the combustion characteristics of propane fuel mixed with different amounts of hydrogen in a can-type combustor. The volume fraction of the hydrogen fuel varies from 0% to 100% in the fuel mixture. The results indicate that the hydrogen enrichment of the fuel significantly affects the flow structure, mixture fraction, and combustion characteristics. An increase in the volume fraction of hydrogen significantly affects the mean mixture fraction distribution, promotes combustion, and increases the flame temperature and the width of the flammable range within the combustor. Therefore, the degree of temperature uniformity at the outlet of the combustor increases with hydrogen enrichment, corresponding to an increase of 49.64% in the uniformity factor. The hydrogen enriched fuel can also reduce the emissions of CO and CO₂, owing to the reduced amount of carbonaceous fuel.     

多流体模型在燃气轮机燃烧室三维反应流中的应用

对一种模型燃气轮机燃烧室中的三维反应流进行了数值模拟，模型燃烧室的燃料是CH4，燃烧类型是预混燃烧，在数值模拟过程中，采用了Spalding于1995年提出来的多流体模型来对燃烧室中的湍流预混燃烧进行了数值模拟，在数值模拟过程中考虑了辐射问题，采用了六通量辐射模型。通过数值模拟给出了速度，压力，湍流脉动动能，湍流动能耗散率，焓值，湍流粘度，温度，密度，燃烧产物质量分数，氧的质量分数，燃料/空气混合比，燃料质量分数，空间三个方向的辐射热通量以及各种流体的质量分数等变量的分布情况，此外，还采用传统的旋涡破碎模型对此燃烧室进行了数值模拟，并对两种方法的结果进行了分析比较，由分析可以看出多流体模型的结果接近于实际情况，对模型燃烧室进行三维反应流数值模拟的工作为今后对实际燃烧室反应流的数值模拟打下了一定的基础。     

Effect of ignition timing and hydrogen fraction on combustion and emission characteristics of natural gas direct-injection engine

An experimental study on the combustion and emission characteristics of a direct-injection spark-ignited engine fueled with natural gas/hydrogen blends under various ignition timings was conducted. The results show that ignition timing has a significant influence on engine performance, combustion and emissions. The interval between the end of fuel injection and ignition timing is a very important parameter for direct-injection natural gas engines. The turbulent flow in the combustion chamber generated by the fuel jet remains high and relative strong mixture stratification is introduced when decreasing the angle interval between the end of fuel injection and ignition timing giving fast burning rates and high thermal efficiencies. The maximum cylinder gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate increase with the advancing of ignition timing. However, these parameters do not vary much with hydrogen addition under specific ignition timing indicating that a small hydrogen fraction addition of less than 20% in the present experiment has little influence on combustion parameters under specific ignition timing. The exhaust HC emission decreases while the exhaust CO₂ concentration increases with the advancing of ignition timing. In the lean combustion condition, the exhaust CO does not vary much with ignition timing. At the same ignition timing, the exhaust HC decreases with hydrogen addition while the exhaust CO and CO₂ do not vary much with hydrogen addition. The exhaust NOx increases with the advancing of ignition timing and the behavior tends to be more obvious at large ignition advance angle. The brake mean effective pressure and the effective thermal efficiency of natural gas/hydrogen mixture combustion increase compared with those of natural gas combustion when the hydrogen fraction is over 10%. __________ Translated from Transactions of CSICE, 2006, 24(5): 394–401 [译自:内燃机学报]     

Study of combustion and emission characteristics of turbocharged diesel engine fuelled with dimethylether

An experimental study of a turbocharged diesel engine operating on dimethyl ether (DME) was conducted. The combustion and emission characteristics of the DME engine were investigated. The results show that the maximum torque and power of DME are greater than those of diesel, particularly at low speeds; the brake specific fuel consumption of DME is lower than that of diesel at low and middle engine speeds, and the injection delay of DME is longer than that of diesel. However, the maximum cylinder pressure, maximum pressure rise rate and combustion noises of the DME engine are lower than those of diesel. The combustion velocity of DME is faster than that of diesel, resulting in a shorter combustion duration of DME. Compared with the diesel engine, NO _x emission of the DME engine is reduced by 41.6% on ESC data. In addition, the DME engine is smoke free at any operating condition. __________ Translated from Transactions of CSICE, 2006, 24(3): 193–199 [译自: 内燃机学报]     

Development of high intensity CDC combustor for gas turbine engines

Colorless distributed combustion (CDC) has been demonstrated to provide ultra-low emission of NOx and CO, improved pattern factor and reduced combustion noise in high intensity gas turbine combustors. The key feature to achieve CDC is the controlled flow distribution, reduce ignition delay, and high speed injection of air and fuel jets and their controlled mixing to promote distributed reaction zone in the entire combustion volume without any flame stabilizer. Large gas recirculation and high turbulent mixing rates are desirable to achieve distributed reactions thus avoiding hot spot zones in the flame. The high temperature air combustion (HiTAC) technology has been successfully demonstrated in industrial furnaces which inherently possess low heat release intensity. However, gas turbine combustors operate at high heat release intensity and this result in many challenges for combustor design, which include lower residence time, high flow velocity and difficulty to contain the flame within a given volume. The focus here is on colorless distributed combustion for stationary gas turbine applications. In the first part of investigation effect of fuel injection diameter and air injection diameter is investigated in detail to elucidate the effect fuel/air mixing and gas recirculation on characteristics of CDC at relatively lower heat release intensity of 5 MW/m³ atm. Based on favorable conditions at lower heat release intensity the effect of confinement size (reduction in combustor volume at same heat load) is investigated to examine heat release intensity up to 40 MW/m³ atm. Three confinement sizes with same length and different diameters resulting in heat release intensity of 20 MW/m³ atm, 30 MW/m³ atm and 40 MW/m³ atm have been investigated. Both non-premixed and premixed modes were examined for the range of heat release intensities. The heat load for the combustor was 25 kW with methane fuel. The air and fuel injection temperature was at normal 300 K. The combustor was operated at 1 atm pressure. The results were evaluated for flow field, fuel/air mixing and gas recirculation from numerical simulations and global flame images, and emissions of NO, CO from experiments. It was observed that the larger air injection diameter resulted in significantly higher levels of NO and CO whereas increase in fuel injection diameter had minimal effect on the NO and resulted in small increase of CO emissions. Increase in heat release intensity had minimal effect on NO emissions, however it resulted in significantly higher CO emissions. The premixed combustion mode resulted in ultra-low NO levels (<1 ppm) and NO emission as low as 5 ppm was obtained with the non-premixed flame mode.     

Evaluation of srk equation of state in calculating the thermophysical properties of gas turbine combustion gases

The purpose of this work is to evaluate the thermophysical properties of combustion gases of the gas turbine engine using the Soave-Redlich-Kwong equation of state and to compare the results with those obtained from the virial equation of state and the experimental values obtained from experiment and the generalized charts. The properties which have been considered in this work were, density, specific heat at constant pressure, enthalpy, entropy, viscosity and thermal conductivity. The temperature range was (200–2600 K) theoretically, while the pressure range was (3–12 atmospheres). The Soave-Redlich-Kwong (SRK) equation of state generally predicted better values for thermophysical properties than those predicted by the virial equation of state. A computer program, to evaluate the departure of thermophysical properties using virial and SRK equations of state, was used.     

Thermodynamic characteristics of a low concentration methane catalytic combustion gas turbine

Low concentration methane, emitted from coal mines, landfill, animal waste, etc. into the atmosphere, is not only a greenhouse gas, but also a waste energy source if not utilised. Methane is 23 times more potent than CO₂ in terms of trapping heat in the atmosphere over a timeframe of 100 years. This paper studies a novel lean burn catalytic combustion gas turbine, which can be powered with about 1% methane (volume) in air. When this technology is successfully developed, it can be used not only to mitigate the methane for greenhouse gas reduction, but also to utilise such methane as a clean energy source. This paper presents our study results on the thermodynamic characteristics of this new lean burn catalytic combustion gas turbine system by conducting thermal performance analysis of the turbine cycle. The thermodynamic data including thermal efficiencies and exergy loss of main components of the turbine system are presented under different pressure ratios, turbine inlet temperatures and methane concentrations.     

Numerical simulation of a hydrogen fuelled gas turbine combustor

The interest for hydrogen-fuelled combustors is recently growing thanks to the development of gas turbines fed by high content hydrogen syngas. The diffusion flame combustion is a well-known and consolidated technology in the field of industrial gas turbine applications. However, few CFD analyses on commercial medium size heavy duty gas turbine fuelled with pure hydrogen are available in the literature. This paper presents a CFD simulation of the air-hydrogen reacting flow inside a diffusion flame combustor of a single shaft gas turbine. The 3D geometrical model extends from the compressor discharge to the gas turbine inlet (both liner and air plenum are included). A coarse grid and a very simplified reaction scheme are adopted to evaluate the capability of a rather basic model to predict the temperature field inside the combustor. The interest is focused on the liner wall temperatures and the turbine inlet temperature profile since they could affect the reliability of components designed for natural gas operation. Data of a full-scale experimental test are employed to validate the numerical results. The calculated thermal field is useful to explain the non-uniform distribution of the temperature measured at the turbine inlet.