Performance evaluation of novel surface flame self-aspirated porous radiant burners for cooking applications

Porous radiant burners (PRBs) are based on the principle of porous media combustion (PMC) in which both combustion and stabilization of the flame take place towards the end of combustion zone (CZ). It has lot of advantages over conventional free flame burners. The porous matrix has high thermal conductivity and high emissivity. Hence, contributions to conduction, convection and radiation in the PMC are significant. This paper presents experimental results on the thermal and emission performance of newly developed, bi-layered, self-aspirated porous radiant surface flame burners used in cooking applications. It comprises firebrick material in the CZ and steel balls in the preheating zone (PZ). Performance of this burner is compared to that of a conventional cooking burner (CB) within the operating range of 0.5–2 kW. The effect of burner geometry (one is circular and the other one is square in cross section) on the thermal performance and emission using liquefied petroleum gas (LPG) as the fuel is also studied and their thermal performances are compared to the conventional ones. The experimental results have revealed that the thermal efficiencies of circular and square PRBs are much higher than those of the conventional burner. The maximum thermal efficiency of the self-aspirated circular porous radiant burner (SCPRB) is found to be 71.78% at the flow rate (V) of 2.0 m/s with a porosity of 85%, whereas the thermal efficiency obtained from self-aspirated square porous radiant burner (SSPRB) is marginally less than that of SCPRB at the corresponding flow rate and porosity. The emission levels are much lower in these novel PRBs as compared with the conventional burner and these values are well below the World Health Organization (WHO) standard. The NO_x emission values corresponding to the optimum velocity of 2.0 m/s are 87 ppm for CB, and 24 and 27 ppm, respectively, for SCPRB and SSPRB. CO emission values are 32, 33 and 155 ppm for SCPRB, SSPRB and CB, respectively, corresponding to the optimum velocity of flow.     

Durability of YZA ceramic foams in a porous burner

The durability of YZA cellular ceramic foams was investigated in the demanding environment of an instrumented porous burner. Following exposure to the combustion environment, the ceramic foam coupons suffered moderate damage. Coupons exposed to extended duration tests in the burner did not show additional damage compared to coupons exposed to short duration tests indicating that damage occurred during start-up, when temperature gradients were most severe. To compare the results of the burner tests to conventional thermal shock experiments, samples were also exposed to a water quench test. Coupons removed from the burners and coupons exposed to the water quench from high temperatures exhibited similar failure morphologies. In both cases a marked transition in failure morphology was observed as the magnitude of the peak temperatures and thermal gradients were increased. Chemical analysis combined with these thermal shock measurements show that damage sustained by the foams in the burner results from thermal shock and not from chemical degradation.     

CFD modeling of hydrodynamics,combustion and NOx emission in a tangentially fired pulverized-coal boiler at low load operating conditions

With deep peak-load regulations, utility boilers are frequently operated under variable/low load conditions. However, their hydrodynamics, combustion and NOx emission characteristics are uncertain and relevant theoretical guidance are lacking. For this purpose, a comprehensive CFD model including flow, coal combustion and NOx formation is established for a 630 MW tangentially fired pulverized-coal boiler, aiming at solving the problem of decreasing combustion stability and increasing NOx emission in low-load operation. Based on the grid independence and model validation, the flow field, temperature profile, species concentration profile and NOx emission are predicted, and the influences of angle/arrangement of burners are further evaluated. Simulation results indicate that under low-load conditions, residual airflow rotation still persists at the top of boiler regardless of how to adjust the angle/arrangement of burners. With tilting the burner angle upward, flame is more concentrated, combustion becomes more stable, and heat flux rises in the upper zone; the burner arrangement of ABDE gives more uniform temperature distribution in the combustion zone. CO species shows higher content in the combustion zone; the 0° tilt angle gives maximum CO content, followed by the 15° angle, and finally the ?15° angle; compared to the ACDE and ABCE arrangement, the ABDE arrangement mode gives much lower CO contents. Burner tilt angle of ?15° benefits for lower NOx emission (183 mg/m³) but goes against stable combustion; the burner arrangement mode of ABDE is optimal for the present boiler, which ensures both stable combustion and lower NOx emission (209 mg/m³).     

Concerning self-excited oscillations in frontal combustion of a fuel mixture in a resonator with lumped parameters

The conditions needed to stimulate harmonic self-excited oscillations in frontal combustion of a fuel mixture in the throat or cavity of a Helmhholtz resonator are considered. It is shown that they depend on the properties of the fuel mixture and the position and orientation of the front of the flame and can be satisfied only in the presence in the zone of combustion of a surface of discontinuity of the parameters that determine the rate of combustion. It is noted that the results of analysis do not come into conflict with the facts and dependences that are observed in combustion of fuel mixtures in tunnel burners, piston carburetors, and rocket engines.     

纯氧点火技术在300MW机组的应用

纯氧点火技术是利用氧气替代空气作为助燃剂,直接送入燃烧器内部参与燃料点燃的点火技术。通过将原有最下层四只燃烧器改造为装有微油枪加氧点火助燃的煤粉燃烧器以及在炉前加装供氧系统来保证纯氧的安全输送和稳定燃烧。纯氧的投入使燃料得到充分燃烧,加强了燃烧初期的稳定性,提高了燃烧效率,直接使机组在启停以及低负荷稳燃过程中的安全性、经济性、环保性得到较好的提升。     

Calculation of a Three-Dimensional Temperature Field with Allowance for the Radiation Heat Exchange in Chambers of Tubular Ovens with Acoustic Burners

A three-dimensional calculation of the heat transfer in the chamber of a technological tubular oven with the combustion of methane in air with acoustical burners of a floor flame has been carried out. The calculation method is based on the joint numerical solution of the difference analogs of the three-dimensional equations of radiation, energy transfer, and turbulent motion of flue gases and the model of methane combustion in air. The entire spectral region is divided into six bands to account for radiation selectivity. The organization scheme of three-dimensional modeling of the burner operation is shown. Some results of numerical studies of heat and mass transfer in a combustion chamber are given.     

Nanostructure and reactivity of nascent carbon particles from 2,5-dimethylfuran/n-heptane swirling inverse diffusion flames

Carbon particles (Soot) have been the one of primary pollutants inevitably with the combustion of fossil fuels. A better understanding on incipient soot was useful to build the models of soot formation and even control soot emissions. The present work focuses on the nanostructure and oxidation reactivity of nascent carbon particles (soot) formed from 2,5-dimethylfuran (DMF)/n-heptane non-swirling and swirling inverse diffusion flames (IDFs). The nascent soot samples were derived from three different fuels: 100% n-heptane, 50% n-heptane/50% DMF and 100% DMF. In addition, the effects of swirling combustion and collection time on characteristics of nascent soot were investigated in detail using the high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Results demonstrated that nascent soot from pure n-heptane flames presented the film-like morphology and nanostructure of amorphous nature, while the nearly primary particles with more well-organized nanostructure were found in pure DMF soot. Swirling combustion increased the entire flame front areas and diameters due to the existence of tangential velocity at the outlet of burner. Moreover, swirling combustion could enhance the mixability of the oxidizer stream and fuel stream, leading to more young soot within the fuel stream being oxidized in the inception stage. However, the collection time on soot characteristics exhibited quite negligible impacts in comparison to the swirling effects.     

直喷柴油机两种燃烧方式混合气形成的比较

利用KIVA-3V软件模拟了柴油机两种燃烧方式的混合气形成过程中的浓度场和温度场.模拟计算与实验结果表明,在常规柴油机燃烧方式中,燃油边喷边烧,混合气浓度和温度变化很大,导致预混合燃烧和扩散燃烧并存,NOx和碳烟比较高,CO和HC排放很低;利用早喷可以形成浓度场和温度场分层分布的均质混合气,实现均质充量压燃(HCCI)燃烧,碳烟和NOx很低,但CO和未燃烧的燃油排放很高.     

SIZE AND HYDRATION CHARACTERISTICS OF LABORATORY SIMULATED JET ENGINE COMBUSTION AEROSOLS

Size and hydration characteristics for laboratory simulated jet engine combustion aerosols are reported and the validity of these simulated data is discussed. The jet fuels JP4, JP5, JP8 and JET A were burned in laboratory burners designed to simulate the lean pre-mixed, pre-vaporized advanced combustor concept. Significant quantities of aerosols were detected and in most cases their size and hydration properties were similar. Dry particle size distributions were single mode extending over the diameter range 0.014 to 0.200 microns, with peak diameters in the range 0.020 to 0.050 microns. The distributions were observed to vary with combustion stoichiometry, increasing the peak particle diameter as the combustion stoichiometry shifted from leaner to richer conditions. Critical supersaturation spectra for each fuel are presented. A mean ratio of cloud condensation nuclei to condensation nuclei (CCN/CH) has been calculate for each fuel: JP4 = 32%, JP5 = 42%, JET A = 39%, and JP8 = 35% indicating that in general 30 - 40% of the combustion aerosols generated with these laboratory burners can be considered cloud condensation nuclei.     

Tests of NASA ceramic thermal barrier coating for gas turbine engines

A two-layer thermal barrier coating system with a bond coating of nickel-chromium-aluminum-yttrium (Ni-16Cr-6Al-0.6Y, in wt.%) and a ceramic coating of yttria-stabilized zirconia (ZrO₂12Y₂O₃, in wt.%) was tested for corrosion protection, thermal protection and durability. Full-scale gas turbine engine tests demonstrated that this coating eliminated burning, melting and warping of uncoated parts. During cyclic corrosion resistance tests made in marine diesel fuel products of combustion in a burner rig, the ceramic cracked on some specimens. However, metallographic examination showed no base metal deterioration.     

Complex of Programs for Imitative Simulation of Acceleration, Heating, and Melting of Particles in Gas‐Dynamic Channels of Technological Devices

This paper describes an interactive complex of programs designed for investigating the processes of acceleration, heating, and melting of particles in the gasdynamic channels of burners. To illustrate the efficiency of this method, we have investigated the possibility of melting of tungsten particles in the process of their acceleration and heating by combustion products of hydrocarbon fuel in the gasdynamic channel of the burner with the discharge method of acting on the flow.     

Tube-in-Basket burner for rice husk. II: Performance of TiB burners

Three working models, TiB MK II, MK IIK and III, capable of continuous combustion, are described. It is shown that these burners can be operated continuously in a stable pseudo-steady-state manner by means of intermittent charging of husk from the top and discharging of ash from the bottom. Mass and heat balance data, flame temperatures, combustion efficiencies and heat transfer efficiencies for heating water in a vessel are included. Combustion efficiency of about 72% was achieved in TiB MK II by making a significant change in the basket design, the lower half being made conical. The efficiency was boosted further to roughly 82% in MK IIK by extending the bottom rim of the cone straight down by an additional 7·5 cm and replacing the upper basket cylinder by a fully enclosed box. A water heating jacket was also incorporated in this model around the upper end of its burner tube. This modification resulted in a highly efficient water heating or steam raising device. Comparison with step-grate furnaces shows that TiB burners have similar or superior performance characteristics with additional advantages of simplicity, compactness and low cost.     

Vorstellung eines neuartigen Brenners zur Erzeugung von turbulenten, verdrallten Kohlenwasserstoff – Diffusionsflammen

Technische industrielle Verbrennung ist meistens turbulente Verbrennung von Kohlenwasserstoffen in Diffusionsflammen. Die Grundlagenforschung auf diesem Gebiet basiert auf den drei Säulen physikalische Modellierung, numerische Simulationen und Validierung durch Experimente meistens mittels Laserdiagnostik. Es gibt eine lange Historie über die Konstruktion und den Bau von geeigneten Brennern, mit denen turbulente Kohlenwasserstoff Diffusionsflammen erzeugt werden können, die sowohl simuliert als auch vermessen werden können. Von diesen beiden Methoden ausgehend gibt es eine Reihe von Restriktionen bezüglich des endgültigen Designs des Brenners und der Flammen, die untersucht werden sollen. Ein kritischer Aspekt sind dabei die lokalen Ruß- und PAH- Konzentrationen in den Flammen, weil alle spektroskopischen Messtechniken, die für Konzentrationsmessungen verwendet werden müssen, durch Ruß und PAH stark gestört werden. Mit den meisten Brennern, die man bis jetzt verwendet hat, hat man versucht, dieses Problem mit mehr oder weniger Erfolg und mit mehr oder weniger Nachteilen bezüglich anderer Aspekte zu überwinden, indem man Kompromisse einging. Wir haben einen neuartigen Brenner entwickelt, der einige dabei auftretenden Probleme löst und den wir als neuen Testfallbrenner vorschlagen. Mit diesem Brenner werden verdrallte turbulente Diffusionsflammen mit sehr wenig lokalen Ruß- und PAH -Konzentrationen geschaffen. Bis jetzt wurde Methan als Brennstoff verwendet. Die Vor- und Nachteile des Brenners und der Flammen werden in diesem Artikel detailliert diskutiert. Weiterhin werden erste Ergebnisse vorgestellt. Mehr Informationen zu diesen Arbeiten sind zu finden unter: http://www. ltt-rostock.de/text/tmd_vbfltt.htm.Technical and industrial combustion is mostly turbulent diffusion combustion with hydrocarbon fuels. Fundamental research on this field is based on three columns, physical modeling, numerical simulations and validation experiments mostly done by laser diagnostics. There is a long tradition in constructing and building burners that will create turbulent hydrocarbon diffusion flames which can be both, simulated and measured. From these both methods result a number of different requirements for the final design of burner and flames to be investigated. One critical aspect is local soot and PAH concentration within the flames due to the fact, that spectroscopic measurement techniques which have to be used for concentration determination are strongly hampered by soot or PAHs. With most of the burners used so far it has been tried to overcome this problem with more or less success and with more or less disadvantages on other aspects as they tried to make a trade-off. We have developed a new kind of burner which will overcome some problems and which we propose as a new test case burner. It creates swirling turbulent diffusion hydrocarbon flames with very low level of local soot or PAHs. So far we used methane as fuel. The advantages and disadvantages of the burner and flames are discussed in detail within this paper. First results are also reported, more information about this work can be found under http://www.ltt-rostock.de/text/tmd_vbfltt.htm.

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SIZE AND HYDRATION CHARACTERISTICS OF LABORATORY SIMULATED JET ENGINE COMBUSTION AEROSOLS

ABSTRACT

Size and hydration characteristics for laboratory simulated jet engine combustion aerosols are reported and the validity of these simulated data is discussed. The jet fuels JP4, JP5, JP8 and JET A were burned in laboratory burners designed to simulate the lean pre-mixed, pre-vaporized advanced combustor concept. Significant quantities of aerosols were detected and in most cases their size and hydration properties were similar. Dry particle size distributions were single mode extending over the diameter range 0.014 to 0.200 microns, with peak diameters in the range 0.020 to 0.050 microns. The distributions were observed to vary with combustion stoichiometry, increasing the peak particle diameter as the combustion stoichiometry shifted from leaner to richer conditions. Critical supersaturation spectra for each fuel are presented. A mean ratio of cloud condensation nuclei to condensation nuclei (CCN/CH) has been calculate for each fuel: JP4 = 32%, JP5 = 42%, JET A = 39%, and JP8 = 35% indicating that in general 30 – 40% of the combustion aerosols generated with these laboratory burners can be considered cloud condensation nuclei.     

Experimental analysis of fuel from fish processing industry waste in a diesel engine

In the present work, biofuel derived from industrial fish processing industry waste is used in diesel engines to study its suitability . Biofuel from industry fish waste is produced through catalytic cracking, and its quality has been improved through distillation. A single cylinder 4.5 kW at 1500 rpm was used to find the suitability of biofuel and undistilled biofuel in diesel engine. Experimental results show that the brake thermal efficiency of biofuel and undistilled biofuel is similar. Brake thermal efficiency for diesel, undistilled biofuel and biofuel is 29.98, 32.12 and 32.4%, respectively, at 80% load. Carbon monoxide, unburnt hydrocarbons, particulate matter and oxides of nitrogen emissions increase with undistilled biofuel compared to biofuel. There is a small reduction in carbon dioxide emission with undistilled biofuel compared to biofuel. Even though the cylinder pressure is high with undistilled biofuel, the intensity of premixed combustion is lower than distilled biofuel. The ignition delay and combustion duration increase with undistilled biofuel. Finally, it is concluded that the fuel derived from fish processing industry waste can be used as a fuel for diesel engine after distillation.     

Computational modelling of turbulent flow,combustion and heat transfer in glass furnaces

For the combustion of natural gas in high temperature glass furnaces a computational model “Furnace” has been developed. It includes 3-D turbulent flow, flame chemistry, radiative heat transfer and the formation of soot and of the pollutant NO. Turbulent fluctuations have been taken into account, and are shown to have a large effect on thermal radiation and NO-formation. Spectral behaviour of gas radiation results in changes of heat transfer efficiency up to 5%, depending on refractory emissivity. The model has been employed to predict NO formation for different burner geometries. In general, a decrease in mixing of gas and air results in a reduction of 1600 to 400 ppm in flue gas NO concentration. Except for some of the low mixing flames, however, they lead to a lower burnout and a very high CO level in the flue gas. A comparison with semi-technical furnace tests shows that the model can predict NO formation reasonably well. With this computational model the designer of furnaces and burners can study further possibilities for increased furnace performance and low NO emissions.     

Emission spectroscopy for coal-fired cyclone furnace diagnostics

Using a spectrograph and charge-coupled device (CCD) camera, ultraviolet and visible light emission spectra were obtained from a coal-burning electric utility's cyclone furnaces operating at either fuel-rich or fuel-lean conditions. The aim of this effort is to identify light emission signals that can be related to a cyclone furnace's operating condition in order to adjust its air/fuel ratio to minimize pollutant production. Emission spectra at the burner and outlet ends of cyclone furnaces were obtained. Spectra from all cyclone burners show emission lines for the trace elements Li, Na, K, and Rb, as well as the molecular species OH and CaOH. The Ca emission line is detected at the burner end of both the fuel-rich and fuel-lean cyclone furnaces but is not detected at the outlet ends of either furnace type. Along with the disappearance of Ca is a concomitant increase in the CaOH signal at the outlet end of both types of furnaces. The OH signal strength is in general stronger when viewing at the burner end rather than the exhaust end of both the fuel-rich and fuel-lean cyclone furnaces, probably due to high, non-equilibrium amounts of OH present inside the furnace. Only one molecular species was detected that could be used as a measure of air/fuel ratio: MgOH. It was detected at the burner end of fuel-rich cyclone furnaces but not detected in fuel-lean cyclone furnaces. More direct markers of air/fuel ratio, such as CO and O2 emission, were not detected, probably due to the generally weak nature of molecular emission relative to ambient blackbody emission present in the cyclone furnaces, even at ultraviolet wavelengths.     

Characterization of combustion synthesized zirconia powder by UV-vis, IR and other techniques

Fine powders of zirconia were prepared by employing combustion method with varying fuel to pre-cursor molar ratios. The zirconia powders contained more amount of monoclinic phase as the fuel content was increased. This aspect was studied using XRD, IR and UV-vis diffuse reflectance techniques. The surface acid-base properties of these samples were also investigated by indicator titration method. The catalytic activity was probed with transfer hydrogenation reaction in liquid phase. It was found that combustion synthesized zirconia did not provide required active sites for transfer hydrogenation reactions in liquid phase unlike hydrous zirconia.     

Nanocluster initiation of combustion of off-grade hydrocarbon fuels

We have performed large-scale experiments on burning, in the regime of nanocluster pulsating combustion, such off-grade fuels as straw oil, hydrocarbon fuel, exhaust crankcase waste, crude oil, and others on the laboratory prototype of the self-contained burner of the Institute of Thermal Physics, Siberian Branch of the Russian Academy of Sciences. The application of modern diagnostics has made it possible to obtain a large body of information on the features of the physicochemical processes of such combustion in the presence of superheated steam. The experimental and theoretical studies have shown that as a result of the heterogeneouscatalytic decomposition of water molecules on soot nanoclusters in the mixing zone, high concentrations of the OH radical are formed and that this decomposition can be effective on carbon particles of size 1–5 nm at temperatures characteristic of traditional flares. The generation of an active OH radical leads to a significant increase in the rates of chemical reactions and a stable high-temperature combustion of "heavy" fuels with the observance of ecological norms.