Oil Spray Flames Research Articles

Sizing soot and micronic carbonaceous particle in spray flames based on time resolved LII

A strategy for a comprehensive discrimination between soot and larger carbonaceous particles through numerical approach and particle sizing based on time resolved laser-induced incandescence (TIRE-LII) was investigated in this paper. TIRE-LII technique which is already a powerful tool for soot particle sizing in gaseous flames, was applied to more practical system as spray turbulent flames. Temporal decay of theoretical LII signals were computed for different classes of particles: soot, cenosphere and full carbonaceous sphere called by analogy “pleosphere”, pleo- from the Greek pleos, solid. The temporally resolved LII emissions obtained in a heavy fuel oil and in a diesel oil spray flames were compared to theoretical calculations and to sampling results. This first approach showed that it was possible to discriminate the three classes of particle produced during heavy fuel combustion and to size soot particles during the diesel oil combustion. Moreover, it was also possible to obtain a qualitative tendency of the evolution of the relative volume fraction of each class of particle along the flame axis.

Soot and PAH Formation in Rapeseed Oil Spray Combustion

The performance of rapeseed oil combustion in regard to organic pollutant production (solid particulate, light hydrocarbons, aldehydes and PAH) was investigated and compared to the performance of a typical heavy fuel oil burned in the same experimental conditions. C1 C6 hydrocarbons were formed in lower amounts in the rapeseed oil flame, but the composition and distribution was found to be very similar for both fuels. Due to the very high-temperature environment typical of stationary combustion a very low presence of aldehydes like acrolein was found only in the initial region of the rapeseed oil spray flame. Rapeseed oil was found to be a ''cleaner'' fuel compared to the heavy fuel oil also in respect to the formation of particulates, condensed species, and in particular PAH. The composition of PAH formed from the combustion of both fuels was that typically measured in rich combustion irrespective of the fuel utilised.

Time Resolved Laser Induced Incandescence for Soot and Cenospheres Measurements in Oil Flames

The quantitative characterization of sooting flames in terms of soot load and total soot surface area continues to be a major challenge in both fundamental investigations and practical applications. More particularly, a major interest can be found to discriminate the two classes of particulate, namely soot and cenosphere, presents in power generation plants fuelled with heavy fuel oils. The Laser-Induced Incandescence (LII) technique is widely employed for the determination of soot volume fraction but LII may also be used to derive the particle diameter, profiting from the size-dependent cooling behavior of the laser-heated particles. The temporally resolved LII emissions has been successfully used in a heavy fuel oil spray flame to distinguish the two classes of carbonaceous panicles produced during the heavy fuel oil combustion. Moreover, it has been possible to follow along the flame axis the formation and bum-out of these two classes of particulate and their relative amount in terms of volume fraction.

Contrôle actif de la combustion par injection instationnaire du combustible

Active combustion instability control through modulated liquid fuel injection is investigated. The flame response to external excitation is determined by phase-locked radical emission imaging. A fuel oil spray flame is destabilized by a controlled external acoustic excitation. The actuator is used to modulate the liquid fuel spray, imposing a phase shift between the pressure and heat release fluctuations. This system can efficiently control the level of heat release oscillations in the combustion zone and the corresponding pressure fluctuations.

Performance of numerical spray combustion simulation

The aim of this study is to examine the performance of numerical spray combustion simulation. A numerical simulation for the prediction of local properties of heavy oil spray flames stabilized by a baffle plate is described. Time-averaged governing conservation equations are solved to estimate the combustion gas flow, gas composition and temperature fields in the experimental combustor. The κ-ε turbulence model is used to describe the turbulent flow field. The behavior of fuel droplets in the turbulent combustion gas flow is calculated by the Lagrangian method. The combustion rate of fuel vapor is estimated by the eddy dissipation model. The effects of radiation are accounted for by the six-flux model of radiation. The performance of the simulation is examined by comparison with measured data. In the isothermal (cold) case, the calculated flow pattern is compared with the data measured by LDA, and it is clear that the calculated results show quantitative agreement with the measured data. In the combustion case, however, the simulation cannot predict well the measured profiles of temperature, O 2 and CO 2 concentrations near the baffle plate. It is inferred that this simulation cannot estimate accurately the interaction between the recirculation flow induced by the baffle plate and fuel droplets.

THE CHARACTERISTICS OF CYLINDRICAL WATER-COOLED FURNACES WHEN BURNING LIQUID, GASEOUS, OR DUAL LIQUID-GAS FUELS

Measurements inside a flame tube are presented and compared for a range of confined liquid fuel oil, gaseous fuel and dual fuel flames. The operating conditions include a range of three heat inputs 29 kW, 38 kW and 48 kW. For dual fuel flames three gaseous fuel ratios 25 %, 50 % and 75 % are considered. The experimental work takes place using an industrial type, dual fuel burner that is especially designed and constructed to utilize the three types of firing. This burner is fitted to a water cooled cylindrical furnace (the Combustor). [t is found that. Burning gaseous fuel simultaneously with liquid fuel oil, acts as a hot shield surrounding the oil spray flame. This shield serves to reduce significantly the loss of combustibles from oil flames, mainly through enhancing the evaporation process of fuel oil droplets and increasing soot burnout at the flame region as well as preventing the surviving soot particles from being deposited on furnace walls. The importance of these conclusions emerges when burning low grade fuels or bituminous fuels which needs a more carefully designed combustion system.

New Nonintrusive Laser Diagnostic Tools for Design and Optimization of Technically Applied Combustion Systems

The purpose of this paper is to present the latest developments of laser diagnostic techniques for the application in technically applied turbulent combustion systems (i. e. an oil spray flame burner from KoRTING HANNOVER AG) as a tool for design and optimization purposes of furnaces and boilers. The advantages of those laser based nonintrusive measurement techniques over classical mechanical probes are multiple. The most important are : The nonintrusive character of laser diagnostics offers the possibility to investigate the combustion process without any disturbing effect on the occuring reactions and the actual flow field. Second the application of new pulsed powerful UV-lasers in combination with high-tech intensified CCD-camera technology yield instantaneous spatial information about the occurring processes as well as temporal data. Third beside pure qualitative information about spatial distributions (OH, NO, O 2 , liquid fuel, vapor phase fuel), turbulence and temporally recurring structures also quantitative data about molecular densities can be obtained. It will be shown that locally limited gas tracer seeding at different positions into the air stream inside the mixing device and subsequent planar detection in the fuel/air mixing area lead to very important information for optimization and design purposes.

Measurements and predictions of nitric oxide and particulates emissions from heavy fuel oil spray flames

The results of extensive experimental and predictive studies of nitric oxide (NO) and particulates (unburned coke) emissions from a large-scale laboratory furnace, fired by a heavy fuel oil (HFO) swirl burner with a rotary cup air blast atomizer are presented. A detailed in-flame data archive of gas temperature and O 2 , CO, CO 2 , and NO concentrations has been obtained for five flames for differing excess air levels (15% and 20%), swirl numbers (1.05 and 1.2), primary air-to-fuel ratios (2.5 and 3.0), and atomizer cup speeds (1.0×10 4 and 2.0×10 4 rpm). A wider range of operating parameters has been established to quantify their effects on NO and particulate concentrations at the exit of the furnace. In a parallel modeling study, a two-dimensional computational fluid dynamics code for the prediction of HFO spray combustion and NO and particulates emissions has been constructed. Validation of the code against the experimental data reveals reasonably good quality predictions in the near burner region. The code is capable of simulating the measured trends of flue-gas NO and particulates emissions with useful precision for a wide range of atomizer/burner operating conditions. A scrutiny of the in-flame and flue-gas data, with the aid of the predictions, has provided an enhanced understanding of combustion and combined NO/particulate emissions characteristics of the HFO flames generated by the rotary cup atomizer and establishes the foundation for future work in optimizing combustion and emissions performance.

Prediction of the near burner region and measurements of NO x and particulate emissions in heavy fuel oil spray flames

Fuel oil combustion is difficult to model because of the lack of detailed knowledge about the spray. In the present article a mathematical model developed at Instituto Superior Técnico and Imperial College is described. The model is validated against data for a combustor fired by an industrial-type swirl burner, for which the initial conditions of the spray have been characterized. With this advantage it is found that a fair simulation of the subsequent aerodynamics and combustion is achieved. Systematic testing has shown that such model failings as exist are linked to the prediction of the gas phase aerodynamics. Improvements will be hard won with recourse to advanced models of turbulence. Burner designs that reduce NO x emissions are frequently found to do so at the expense of augmented particulates emissions. New data are reported for the emissions of NO x and particulates as a function of the burner swirl number. With the aid of the present mathematical model the observed trends may be explained. It is concluded that the preferred burner that minimizes the emissions of both is one that ensures rapid droplet vaporization and long residence times for particulates in the internal recirculation zone of the burner. This is an aerodynamically achievable condition.

The formation of NH 3, HCN, and N 2O in an air-staged fuel oil flame

Experimental data are presented on the formation on NO, N 2O, NH 3, and HCN from an oil spray flame together with the effect of staging the combustion air on the in-flame concentrations of these species. By staging up to 40% of the combustion air a 45% reduction in the emission of NO was achieved for a flame characterized by a lower axial NO concentration and HCN NH 3 ratio. N 2O as an active species was only observed in the early part of the flame, with the staged flame producing the higher concentrations. Final flue gas emissions of N 2O were less than 2 vpm for the range of experimental conditions studied.

火炎内の高級多環芳香族炭化水素とすす濃度の相関について

The relationship of soot concentration, gas temparature and intermediate hydrocarbon (polynuclear aromatic) compounds produced in the pyrolytic combustion paths in an important to understand the pathway of soot formation. This experimental object become evident the presence of emission excited in oilspray flame by the blue laser light (λ=488nm, 1.8W) . The scattering characteirgation from polynuclear aromatic hydrocarbons are not dealing here with elastic scattering phenomena, but rather with a fluoreseent emission.The results obtained are as follows.The maximum peak wavelength is in the neighbourhood of 530 nm. The fluorescent emissve intensity increases rapidly with soot concentration along the flow near the nozzle tip where fuel-rich condition prevail and hydrocarbons are formed by being reacted from original fuel of A oil. The decay of fuloreseus emissive intensity and soot concentration becomes significant near the maximum temperature. The peak of the fluorescent emissive intensity in the radial profiles near the nozzle tip is located just inside the position of the temperature peak, which indicates that hydrocarbons are produced in the fuel rich region near the peak of the temperature. In this experimental result the fluorecent matter is able to estimate the aromatic hydrocarbon such as Pyrene.

Fuel spray burning regime and initial conditions

The structures of air blast atomized heavy fuel oil spray flames, in particular, the mechanisms of droplet burning, are examined as functions of initial conditions by using a novel atomizer design. A particle sizing instrument and a spray momentum measurement device are used to calibrate this atomizer so that parametric variations can be made of the initial droplet size distribution, spray momentum, fuel flow rate, and air/fuel ratio. Information is obtained on flame length, droplet burning regime (individual or group combustion of droplets), and combustion chamber wall temperature as a function of initial conditions. Supported by this information, reasoning regarding the physics of the flows is used to propose that the relative values of two parameters, which incorporate initial spray momentum, droplet size distribution, and fuel flow rate, can give a good indication of the likely burning regime and other important features of spray flames.

Soot and pah distributions in oil spray flames, inferred by elastic and inelastic laser light scattering

The space distribution of droplets, soot particles and fluorescing PAH species have been determined for vertical unconfined swirled oil spray flames, by analyzing light scattering, and laser-excited fluorescence coefficients, and radially inverted emission of OH radicals. The angular patterns of the scattering coefficient on vertical and horizontal polarization planes have been measured in the flame and compared with theoretical predictions for transparent and absorbing large spheres and soot particles and with the measured patterns on isothermal sprays. The fuel droplets were mainly concentrated in the initial part of the flame around the axisand the maximum concentration of the fluorescing species were detected on the periphery of this zone, which is externally bounded by a layer of intense OH emission. Soot was produced in a small toroidal zone near the burner outlet and more massively in a high temperature recirculation region downstream. The influence of swirl strength on the combustion process has been studied by means of the axial scattering and the radial fluorescence profiles. Vaporization was delayed along the centerline and the off-axis maximum concentration of the fluorescing PAH increased up to an intermediate swirl level. These effects were attributed to the outward displacement of the swirled air jet, which thus reduced the mixing rate between fuel and air in the central part of the flame. Further increase of the swirl level reduced the PAH concentration because the recirculation of hot gases accelerated the vaporization and combustion processes.

Laser light scattering, emission/extinction spectroscopy and thermogravimetric analysis in the study of soot behaviour in oil spray flames

Vertical unconfined spray diesel oil flames was generated on a variable swirl burner with 90 KW power. 90° laser light scattering was employed to distinguish the fuel droplets and soot particles in the first part of the flames. Local values of the OH emission at λ=309.0 nm and of the λ=632.8 nm extinction and emission coefficients in the same region were obtained by Abel inverted chordal measurements. Profiles of soot particle size and number concentrations were obtained from scatter-extinction ratios, assuming a monodisperse spherical model; soot temperature distribution were evaluated by the Kirchhoff law. A new thermogravimetric technique, employed on the material sampled in the upper part of the flames, allowed quantitative distinction among the unburnt fuel, the heavy molecular mass products and the carbonaceous matrix. Flame development and spray penetration are studied to show the potentialities of laser light scattering and the thermogravimetric analysis. The results indicate that the two techniques can both detect and distinguish the fuel and soot particles, but they operate in different ranges of the droplet and soot volume fractions.

Visible and U.V. Spectral Emission and Extinction Measurements in Oil Spray Flame

Abstract Emission and extinction measurements in the visible and U.V. were performed along the axis of vertical unconfined fuel oil flames produced on a variable swirl burner. The flow rate of the fuel was around 6 Kg/hr and the theoretical equivalence ratios was varied from 0.9 to 1.15. The emissions due to the radicals OH, CH and C2 were compared with the continuum emission due to the soot particles. The profiles of the brightness and colour temperature were obtained from the measurements of the absolute intensity of the continuum in the spectral range 4000÷8000A. The colour temperature was much higher than the brightness temperature near the burner nozzle while the difference decreased in the final part of the flames. In the first part of the flame the monochromatic extinction coefficient at λ = 6500A decreases, due to fuel droplets, which are evaporating, but increases downstream where the soot formation process prevails. The study of its spectral variation in the range 4000A-8000A allows the determin...