Sooting Tendencies Of Fuels Research Articles

A comparative study on soot and PAH formation of C10 naphthenic ring-containing species in laminar coflow diffusion flames

C10 naphthenic ring-containing species are important components in transportation fuels and have been widely used for surrogate formulation of diesel and jet fuels to represent cycloalkanes or aromatic fractions. In this study, experimental and modeling studies were carried out to compare the formation of typical polycyclic aromatic hydrocarbons (PAHs) and soot in coflow methane/air diffusion flames doped with n-butylcyclohexane, decalin and tetralin. The laser-induced incandescence (LII) and laser-induced fluorescence (LIF) techniques were applied to measure 2D maps of soot volume fractions and relative PAH concentrations, respectively. Yield sooting index (YSI) was obtained experimentally to indicate the fuel sooting tendency. It can be observed that the soot volume fractions, sooting tendencies and pyrene concentrations of C10 naphthenic ring-containing species follow the order of tetralin > decalin > n-butylcyclohexane. The chemical kinetic simulation reveals that decalin decomposes through two main pathways, including the H-atom abstraction route and ring opening route. Especially, the pathway of ring opening reactions coupled with dehydrogenation results in the strongest benzene formation process among the test components. In the reacting system of tetralin flames, ring opening reactions are suppressed, while the dominant decomposition way of tetralin is via H-atom abstraction reactions, which offer a more direct pathway to form naphthalene and indene without benzene formation, leading to the highest naphthalene concentration of tetralin flame and the strongest soot formation process among all the test components. This fundamental investigation aims to provide valuable data on sooting behaviors and PAH formation characteristics of typical C10 naphthenic ring-containing species and get insight into the kinetic pathways from fuels to soot precursors. Useful information has been obtained for soot reduction from the perspective of the fuel design and surrogate formulation in terms of the sooting tendency.

Effects of the addition of a high energy density fuel, adamantane to diesel on its cetane number, sooting propensity, and soot nanostructural properties

Soot particles, released during diesel combustion, adversely affect human health and the environment. Some studies suggest blending diesel with oxygenated fuels to reduce soot emissions, though it also reduces fuel economy and may produce new pollutants such as aldehydes. Another method to reduce soot could be to increase its reactivity by altering its physicochemical properties (e.g., introducing curvatures in its nanostructures) so that it oxidizes inside the engine or flame. In this direction, a cyclic high-density hydrocarbon fuel, adamantane is studied as an additive for diesel to determine its effect on cetane number, threshold sooting index, soot reactivity, and soot nanostructural properties. The addition of up to 6.75 wt% of adamantane in diesel significantly increased the smoke point of diesel from 18 to 29 mm (and threshold sooting index decreased by 44%), indicating a drastic drop in fuel sooting tendency. Adamantane addition in a small amount to diesel minimally affected the cetane number. To understand the impact of adamantane addition to diesel on the characteristics of soot particles, different techniques including TGA, HRTEM, XRD, EDX, and EELS were used. It is observed that adamantane enhances curvatures in soot nanostructures and reduces the size of fringes in soot and its aromatic content, and all of these property variations improve soot reactivity to improve its oxidation in flames or engines and reduce soot emission.

Synergistic effect analysis on sooting tendency based on soot-specialized artificial neural network algorithm with experimental and numerical validation

Interaction between components is an important characteristic in a fuel mixture, which has significant influence on sooting tendency and is strongly related to chemical structures of components. It is time-consuming to study mixing effects between multiple fuels on soot formation through experimental methods, so it is essential to develop a simple and reliable statistical method to supplement experimental data. All sooting tendency data was transformed into a dimensionless index called Yield Sooting Index (YSI). A machine learning algorithm, named soot-specialized artificial neural network (S-ANN), was developed in this paper to predict sooting tendency of fuel surrogates. The mean relative error of S-ANN prediction results can be reduced to about 6%, which is better than that of linear method (13.72%). As a widely used index, YSI can characterize the relative scale of fuel sooting tendency but cannot clearly represent the synergistic or neutralization effects of mixture components. Therefore, this work proposes Soot Synergistic/Neutralization Index (SSNI) using the deviation between predicted value and linear fitting value. SSNIs are transformed from the prediction results of S-ANN and can indicate the interactions between fuels in terms of sooting tendency, which can also provide important information for component selection and sooting tendency adjustment during formulation process of surrogates. Two groups of binary mixtures were selected to validate the algorithm and index. From validation experiment, it is indicated that negative synergistic effect exists between n-cetane and iso-cetane; positive synergistic effect exists between iso-cetane and butylcyclohexane. These two synergistic effects are simulated and analyzed through previously developed chemical mechanism. The results reveal that soot-specialized artificial neural network algorithm have a strong ability to predict sooting tendency of fuel mixtures, which can be used as an accurate and low-cost approach to supplement experimental data. SSNI can help to understand the interactions of fuel mixtures and provide valuable guidance for the construction of surrogates.

Machine learning and deep learning enabled fuel sooting tendency prediction from molecular structure

Soot formation models become increasingly important in advanced renewable fuels formulation for soot reduction benefit. This work evaluates performance of machine learning (ML) and deep learning (DL) to predict yield sooting index (YSI) from chemical structure and proposes a tailor-made convolution neural network (CNN)-SDSeries38 for regression problem. In ML, a novel quantitative structure-property relationship (QSPR) is developed for feature extraction and the relationship between molecular structure and YSI is built by ML algorithm. In DL, SDSeries38 contains 9 feature learning modules, 1 regression module for automated feature learning and regression. It adopts standard series network architecture and modular structure, each feature learning module is a stack of convolution, batch normalization, activation, pooling layers. ML-QSPR model outperforms SDSeries38 in accuracy (RMSE = 7.563 vs 19.58), computational speed and the former applies to fuel mixtures. In DL, SDSeries38 network exceeds 10 classical CNN and provides a generic architecture enabling transfer application to other regression problem. DL application to regression is still in its infancy and there is no complete guide on how to develop specific CNN architectures for regression. Some gaps need to be filled: (1) Specially developed CNN architectures for regression are required; (2) The performances of direct transfer learning the classical CNN architectures from classification to regression are modest. A modular structure with typical function modules may provide an ideal solution; (3) Going deeper into the sequence of convolution layers improves predictive accuracy, but bears in mind to keep the number of layers below the threshold to avoid vanishing gradient.

Experimental investigation of the lift-off height and soot formation of a spray flame for different co-flow conditions and fuels

Since the combustion process in spray flames is a highly complex multi-phase phenomenon, which involves several simultaneous processes such as atomization, vaporization, and chemical kinetics, it is still not fully understood. In the present work, an experimental investigation has been performed for three different hydrocarbon fuels (n-Heptane, n-Decane, n-Dodecane), in order to understand the effect of varying co-flow conditions, fuel mass flow rate, and fuel type on both the flame lift-off height and soot formation. The fuels were injected through a hollow-cone spray injector, with a nominal spray cone angle of 80∘ and orifice diameter of 120μm in an annular non-swirled preheated air co-flow. The flame lift-off height was determined by recording the OH* chemiluminescence, whereas soot formation has been determined through the color diffused back-illumination extinction technique. From the results, it has been observed for a certain fuel that the flame lift-off height is mainly controlled by the co-flow velocity and air co-flow temperature. The results also show that the fuel that yields largest droplet size and that possesses the lowest volatility exhibits the highest flame lift-off height. Furthermore, the results evidence a strong influence of the co-flow velocity on the soot formation. With an increase in co-flow velocity, the flame lift-off height is increased and so the amount of air entrainment, leading to a less rich reaction zone just downstream of the lift-off height, which in turn results in less soot formation. Finally, the comparison among different fuels shows that their differences in soot formation are likely related to fuel sooting tendency. This property, in turn, depends on the fuel molecular structure playing an important role on its determination.

Predicting sooting tendencies of oxygenated hydrocarbon fuels with machine learning algorithms

The use of oxygenated components is an effective way to suppress soot formation and reduce particulate matter emission in diesel engines. Based on the group additivity method, we proposed a new statistical model with kernel ridge regression (KRR) to predict the sooting tendencies of oxygenated components and interpret the experimental results of fuel sooting tendency. Through a training process, the relationship between fuel molecular structure and sooting tendency was built. In the testing process, the predicted values of the yield sooting index were in good agreement with the measured values, indicating that the KRR model had good predictive performance. The KRR method can be used to compare the sooting tendencies of various components that are important in traditional or new fuels. For example, based on the predicted results of typical five-carbon oxygenated compounds, the inhibiting effects of oxygen functional groups on sooting tendency are in the following order: esters > ketones ≈ aldehydes > ethers > alcohols. In addition, the proposed method provides statistical evidence for the effects of structural features on sooting tendencies. The predictive results for typical ethers indicate that although sooting tendencies increase as carbon chains become more branched, they are not very sensitive to the specific arrangement of the branches compared with the effect of carbon chain length. Moreover, the KRR method is useful for studying non-nearest-neighbor interactions, including functional group interactions. By predicting the sooting tendencies of typical esters, the coupling of ester moiety and CC double bonds shows an overall enhancing effect on sooting tendency, which indicates that CC double bonds play a dominant role in soot formation. This method provides an alternative way to obtain the sooting tendencies of fuel compounds and verifies the selection of low-sooting fuels from a wide range of feedstocks.

Vision based algorithm for automated determination of smoke point of diesel blends

Current regulations restrict NOx and particulate emissions (PM) produced by new vehicles. One solution for reducing these emissions, mainly PM, is focused on the use of cleaner fuels. In this sense, the smoke point test (SP) has been proved to be a fast tool when comparing the sooting tendency of fuels. As manual SP determination can imply an error owing to the inherent uncertainty of visual flame observation, the updated ASTM D1322-18 has stated that the new commercial equipment SP10 Automated Smoke Point Analyser is the reference for SP determination. However, its high cost has motivated this work where a vision based algorithm for automated determination of SP without wick-fed modifications is proposed. Experimental results demonstrate the accuracy and repeatability of the proposed method.

The sooting tendency of aviation biofuels and jet range paraffins: effects of adding aromatics, carbon chain length of normal paraffins, and fraction of branched paraffins

ABSTRACTThe smoke point of several fuel mixtures was measured using a smoke meter defined by American Society for Testing Material D1322. The threshold soot index (TSI) was calculated to compare the sooting tendency of fuels. Two aviation biofuels produced by hydroprocessing of coconut oil, four jet range normal paraffins (n-paraffins), iso-octane, and propylbenzene were used to investigate the effects of chain length of n-paraffins, iso-paraffins, and aromatics on the sooting tendency. The results show that the effect of propylbenzene on the smoke point of the mixtures is dominant compared to that of the chain length of n-paraffins and the fraction of iso-paraffins. The differences in the sooting tendency among these n-paraffins are insignificant. In addition, blending aviation biofuels with Jet A1 leads to a decrease in the sooting tendency. Aromatics in Jet A1 play an important role on the sooting tendency of the mixtures of aviation biofuels and Jet A1.

On the characteristics and reactivity of soot particles from ethanol-gasoline and 2,5-dimethylfuran-gasoline blends

With strict environmental legislations and to reduce our dependence on fossil fuels, biofuels and their blends with hydrocarbon fuels are being seen as cleaner alternatives to meet the world’s energy demand. This paper explores the effect of adding ethanol and 2,5-dimethylfuran (DMF) to gasoline on its sooting tendency as well as on the characteristics and oxidative reactivity of soot. The fuel sooting tendency is determined through its smoke point using a diffusion flame setup. Several characterization techniques such as thermogravimetric analysis, high resolution transmission electron microscopy, electron energy loss spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, elemental analysis, and Raman spectroscopy are employed to reveal the changes in the physicochemical properties of soot collected at a flame height of 25 mm. With 20% ethanol or DMF addition to gasoline, the rate of soot production, the sizes of polycyclic aromatic hydrocarbons and primary particles in soot, and its aromatic character decreased, while its amorphous character and the concentrations of oxygenated and aliphatic functional groups on it increased. These led to the increased oxidative reactivity of soot from the blended fuels. The differences in the characteristics of soot from ethanol/gasoline and DMF/gasoline blends are reported.

Advanced Methodology for the Detection of Smoke Point Heights in Hydrocarbon Flames

The American Society for Testing and Materials (ASTM) D1322 assesses the sooting tendency of fuels using smoke points. Recently, the fuel uptake rate measurement with threshold imaging (FURTI) method has improved smoke point determination. Herein, a precise and accurate detection of smoke point heights is investigated when tests are conducted with the FURTI method. First order gradients of the soot luminosity, recorded with a charge-coupled device camera, are used to detect the flame height. The analysis of several iso-octane/toluene calibration blends shows a significant diminution in the height experimental error in comparison to the ASTM D1322 standard, ranging from a minimum of 67% to a maximum of 86%. A low flame height bias, ranging from 1% to 5%, and a negligible sensitivity to the fuel sample composition is present when additional hydrocarbons are analyzed, owing to a high measuring accuracy and a robust height detection method.

Sooting tendencies of diesel fuels, jet fuels, and their surrogates in diffusion flames

Surrogates of transportation fuels are useful design tools for developing engines with cleaner and more efficient combustion. It is important that information about the sooting tendency of the target fuel be incorporated in the formulation of these surrogates. Toward that end, in this work we report experimentally measured sooting tendencies of several diesel and jet fuels, surrogates of these fuels, and pure compounds which are components of these surrogates. These fuels, surrogates, and compounds were separately doped in trace quantities (0.5% by mass) into the fuel of a methane-air laminar coflow flame. The sooting tendencies, expressed as Yield Sooting Indices (YSIs), were quantified from spatially resolved two-dimensional soot volume fraction distributions of these flames as measured with color ratio pyrometry. Previous means of matching the sooting behavior of the surrogate to the fuel, such as by matching the fuel’s hydrogen content or its double bond equivalent, were found to be inadequate because these approaches do not fully account for the effects on the fuel’s sooting tendency of branching in aliphatics and alkyl substitutions in aromatics. A strong correlation was observed between the YSI and the relative abundance of different types of carbon atoms (as quantified by 1H and 13C NMR spectroscopy) in these fuels and compounds, indicating that such NMR characterization can capture essential structure-specific sooting information of relevance to surrogate formulation. Based on these YSI measurements, we demonstrate two approaches to predict the sooting tendency of a fuel surrogate. These approaches, based on (1) the choice of pure compounds that are blended to create a surrogate, or (2) the distribution of carbon atom types in a surrogate, can be used to tune the surrogate’s formulation to match the sooting tendency of its target fuel.

Group additivity in soot formation for the example of C-5 oxygenated hydrocarbon fuels

Sooting tendencies have been measured for 29 compounds with 5 carbon atoms and different oxygen contents, along with 12 additional oxygenated pure compounds and 10 blends of commercial fuels. The test compounds include alcohols, ethers, aldehydes, ketones, acids, esters, keto-esters and hydroxy-esters. The Threshold Sooting Index (TSI), as defined and used in the literature, was primarily used to quantify the sooting tendency of the compounds. It is shown that this index does not account for the presence of oxygen atoms in the fuel molecules, and the impact of fuel oxygen on the stoichiometric air requirement. The application of TSI to oxygenated fuels leads to sooting tendencies inconsistent with those reported in the literature. A new sooting index is proposed for oxygenated and non-oxygenated compounds, which considers the relation between the height of the flame tip and the volumetric stoichiometric air requirement of the flame. This new index is denoted as the Oxygen Extended Sooting Index (OESI). The results obtained by this new index corroborate that not only the oxygen content but also the molecular structure has an influence on the sooting tendency of fuels. Different functional groups, not only those including oxygen atoms, impart different sooting tendencies. A structural group contribution approach based on group additivity is proposed to interpret experimental observations on the effect of oxygen functional groups on the sooting tendency of fuels using the example of C-5 oxygenated fuels. Groups with a higher fraction of carbon–carbon bonds showed a higher contribution to the sooting tendency than those with a higher concentration of carbon–hydrogen bonds. Among the C-5 mono-oxygenated compounds, the sooting tendency increased in this order: aldehydes<alcohols<ketones<ethers<n-alkanes and for the C-5 di-oxygenated compounds, the sooting tendency order was: acids<esters<di-ethers. In general, both unsaturated and branched compounds showed slight increases in sooting tendency with respect to their saturated and linear counterparts. Finally, the new sooting index was applied to commercial biofuel blends (denatured ethanol–gasoline and soybean-derived biodiesel–diesel) and empirical correlations were obtained.

Novel Micropyrolyis Index (MPI) to Estimate the Sooting Tendency of Fuels

A new fuel quality indicator called micropyrolysis index (MPI) is proposed for quantifying sooting tendencies of fuels in research laboratories. The MPI has been designed with the following characteristics: (i) oxygen independence, since sooting tendencies can change dramatically with varying oxygen concentration, (ii) reduced sample volume that can be utilized on a laboratory scale, (iii) improved repeatability over traditional methods, and (iv) use of common laboratory equipment so that the method may easily be implemented in multiple laboratories. MPI measurements were conducted by pyrolyzing 20 µL of fuel across a bed of R-Al2O3 beads at a temperature of 850 °C. Subsequently, the carbon-containing beads were transferred to a clean reactor where the deposited carbon was burned via temperature programmed oxidation (TPO) in order to quantify the amount. The amount of deposited carbon provides an indication of the tendency of a particular fuel to form soot when pyrolyzed. The observed tendency is independent of operating conditions, such as flame temperature and stoichiometric oxygen/fuel ratios, which greatly affect the measurements in other techniques used to estimate sooting tendency. An MPI value of 5 was assigned to the amount of carbon deposited from n-octane, and a value of 20, to the value corresponding to decalin. These two compounds were used as reference. Repeatability tests showed that MPI measurements had a standard deviation of 1.02 MPI at MPI ) 94.7 which scaled down to 0.11 at MPI ) 3.3. MPI values of pure nonaromatic hydrocarbons were found to correlate well with traditional threshold soot index (TSI) values. However, MPI was found to be more differentiating than TSI among the different hydrocarbon families: n-alkanes, isoalkanes, and cycloalkanes. A quantitative structure-property relationship (QSPR) model was developed in order to predict the MPI of other pure compounds not measured experimentally and further expand the database. Blending issues with aromatics are discussed, as well as the effects of aromatic content in real feeds.

A study of jet fuel sooting tendency using the threshold sooting index (TSI) model

Fuel composition can have a significant effect on soot formation during gas turbine combustion. Consequently, this paper contains a comprehensive review of the relationship between fuel hydrocarbon composition and soot formation in gas turbine combustors. Two levels of correlation are identified. First, lumped fuel composition parameters such as hydrogen content and smoke point, which are conventionally used to represent fuel sooting tendency, are correlated with soot formation in practical combustors. Second, detailed fuel hydrocarbon composition is correlated with these lumped parameters. The two-level correlation makes it possible to predict soot formation in practical combustors from basic fuel composition data. Threshold sooting index (TSI), which correlates linearly with the ratio of fuel molecular weight and smoke point in a diffusion flame, is proposed as a new lumped parameter for sooting tendency correlation. It is found that the TSI model correlates excellently with hydrocarbon compositions over a wide range of fuel samples. Also, in predicting soot formation in actual combustors, the TSI model produces the best results overall in comparison with other previously reported correlating parameters, including hydrogen content, smoke point, and composite predictors containing more than one parameter.

06/00274 Self-ignition of a lean mixture of n-pentane and airover a wide range of pressures : Zhukov, V. P. et al. Combustion and Flame, 2005, 140, (3), 196–203

Sooting tendencies of fuels are analyzed with respect to the type of experimental configuration used—per-mixed flames, normal and inverse co-annular, Wolfhard-Parker and counter-flowing diffusion flames, or shock tubes. The important effect of temperature in each type of experiment is examined. The relative tendency of various fuels to soot when consumed in pre-mixed and diffusion flames has been determined by the qualitative measurements of critical sooting equivalence ratios and smoke heights at various temperatures and quantitatively confirmed by measurements of chemical species, soot number density and volume fraction.Fuel structure has a significant effect on the sooting tendency of diffusion flames, but little influence in premixed flames. Irrespective of the fuel in diffusion flames soot inception occurs around 1400 K and is dependent somewhat on H atom diffusion. Particle burnout ceases at about 1300 K and is responsible for the smoke height.Incipient particle formation determines the volume fraction of soot and is controlled by the rate of formation of the first aromatic species containing one to two rings. The particle growth process is found to be the same regardless of flame type. A generalized chemical mechanism of soot formation irrespective of flame type or process is presented. The various routes in this mechanism support the relative sooting tendency of fuels found in both flame and shock tube experiments. The effect of oxygen added to various fuel in diffusion controlled experiments is analyzed.

The Effects of Fuel Sooting Tendency and the Flow on Flame Radiation in Luminous Turbulent Jet Flames

Abstract In this paper two observations are emphasized with regard to flame radiation in luminous turbulent jet flames: (a) the radiant fraction in turbulent buoyant jet flames is a weak function of the fuel sooting tendency as expressed by the laminar smoke-point heat release rate; and (b) moreover, for very sooty fuels, the radiant fraction saturates to a constant value which is independent of the laminar smoke-point heat release rate, although it depends on the adiabatic flame temperature. These observations can be explained by considering that cooling of the flames is enhanced and the effective radiation temperature drops as soot increases and thus radiant losses increase, until for very sooty fuels flame extinction in the upper part of the flames occurs. The physics of flame radiation phenomena are discussed in the light of a global similarity analysis for flame radiation together with the use of extensive experimental data. In the analysis, complementary to the usual hydrodynamic length scale for combustion, a new radiation length scale is introduced which characterizes the effects of radiant losses on the flow. Scaling relationships of the turbulent radiant fraction in terms of the laminar smoke-point heat release rate are developed first for turbulent buoyant jet flames, wherein flow effects are small, and then extended to momentum-dominated turbulent jet flames. The present results have direct practical significance (a) Tor predicting radiant fractions in fires, and (b) for the design of enhanced flame radiation burners. The physics presented here for soot concentration and radiant cooling can be incorporated in detailed k-ε-g or other turbulence models.

Wall-fire radiant emission—Part 2: Radiation and heat transfer from porous-metal wall burner flames

Radiant emission and heat transfer from methane, ethane, ethylene and propylene fires burning on a vertical porous-metal surface have been measured. The water-cooled burner provides up to ten 380-mm wide and 132-mm high porous-metal panels topped by a 660-mm-high solid-metal heat-transfer plate. A scanning radiometer was used to obtain the vertical distribution of the outward-directed radiance No emitted normal to the burner surface. Results from six-panel fires, with fuel mass flux maintained constant over the active burner height, are reported. For any fixed fuel mass flux, the radiance No was found to increase linearly with height, z, after an initial jump at the flame base. At fixed z, linear relationships between reciprocal radiance No−1 and reciprocal mass flux m˙″-1 were obtained. For methane and ethane these relationships held over the entire range of mass flux, while, for ethylene and propylene, an abrupt transition separating two regimes occurred at critical mass fluxes. The ordinate intercept N∞, representing an asymptotic radiance, and the slope s of the linear relationship, are functions of height z. N∞ and s−1 increase with fuel sooting tendency at fixed z. Heat fluxes to the porous-metal panels decreased with increasing mass flux near the flame base, but were nearly independent of mass flux near the top portion of the porous-metal burner. These heat fluxes increased with fuel sooting tendency except for a reversed trend between methane and ethane. At sufficiently high mass flux, a jump of heat flux occurred at the junction between the porous-metal burner and the solid-metal heat-transfer plate, and the heat flux increased further with height in this over-fire region. In this zone, the data were separated into a lower overlapping set for alkane fuels, methane and ethane, and a higher overlapping set for the alkenes, ethylene and propylene.

Soot formation in combustion processes

Sooting tendencies of fuels are analyzed with respect to the type of experimental configuration used—per-mixed flames, normal and inverse co-annular, Wolfhard-Parker and counter-flowing diffusion flames, or shock tubes. The important effect of temperature in each type of experiment is examined. The relative tendency of various fuels to soot when consumed in pre-mixed and diffusion flames has been determined by the qualitative measurements of critical sooting equivalence ratios and smoke heights at various temperatures and quantitatively confirmed by measurements of chemical species, soot number density and volume fraction. Fuel structure has a significant effect on the sooting tendency of diffusion flames, but little influence in premixed flames. Irrespective of the fuel in diffusion flames soot inception occurs around 1400 K and is dependent somewhat on H atom diffusion. Particle burnout ceases at about 1300 K and is responsible for the smoke height. Incipient particle formation determines the volume fraction of soot and is controlled by the rate of formation of the first aromatic species containing one to two rings. The particle growth process is found to be the same regardless of flame type. A generalized chemical mechanism of soot formation irrespective of flame type or process is presented. The various routes in this mechanism support the relative sooting tendency of fuels found in both flame and shock tube experiments. The effect of oxygen added to various fuel in diffusion controlled experiments is analyzed.

The Influence of Fuel Hydrogen Content Upon Soot Formation in a Model Gas Turbine Combustor

The sooting tendencies of various fuel blends containing either single-ring or polycyclic aromatics have been studied in a model gas turbine combustor at a pressure of 1.0 MPa and varying values of air/fuel ratio. Sooting tendencies were determined by flame radiation, exhaust soot, and infra-red absorption measurements. The results of this study have indicated that, even for fuels containing high concentrations of naphthalenes or tetralins (&gt; 10 percent v), fuel total hydrogen content correlates well with fuel sooting tendency. The present results are explained by a hypothesis that assumes that the majority of soot is formed in regions of high temperature, low oxygen content, and low fuel concentration, e.g., the recirculation zone.

The Effect of Hydrocarbon Structure Upon Fuel Sooting Tendency in a Turbulent Spray Diffusion Flame

The sooting tendencies of various hydrocarbon structures have been studied in a model gas turbine combustor at a pressure of 0.35 MPa and a preheated air temperature of 530 K. The results of this study have indicated that the sooting tendencies of fuels containing only single ring aromatics, fused bicyclic saturates, and unsaturated nonaromatics will be related to the overall hydrogen content of the fuel. However, experimental fuel blends with high concentrations (&gt; 20 percent wt) of naphthalenes or tetralins exhibit sooting properties that are dependent upon the presence of such components. It is suggested that a kinetic scheme utilizing aromatic rings as nuclei upon which reactive fragments may stabilize can explain the present results.