Inert Dilution Research Articles

Stabilization, propagation and instability of tribrachial triple flames

A tribrachial (or triple) flame is one kind of edge flame that can be encountered in nonpremixed mixing layers, consisting of a lean and a rich premixed flame wing together with a trailing diffusion flame all extending from a single point. The flame could play an important role on the characteristics of various flame behaviors including lifted flames in jets, flame propagation in two-dimensional mixing layers, and autoignition fronts. The structure of tribrachial flame suggests that the edge is located along the stoichiometric contour in a mixing layer due to the coexistence of all three different types of flames. Since the edge has a premixed nature, it has unique propagation characteristics. In this review, the propagation speed of tribrachial flames will be discussed for flames propagating in mixing layers, including the effects of concentration gradient, velocity gradient, and burnt gas expansion. Based on the tribrachial edge structure observed experimentally in laminar lifted flames in jets, the flame stabilization characteristics including liftoff height, reattachment, and blowout behaviors and their buoyancy-induced instability will be explained. Various effects on liftoff heights in both free and coflow jets including jet velocity, the Schmidt number of fuel, nozzle diameter, partial premixing of air to fuel, and inert dilution to fuel are discussed. Implications of edge flames in the modeling of turbulent nonpremixed flames and the stabilization of turbulent lifted flames in jets are covered.

On the off-stoichiometric peaking of adiabatic flame temperature

The characteristic rich shifting of the maximum adiabatic flame temperature from the stoichiometric value for mixtures of hydrocarbon and air is demonstrated to be caused by product dissociation and hence reduced amount of heat release. Since the extent of dissociation is greater on the lean side as a result of the stoichiometry of dissociated products, the peaking occurs on the rich side. The specific heat per unit mass of the mixture is shown to increase monotonically with increasing fuel concentration, and as such tends to shift the peak toward the lean side. It is further shown that this is the cause for the lean shifting of the adiabatic flame temperature of oxidizer-enriched mixtures of N m H n and F 2 and of NH 3 and O 2, with various amounts of inert dilution, even though their maximum heat release still peaks on the rich side.

Experimental low-stretch gaseous diffusion flames in buoyancy-induced flowfields

The present study experimentally investigates the structure and instabilities associated with extremely low-stretch (∼1 s −1) gaseous diffusion flames. Ultra-low-stretch flames are established in normal gravity by bottom burning of a methane/nitrogen mixture discharged from a porous spherically symmetric burner of large radius of curvature. OH-PLIF and IR imaging techniques are used to characterize the reaction zone and the burner surface temperature, respectively. A flame stability diagram mapping the response of the ultra-low-stretch diffusion flame to varying fuel injection rate and nitrogen dilution is explored. In this diagram, two main boundaries are identified. These boundaries separate the stability diagram into three regions: sooting flame, non-sooting flame, and extinction. Two distinct extinction mechanisms are noted. For low fuel injection rates, flame extinction is caused by heat loss to the burner surface. For relatively high injection rates, at which the heat loss to burner surface is negligible, flame radiative heat loss is the dominant extinction mechanism. There also exists a critical inert dilution level beyond which the flame cannot be sustained. The existence of multi-dimensional flame phenomena near the extinction limits is also identified. Various multi-dimensional flame patterns are observed, and their evolutions are studied using direct chemiluminescence and OH-PLIF imaging. The results demonstrate the usefulness of the present burner configuration for the study of low-stretch gaseous diffusion flames.

Important aspects in source PM 2.5 emissions measurement and characterization from stationary combustion systems

During the construction and evaluation of a sampler for measurement and characterization fine particulate matter (PM) emissions from stationary combustion equipment, several technical challenges were noted. The sampler design incorporated dilution, cooling and moisture addition to the stack gas inside an inert dilution tunnel to closely simulate near-ambient conditions to promote atmospheric transformation of source particles. The automated and on-line process control capabilities of the system allows for simulation of a range of ambient-like humidity and temperature conditions for PM sampling, while providing reproducible particulate mass emission results. Subsequent analyses of the size segregated PM 2.5, PM 10 and total particulate samples yield concentrations of particle mass, carbons, acidic species and trace elements. The first-generation sampling system was applied on a 150-kW oil-fired boiler and a 0.7-MW th coal-fired pilot scale boiler to provide source PM characteristic profiles. Challenges noted during the initial studies included (a) difficulty in achieving optimum dilution and residence time while sustaining isokinetic sampling for high flue gas velocities; (b) inaccuracies in measurement and control of sampling system flow rates to maintain a balanced flow system; and (c) particle depositions in several system components. A second-generation system was later constructed that provided a higher dilution up to 80-fold and the extended residence times up to 80 s. Reliable measurement and control of the gas flow rates were achieved using a CO 2 tracer technique. Samplings from the combustion units with stack velocities ranging from 3 to 10 m/s were successfully performed. For PM measurement on boilers with a stack velocity higher than 10 m/s, a flue pre-separator or splitter is required. The sampler’s overall design is being further modified for additional improvements including a suitable splitter design. This paper focuses primarily on the technical issues relating to source PM sampling equipment, while initial PM 2.5 mass emission results from the combustion of a No. 4 fuel oil are reported simply to illustrate its capabilities.

Catalyst performance testing: the influence of catalyst bed dilution on the conversion observed

A study was performed to investigate the influence of inert dilution on the conversion in a gas–solid laboratory micro-reactor for an irreversible reaction, viz. the catalyzed N 2O decomposition over two different catalysts: FeZSM-5 and Co-La, Al mixed oxide (denoted as Co-La Al-ox). Vertically and horizontally segregated beds, as well as mixed beds with different degrees of dilution were considered. The results showed that catalyst dilution should be applied with caution since it may significantly influence the conversion and lead to an erroneous interpretation of data from catalyst activity measurements and kinetic studies. If the catalyst and the diluting particles are not well-mixed, the conversion reduces significantly due to bypassing and axial dispersion. Also apparent activation energies are reduced. The effects are stronger at high conversion levels (>0.4). Also over beds in which the catalyst and the diluent are perfectly mixed the conversion may be negatively affected by the dilution. It was found that the relative deviation in conversion caused by the dilution can be well estimated from observable parameters, i.e. the observed conversion, the volume fraction of bed dilution, the bed height, and the particle diameter. The relative deviation is approximately proportional to the reaction order. The combination of a high degree of dilution and high conversion should be avoided in catalyst activity measurements.

Effect of bed materials and additives on the sintering of coal ashes relevant to agglomeration in fluidized bed combustion

Agglomeration propensity of Thai low-rank coal ashes was determined by measuring the compressive strength of sintered ash pellets over the temperature range of fluidized bed combustion. Physical and chemical changes of the sintered products were ascertained from scanning electron microscope-energy dispersive X-ray detection (SEM-EDX) and X-ray diffractometry (XRD). A clear difference existed in the strength–temperature relationship between these ashes. This difference was attributed to the role and relative amounts of clays and anhydrite components that form the low temperature melting eutectics. The bed materials (sand, CaO, CaCO 3, and CaSO 4) and additives (gibbsite and andalusite) when combined with the ashes caused a strength reduction due to the inert dilution effect that prevented the interaction of anhydrite and clays. To comprehend the mechanism of sintering and bed agglomeration more clearly, modified ashes which produced extra amount of amorphous silicate materials were prepared and tested. The bed materials and additives, when sintered with these modified ashes, gave reduction of pellet strength by varying extents based on three possible mechanisms namely, a pure inert effect, an inert/reaction effect and an inert/adsorption effect, with gibbsite being the most effective. Of the four test ashes, Lanna ash was the only ash that exhibited almost no strength development under all conditions, due principally to its very low clays content and relatively stable forms of mineralogical compositions.

Ignition of ethane, propane, and butane in counterflow jets of cold fuel versus hot air under variable pressures

This study investigates experimentally the nonpremixed ignition of ethane, propane, n-butane, and isobutane in a configuration of opposed fuel versus heated air jets. For each of these fuels we explore the effects of inert dilution, system pressure, and flow strain rate, for fuel concentrations ranging between 3–100% by volume, pressures between 0.2 and 8 atm, and strain rates of 100–600 s −1. Qualitatively, these fuels share a number of characteristics. First, flame ignition typically occurs after an interval of mild oxidation, characterized by minimal heat release, fuel conversion, and weak light emission. The temperature extent of this regime decreases with increasing the fuel concentration, the ambient pressure, or the flow residence time. Second, the response to strain rate, pressure, and fuel concentration is similar for all investigated fuels, in that the ignition temperatures monotonically decrease with increasing fuel content, decreasing flow strain, and increasing ambient pressure. The C 4 alkanes, however, exhibit three distinct p-T ignition regimes, similar to the homogeneous explosion limits. Finally, at 1 atm, 100% fuel, and a fixed flow strain rate the ignition temperature increases in the order of ethane < propane < n-butane < i-butane. Numerical simulation was conducted for ethane ignition using detailed reaction kinetics and transport descriptions. The modeling results suggest that ignition for all fuels studied at pressures below 5 atm is initiated by fuel oxidation following the high-temperature mechanism of radical chain branching and with little contribution by low-to-intermediate temperature chemistry.

Combustion synthesis of multiphase powders in the SiCN system

The authors present the results of investigations on combustion synthesis (SHS) in the SiCN system in order to prepare composite Si 3N 4SiC powders. A new approach by a realisation of self-sustaining combustion in the SiCN system without an inert dilution is reported. This makes possible the preparation of a full range of carbide-nitride composite powders, including pure SiC and Si 3N 4 powders. An analysis of the SHS process in the SiCN system is based on temperature profiles of a propagated heat wave. The temperature phenomena are correlated with the product phase composition, specific surface area and morphology. The simultaneous reactions occurring during SHS are identified, namely: nitridation of silicon, direct reaction between silicon and carbon and carbothermal reduction of silicon nitride. A complex mechanism of SHS in the SiCN system is next discussed.

Combustion synthesis of multiphase powders in the Si-C-N system

The authors present the results of investigations on combustion synthesis (SHS) in the SiCN system in order to prepare composite Si3N4SiC powders. A new approach by a realisation of self-sustaining combustion in the SiCN system without an inert dilution is reported. This makes possible the preparation of a full range of carbide-nitride composite powders, including pure SiC and Si3N4 powders. An analysis of the SHS process in the SiCN system is based on temperature profiles of a propagated heat wave. The temperature phenomena are correlated with the product phase composition, specific surface area and morphology. The simultaneous reactions occurring during SHS are identified, namely: nitridation of silicon, direct reaction between silicon and carbon and carbothermal reduction of silicon nitride. A complex mechanism of SHS in the SiCN system is next discussed.

Laminar premixed flame extinction limits. I. Combined effects of stretch and upstream heat loss in the twin-flame unburnt-to-unburnt opposed flow configuration

Numerical methods have been used to examine the combined effects of stretch and localized upstream heat loss on the properties of a stoichiometric laminar premixed methane-air flame. A symmetric unburnt-to-unburnt opposed flow configuration was investigated, in which fresh combustible premixture was discharged towards the stagnation plane from identical coaxial plug flow nozzles maintained at constant temperature, and separated by a fixed distance. A continuation method was used in tandem with Newton solutions for individual flame structures, in order to study the flame behaviour as the stretch rate (or nozzle inlet velocity) was varied. High- and low-stretch extinction limits were observed as positions of vertical tangency on the steady-state solution curves of flame property versus stretch rate. The complete series of solutions between these positions formed a set of isolae with both stable and unstable branches. The chemical behaviour at the limits and along both branches is discussed, with particular emphasis on the behaviour near the low-temperature low-stretch-rate limit. The importance of changes not only in the size of the radical pool, but also in the ratio of hydrocarbon (CH 3 ) to non-hydrocarbon (H, O and OH) species therein, is demonstrated both near the limits and along the unstable solution branch. Attention is drawn to the significance of the conclusions in the context of flame extinguishment. The presentation and discussion of the flame behaviour is preceded by a full description of the computational approach.

A New Expression for Velocity of the Combustion Front during Self-Propagating High-Temperature Synthesis

Abstract The method of self-propagating high-temperature synthesis (SHS) can be utilized to produce a variety of advanced materials. After ignition, due to high exothermicity of the reactions involved, the process is characterized by a combustion wave which propagates through the reacting mixture in a self-sustained manner without requiring additional heat. By assuming that the reaction rate is proportional to the instantaneous surface area of the nonmelting component and to the instantaneous concentration of the melting reactant in the formed outlying melt, a new analytical expression for the velocity of the combustion front is developed. This expression accounts for the influence of temperature, particle size, reactant proportions and inert dilution. Experimental data for front propagation velocity for the titanium-carbon reaction available in the literature are described with good accuracy by the expression developed in this work.

Thermal Properties and Flammability of Chlorine-Containing Substances

Abstract Thermal analysis of chlorine-containing substances obtained from C13–C14 n-paraffins (chlorine content is 8–75 wt%) and olygoolefines with MM ≈ 104 (to 30 wt% Cl) is made. It is found that the kinetics and mechanism of the substances' gasification depend on their chlorine content and the nature of the original hydrocarbon. A method for the evaluation of flammability parameters of the substances used as flame retardants is developed. The increase of the limiting oxygen index of the substances with increasing chlorine content and hydrocarbon chain length may be described in accordance with the heat model as a result of the inert dilution of the gaseous fuel by the incombustible component. However, in addition to the change in the stoichiometric combustion coefficient, the additional heat losses related to the formation, evaporation and also the heating of HCl to flame temperature must be taken into account. It is found that the additional heat losses are equal to about 2.5 kJ per chlorine mass frac...

Inert dilution method for geological prospecting of nickeliferous laterite

The limitations of the conventional methods of x-ray fluorescence spectroscopy to meet with the demand for rapid determination of nickel and cobalt in nickeliferous laterite samples for geological prospecting have been described. The suitability of the inert dilution method has been tested. A comparison of the results obtained by this method with those of the wet chemical method indicates that this method can successfully be adopted for the estimation of nickel and cobalt in nickeliferous laterite samples.

Relation between the inhibition of the laminar diffusion flame of polymers, soot formation, and radiation

This article investigates the action of effective combustion inhibitors of premixed C/sub 2/F/sub 4/Br/sub 2/ and CC1/sub 4/ mixtures on the flame propagation rate over a polymer surface in an oxidizer counterflow. The cellulose-based polymers (paper, methyl cellulose, cellophane) examined included specimens in the form of films in a frame, polymethyl methacrylate (PMMA), polystyrene in the form of plates 4 mm thick and 20 mm wide on an asbestos substrate, and STD (a copolymer of formaldehyde with trioxane) in the form of cylindrical 10-mm-diameter specimens. The flame propagation rate is related to the total heat flux, which includes the conductive or convective flux and radiation on the polymer surface. It is concluded that when considering the inhibition of diffusion flames it is necessary to take account of the possible effect associated with the change in flame luminance, and not only the chemical effects of the inert dilution of the flame by the inhibitors.

Pentafluorophenylcompounds of polyvalent iodine

Abstract The oxidation of C 6 F 5 I by oxidizers containing positive chlorine was investigated with the intention to prepare pentafluorophenyliodine (III) compounds: C 6 F 5 IX 2 , where X are halides or oxoderivatives. Using ClF, ClOCF 3 , Cl 2 /AlCl 3 or Cl 2 O as oxidizers C 6 F 5 IF 2 , C 6 F 5 I Cl 2 and C 6 F 5 I (OCl) 2 - all thermally unstable - could be prepared and characterized. In contrast to these compounds the perfluoroaromatic carboxylates: C 6 F 5 I [O(O)C R F ] 2 are crystalline solids thermally stable up to 200 °C. Single crystal investigations show T-coordinated iodine with significant secondary bonding between iodine and the keto oxygens. C 6 F 5 IO-formed by hydrolysis of C 6 F 5 IX 2 - changes if stored at RT forming (C 6 F 5 ) 2 I IO 3 . (C 6 F 5 ) 2 I + - formation is also observed when C 6 F 5 IO is heated in inert (C 6 F 5 I, C 6 H 6 , CCl 4 …), protic (H 2 O, CH 3 OH, …) and strong acidic (FSO 3 H …) dilution medium. C 6 F 5 IO reacts with acids, acid anhydrides and acid halides as could be shown by the preparation of C 6 F 5 ICl 2 and C 6 F 5 ICl (NO 3 ). Starting with C 6 F 5 IX 2 different preparative ways for (C 6 F 5 ) 2 I + - compounds were successful. Principly (C 6 F 5 ) 2 IX - compounds decompose thermally forming C 6 F 5 I + C 6 F 5 X. C 6 F 5 IX 4 - compounds can be obtained from C 6 F 5 IF 4 which is the specific displacement product of IF 5 with Si (C 6 F 5 ) 4 . By nucleophilic displacement it is possible to prepare C 6 F 5 IF 2 O, C 6 F 5 IO 2 , C 6 F 5 IO (OAc F ) 2 and C 6 F 5 I [OC(CH 3 ) 2  C(CH 3 ) 2 O] 2 ,wich are all white, thermally stable solids. For the fluorine-ligand-exchange we used silycompounds as reagents. If the ligand is oxidable by C 6 F 5 I(V) a stepwise reduction via C 6 F 5 I(III) to C 6 F 5 I could be shown by NMR-measurements.

Enhancement of gas—solid chromatographic column performance by inert solid dilution

Column packings comprising an active solid sorbent diluted with an appropriately chosen inert, diluent solid have extremely desirable chromatographic characteristics. Theoretical plate heights can be substantially reduced in gas—solid chromatography (GSC) and at least maintained in gas—solid—liquid chromatography (GSLC) or high-performance liquid chromatography. Of greater importance, total analysis times can be reduced to any desired extent without loss of efficiency, and often with gain. Reduced analysis time can be traded-off for operation at lower temperature, a valuable option where samples are thermally labile or subject to catalytic reaction. Examples of difficult C 1C 4 aliphatic hydrocarbon analyses, both by GSC and GSLC, are given and it is concluded that the inert dilution technique provides a viable route to the extension of these modes of chromatography to a wider range of sample types than is currently common.

Distribution of fluoride and a dilution indicator ( 51 Cr-EDTA) in bacterial suspensions.

abstract – Three strains of oral streptococci were grown in dextrose broth, washed, and re‐suspended in saline (1.0 ml) containing 0.6 and 5.7 parts/106 fluoride. The final suspensions also contained an inert dilution indicator (51Cr‐EDTA). This water‐soluble, non‐absorbable compound was added to compare its distribution with that of fluoride. The concentrations of fluoride and 51Cr‐EDTA were determined in the supernatants of the bacterial suspensions. A linear relationship was noted between the volume of the bacteria and the increase in concentration of 51Cr‐EDTA. The fluoride concentrations were independent of the amount of bacteria, indicating that the bacteria were permeable to fluoride. The recovery of fluoride from the supernatants and the water used for washing of the bacteria amounted to 97 ± 2%. The fluoride which was demonstrated in washed and dried bacteria seemed to be due to an incomplete washing. Neither direct nor indirect fluoride determinations indicated that fluoride was concentrated in the bacteria.

Determination of silica in silicate materials by an X-ray fluorescence (standardised inert dilution) method

An X-ray fluorescence standardised inert dilution method has been developed for the determination of silica in quartz-sand, glass and cementclinker samples.By using the fused sample technique, the method can be applied satisfactorily (standard deviation 0·7 per cent.) to the rapid routine determination of silica.The results for determinations of silica in quartz sand are compared with those obtained by four different chemical methods.

Standardized inert dilution method in x-ray fluorescence analysis

Standardized inert dilution method in x-ray fluorescence analysis

X-Ray Spectrographic Analysis of Automotive Combustion Deposits Without the Use of Calibration Curves

AbstractArt X-ray spectrographic technique requiring no calibration curves is used to determine chlorine, bromine, and lead in automotive combustion deposits. Other elements, such as zinc and barium, can probably be determined by the same X-ray technique. The inert dilution method, described by Sherman in 1957, is employed. Improvements in sample preparation have been made to make the procedure more reliable. Results are calculated by the use of a formula, which is shown to be valid even though sample and standard have composition differences which cause interelement-effect errors if calibration-curve techniques are used. Adequate agreement is obtained between the inert dilution X-ray method and chemical procedures.