Laminar burning velocities and transition to unstable flames in H2/O2/N2 and C3H8/O2/N2 mixtures

Effects of positive flame stretch on laminar burning velocities, and conditions for transition to unstable flames, were studied experimentally for freely propagating spherical flames at both stable and unstable preferential-diffusion conditions. The data base involved new measurements for H₂/O₂/N₂ mixtures at values of flame stretch up to 7600 s⁻¹, and existing measurements for C₃H₈/O₂/N₂ mixtures at values of flame stretch up to 900 s⁻¹. Laminar burning velocities varied linearly with increasing Karlovitz numbers—either decreasing or increasing at stable or unstable preferential-diffusion conditions—yielding Markstein numbers that primarily varied with the fuel-equivalence ratio. Neutral preferential-diffusion conditions, however, were shifted toward the unstable side of the maximum laminar burning velocity condition that the simplest preferential-diffusion theories associate with neutral stability. All flames exhibited transition to unstable flames: unstable preferential-diffusion coditions yielded early transition to irregular flame surfaces, and stable preferential-diffusion conditions yielded delayed transition to cellular flames by hydrodynamic instability. Conditions for hydrodynamic instability transitions for H₂/O₂/N₂ mixtures were consistent with an earlier correlation due to Groff for propane/air flames, based on the predictions of Istratov and Librovich.     

Synthesis and electrochemical studies of the 4 V cathode, Li(Ni2/3Mn1/3)O2

Layered Li(Ni_2/3Mn_1/3)O₂ compounds are prepared by freeze-drying, mixed carbonate and molten salt methods at high temperature. The phases are characterized by X-ray diffraction, Rietveld refinement, and other methods. Electrochemical properties are studied versus Li-metal by charge–discharge cycling and cyclic voltammetry (CV). The compound prepared by the carbonate route shows a stable capacity of 145 (±3) mAh g⁻¹ up to 100 cycles in the range 2.5–4.3 V at 22 mA g⁻¹. In the range 2.5–4.4 V at 22 mA g⁻¹, the compound prepared by molten salt method has a stable capacity of 135 (±3) mAh g⁻¹ up to 50 cycles and retains 96% of this value after 100 cycles. Capacity-fading is observed in all the compounds when cycled in the range 2.5–4.5 V. All the compounds display a clear redox process at 3.65–4.0 V that corresponds to the Ni^2+/3+–Ni^3+/4+ couple.     

Energy efficient simultaneous oxidative conversion and thermal cracking of ethane to ethylene using supported BaO/La2O3 catalyst in the presence of limited O2

An energy efficient conversion of ethane to ethylene involving simultaneous oxidative conversion (which is exothermic) and thermal cracking (which is endothermic) reactions of ethane in the presence of steam (steam/C₂H₆ mol RATIO=1.0) and limited O₂ (C₂H₆/O₂ mol ratio 4.0) over a BaO-promoted La₂O₃ supported on low surface area macroporous silica-alumina commercial catalyst carrier has been thoroughly investigated. Influence of various process parameters such as temperature (700–850°C), C₂H₆/O₂ feed ratio (4.0–8.0) and space velocity (50,000–200,000 cm³ g⁻¹ h⁻¹) on the conversion, product selectivity and net heat of reactions in the process has also been studied. At all the process conditions, there was no coke deposition on the catalyst. High selectivity ( 85%) for C₂₊ olefins (at 50–60% conversion) can be obtained in the process at a low contact time (<10 ms), particularly for the higher C₂H₆/O₂ ratios ( 6.0) and temperatures ( 800°C). The process exothermicity is decreased appreciably with increasing the temperature and/ or the C₂H₆/O₂ ratio. The net heat of reaction in the process can be controlled by manipulating the C₂H₆/O₂ ratio and reaction temperature. Also, because of simultaneously occurring endothermic and exothermic reactions, the process is highly energy efficient and non-hazardous.     

Kinetic study on fermentation from CO2 and H2 using the acclimated-methanogen in batch culture

Methane was produced from H₂ and CO₂ using the acclimated-mixed methanogens in a 3.71 fermentor in batch culture at pH 7.2 and 37°C. The Fermentation kinetics parameter for the growth of methanogens, overall mass transfer coefficient of the reactor, and the conversion rate of H₂ and CO₂ to CH₄ by the acclimated-mixed culture were determined using the technique of Vega et al. The maximum specific growth rate (μ_max) and H₂ specific consumption rate (q_max) were found to be 0.064(h⁻¹) and 104.8 (mmol h⁻¹ g⁻¹) respectively. Monod saturation constants for growth (Kp) and for inhibition (K′p) were found to be 3.54 (kPa) and 0.57 (kPa), respectively. These findings indicate that without very low dissolved H₂ levels, the fermentations are carried out under μ_max, and the specific uptake rate (q) was almost not affected at any dissolved H₂ level in the range studied. The yield of CH₄ (Yp/s) was calculated to be 0.245 (mol CH₄ mol⁻¹ H₂), which is near the stoichiometric value of 0.25. DH₂ was also measured using the Teflon tubing method and was in good agreement with those estimated by kinetic calculations.     

Environmental assessment and extended exergy analysis of a “zero CO2 emission”, high-efficiency steam power plant

Aim of this paper is to analyze the performance of an innovative high-efficiency steam power plant by means of two “life cycle approach” methodologies, the life cycle assessment (LCA) and the “extended exergy analysis” (EEA).

The plant object of the analysis is a hydrogen-fed steam power plant in which the H₂ is produced by a “zero CO₂ emission” coal gasification process (the ZECOTECH^© cycle). The CO₂ capture system is a standard humid-CaO absorbing process and produces CaCO₃ as a by-product, which is then regenerated to CaO releasing the CO₂ for a downstream mineral sequestration process.

The steam power plant is based on an innovative combined-cycle process: the hydrogen is used as a fuel to produce high-temperature, medium-pressure steam that powers the steam turbine in the topping section, whose exhaust is used in a heat recovery boiler to feed a traditional steam power plant.

The environmental performance of the ZECOTECH^© cycle is assessed by comparison with four different processes: power plant fed by H₂ from natural gas steam reforming, two conventional coal- and natural gas power plants and a wind power plant.     

Modeling of single coal particle combustion in O2/N2 and O2/CO2 atmospheres under fluidized bed condition

A one-dimensional transient single coal particle combustion model was proposed to investigate the characteristics of single coal particle combustion in both O₂/N₂ and O₂/CO₂ atmospheres under the fluidized bed combustion condition. The model accounted for the fuel devolatilization, moisture evaporation, heterogeneous reaction as well as homogeneous reactions integrated with the heat and mass transfer from the fluidized bed environment to the coal particle. This model was validated by comparing the model prediction with the experimental results in the literature, and a satisfactory agreement between modeling and experiments proved the reliability of the model. The modeling results demonstrated that the carbon conversion rate of a single coal particle (diameter 6 to 8 mm) under fluidized bed conditions (bed temperature 1088 K) in an O₂/CO₂ (30:70) atmosphere was promoted by the gasification reaction, which was considerably greater than that in the O₂/N₂ (30:70) atmosphere. In addition, the surface and center temperatures of the particle evolved similarly, no matter it is under the O₂/N₂ condition or the O₂/CO₂ condition. A further analysis indicated that similar trends of the temperature evolution under different atmospheres were caused by the fact that the strong heat transfer under the fluidized bed condition overwhelmingly dominated the temperature evolution rather than the heat release of the chemical reaction.     

The ignition of oxetane in shock waves and oxidation in a jet-stirred reactor: An experimental and kinetic modeling study

The ignition and oxidation of oxetane have been studied in a single-pulse shock tube under reflected shock wave conditions and also in a jet-stirred reactor (JSR). These experiments cover a wide range of conditions: 1–10 atm, 0.5 ≤ φ ≤ 2.0, 800–1780 K. The ignition delays of oxetane measured in a shock tube have been used to propose an overall dependence of ignition delay time on the concentrations of each component in the gas as: τ = 10^−13.5 exp(13389/T₅)[C₃H₆O]^−0.36[O₂]^−0.59[Ar]^0.088 (units: seconds, moles per cubic decimeters, and Kelvin). Concentration profiles of the reactants, intermediates, and products of the oxidation of oxetane were measured in a JSR. A numerical model, consisting of a detailed kinetic reaction mechanism with 423 reactions (most of them reversible) of 63 species describes the ignition of oxetane in reflected shock waves and its oxidation in a jet-stirred reactor. Fairly good agreement between the observations and the model was obtained. The major reaction paths have been identified through detailed kinetic modeling.     

Selective removal of CO from hydrogen-rich stream over CuO/CexSn1−xO2–Al2O3 catalysts

The solid solutions of Ce_xSn_1−xO₂ incorporated with alumina to form Ce_xSn_1−xO₂–Al₂O₃ mixed oxides, by the suspension/co-precipitation method, were used to prepare CuO/Ce_xSn_1−xO₂–Al₂O₃ catalysts for the selective oxidation of CO in excess hydrogen. Incorporating Al₂O₃ increased the dispersion of Ce_xSn_1−xO₂, but did not change their main structures and did not weaken their redox properties. Doping Sn⁴⁺ into CeO₂ increased the mobility of lattice oxygen and enhanced the activity of the 7%CuO/Ce_xSn_1−xO₂–Al₂O₃ catalyst in the selective oxidation of CO. The selective oxidation of CO was weakened as the doped fraction of Sn⁴⁺ exceeded 0.5. Incorporating appropriate amounts of Sn⁴⁺ and Al₂O₃ could obtain good candidates 7%CuO/Ce_xSn_1−xO₂–Al₂O₃(20%), 1–x=0.1–0.5, for a preferential oxidation (PROX) unit in a polymer electrolyte membrane fuel cell system for removing CO. Its activity was comparable with, and its selectivity was much larger than, that of the noble catalyst 5%Pt/Al₂O₃.     

Characterization of Cu(InxGa1−x)2Se3.5 thin films prepared by rf sputtering

Cu(In_xGa_1−x)₂Se_3.5 thin films were fabricated by rf sputtering from CuIn_xGa_1−xSe₂ and Na mixture target by controlling the mixture ratio. X-ray diffraction analyses show that the structure of Cu(In_xGa_1−x)₂Se_3.5, thin films is different from chalcopyrite structure: especially, CuIn₂Se_3.5 thin films have a defect chalcopyrite structure. The lattice parameters for Cu(In_xGa_1−x)₂Se_3.5 thin film are slightly smaller than those for CuIn_xGa_1−xSe₂ thin film and linearly decreased with increasing Ga content. The optical absorption coefficients for Cu(In_xGa_1−x)₂Se_3.5, thin films exceed 2 × 10⁴ cm⁻¹ in energy region above the fundamental band edge. The band gap for Cu(In_xGa_1−x)₂Se_3.5 thin films is larger than that for CuIn.Ga_1−x2Se₂ with the same Ga content and increased with increasing Ga content.     

Factors regulating nitrogenase activity and hydrogen evolution in Azolla-anabaena symbiosis

Nitrogenase activity and H₂ production capacity have been studied in intact Azolla plants. Under aerobic conditions the plants showed a C₂H₂ reduction rate of 6.65 nmoles C₂H₄ mg⁻¹ fresh weight in light at 48h. Considerable activity was also present in the dark. Though H₂ evolution was detected under aerobic conditions there was multifold stimulation under anaerobic conditions. There was no significant change in nitrogenase activity under anaerobic conditions. Increasing concentrations of O₂ inhibited nitrogenase activity but 5% O₂ proved stimulatory for H₂ evolution in light. In the dark, there was a gradual stimulation in H₂ evolution even up to 20% O₂. Addition of combined nitrogen sources, namely NH₄Cl or KNO₃ (10 mM) resulted in complete inhibition of C₂H₂-reduction activity within 48 h, but H₂ evolution was not inhibited. Indeed these combined nitrogen sources stimulated H₂ evolution. Though nitrogenase activity was affected, the heterocyst frequency remained unaltered. Phosphate addition resulted in significant stimulation of nitrogenase and H₂ evolution activity. These results suggest that on nitrogenase and H₂ evolution activity in Azolla are affected by a number of factors which show a differential effect on nitrogenase and H₂ evolution. Furthermore, our results indicate the presence of a soluble reversible hydrogenase in Azolla.     

Additive effect of CF3Cl on OH, CH, and C2 emissions: Shock tube study with C2H4---O2---CF3Cl and CH4---O2---CF3Cl mixtures

Mixtures of C₂H₄---O₂---CF₃Cl and CH₄---O₂---CF₃Cl, highly diluted with argon, were heated to the temperature range 1350–2200K behind reflected shock waves, and the additive effects of CF₃Cl on OH^*, CH^*, and C₂^* emissions in the ethylene and methane combustion processes were examined by observing the delay time, and the intensities of OH^*, CH^*, and C₂^* emissions. It was found that, in ethylene combustion, the addition of CF₃Cl prolonged the delay times to the maximum intensities, decreased the intensities of OH^* and CH^* emissions, and had little influence on that of C₂^* emission. However, in methane combustion, it was found that the addition of CF₃Cl shortened the delay times to the maximum intensities and to the onset of ignition, increased the intensities of CH^* and C₂^* emissions, and had little influence on that of OH^* emission.     

Singlet methylene removal by saturated and unsaturated hydrocarbons

The technique of laser flash phyotolysis/laser absorption has been used to obtain absolute removal rate constants for singlet methylene, ¹CH₂ (ã¹A₁), with various saturated and unsaturated hydrocarbons. The removal rate constants for CH₄, C₂H₆, C₃H₈, C₂H₄, C₃H₆, C₂H₂, CH₂CCH₂, and C₆H₆ were found to be in excellent agreement with previously reported results. Removal rate constants were also measured for n-C₄H₁₀, i-C₄H₁₀, n-C₅H₁₂, c-C₃H₆, c-C₆H₁₂, 1-C₄H₈, cis-2-C₄H₈, trans-2-C₄H₈, and 1-C₄H₆, and determined to be (3.17 ± 0.15), (2.53 ± 0.11), (3.35 ± 0.24), (1.63 ± 0.08), (3.77 ± 0.21), (3.80 ± 0.20), (3.67 ± 0.16), (3.43 ± 0.16) and (4.05 ± 0.18) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, respectively. This series of hydrocarbons forms the basis of a larger series of compounds containing a wide variety of organic functional groups. The removal rate constants are reported here, both as a series within its own right, and as a reference point for future work.     

Ignition of CO/H2/N2 versus heated air in counterflow: experimental and modeling results

Nonpremixed ignition in counterflowing CO/H₂ vs. heated air jets is experimentally and computationally investigated. The experiments confirm the numerical modeling observation of the existence of three ignition regimes as a function of the hydrogen concentration. In all three regimes, we first detect experimentally the onset of chemiluminescent glow due to excited CO₂ followed by flame ignition, as the temperature of the air jet is raised gradually. The temperature extent of the glow regime, however, is progressively reduced with increasing hydrogen addition; no glow is detected for H₂ concentrations in excess of 73%. The temperatures for glow onset and flame ignition are represented by the boundary air temperatures for each threshold. The variation of these temperatures with system pressure and flow strain rate is explored, for pressures between 0.16 and 5 atm, and strain rates of 100 to 600 s⁻¹. The pressure variation is found to result in three p-T ignition limits, similar to the ignition limits observed in the H₂/O₂ system. This similarity is also observed on the effects of aerodynamic transport on ignition: within the second limit the ignition temperatures are found to be essentially insensitive to flow strain rate, whereas the other two limits are significantly affected by strain. The transport insensitivity is maintained even in the limit of very low H₂ concentrations, where an analogous H₂/N₂ mixture would fail to ignite. This behavior is explained computationally by the replacement of the shift reaction OH + H₂ → H₂O + H with the reaction CO + OH → CO₂ + H, thereby minimizing the effect of diminishing H₂ concentration. The experimental data are found to agree well with the calculated results, although discrepancies are noted in modeling the onset of chemiluminescence and its response to pressure variations.     

Structural and electrochromic properties of nanosized Fe/V-oxide films with FeVO4 and Fe2V4O13 grains: comparative studies with crystalline V2O5

Various mixed Fe/V-oxides can be used as anodes in Li⁺ rocking chair batteries, however, their small optical modulation during the insertion/extraction of Li⁺ ions makes them candidates for the counter electrodes in electrochromic (EC) devices. The sol–gel route in combination with dip-coating deposition was used for the preparation of Fe/V-oxide films with molar ratios Fe:V=0.1:1, 1:2, 1:1 and 2:1. X-ray diffraction combined with Fourier transform infrared (FT-IR) spectroscopy studies of films and powders reveal that heating of xerogel films at 400°C produces films with nanosized FeVO₄ (Fe:V=1:1) and Fe₂V₄O₁₃ (Fe:V=1:2) grains, while the corresponding crystalline powders were obtained at 500°C (8 h). Charge capacities (Q) of Fe/V-oxide films (300 and 400°C) were determined using cyclic voltammetry (CV) from 1.5 to −1.5 V vs. Ag/AgCl (4.8 to 1.8 V vs. Li) in 1 M LiClO₄/propylene carbonate (PC) electrolyte. Our results revealed that Q values of Fe/V-oxide films are up to 20 mC cm⁻² depending on the thickness (40–100 nm), temperature of heating and the Fe:V molar ratio (1:2, 1:1). During the first 300 cycles the cycling stability of the Fe-containing films is better than that of V₂O₅ crystalline films. UV-visible spectra of charged/discharged films revealed that these films, similar to V₂O₅ films, exhibit a mixed anodic/cathodic electrochromism. It was established that with regard to the colouring/bleaching changes of V₂O₅ crystalline films, the Fe/V-oxide films exhibit smaller cathodic colouring at wavelengths λ>600 nm and higher visible transmittance. IR spectroscopy of charged/discharged Fe/V-oxide films confirmed that the reduction of Fe³⁺ prevents the overreduction of V⁵⁺ to V³⁺, which takes place in V₂O₅ films cycled in the same potential range.     

Optimization of process parameters for preparation of powdered activated coke to achieve maximum SO2 adsorption using response surface methodology

Powdered activated coke (PAC) is a good adsorbent of SO₂, but its adsorption capacity is affected by many factors in the preparation process. To prepare the PAC with a high SO₂ adsorption capacity using JJ-coal under flue gas atmosphere, six parameters (oxygen-coal equivalent ratio, reaction temperature, reaction time, O₂ concentration, CO₂ concentration, and H₂O concentration) were screened and optimized using the response surface methodology (RSM). The results of factor screening experiment show that reaction temperature, O₂ concentration, and H₂O (g) concentration are the significant factors. Then, a quadratic polynomial regression model between the significant factors and SO₂ adsorption capacity was established using the central composite design (CCD). The model optimization results indicate that when reaction temperature is 904.74°C, O₂ concentration is 4.67%, H₂O concentration is 27.98%, the PAC (PAC-OP) prepared had a higher SO₂ adsorption capacity of 68.15 mg/g while its SO₂ adsorption capacity from a validation experiment is 68.82 mg/g, and the error with the optimal value is 0.98%. Compared to two typical commercial activated cokes (ACs), PAC-OP has relatively more developed pore structures, and its S_BET and V_tot are 349 m²/g and 0.1475 cm³/g, significantly higher than the 186 m²/g and 0.1041 cm³/g of AC1, and the 132 m²/g and 0.0768 cm³/g of AC2. Besides, it also has abundant oxygen-containing functional groups, its surface O content being 12.09%, higher than the 10.42% of AC1 and 10.49% of AC2. Inevitably, the SO₂ adsorption capacity of PAC-OP is also significantly higher than that of both AC1 and AC2, which is 68.82 mg/g versus 32.53 mg/g and 24.79 mg/g, respectively.     

The oxidation of benzene under conditions encountered in waste incinerators

The oxidation of benzene was studied as a function of residence time (τ_res=0–2.5 s), temperature (850–960 K), and oxygen concentration (O₂=0.2–2.3%) in a heated laminar flow reactor at atmospheric pressure. Nitrogen, doped with 350 ppm benzene, was injected downstream of the burned gas from a near stoichiometric flame of methane + air. Gas samples were taken at different heights up the reactor and analyzed using GC-FID/TCD and HPLC techniques. Phenol and partially oxidized hydrocarbons such as acetaldehyde, formaldehyde, and acrolein were found with concentrations up to 50 ppm. At relatively low temperatures, the conversion of benzene was observed to proceed considerably more slowly at higher oxygen concentrations. Measured concentration profiles were modeled using detailed reaction schemes. A modified mechanism for the oxidation of benzene called BenWas was constructed from the mechanism of Zhang and McKinnon (Combust. Sci. Technol. 107 (1995) 261) by incorporating a submechanism for benzoquinone (OC₆H₄O) and by updating and enlarging the reaction scheme of cyclopentadiene (C₅H₆). The agreement between observed and predicted concentration profiles, e.g., of phenol (C₆H₅OH), acetylene (C₂H₂), and carbon monoxide (CO), was considerably improved by the use of the BenWas mechanism for rich and lean conditions, mainly due to the introduction of an additional pathway for phenyl oxidation (C₆H₅ + O₂ = OC₆H₄O + H) and due to the changed kinetics of the oxidation of cyclopentadienyl (C₅H₅) in C₅H₅ + O₂ = C₅H₄O + OH. The measured retardation of benzene oxidation with higher amounts of oxygen can be explained by the formation and reactions of peroxy radicals.     

Mechanism of soot initiation in methane systems

Thermochemical and kinetic evaluations of the very rapid elementary radical reactions consuming the C₂H₂ produced in a chlorine catalyzed polymerization of CH₄ are presented. An earlier examination of the data and mechanism leading to C₂H₂ supports a methyl and chloromethyl recombination path to C₂ hydrocarbons. The relative yield of CH₃ and CH₂Cl depends on the excess of methane.

In the CH₄, system consumption of C₂ species to ultimately form benzene is shown to proceed by a stepwise addition of CH₃ radicals to C_nH_m species. When n is even the dominant species is an unsaturated polyolefin molecule. When n is odd the dominant species is a conjugated, unsaturated radical such as allyl, pentadienyl, benzyl, etc. Mono-olefins or saturated molecules are rapidly stripped to these species by radical catalyzed dehydrogenations. In the current system chloromethyl radicals are equivalent kinetically to methyl and play a dominant role. Their addition to unsaturated species produces chlorinated radicals that dechlorinate rapidly or recombine with chloromethyl to produce dichlorohydrocarbons that dehydrochlorinate very rapidly.

A very important reaction in the sequence is the isomerization of propenyl and chloropropenyl radicals to allyl and chlorallyl by a 1–3 H (or Cl) atom shift. Its high pressure Arrhenius parameters at 1300 K are estimated to be log [k(sec⁻¹)] = 13.7 − 37/θ = 13.7 - 37/0 where 0 = 2.303 RT in kcal/mol. It appears likely that benzene conversion to soot also proceeds via a CH₃/CH₂Cl radical, sequential addition mechanism.

Stoichiometry considerations applied to the product yield distribution support the role of methyl and chloromethyl predicted by the proposed mechanism. Ionic pathways are shown to be insignificant in the formation of aromatics.     

A highly active catalyst, Ni/Ce–ZrO2/θ-Al2O3, for on-site H2 generation by steam methane reforming: pretreatment effect

The steam treatment effect has been investigated over the doubly impregnated catalyst, Ni/Ce–ZrO₂/θ-Al₂O₃, in steam methane reforming (SMR). The catalyst was remarkably deactivated by steam treatment but reversibly regenerated by H₂-reduction. XRD results showed that the steam treatment resulted in the formation of NiAl₂O₄ which is inactive for SMR but it was reversibly converted to Ni by the reduction. The reversible oxidation-reduction of Ni state was also evidenced by XPS and it was observed that the formation of NiAl₂O₄ is more favorable at higher temperature. It is most likely that the alumina support is only partially covered with Ce–ZrO₂ and most Ni directly interacts with θ-Al₂O₃ which would probably make easy formation of NiAl₂O₄ in the presence of steam alone. The results imply that, during the start-up procedure in SMR, too high concentration of steam could deactivate seriously Al₂O₃ supported Ni catalysts.     

The origin of soot in flames: is the nucleus an ion?

There are two schools of thought on how soot originates in a fuel-rich flame. On the one hand, the ionic theory postulates that small ions, such as C₃H₃⁺, act as nuclei, so that species such as C₂H₂ and C₄H₂ add on to them, and occasionally liberate H₂ in a repetitive growth process. Once these ions become large (≈2000 a.m.u.) they supposedly dissociate and produce an uncharged, but large, hydrocarbon “molecule,” which can grow, coalesce or coagulate to give soot particles. Simultaneously this dissociation produces a very small ion, which repeats the process of adding on C₂, C₃, and C₄ species, etc. The other school of thought believes that fairly similar processes occur, but the species involved are not ions, but uncharged radicals and molecules. This present study has spectroscopically monitored the level of sooting in the earliest stages of its production in a premixed, oxyacetylene flame at 1 atm. If soot originates from ions such as C₃H₃⁺, the addition of a relatively large quantity of easily ionized cesium removes C₃H₃⁺ ions from the flame. In that case there should also be less soot produced. When either distilled water or a strong aqueous solution of CsCl was nebulized into the sooting flame, the intensity of the emission fell by the same amount. This was by only 1% in the earliest part of the burned gas, but rose to a larger drop farther downstream of the reaction zone. Thus cesium itself has no effect on the sooting level early in this premixed flame, indicating that there is no evidence here for ions acting as nuclei for soot. However, the addition of water alone does inhibit the production of soot.     

High temperature rate coefficient for the reaction of O(P) with H2 obtained by the resonance absorption of O and H atoms

The reaction of O(³P) with H₂ has been studied behind reflected shock waves in the temperature range of 1713–3532K at total pressures of about 1.4–2.0 bar by Atomic Resonance Absorption Spectroscopy using mixtures of N₂O and H₂ highly diluted in Ar. The O atoms were generated by the fast thermal decomposition of N₂O and the reaction with H₂ was followed by monitoring the time dependent O and H atom concentrations in the postshock reaction zone. For the experimental conditions chosen, the measured O and H atom concentrations were primarily sensitive to the well-known N₂O dissociation and to the studied reaction and hence its rate coefficient could be deduced. The measured rate coefficient data are fitted by the least-squares method to obtain the following three parameter expression: K₄=3.72×10⁶(T/K)^2.17exp(−4080K/T)cm³ mol⁻¹8⁻, which is in excellent agreement with the recent ab initio calculations for the rate coefficient of this reaction in the overlapping temperature range. The present result is also compared to the experimental results reported by earlier investigators.