Soot Measurements in Steady and Pulsed Ethylene/Air Diffusion Flames Using Laser-Induced Incandescence

Combustion-generated carbon black nano particles, or soot, have both positive and negative effects depending on the application. From a positive point of view, it is used as a reinforcing agent in tires, black pigment in inks, and surface coatings. From a negative point of view, it affects performance and durability of many combustion systems, it is a major contributor of global warming, and it is linked to respiratory illness and cancer. Laser-Induced Incandescence (LII) was used in this study to measure soot volume fractions in four steady and twenty-eight pulsed ethylene diffusion flames burning at atmospheric pressure. A laminar coflow diffusion burner combined with a very-high-speed solenoid valve and control circuit provided unsteady flows by forcing the fuel flow with frequencies between 10 Hz and 200 Hz. Periodic flame oscillations were captured by two-dimensional phase-locked LII images and broadband luminosity images for eight phases (0°- 360°) covering each period. A comparison between the steady and pulsed flames and the effect of the pulsation frequency on soot volume fraction in the flame region and the post flame region are presented. The most significant effect of pulsing frequency was observed at 10 Hz. At this frequency, the flame with the lowest mean flow rate had 1.77 times enhancement in peak soot volume fraction and 1.2 times enhancement in total soot volume fraction; whereas the flame with the highest mean flow rate had no significant change in the peak soot volume fraction and 1.4 times reduction in the total soot volume fraction. A correlation (ƒv Reˉ1 = a+b· Str) for the total soot volume fraction in the flame region for the unsteady laminar ethylene flames was obtained for the pulsation frequency between 10 Hz and 200 Hz, and the Reynolds number between 37 and 55. The soot primary particle size in steady and unsteady flames was measured using the Time-Resolved Laser-Induced Incandescence (TIRE-LII) and the double-exponential fit method. At maximum frequency (200 Hz), the soot particles were smaller in size by 15% compared to the steady case in the flame with the highest mean flow rate.

Tribology of ethylene-air diffusion flame soot under dry and lubricated contact conditions

Soot particles are generated in a flame caused by burning ethylene gas. The particles are collected thermophoretically at different locations of the flame. The particles are used to lubricate a steel/steel ball on flat reciprocating sliding contact, as a dry solid lubricant and also as suspended in hexadecane. Reciprocating contact is shown to establish a protective and low friction tribo-film. The friction correlates with the level of graphitic order of the soot, which is highest in the soot extracted from the mid-flame region and is low in the soot extracted from the flame root and flame tip regions. Micro-Raman spectroscopy of the tribo-film shows that the a priori graphitic order, the molecular carbon content of the soot and the graphitization of the film as brought about by tribology distinguish between the frictions of soot extracted from different regions of the flame, and differentiate the friction associated with dry tribology from that recorded under lubricated tribology.

Cross linked Poly (4-Vinylpyridine-Ethylene Glycol Dimethacrylate) Used for Preconcentration of Cd(II) and its Determination by Flow Injection Flame Atomic Absorption Spectrometry

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Thermal decomposition of ethylene diamine diperchlorate

Thermal decomposition of ethylene diamine diperchlorate (EDDP) has been studied by differential-thermal analysis (DTA), thermogravimetric analysis (TGA), isothermal weight-loss measurements and mass-spectrometric analysis of the decomposition products. It has been observed that EDDP decomposes in two temperature regions. The low-temperature decomposition stops at about 35 to 40 percent weight loss below 250°C. The reason for the low-temperature cessation may be the adsorption of excess ethylene diamine on the crystal surface of EDDP. An overall activation energy of 54 kcal per mole has been calculated for the thermal decomposition of EDDP. Mass-spectrometric analysis shows that the decomposition products are mainly CO2, H2O, HCl and N2. The following stoichiometry has been proposed for the thermal decomposition of EDDP: (−CH2NH3CIO4)2→2CO2O+2HCl+N2

Polyethylene stibinite phosphate esters: Novel flame-retardant plasticizers for PVC

A new series of multielement flame-retardant plasticizers containing polyethylene stibinite phosphate esters have been prepared by bulk polymerization from ethylene glycol with various antimony (III) aryloxydichlorides and arylphosphorodichloridates possessing various combinations of substituent [Cl,Br,NO2]. All the polymers are pink-coloured viscous fluids. They were characterized by inherent viscosity, density, IR, H-1, C-13 and P-31 NMR spectroscopy. The thermal behaviour of the polymers was compared by thermogravimetric analysis and correlated with their structures. The flammability studies were carried out by the limiting oxygen index test. The polymers containing P, Sb, N and Pr elements in their backbone show superior thermal-and flame-retardant characteristics than the other polymers. A comparative study was carried out with one of the synthesized polymers as a polymeric flame-retardant additive to plasticized PVC. The results showed improved LOI and mechanical properties to that of the conventional flame-retardant additive composition. (C) 1997 Elsevier Science Ltd.

Relationship Between Physical Structure and Tribology of Single Soot Particles Generated by Burning Ethylene

Ethylene gas is burnt and the soot generated is sampled thermophoretically at different heights along the flame axis starting from a region close to the root of the flame. The morphology and crystallinity of the particle are recorded using high resolution transmission electron microscopes. The hardness of a single particle is measured using a nanoindenter. The frictional resistance and material removal of a particle are measured using an atomic force microscope. The particles present in the mid-flame region are found to have a crystalline shell. The ones at the flame root are found to be highly disordered and the ones at the flame tip and above have randomly distributed pockets of short range order. The physical state of a particle is found to relate, but not very strongly, with the mechanical and tribological properties of the particles.

Dry tribology and nanomechanics of gaseous flame soot in comparison with carbon black and diesel soot

Ethylene gas is burnt and the carbon soot particles are thermophoretically collected using a home-built equipment where the fuel air injection and intervention into the 7.5-cm long flame are controlled using three small pneumatic cylinders and computer-driven controllers. The physical and mechanical properties and tribological performance of the collected soot are compared with those of carbon black and diesel soot. The crystalline structures of the nanometric particles generated in the flame, as revealed by high-resolution transmission electron studies, are shown to vary from the flame root to the exhaust. As the particle journeys upwards the flame, through a purely amorphous coagulated phase at the burner nozzle, it leads to a well-defined crystalline phase shell in the mid-flame zone and to a disordered phase consisting of randomly distributed short-range crystalline order at the exhaust. In the mid-flame region, a large shell of radial-columnar order surrounds a dense amorphous core. The hardness and wear resistance as well as friction coefficient of the soot extracted from this zone are low. The mechanical properties characteristics of this zone may be attributed to microcrystalline slip. Moving towards the exhaust, the slip is inhibited and there is an increase in hardness and friction compared to those in the mid-flame zone. This study of the comparison of flame soot to carbon black and diesel soot is further extended to suggest a rationale based on additional physico-chemical study using micro-Raman spectroscopy.

Scaling of turbulent flame speed for expanding flames with Markstein diffusion considerations

In this paper we clarify the role of Markstein diffusivity, which is the product of the planar laminar flame speed and the Markstein length, on the turbulent flame speed and its scaling, based on experimental measurements on constant-pressure expanding turbulent flames. Turbulent flame propagation data are presented for premixed flames of mixtures of hydrogen, methane, ethylene, n-butane, and dimethyl ether with air, in near-isotropic turbulence in a dual-chamber, fan-stirred vessel. For each individual fuel-air mixture presented in this work and the recently published iso-octane data from Leeds, normalized turbulent flame speed data of individual fuel-air mixtures approximately follow a Re-T,f(0.5) scaling, for which the average radius is the length scale and thermal diffusivity is the transport property of the turbulence Reynolds number. At a given Re-T,Re-f, it is experimentally observed that the normalized turbulent flame speed decreases with increasing Markstein number, which could be explained by considering Markstein diffusivity as the leading dissipation mechanism for the large wave number flame surface fluctuations. Consequently, by replacing thermal diffusivity with the Markstein diffusivity in the turbulence Reynolds number definition above, it is found that normalized turbulent flame speeds could be scaled by Re-T,M(0.5) irrespective of the fuel, equivalence ratio, pressure, and turbulence intensity for positive Markstein number flames.

Soot measurements in steady and pulsed ethylene/air diffusion flames using Laser-Induced Incandescence

Combustion-generated carbon black nano particles, or soot, have both positive and negative effects depending on the application. From a positive point of view, it is used as a reinforcing agent in tires, black pigment in inks, and surface coatings. From a negative point of view, it affects performance and durability of many combustion systems, it is a major contributor of global warming, and it is linked to respiratory illness and cancer. Laser-Induced Incandescence (LII) was used in this study to measure soot volume fractions in four steady and twenty-eight pulsed ethylene diffusion flames burning at atmospheric pressure. A laminar coflow diffusion burner combined with a very-high-speed solenoid valve and control circuit provided unsteady flows by forcing the fuel flow with frequencies between 10 Hz and 200 Hz. Periodic flame oscillations were captured by two-dimensional phase-locked LII images and broadband luminosity images for eight phases (0° – 360°) covering each period. A comparison between the steady and pulsed flames and the effect of the pulsation frequency on soot volume fraction in the flame region and the post flame region are presented. The most significant effect of pulsing frequency was observed at 10 Hz. At this frequency, the flame with the lowest mean flow rate had 1.77 times enhancement in peak soot volume fraction and 1.2 times enhancement in total soot volume fraction; whereas the flame with the highest mean flow rate had no significant change in the peak soot volume fraction and 1.4 times reduction in the total soot volume fraction. A correlation (fvRe-1 = a + b·Str) for the total soot volume fraction in the flame region for the unsteady laminar ethylene flames was obtained for the pulsation frequency between 10 Hz and 200 Hz, and the Reynolds number between 37 and 55. The soot primary particle size in steady and unsteady flames was measured using the Time-Resolved Laser-Induced Incandescence (TIRE-LII) and the double-exponential fit method. At maximum frequency (200 Hz), the soot particles were smaller in size by 15% compared to the steady case in the flame with the highest mean flow rate.

Solid-state nanocrystalline dye-sensitized solar cell using 2-mercapto benzimidazole doped poly(ethylene oxide) as a new polymer electrolyte

New composite doped poly (ethylene oxide) polymer electrolyte was developed using 2-mercapto benzimidazole as plasticizer and iodide/triiodide as redox couple. The fabrication of the cell involves Poly(ethylene oxide)/ 2-mercapto benzimidazole / iodide/triiodide as polymer electrolyte in dye-sensitized solar cell fabricated with N3 dye and TiO2 nanoparticles as the photoanode and Platinum coated FTO (fluorine doped SnO2) as counter electrode. The current-volatage characteristics under simulated sunlight AM1.5 shows a short circuit current Isc of 8.7mA and open circuit photovoltage 508 mV. The conductivity measurements for the new polymer electrolyte and the photoelectrochemical measurments were carried out systematically. In 2-mercapto benzimidazole the electron rich sulphur and nitrogen atoms, act as pi-electron donors that form good interaction with iodine which plays a vital role in the performance of the fabricated dye-sensitized solar cells. The resonance effect increases the stability of the cell to a considerable extent. These results suggest that the new composite polymer electrolyte performs as a promising new doped polymer-electrolyte.

Designed biodegradable hydrogel structures prepared by stereolithography using poly(ethylene glycol)/poly(D,L-lactide)-based resins

Designed three-dimensional biodegradable poly(ethylene glycol)/poly(D,L-lactide) hydrogel structures were prepared for the first time by stereolithography at high resolutions. A photopolymerisable aqueous resin comprising PDLLA-PEG-PDLLA-based macromer, visible light photo-initiator, dye and inhibitor in DMSO/water was used to build the structures. Porous and non-porous hydrogels with well-defined architectures and good mechanical properties were prepared. Porous hydrogel structures with a gyroid pore network architecture showed narrow pore size distributions, excellent pore interconnectivity and good mechanical properties. The structures showed good cell seeding characteristics, and human mesenchymal stem cells adhered and proliferated well on these materials.

Designed poly(ethylene glycol)/poly(D,L-lactide)-based hydrogel structures prepared by stereolithography

Three-dimensional biodegradable poly(ethylene glycol)/poly(D,L-lactide) hydrogel structures were prepared by stereolithography. A photo-polymerisable liquid resin comprising PDLLA-PEG-PDLLA-based macromer, visible light photo-initiator, dye and inhibitor in DMSO/water was used to build the structures. Hydrogels with welldefined architectures and good mechanical properties were prepared. Hydrogel structures with a gyroid pore network architecture showed narrow pore size distributions, excellent pore interconnectivity and good mechanical properties. The structures showed good cell seeding characteristics, and human mesenchymal stem cells adhered and proliferated on these materials.

Melt electrospinning of polycaprolactone and its blends with poly(ethylene glycol)

Melt electrospinning is one aspect of electrospinning with relatively little published literature, although the technique avoids solvent accumulation and/or toxicity which is favoured in certain applications. In the study reported, we melt-electrospun blends of poly(ε-caprolactone) (PCL) and an amphiphilic diblock copolymer consisting of poly(ethylene glycol) and PCL segments (PEG-block-PCL). A custom-made electrospinning apparatus was built and various combinations of instrument parameters such as voltage and polymer feeding rate were investigated. Pure PEG-block-PCL copolymer melt electrospinning did not result in consistent and uniform fibres due to the low molecular weight, while blends of PCL and PEG-block-PCL, for some parameter combinations and certain weight ratios of the two components, were able to produce continuous fibres significantly thinner (average diameter of ca 2 µm) compared to pure PCL. The PCL fibres obtained had average diameters ranging from 6 to 33 µm and meshes were uniform for the lowest voltage employed while mesh uniformity decreased when the voltage was increased. This approach shows that PCL and blends of PEG-block-PCL and PCL can be readily processed by melt electrospinning to obtain fibrous meshes with varied average diameters and morphologies that are of interest for tissue engineering purposes. Copyright © 2010 Society of Chemical Industry