Chemical kinetic considerations for postflame synthesis of carbon nanotubes in premixed flames using a support catalyst

Multiwalled carbon nanotubes (MWCNTs) on a grid supported cobalt nanocatalyst were grown, by exposing it to combustion gases from ethylene/air rich premixed flames. Ten equivalence ratios (φ) were investigated, as follows: 1.37, 1.44, 1.47, 1.50, 1.55, 1.57, 1.62, 1.75, 1.82, and 1.91. MWCNT growth could be observed for the range of equivalence ratios between 1.45 and 1.75, with the best yield restricted to the range 1.5–1.6. A one-dimensional premixed flame code with a postflame heat loss model, including detailed chemistry, was used to estimate the gas phase chemical composition that favorsMWCNT growth. The results of the calculations show that the mixture, including the water gas shift reaction, is not even in partial chemical equilibrium. Therefore, past discussions of compositional parameters that relate to optimum carbon nanotube (CNT) growth are revised to include chemical kinetic effects. Specifically, rapid departures of the water gas shift reaction from partial equilibrium and changes in mole fraction ratios of unburned C2 hydrocarbons to hydrogen correlate well with experimentally observed CNT yields

Radiation Intensity of a Turbulent Sooting Ethylene Flame

Turbulent sooting flame radiation is relevant to applications ranging from fire safety to gas turbine engines. The complex direct interactions of soot and radiation intensity are of particular importance when creating accurate soot prediction models. Previous studies have measured gas-band and broadband radiation intensity from turbulent sooting flames. The focus of the current study is the characterization of radiation intensity emanating from soot. A high-speed infrared camera (FLIR Phoenix) was used to acquire time-dependent quantitative images of radiation intensity of a turbulent sooting ethylene flame. The flame had a Reynolds number of 15,200 and was stabilized on a burner with an exit diameter of 8mm. The radiation intensity was collected utilizing a bandpass filter (3.77 ± .12 μm) to limit the radiation intensity source to soot. Time-dependent and time-averaged soot radiation intensities are plotted. Radiation intensity structures similar to those found in soot volume fraction diagnostics are observed and statistical analyses are employed to characterize the distribution of soot radiation intensity. The centerline distribution of radiation intensity from soot was qualitatively similar to earlier measurements of gas-band radiation intensity. Time-dependent images of radiation intensity exhibited discrete structures similar to images of soot volume fraction measured by laser-induced incandescence

Radiation Measurements and Data Analysis of Turbulent Premixed Lean Flame

An accurate understanding of the radiation transfer in turbulent premixed lean flame is critical for improving energy efficiencies and reducing emissions such as nitric oxide and soot. Radiation measurement is an effective and nonintrusive way to study the radiation properties of turbulent premixed lean flames. In this study, a high-speed infrared camera was utilized to measure the planar radiation from turbulent premixed lean flames under different conditions. Time-dependent flame images were acquired and radiation statistics were calculated and compared to investigate the effects of equivalence ratio, heat release rate, hydrogen pilot flame rate, and co-flow rate on the radiation intensity of the flames. Results show that radiation intensity increases with equivalence ratio and heat release rate. However, changes of hydrogen pilot flame rate and co-flow rate have little impact on the radiation intensity. These experimental data are essential for the study of turbulent premixed lean flames and the calibration of the empirical relations in the simulation models

Experimental Study of CO2 Recycling using Metal-Oxide Enhanced Coconut Char Gasification: Catalytic Effect of Potassium Carbonate on Gasification

Biomass gasification is an important process in the production of bio-derived fuels and renewable energy. Biomass gasification with CO2 is an endothermic process requiring high temperatures, resulting in low process-efficiency. Metals found in the ash in biomass feedstock have shown rate-promoting effects on the C-CO2 reaction and have motivated the study of low-temperature catalytic gasification. The present study investigates the catalytic effects of potassium (K) on the biomass gasification reactivity of a coconut-derived char (\u3e99.9% carbon) within the temperature range of 600 – 1000 oC. A wet-impregnation technique is used to prepare K-treated chars. Gasification of the coconut char is conducted within a fixed-bed gasifier with sensitive temperature control (± 10 K). Optical diagnostics, such as laser absorption spectroscopy and non-dispersive infrared absorption spectroscopy, are used to quantify the char mass-loss and instantaneous conversion rate histories. Experimental data show significant increase in gasification rates with the addition of potassium to the chars. Peak gasification rates are observed to increase significantly with addition of K within the temperature range of 600-800 oC. Peak gasification rates beyond 800 oC show a non-monotonic trend, which suggests that the high temperature stability of K may have significant effects on its catalytic activity

The Role of Surface Area in Catalytic Gasification of Biomass

Gasification of biomass has the potential to provide a carbon-negative source of liquid fuels. The current limited use of gasification is due in part to the high temperatures necessary to achieve high conversion levels. These temperatures can be lowered by the use of catalysts, but the mechanisms by which catalysts affect the reaction rate are not fully understood. Here, the structural component of potassium carbonate’s role in the gasification process was examined. Samples of pinewood sawdust were impregnated with potassium carbonate, then pyrolyzed with N2 in a fixed bed reactor at 750°C (heater thermocouple reading). Half of the char was washed with deionized water twice to remove potassium ions. The char was ground to a 150 micron diameter. Gasification of the samples was performed using CO2 at 750°C and 900°C. Reaction rates over time were compared to the reaction rate of pure pinewood sawdust char. The pure char was then impregnated with K2CO3 and gasified, allowing a comparison to be made between the efficacy of impregnating the sawdust versus the char. Results show that after washing, the impregnated char shows similar or decreased reactivity compared to the pure char. Preliminary results do suggest that impregnation of the sawdust leads to greater reactivity over time than impregnation of the char. The results do not suggest a strong influence of surface area change during impregnation on the reactivity of the char

Hot Surface Ignition

Undesirable hot surface ignition of flammable liquids is one of the hazards in ground and air transportation vehicles, which primarily occurs in the engine compartment. In order to evaluate the safety and sustainability of candidate replacement fuels with respect to hot surface ignition, a baseline low lead fuel (Avgas 100 LL) and four experimental unleaded aviation fuels recommended for reciprocating aviation engines were considered. In addition, hot surface ignition properties of the gas turbine fuels Jet-A, JP-8, and JP-5 were measured. A test apparatus capable of providing reproducible data was designed and fabricated to experimentally investigate the hot surface ignition characteristics. A uniform surface temperature stainless steel plate simulating the wall of a typical exhaust manifold of an aircraft engine was used as the hot surface. Temperature uniformity of ±5°C was achieved on the stainless steel plate by virtue of its being bolted to a copper plate in which five automatically controlled 1000 W electrical cartridge heaters were inserted. A programmable syringe pump was used to dispense ~25 μL fuel drops onto the hot surface. Testing was performed in a quiescent environment with the exception of a mild upward flow created by an exhaust fan aiding the buoyant plume created by the hot plate. Ignition and flame propagation events were recorded using visible and mid-infrared still and video imaging. The ignition and flame propagation events are transient and occur at randomly distributed locations on the hot surface. To characterize the ignition event statistically, the surface temperature leading to at least one ignition out of the number of drops and the surface temperature resulting in the ignition of all of the drops were recorded. The results of the experiment confirmed that the experimental variations in the drop size, drop velocity, plume characteristics, surface properties including temperature changes, and the nonlinear dependence of temperature of the chemical reaction rate lead to the probabilistic nature of the ignition event. The results of the experiment are of practical value in designing vehicular ignition and safety systems

Genome-wide analysis of the omega-3 fatty acid desaturase gene family in Gossypium

Background The majority of commercial cotton varieties planted worldwide are derived from Gossypium hirsutum, which is a naturally occurring allotetraploid produced by interspecific hybridization of A- and D-genome diploid progenitor species. While most cotton species are adapted to warm, semi-arid tropical and subtropical regions, and thus perform well in these geographical areas, cotton seedlings are sensitive to cold temperature, which can significantly reduce crop yields. One of the common biochemical responses of plants to cold temperatures is an increase in omega-3 fatty acids, which protects cellular function by maintaining membrane integrity. The purpose of our study was to identify and characterize the omega-3 fatty acid desaturase (FAD) gene family in G. hirsutum, with an emphasis on identifying omega-3 FADs involved in cold temperature adaptation. Results Eleven omega-3 FAD genes were identified in G. hirsutum, and characterization of the gene family in extant A and D diploid species (G. herbaceum and G. raimondii, respectively) allowed for unambiguous genome assignment of all homoeologs in tetraploid G. hirsutum. The omega-3 FAD family of cotton includes five distinct genes, two of which encode endoplasmic reticulum-type enzymes (FAD3-1 and FAD3-2) and three that encode chloroplast-type enzymes (FAD7/8-1, FAD7/8-2, and FAD7/8-3). The FAD3-2 gene was duplicated in the A genome progenitor species after the evolutionary split from the D progenitor, but before the interspecific hybridization event that gave rise to modern tetraploid cotton. RNA-seq analysis revealed conserved, gene-specific expression patterns in various organs and cell types and semi-quantitative RT-PCR further revealed that FAD7/8-1 was specifically induced during cold temperature treatment of G. hirsutum seedlings. Conclusions The omega-3 FAD gene family in cotton was characterized at the genome-wide level in three species, showing relatively ancient establishment of the gene family prior to the split of A and D diploid progenitor species. The FAD genes are differentially expressed in various organs and cell types, including fiber, and expression of the FAD7/8-1 gene was induced by cold temperature. Collectively, these data define the genetic and functional genomic properties of this important gene family in cotton and provide a foundation for future efforts to improve cotton abiotic stress tolerance through molecular breeding approaches

An Energy-Water Corridor Along the US/Mexico Border: Changing the \u27Conversation\u27

Over the last decade, migration has become a divisive issue around the world. A large number of countries have erected barriers along their borders to prevent migration, leading to geopolitical tension. Climate change effects will likely exacerbate migration tensions, which will require bold and creative solutions to this difficult social predicament. Here we detail a plan to construct an energy-water corridor along a border that has been the focus of much attention recently: The U.S.-Mexico border. Our proposed solution helps to alleviate some of the negative effects of climate change, while providing energy and economic stimulus to an area that begs for sustainable development. The energy-water corridor will take advantage of the unique renewable energy resources along the border states and will use state-of-the-art water desalination and treatment systems to provide the resources for economic development in the region