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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Cetyltrimethylammonium Bromide (CTAB) Surfactant-Assisted Synthesis of BiFeO{sub 3} Nanoparticles by Sol-Gel Auto-Combustion Method

In this research, BiFeO{sub 3} nanoparticles were synthesized by sol-gel auto-combustion method with and without the addition of cetyltrimethylammonium bromide (CTAB) surfactant. The effect of different amounts of CTAB addition (0, 1.5, 3, and 6 wt.%) on phase constituents, microstructure, and magnetic properties of the synthesized samples were evaluated using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and vibration sample magnetometer (VSM). Also, BiFeO{sub 3} nanoparticles were used for the degradation of methylene blue (MB) as a typical dye pollutant under UV irradiation. XRD results showed the formation of BiFeO{sub 3} mainly with some minute impurity phases such as Bi{sub 2}O{sub 3} and γ-Fe{sub 2}O{sub 3}. Proper amounts of CTAB addition (1.5 wt.%) considerably eliminates Bi{sub 2}O{sub 3} and γ-Fe{sub 2}O{sub 3} residuals in the combustion product. FESEM micrographs show particle size reduction and also more uniform particle size distribution when using 0.75 wt.% of CTAB addition. In the presence of the BiFeO{sub 3}, the UV irradiation for 120 min resulted in 26% degradation of MB, in a sample with 0.75 wt.% CTAB. The synthesized nanoparticles of BiFeO{sub 3} in the sample with 0.75 wt.% CTAB after calcination at 650 {sup ∘}C showed a weak ferromagnetism behavior with saturation magnetization of 0.54 emu/g. {sub i}H{sub C} values of the samples are in the range of 200 to 238 Oe, depending on the crystallite size and phase constituents of the samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Salt-Assisted Solution Combustion Synthesis of Ni and Ni/NiO Powders

In this work, Ni and Ni/NiO composite powders were synthesized by one-pot solution combustion method using different fuel to oxidant (φ) ratios (φ = 1, 1.25, 1.5, and 1.75). Phase evolution studied by X-ray diffraction (XRD) method showed that single phase Ni powders were formed at high fuel contents, while the low fuel contents led to the formation of Ni/NiO composite powders. The high combustion temperature resulted in the sintered and large Ni particles (1.1 μm). The particle size decreased up to 50 nm by adding KCl as diluent. However, the amount of NiO phase increased by addition of KCl. The saturation magnetization (Ms) of Ni powders decreased from 51 to 42 emu/g with the increase of φ values from 1.25 to 1.75. The Ms decreased up to 18.5 emu/g, due to the formation of a large amount of NiO phase by addition of KCl. The coercivity of the synthesized powders was in the range of 78 to 111 Oe, as a function of particle size.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

The superior hydrothermal stability of Pd/SSZ-39 in low temperature passive NOx adsorption (PNA) and methane combustion

We successfully synthesized uniform SSZ-39 with an average crystal size of about a micron. Pd (0.7 - 3 wt%) was supported on SSZ-39 with Si/Al ratio ~12. The as-synthesized materials were characterized by FTIR, XRD, Helium Ion Microscopy, HAADF-STEM imaging, 27 Al, 29 Si and H solid state NMR spectroscopic techniques. FTIR studies with CO and NO probe molecules reveal that the 0.7 wt% Pd/SSZ-39 material with Si/Al ~12 has the majority of Pd dispersed atomically as isolated Pd(II) and Pd(II)-OH centers, and thus can be used as a low-temperature passive NOx adsorber. Pd(II)-NO, Pd(II)(OH)(NO) and Pd(II)(CO)(NO) complexes form during PNA in this material. We compare this PNA material directly with the Pd/SSZ-13 system (with Si/Al ratio ~12) and show its superior hydrothermal stability. Remarkably, Pd/SSZ-39 with Si/Al ratio ~12 survives hydrothermal aging up to 815 ºC in 10% H 2 O/Air vapor for 16 hours without significant loss in activity. The SSZ-39 crystal structure remains intact during hydrothermal aging up to 1,000 ºC as we elucidate it with XRD and HAADF-STEM imaging/EDS mapping. However, changes to the framework during such harsh hydrothermal treatment significantly change the NOx release profiles during PNA as evidenced by high-field 27 Al NMR on fresh and aged Pd/SSZ-39 samples as well as PNA performance measurements. Besides PNA application, these hydrothermally very stable materials (3 wt% Pd on SSZ-39 with Si/Al ratio ~12) can be used as a robust methane combustion catalyst under industrially relevant conditions (GHSV~600,000hr -1 ). This catalyst shows minimal deactivation after both harsh hydrothermal aging at 750 and 800 ºC, and prolonged time on stream (105 hrs) at 425 °C. In contrast, both 3wt% Pd/alumina and 3wt% SSZ-13 supported samples lose a significant portion of their activity. Our study opens new avenues to prepare the most hydrothermally stable known Pd/zeolite materials with applications for adsorption and catalytic hydrocarbon combustion under industrially relevant conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

50-kWth methane/air chemical looping combustion tests with commercially prepared CuO-Fe 2 O 3 -alumina oxygen carrier with two different techniques

CuO-Fe 2 O 3 /alumina oxygen carriers were manufactured using two different techniques (i.e., spray drying and wet granulation). The spray drying method produced porous, spherical particles in the range of 100–200 µm. The wet granulation, or tumbling method, produced particles in the range of 200–600 µm. Both batches of material showed good gas conversion and particle durability during tests in NETL’s 50-kWth chemical looping circulating fluidized bed combustor unit at 700–900 °C. No agglomeration was observed, even though the oxygen carrier had a high CuO concentration (30%). The particle losses with 200–600 µm batch were significantly lower than that with the 100–200 µm batch. The oxygen carrier materials in the 200–600 µm range were circulated for approximately 3.1 days in the target temperature range (700–850 °C) and a total of approximately 40 h of chemical looping combustion testing was conducted during that time. The average fuel reactor temperatures ranged from 760 to 815 °C for the chemical looping combustion test periods, and the average air reactor temperature ranged from 840 to 915 °C. The fuel conversion from natural gas to CO 2 ranged from 50 to 80%. Approximately 1.6 h of continuous operation was achieved with no gas preheat and no natural gas augmented heating. During this test period, the average fuel reactor temperature ranged from 780 to 825 °C, the air reactor temperature ranged from 930 to 960 °C, and the natural gas to CO 2 conversion ranged from 50 to 65%. Finally, analysis of the oxygen carrier after the test indicated that there were no significant changes in the particle size or the surface morphology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Cycle Design and Optimization of Pressure Swing Adsorption Cycles for Pre-Combustion CO 2 Capture

Novel pressure-swing adsorption (PSA) cycles were developed based on patented TDA AMS- 19 (activated carbon) adsorbent for pre-combustion CO 2 capture in integrated gasi cation combined cycle (IGCC) power plants. A variety of cycles comprising of counter-current blowdown, pressure equalization, steam purge and light product pressurization steps were designed and simulated using an in-house one dimensional detailed model. Full process opti- mization studies were performed for all cycles to evaluate their feasibility for pre-combustion CO 2 capture. The CO 2 purity and recovery Pareto fronts obtained using the multi-objective optimization were used to assess their ability to simultaneously achieve high CO 2 purity (>95%) and recovery (>90%). The cycles that achieved the purity-recovery (95%-90%) requirements were subjected to energy-productivity optimizations under the constraints of CO 2 purity and recovery. Three cycle designs were ranked in terms of lowest energy con- sumption at 95% CO 2 purities and 90% CO 2 recoveries. It was found that a 10-step cycle with three pressure equalization steps achieved a minimum energy consumption of 95.7 kWhe/tonne of CO 2 captured at a productivity of 3.3 mol CO 2 captured/m 3 adsorbent/s.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Kinetic modeling of the formation and growth of inorganic nano-particles during pulverized coal char combustion in O 2 /N 2 and O 2 /CO 2 atmospheres

In this formation of nano-particles during coal char combustion, the vaporization of inorganic components in char and the subsequent homogeneous particle nucleation, heterogeneous condensation, coagulation, and coalescence play decisive roles. Furthermore, conventional measurements cannot provide detailed information on the dynamics of nano-particle formation and evolution, In this study, a sophisticated intrinsic char kinetics model that considers ash effects (including ash film formation, ash dilution, and ash vaporization acting in tandem), both oxidation and gasification by CO 2 and H 2 O, homogeneous particle nucleation, heterogeneous vapor condensation, coagulation, and and coalescence mechanisms is developed and used to compare the temporal evolution of the number and size of nano-particles during coal char particle combustion as a function of char particle size, ash content, and oxygen content in O 2 /N 2 and O 2 /CO 2 atmospheres .

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2017

A comprehensive iso-octane combustion model with improved thermochemistry and chemical kinetics

Iso-Octane (2,2,4-trimethylpentane) is a primary reference fuel and an important component of gasoline fuels. Furthermore, it is a key component used in surrogates to study the ignition and burning characteristics of gasoline fuels. This paper presents an updated chemical kinetic model for iso-octane combustion. Specifically, the thermodynamic data and reaction kinetics of iso-octane have been re-assessed based on new thermodynamic group values and recently evaluated rate coefficients from the literature. The adopted rate coefficients were either experimentally measured or determined by analogy to theoretically calculated values. New alternative isomerization pathways for peroxy-alkyl hydroperoxide ($\dot{O}$OQOOH) radicals were added to the reaction mechanism. The updated kinetic model was compared against new ignition delay data measured in rapid compression machines (RCM) and a high-pressure shock tube. Our experiments were conducted at pressures of 20 and 40 atm, at equivalence ratios of 0.4 and 1.0, and at temperatures in the range of 632–1060 K. The updated model was further compared against shock tube ignition delay times, jet-stirred reactor oxidation speciation data, premixed laminar flame speeds, counterflow diffusion flame ignition, and shock tube pyrolysis speciation data available in the literature. Finally, the updated model was used to investigate the importance of alternative isomerization pathways in the low temperature oxidation of highly branched alkanes. When compared to available models in the literature, the present model represents the current state-of-the-art in fundamental thermochemistry and reaction kinetics of iso-octane; and thus provides the best prediction of wide ranging experimental data and fundamental insights into iso-octane combustion chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Investigating the effect of oxy-fuel combustion and light coal volatiles interaction: A mass spectrometric study

Given the multi-physical nature of coal combustion, the development and validation of detailed chemical models reproducing coal volatiles combustion under oxy-fuel conditions is a crucial step towards the advancement of predictive full-scale simulations. During the devolatilization process, a large variety of gases is released and undergoes secondary pyrolysis and oxidation reactions. Therefore, the ability to capture their interactions is a prerequisite for each chemical model used in its detailed or reduced form to simulate these processes. In this work, a high-resolution time-of-flight molecular-beam mass spectrometer was employed to enable fast and simultaneous detection of stable and unstable species in counterflow flames of typical light volatiles. Following an approach of increasing complexity, carbon dioxide and methane were progressively added to an argon diluted acetylene base flame. For the three flames investigated here, results showed a significant increase in the concentration of C 2 and C 3 hydrocarbons and oxygenated compounds caused by methane addition to the acetylene flame. By hindering the production of the butadienyl radical, the addition of methane induces the reduction of benzene which triggers the decrease of aromatic species. Conversely, CO 2 addition did not have significant effects on intermediates. To guide and interpret the measurements, numerical simulations with two existing chemical models were performed and the results were found to be consistent with the experimental data for small hydrocarbons. Some discrepancies were found between the two model predictions and between simulations and experiments for C 4 and C 5 species. In addition, numerical simulations were found to overestimate the role of the methyl radical in aromatics formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

An a priori Analysis of Mixture Fraction-Based Modeling of Coal Combustion

Due to the high computational cost associated with using detailed kinetic mechanisms, it is common practice to implement reaction models which rely on relatively small number of variables when simulating turbulent combustion systems. In this study, we perform an a priori assessment of the accuracy of three chemistry models: a Burke-Schumann chemistry model, an equilibrium chemistry model, and a steady laminar flamelet model. All chemistry modeling approaches considered include a mixture fraction for devolatilization products, and a normalized enthalpy deficit as parameters, with scalar dissipation rate as an additional input parameter for the flamelet model. Data used as a basis for the study is generated through One-Dimensional Turbulence (ODT) simulation of a coal combustion system in which high-fidelity models are used for gas phase chemistry and devolatilization. The flamelet model was found to be more accurate than both the equilibrium and Burke-Schumann models over a majority of parameter space. The performance of all models considered declined substantially for sufficiently fuel-rich conditions. Furthermore, the analysis in this work indicate that both differential diffusion and speciation of volatiles have a perceptible negative impact on flamelet reconstructions, though the effect of differential diffusion was more substantial.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

A direct numerical simulation study of the dilution tolerance of propane combustion under spark-ignition engine conditions

Modern spark ignition internal combustion (IC) engines rely on highly diluted fuel-air mixtures to achieve high brake thermal efficiencies. To support this, new engine designs have introduced high stroke-to-bore ratios and cylinder head designs that promote high tumble flow and turbulence intensities. However, mixture dilution through exhaust gas recirculation (EGR) is limited by combustion instabilities manifested in the form of cycle-to-cycle variability. Propane has been observed to have superior EGR dilution tolerance than gasoline, which makes it a very competitive low-carbon fuel for the new IC engines without sacrificing efficiency. Two-dimensional direct numerical simulations (DNS) are performed with detailed chemistry to study and contrast the effect of turbulence intensity and dilution on propane and iso-octane premixed flames at high pressure conditions similar to those in-cylinder. A new reduced mechanism for propane consisting of 53 transported species and 17 quasi-steady state species is developed based on a previously published mechanism and used in these simulations. Three levels of turbulence intensity and two levels of exhaust gas dilution are chosen based on conditions relevant to IC engine operation. The DNS results are analyzed based on the evolution of the flame surface area and the statistics of its driving terms, which are found to be similar for both fuels when there is no dilution but considerably different under high dilution. The analysis of the DNS data provides fundamental insights into the underlying mechanisms for improved stability under dilution.

42 ENGINEERING↗
DOE OSTI2023

Limitations of cetane number to predict transient combustion phenomena in high-pressure fuel sprays

Fundamental understanding of in-cylinder processes in diesel engines is important to screen emerging biofuels and advanced combustion modes that can reduce greenhouse gas emissions and regulated pollutants including soot. In this study, the role of fuel properties on spray development and combustion is investigated by systematically isolating chemical and thermophysical effects. Three different fuels are considered, two with similar chemical properties and two with similar thermophysical properties with one fuel common to both groups. Experiments are performed in a constant-pressure flow chamber de-signed to provide stable test conditions and facilitate acquisition of at least 150 injections in quick succession for each fuel under reacting conditions at high-pressure, high-temperature ambient conditions using a modified conventional diesel engine injector. Further, high speed optical diagnostics including rainbow schlieren deflectometry, OH* chemiluminescence, and a two-color pyrometry system are employed to simultaneously image the transient spray and reacting jets. Image analysis is performed to determine liquid length, vapor penetration length, timing and location of first stage and main ignition events, lift-off location, total soot mass, and more. Results show that fuels with similar chemical properties or cetane number (CN) exhibit similar delay times for first stage and main ignition events as may be expected, but very different liquid length, first stage and main ignition locations, lift-off length, apparent turbulent flame speed, and soot formation. As such, the ability to characterize candidate biofuels with CN or other parameters derived from simple flame configurations is called into question. In this study, thermo-physical properties controlling the liquid length are identified as the main contributing factor for the observed differences.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2022

Transient simulation of biomass combustion in a circulating fluidized bed riser

Interest in circulating fluidized bed (CFB) boilers as a power generation technology has sky-rocketed in recent years because of several advantages this technology offers over conventional boilers, such as increased gas-solid mixing, which results in higher combustion efficiency and the ability to use lower rank fuels. CFB combustors are operated at lower temperatures than conventional thermal power generation combustors, thus reducing NO x emissions, while SO 2 emissions can be conveniently controlled through the addition of Ca-based sulfur sorbents within the combustor. Herin this paper summarizes the modeling effort on a 50 kW th CFB combustor designed, built, and operated at CanmetENERGY in Ottawa, Canada. The numerical model employs the multiphase particle-in-cell (PIC) approach in the open-source Multiphase Flow with Interphase eXchanges (MFiX) Software Suite. The MFiX-PIC model parameters for the simulation are tuned against cold-flow experiments from CanmetENERGY using olivine sand as the inert bed material. It is shown that for the relatively coarse fluid meshes and large parcel sizes necessitated by the scale of the simulation, filter size dependent corrections to the drag law must be incorporated to ensure accuracy of the simulation results. The validated cold flow model is extended to simulate reacting flow with torrefied hardwood as the feedstock and to validate the combustion reaction scheme. The species concentrations at the riser outlet are compared against CanmetENERGY’s experiments and show satisfactory agreement. The simulations demonstrate the ability of MFiX-PIC to accurately capture both the physics and chemistry of a CFB combustor at bench scales, which can be further extended to pilot- and industrial-scale systems.

09 BIOMASS FUELS↗
DOE OSTI2018

Multifaceted processes controlling the distribution of hazardous compounds in the spontaneous combustion of coal and the effect of these compounds on human health

Highlights: • Electron bean reveals the interactions among nanoparticles and hazardous compounds. • Samples were obtained from the most big Brazilian coal power plant. • Overall, exposure to hazardous compounds in coal fire pose health risks. Pollution generated by hazardous elements and persistent organic compounds that affect coal fire is a major environmental concern because of its toxic nature, persistence, and potential risk to human health. The coal mining activities are growing in the state of Santa Catarina in Brazil, thus the collateral impacts on the health and economy are yet to be analyzed. In addition, the environment is also enduring the collateral damage as the waste materials directly influence the coal by-products applied in civil constructions. This study was aimed to establish the relationships between the composition, morphology, and structural characteristics of ultrafine particles emitted by coal mine fires. In Brazil, the self-combustions produced by Al–Ca–Fe–Mg–Si coal spheres are rich in chalcophile elements (As, Cd, Cu, Hg, Pb, Sb, Se, Sn, and Zn), lithophile elements (Ce, Hf, In, La, Th, and U), and siderophile elements (Co, Cr, Mo, Fe, Ni, and V). The relationship between nanomineralogy and the production of hazardous elements as analyzed by advanced methods for the geochemical analysis of different materials were also delineated. The information obtained by the mineral substance analysis may provide a better idea for the understanding of coal-fire development and assessing the response of particular coal in different combustion processes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

A predictive 0-D HCCI combustion model for ethanol, natural gas, gasoline, and primary reference fuel blends

Homogeneous Charge Compression Ignition (HCCI) is a promising advanced combustion concept with high thermal efficiency and low exhaust emissions. This work purposes a computationally-efficient, zero-dimensional (0-D) HCCI combustion model that does not need to solve any differential equations. To develop the burn rate correlations, experimental HCCI data of ethanol, natural gas, E10-gasoline, and Primary Reference Fuel (PRF) blends was collected on a CFR engine. The burn rate model is built based on the individual cycle mass fraction burned (MFB) curves calculated from the experimental data. CA0 can be predicted from an ignition delay correlation. Once CA0 is known, CA50 and CA90 can be predicted based on CA0 and the charge-mass equivalence ratio Φ'. Then, with CA0, 50 and 90 known, a Wiebe function can be constructed to represent the MFB curve and burn rate. For PRF blends, low-temperature and high-temperature heat releases (LTHR and HTHR) are modeled by two Wiebe functions with Φ' and PRF number dependence. The fitted model has high accuracy compared to the experimental data with R 2 values generally greater than 0.97. Finally, various ignition delay correlations from the literature are also tested against the experimentally collected data and some modifications to the correlations are suggested.

42 ENGINEERING↗
DOE OSTI2021

Assessment of sulfur trioxide formation due to enhanced interaction of nitrogen oxides and sulfur oxides in pressurized oxy-combustion

Pressurized oxy-combustion is emerging to be one of the best technologies for significantly decreasing the energy penalty for CO 2 capture in coal-fired power plants. However, the higher pressure boosts the formation of acid gases, including SO 3 and NO 2 , which could increase the risk of corrosion. The synergistic promotion of SO 3 and NO 2 formation in pressurized oxy-combustion is kinetically evaluated under representative conditions (1 ~ 30 atm, 600 ~ 1200 °C, NO/SO 2 = 0.1 ~ 5). We begin with a comprehensive mechanism (72 species and 428 reactions), covering nitrogen and sulfur chemistry, relying on GRI-Mech 3.0. This analysis shows that the interaction of SO X and NO X enhances the conversion rates of SO 2 → SO 3 , and this effect is more apparent at elevated pressures and lower temperatures. Mechanism analyses indicate that at elevated pressures, the formation pathways of SO 3 through HOSO 2 + O 2 = SO 3 + HO 2 , and NO 2 through HO 2 + NO = NO 2 + OH, are promoted due to the strong interaction between SO X and NO X . The intermediate between these two reactions is SO 2 + OH + M = HOSO 2 + M, resulting in a strong cycle, that can be expressed by the global reaction NO + SO 2 + O 2 = NO 2 + SO 3 . Finally, a nine-step reduced chemistry is developed and validated to accurately predict the formation of SO 3 in the post-flame region at elevated pressures.

42 ENGINEERING↗
DOE OSTI2021

Spray and combustion characteristics of pure hydrothermal liquefaction biofuel and mixture blends with diesel

Hydrothermal liquefaction (HTL) is the process in which biological compounds can be converted into biocrude diesel; various feedstocks, such as algae and wet biowaste, can be utilized. Almost 20 million dry tons of wet biowaste is deposited in U.S. municipal wastewaters annually. If recovered and converted into biodiesel, it can act as a massive source of renewable energy. Preliminary experiments on a diesel engine show that HTL fuel can achieve similar performance and emission levels to diesel. In order to further understand the influence of the HTL fuel properties, the HTL fuel and blends with diesel are observed in a constant volume chamber. Previously, 10% and 20% of the HTL fuel were blended with diesel by volume and demonstrated properties that roughly matched diesel in terms of combustion. In this study, 50% and 100% HTL fuel blends are tested on the same apparatus. It was discovered that the workability of HTL is almost the same as that of diesel and is less sensitive to ambient temperatures. When the ambient temperature is reduced from 1200 K to 800 K, the change ratio of ignition delay is only 62% of diesel. By analyzing the combustion process, it can be seen that there is no need to make major modifications to the engine control strategy if HTL fuel is applied to diesel engines. Though, under low temperature and low oxygen conditions, the soot luminosity peak of HTL100 is 3.12 times than that of diesel.

09 BIOMASS FUELS↗
DOE OSTI2023

Quantitative investigation of sooting dynamics in droplet combustion using an automated image analysis algorithm

This paper reports an image analysis approach using a newly-developed open-source program to extract quantitative measurements of soot volume fraction (SVF) from digital video images of burning n-heptane droplets. The automated program developed in this work can analyze images of fixed and untethered droplets to quantify sooting dynamics. The images analyzed in the program were taken from experiments carried out in the Multi-user Droplet Combustion Apparatus (MDCA) onboard the International Space Station (ISS). In these experiments, video imaging of burning droplets was obtained using backlighting by a laser diode with a wavelength of 653 nm. Here, the light was collimated before it passed through the droplet and soot-containing region, after which the light was then attenuated and projected onto the camera’s sensors. This technique facilitates the measurements of SVF based on the principles of the full field light extinction method (FFLEM). The measurements provide quantitative data that reveal the sooting dynamics of liquid fuels during droplet combustion processes. The analyses of a soot-attenuating image (ISS n-heptane, untethered droplet) at an instant during the burning show that the SVF distribution has a peak at the soot shell location. It then decreases due to soot oxidation when the location is further away from the burning droplet. Regarding temporal effects on the maximum SVF (SVF max ), results show that SVF max first increases after the burning is initiated until a peak value is reached, after which SVF max decreases. The SVF max values identified in this study for n-heptane are quantitatively consistent with previously reported values for fiber-supported droplets and are reached relatively early in the burning history. n-Heptane images are also analyzed to show the effects of initial droplet sizes on the maximum soot volume fraction. Results show that SVF max decreases with increasing initial droplet size, which is consistent with visual observations of less soot formed and dimmer flame brightness as Do increases.

42 ENGINEERING↗
DOE OSTI2025

Photoionization of seeded combustion products as a method of enhancing the efficiency of magnetohydrodynamic power generators

Here, in this study, we performed an experimental and computational investigation into the feasibility of utilizing photoionization to enhance the electrical conductivity of seeded oxy-fuel combustion products and improve the performance of magnetohydrodynamic (MHD) power generators. We applied a variety of optical and microwave diagnostics to study the ionization and recombination processes of potassium excited by an excimer laser in a high-velocity oxy-fuel free jet. Computational fluid dynamic (CFD) simulations were performed to model the thermophysical properties and species densities of the free jet. The CFD results were validated with position-dependent potassium concentration measurements. Electron recombination exponential lifetimes were measured through time-resolved microwave transmission. The experimental electron lifetimes were compared with lifetimes calculated from CFD-predicted species densities and literature recombination rates. It was determined that K + or O 2 are the most likely recombination partners for photoionized electrons. Time-resolved fluorescence measurements provided evidence of an ionization pathway involving a two-photon ionization of KOH . Finally, a zero-dimensional chemical kinetic model was developed to assess the fundamental viability of inducing a non-equilibrium electron population to provide a net energy return in combustion-driven MHD power generators. We determined that a high energy return is feasible for targeting electrode boundary layers with ultraviolet photoionization. We also found that photoionization could potentially lower the required temperature of the bulk gas flow.

20 FOSSIL-FUELED POWER PLANTS↗