Combustion Of Particles Research Articles

Effect of the temperature control device on the emission character of condensable particulate matter from industrial heating plant

Condensable particulate matter (CPM) is one of the major emissions of primary particles in coal combustion. The removal efficiency of CPM using the temperature control device (TCD) based on the concept of a heat exchanger application with lower capital cost was investigated in an industrial heating plant. TCD operates without water and flue gas interactions and ensures efficient control of CPM emissions, and it also minimizes the potential ion accumulation in recycled WESP water, which could otherwise hinder the removal of CPM. The total mass and chemical speciation were determined by EPA method 202. The total mass of CPM was removed by 25.7–60.6% after the TCD. The CPM captured by CPM filters (CPMspa) was down to around 15–21% and the FPM also was reduced by around 11–26%. The occurrence of vapor gradient forces and thermophoresis forces could enhance the contact between CPM and water film, which was built up on the surface of the cooling tubes during the process of TCD. Then, part of the CPM was removed with a water film. The low capital and operating cost of TCD can be installed in the industrial heating plant or be set up after the WESP in the coal-fired power plant to enhance the CPM removal efficiency.

Numerical study on multiphase combustion characteristics of aluminum-based powder-fueled water ramjet engine

Powder-Fueled Water Ramjet Engine (PFWRE) is of great attraction for high-speed and long-voyage underwater propulsion, as well as air-water trans-media navigation applications due to its high energy density and thrust adjustability. However, the complex multiphase combustion process in the combustor significantly affects engine performance. In this study, a detailed model for aluminum particle combustion in water vapor is developed and validated via literature data as well as the ground direct-connected test we conducted. Thereafter, the numerical study on the multiphase combustion process inside the aluminum-based PFWRE combustor is carried out within the Euler–Lagrange framework using the developed model. Results show that a reverse rotating vortex pair before the primary water injection causes particles to flow back towards the combustor head and leads to product deposition. Aluminum particles external to the powder jet have shorter preheating time than internal particles and burn out in advance. The analysis of the particle combustion process indicates that the flame structure inside the combustor consists of the particle preheating zone, the surface combustion heat release zone, the gas-phase combustion heat release zone, and the post-flame zone. In the present configuration, as the particle size increases from 10 μm to 20 μm, the preheating zone length increases from 35 mm to 85 mm. Meanwhile, heat release from gas-phase combustion decreases, and the average temperature of the combustor head first increases and then decreases. This study not only provides insight into the multiphase combustion characteristics of the aluminum-based PFWRE combustor but also offers guidance for the design of the combustion organization schemes and engine structure optimization.

FOS: A fully integrated open-source program for Fast Optical Spectrum calculations of nanoparticle media

FOS, which means light in Greek, is an open-source program for Fast Optical Spectrum calculations of nanoparticle media. This program takes the material properties and a description of the system as input, and outputs the spectral response including the reflectance, absorptance, and transmittance. Previous open-source codes often include only one portion of what is needed to calculate the spectral response of a nanoparticulate medium, such as Mie theory or a Monte Carlo method. FOS is designed to provide a convenient fully integrated format to remove the barrier as well as providing a significantly accelerated implementation with compiled Python code, parallel processing, and pre-trained machine learning predictions. This program can accelerate optimization and high throughput design of optical properties of nanoparticle or nanocomposite media, such as radiative cooling paint and solar heating liquids, allowing for the discovery of new materials and designs. FOS also enables convenient modeling of lunar dust coatings, combustion particulates, and many other particulate systems. In this paper we discuss the methodology used in FOS, features of the program, and provide four case studies.

Oxidation progress and inner structure during single micron-sized iron particles combustion in a hot oxidizing atmosphere

The present experimental study focuses on the determination of the oxidation progress and internal structures during the combustion of single iron particles using combined in-situ optical measurements and ex-situ material examination of rapidly quenched particles. Narrowly sieved iron particles with a mean diameter of 49µm are ignited and burn in the hot exhaust of a premixed CH4/O2/N2 flat flame with remaining 20vol% O2, provided by a laminar flow reactor with well-defined thermal and flow boundary conditions. During particle combustion, key parameters of oxidation progress are determined optically in a time-resolved manner, such as the time-resolved particle surface temperature and the reaction time relative to the instant of the particle peak temperature. Furthermore, individually burning particles are rapidly quenched at different combustion stages and then extracted from the exhaust gas using an isokinetic extraction probe. The bulk composition of the quenched particles with respect to α-Fe and its three oxides FeO, Fe3O4, and Fe2O3 is determined using Wide-angle X-ray Scattering and 57Fe Mössbauer Spectroscopy. Combining the information obtained from in-situ and ex-situ measurements, it is shown that iron particles oxidize rapidly to FeO during the initial stage of combustion, followed by a much slower oxidation to Fe3O4 as the particles cool down. The peak particle temperatures are measured during the fast initial oxidation. Finally, particles sampled from representative positions of the oxidation process are analyzed by Energy-Dispersive X-ray Spectroscopy and Focused Ion Beam Scanning Electron Microscopy, revealing different particle morphology and internal structures. For the first time, the clear presence of an oxide shell and iron-core structure in quenched particles suggests that liquid iron and liquid iron oxide are layered during liquid phase combustion, if the particle remains within the miscible gap.

Morphology and elemental composition of individual solid dust particles: From different sources to the atmosphere

This study investigates the morphology and elemental composition of individual solid dust particles from various sources (e.g., thermal power plant, domestic coal combustion, building construction dust, wind-blown dust, Asian dust storm, and road related dust) to the atmosphere under high and low relative humidity (RH) conditions in a coastal city of north China by using high-resolution electron microscopes. The results showed that distinct variations between dust particles from thermal power plant and domestic coal combustion, despite both using coal as fuel. Specifically, 88.6% (by number) of thermal power plant particles were spherical, whereas only 2 out of 347 particles from domestic coal combustion exhibited a spherical shape. Furthermore, domestic coal combustion particles showed a higher proportion of Ca-rich particles compared to those from thermal power plant. The wind-blown dust and Asian dust storm particles were mainly “Si + Al” subtype (52.0% v.s. 75.3%) and Si-dominant subtype (16.4% v.s. 11.7%) particles, which were mainly from crustal sources. However, wind-blown dust contained a higher fraction of Ca-rich (11.6%) and Fe-rich (5.3%) particles than Asian dust. The building construction dust particles primarily consisted of irregular Ca-dominant (39.4%) and “Ca + Si” subtype (29.8%) particles. Road related dust were also mainly Si-rich particles (52.9%), likely from re-suspended soil, along with a notable presence of spherical (8.0%) and Fe-rich particles (19.3%), possibly linked to vehicle emissions and brake wear. Additionally, relative number percentage of Na-rich particles and the average weigh ratios of Na in the atmospheric particles were higher than those from all above-mentioned source samples, suggesting that sea-salt related particles might be an important source of the atmospheric dust at the coastal city. The results indicated that Ca-rich particles were significantly modified by S and NaCl particles might lose Cl through heterogeneous reactions under higher RH.

The effects of photochemical aging and interactions with secondary organic aerosols on cellular toxicity of combustion particles

Fine particulate matter (PM2.5) is associated with numerous adverse health effects, including pulmonary and cardiovascular diseases and premature death. Significant contributors to ambient PM2.5 include combustion particles and secondary organic aerosols (SOA). Combustion particles enter the atmosphere and undergo an aging process that changes their shape and composition, but there is limited study on the health effects of combustion particle aging and interactions with SOA. This study aimed to understand how biological responses to combustion particles would be affected by atmospheric aging and interaction with anthropogenic SOA. Fresh combustion particles underwent photochemical aging in a potential aerosol mass (PAM) oxidation flow reactor and interacted with SOA produced by the oxidation of toluene vapor in the PAM reactor. Photochemical aging and SOA interactions lead to significant changes in the PAH content and oxidative potential of the particle. Photochemical aging and SOA interactions also affected the biological responses, such as the inflammatory response and CYP1A1 induction of the particles in monoculture and coculture cells. These findings highlight the significance of photochemical aging and SOA interactions on the composition and cellular responses of combustion particles.

Simulation of electrostatic particulate matter sensor regeneration based on the particulate deposition patterns

Purpose This study aims to establish a multi-physics-coupled model for an electrostatic particulate matter (PM) sensor. The focus lies on investigating the deposition patterns of particles within the sensor and the variation in the regeneration temperature field. Design/methodology/approach Computational simulations were initially conducted to analyse the distribution of particles under different temperature and airflow conditions. The study investigates how particles deposit within the sensor and explores methods to expedite the combustion of deposited particles for subsequent measurements. Findings The results indicate that a significant portion of the particles, approximately 61.8% of the total deposited particles, accumulates on the inside of the protective cover. To facilitate rapid combustion of these deposited particles, a ceramic heater was embedded within the metal shielding layer and tightly integrated with the high-voltage electrode. Silicon nitride ceramic, selected for its high strength, elevated temperature stability and excellent thermal conductivity, enables a relatively fast heating rate, ensuring a uniform temperature field distribution. Applying 27 W power to the silicon nitride heater rapidly raises the gas flow region's temperature within the sensor head to achieve a high-temperature regeneration state. Computational results demonstrate that within 200 s of heater operation, the sensor's internal temperature can exceed 600 °C, effectively ensuring thorough combustion of the deposited particles. Originality/value This study presents a novel approach to address the challenges associated with particle deposition in electrostatic PM sensors. By integrating a ceramic heater with specific material properties, the study proposes an effective method to expedite particle combustion for enhanced sensor performance.

Extreme wildfires over northern Greece during summer 2023 – Part A: Effects on aerosol optical properties and solar UV radiation

In Mediterranean countries, such as Greece, the frequency of forest fires has increased in recent years, primarily due to the widespread impacts of climate change. At the end of August 2023, Greece experienced a record-breaking heatwave that triggered severe wildfire incidents, significantly impacting the atmospheric conditions of several cities, among them Thessaloniki. A significant number of wildfires occurred in northern Greece (Evros), burning thousands of hectares of the protected Dadia forest (Natura 2000) and releasing a significant load of smoke into the atmosphere. According to the European Strategy Forum on Research Infrastructures (ESFRI) a total area of 90,000ha was burnt collectively by the Evros extreme wildfires during August 2023. The emissions led to severely adverse air pollution conditions, causing reduced visibility across an extended eastern Mediterranean region for several days. In this work, we analyze the influence of the transported biomass burning particles on the aerosol properties in the free troposphere, as well as on the surface UV radiation levels over Thessaloniki during the last week of August 2023. The transported smoke plume was detected over the Laboratory of Atmospheric Physics (LAP) in Thessaloniki, approximately 240 km away from the burning area, from August 22nd to the 25th. During this period, the presence of smoke led to exceptionally increased levels of aerosol optical depth (AOD), reaching up to 3.4 at 340nm (the highest ever recorded in Thessaloniki), as well as high Ångström exponent (AE) values, peaking at 2.4 for the 440–870nm range, followed by high Fine Mode Fractions (FMFs), indicating the prevalence of fine-mode smoke aerosol particle. Moreover, during the event, the presence of the biomass burning aerosols led to a strong attenuation of the solar UV irradiance by up to 90 %, reaching unprecedented levels, similar of a solar eclipse. The primary goal of this study is to highlight the extensive impacts that wildfires have, which are anticipated to increase in frequency in the near future, due to the predicted rise in the rate of occurrence of summer heatwaves especially for Mediterranean areas and specifically for Greece. Furthermore, the great value of the synergistic monitoring of the event with ground-based remote sensing instrumentation, along with satellite aerosol observations and modeling tools, is made prominent.

Ce(III) formate-derived hierarchical cerium oxide particles with icosahedral symmetry-based architectures: Effect of third level of structural hierarchy in soot and propane oxidation

The article investigates the role of architecture of complex hierarchically structured ceria and gadolinium doped ceria particles in soot combustion (solid-solid reaction) and propane oxidation (gas-solid reaction). Synthesis of hierarchical ceria mesostructures showing icosahedral symmetry-based architecture has been presented for the first time. Carefully choosing synthetic conditions allows to obtain particles with intended morphology of dodecahedron, rhombic hexecontahedron, great stellated dodecahedron, fractal-like branched great stellated dodecahedron and great dodecahemicosacron polyhedra. Twinning-based multiple branching of Ce(III) formate crystals by {101} twin orientation relation was proposed as a driving mechanism for the formation of macroparticles architecture that has been confirmed by the construction of macroparticle models using the identified twinning law. In the catalytic studies, the third level of the material organizational structure referring to shape of hierarchical macroparticles was chosen as a tested variable, while other architecture-related properties were controlled to be alike. In result, the shape of hierarchical particles plays a vital role in the catalytic soot oxidation, and architecture modulation allows the catalytic properties of the material to be enhanced through increasing the geometrical fit between ceria and soot particles. The best sample lowers temperature of half oxidation by 143 °C as compared to non-hierarchically organized ceria nanocrystals. The shape of hierarchical particles does not play leading role in gas-solid propane oxidation, but introduction of Gd dopant diversifies catalytic activity. The architecture of the particles may serve as a modifier of the catalytic activity through grain boundary engineering of gadolinium doped ceria.

Effect of airflow velocity in vessel-pipelines on dust explosion during pneumatic conveying

In order to investigate the flame propagation and pressure characteristics of dust particles during airflow transportation, a dust explosion experimental apparatus simulating dust handling processes was designed. The system is supplied with a stable airflow by a high-pressure fan, capable of continuously transferring dust from the vessel to the pipeline at a controllable speed. Dust explosion experiments were meticulously executed by applying 1 kJ of ignition energy to the transported dust particles at airflow velocities of 5, 10, and 15 m/s. This study examines the effects of airflow velocity, pipe diameter, and ignition position on explosion characteristics and delves into the mechanisms of these effects through a detailed analysis of experimental results. For the maximum explosion pressure, an increase in airflow velocity causes the maximum explosion pressure to rise. As the pipe diameter increases, the maximum explosion pressure first rises and then falls. The maximum explosion pressure occurs in the case of bottom ignition. The range of maximum explosion pressure values is expected to provide a reference for explosion detection and explosion venting. For flame propagation, the flame undergoes five processes within the vessel, including ignition of dust particles, spherical flame development, flame stretching towards the mouth of the pipe, complete combustion of particles, and near exhaustion of particle combustion. The higher the airflow velocity and the larger the pipe diameter, the more pronounced the flame stretching and development towards the pipe opening become. Within the pipe, two distinct flame propagation behaviors were observed under conditions of high and low airflow velocities. Compared with the experimental results of high-pressure pneumatic powder spraying forming a dust cloud within a vessel-pipeline, this study measures the maximum explosion pressure at specific turbulence levels and establishes a quantitative relationship between airflow velocity and explosion characteristics. Utilizing this correlation can provide a reference for predicting industrial-grade dust explosion characteristics at different airflow velocity levels, thereby offering a more optimized design basis for the design and safety protection of industrial equipment.

A quantitative theory for heterogeneous combustion of nonvolatile metal particles in the diffusion-limited regime

The paper presents an analytical theory quantitatively describing the heterogeneous combustion of nonvolatile (metal) particles in the diffusion-limited regime. It is assumed that the particle is suspended in an unconfined, isobaric, quiescent gaseous mixture and the chemisorption of the oxygen takes place evenly on the particle surface. The analytical solution of the particle burn time is derived from the conservation equations of the gas-phase described in a spherical coordinate system with the utilization of constant thermophysical properties, evaluated at a reference film layer. This solution inherently takes the Stefan flow into account. The approximate expression of the time-dependent particle temperature is solved from the conservation of the particle enthalpy by neglecting the higher order terms in the Taylor expansion of the product of the transient particle density and diameter squared. Coupling the solutions for the burn time and time-dependent particle temperature provides quantitative results when initial and boundary conditions are specified. The theory is employed to predict the burn time and temperature of 10–100 μm iron particles, which are then compared with measurements, as the first validation case. The theoretical burn time agrees with the experiments almost perfectly at both low and high oxygen levels. The calculated particle temperature matches the measurements fairly well at relatively low oxygen mole fractions, whereas the theory overpredict the particle peak temperature due to the neglect of evaporation and the possible transition of the combustion regime.Novelty and significance statementFor the first time, we present a comprehensive and quantitative analytical theory elucidating the heterogeneous combustion of nonvolatile (metal) particles in the diffusion-limited regime. This novel theoretical model exhibits a remarkable capacity for quantitative prediction, obviating the need for supplementary information from numerical simulations or experimental data. The derivation process of analytical solutions for burn time and time-dependent particle temperature from conservation equations is elaborated, offering transparency and insight into the model’s foundations. To demonstrate the practical utility of the theory, we apply it to analyze the combustion of iron particles, providing valuable mathematical perspectives on the underlying processes. The model’s predictions for burn time and temperature align closely with experimental results, offering a partial validation of the theory within the realm of its applicable assumptions. This pioneering work contributes a robust and versatile analytical framework, advancing our understanding of diffusion-limited combustion phenomena of nonvolatile particles.

Dry deposition fluxes, source, and potential ecological impact of amino acids in the Danjiangkou Reservoir of China's South-to-North water transfer project

As a nitrogen source for biological growth, amino compounds can participate in global nitrogen cycle processes and directly impact ecosystems. Dry deposition samples were collected from September 2020 to August 2021 from the Danjiangkou Reservoir of the South-to-North Water Transfer Project. The dry deposition characteristics of amino acids in the reservoir area were analyzed, their sources were resolved, and the potential ecological impacts were evaluated. The results showed that the dry deposition flux of dissolved free amino acids was 0.48 kg N ha−1 yr−1 and that of dissolved combined amino acids was 1.09 kg N ha−1 yr−1 in Danjiangkou Reservoir. The dominant amino acid fractions were glutamic acid and aspartic acid. Agricultural activities, coal combustion, and primary biogenic particles influenced the amino acid deposition in the reservoir area. The potential source areas for amino acid deposition mainly influenced the northeast, southwest, northwest, and south of the reservoir. The amounts of amino acids entering the water bodies via dry deposition was 85.72 t N yr−1, contributing 0.83 g C m−2 yr−1 of new production to the reservoir water bodies. To summarize, this research depicted that the potential ecological impact of dry deposition of amino acids on artificial freshwater lakes should not be overlooked.

Amino acids in the water-soluble and water-insoluble fractions of the aerosols at a forested site in Japan

In order to clarify the concentration levels and sources of the water-insoluble amino acids (WIAA) in aerosols that have been received little attention in previous studies and to discuss their potential impact on nitrogen deposition, the WIAA in the coarse-mode (d = 2.0–10 μm) and fine-mode (d < 2.0 μm) aerosols were measured at a forested site in Japan together with the water-soluble free and combined amino acids. The sum of the WIAA showed more than a 6-times higher concentration than that of the water-soluble amino acids in the coarse-mode range and a similar concentration to that in the fine-mode range, which suggests a significant contribution of the WIAA to the amino acids pool in aerosols. The WIAA were predominantly partitioned into the coarse-mode range. The concentration of the coarse-mode WIAA was the highest in the summer and a strong correlation was found between the coarse-mode WIAA and nss-K+ concentrations. These results suggest that plant debris and the associated materials are important sources for the coarse-mode WIAA and the increase in the suspension of these particulate materials caused the enhancement of the WIAA in the summer. Remarkably higher concentrations of the coarse-mode WIAA than the water-soluble amino acids would be caused by these particulate materials. In the fine-mode range, on the other hand, the concentration of the WIAA was the highest in the spring and strongly correlated with the fine-mode nss-K+ concentrations. The fine-mode WIAA would be mainly derived from the biomass burning particles. The coarse-mode WIAA were estimated to significantly contribute to the dry deposition flux of the total nitrogen. The present study implies a potential impact of the WIAA in the coarse aerosols on nitrogen deposition.

Combustion and energy performance of multiple aluminum-based alloy particles

The long ignition delay time, high ignition temperature and agglomeration prevent the aluminum (Al) particles from fully releasing the chemical energy stored within them during combustion. Al-based alloy fuels with high energy density and excellent combustion performance have become a potential candidate for replacement with pure Al. Therefore, understanding the combustion and energy performance of Al-based alloys is beneficial for the development of Al-based energetic materials. Herein, the combustion and energy performance of pure Al and three Al-based alloys were comparatively investigated by means of a thermal analysis system, an ignition and combustion test apparatus, and a variety of physicochemical property characterizations. The results showed that all three Al-based alloys contained at least one intermetallic compound. Al-boron (B) and Al-magnesium (Mg)-B alloys had higher theoretical energy densities than pure Al, while Al-Mg did not. The thermal oxidation properties of all three alloys were significantly better than those of pure Al. Compared with pure Al, the three alloys showed higher burning rate, shorter ignition delays, more vigorous combustion, and higher burnout at room pressure in air. This is still true after adding AP. According to the compositions of the condensed combustion products, the possible chemical reactions during the combustion of the alloys were speculated. Grasping the combustion mechanisms of the alloys is challenging due to the relative lack of thermodynamic data on intermetallic compounds. Finally, a comprehensive comparison of the combustion processes of pure Al and alloys was made. Although the Al-Mg alloy does not have the same theoretical energy density as pure Al, the more outstanding combustion performance and fewer two-phase flow losses may make up for the gap in theoretical energy density.

Mapping the constituent preference of tree species for capturing particulate matter on leaf surfaces using single-particle mass spectrometry and supervised machine learning

Respiratory health is negatively influenced by the dimensions and constituents of particulate matter (PM). Although mass concentration is widely acknowledged to be key to assessing dust retention by urban trees, the role of plant leaves in filtering PM from the urban atmosphere, particularly regarding the particle dimensions and chemical constituents of retained PM on the leaf, remains elusive. Here we combined single-particle aerosol mass spectrometry and a particle resuspension chamber to investigate how urban tree species capture PM constituents. Results indicate that leaves are efficient in capturing relatively larger particles (1.0–2.0 μm). Compositionally, airborne particles were mostly composed of elemental carbon (EC, 20%), organic carbon (OC, 17%), and secondary reaction products (13%). However, leaf surfaces revealed a preference for retaining crustal species, comprising 55% of captured particulates. Notably, specific tree species demonstrated varied affinities for different PM constituents: Osmanthus fragrans Lour. predominantly captured levoglucosan (LEV), indicative of its efficiency against biomass burning particles, whereas Cinnamomum camphora (L.) J.Presl and Sabina chinensis var. kaizuca W.C.Cheng & W.T.Wang were more effective in capturing heavy metals (HMs). XGBoost modelling identified indicator ions, e.g., CN−, NO3−, NO2−, PO3−, with SHAP values surpassing 0.035, suggesting a preferential adsorption of these ions among different tree species. These findings demonstrate that the particulate capture efficiency of urban tree species varies with species-specific leaf properties, particularly in their ability to selectively adsorb particles containing hazardous constituents such as LEV and HMs. This study provides a scientific basis for the strategic selection of tree species in urban forestry initiatives aimed at improving air quality and public health.

Spatiotemporal of Particulate Matter (PM2.5) and Ozone (O3) in Eastern Northeast Brazil

ABSTRACT This research examines particulate matter with a diameter of 2.5 micrometers (PM2.5) and ozone (O3) variation across the climatic mesoregions of Alagoas. Mean PM2.5 and O3 concentrations across three mesoregions were as follows: East (5.91; 44.22 μg.m−3), Hinterland (6.90; 44.18 μg.m−3), and Arid (7.03; 44.23 μg.m−3). Spatial and temporal variations were observed, with PM2.5 concentrations highest in the northwest (NW) and O3 concentrations in the east (E), influenced by local sources, weather, and transportation. Differences between rainy and dry years were noted, attributed to biomass burning and dust particle transport. This study establishes a baseline for understanding air quality, lacking monitoring stations, aiding policymaking. It provides insights into PM2.5 and O3 dynamics, with PM2.5 concentrations highest in the NW and lower O3 concentrations in the E. Temporal variations emphasize the need for dynamic monitoring. Positive correlations between PM2.5 and O3 highlight complex relationships. Practical implications include proactive policymaking and the necessity for monitoring stations. Rigorous statistical methodologies inform model selection, enhancing environmental data understanding. Despite changes in land use, studies on extreme probability distributions are limited, emphasizing the need for robust methodologies for environmental data analysis to address air pollution challenges effectively in Alagoas.

Impact of Aluminium and Titanium Additives on Ignition and Combustion in Boron-Loaded Gelled Jet A-1 Fuel

ABSTRACT A high-energy metal has been identified as a possible supplementary energy source for liquid fuel, which can be used to fuel volume-limited propulsive devices. However, the stability of metal particles in liquid fuel is a significant disadvantage, which can be overcome by suspending the particles in the gel fuel network. Boron’s (B) high energy density makes it a potential choice as fuel or energetic fuel additive for propulsion systems. However, the combustion of boron particles is challenging due to a native oxide layer on the boron particle surface that acts as an inhibitor. The influences of aluminum and titanium addition into the gel fuel containing boron particles have been investigated in the present study to understand whether Al or Ti positively enhances the ignition and combustion of boron particles. A droplet combustion study was conducted for gel fuel samples containing boron, boron-aluminum, and boron-titanium combinations. The key analyses include the feature of droplet diameter regression, the effect of Al/Ti additive on the ignition delay of boron particles through spectroscopic analysis, combustion of boron particles through chemiluminescence measurement of intermediate species of boron combustion (BO2) and flame imaging, and analysis of combustion residues. The obtained results and corresponding analyses suggest that the addition of Al particles improves the ignition of boron. In contrast, Ti particles significantly enhance the combustion of boron particles loaded in gel fuel.

Temperature evolution of laser-ignited micrometric iron particles: A comprehensive experimental data set and numerical assessment of laser heating impact

This study examines the effects of laser heating on the ignition and critical combustion characteristics, such as temperature and burn time, of individual iron particles. It provides time-dependent temperature profiles of laser-ignited particles across a broad spectrum of particle size distributions and oxygen concentrations obtained from experiments, which are a useful database for further development and validation of iron particle combustion models. The herein reported datasets significantly complement those existing in the literature. In the current study, the raw data are thoroughly re-evaluated using refined approaches. For the experimental canonical configuration of single iron particle combustion, an ignition system based on laser heating provides several advantages in overcoming temperature field uncertainties and facilitating controlled environments for optical diagnostics. Despite the inherent uncertainties in laser heating, associated with non-uniform intensity profiles and particle size variations, this study addresses the critical question of how these uncertainties affect in situ measurements of particle temperature and time to reach peak temperature. This study, conducted using a numerical model, reveals a dependence of the particle temperature after laser heating on particle size. However, this dependence does not significantly impact the key parameters of iron-particle combustion, such as the maximum temperature and burn time of the laser-ignited iron particle. The study also presents a comparison between the simulated particle temperature histories and those derived from two-color pyrometry measurements for a wide range of particle size distributions and oxygen concentrations. Notably, by implementing a laser-heating sub-model into an iron particle combustion model, assuming external-diffusion-limited oxidation only up to stoichiometric FeO, the temperature evolution up to the maximum temperature is reasonably captured for a wide range of particle sizes (20–53μm) and oxygen volumetric fractions (14–21vol% O2 mixed with N2). However, with increasing oxygen concentration, the external-diffusion limited model significantly overestimates the heating rate and subsequently the maximum particle temperature.

Micron-sized aluminum particle combustion under elevated gas condition: Equivalence ratio effect

Micron-sized aluminum (Al) particle combustion under elevated gas condition is critical for improving energetic material performance, impacting propulsion and explosives technology. This study utilizes Eulerian-Lagrangian method to investigate Al particle combustion dynamics, encompassing both heterogeneous reaction (HTR) and homogeneous reaction (HMR). It focuses on the critical role of the equivalence ratio in single Al particle combustion, highlighting the interplay between HTR and HMR, aiming to optimize energy release and emission control. Our study identifies four stages in the combustion of a single Al particle, where the highest heat release is attributed to HTR, succeeded by HMR, and the minimal from unburned Al vapor. We observe a decline in the total heat release rate with an increasing equivalence ratio, primarily due to the differential impacts of heterogeneous and homogeneous reactions. The thermal-runaway stage in HTR is governed by the particle temperature, while the subsequent decaying stage is influenced by either the diminishing effective Al droplet diameter or the availability of oxygen, contingent upon the fuel conditions. Utilizing Cantera software to analyze HMR allows us to elucidate the thermal effects of elementary reactions and the key reaction pathways. These findings underscore the complex interactions between Al particles and the surrounding gas, providing insights into optimizing the conditions for Al-containing reaction systems.

New experimental method for the simultaneous determination of concentration and size profiles of condensed combustion products around a burning aluminum droplet

When an aluminum particle burns in the diffusive regime, a cloud of nanometric particles of its primary oxide, alumina, is formed around the droplet. Characterizing this oxide smoke surrounding a burning aluminum droplet is essential. The original contribution of this paper is to introduce an experimental approach that allows for simultaneous size and concentration measurement of the particles composing the oxide smoke. This paper employs an electrodynamic levitator to facilitate the self-sustained combustion of an isolated aluminum particle, with a radius of 35μm, in atmospheric air. This levitation apparatus is paired with an optical setup that allows for a multi-spectral light extinction method. This technique is specifically designed to measure the size and concentration of alumina particles below the micrometric scale, which is scarcely documented in existing literature. Consequently, spatially resolved concentration and size profiles of the nanometric alumina particles are measured and compared to simulated data from the literature. The radii of alumina particles in the cloud are found to evolve closely around 80 nm. Volume fractions are evaluated from 2.8⋅10−4 near the particle surface to 3⋅10−5 further in the cloud. Therefore, significant concentrations of alumina particles are revealed during the short (15 to 20 ms) combustion process at distances of the order of magnitude of a few initial particle diameters. Such characterization could then lead to a better assessment of the interaction distance among aluminum particles as they burn collectively.Novelty and significance statementThis article introduces the first experimentally determined profiles of alumina concentration and size distribution surrounding a single burning aluminum droplet. The uniqueness of our experimental setup lies in its ability to study of the most fundamental case of the autonomous combustion of a single levitating particle, without any convective effects. A new non-intrusive method specifically designed provides unprecedented results in the field of metallic particle combustion. Data provided in the paper are crucial as they serve as the first reference case for future simulation and experiments. The results introduced in this paper highlight the inability of current simulation methods to accurately account for nucleation and condensation processes, and emphasize the need for a non-invasive characterization method.