Combustion Of Particles Research Articles

Features of the Mechanism of Gas-phase Ignition of Wood Biomass Particles

ABSTRACT Use of woody biomass instead of coal as fuel for thermal power plants (TPP) is considered a promising direction for reducing emissions of anthropogenic substances during the operation of coal-fired thermal power plants. But the process of replacing coal with wood in the thermal power industry is happening very slowly due to objective reasons. The main one is the deposition of particles that have not fully passed the pyrolysis stage (in this case, a layer of substance in a resinous state is retained in the wood particle) on heating surfaces (for example, superheaters) and a decrease in the efficiency of using the heat of combustion of fuel as a result of contamination of the heating surfaces. Therefore, when developing technologies for burning dispersed wood in the furnaces of boiler units, reliable experimental data are required on the characteristic times of ignition and combustion of woody biomass particles, taking into account the time of transition from local (focal) gas-phase ignition to the combustion of volatiles in the entire vicinity of the particle (tsf). The article presents the results of experimental studies of flame propagation processes in the small vicinity of a particle during the ignition period. The experiments made it possible to establish that the flame propagation velocity in the small vicinity of the particle significantly depends on the ambient temperature. It is shown that under conditions of low-temperature heating (air temperature Tg = 873 K), the propagation velocity of the combustion (flame) is minimal. An increase in Tg values (from 873 K to 1273 K) leads to a significant (4–5 times) increase in the time of complete flame coverage of the particle. According to the results of the experiments, two heating modes were identified: high-temperature and low-temperature with a conditional interface Tg = 873 K. At Tg = 873 K, the characteristic particle size of wood biomass has no significant effect on the characteristics and conditions of flame propagation in a small vicinity of the particle. An increase in the ambient temperature (up to 1273 K) leads to an increase in the influence of particle size on the characteristics and conditions of flame propagation. A hypothesis describing the process of flame propagation has been developed.

Cofiring of renewable biodiesel fuels inside natural gas flame for enhancement of thermal properties of flame and NOx reduction

AbstractThis study investigates the co‐combustion of palm oil biodiesel fuel, as a renewable alternative for diesel fuel, inside natural gas flame to enhance the flame thermal specifications and NOx reduction. A power natural gas burner with a maximum heat capacity of 418,400 kJ/h was installed at the inlet of a laboratory furnace and biodiesel fuel was injected inside natural gas burner with a 100 μm in diameter solid cone nozzle. Flame temperature, thermal radiation, Infrared radiation, and CO, CO2 and NOx emission were measured. The results revealed that biodiesel injection increases the flame size and turns the non‐luminous blue flame into yellow‐colored flame. Furthermore, higher flash point and Sauter Mean Diameter of biodiesel promote the thermal decomposition of fuel droplets and increase the concentrations of Intermediate Soot Particles in the flame which in turn increases the flame emissivity coefficient and consequently flame thermal radiation. Also, the oxygen content of biodiesel fuel has an important role in the complete combustion of Intermediate Soot Particles to CO2 which increases the heat release of biodiesel combustion and raises the flame temperature. The average enhancement in thermal radiation and flame temperature were 5.6% and 43.38%, respectively. Finally, although biodiesel injection increases the flame temperature, it also increases the flame surface reaction and eliminates the hot spot region in the flame. Therefore, the rate of heat generation per unit volume of flame decreases and this decreases the rate of NOx emission as much as 10.84%.

Comparative radiative property measurements of single biomass and coal particles burning at high reactor temperatures

This research measured the emissivity, temperature and soot loading of pulverized bituminous coal and three types of renewable biomass. Combustion occurred in a laboratory-scale drop tube furnace (DTF), where the fuels experienced high heating rates and ignited and burned in two distinct phases: devolatilization accompanied by volatile matter combustion in envelope flames, and sequential combustion of the char residues. Multi-wavelength spectrometry was used to concurrently determine the emissivity and the temperature of burning particles at discrete points in their history. Three-wavelength pyrometry was used to obtain entire temperature-time histories, and high-speed photography was used to provide both visual observations of phenomena and to obtain two-dimensional temperature distributions. Results showed that soot in volatile matter flames of burning single particles of the bituminous coal and of the three types of torrefied biomass had spectral emissivities in the range of 0.03–0.10, in the wavelength domain of 600–1000 nm. Emissivities were nearly constant with wavelength, i.e., soot mantles in these flames radiated as graybodies. Spectral emissivities of the chars of the bituminous coal and the three types of torrefied biomass were in the range of 0.29–0.5 and varied with wavelength, i.e., they radiated as non-graybodies. The highest measured temperatures of soot in volatile flames for all fuels were between 2150 and 2360 K and maximum temperatures of chars were between 1700 and 2000 K, based on the three measurement techniques. The graybody assumption caused negligible (± 10 K) deviations in volatile matter flame temperatures; however, it caused significant deviations (± 20–100 K) in char temperatures. Envelope flame diameters of torrefied biomass particles were larger than those of coal. To the contrary, soot volume fractions in the envelope flames of coal particles were found to be higher than those in biomass particle flames. Finally, the soot volume fractions in the flames of these fuels were inversely proportional to particle size.

Studying the Structure‐Reactivity Relationship of CuO/CeO2 for Catalytic Soot Particulate Combustion: On the Monolayer Dispersion Threshold Effect

AbstractTo elucidate structure‐reactivity relationship and prepare improved catalysts for soot combustion, a series of CuO/CeO2 with different loadings have been fabricated by the impregnation method. With XRD and XPS extrapolation methods, it is disclosed that CuO disperses finely on the CeO2 support to form a monolayer with a capacity around 1.06 mmol 100 m−2, which equals to 2.9 wt. % CuO loading. Below this capacity, CuO is in a sub‐monolayer state. However, above this capacity, CuO micro‐crystallites are formed, and co‐exist with the monolayer CuO. By increasing CuO loading, soot combustion activity of the catalysts increases as well until it reaches the monolayer dispersion capacity. Further increasing the CuO loading to 5 % decreases the activity slightly, and then remains constant. Therefore, an apparent monolayer dispersion threshold effect is observed for soot combustion on CuO/CeO2 catalysts. It is found that the amount of surface‐active O2− sites plays critical role for the catalytic activity. To obtain the most active CuO/CeO2 catalyst, a monolayer amount of CuO should be loaded on the supports.

Combustion in a chamber furnace with a tangentially swirling vortex

Relevance. The need to analyze the furnace processes in boiler units with vertical vortex when arranging pulverized coal combustion with the enhancement of environmental parameters through the installation of tertiary blast nozzles. Despite the carbon-free policy in modern power engineering coal remains one of the main sources of energy, so the reconstruction of boiler units in order to reduce harmful emissions is very relevant. Aim. To study aerodynamics and combustion processes of pulverized coal fuel in the furnace chamber of a boiler unit with a tangential arrangement of burner devices using a combustion scheme with tertiary air blowing. Methods. The Eulerian–Lagrangian approach was applied to numerical study of flow characteristics, heat transfer and combustion in a furnace with a tangential burner arrangement. Also, k-ε model of gas turbulence, particle-turbulence interaction, diffusion model of particle dispersion, P-1 radiation modeling method and pulverized coal particle combustion model based on global particle kinetics and experimental data were used for numerical calculations. Results. Based on numerical calculations and analysis, the dependences of combustion product concentrations, temperature, hydrodynamics at combustion of Kuznetsky coal grade D in the furnace chamber with tangential arrangement of burners for brown coal, as well as at installation of tertiary blast nozzles have been obtained. Insufficient redistribution of air between burners and tertiary nozzles is revealed, as for maintenance of stable twist of vertical vortex and accordingly presence of high values of velocities at the outlet of burner devices it is not possible to increase the portion of tertiary air without reconstruction of burners. It is also established that the volume of the furnace chamber below the burners is poorly involved in heat exchange.

Ignition characteristics of single coal particles under ammonia co-firing conditions

To meet the goal of an international carbon-neutral framework, the promotion of clean coal utilization occupies a vital position in reducing greenhouse gas emissions. Ammonia co-firing is considered as a potential strategy for future power generation to reduce fossil energy consumptions, soot, CO2 emissions, and hydrocarbon pollutants. In the present work, the ignition characteristics of single coal particles under ammonia (NH3) co-firing conditions were investigated. Particles were injected with NH3 or N2 into a hot flue gas environment at 1550 K generated by a CH4-fired Hencken burner. Temporally resolved images of CH* chemiluminescence and char thermal radiation were captured. Combining the signal profiles, ignition modes and characteristic times of single burning particles were studied with different coal types, carrying atmospheres, and O2 contents. When the carrier gas was replaced by NH3 atmosphere, the ignition delay time of all coal particles was greatly shortened, and the time interval from ignition to peak, as well as the combustible component burnout time, were both lengthened due to the promoted devolatilization and combustion reaction rates of coal particles caused by the NH3 flame. Concerning the ignition mode in the NH3-blended cases, the homogeneous ignition behaviors of the lignite particles were further enhanced, while the bituminous particles transitioned to the homogeneous-heterogeneous united ignition mode. As the O2 content in the flue gas increased, the ignition of all coal particles was advanced monotonously, and the chemiluminescence became more intense in both N2 and NH3 atmospheres.

Combustion of iron particles in solid propellants at elevated pressure

Metal fuels, such as aluminum (Al) and iron (Fe), can be added to composite solid propellants to improve their performance, such as specific impulse, density, and burning rate. In comparison to aluminum, iron can theoretically provide improved density specific impulse and higher flame temperatures; reduce condensed combustion product (CCP) concentration and the associated two-phase flow losses; and eliminate hydrochloric acid (HCl) in the exhaust products. A fundamental and quantitative understanding of metal particle aggregation and agglomeration processes in solid propellants is required to understand the underlying combustion mechanisms in these systems. In the current study, composite strand and laminate AP/HTPB/AP propellant samples loaded with Fe microparticles (∼45 μm in diameter) were burned at elevated pressures in an optically accessible strand bomb. Combustion processes were monitored with transient pressure diagnostics and a high-speed camera fitted with a high-magnification lens system (3.83 μm/pixel resolution) for the laminate propellant experiments. An automated image processing algorithm was developed to measure burning rates and ejected particle/agglomerate sizes and velocities. Time-resolved statistical distributions of both particle size and velocity are presented at elevated pressure for multiple laminate propellant experiments with a high degree of repeatability and low measurement error estimated as < ±5% and < ±1.5% for particle size and velocity, respectively. The incorporation of iron microparticles into the composite strand propellants yielded over a 20% increase in the global burning rate over the range of pressures evaluated (3.45–13.8 MPa). Similarly, the addition of iron to the fuel lamina in laminate propellant samples led to an approximately 30% increase in the global burning rate at the evaluated pressure (3.45 MPa). Additive particles were observed to eject near the oxidizer/fuel interface, or to melt, aggregate, coalesce, and agglomerate on the fuel lamina surface prior to ejection. Particle velocities are controlled by a balance of gravitational forces, drag forces imparted by expanding combustion product gases, and particle inertia. The observed combustion enhancements are attributed to the combined effects of catalytic mechanisms, increased radiation heat transfer, and local energy release from reacting iron particles. In addition, discussions on the image processing methods developed in the current study, corresponding potential sources of error, and prospective areas of improvement are provided. The experimental approach developed enables high-speed and high-magnification visualization of propellant combustion at high pressures and can be utilized to better understand the fundamental combustion behavior of energetic systems.

Neurodegenerative effects of air pollutant Particles: Biological mechanisms implicated for Early-Onset Alzheimer’s disease

BackgroundSporadic Alzheimer’s disease (AD) occurs in 99% of all cases and can be influenced by air pollution such as diesel emissions and more recently, an iron oxide particle, magnetite, detected in the brains of AD patients. However, a mechanistic link between air pollutants and AD development remains elusive. AimTo study the development of AD-relevant pathological effects induced by air pollutant particle exposures and their mechanistic links, in wild-type and AD-predisposed models. MethodsC57BL/6 (n = 37) and APP/PS1 transgenic (n = 38) mice (age 13 weeks) were exposed to model pollutant iron-based particle (Fe0–Fe3O4, dTEM = 493 ± 133 nm), hydrocarbon-based diesel combustion particle (43 ± 9 nm) and magnetite (Fe3O4, 153 ± 43 nm) particles (66 µg/20 µL/third day) for 4 months, and were assessed for behavioural changes, neuronal cell loss, amyloid-beta (Aβ) plaque, immune response and oxidative stress-biomarkers. Neuroblastoma SHSY5Y (differentiated) cells were exposed to the particles (100 μg/ml) for 24 h, with assessments on immune response biomarkers and reactive oxygen species generation. ResultsPollutant particle-exposure led to increased anxiety and stress levels in wild-type mice and short-term memory impairment in AD-prone mice. Neuronal cell loss was shown in the hippocampal and somatosensory cortex, with increased detection of Aβ plaque, the latter only in the AD-predisposed mice, with the wild-type not genetically disposed to form the plaque. The particle exposures however, increased AD-relevant immune system responses, including inflammation, in both strains of mice. Exposures also stimulated oxidative stress, although only observed in wild-type mice. The in vitro studies complemented the immune response and oxidative stress observations. ConclusionsThis study provides insights into the mechanistic links between inflammation and oxidative stress to pollutant particle-induced AD pathologies, with magnetite apparently inducing the most pathological effects. No exacerbation of the effects was observed in the AD-predisposed model when compared to the wild-type, indicating a particle-induced neurodegeneration that is independent of disease state.

Carrier-Phase DNS of Ignition and Combustion of Iron Particles in a Turbulent Mixing Layer

Three-dimensional carrier-phase direct numerical simulations (CP-DNS) of reacting iron particle dust clouds in a turbulent mixing layer are conducted. The simulation approach considers the Eulerian transport equations for the reacting gas phase and resolves all scales of turbulence, whereas the particle boundary layers are modelled employing the Lagrangian point-particle framework for the dispersed phase. The CP-DNS employs an existing sub-model for iron particle combustion that considers the oxidation of iron to FeO and that accounts for both diffusion- and kinetically-limited combustion. At first, the particle sub-model is validated against experimental results for single iron particle combustion considering various particle diameters and ambient oxygen concentrations. Subsequently, the CP-DNS approach is employed to predict iron particle cloud ignition and combustion in a turbulent mixing layer. The upper stream of the mixing layer is initialised with cold particles in air, while the lower stream consists of hot air flowing in the opposite direction. Simulation results show that turbulent mixing induces heating, ignition and combustion of the iron particles. Significant increases in gas temperature and oxygen consumption occur mainly in regions where clusters of iron particles are formed. Over the course of the oxidation, the particles are subjected to different rate-limiting processes. While initially particle oxidation is kinetically-limited it becomes diffusion-limited for higher particle temperatures and peak particle temperatures are observed near the fully-oxidised particle state. Comparing the present non-volatile iron dust flames to general trends in volatile-containing solid fuel flames, non-vanishing particles at late simulation times and a stronger limiting effect of the local oxygen concentration on particle conversion is found for the present iron dust flames in shear-driven turbulence.

A Long-Term Comparison between the AethLabs MA350 and Aerosol Magee Scientific AE33 Black Carbon Monitors in the Greater Salt Lake City Metropolitan Area.

Black carbon (BC) or soot contains ultrafine combustion particles that are associated with a wide range of health impacts, leading to respiratory and cardiovascular diseases. Both long-term and short-term health impacts of BC have been documented, with even low-level exposures to BC resulting in negative health outcomes for vulnerable groups. Two aethalometers-AethLabs MA350 and Aerosol Magee Scientific AE33-were co-located at a Utah Division of Air Quality site in Bountiful, Utah for just under a year. The aethalometer comparison showed a close relationship between instruments for IR BC, Blue BC, and fossil fuel source-specific BC estimates. The biomass source-specific BC estimates were markedly different between instruments at the minute and hour scale but became more similar and perhaps less-affected by high-leverage outliers at the daily time scale. The greater inter-device difference for biomass BC may have been confounded by very low biomass-specific BC concentrations during the study period. These findings at a mountainous, high-elevation, Greater Salt Lake City Area site support previous study results and broaden the body of evidence validating the performance of the MA350.

Combustion Enhancement of Gel Propellant Containing High Concentration Aluminum Particles Based on Carbon Synergistic Effect.

The addition of aluminum particles to gel propellants can improve combustion performance. However, the agglomeration of aluminum during the combustion process can result in a series of negative effects. In this paper, the aluminum agglomeration inhibition method of gel propellant based on carbon synergistic effect is proposed. Carbon particles exhibit excellent combustion properties, and the gaseous product CO2 generated during combustion can mitigate the agglomeration of aluminum. The research demonstrates that incorporating carbon particles into aluminum-containing gel effectively reduces the incomplete combustion of aluminum particles and increases the volumetric calorific value of the gel. When the mass fraction of carbon is 5 wt%, the volume calorific value of the gel reaches the highest. Meanwhile, the rheological experiments show that the addition of carbon particles can improve the shear-thinning properties of the gel, which is beneficial to the atomization and combustion processes of the gel.

Energy balance and global characteristics of metal dust flames

Recently demonstrated high values of radiative loss during metal combustion require a new approach to describing dust flames. In particular, given strong light emission, the adiabatic flame temperature (AFT) concept is not applicable due to high radiative losses. Accordingly, global flame characteristics such as an expansion factor become unrelated to the AFT. That expansion factor can be directly inferred from the flame geometry, and therefore, its analysis offers a simple path to justify the need for a detailed energy balance in metal dust combustion. The analysis can also provide insight into peculiarities of the temperature distribution within the flame. In the current paper, previously published data on flow velocities in a metal dust flame are used for the expansion factor analysis. A relatively low value of the obtained expansion factor is reconciled with the advanced comprehension of metal particle combustion.

Temperature of Wood Char Particles Burning in a Fluidized Bed Reactor

In the present work it was studied the fluidized bed combustion of char particles made with wood of Mozambican origin to find out the evolution of the particles temperature during the combustion process. Samples of wood species Afzelia quanzensis and Pterocarpus angolensis were carbonized at 850 ºC in a nitrogen flow. Afterwards some of these char particles with sizes in the 9 to 13 mm range were burned in a bubbling fluidized bed, while at the same time their interior temperatures were measured. From the experiments, it was found that for these chars fragmentation was absent and that the measured temperatures with a thermocouple inserted into the particles was similar to the values that were obtained by means of an energy balance carried out at the surface of the particle.

Optimization of convection cooling by pressed brick structure and coke conversion rate in coke dry quenching furnace

Segregation of coke temperature and gas flow in Coke Dry Quenching furnace is a crucial issue in coke production, and the pressed brick structure of Coke Dry Quenching furnace plays a significant role in the problem of segregation. In this work, computational fluid dynamics simulation software Ansys Fluent and self-programmed equations were utilized to investigate the fluid flow and heat transfer processes, as well as coke particle combustion behavior, based on the No. 2 Coke Dry Quenching furnace at the Bayuquan coking plant of Ansteel. The focus was on analyzing the impact of gas flow rate and pressed brick structure on the furnace’s flow and temperature fields, as well as assessing the extent of coke particle combustion under different gas flow rates. The simulation involved the use of porous media models, pseudo-fluid models, and non-local thermal equilibrium to simulate the heat transfer processes within the CDQ furnace. The simulation results show that when the coke discharge rate was set at 160 t/h, selecting a circulating gas flow rate of 180,000 m3/h could ensure that the outlet temperature of coke meet the production requirement and reducing energy consumption. Optimizing the pressed brick structure appropriately can clearly improve the segregation in gas flow and temperature within the furnace. This led to a reduction of approximately 0.3 m in the height of coke isotherm line segregation at 500 K, while also lowered the average temperature at the coke outlet. Furthermore, we established the improved random pore model with two new equations to describe the evolution of coke porosity and the molar composition of the ambient gas, and real-time tracking of changes in coke porosity and considered the impact of variable gas concentration on coke conversion rate were provided. These findings offer valuable insights and reference for optimizing operational conditions and coke quality prediction in actual production scenarios.

Quantifying particulate matter optical properties and flow rate in industrial stack plumes from the PRISMA hyperspectral imager

Abstract. Industrial activities such as metallurgy, coal and oil combustion, cement production, and petrochemistry release aerosol particles into the atmosphere. We propose analyzing the aerosol composition of plumes emitted by different industrial stacks using PRISMA (PRecursore IperSpettrale della Missione Applicativa) satellite hyperspectral observations. Three industrial sites have been observed: a coal-fired power plant in Matla, South Africa (imaged on 25 September 2021); a steel plant in Wuhan, China (24 March 2021); and gas flaring at an oil extraction site in Hassi Messaoud, Algeria (9 July 2021). Below-plume surface reflectances are constrained using a combination of PRISMA and Sentinel-2/MSI images. Radiative transfer simulations are performed for each scene including the surface, background atmosphere, and plume optical properties. The plume aerosol optical thickness (AOT), particle radius, volume of coarse-mode aerosol, and soot are then retrieved within the plumes following an optimal estimation framework. The mean plume retrieved AOT at 500 nm ranges between 0.27 and 1.27 and the median radius between 0.10 and 0.12 µm. We found a volume fraction of soot of 3.6 % and 10.4 % in the sinter plant and coal-fired plant plumes, respectively. The mass flow rate of particulate matter at a point source estimated by an integrated mass enhancement method varies from 840 ± 155 g s−1 for the flaring emission to 1348 ± 570 g s−1 at the coal-fired plant.

The Role of Target Melting in Particle Impact Ignition with Inert Particulate

The high gas temperatures and oxygen pressures in the turbine of oxygen-rich turbomachinery put conventional engineering alloys such as IN718 at risk of particle impact ignition, i.e., metal fires initiated when particulate strikes a solid surface. The standard model of particle impact ignition assumes that the impacting particle must first ignite in order to kindle to the target material. Here, we invalidate this belief through particle impact ignition experiments which show that IN718 can ignite when struck by inert Al2O3 particles with supersonic impact velocities. Through post-mortem analysis of non-ignited samples, we find that subsonic particle impact causes minimal crater damage whereas supersonic particle impact leaves extensive crater plasticity and pileup, with evidence of molten ejecta near the impact site. Complementary finite element simulations of supersonic impact events confirm extreme adiabatic heating and localized melting. These findings demonstrate that particle impact can drive target ignition even in the absence of particle burning provided the thermal excursion at impact exceeds the melting point of the target material.

Effect of Horizontal Tube Position on Wall-to-Bed Heat Transfer in Air-Solid Fluidized Bed of Large Particles

Fluidized beds are extensively used in a variety of industrial applications, such as heat recovery systems, coal combustion, and solid particle drying. The effect of the position of the heat transfer tube on heat transfer from a horizontal bare tube in a 150 mm square cross-section fluidized bed containing large particles, ragi, and mustard is investigated. The influence of varying fluidizing velocities on heat transport is also examined for a fixed bed height of the large particles. When the position of the tube from the distributor plate was increased in 0.028m increments from 0.52 m to 0.080 m and then to 0.108 m, the heat transfer coefficient was reduced. Due to enhanced fluidization, all bed heights yielded almost comparable heat transfer coefficient values at velocities exceeding 1 m/s, 170 and 160 W/m2K for ragi and mustard, respectively. The dependency of the heat transfer coefficient on fluidizing velocity is qualitatively like that of small particles. An error deviation of around 8.8% was found when comparing experimental heat transfer coefficient values to those predicted from empirical correlations in the published literature.

Iron particles ignition in different hot coflow temperatures

Understanding the ignition of iron particle combustion in hot environments is critical for harnessing the use of metal fuels in clean energy production. In this research work, a new single particle burner is implemented to disperse and burn iron particles using hot air coflow. The burner disperses iron particles through Coulomb forces between two air-spaced capacitor electrodes. The oxidizer coflow is heated up as it passes through a newly designed induction gas heater. Electromagnetic induction is used to heat up multiple metallic and porous heat discs by Joule heating. When the coflow gas passes through the pores of the discs, it carries the heat generated within the porous discs and delivers it to the travelling iron particles which provides ultimate heat transfer effectiveness. Coflow temperature homogeneity is examined using Schlieren imaging and confirmed by thermocouple measurements at the outlet of the coflow tube. Particle ignition and combustion occur in open space, providing excellent conditions for optical diagnostics. Two synchronized high-speed cameras were used to simultaneously determine the particle size using green laser shadowgraphy and detect iron particles ignition. Iron particles ignition experiments were conducted for a sieved patch (45–53 μm) at different hot coflow temperatures starting at 700℃ up to 900℃. The burner showed extensive capabilities to maintains a stable and homogeneous hot coflow for a wide range of temperatures up to 900℃. Ignition experiments showed 5.67 % of ejected particles are burnt at 700 ℃, while full ignition (99.33 %) can be achieved at 900 ℃.

Carrier-phase DNS study of particle size distribution effects on iron particle ignition in a turbulent mixing layer

The ignition and combustion of iron particles in a turbulent mixing layer is studied by means of three-dimensional carrier-phase direct numerical simulations (CP-DNS). A particular focus is set on particle size distribution (PSD) effects on the ignition behaviour by comparing CP-DNS results from using a realistic experimental PSD to DNS data based on a monodisperse (MD) particle cloud with the same equivalence ratio. The CP-DNS solves the Eulerian transport equations of the reacting gas phase and resolves all turbulent scales, while the particle boundary layers are modelled in the Lagrangian point-particle framework. A previously validated sub-model for the oxidation of iron to Wüstite (FeO) that accounts for both diffusion- and kinetically-limited combustion is employed. The mixing layer is initialised with an upper stream of air carrying cold iron particles and an opposed lower stream of hot air. Simulation results show distinct differences in the ignition behaviour between the MD and PSD cases. The ignition of the PSD case is delayed compared to the MD case and does not show any significant particle clustering prior to ignition. Further investigations indicate that the particle size has a crucial effect on the mixing process and ignition time. Small particles start their oxidation process early and already consume some of the available oxygen, while not crucially affecting the gas temperature due to their limited iron mass contribution. Conversely, a slower entrainment into the lower stream combined with higher thermal inertia and the prior oxygen depletion by the small particles leads to a delayed oxidation of the larger particles. As a net result, the PSD case shows a wide spread of individual particle ignition delay times and overall delayed bulk ignition compared to the MD case, where the majority of the particles ignites over a shorter period of time.

In-situ light extinction nano-oxide volume fraction measurements during single iron particle combustion

In-situ measurements of the volume fraction of nanoparticles generated during the combustion of single iron particles were conducted using a high-speed light extinction method. The process of nanoparticles generation from iron particles burning under conditions of 21% oxygen concentration and ambient temperatures of 1400 K and 1850 K can be divided into three stages: acceleration of productivity, stable productivity, and continuous growth of volume fraction after the cessation of nanoparticles generation on the iron particle's surface. The productivity of nanoparticles in stage 2, which is proportional to the particle diameter, suggests that the nanoparticles generation process in this stage may be influenced by the outward diffusion of gaseous Fe and FeO. Approximately 2% to 4% of iron is converted into nanoparticles after combustion, and the conversion rate decreases with increasing particle diameter. Accurate values of the refractive index of iron and its oxides at high temperatures and in the liquid phase will contribute to improving the accuracy of the light extinction measurement since those values significantly affect the measured results of the volume fraction of nanoparticles.