Soot Distribution Research Articles

Endoscopic visualization of engine combustion chamber using diesoline, diesosene and mineral diesel for comparative spatial soot and temperature distributions

Diesel engines are the prime workhorses of global transport and agriculture sectors. However, they emit significantly higher quantities of oxides of nitrogen (NOx) and particulate matter (PM). This unique study involves evaluation of in-situ spatial distribution of temperature and soot in the engine combustion chamber using high-temperature endoscopy, while the engine was being fuelled with emerging fuels so that suitable strategies for effective control of emissions could be devised. Two new test fuels namely diesosene (K20) (20% kerosene (v/v) blended with mineral diesel) and diesoline (G20) (20% gasoline (v/v) blended with mineral diesel) were compared with the baseline mineral diesel in a conventional direct injection compression ignition (DICI) engine. These two fuels represent relatively inferior quality diesel, which is increasingly available in global markets due to gradually exhausting petroleum resources and is produced from heavier/residual crude left in the oil wells. Diesoline showed superior combustion characteristics compared to diesel and diesosene. Endoscopic visualization technique emerged to be an effective tool, wherein real-time combustion characteristics of various test fuels could be successfully evaluated in a time efficient and cost-effective manner. This research article shows the experimental implementation of an emerging optical technique, which might be potentially useful in designing more efficient engines in quicker turn-around time for research and development.

Treatment of efficiency for temperature and concentration profiles reconstruction of soot and metal-oxide nanoparticles in nanofluid fuel flames

The choice of the step size plays an important role in one dimensional searching (ODS) algorithm in the inverse radiation problem to simultaneously estimate temperature and concentration distributions of soot and metal-oxide nanoparticles in nanofluid fuel flames. In practice, it is difficult to determine the optimal step size and the inappropriate step size can introduce significant reconstruction error and cause high computation time. This paper adopts a nonlinear optimization (NLP) technique without the needing of setting up the step size to improve the reconstruction efficiency. The reconstruction performances of NLP technique were compared with the ODS algorithm with different step sizes. It was found that the NLP technique can reach the same or better reconstruction accuracy and experience much lower computation time in comparison with the ODS algorithm even with the optimal step size.

Effects of large aromatic precursors on soot formation in turbulent non-premixed sooting jet flames

In this paper, we computationally study the effects of large Polycyclic Aromatic Hydrocarbons (PAH) (more than two aromatic rings) on soot yield and distribution in turbulent flames, when they are considered as nucleating species for soot formation. This is examined in two turbulent non-premixed sooting jet flames using ethylene and a jet fuel (JP-8) surrogate as fuels. For each flame, two Large-Eddy Simulations (LES) are performed with two different soot nucleation strategies. In the first strategy, a range of PAH from naphthalene to cyclopenda[cd]pyrene are considered as nucleating species, while in the second strategy, naphthalene is considered as the only soot nucleating species and the effects of larger PAH are represented entirely by naphthalene. Flamelet-based chemistry-tabulation is used for the major thermochemical quantities, such as density, temperature, and major species mass fractions. Turbulence-chemistry interactions for PAH are accounted for by transporting their mass fractions and using a recently developed PAH relaxation model for their source term closure. The effects of large PAH on soot are highlighted by comparing the PAH profiles, soot nucleation rate, and soot volume fraction distributions obtained from both simulations for each test flame. These results are also compared against experimental measurements, when available. From these comparisons, it is first shown that naphthalene is predominantly formed along the flame centerline, and larger PAH species with more than two aromatic rings are primarily formed away from the centerline. Further, it is found that these larger PAH species only contribute to around of the overall soot nucleation rate along the flame centerline but their contributions are more substantial (up to ) away from the centerline. Finally, it is shown that representing the effects of these large PAH species by naphthalene leads to an under-prediction of around for the soot volume fraction magnitude along the flame centerline. Away from the centerline, this under-prediction can be as much as 100

Effect of methane addition to ethylene on the morphology and size distribution of soot in a laminar co-flow diffusion flame

The characteristics of soot in the diffusion flames of methane and ethylene under different oxygen concentrations and the influence of mixing methane in ethylene on soot generation were investigated using thermophoretic sampling and subsequent transmission electron microscopy image analysis. The process of soot particle nucleation, surface growth, coagulation, agglomeration and oxidation along the flame axis was analyzed. The variation of soot particle size distribution and aggregate characteristics at different heights along the centerline of the flame at different oxygen concentrations and methane doping ratios were obtained. Results show that the various stages of soot generation in methane flame obviously lags behind the ethylene flame at different oxygen concentrations, and increasing the oxygen concentration makes the various stages of soot formation in the flame advance. A 10% methane doping can promote soot generation at low flame locations. Increasing the doping amount to 30%, the generation of soot can be promoted at high flame locations. The synergistic effect of soot formation in fuel combustion occurs in the above two cases. However, the synergistic effect of the fuel will disappear under high blending ratio conditions. The effect of methane-ethylene at high blend ratios is more like a neutralization effect.

Experimental and numerical investigation of effects of premixing on soot processes in iso-octane co-flow flames

Abstract The goal of the current work is to understand the effects of premixing on soot processes in an iso-octane, axisymmetric, co-flow, laminar flame at atmospheric pressure. The flames investigated are non-premixed and partially-premixed (jet equivalence ratios of 24, 15, 12, 9 and 6). The total carbon flow rate is kept constant to facilitate comparison among the six flames. Laser-induced incandescence and laser extinction are applied to obtain two-dimensional soot volume fraction. The experimental results show that the spatial distribution of soot changes with premixing; the peak soot volume fraction location is in the annular region in the non-premixed flame and transitions to the centerline as the jet equivalence ratio is reduced. Numerical simulations are performed using a detailed iso-octane fuel chemistry and bi-variate soot model. The numerical model captures the changes in the spatial distribution of soot due to premixing, as in the experiment. Similar to the change in the soot distribution, the soot production processes, including nucleation, surface growth, and PAH condensation, show the transition behavior with premixing. The simulation shows that the location of peak PAH dimer concentration shifts from the annular region towards the centerline with premixing. As a result, the location where soot nucleation and PAH condensation rates peak show similar transition as observed in the PAH dimer concentration. Furthermore, PAH dimer concentration decreases due to premixing, leading to a decrease in the soot nucleation and soot growth due to PAH condensation. Additionally, soot growth due to surface reactions decrease with premixing due to the reduction in number of active sites on the soot surface.

Experimental investigation of in-cylinder soot distribution and exhaust particle oxidation characteristics of a diesel engine with nano-CeO2 catalytic fuel

According to the dispersion principle of solid particles in the liquid and polar phase solubility principle, nano-CeO2 catalytic fuels were prepared with 50 and 100 mg/L mass fractions of CeO2. The in-cylinder soot distribution was investigated on a common-rail engine using the visualization technology. The combustion characteristics and smoke emissions were also analyzed. The effects of heating rates and nano-CeO2 concentration on particle oxidation characteristics were studied using thermogravimetric analysis method. The results show that the combustion starting point of the engine with catalytic diesel advances, while the peak values of in-cylinder pressure and heat release rate increase. The location of soot flame occurrence advances, and its vanishing moment comes earlier with the addition of nano-CeO2. Compared with diesel fuel, soot concentration, soot area occupation ratio and smoke emissions are smaller with catalytic diesel. As the heating rate increases, the oxidation process of particles moves to high temperature region, however, its peak weight loss rate decreases. At a certain heating rate, the particle activation energy and initial temperature decrease with the increment of nano-CeO2 concentration. It is found that the catalytic diesel could decrease particle sizes, promote the oxidation of particles, and reduce the ignition combustion temperature of particles.

Effects of molecular O2 and NO2 on particle size distribution, morphology and nanostructure of diffusion flame soot oxidized in a flow reactor

The oxidation process of soot particles in O2 and NO2 atmospheres is investigated in a flow reactor at various temperatures. The particles are generated using an ethylene diffusion flame and sampled at the tip of the flame using an ejector diluter sampling system. Soot is oxidized by three kinds of diluted gas (pure N2, 10000 ppm O2 with N2 and 10000 ppm NO2 with N2) in the flow reactor and measured with DMS500, transmission electron microscopy (TEM), high-resolution TEM, Raman microscopy and thermogravimetric analysis (TGA). The results show that the particle size, primary particle diameter, agglomeration degree and concentration of soot particles decrease as the oxidation temperature increases. The overall oxidation capacity of NO2 is stronger than that of O2 at low temperatures (200 and 400 °C), whereas at high temperatures (600 and 800 °C) O2 is stronger. Both internal oxidation and external oxidation exist during the oxidation process of soot with O2 and NO2. The average fringe length of the lattice increases and the tortuosity of the lattice and the Id/Ig ratios of the soot particles decrease as temperature increases, meaning that the nanostructure of the soot particles becomes more ordered. The results of the multi-diagnostics above indicate three main forms of oxidation during the overall oxidation process: internal oxidation, external oxidation and internal collapse. The oxidation of O2 is dominated by internal oxidation and internal collapse at high temperatures (600 and 800 °C), whereas the oxidation of NO2 is dominated by external oxidation throughout the oxidation temperature range.

Transported probability density function based modelling of soot particle size distributions in non-premixed turbulent jet flames

The need to establish actual particle size distributions (PSDs) of soot emissions from the nanoscale upwards, along with the current global indicators based on soot mass, stems from increasingly strict regulatory demands. In the current work, a mass and number density preserving sectional model is coupled with a transported probability density function (PDF) method to study the evolution of soot PSDs in two non-premixed turbulent jet flames at Reynolds numbers of 10,000 and 20,000. The transported PDF approach is closed at joint-scalar level and includes mass fractions of gas phase species, soot sections, as well as enthalpy, leading to a fully coupled 78-dimensional joint-scalar space, treating interactions between turbulence and gas phase/soot chemistry as well as radiation without further approximation. The gas phase chemistry features 144 reactions, 15 solved and 14 steady-state species and an acetylene-based soot inception model is calibrated using comprehensive detailed chemistry up to pyrene and applied to a well-stirred/plug flow reactor configuration. The derived nucleation rate is subsequently applied in the turbulent flame calculations. Soot surface growth is treated via a PAH analogy and oxidation via O, OH and O2 is accounted for. The sectional model features 62 sections covering particle sizes in the range 0.38 nm ≤ dp ≤ 4.4 µm and includes a model for the collision efficiency of small particles ( ≤ 10 nm) based on the Lennard–Jones potential. The computed results reproduce the evolution of the PSDs with encouraging accuracy. It is also shown that the distribution of soot in mixture fraction space is affected by local extinction events.

Soot and flow field in turbulent swirl-stabilized spray flames of Jet A-1 in a model combustor

Soot production processes and their interaction with the swirling flow field were studied experimentally in turbulent spray flames in a model gas turbine combustor. Two Jet A-1/air spray flames with two different air flow rates both with constant fuel flow corresponding to a thermal power of 10 kW were stabilized in the combustor with a swirl number of 0.55. Soot measurements were collected using auto-compensating laser-induced incandescence and velocity measurements were obtained using stereoscopic particle image velocimetry techniques. The particle image velocimetry displayed a distinct change in spray pattern from a V-shaped hollow cone to a V-shaped solid cone when the air flow rate was increased. The first soot event was not detected until 30 mm above the combustor inlet was reached, which was expected as it was necessary for liquid fuel to disperse and evaporate. The flow field featured strong inner and outer recirculation zones as well as the inner and outer shear layers. Soot concentration distributions were found to be confined to the outside of the inner recirculation zone; this is in contrast to the gaseous fuel swirl-stabilized flames in which soot particles are mainly detected within the inner recirculation zone. Time-averaged maximum soot volume fraction level decreased by about 60% with a 20% increase in air mass flow rate instigated by enhanced oxidation rate and turbulent mixing. The primary soot particle size was found to fall in the range of 30 and 60 nm for both cases. The results obtained emphasize the role played by the intermittent structures and air flow rate on soot processes in swirling spray combustion. Observed soot distributions in liquid spray flames in this work differ drastically from those reported previously for gaseous fuel combustion in swirl-stabilized flames.

Experimental and numerical study of variable oxygen index effects on soot yield and distribution in laminar co-flow diffusion flames

We study experimentally and numerically a series of methane-fueled laminar co-flow diffusion flames to investigate the effects of variable Oxygen Index (OI) on soot yield and distribution. OI is defined as the mole fraction of oxygen in the oxidizer. Sixteen flames are studied with OI ranging from 21% (air) to 76.3%, so that OI varies in small increments and its effects are precisely resolved. The soot volume fraction distribution is measured experimentally for all flames using color-ratio pyrometry. Simulations are carried out using an extensively validated chemical kinetic mechanism and an aggregate-based soot model that accounts for all major processes of soot inception, growth, and oxidation. The experimental measurements show that the visible flame height decreases with increasing OI, which is consistent with theoretical estimates and the numerical simulations. The measurements also indicate that increasing OI (from 21% to 36.8%) first results in an increase in the maximum soot concentration, but a further increase in OI leads to a decrease in the soot yield. Additionally, the maximum soot concentration occurs on the flame centerline for low OI flames (below 36.8%), but for higher OI, the peak soot yield occurs in the flame wings. All of these experimental observations are well reproduced by the simulations, with the maximum soot volume fraction magnitudes lying within the error bounds of the experimental measurements. The computational results are used to reveal the underlying physical mechanisms, by examining soot evolution along characteristic Lagrangian trajectories through flame regions. We find that increasing OI leads to higher flame temperature, which results in a stronger soot production rate, but also reduced soot residence time in flame regions, which allows less time for soot production. These competing effects cause the initial increase and subsequent decrease in the maximum soot yield and the shift in the maximum soot yield location with increasing OI.

Visualization of combustion performance and emission characteristics of a four-cylinder diesel engine at various inlet oxygen concentrations at part loads

Although exhaust gas recirculation (EGR) is a common way to suppress the nitrogen oxide (NOX) emissions, it also brings some negative impact on soot emissions and the thermal efficiency in internal combustion engines. We investigated the effects of ambient oxygen concentrations on engine performance, combustion characteristics, and emissions using a four-cylinder diesel engine equipped with an endoscopic visualization system. To estimate the flame temperature and soot distribution, we analyzed these images using a postprocessing program. Experimental results showed that the luminosity of flames in the images was degraded comparatively for the reduced oxygen concentration. Flame temperature distribution also showed similar behavior. As the oxygen concentration decreased, area of soot distribution significantly reduced at IMEP = 0.13 MPa, and only a slight decrease at IMEP = 0.3 MPa. But locally high soot concentration regions increased.

Effect of aromatic fuels and premixing on aromatic species and soot distributions in laminar, co-flow flames at atmospheric pressure

The aim of the present study is to investigate the effects of aromatic fuel structure on the aromatic species and the soot volume fraction in laminar, co-flow flames at atmospheric pressure. Both non-premixed and partially-premixed flames (jet equivalence ratios of 24 and 6) are studied. The four fuels consist of binary mixtures of n-dodecane with one of four aromatic species: n-propylbenzene, toluene, m-xylene, and 1,3,5-trimethylbenzene. For all flame conditions, the total carbon flow rate of the fuel mixture is kept constant. Furthermore, in each binary mixture, the carbon mole fraction from the n-dodecane and the aromatic component is kept constant. Laser-induced incandescence (LII) and laser extinction are used to obtain two-dimensional soot volume fraction in the flames. Laser-induced fluorescence (LIF) is used to obtain the two-dimensional aromatic species distribution in the flames. The experimental results indicate that the 1,3,5-trimethylbenzene/n-dodecane flame has the highest peak soot volume fraction amongst the four fuels; the other three fuel mixtures, within measurement uncertainty, have similar peak soot volume fraction. In addition, premixing changes the spatial distribution of polycyclic aromatic hydrocarbons and soot in the flames. In the non-premixed cases, the peak soot volume fraction is located in an annular region near the flame sheet, whereas the soot field is more uniform across the cross-section of the flame at a jet equivalence ratio of 6. A published aromatic fuel chemical mechanism is used to understand the differences in the pathways to soot precursors among the aromatic fuels. The combined 2D LIF and LII result provide a unique dataset to validate soot and chemical numerical models for the four aromatic fuels: n-propylbenzene, toluene, m-xylene, and 1,3,5-trimethylbenzene.

A comparison of high-temperature reaction and soot processes of conventional diesel and methyl decanoate

This paper aims to improve a knowledge base of methyl decanoate, a long alkyl-chain biodiesel surrogate fuel gaining popularity in engine combustion research. To this end, a comparative study on diesel and methyl decanoate combustion has been conducted with a focus on high temperature flame structures and soot distributions in an optically accessible single-cylinder light-duty common-rail diesel engine. The in-cylinder pressure trace and apparent heat release rate curves were well matched for both fuels when the same amount of fuel energy was supplied, which confirmed very similar combustion phasing. Planar laser induced fluorescence of hydroxyl radicals (OH-PLIF) and planar laser induced incandescence (PLII) as well as line-of-sight integrated chemiluminescence imaging of cool-flame signals and electronically excited OH (OH∗) were performed for various crank angles to capture the temporal and spatial development of diesel and methyl decanoate flames. The results show that both the cool-flame and OH radical signals are higher during methyl decanoate combustion with their wider distributions and larger in-cylinder volume fraction when compared to that of diesel, suggesting enhanced low- and high-temperature reactions due to oxygen in fuel. The oxygenated methyl decanoate with no aromatics in its molecular structure shows a lower soot formation rate than diesel as evidenced by delayed appearance of LII signals and lower overall intensity. This difference is significant even if the lower sooting propensity of methyl decanoate and thus less attenuation in the laser beam is considered. The rate of soot oxidation is also higher for methyl decanoate not only due to oxygen in fuel but also higher OH radicals surrounding smaller soot pockets compared to diesel.

Effects of self-absorption on simultaneous estimation of temperature distribution and concentration fields of soot and metal-oxide nanoparticles in nanofluid fuel flames using a spectrometer

An improved inverse reconstruction model with consideration of self-absorption effect for the temperature distribution and concentration fields of soot and metal-oxide nanoparticles in nanofluid fuel flames was proposed based on the flame emission spectrometry. The effects of self-absorption on the temperature profile and concentration fields were investigated for various measurement errors, flame optical thicknesses and detecting lines numbers. The model neglecting the self-absorption caused serious reconstruction errors especially in the nanofluid fuel flames with large optical thicknesses, while the improved model was used to successfully recover the temperature distribution and concentration fields of soot and metal-oxide nanoparticles for the flames regardless of the optical thickness. Through increasing detecting lines number, the reconstruction accuracy can be greatly improved due to more flame emission information received by the spectrometer. With the adequate detecting lines number, the estimations for the temperature distribution and concentration fields of soot and metal-oxide nanoparticles in flames with large optical thicknesses were still satisfying even from the noisy radiation intensities with signal to noise ratio (SNR) as low as 46 dB. The results showed that the improved reconstruction model was effective and robust to concurrently retrieve the temperature distribution and volume fraction fields of soot and metal-oxide nanoparticles for the exact and noisy data in nanofluid fuel sooting flames with different optical thicknesses.

Direct simultaneous reconstruction for temperature and concentration profiles of soot and metal-oxide nanoparticles in nanofluid fuel flames by a CCD camera

A reconstruction model based on inverse radiation analysis is presented to determine the temperature and concentration distributions of soot and metal-oxide nanoparticles in nanofluid fuel sooting flames using radiative intensities received by a CCD camera. The combined method consisting of the least-square QR decomposition (LSQR) algorithm and one dimensional searching was adopted to solve the inverse problem. Influences of ray number, wavelength combination, measurement error and metal-oxide nanoparticle concentration on the reconstruction accuracy were studied in details. The reconstructed results illustrated that the temperature distribution and soot concentration fields can be accurately retrieved, even with the measurement signal to noise ratio (SNR) as low as 39 dB, whereas the metal-oxide nanoparticle concentration field estimation process was more easily influenced by the measurement error and the practical metal-oxide nanoparticle concentrations. The proposed reconstruction method here is effective and robust for simultaneously retrieving the temperature distribution and concentration fields of soot and metal-oxide nanoparticles, even with noisy data.

Effect of hybrid breakup modelling on flame lift-off length and soot predictions

An improved droplet breakup model coupled with the effect of turbulence flow within the nozzle was implemented into the general transport equation analysis code to describe the flame lift-off length and predict the soot distribution. This model was first validated by the non-evaporating and evaporating spray experimental data. The computational results demonstrate that the breakup model is capable of predicted spray penetration and liquid length with reasonable accuracy. The inclusion of turbulence enhanced the breakup model, increased the droplet breakup rate, decreased spray penetration for about 6–12% compared to the results of Kelvin-Helmholtz Rayleigh-Taylor (KH-RT) breakup model. Then, the model was applied to investigate the influence of ambient density, temperature, oxygen concentration and injection pressure on the flame lift-off length under typical diesel combustion conditions. The predictions showed good agreement with the experimental data. The result also indicated that the turbulence inside the nozzle strengthen the rate of breakup, resulting in more smaller droplets, leading to high evaporation rate and smaller vapour penetration lengths, thus decreases the lift-off length about 8%. Finally, the model was used to explore the soot distribution. The overall trend of soot with the variations in injection pressure was well reproduced by the breakup model. It was found that the droplet with faster velocity under high injection pressure, this could lead to larger lift-off length, which will play a significant role for the fuel–air mixing process and thus cause a decrease in soot in the fuel jet. Results further indicated that the turbulence term can decrease the soot mass about 5–9% by improved the droplet breakup process.

Soot formation modelling for n-dodecane sprays using the transported PDF model

Soot formation in an n-dodecane spray flame under diesel engine conditions, known as Spray A, is modelled with the transported probability function (TPDF) method. The approach employs an acetylene-based two-equation soot model coupled with a Reynolds-averaged turbulence model and a Lagrangian discrete phase spray model. The aims are to evaluate, in the context of soot, the predictive capability of the model, the effects of turbulence–chemistry interactions (TCI), and various available chemistry mechanisms. TCI effects are evaluated by comparisons between the TPDF model and simulations using a well-mixed model neglecting turbulent fluctuations. Five test cases having variations in ambient temperature and oxygen concentration are considered.Five chemical mechanisms are first compared to experiments in terms of their ignition delay (ID) and lift-off length (LOL) under ambient O2 and temperature variations. Three relatively new mechanisms exhibit good ID performance (with both TCI approaches), while two short mechanisms also provide good LOL performance in conjunction with the TPDF approach. The two short mechanisms are considered for further comparisons. The auto-ignition process is analysed by comparing TPDF simulations with measurements from schlieren and 355 nm planar laser-induced fluorescence, detecting CH2O and polycyclic aromatic hydrocarbons, with overall good qualitative agreement, though with some differences on low-temperature reactivity.The experimental comparisons for soot consider transient soot mass and KL in the baseline condition, and steady state soot volume fraction (SVF) fields and total soot masses for all five ambient conditions. In terms of comparisons to experiment, the transient stage of the soot mass development is not well captured. An analysis of the transient KL in the baseline case shows the soot-containing region is larger in the experiment than the model, with soot extending in the experiment much closer to the jet boundary, suggesting that the model underestimates gradients around the jet head. During the steady period, however, the SVF agrees quite well. The soot models with both chemistry and TCI approaches were able to reproduce the overall soot trends with varying ambient temperature and oxygen, though the effect of the ambient temperature on the soot mass was under-predicted, in particular in its variation from 900 to 1000 K. TCI effects on soot were in overall terms relatively minor, in part due to compensating errors. Neglecting TCI showed generally higher peak soot amounts, narrower soot distributions, and more downstream soot onset and soot peak locations. These differences between the models are explained with the help of a detailed analysis of the soot phenomena.

Effect of Alcohol Addition to Gasoline on Soot Distribution Characteristics in Laminar Diffusion Flames

AbstractAlcohols are widely used as alternative fuel for spark ignition engines to reduce soot emission. 2D soot distributions of alcohols‐gasoline blends were studied in laminar diffusion flames by two‐color laser‐induced incandescence technique. The soot volume fraction decreases significantly with the alcohol blending ratio. At the same blending ratio, the soot‐reducing ability declined with the carbon length of the alcohol, but the reducing effect for short‐chain alcohols, i.e., methanol and ethanol, deteriorated at high blending ratio while it remained constant for the long‐chain alcohol n‐butanol. At fixed oxygen content, the soot‐reducing ability of a short‐chain alcohol is still higher than that of a long‐chain alcohol, i.e., not only the oxygen content but also the molecular structure dominates the soot‐reducing ability.

Numerical Study of Heptane Pool Fires on a Hollow Square Pan

Abstract Heptane pool fires with different mass burning rates ranging from 0.00123kg/s (corresponding to steady burning stage in experiments) to 0.0247kg/s (corresponding to fuel boiling burning stage) on a hollow square pan are numercally studied in this paper. The fireFoam, the large eddy simulation (LES)–based fire simulation code within OpenFOAM®, was employed with the modified Eddy Dissipation Concept combustion model[13] and PaSR based soot model[14]. The predictions achieved good qualitative and quantitative agreement with the experimental data[9]. Further analysis was conducted on the fire behaviour and in particular the fire merging phenomena. The dependency betwwen the key parameters such as flame height, centerline temperature and soot distributions on the mass burning rate was also discussed.

Size Distribution of Ultrafine Particles Generated from Residential Fixed-bed Coal Combustion in a Typical Brazier

Ultrafine particles (with a small mean diameter) released from domestic coal combustion are an important parameter to consider in air pollution, as they affect air quality and human health. It has been suggested that poor combustion conditions release particles of different sizes enriched with health-damaging chemicals, such as polycyclic aromatic hydrocarbons. Furthermore, both smouldering and highly efficient combustion conditions release particles, which are often carcinogenic. Information on the particle size distribution (PSD) of char or soot emitted from fixed-bed domestic coal combustion is limited, with many studies reporting on wood combustion. This study investigated the influence of coal combustion phases (ignition, flaming, and coking) on the particle number concentration and size distribution of ultrafine particles. D-grade bituminous coal was crushed to a particle diameter (O) of 40–60 mm and combusted in a laboratory designed coal brazier (Imbaula) during experimental investigations of the particle size distribution normalised to the particle number concentration against the particle diameter. Experiments were carried out using the reduced smoke top-lit updraft method, colloquially known as the Basa njengo Magogo (BnM) method. The tests were carried out in a laboratory-controlled environment. Particulate matter was monitored using a NanoScan Scanning Mobility Particle Sizer (SMPS). Particles from the top-lit updraft (TLUD) showed an ultrafine geometric mean diameter centred at approximately 109 ± 18.4 nm for the ignition phase, 54.9 ± 5.9 nm for the pyrolysis/flaming phase, and 31.1 ± 5.1 nm for the coking phase. The particle mode diameter rapidly increased during the ignition phase (145 nm) and gradually decreased during the flaming phase (35 nm) and the coking phase (31 nm). This study shows that during smouldering combustion conditions (ignition), the particle diameter increases, whereas it decreases as the temperature increases. This information is essential for estimating particle deposition in the lungs and the associated health risks.