Soot Density Research Articles

Spray, combustion and soot of water-in-fuel (n-dodecane) emulsions investigated in a constant volume combustion chamber part 1: Influence of low water content

This experimental study focuses on the characteristics of water-in-fuel-emulsions (WFE) with low water mass fractions (⩽10wt%) on injection, spray combustion and soot in regard to direct-injection (DI) diesel fuel engines. Investigations have been performed in an optically accessible constant volume combustion chamber (CVCC) at engine relevant conditions (Tgas=860K/ρgas=22.8kg/m3) with n-dodecane as a reference diesel fuels surrogate fuel. Optical diagnostics has been applied to characterize the influences related to the water content in the fuel on injection such as spray momentum flux and hence, air entrainment as well as on spray combustion and soot formation/oxidation.In order to further enhance the fundamental understanding of the fuel mixing and chemical effects of WFE, two injection strategies have been employed: first, a constant injection pressure as for neat fuel and thus a prolonged injection duration was employed. Second, a constant energy input flow has been obtained by increasing injection pressure dependent on water content while keeping the injection duration constant. The injection is described by injection rate/momentum analysis. The spray parameters (penetration length, cone angle) have been assessed by Schlieren imaging and the combustion characteristics (ignition delay, flame lift-off length) were acquired by OH∗-chemiluminescence. To investigate the (temporal and spatial) soot behaviour two-color pyrometry has been applied and is compared with diffused back-illumination extinction imaging (DBIEI).n-Dodecane and WFE show nearly equal momentum flux and spray penetrations for constant injection pressure, i.e. the first injection strategy. Compared to neat fuel, ignition delay is gradually increased with addition of water. Measured quasi-steady lift-off lengths (LOL) increased and evaluated fuel-to-air ratios Φ at axial LOL decreased, however, for both WFEs differences of Φ are within their respective standard deviation. Increasing water contents reduce axial and radial soot extension as well as the optical soot densities (KL factor). Moreover, the injection strategy of constant injected energy input flow further decreased soot area and optical soot densities (KL). Decreasing fuel-to-air ratios Φ on the spray centerline at the axial soot inception location and increasing fuel flow residence times from LOL to axial start of soot formation with increasing water mass fractions indicate a direct influence of the water content in WFE on soot formation/oxidation processes.

Semi-empirical model for indirect measurement of soot size distributions in compression ignition engines

This work proposes a semi-empirical model, which provides soot particle size distribution functions emitted by compression ignition engines. The model is composed of a phenomenological model based on the collision dynamics of particle agglomerates and an empirical model, which provides key input parameters such as primary particle size and a mathematical relationship between the size of the agglomerate and number of primary particles. The phenomenological model considers the relevant fluid-dynamics phenomena influencing the collision frequency function. It is observed that Brownian motion is the predominant phenomenon and in a much lesser degree inertial turbulent motion. The experimental model requires air/fuel ratio, engine speed, soot density and mean instantaneous in-cylinder pressure. A Dirac delta is used as a seed for the agglomerate size function whose magnitude depends on the soot volume concentration and the mean primary particle size at each engine operation condition. In a further step, the obtained modelled agglomerate size functions are fitted to lognormal size distributions defined by the modelled mean size and standard deviation. Modelled lognormal agglomerate size distribution functions are validated with respect to experimental distributions obtained using a Scanning Mobility Particle Sizer (SMPS).

Fire Emergency Evacuation Simulation of a shopping mall using Fire Dynamic Simulator (FDS)

Fire accident in a shopping mall, garments factory and other labor intensive industries nowadays has become a common incident in Bangladesh and poses a great threat to life, facilities and economy of our country. In this work, fire and evacuation simulation was performed for a single stored shopping complex utilizing computational fluid dynamic techniques. Fire Dynamic Simulator with evacuation (FDS+Evac) software was used to simulate a shopping mall fire and study the effects of fire on the emergency egress process of people. The shopping mall of area 64 m2 comprises of seven rooms with a pool fire at the center of the mall is modeled for simulation. The total evacuation time (TET) for a fixed population density were estimated with the change of heat release rate, soot yield, soot density and the design pattern or geometry of shopping mall. The evacuation of agents in different time and different design pattern of the mall has been assessed using the data obtained from the simulation. FDS+Evac provides an integrating platform where the interaction between fire growth and evacuees can be taken into account by simultaneous simulation allowing a full coupling of the fire conditions and human behavior. This makes FDS is an effective tool for simulating large and high density crowds where the movement dynamics of evacuees is affected by the crowd pressure. Full scale fire experiment is often quite difficult to study the fine and crowds evacuation behavior. This paper illustrates a promising application of fire dynamic simulator (FDS+Evac) for fire and evacuation modeling to predict the total evacuation time.Journal of Chemical Engineering, Vol. 30, No. 1, 2017: 32-36

Effect of injection pressure on soot formation/oxidation characteristics using a two-color photometric method in a compression-ignition engine fueled with biodiesel blend (B20)

Biofuels are an alternative to petroleum fuels in transportation. Among various biofuels, biodiesel has been mixed with diesel fuel for use in compression ignition (CI) engines. Many countries legislate that standard diesel fuels contain a certain amount of biodiesel to reduce exhaust emissions. An increase in biodiesel content to a 20% volumetric ratio (B20) requires only minor modification to existing vehicle systems. Since discrepancies in fuel properties between B20 and conventional diesel fuel, much research has been performed on B20 combustion and emissions for the implementation of vehicles. The present study investigated spatial B20 combustion and soot emission processes in an optical CI engine under various injection pressure conditions. Volumetric 20% of soybean biodiesel added to diesel fuel and both blend fuel and conventional diesel fuel were used as test fuels. Apparent combustion and emissions were observed with respect to auto-ignition, brake power, and thermal efficiency. In addition, visualization system permitted a profound analysis of the spatial combustion flame and soot propagation. A two-color photometric method extracted quantitative soot density from the captured combustion images, which allowed to study the soot formation and oxidation processes. Although soot emissions decreased significantly out of the engine, the variations in the soot formation and oxidation processes in the combustion chamber were remarkable. Compared with neat diesel flame B20 fuel produced higher flame temperature over all injection pressure conditions. While B20 flame temperature was increased, soot emission of B20 fuel was exhausted with higher concentrations. Under a low load and high speed condition, B20 emissions revealed different results from those of general bio-blends with high thermal efficiency regardless of the injection pressure.

Morphology and mobility diameter of carbonaceous aerosols during agglomeration and surface growth

Agglomeration and surface growth of fractal-like carbonaceous aerosols in the absence of oxidation and condensation of volatiles are investigated by Discrete Element Modeling (DEM) from the free molecular to transition regime, accounting for primary particle polydispersity and chemical bonding (aggregation). That way, carbon black or soot formation is elucidated in plasma reactors, quenched flames and combustion engines running at high exhaust gas recirculation where oxidation of carbon is limited or non-existent. During nascent soot formation polydisperse spheres and aggregates are formed, attaining an asymptotic geometric standard deviation of 1.2 ± 0.01, in agreement with experiments in premixed, diffusion flames and wood combustion. When surface growth stops, mature soot grows by agglomeration of these polydisperse spheres and aggregates before oxidation and condensation take over. The evolution from nascent to mature soot morphology quantified by its fractal dimension, Df, and mass-mobility exponent, Dfm, is in good agreement with measurements in premixed, diffusion flames and the Cast soot generator. The mobility diameter, dm, can be related to the average number of primary particles per agglomerate by nva = (dm/dva)0.45 and the relative effective density of soot by ρeff/ρs = (dm/dva)−0.78, where dva is the primary particle diameter and ρs the soot bulk density.

Diesel reformulation using bio-derived propanol to control toxic emissions from a light-duty agricultural diesel engine.

In the Indian agricultural sector, millions of diesel-driven pump-sets were used for irrigation purposes. These engines produce carcinogenic diesel particulates, toxic nitrogen oxides (NOx), and carbon monoxide (CO) emissions which threaten the livelihood of large population of farmers in India. The present study investigates the use of n-propanol, a less-explored high carbon bio-alcohol that can be produced by sustainable pathways from industrial and crop wastes that has an attractive opportunity for powering stationary diesel engines meant for irrigation and rural electrification. This study evaluates the use of n-propanol addition in fossil diesel by up to 30% by vol. and concurrently reports the effects of exhaust gas recirculation (EGR) on emissions of an agricultural DI diesel engine. Three blends PR10, PR20, and PR30 were prepared by mixing 10, 20, and 30% by vol. of n-propanol with fossil diesel. Results when compared to baseline diesel case indicated that smoke density reduced with increasing n-propanol fraction in the blends. PR10, PR20, and PR30 reduced smoke density by 13.33, 33.33, and 60%, respectively. NOx emissions increased with increasing n-propanol fraction in the blends. Later, three EGR rates (10, 20, and 30%) were employed. At any particular EGR rate, smoke density remained lower with increasing n-propanol content in the blends under increasing EGR rates. NOx reduced gradually with EGR. At 30% EGR, the blends PR10, PR20, and PR30 reduced NOx emissions by 43.04, 37.98, and 34.86%, respectively when compared to baseline diesel. CO emissions remained low but hydrocarbon (HC) emissions were high for n-propanol/diesel blends under EGR. Study confirmed that n-propanol could be used by up to 30% by vol. with diesel and the blends delivered lower soot density, NOx, and CO emissions under EGR.

Coal type identification based on the emission spectra of a furnace flame

This paper presents a novel method of identifying coal type based on mechanistic methods. The ratio of the resonance line spectrum of a luminous flame and the continuous spectrum at the same wavelength eliminates the influence of temperature on spectral intensity. The atomic line spectra of Na and K are typical and significant over continuous flame spectra. The concentrations of elemental Na and K in the flame are exclusively relative to coal type and composition. Using an experimental furnace and charge-coupled device (CCD) optical spectrometer apparatus, the continuous spectra and atomic line spectra of Na and K elements were sampled from coal flames in real time. An empirical fitting method was used to simplify the formulas of absorption strength and flame temperature calculation, and rational solutions were obtained by using an iterative algorithm. Due to the change in reaction rate and absorption by soot particles, the relative contents of Na and K in a flame vary with the temperature and absorption strength. Arrhenius’s equation for temperature compensation was adopted. Compensation for soot density in the furnace was also satisfied by an exponential expression. At any one sampling position, the compensation parameters were identical for all coal types. After compensation for temperature and density of soot particles, the relative strength of the Na and K signals and the ratio between them uniquely matched the coal type burnt in various conditions. The results were replicated and verified in various conditions, and the response time of the system was of the order of seconds.

Smog chamber study on aging of combustion soot in isoprene/SO2/NOx system: Changes of mass, size, effective density, morphology and mixing state

Atmospheric soot aging process is always accompanied by secondary particle formation, which is a comprehensive environmental issue that deserves great attention. On one hand, aging of primary soot could change its own physicochemical properties; on the other hand, complex air pollution caused by pollutant emission from various sources (e.g., vehicle exhausts, coal-fired flue gases and biogenic VOCs emission) may contribute to secondary particle formation onto primary particle surface. In this study, aging of combustion soot in isoprene/SO2/NOx system was investigated under controlled laboratory conditions in several smog chamber experiments. During the evolution of soot, several physical properties such as mass, size, effective density, morphology and mixing state were determined simultaneously by an integrated aerosol analytical system of Scanning Mobility Particle Sizer (SMPS), Differential Mobility Analyzer-Aerosol Particle Mass Analyzer-Condensation Particle Counter (DMA-APM-CPC) and Transmission Electron Microscopy coupled with Energy-dispersive X-ray Spectrometry (TEM/EDX) techniques. Here, based on the experimental results of soot aging under different gas-phase composition and relative humidity (RH), we firstly proposed possible aging pathways of soot in isoprene/SO2/NOx system. A synergetic effect was speculated to exist between SO2 and isoprene on soot aging process, which led to more secondary particle formation. At the same time, TEM/EDX analysis showed that a competitive mechanism between H2SO4(g) and isoprene oxidation vapor may exist: H2SO4(g) firstly condensed onto fresh soot, then an acceleration of isoprene oxidation products formed onto H2SO4 pre-coated soot. In isoprene/SO2/NOx system, high RH conditions could contribute to soot aging and new particle formation. The changes of effective density and dynamic shape factor of soot also indicated that high RH conditions could accelerate soot aging process, and led chain-like soot into more spherical morphology, which was further confirmed from the STEM image. Moreover, it was found that volume equivalent coating thickness (Δrve) could also be applied to normalized characterize soot aging parameters like diameter growth factor (Gfd) and mass growth factor (Gfm) in a complex reaction system like isoprene/SO2/NOx. Our results revealed the dual mechanism (competitive effect&cooperative effect) of isoprene and SO2 on photochemical aging of soot, which is of significance for improving understanding of complex air pollution in China.

Soot particle size distributions in premixed stretch-stabilized flat ethylene–oxygen–argon flames

Evolution of particle size distribution function (PSDF) was studied in premixed stretch-stabilized flat flames for the first time. The purpose is to demonstrate that stretch-stabilized flames can broaden the experimental flame condition space for studying soot formation in a pseudo-one dimensional flow configuration. PSDFs were measured in three series of atmospheric-pressure ethylene–oxygen–argon flames with maximum temperatures around 1980, 2000, and 2160K. The measured PSDFs show a strong effect of flame temperature as nucleation and growth of soot is found to be suppressed towards high temperatures. Simulations using a population balance soot model show reasonably good agreement with the 1980 and 2000K series of flames, but it significantly overpredicts the number density and size of soot in the highest temperature flame. Numerical tests suggest that the discrepancy can be caused by high-temperature reversibility in surface growth and other processes.

Human evacuation affected by smoke movement in mine fires

The objective of this work is to investigate the influence of smoke movement during mine fires on miner evacuation behaviors. A three-dimensional computational fluid dynamics method was conducted to reconstruct the laneway conveyor belt fire scenes under two ventilating conditions. The parameters, including temperature–time histories, soot density, carbon monoxide and heat release rate, were simulated to characterize the mine fires at various ventilating speeds. A miner evacuation model affected by fire smoke movement was advanced to describe the miner evacuation behaviors, which can be divided into three stages. Based on the evacuation model coupled with the mine fire smoke movement, the available safety evacuation time for miners involved in coal mine fire located in different sites was estimated. Two evacuation patterns were advanced according to the ventilating speeds combined with the model of miner evacuation behaviors. The results show that the miners located between the inlet-air end and the air door in lane 1 should be evacuated to the inlet-air end and other miners involved in coal mine fire could choose the air door as the escaping destination, when the ventilation speed is greater than 3 m/s. Accordingly, the research can be used as references for the mine safety administration authorities to design the safety evacuation.

Determination of particle mass, effective density, mass–mobility exponent, and dynamic shape factor using an aerodynamic aerosol classifier and a differential mobility analyzer in tandem

A differential mobility analyzer (DMA) and an aerodynamic aerosol classifier (AAC) are used in tandem to measure the effective density, dynamic shape factor, and mass of soot and dioctyl sebacate (DOS) particles. Soot particles were generated from an inverted burner. The mass–mobility exponent of the soot particles was determined to be 2.17. The effective density of soot decreases from 0.86±0.08 to 0.18±0.02g/cm3 over the range of 95–637nm in mobility diameter and the shape factor increased from 1.51±0.06 to 2.62±0.10 over the same range. The effective density of the DOS particles was determined to be 0.903±0.90g/cm3 (which is within uncertainty of the material density of DOS), the mass–mobility exponent was 3.01, and the dynamic shape factor was 1.03±0.05, which illustrate the spherical shape of the DOS droplets.

Prediction of the spread of smoke in a huge transit terminal subway station under six different fire scenarios

A fire at a subway station can cause tremendous loss of property and heavy casualties, and smoke has been reported to be the main cause of these casualties. This article reports the use of Large Eddy Simulation (LES) simulation to study the dispersion of fire-induced smoke that is buoyancy driven in a subway station. This station was located within a huge transit terminal at Xi’an, China. The influence of natural and mechanical ventilation was studied in this station, which has atrium height ranging from 0 to 15m, roof window dimensions of 1×1m2 and 5×1m2, and rates of air change ranging between 5 and 11h−1. In addition, six different fire-source locations with heat-release rates (HRRs) of 4 and 7.5MW are discussed. Four grid systems were compared, and the sensitivity of these grid systems was checked to ensure grid independence. Preliminary analysis of results indicates that the atrium of a subway station poses significant limitations on the horizontal dispersion of smoke. A large soot-density gradient has also been observed in stations with a high atrium. An exponential relationship has been proposed to define the correlation between atrium height and duration of smoke filling, with a relative coefficient (R) of 0.9995. The results indicate that mechanical ventilation can markedly control the spread of smoke in the horizontal direction but it has little effect on the dispersion of smoke in the vertical direction. If a fire starts directly below the atrium, most of the smoke generated will converge toward the upper regions of the atrium. In addition, the simulation helps predict the maximum soot density of smoke generated by different heat releases (4 and 7.5MW).

Simulation of temporal and spatial soot evolution in an automotive diesel engine using the Moss–Brookes soot model

In this reported work, computational study on the formation processes of soot particles from diesel combustion is conducted using an approach where Computational Fluid Dynamics (CFD) is coupled with a chemical kinetic model. A multi-step soot model which accounts for inception, surface growth, coagulation and oxidation was applied. Model constant values in the Moss–Brookes soot formation and Fenimore–Jones soot oxidation models were calibrated, and were validated against in-cylinder soot evolution and exhaust soot density of both heavy- and light-duty diesel engines, respectively. Effects of various injection parameters such as start of injection (SOI) timing, split-main ratio and dwell period of the split-main injection strategy on in-cylinder temporal/spatial soot evolution in a light-duty diesel engine were subsequently investigated. The spatial soot distributions at each crank angle degree after start of injection were found to be insensitive to the change of values in SOI and split-main ratio when close-coupled injection was implemented. Soot cloud was also observed to be distributed towards the cylinder wall when a large separation of 20° was used, even with an advanced SOI timing of −6° after top dead centre (ATDC). The use of large separation is hence not desired for this combustion system as it potentially leads to soot deposition on surface oil film and greater tailpipe soot emissions.

Investigation of fuel injection pattern on soot formation and oxidation processes in a light-duty diesel engine using integrated CFD-reduced chemistry

In this reported work, simulation studies of in-cylinder diesel combustion and soot formation processes under different configuration of the split-main injection scheme were presented. Numerical computation was performed by linking a plug-in chemistry solver CHEMKIN-CFD into ANSYS FLUENT package, in order to integrate chemical kinetic mechanism and Computational Fluid Dynamics (CFD) computations. For improved computational runtime, an in-house reduced chemical mechanism was coupled with the CFD code. The reduced mechanism comprises 112 reactions with 46 species essential to diesel ignition/combustion and the formation of soot precursors and nitrogen monoxide (NO). Numerical models were first validated against experimental combustion characteristics as well as concentrations of engine-out soot and NO of a single-cylinder, light-duty diesel engine when using a split-main injection scheme. Parameters of this injection scheme were then investigated, which included start of injection (SOI) timings, fuel mass ratios of the injection pulses and the dwell period in between injections. The key interest here was to elucidate how these affect exhaust NO and soot levels, and in particular the in-cylinder soot formation and oxidation events. Fuel mass injected, duration of the injection and in-cylinder temperature were found to shape the soot formation and oxidation processes, which eventually produced the observed variations in the soot density at exhaust valve opening time. Based on all the simulation data from this reported work, power law was found to accurately describe the correlations between soot surface growth rate and gas mass fraction with a temperature range of 1400–2800K and an equivalence ratio values of greater than unity. The values of both constants of the power law were highly sensitive to the in-cylinder mean gas temperatures. The findings here are helpful in providing a better understanding of in-cylinder diesel soot formation and oxidation processes in this combustion system.

Life Safety Evacuation for Cross Interchange Subway Station fire

Fire accidents in a cross interchange subway are analyzed. At present, the primary focus of subway evacuation behavior analysis is mainly concern on normal state; evacuations in case of fire have rarely been under research. The relationship of soot density and extinction coefficient of fire smoke with average walking speed of occupants is linearly dependent. In this paper, FDS+Evac program is used to simulate the evacuation in a fire scenario. It has been found that not only some occupants’ evacuation routes become longer, but also the utilization of some of the exits is reduced, therefore congestion is caused at other safe exits in a cross subway station fire.

Numerical Simulation on Fire Smoke Flow with Jet Fans in an Underground Garage

With the aim of evaluating capabilities of a ventilation system with jet fans to control fire smoke in an underground garage, we carried out a set of FDS simulation. According to the results, temperature and soot density of fire has reduced within an acceptable range. We believe that the ventilation system based on the jet fans has indeed controlled fire smoke effectively, thereby we have enough time for safety rescue.

Experimental and numerical investigation of fuel mixing effects on soot structures in counterflow diffusion flames

Experimental and numerical analyses of laminar diffusion flames were performed to identify the effect of fuel mixing on soot formation in a counterflow burner. In this experiment, the volume fraction, number density, and particle size of soot were investigated using light extinction/scattering systems. The experimental results showed that the synergistic effect of an ethylene-propane flame is appreciable. Numerical simulations showed that the benzene (C6H6) concentration in mixture flames was higher than in ethylene-base flames because of the increase in the concentration of propargyl radicals. Methyl radicals were found to play an important role in the formation of propargyl, and the recombination of propargyl with benzene was found to lead to an increase in the number density for cases exhibiting synergistic effects. These results imply that methyl radicals play an important role in soot formation, particularly with regard to the number density.

Spectrally resolved light absorption properties of cooled soot from a methane flame

The optical properties of combustion-generated soot, crucial information for quantitative soot emission diagnostics and for climate modeling, have been determined for the particular case of cooled soot from a methane flame. Optical extinction measurements were performed over a wavelength range of 450–750 nm using a novel diffuse-light, spectrally resolved line-of-sight attenuation experiment, and quantified using extractive methods coupled with scanning and transmission electron microscopy in conjunction with a detailed uncertainty analysis. The absorption component of the total measured extinction was isolated by calculating the expected scattering contribution, according to the Rayleigh–Debye–Gans approximation for polydisperse fractal aggregates. In contrast to the large degree of scatter seen in data previously reported in the literature, a consistent trend of negligible variation of the soot absorption refractive index function E(m) with wavelength over the visible was observed (E(m)=0.35±0.03 at wavelengths of 450–750 nm). These new data are also cast in the form of dimensionless extinction, which is independent of the scatter correction, as well as mass absorption cross section, which is independent of the mass density of soot and is commonly used by atmospheric modelers.

Soot emission prediction of a waste-gated turbo-charged DI diesel engine using artificial neural network

This study is about soot emission prediction of a waste-gated turbo-charged DI diesel engine using artificial neural network (ANN). For training the ANN model, six ranges of experimental data in previous study were used, and one range of data was kept for testing the accuracy of ANN predictions. The input parameters for the ANN are inlet manifold pressure, inlet manifold temperature, inlet air mass flow rate, fuel consumption, engine torque, and speed. Output parameter is the density of soot in the exhaust. The results show the ANN approach can be used to accurately predict soot emission of a turbo-charged diesel engine in different opening ranges of waste-gate (ORWG). Root mean-squared error (RMSE), fraction of variance (R 2), and mean absolute percentage error (MAPE) for predictions were found to be 1.19 (mg/m3), 0.9998, and 6.4%, respectively.

Developing the PAH-PP soot particle model using process informatics and uncertainty propagation

In this work we present the new PAH-PP soot model and use a data collaboration approach to determine some of its parameters. The model describes the formation, growth and oxidation of soot in laminar premixed flames. Soot particles are modelled as aggregates containing primary particles, which are built from polycyclic aromatic hydrocarbons (PAHs), the main building blocks of a primary particle (PP). The connectivity of the primary particles is stored and used to determine the rounding of the soot particles due to surface growth and condensation processes. Two neighbouring primary particles are replaced by one if the coalescence level between the two primary particles reaches a threshold. The model contains, like most of the other models, free parameters that are unknown a priori. The experimental premixed flame data from Zhao et al. [B. Zhao, Z. Yang, Z. Li, M.V. Johnston, H. Wang, Proc. Combust. Inst. 30 (2) (2005) 1441–1448] have been used to estimate the smoothing factor of soot particles, the growth factor of PAHs within particles and the soot density using a low discrepancy series method with a subsequent response surface optimisation. The optimised particle size distributions show good agreement with the experimental ones. The importance of a standardised data mining system in order to optimise models is underlined.