Fengshan Liu

National Research Council Canada | NRC · Measurement Science and Standards Research Area

This paper reports an experimental study on the effects of O2 concentration and CO2 concentration on soot volume fraction and primary particle size of flame centre in ethylene laminar co-diffusion flame. The incandescent light was induced by a two-color band method and laser-excited by wavelength 1064 nm. Previous studies have shown that the oxygen...

Thermal radiation plays an important role in heat transfer process in oxy-fuel sooting flame (OFS). The accuracy of Full-Spectrum Correlated K-distribution (FSCK) methods with the original scheme (Modest and Zhang, 2002), the improved one (Cai and Modest, 2014), and the rank correlated one (Solovjov and Webb, 2018) is evaluated in two OFSs. As a co...

Despite the extensive studies, accurate and reliable modeling of the soot inception process, especially at high pressure conditions, amenable to multi-dimensional flame simulations remains a challenge. In this study, the physical inception model was comprehensively evaluated in the fully-resolved simulations of laminar normal diffusion flame (NDF)...

Catalyst degradation due to soot formation is one of the main issues in the autothermal reforming (ATR) process, which is widely regarded as the future technology for hydrogen production from natural gas. In this work, soot formation under conditions similar to ATR was systematically investigated, focusing specifically on the effects of pressure on...

The auto-compensating laser-induced incandescence (AC-LII) technique has been frequently used to measure soot volume fraction (fv) in flames. AC-LII relies on an assumption about the spectral variation of soot absorption function E(m,λ) at the two detection wavelengths for soot temperature determination. It has been a common practice to assume a co...

The particle filtration efficiency (PFE) of a respirator or face mask is one of its key properties. While the physics of particle filtration results in the PFE being size-dependent, measurement standards are specified using a single, integrated PFE, for simplicity. This integrated PFE is commonly defined with respect to either the number (NPFE) or...

In practical combustion chambers, the emissivity of wall materials in general varies spectrally and inappropriate treatments may lead to significant errors in modeling radiative heat transfer. To reduce the error of the Full-Spectrum Correlated K-distribution (FSCK) method in practical problems involving nongray walls, a nongray-wall model is propo...

The complex morphology of soot aggregates is a major source of uncertainty in evaluating their warming effects in the atmosphere. Fractal dimension (Df) is a key parameter in quantifying the morphology of soot particles. Previous studies are mostly based on manual identification of soot monomers in electron microscopic images and are hard to provid...

The mass absorption cross-section (MAC) of combustion-generated soot is used in pollution and emissions measurements to quantify the mass concentration of soot and in atmospheric modelling to predict the radiative effects of soot on climate. Previous work has suggested that the MAC of soot particles may change with their size, due to (1) internal s...

The mass absorption cross-section (MAC) of combustion-generated soot is used in pollution and emissions measurements to quantify the mass concentration of soot and in atmospheric modelling to predict the radiative effects of soot on climate. Previous work has suggested that the MAC of soot particles may change with their size, due to (1) internal s...

The particle filtration efficiency (PFE) of a respirator or face mask is one of its key properties. While the physics of particle filtration results in the PFE being size-dependent, measurement standards are specified using a single, integrated PFE, for simplicity. This integrated PFE is commonly defined with respect to either the number (NBFE) or...

Black carbon (BC) strongly absorbs solar radiation, contributing to global warming. Absorption enhancement of BC particles is difficult to quantify due to an inadequate representation of their complex morphology and mixing structures, as well as interaction with radiation. Here, we apply a 3D method accounting for detailed BC mixing structures to p...

This work presents a layer-peeling (LP) algorithm to correct the signal trapping effect in planar laser-induced incandescence (LII) measurements of soot volume fraction. The method is based on measurements of LII signals captured by an intensified CCD camera at a series of parallel planes across a diffusion flame. A method based on presumed functio...

Respirators, medical masks, and barrier face coverings all filter airborne particles using similar physical principles. However, they are tested for certification using a variety of standardized test methods, creating challenges for the comparison of differently certified products. We have performed systematic experiments to quantify and understand...

The walls of high-temperature combustion devices are usually assumed to be black or gray in radiative heat transfer calculations to save computing resources; however, this simplification may introduce large errors. To improve the accuracy of the Full-Spectrum Correlated K-distribution (FSCK) method in calculations of nongray-wall radiative heat tra...

Thermal radiation is an important heat transfer mode in flames and combustion systems. Non-gray gas and soot radiation is one of the most important heat feedback mechanisms to the preheating of fuel particles. The Discrete Ordinates Method (DOM) is used to solve the radiative transfer equation and the statistical Narrow Band k-distribution (SNBCK)...

The main characteristics of pool fire flames are flame height, air entrainment, pulsation of the flame, formation and properties of soot particles, mass burning rate, radiation feedback to the pool surface, and the amount of pollutants including soot released to the environment. In this type of buoyancy controlled flames, the soot content produced...

A numerical study is conducted using the CoFlame code to investigate the sooting characteristics of ethylene-fueled laminar coflow inverse diffusion flames (IDFs), aiming to gain insights into the different flame structure and soot formation features between an IDF and a normal diffusion flame (NDF). The effects of oxygen mole fraction in the oxidi...

Respirators, medical masks, and barrier face coverings all filter airborne particles using similar physical principles yet are tested using a variety of variety of standardized test methods. To quantify and understand the effects of differences between the standardized test methods for N95 respirators (NIOSH TEB-APR-STP-0059 under US 42 CFR 84), me...

Laser-induced incandescence (LII) is an optical technique that is widely used for the in situ measurement of the soot volume fraction in flames. The low intensity of LII signals in low-sooting turbulent flames means that long camera acquisition times are needed to achieve sufficiently high signal-to-noise ratios. The direct application of auto-comp...

In-flame optical characterization of soot is of vital importance to understand soot formation mechanisms as well as to develop and validate accurate soot models. The present work introduces an unconventional methodology adapted to laminar axisymmetric flames that avoids the issue of variable measurement vol- ume with varying scattering angle in the...

Dilution combustion has been widely utilized due to various merits, such as enhanced efficiency, fewer pollutants emissions, and even a promising future in alleviating global warming. Diluents can be introduced through the oxidizer or fuel side to achieve the desired combustion properties, and H2O and CO2 are the most common ones. A comprehensive c...

The CAPS PMssa monitor is a recently commercialized instrument designed to measure aerosol single-scattering albedo (SSA) with high accuracy (Onasch et al., 2015). The underlying extinction and scattering coefficient measurements made by the instrument also allow calculation of aerosol absorption coefficients via the extinction-minus-scattering (EM...

A novel diagnostic is proposed to characterize the maturity of soot particles in a laminar axisymmet- ric coflow ethylene diffusion flame in terms of the spectral dependence of soot absorption function. The method relies on the combination of line-of-sight attenuation (LOSA) and emission measurements at four wavelengths (500, 532, 660 and 810 nm)....

Radiative heat transfer (RHT) is often the dominant mode of heat transfer in flames, fires, and combustion systems and affects significantly temperature distributions directly and kinetically controlled chemical processes indirectly. Modeling RHT accurately in multidimensional flames and combustion systems is challenging mainly due to the highly sp...

The walls of combustion systems are usually assumed to be black or gray in radiative calculations, which may cause large errors. The Planck-function-weighted emissivity is usually used as the gray-wall emissivity when using the Wide-Band Correlated K-distribution method. This approach can demonstrate good accuracy when coupled with the emissivity-b...

This work presents a novel method to auto-correct the trapping effect of laser-induced incandescence (LII) signals inside the flame to obtain soot volume fraction distributions in laminar axisymmetric (2D) and three-dimensional (3D) flames using planar LII. The development of the proposed model is described with an estimation of the propagated unce...

The CAPS PMssa monitor is a recently commercialized instrument designed to measure aerosol single scattering albedo (SSA) with high accuracy (Onasch et al., 2015). The underlying extinction and scattering coefficient measurements made by the instrument also allow calculation of aerosol absorption coefficients via the extinction-minus-scattering (EM...

There is currently a lack of adequate understanding of soot formation in flames fueled with liquid hydrocarbons at elevated pressures. In this study, laminar coflow n-heptane and toluene doped CH4/air diffusion flames were numerically investigated under a constant carbon mass flow rate at pressures between 2 and 8 atm to understand how pressure aff...

This report describes the instruments, supporting equipment, and test methods used in the development of the NRC Metrology research-grade N95 respirator Particle Filtration Efficiency Measurement System (PFEMS). The report also presents data acquired to validate the performance of the system in terms of range, repeatability, intermediate precision,...

The thermal-optical analysis (TOA) of carbon in particulate matter (PM) collected on filters has been recommended and used for the calibration of mass-concentration instruments. However, filter-based TOA calibrations have substantial practical limitations, requiring high sample flow rates (>10 L min⁻¹), long sampling times (up to 3 h), and subseque...

The thermal and chemical structures of laminar coflow syngas diffusion flames burning in O2/H2O atmosphere were experimentally and numerically studied at 1 atm and initial temperature of 400 K. The O2/H2O molar ratio was varied from 20/80 to 100/0 to investigate the effects of oxygen concentration. An intensified CCD was used to capture the OH*-che...

The effect of water-vapor addition to oxidizer on flame radiation is assessed experimentally and numerically through the study of laminar coflow ethylene-fueled non-premixed flames. Oxygen-deficient conditions were studied to closely represent real confined fire situations. Experimental soot volume fraction distributions, presented in a previous st...

Soot primary particle size distribution along the centerline of a laminar coflow methane/air diffusion flame doped with vaporized n-heptane at atmospheric pressure was studied using the planar two-color time-resolved laser-induced incandescence (TiRe-LII) technique and analysis of transmission electron microscope images. An improved thermophoretic...

Radiation heat transfer in oxy-fuel flames is more important than in conventional fuel-air flames. The Full-Spectrum Correlated K-distribution methods (FSCK) with the original correlated-K solution scheme (Modest and Zhang, 2002) and a newly proposed one (Cai and Modest, 2014), and the Rank Correlated Full-Spectrum K-distribution method (RC-FSK) ar...

This article investigates the effects of increasing pressure up to 4 atm on radiative heat transfer in momentum-driven methane turbulent jet flames by using well-established chemical mechanism, combustion, soot production and radiation models. A transported PDF method is used to close properly the soot-production turbulence interaction and the emis...

The study is aimed at investigating the radiative properties of soot aggregates at determined morphological features using both experimental and numerical methods. Soot aggregates collected from air monitoring stations in different locations were examined. The locations were divided into three groups. The first group (Case 1) included the coastal a...

Ship emissions are dominated by a different type of particle than once thought. Ships typically use heavy fuel oil for combustion, releasing small light-absorbing particles such as black and brown carbon (brC). However, the properties and composition of such ship-related carbonaceous emissions is not well-known, complicating the quantification of t...

The effects of adding water-vapor to the oxidizer stream on soot production in laminar coflow diffusion flames under different oxygen indices (OI) were investigated both experimentally and numerically. A modified coflow Gülder-type burner was employed to produce the laminar ethylene flames for fifteen different conditions of the oxidizer stream fro...

Radiation heat transfer is important in spherical flame modeling, such as to determine the flame speed. It is beneficial to use one-dimensional (1D) model to solve the three-dimensional problems with spherical symmetry, while little work reports the 1D non-gray radiation heat transfer in spherical coordinates. This paper developed a 1D first order...

Knowledge of the optical properties of soot black carbon (BC) is required for the prediction of the radiative effects of freshly-emitted and aged BC particles. Here we review BC mass absorption cross section (MAC) and absorption function E(m) measurements, focusing on freshly-emitted BC. First, we review recently reported MACs at 550 nm wavelength...

Soot particles in the detection volume in general have different temperatures due to non-uniform laser fluence and particle size distribution. The thermal radiation intensity displays different temperature dependence at different wavelengths. The effective soot temperature inferred from the ratio of laser-induced incandescence (LII) signals in the...

This paper investigates the effects of soot inception and condensation polycyclic aromatic hydrocarbon (PAH) species and fuel preheating on soot prediction in 2D coflow laminar CH4/air diffusion flames doped with vaporized gasoline surrogate fuels, i.e., n-heptane/toluene mixtures. To evaluate the importance of considering multiple PAHs in soot inc...

The effect of char during the heterogeneous reduction of N2O by CO has been studied using density functional theory (DFT). The armchair and zigzag configurations with six and seven aromatic ring clusters are selected as the carbonaceous surfaces. The calculation results show that heterogeneous reduction of N2O by CO on char surface undergoes two st...

The Multi-Group Full-Spectrum K-distribution method (MGFSK) is a promising method for efficient and accurate thermal radiation calculations in participating media with strong temperature inhomogeneity. The current MGFSK method cannot be used for modeling radiative transfer in gas mixtures since it is applicable only to a single radiating gas. To ma...

Soot primary particle size distribution along the centerline of a laminar coflow methane/air diffusion flame doped with vaporized n-heptane at atmospheric pressure was studied using the planar two-color time-resolved laser-induced incandescence technique and analysis of transmission electron microscope images. An improved thermophoretic probe sampl...

Oxygen plays an important role in heterogeneous reduction of N2O by char in coal-fired power plants. In this study, we use quantum chemistry to investigate the most probable transition states, intermediates and products in the process of heterogeneous reduction between char and N2O and to study the behavior of oxygen remaining on the surface of cha...

In the last two to three decades many efforts have been made to evaluate the radiative properties of soot in flames. Due to the strong impact of soot on global warming and the aging process of soot particles in the atmosphere, it is necessary to gain a better understanding on how the radiative properties of soot are affected by coating with non-abs...

The radiative properties of hematite (α-Fe2O3) samples of different particle size distributions obtained by the pressure welding procedure were investigated. Measurements were made in the ultraviolet and visible spectra, and the radiative properties of samples were assessed using the discrete dipole approximation (DDA) in the visible spectrum. The...

This paper experimentally documents the transition from the “closed-tip” flame configuration to the “open-tip” one that a laminar axisymmetric coflow ethylene/air non-premixed flame experiences with increasing the fuel flow rate at the smoke point in terms of soot temperature and volume fraction distributions. To this end, the two-dimensional soot...

The effective density and mixing state of particles emitted from a natural gas–diesel dual fuel engine are investigated. Measurements were conducted at three different fuel compositions including 100% diesel fuel (0% NG), 75% diesel–25% natural gas (25% NG) and 50% diesel–50% NG (50% NG). The particle effective density was measured using a differen...

The paper presents an experimental investigation of the effect of oxygen concentration in the oxidizer (O 2 +N 2 )on distributions of soot volume fraction (SVF)and flame centerline primary particle size in laminar coflow ethylene diffusion flames. The base flame has an oxygen index (OI, oxygen mole fraction in the oxidizer stream)of 21%. Three addi...

Black carbon (BC) aerosol is the strongest sunlight-absorbing aerosol, and its optical properties are fundamental to radiative forcing estimations and retrievals of its size and concentration. BC particles exist as aggregate structures with small monomers and are widely represented by the idealized fractal aggregate model. In reality, BC particles...

In this study, the tunable algorithm of cluster–cluster aggregation developed by Filippov et al. (2000) for generating fractal aggregates formed by monodisperse spherical primary particles is extended to polydisperse primary particles. This new algorithm, termed FracVAL, is developed by using an innovative aggregation strategy. The algorithm is abl...

In this study, the impact of various treatments of gas and particle radiative properties on modelling radiative heat transfer in a 2D-squared enclosure with conditions representative to the post-burner region of an oxy-coal furnace with wet flue-gas recirculation is systematically investigated. The benchmark solutions for the radiative source terms...

The laser-induced incandescence (LII) and cavity ring-down extinction (CRDE) optical techniques offer excellent sensitivity to allow in situ soot volume fraction \(({f_{\text{v}}})\) measurements over a wide dynamic range. The objective of this work is to quantitatively measure the axial \({f_{\text{v}}}\) profiles in two n-butane premixed flames w...

Black carbon (BC) aerosol is the strongest sunlight-absorbing aerosol, and its optical properties are fundamental to radiative forcing estimations and retrievals of its size and concentration. During incomplete combustion, BC particles exist as aggregate structures with small monomers, which are widely represented by the idealized fractal aggregate...

A numerical study is carried out to, first of all, investigate the capability of a Polycyclic Aromatic Hydrocarbon (PAH)-based sectional particle dynamics soot model in the prediction of soot production in laminar coflow ethylene diffusion flames. The effects of different oxygen mole fractions in the oxidizer stream, called Oxygen Index (OI), rangi...

The effects of CO2 and H2O addition on benzene and PAH formation in a laminar premixed CH4/O2/Ar flame at atmospheric pressure were numerically investigated using two recently developed kinetic mechanisms with PAH formation up to at least benzopyrene. To distinguish the chemical effects of CO2 and H2O addition through partial replacement of Ar from...

The morphological characteristics of soot are of primary importance to quantify its effect on climate forcing and human health and also to interpret the signals acquired in optically based soot diagnostics. In the present study, the morphology of soot particles produced in laminar coflow diffusion flames was investigated under different fuel and ox...