Numerical and experimental study on the soot formation in methane multi-jet flames under microgravity

Sooting characteristics of partially-premixed flames of ethanol and ethylene mixtures: Unravelling the opposing effects of ethanol addition on soot formation in non-premixed and premixed flames

Experimental characterization of the different nitrogen dilution effects on soot formation in ethylene diffusion flames

This paper aims to provide a physical understanding of the pressure effect on soot formation in laminar diffusion flames. Soot formation in laminar coflow diffusion flames is strongly influenced by pressure. Although predicting soot formation at atmospheric pressure has been very accurate in literatures, there is still a lack of understanding of multiple soot formation processes at high pressures. However, few researches studied the effects of pressure on multiple steps in the soot formation. This work studies the pressure effect on detailed soot formation, which includes multiple physical processes of surface growth, surface OH oxidation, surface O2 oxidation, and collision kinetics. A pressure-dependent model is proposed by analyzing the pressure-dependent surface reactivity in surface reactions and the pressure-dependent collision kinetics in soot formation. Simulation is conducted in the pressure range from 1 atm to 20 atm, with experimental validation in the pressure range from 1 atm to 3.5 atm. In the pressure range from 1 atm to 3.5 atm, the predicted primary soot particle diameter and soot yield of cases with the pressure-dependent model are validated by experimental result. As pressure further increases from 5 atm to 20 atm, the pressure dependence of soot yield and surface reaction rate decreases due to the limit of oxidation. This study contributes to the understanding of the pressure effect on soot formation at high pressures in soot formation.

Ionization and soot formation in premixed flames

On the opposing effects of methanol and ethanol addition on PAH and soot formation in ethylene counterflow diffusion flames

<p>Soot formation from combustion devices is a health and environmental concern. Therefore, a comprehensive understanding of soot is a necessity; however, due to its complexity, it is poorly understood, especially with high-pressure combustion. In this thesis, a detailed numerical soot formation code, CoFlame, has been successfully utilized to model varying-pressure coflow laminar diffusion flames. The results of this thesis are divided into two sections; first, an investigation of the impact of a novel pressure-based reaction rate of acetylene addition in the Hydrogen- Abstraction-Carbon-Addition (HACA) mechanism on soot formation in varying pressure flames is addressed in chapter 4. Second, an assessment of the influence of pressure on the formation of recirculation zones along the centerline of the flame and the subsequent effect of the flow field on soot formation in elevated-pressure coflow diffusion flames is addressed in chapter 5.</p> <p><br></p>

Chemical effects of hydrogen addition on soot formation in counterflow diffusion flames: Dependence on fuel type and oxidizer composition

The synergistic effect of soot formation refers to the interaction between different fuels during soot forming processes, which results in higher soot formation than any individual fuels. The present study experimentally investigates the synergistic effect of soot formation in co-flow diffusion flames of propane/ethylene fuel mixtures. The total carbon mass flow rate of the propane/ethylene mixture was kept constant at 0.5 mg/s, and the propane carbon ratio (RC) was defined as the ratio of carbon mass flow rate of propane to the total carbon mass flow rate. The laser-induced incandescence (LII) and light extinction (LE) techniques were applied to measure the soot volume fractions (SVF) at pressures of 0.1–0.5 MPa. The results showed strong synergistic effect in propane/ethylene mixtures at atmospheric conditions; however, increasing pressure weakens the synergistic effect. The LII intensity contours showed that the soot formation zone extends when synergistic effect occurs at RC = 0.1 and 0.2 for 0.1 and 0.3 Mpa. The normalized peak SVF showed that synergistic effect monotonically becomes weak with increasing pressure from 0.1 to 0.3 Mpa; meanwhile, the it still stayed strong at 0.2 Mpa when using normalized maximum soot yield, and then turned to be weaker as pressure increases. Further comparison analysis of the SVF profiles between RC = 0 and 0.1 revealed that the synergistic effect occurs at the two-wing area of the sooty flame at low axial flame height, and then gradually becomes stronger with increasing axial flame height in the soot zone for 0.1–0.3 Mpa. To illustrate the pressure effects on synergistic soot formation, numerical analysis in homogeneous closed reactor was conducted and it was found that The PAHs formation competition between C3H3 pathway and HACA mechanism results in the different soot formation phenomenon of ethylene/propane flames.

Obtaining quantitative experimental data on soot properties of aviation kerosene at elevated pressures is a significant concern for the surrogate fuel kinetic model of aviation kerosene. However, there are scarce studies on soot formation and properties of aviation kerosene in tractable flames at elevated pressures in literature. In this study, Chinese RP-3 aviation kerosene is used in relevant experiments and numerical simulations up to 3.5 atm to evaluate the effect of pressure on soot formation and properties. Soot morphology, nanostructure, and concentration are studied by transmission electron microscopy and laser extinction method. Then, an RP-3/PAH kinetic model containing the 5-aromatic rings (A5) growth mechanism is proposed to simulate the soot formation processes at elevated pressures. Quantitative experimental results show that pressure significantly affects the soot morphology, nanostructure parameters. The peak soot volume fractions in the RP-3 flame scale with the pressure as P 1.62 . The numerical results show that the RP-3/PAH model can depict the trends of soot particle size and soot volume fraction with pressure. At 1.0–3.5 atm, the rates of soot growth processes increase with pressure, especially the PAHs condensation. The significantly increased soot surface growth rate may be one of the main factors for the variation of soot properties with pressure. The quantitative experimental and numerical results contribute to the understanding of the kinetic mechanism of soot formation for RP-3 kerosene at elevated pressures.

Synergistic effects on soot formation in counterflow diffusion flames of acetylene-based binary mixture fuels

: The ionic theory of incipient soot formation has been further evaluated. Accurate temperature profiles through a series of low pressure, 2.7 kPa, acetylene-oxygen flames on either side of the threshold soot index were measured using radiation loss compensated electrically heated thermocouples. With these data and Langmuir probe curves determined in these same flames the absolute ion concentrations were obtained. These were in excellent agreement with similar data obtained by others using a molecular beam ion sampling technique. It was thus demonstrated that the ion concentration peak precedes the appearance of soot, the ion concentration is greater than the concentration of soot particles, and ions decay as soot appears. Characteristic times were calculated for a phi = 3 flame which indicates that ion molecule reaction rates are sufficient to account for soot formation; they also indicate the reactions which must be included in any detailed computer model of the process of soot formation--the ultimate goal of this study. Experimental temperature measurements at the soot threshold of flames of varying fuel/oxygen/nitrogen mixtures produced the surprising result that the experimental temperature was a constant for a given fuel although the adiabatic flame temperature varied over a large range.

Experiments and numerical simulation on soot formation in opposed-jet ethylene diffusion flames

Effect of the droplet size distribution of fuel spray on the soot formation process in spray flames is investigated. The vibratory orifice atomizer is used to control the droplet size distribution of fuel spray. Two-dimensional soot volume fraction and primary soot particle size are measured by the Time-Resolved Laser Induced Incandescence (Time-Resolved LII) method and direct numerical simulation. The relationship between spatial distribution of fuel droplets and soot formation area are observed by the LII method and Interferometric Laser Imaging Droplet Sizing (ILIDS) method. The results show that flame structures of spray flame and soot formation process are affected critically by the mean droplet size of fuel spray. The mean soot formation area is increased by increase of the mean droplet size of fuel spray. The primary soot particles become large at around the edge of soot formation area. This trend mainly occurs from surface growth of soot particles. The group of some droplets and its vapor forms the soot formation area, and the large droplet of liquid fuel deforms shape of the soot formation area.

Different chemical effect of hydrogen addition on soot formation in laminar coflow methane and ethylene diffusion flames

Soot formation characteristics in laminar coflow flames with application to oxy-combustion