Synergistic Effect of Soot Formation in Ethylene/Propane Co-Flow Diffusion Flames at Elevated Pressures

An experimental and numerical study of the effects of dimethyl ether addition to fuel on polycyclic aromatic hydrocarbon and soot formation in laminar coflow ethylene/air diffusion flames

Although diffusion flame is free from many problems associated with premixed flame, soot formation is a major problem in diffusion flame. The techniques of dilution of fuel or air with inert gases such as nitrogen and argon are used to decrease soot level in the flame. In this work, a CFD code has been developed to predict the flame height, soot volume fraction and soot number density in an axisymmetric laminar confined methane-air diffusion flame after diluting the fuel with nitrogen. The temperatures of the air and fuel at inlet are taken as 300K. Mass flow rate of the fuel stream is considered as 3.71×10−6 kg/s and mass flow rate of the air is taken as 2.2104×10−6 kg/s. The total mass flow rate through the central jet (fuel jet) is, however, kept constant. The radiation effect is also included through an optically thin radiation model. An explicit finite difference technique has been adopted for the numerical solution of reacting flow and two equations soot model with variable thermodynamic and transport properties. The prediction shows that flame height decreases with the addition of nitrogen to the fuel. Temperature of the flame is considerably reduced in the given computational domain. Both soot volume fraction and soot number density decrease with dilution by adding nitrogen in the fuel jet. The soot formation at different nitrogen dilution level of 0%, 10%, 20%, 30%, 40% and 50% are plotted and the soot get considerably reduced as the concentration of nitrogen is increased in the fuel stream.

The influence of hydrogen and methane on the growth of carbon particles during acetylene pyrolysis in a burnt-gas flow reactor

In order to understand the processes involved in the laser-induced incandescence (LII) technique, the value of soot temperature at the peak of the incandescence signal has been studied. To this purpose, an absolute two-color LII technique has been applied on ethylene and methane diffusion flames, based on the comparison with a calibrated tungsten ribbon lamp. The dependence of peak temperature on the fluence has been investigated by using a sharply edged probe beam. Above a certain fluence threshold a value close to 4000 K was obtained for both flames at all locations, that means in largely different soot conditions. At a suitably selected laser fluence, radial and axial profiles of peak soot temperature and volume fraction were performed. Soot volume fraction data have been validated with results from laser extinction technique measurements. The quite low values observed for methane prove the sensitivity of the LII technique. Moreover, a discussion about soot refractive index is presented. In the visible region a test of its influence on both soot volume fraction and soot peak temperature was carried out, while in the infrared the heating process was analyzed.

Measurements of soot, OH, and PAH concentrations in turbulent ethylene/air jet flames

Soot formation in counterflow non-premixed ethylene flames at elevated pressures

Experimental and numerical study on soot formation in laminar high-pressure 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.

In this work, we investigate qualitative backlight imaging-based spray characteristics and laser-induced incandescence (LII) based quantitative soot volume fraction (SVF) in a CFM56 model combustor with a simplex nozzle at 1 bar, 303 K. The soot volume fraction is quantitatively measured using an in situ extinction-based calibration technique. Soot was detected immediately downstream of the swirler exit and in the shear layer region as observed by other authors. In addition, soot was also detected inside the inner recirculation region which could be due to the spray distribution, geometry, or difference in flame anchoring. The number-averaged soot volume fraction is of the order of 20 ppb which is comparable in magnitude to previously reported combustor measurements. Large eddy simulation (LES) modeling of the experimental setup coupled with the simple two-equation Tesner model has been done using ansysfluent® to study soot formation. The model shows good qualitative agreement with the experimental results although quantitatively it is lower by one order of magnitude. Soot formation occurs in the rich region immediately downstream of the swirler while the second half of the primary zone becomes lean and soot oxidation is more dominant.

Soot and NO formation in methane–oxygen enriched diffusion flames

he focus of the present study is to obtain detailed knowledge of the soot formation and oxidation processes in laminar diffusion flames. The present work studies the effects of various flame properties on soot growth and oxidation, and how they affect a flame’s sooting behaviour. Numerically modelling of soot formation in laminar coflow diffusion flames of vaporized gasoline/ethanol blends at atmospheric pressure is performed. The numerical results are compared with experimental data to gain improved understanding of ethanol addition to gasoline on soot formation. Four gasoline/ethanol blends are investigated to quantify how soot loading varies with the amount of ethanol blending in the fuel. The results of experimental and numerical modelling agree relatively well in terms of the levels of soot volume fraction. Both results show a decrease in soot loading as more ethanol is added in the fuel stream. The work continues by numerically studying the oxidation of soot in laminar ethylene/air coflow diffusion flames. A new model for soot oxidation, a complex process in numerical soot modelling, is developed based on the observation that soot ageing reduces surface reactivity. Using this new model, it is possible to capture the correct behaviour of both smoking and non- smoking flames in various flame configurations. Along with a detailed soot sectional model, the new model predicts the correct soot volume fractions, smoke emission characteristics, and primary particle diameters for different flames without any variation in model parameters. The work extends to study soot surface reactivity in the growth and oxidation regions. Laminar ethylene/air and methane/air coflow diffusion flames are numerically studied to develop a unique soot surface reactivity model. A newly developed surface character model simultaneously accounts for soot surface reactivity in surface growth and oxidation by considering soot ageing and its effects on the particle surface. The new model, which eliminates tuning of one modelling parameter, reconciles the quantification of the evolving soot surface character for both growth and oxidation. The model is shown to be uniquely capable of predicting soot concentrations and smoke emissions within experimental uncertainty in a wide range of laminar diffusion sooting flames.

Evolution of the soot particle size distribution along the centreline of an n-heptane/toluene co-flow diffusion flame

Simultaneous planar measurements of temperature and soot volume fraction in a turbulent non-premixed jet flame

Gas-liquid two-phase flows generally have the characteristics of complex and variable flow patterns and flow rate uncertainty of each phase. The entrainment of gas increases errors of the existing non-separated multiphase metering. A novel metering method based on the multi-frequency Coriolis principle is proposed to solve the above problems. Compared to the conventional Coriolis mass flowmeter, the third-order mode of the measuring tube is used to improve the accuracy of the measurement. The influences of bubble effect and resonance effect on vibration responses in different vibrational modes were studied to determine the deviations of the apparent values of total density and mass flowrate by simulation. Simulation results with a single-frequency Coriolis flowmeter show that the maximum relative deviations of total density and total mass flowrate are −37.3% and −9.3%, respectively. Driven by different frequencies, the same two phase fluid in the measuring tube can have different responses of the primary mode and the higher vibrational modes. The vibrational responses characteristics corresponding to the first-order and third-order modes of measuring tube were selected and analyzed. Combined with advantages of high precision and multi-parameter measurement of traditional single-frequency Coriolis flowmeters, a multi-frequency correction model suitable for stratified flow was proposed. The results show that the corrected total density and mass flow deviations of gas-containing fluid are within ±4% and ±3%, respectively, which are significantly reduced. Corrected flowrate deviations of the gas-phase and liquid-phase are ±9.1% and ±7.2%, correspondingly, which also meet the metering requirements of the wellhead.

Investigation of soot formation of spark-ignited ethanol-blended gasoline sprays with single- and multi-component base fuels