Characteristics Of Non-premixed Flame Research Articles

Non-premixed flame characteristics and exhaust gas concentrations behind rifled bluff-body cones

Four bluff-body cones with/without rifled v-grooves were installed behind a non-premixed traditional combustion nozzle to intensify the bluff-body effects and swirl flow. The spiral rifles transformed axial momentum (or axial velocity) into tangential momentum (or tangential velocity). The interaction between the fuel tangential component and axial air flow increased turbulence intensity (T.I.). The Schlieren photography was utilized to visualize the flame structures and classify three flame patterns—jet flame, recirculation flame, and turbulence flame. The jet flame occurs when fuel-jet velocity is high and air-jet velocity (ua) is low. However, the turbulence flame exists at the high air-jet velocity. The flame lengths were measured using the direct photography scheme. The flame length at high ua is significantly shorter than that at low ua. Furthermore, the increase of rifle number (i.e., increasing T.I.) induces the high maximum temperature and low nitric-oxide concentration.

관 내부 메탄-공기 분류 비예혼합 화염의 부상 특성 기초 연구

Flame lift-off conditions determine the operating conditions of burners. It is known that a flame can be lifted when the Schmidt number (Sc), which is the ratio of the dynamic viscosity to the mass diffusivity, is greater than unity. In this study, the flame lift-off characteristics of non-premixed flames of propane (Sc > 1) and methane (Sc

On the Estimation and Validation of Global Single-Step Kinetics Parameters of Ethanol-Air Oxidation Using Diffusion Flame Extinction Data

In this study, based on the extinction characteristics of nonpremixed flames, global single-step kinetics parameters are estimated for ethanol oxidation in air. Using a quasi-steady heterogeneous experimental setup, the air velocity at which an envelope flame surrounding the sphere transits to a wake flame that burns in the rear region of the sphere, termed as the transition or the extinction velocity, were obtained in a previous study. These extinction velocities for different sphere sizes are employed to estimate the single-step kinetics parameters. The estimated global single-step kinetics has been employed in a numerical model and extinction characteristics of opposed-flow ethanol-air diffusion flames have been predicted and validated against the available experimental results in literature.

Flame-wall interaction for a non-premixed flame propelled by a vortex ring

The characteristics of non-premixed flame–wall interaction have been studied in a reacting vortex ring configuration. A finite duration axisymmetric methane jet is injected into a quiescent oxidizer ambient to generate a laminar vortex ring. Fuel and oxidizer temperatures are adjusted such that auto-ignition takes place and results in the formation of a non-premixed flame surrounding the vortex ring. The methane combustion is modelled using detailed kinetic mechanism GRI3.0 with the reactions and the species containing nitrogen removed, except N2. The flame is propelled by the ring induced velocity and interacts with an isothermal inert wall which is perpendicular to the direction of the flame propagation. Interactions have been studied for two different wall conditions – one with and one without a thermal boundary layer. Heat release rate, vorticity, and temperature fields have been examined during the interaction. Various flame–wall interaction parameters like strain rates, flame power, Peclet number and non-dimensional wall heat flux are studied. For all runs, the values of quenching Peclet number are in the range 0.26–0.45. The non-premixed flame quenching distance is found to be approximately of the same order as that of the premixed flame quenching distance obtained in experiments. The quenching values of non-dimensional wall heat flux for non-premixed flames in this study are of the same order of magnitude as those obtained for premixed flames. Flame structure and near wall reaction mechanisms are analysed. In the absence of a thermal boundary layer, various radical mole fractions are increased in the near wall region. In the presence of a thermal boundary layer, HO2 accumulates and contributes primarily to the heat release rate at the wall. Products and unburned hydrocarbon mole fractions are found to be higher for the runs without a thermal boundary layer compared to the runs with a thermal boundary layer.