Structure and Lean Extinction of Premixed Flames Stabilized on Conductive Perforated Plates

Abstract

The structure and lean extinction of premixed liquefied petroleum gas–air flames seated on conductive perforated plates were examined experimentally, with focus on the effects of plate material, thickness, and hole diameter. The lean extinction limit was determined by gradually reducing the fuel-flow rate for a given air-flow rate, until extinction occurred. Flame structure was quantified by mapping the local mean temperature and species concentrations and by imaging the average visual length of the flame plume. Pyrometer measurements of the temperature of the upper plate surface were made to estimate the heat transfer through the plate. It was found that the flames stabilized on plates with higher thermal conductivity were shorter and more stable (i.e., have lower lean extinction limits). This was attributed to preheating of fresh reactant mixture by greater heat transfer through the plate. Increasing the hole diameter (percentage open area) was found to enhance flame stability by reducing the reactant jet velocity for a given flow rate of reactant mixture. Heat transfer through the plate deteriorated with increasing hole size. However, the positive effect of smaller jet velocity on flame stability overpowered the negative effect of reduced heat transfer, and the net result was enhanced stability with larger hole sizes. Plate thickness, on the other hand, was found to have a weak effect on flame stability and structure. Thicker plates showed slightly better stability characteristics because of greater heat transfer through them. Nonetheless, plate heat transfer did not affect flame stability as significantly as jet velocity did.

Boiler dynamic control with optimized nitric oxides and efficiency

“…The data contain 21,600 samples of Steam Flow Rate (SFR) with sampling rate of 1 s. The behavior of all the other variables is simulated using Å stro¨m and Bell's model 7 of boiler. The results of that are validated against experimental data and extensively discussed in Elshafei et al 12 and Gamal et al; 29 but using our PID gains, the entire system is simulated again to provide a modest overview of available results in the literatures. Also, dynamic optimization of efficiency with NOx is examined and detailed discussion is presented in section ''Optimization, results and discussion'' along with simulation results.…”

“…Mixing of fuel and air upstream of the combustion in case of premixed flames can reduce the combustion temperature at the same FFR when compared to diffusion flames. 29 This means that the combustion temperature can be controlled at fixed FFR. Using this conversion factor, the upper limit of NOx is calculated to be 100 ppm It is also noteworthy that this value is dependent on AFR which varies under dynamic conditions and so does the upper limit of NOx in ppm.…”

“…The unoptimized AFR is basically the experimental AFR which has been practically used in boiler without the optimization, while optimized AFR is calculated based on the optimization of efficiency and NOx. The experimental AFR is used to present the main results of Elshafei et al, 12 Alzaharnah et al 17 and Gamal et al 29 to have a composite summary of available literature. All these works including ours are based on a commonly acquired data that come from an industrial boiler installed in eastern province in Saudi Arabia.…”

Frontiers in combustion techniques and burner designs for emissions control and CO2capture: A review

“…Conductive plates were considered with thermal conductivities up to 10 W/m·K only. Jamal et al, 231 however, considered conductivity values as high as 385 W/m·K and proved that if considerable heat is transferred through the plate to preheat the incoming combustible mixture, the flames become shorter and more stable. The authors examined the effects of plate material, thickness, and hole diameter and showed that heat transfer through the plate is the hidden primary control parameter behind all these effects.…”

The Effect of Swirl Number and Oxidizer Composition on Combustion Characteristics of Non-Premixed Methane Flames

“…The swirl is implemented in the air side or the annulus side of the combustor. The swirl number Sn is defined as the ratio of the tangential momentum flux over the axial momentum flux, and it is calculated from the following equation: Chemical reactions under the stoichiometric conditions for the air-fuel and oxy-fuel combustion are presented in eqs and , respectively, , where α is the oxygen fraction. It can be defined as the mole fraction of oxygen in the oxidizer blends can be identified by the following formula of eq where V O 2 ° and V O 2 ° denoted the volumetric flow rate of and carbon dioxide in the oxidizer mixture.…”