Effect of Soot-Inhibitor Additives on the Thermal Structure and Soot Volume Fraction Inside Laminar Diffusion Natural Gas Flames

Abstract

Soot study is a fundamental issue for the combustion process of hydrocarbon fuels. Losses in combustion efficiency, health risks, environmental loosestrife, and damage in furnaces may appear as a result of soot existence. This present paper aims at providing an experimental mapping of the changes in the soot volume fraction and axial flame mean temperature associated with the addition of different percentages of soot inhibitor additives (namely, Argon, Nitrogen, and Helium) in a vertical laminar diffusion natural gas flame issuing from a honeycomb circular burner. The soot volume fraction is acquired by the laser extinction technique, while the axial variations of the mean flame temperature are accomplished by a bare 51 µm (Pt-30%Rh versus Pt-6%Rh) thermocouple to render radiation loss insignificant. The concentration of the individual additives is varied from 5% to 25% (step 5%) and the experiments are conducted at a fixed natural gas throughput (350 mL/min) to ensure unvaried thermal input. Measurement traverses along and across (at fixed radial locations) are conducted. The fuel flowrate is measured by a precision digital gas flowmeter (type: Varian intelligent), while the flow of the individual additive is admitted via solenoid valves (handled with labview program) and is injected through mixing pipes located at burner entry. The different regimes of the soot inception (molecular; zone 1), soot growth zone (zone 2), and soot oxidation (zone 3) are accurately defined and assessed in relation to the temperature results for the different cases under investigation.