Experimental study on turbulent burning velocities of premixed flames for natural gas/air mixtures

Abstract

Experiments on the spherical expanding flame of turbulent premixed natural gas/air mixtures were conducted in a fan-stirred turbulent combustor for the first time. As the belief that the methane burning velocity data can be obtained for natural gas is not justified, natural gas constitutes of 90% CH4, 7% C2H6 and 3% C3H8 by volume fraction was used. The operation conditions are equivalence ratio of 0.7–1.3, initial temperature of 300–400 K, initial pressure of 0.1–0.3 MPa, turbulence intensity of 1.0–2.7 m/s, oxygen volume fraction of 15–21% and carbon dioxide volume fraction of 0–20%. A self-developed program and post-processing procedure was developed to highly restore the real information of flame front without ignoring small local information. It was concluded that methane cannot be taken as a representative of natural gas for studying turbulent burning velocities. The increase of flame propagation speed with initial pressure is not as significant as that with initial temperature and turbulence intensity under low-intermediate pressure range. Dispersions exists for previous correlations relating to turbulent flame Reynolds number, Karlovitz number, Damköhler number, respectively, and a new correlation were proposed based on the ratio of Karlovitz number and Damköhler number. The new correlation was validated by both current and previous experimental data and its advantage and applicability were summarized. It will be validated by turbulent flames of various kinds of fuels over a wide range of working conditions in the further study.