Experimental Investigation of Effect of Density Ratio on Turbulent Flame Speed

• Main Authors: WUN-YI LI, 李文義
• Other Authors: 施聖洋
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/74059641773298614908

碩士 === 國立中央大學 === 能源工程研究所 === 104 === Turbulent combustion rate w ̇_t characterized using either flame (displacement) speed SF or burning (consumption) velocity uc was in the focus of experimental research into premixed combustion for many decades. There is an important mixture characteristic, i.e. the density ratio σ=ρ_u⁄ρ_b , that has yet been rarely used when parameterizing experimental data on SF or uc. While the influence of the density ratio on the combustion rate is of great interest for basic understanding of premixed turbulent flames and was addressed in a couple of numerical and theoretical studies, this issue is still waiting for a target-directed experimental investigation. The goal of this thesis is to fill this gap by measuring turbulent flame speeds in mixtures that have been specially prepared by combining preheating and dilution of unburned reactants in order to retain the laminar flame speed unchanged, but substantially change the density ratio. The experiments are conducted in a dual-chamber explosion facility that has been extensively used to measure propagation speeds of expanding turbulent flames at National Central University. The facility with new modifications for heating consisted of a large inner 3D cruciform burner situated within a huge outer chamber, capable of generating near-isotropic turbulence and producing a uniform high-temperature environment. Experimental data obtained from statistically spherical expanding stoichiometric methane-air flames at various r.m.s. turbulent velocities u' show that the flame speed is very weakly increased by the density ratio at low u'⁄S_L <1 and is independent of the density ratio at moderate u'⁄S_L >1. Moreover, turbulent flame speeds measured at u'⁄S_L = 0.4 are not larger than the laminar flame speeds in all cases investigated.