Effect of Hydrogen Addition on the Turbulent Displacement Speeds of Natural Gas Blends (C1-C5 Alkanes)

摘要

Natural gas is the primary fuel for stationary, power-generation gas turbines, and it is necessary to understand its combustion characteristics under engine-relevant (turbulent) conditions. Since its composition varies depending on the fuel source, a natural gas surrogate (NG2: 81.25% CH_4 + 10% C_2H_6 + 5% C_3H_8 + 2.5% C_4H_(10)+1.25% n-C_5H_(12)) has been utilized recently by the authors to aid chemical kinetics modeling using ignition delay times and laminar flame speed experiments. This study focused on measuring turbulent flame speeds (displacement speeds) of NG2 using a fan-stirred flame bomb. The apparatus is a closed, cylindrical chamber fitted with four radial impellers that generate a central spherical volume of homogeneous and isotropic turbulence with negligible mean flow. Schlieren imaging was used to visually track the growth of the spherically expanding turbulent kernels during the constant-pressure period. The turbulence levels were fixed at an average RMS intensity level of 1.5 m/s and at an integral length scale of 27 mm. Turbulent flame speeds of NG2 blends were measured over a wide range of equivalence ratios between 0.7 and 1.3. The effects of hydrogen addition on the turbulent flame speeds of NG2 (25/75 and 50/50 (by volume) blends of H_2/NG2) were also investigated. Turbulent flame speeds of NG2 agreed closely with that of pure methane thus validating the technique established herein. Furthermore, the displacement speeds followed the trends as the laminar flame speeds for both NG2/H_2 and CH_4/H_2 mixtures.