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• The oxidation and laminar combustion characteristics of natural gas were experimental tested. • A new construction method of the reduced mechanism of natural gas was proposed. • A reduced mechanism containing 40 species and 189 reactions of natural gas was formed. • The reduced mechanism can predict well the characteristics of oxidation, ignition delay and laminar combustion of natural gas. The oxidation process in the flow tube reactor and the laminar combustion process in the constant volume combustion bomb of natural gas (0.9 methane/0.07 ethane/0.03 propane, mole fraction) were experimental tested. Furthermore, a reduced reaction mechanism (including 40 species and 189 reactions) of natural gas was developed based on the Aramco 2.0 mechanism by combining the path sensitivity analysis, rate of production analysis, reaction path analysis and the decoupling method. The results show that, in the oxidation process of natural gas, with the equivalence ratio increasing, the starting and ending temperatures for oxidation reaction of natural gas are increased, the reaction temperatures corresponding to CO generation and consumption are higher, and the amount of NO production is decreased. In the the laminar combustion process of natural gas, with the initial temperature and oxygen content increasing or the initial pressure, CO 2 and H 2 O contents decreasing, the laminar flame speed is increased. Through comparing with the calculated results by the Aramco 2.0 mechanism and the corresponding test data, the reduced reaction mechanism can well predict the oxidation, ignition delay and laminar combustion characteristics of natural gas under various conditions. [ABSTRACT FROM AUTHOR]

• Combustion and emission characteristics of a heavy-duty gas turbine combustor fueled with natural gas were simulated. • Simulated NO x concentration at the outlet of the flame tube is only higher than the experimental value by 5.08%. • Fuel ratios in the duty, uniform, and annular zones of the flame tube were twice redistributed. • After fuel modified redistributed, NO x emission decreases from 157.1 mg/m3 to 139.51 mg/m3. In this paper, the ignition delay and laminar combustion characteristics of natural gas were tested in a chemical shock tube and a constant volume combustion reactor, respectively, and simulated with the Gri_3.0, USC_2.0 and NUI_Galway models, respectively. It is proved that the ignition delay and laminar combustion characteristics of natural gas simulated with the Gri_3.0 model are in better agreement with the experiment than the USC_2.0 and NUI_Galway models. Furthermore, the simulated variation trends of the mole fractions of main species, especially NO and NO 2 with temperature by the Gri_3.0 model are in better agreement with the experimental data in the oxidation of natural gas. The combustion process and pollutants generation characteristics in a single flame tube of a heavy-duty gas turbine burning natural gas were simulated by coupling the Gri_3.0 model with the computational fluid dynamics. It is shown that the simulated average temperature and the NO x concentration at the outlet of the flame tube are slightly higher than the experimental value by 8.06% and 5.08%, respectively. Because the NO x emission is higher than the designed value, fuel flows in the annular, main, and pilot combustion zones of the flame tube were reassigned and effects of the fuel redistributions on the NO x emission characteristics were investigated. It is shown that the NO x concentration at the outlet of the flame tube increases from 157.1 mg/m3 to 175.5 mg/m3 when the fuel flow in the pilot combustion zone is redistributed to the main combustion zone, and decreases from 157.1 mg/m3 to 139.51 mg/m3 when the fuel flow in the pilot combustion zone is redistributed to the annular combustion zone. The research results will provide theoretical basis and technical support for the optimization of this gas turbine operation. [ABSTRACT FROM AUTHOR]

• 3D LES simulation is conducted on spherical expanding flame of premixed natural gas/air mixture. • 3D flame front is decomposed into 36 2D flame fronts by rotation of the ZOX cross-section. • Flame morphology, flame propagation speed, cellular instability and disturbance are analyzed. • Disturbance amplitude and wave number of the flame perturbation are extracted by FFT. • Effects of spark energy, spark radius and time step on the simulation results are discussed. The flame dynamic and cellular instability of spherically expanding flame for premixed natural gas/air mixture were studied by numerically solve the 3D, transient, reactive Navier-Stokes equations. The computational methodology uses large eddy simulation and premixed combustion model with adaptive mesh refinement. The 3D flame front is decomposed into 36 2D flame fronts by every 5° rotation of the ZOX cross-section during post-processing. Fast Fourier Transform (FFT) with Hanning window is adopted to extract the disturbance amplitude and wave number of the flame perturbation. The effects of spark energy, spark radius and time step on the simulation results are also discussed. The computational methodology is first validated by experimental data at atmospheric condition and then applied to premixed natural gas/air mixtures under elevated temperature and pressure. The results showed that the initial temperature has little effect on the flame morphology, while the crack splitting on the flame front intensifies from the initial stage of flame propagation and the number of cells on the flame surface obviously increases as the initial pressure increases. The initial pressure has a more significant effect on the critical flame radius than the initial temperature. This is because increasing the initial pressure leads to the reduction of flame thickness while both the flame thickness and the density ratio decrease with the increase of initial temperature. Moreover, disturbance energy within the wavenumber range of 4–15 increases significantly with the increase of initial pressure, especially at stoichiometry condition. This is because the restriction effect of flame stretch on flame inherent instability reduces with the increase of initial pressure. [ABSTRACT FROM AUTHOR]