Experimental And Numerical Investigation On Laminar Combustion Characteristics Of Premixed Svn-gas Flame

Currently, coal gasification is expected to play an important role in future energy production, particularly for stationary power generation using Integrated Gasification Combined Cycle (IGCC) systems, because it not only can reach the clean combustion of coal, but also can improve the efficiency of power station by combined cycle. The production of coal gasification is called syngas (synthetic gas). The syngas composition and proportions of every constituent can vary widely due to various types of chosen feedstock and various methods of gasification process, which brings a challenge for combustor designers since typical combustor design tools require data on various fundamental gas combustion properties in order to design an efficient fuel flexible combustor. Therefore, it is an essential topic to study the burning properties of syngas over a wide range of composition under representative operating conditions of advanced gas turbines. Various investigations have already begun, and much attainment was achieved, but a lot of work is still needed to be carried out to further understand the burning properties of syngas, especially under high pressure and high temperature.Firstly, in order to investigate the laminar flame speed and Markstein length of syngas at high pressures and temperatures, an existing dual-chambered, pressure-release type high-pressure combustion apparatus which can only be used to measure laminar flame speed at high pressure was improved to measure the laminar flame speed at high pressures and temperatures. Then experiments on typical syngas/O2/diluent flames were conducted at normal and elevated pressures and temperatures using this revised spherical flame bomb. The laminar flame speed and Markstein length were measured and the effects of Lewis number, flame temperature, pressure and initial temperature were investigated. The main results showed that different oxidizers can be used to isolate and assess separately the effects of Lewis number and flame temperature. When the adiabatic flame temperature remains unchanged, the Lewis number was shown to have significant influence on laminar flame speed. When the Lewis number was fixed, increasing of the adiabatic flame temperature results in the increase of the laminar flame speed. The laminar flame speeds of typical syngas/O2/diluent mixtures measured in this study were shown to be accurately predicted by the syngas mechanism available in the literature. However, at elevated temperature, the laminar flame speeds measured in this study were greatly under predicted by the syngas mechanisms of Davis and Sun. Therefore, the present experimental results indicated that the syngas mechanisms of Davis and Sun were not suitable for rich syngas/air at elevated temperatures and these mechanisms should be improved. It also found out that the Markstein length decreases with the increase of pressure and initial temperature. But the Markstein length is less sensitive to change of initial temperature than that of pressure.Furthermore, one-dimensional, laminar premixed flames of H2/CO/air mixtures were investigated numerically in conjunction with OPT model, the effects of initial temperatures and pressures on the dilution limits, the maximum flame temperature, the laminar flame speeds, the mass burning rate, the ratio of flame thickness to reaction zone thickness and the Zeldovich number are evaluated. The major conclusions showed that the dilution limits of H2/CO/air decrease monotonously with increasing pressures and are extended by increasing initial temperature. The laminar flame speeds at the dilution limits increase with increasing of the initial temperature and decrease monotonously with increasing pressures. The mass burning rates increase with the increase of the initial temperatures and pressures. The elevated pressures cause much thinner flames, and the decreased flame thickness renders the flame-let modeling more favorable for turbulent combustion at elevated pressure conditions. Ratios of the flame thickness to reaction thickness and the Zeldovich number increase firstly and then decrease with increasing pressure, but the non-monotonic trend of ratio of the flame thickness to the reaction thickness with pressures is unnoticeable. The sensitivity analysis suggested that the reason for the non-monotonic trend of the Zeldovich number is caused by the elementary reaction: H+O2+Mâ†'HO2+M,2HO2â†'H2O2+O2and H2O2+Mâ†'2OH+M.