| With the development of Integrated Gasification Combined Cycle (IGCC) and Combined Cycle Power Plant (CCPP), there are great interests in the application of medium and low calorific value gas in gas turbine. The combustion characteristics of medium and low calorific value gas are very complex due to its varied composition and processing conditions. Numerical and experimental investigations were carried out to study these unique characteristics. Studying the extinction and laminar flame speeds of medium and low calorific value gas at high pressures is important for achieving stable combustion with high efficiency and low emissions.One-dimensional laminar premixed flames of CO/H2/air mixtures were investigated numerically at different preheating temperatures and a wide range of pressures with different CO2diluted ratio. The statistical narrow-band correlated-K (SNBCK) model which includes radiation emission and re-absorption and the optically thin (OPT) model which only considers radiation emission were used in simulation to assess the impacts of re-absorption on flame behavior near lean flammability limits. Meanwhile, simulations at preheating temperatures of298K,400K and500K without diluents using OPT model were conducted to assess the preheating effects on behavior of the near-limit flames. It was found that radiation re-absorption extended the lean flammability limits and these effects increased with CO2addition. Comparison between these two radiation models indicates that the effects of re-absorption increase with the pressure. With the increase of the pressure, the maximum flames temperature at the lean flammability limit increased first and then decreased with a peak value aroud10atm. Elevated unburned mixture preheating temperature extended lean flammability limits. Ratio of flame thickness to reaction zone thickness and Zeldovich number increased first and then decreased with increasing pressure. And the peaks move to low pressure as preheating temperatures increase. Sensitivity analysis suggested that the reason for it could be caused by the elementary reaction: CO+OH<=>CO2+H.Furthermore, a new dual-chambered pressure-release type high-pressure combustion apparatus was designed and accomplished. Comparing with other single-chambered combustion apparatuses, it can sustain a remarkable higher pressure and operate safely at high pressures. Using the new-built experimental measurement system, the laminar flame speeds of typical gases for IGCC and CCPP were measured at1~15atm and equivalence ratio from0.6to2. It was found that the laminar flame speed increases owing to the increase of Lewis number or flame temperature. Higher Lewis number helps to restrain the hydrodynamic instability. The laminar flame speeds of IGCC gas/6He/O2decrease with pressures increasing. The lean flames of IGCC gas/6He/O2at high pressures are more stable due to higher Lewis number caused by higher He ratio at lean condition. The laminar flame speeds of CCPP gas/O2at normal pressure increase first and then decrease as equivalence ratios from0.6to2, with the peak around equivalence ratio of1.0. |
