Investigation Of MILD Combustion Applied For Gas Turbine

The Moderate or Intense Low-oxygen Dilution (MILD) combustion is characterized by low emission, stable combustion and low noise for various kinds of fuel. This study designed a model MILD combustor applied for gas turbine combustor by improving the jet velocity to induce the recirculation of gas scheme and the scheme was validated by experiments and analyzed by numerical simulation. The reaction zone in the chamber under the MILD model is invisible and NOX and CO emissions are ultra-low, moreover the temperature distribution is uniform.The correlation of the combustor stable operating range with heat intensity is studied by experiments and numerical simulations. It is shown that the lean blow out limit has a strong dependence on the combustor heat intensity, and φLBO increases with rising heat intensity significantly. When the operation condition near to LBO, CO emission will increase immediately and the thermoacoustic phenomenon will happen, both the reaction zone will back to fore body of the chamber with a quit low temperature so that the generated CO is not oxidized well at downstream section and the combustion efficiency declined. A tendency shows that every heat intensity has an interval that both NO and CO emissions are below 10ppm@15%O2, and an optimal condition point that both NO and CO are close to the minimum value in the stable operating range. The CFD results shows that as the equivalence ratio φ decreasing, the burnt temperature is declined and the reaction zone is dispersive. The reaction intensity and temperature are increasing with heat intensity slightly. The mean square temperature fluctuations over the combustor of all the stable MILD operation are below 13%.The influences of the pilot air and fuel flow rate to combustion are studied by experiments and numerical simulations. The distributions of the optimum pilot air and fuel flow rate are got in experiments and the combustion characteristics are analyzed by CFD simulations. It is shown that the optimal A-P/M=0.2 and F-P/M below 0.25.When F-P/M greater than 0.25, the peak temperature and NOX emission are higher and the combustion efficiency declined.Based on this model combustor, the influences of different structure schemes and inlet parameters to combustion performance are studied by CFD simulations. It is revealed that higher inlet temperature enhance the whole chamber temperature and the dispersion of reaction zone, the lower jet momentum lead to lower pressure loss. The higher inlet pressure enhance the heat release rates as well as the combustion efficiency and the whole chamber temperature, but the gas recirculation ratio is lower so that the mean square temperature fluctuation over the combustor increased. The combustion performances of the scaled up combustor are similar to the model one, it means that the results from the model combustor can be used as a reference for the design and operation of gas turbine MILD combustor.