Emilien Varea

Actuation Studies for Active Control of Mild Combustion for Gas Turbine Application

MILD combustion (Moderate or Intense Low Oxygen Dilution) is a well known technique that can substantially reduce high temperature regions in burners and thereby reduce thermal NOx emissions. This technology has been successfully applied to conventional furnace systems and seems to be an auspicious concept for reducing NOx and CO emissions in stationary gas turbines. To achieve a flameless combustion regime, fast mixing of recirculated burnt gases with fresh air and fuel in the combustion chamber is needed. In the present study, the combustor concept is based on the reverse flow configuration with two concentrically arranged nozzles for fuel and air injections. The present work deals with the active control of MILD combustion for gas turbine applications. For this purpose, a new concept of air flow rate pulsation is introduced. The pulsating unit offers the possibility to vary the inlet pressure conditions with a high degree of freedom: amplitude, frequency and waveform. The influence of air flow pulsation on MILD combustion is analyzed in terms of NOx and CO emissions. Results under atmospheric pressure show a drastic decrease of NOx emissions, up to 55%, when the pulsating unit is active. CO emissions are maintained at a very low level so that flame extinction is not observed. To get more insights into the effects of pulsation on combustion characteristics, velocity fields in cold flow conditions are investigated. Results show a large radial transfer of flow when pulsation is activated, hence enhancing the mixing process. The flame behavior is analyzed by using OH* chemiluminescence. Images show a larger distributed reaction region over the combustion chamber for pulsation conditions, confirming the hypothesis of a better mixing between fresh and burnt gases.Copyright

Evaluation of partially premixed turbulent flame stability from mixture fraction statistics in a slot burner

Partially premixed combustion is characterized by mixture fraction inhomogeneity upstream of the reaction zone and occurs in many applied combustion systems. The temporal and spatial fluctuations o...

Potential and Challenges of MILD Combustion Control for Gas Turbine Applications

Moderate and Intense Low Oxygen Dilution (MILD) combustion is characterized by substantial reduction of high temperature regions and thereby reduction of thermal NO x emissions. Beside the application in furnaces, the MILD combustion seems to be also an auspicious concept in stationary gas turbines for simultaneous reduction of NO x and CO emissions. Nonetheless, the maintenance of MILD combustion for gas turbine relevant conditions, as the high temperature, at different operating points poses a challenge. The reason is the necessary fast mixing of recirculated burnt gases with fresh air and fuel in the combustion chamber. In this work the application of control for dealing with this task is investigated. As research approach the pulsation of the fresh gas is examined. On the one side the potential of using control for reducing the emissions level is evaluated. On the other side it is analyzed which challenges have to be solved in future concerning the control algorithm, if control shall be applied.