Acoustics of turbulent non-premixed syngas combustion

Coal gasification is one of the options for clean coal technology. Gasification of coal takes place when coal is exposed to superheated steam. During this process, a mixture of hydrogen H2, carbon monoxide and inert components (usually CO2 and H2O) are produced in a carrier flow of nitrogen. This product gas is called syngas, which can be fired in a gas turbine. The turbulent flame in the combustion chamber of a gas turbine can act as a source of sound. As the syngas is a low calorific gas (the calorific value of syngas is approximately 5 MJ/kg which is a factor of 8 lower than natural gas), the mass flows are high. To prevent a too high pressure drop over the fuel line, the cross-sectional areas of the fuel lines are relatively large. The acoustic field generated by the turbulent syngas flame can induce a fluctuation in the fuel mass flow. These fluctuations are then transported to the flame front and can result in heat release fluctuations. As a result the flame radiates more noise, which is fed back to fuel mass flow fluctuations. The amplitudes of the fluctuations will increase in time and a so-called thermoacoustic instability may occur. During such a thermoacoustic instability the acoustic pressure can become excessively high. Often, already within a minute very serious damage can occur at the burner or other parts of the combustor. This thesis is written to add insight in the processes that take place during the formation and break down of thermoacoustic instabilities in turbulent syngas combustion. Additional to this, methods are investigated to predict acoustic fields and instabilities during this type of combustion.