Research Interests

Combustion instabilities are physical phenomena occurring in a reacting flow (e.g., a flame) in which some perturbations, even very small ones, grow and then become large enough to alter the features of the flow in some particular way. In many practical cases, the appearance of combustion instabilities is undesirable. For instance, thermoacoustic instabilities are a major hazard to gas turbines and rocket engines. Moreover, flame blowoff of an aero-gas-turbine engine in mid-flight is clearly dangerous. n this type of instabilities the perturbations that grow and alter the features of the flow are of an acoustics nature. Their associated pressure oscillations can have well defined frequencies with amplitudes high enough to pose a serious hazard to combustion systems. For example, in rocket engines, such as the Rocketdyne F-1 rocket engine  in the Saturn V program, instabilities can lead to massive damage of the combustion chamber and surrounding components. Furthermore, instabilities are known to destroy gas-turbine-engine components during testing. They represent a hazard to any type of combustion system. Thermoacoustic combustion instabilities can be explained by distinguishing the following physical processes:

• the feedback between heat-release fluctuations (or flame fluctuations) with the combustor or combustion chamber acoustics

• the coupling of these two processes in space-time

• the strength of this coupling in comparison with acoustic losses

• the physical mechanisms behind the heat-release fluctuations

The simplest example of a thermoacoustic combustion instability is perhaps that happening in a horizontal Rijke tube. Consider the flow through a horizontal tube open at both ends, in which a flat flame sits at a distance of one-quarter the tube length from the leftmost end. In a similar way to an organ pipe, acoustic waves travel up and down the tube producing a particular pattern of standing waves. Such a pattern also forms in actual combustors, but takes a more complex form. The acoustic waves perturb the flame. In turn, the flame affects the acoustics. This feedback between the acoustic waves in the combustor and the heat-release fluctuations from the flame is a hallmark of thermoacoustic combustion instabilities. It is typically represented with a block diagram (see figure). Under some conditions, the perturbations will grow and then saturate, producing a particular noise. In fact, it is said that the flame of a Rijke tube sings.