Chapter 4 - Intrinsic thermoacoustic instability

Abstract

It is conventionally believed that there are no self-sustained thermoacoustic oscillations (also known as combustion instability) in combustors in the absence of acoustic resonance modes. However, such oscillations have been recently found to occur in a premixed combustor with a mean flow present but no acoustic eigenmodes involved by applying an acoustic horn to minimize the reflected acoustic waves. It is known as intrinsic thermoacoustic instability (ITI). Practical combustors are associated with entropy, vorticity perturbations, pressure jump, and mean flow. In this chapter, an entropy-involved energy measure is defined and used to study the stability behaviors of intrinsic thermoacoustic modes. Further studies on the intrinsic instability in a non-uniform cross-sectional area combustor with a moving flame front are conducted. Finally, the effect of vorticity coupling with acoustics-flame-entropy interaction is examined and reported. This chapter sheds lights on the generation mechanisms of ITI.