Session: 04-45 Combustion dynamics - modeling III

Paper Number: 124462

124462 - Dynamical Systems Characterisation and Reduced Order Modelling of Thermoacoustics in a Lean Direct Injection (LDI) Hydrogen Combustor 

Hydrogen is a promising zero-carbon fuel for decarbonised energy and transportation sectors. While carbon emission is not a concern for hydrogen combustion, its higher adiabatic flame temperature poses challenges of mitigating thermal NO_x emissions. The wide flammability limits of hydrogen allow a fuel-lean operation, which can reduce NO_x emissions. However, lean operation makes the combustion chamber susceptible to thermoacoustic oscillations. In this study, the thermoacoustic instabilities of partially premixed hydrogen flames in a lean direct injection (LDI) multi-cluster combustor are characterised using dynamical systems theory. The combustor was operated at a range of bulk velocities (30 - 90 m/s) and equivalence ratios (0.2-0.6), and time-resolved pressure oscillations and integrated OH* chemiluminescence measurements were taken. The thermoacoustic system reveals a variety of dynamical states in pressure such as period-1 Limit Cycle Oscillation (LCO) with a single characteristic frequency, period-2 LCO with two characteristic frequencies, intermittent, quasi-periodic and chaotic states as either bulk velocity or equivalence ratio is varied.  At a bulk velocity of 30 m/s, as the equivalence ratio is gradually decreased from 0.6 to 0.2, the dynamical behaviour follows a sequence from an intermittent state to a period-1 LCO, then to a quasi-periodic state, and eventually reaches a chaotic state. As the equivalence ratio is decreased for a bulk velocity of 60 m/s, the pressure oscillations evolve from a period-2 LCO to quasi-periodic state before flame blows off. The emergence of period-2 and quasi-periodic states indicates the presence of strong non-linear interactions among the cavity acoustic modes. These modes and their spatial behaviour are investigated using a reduced order model which solves the 3D inhomogeneous Helmholtz equation with an n-tau flame model. The results show that the period-2 and quasi-periodic states can arise due to the interaction between the plenum and combustion chamber modes indicating that hydrogen flames may excite a wide range of cavity acoustic modes.

Presenting Author: Ankit Dilip Kumar University of Cambridge

Presenting Author Biography: PhD student at University of Cambridge working on thermoacoustic instabilities in turbulent hydrogen flames.

Authors:

Ankit Dilip Kumar University of Cambridge
Chinonso Ezenwajiaku University College London
Ramanarayanan Balachandran University College London
Andrea Ducci University College London
Midhat Talibi University College London
James Massey University of Cambridge
Nedunchezhian Swaminathan University of Cambridge