Traditionally, hydrocarbon-based fuels have been used in different industries for generating a
large amount of power. However, due to the increasing demand for power and increasing
level of pollution, different approaches for the generation of power are trying. Using
hydrogen as a fuel is a promising alternative as it is a clean fuel. The combustion of hydrogen
generates a very high flame temperature, which leads to the production of NOx. So, the
combustion of a lean mixture of hydrogen and hydrocarbon solves the problem of very high
flame temperatures. However, with lean fuel operation, combustors are susceptible to
thermoacoustic instability, characterized with the generation of large amplitude periodic
oscillations in acoustic pressure.
With the sequential increment of hydrogen, different dynamical changes along with
thermoacoustic instability and their underlying mechanism have not been previously
explored. Successive increments in hydrogen fuel fraction cause the dominant frequency of
the acoustic pressure to gradually increase to higher values due to increased reactivity in the
system. We notice that different modes can be excited with hydrogen enrichment. With the
help of tools from the synchronization theory, we also characterize different dynamical states
that the combustor exhibits as a result of interaction among different acoustic modes. Along
with the dynamical characterization, we also study the transition from period-2 limit cycle
oscillations to period-1 limit cycle oscillations via chaotic oscillations due to increment of
hydrogen in the fuel.
Moreover, we study the coupling behaviour between the acoustic pressure fluctuations, heat
release rate oscillations and flow field in the combustor during different states of
thermoacoustic instability. We use a data driven method known as proper orthogonal
decomposition (POD). Using POD method, we also calculate the temporal coefficients of
each POD mode. Using the temporal coefficients of dominating modes, we analyse the
temporal signals and observe 1:1 and 2:1 frequency locking among the acoustic pressure, heat
release rate and flow velocity fluctuations during the states of thermoacoustic instabilities.