Thermoacoustic Instability Characteristics and Flame/Flow Dynamics in a Multinozzle Lean Premixed Gas Turbine Model Combustor Operated with High Carbon Number Hydrocarbon Fuels

Abstract

The impact of fuel variations on thermoacoustic instability characteristics and flame/flow dynamics in a lean premixed prevaporized, multinozzle gas turbine model combustor was experimentally investigated with high-speed particle image velocimetry (PIV) and flame OH* chemiluminescence (CL) measurements. The fuels studied included three hydrocarbons with high carbon numbers from distinct chemical classes, including n-decane (C10H24, linear alkane), iso-octane (C8H18, branched alkane), and methylcyclohexane (C7H14, MCH, cyclic alkane). When operated with these three fuels, time-resolved measurements of the unsteady flame/flow dynamics indicated that the combustion system exhibited similar sequences of periodic flame/flow dynamics; however, distinct characteristics were observed in terms of the instability frequencies and amplitudes. Under the test conditions, it was shown that the MCH flame featured the highest (421 Hz) instability frequency, which was 385 Hz for n-decane and 382 Hz for iso-octane flames. Regarding the amplitude of the instability, experimental results indicated that the instability was the strongest for the iso-octane flame (132 dB), which was followed by n-decane (129 dB) and MCH (123 dB) flames. A joint analysis between the calculated fuel fundamental kinetic properties and experimental data suggested that a higher adiabatic flame temperature could lead to a higher instability frequency, whereas the ignition delay time (IDT) and heat release rate properties of the fuels determined the amplitudes of the instabilities together. Additionally, phase-averaged sequences and spectrum and proper orthogonal decomposition (POD) analysis of the instantaneous measurements revealed that large-scale longitudinal oscillations along with side-to-side interactions of the adjacent flame roots dominated the unsteady flame/flow dynamics in this multinozzle combustor.