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Thermo-acoustic instabilities are mainly formed due to in-phase superposition of non-uniform heat release and pressure variation in the combustors of gas turbines, rocket engines and other acoustically confined spaces. These instabilities not only damage the structural system but also reduce its combustion efficiency and heat transfer rate. Hence suppression of thermo-acoustic instabilities is a prominent requirement for stable and safe heat generation in the combustors. In this work, the Helmholtz resonator has been used to suppress the instability. The efficacy of the resonator has been further increased by the addition of absorptive material to it. This work concentrates on inspecting the influence of cavity volume, neck length and neck diameter of the Helmholtz Resonator and the thickness of the absorptive material in the damping process of thermo-acoustic instabilities. The experimentation was carried out for various combinations of resonator cavity volume, neck diameter and neck length, and the best combination was found to be 6 mm neck diameter with 20 mm neck length at 60% volume which provided an acoustic damping of around 30 dB. Further, it was noticed that the addition of absorptive material is effective at lower volumes of Helmholtz resonator, and with an increase in thickness of absorptive material beyond a certain limit, the damping ability of the resonator reduces. [ABSTRACT FROM AUTHOR]

• The developed sensor is a low cost sensor to measure unsteady heat release. • The developed sensor is able to capture temperature fluctuation in presence of thermo-acoustic instabilities. • The developed sensor is free from thermal inertia effect, which improves the sensitivity. • The developed sensor shows the linearity over a wide range of temperature. The temperature measurement is an important parameter in industrial process equipments. Various techniques were developed to measure the transient temperature of the fluid and the solid surface. The precise and accurate measurement of transient fluid temperature is also important in combustors of various power producing devices. During the combustion process in the combustor, when the coupling between heat release and pressure fluctuations takes place, thermo-acoustic instabilities are developed. These instabilities have adverse effect on the combustor. For predicting the instabilities Rayleigh index is very much essential, which can be estimated from unsteady heat release and pressure fluctuation measurement. In this study, the development of sensor, based on hot wire method, to measure unsteady heat release in combustion chamber is presented. For transient heat release measurement, fast response of a sensor is very much important. For fast response, the wire diameter of probe should be as small as possible. To develop a sensor, wire of different diameters and materials are used as probe materials. The stainless steel wire is used as prongs. The constructed sensor is kept in one of the arm of Wheatstone bridge to measure the resistance of sensor. For this NI LabVIEW software and NI-DAQ 6211 is used. From different results, it is observed that the resistance of sensor varies linearly with rise in temperature. The plunge test method is used to measure the response time of sensors. A 0.1 mm Pt wire sensor is checked for different diameter of SS prongs i.e. 0.5, 0.55 and 0.9 mm. A modified 0.1 mm Pt wire sensor with 0.5 mm SS prongs has response time of 50 ms, which is calibrated using FLUKE-9144 bath-tub from 0 °C to 500 °C temperature. Then it is tested in combustion chamber to measure unsteady temperature, in the presence of thermo-acoustic instability with J-Type thermocouple and variation in measured temperature was found to be 8.11%. [ABSTRACT FROM AUTHOR]