Periodic Reporting for period 4 - TORCH (ThermoacOustic instabilities contRol in sequential Combustion cHambers)
Periodo di rendicontazione: 2024-03-01 al 2024-08-31
A new type of combustor architecture for large gas turbines has emerged in recent years: sequential combustion systems operated at constant pressure. This major technology change results from the need for more operationally and fuel flexible gas turbines, for future sustainable energy networks. A gas turbine equipped with such combustor produces several hundred megawatt of electricity, and this new architecture enables clean combustion of Hydrogen at high efficiency and high power output, which was out of reach a few years ago. As for regular gas turbines, the risk of combustor breakdown due to thermoacoustic instabilities is a major challenge. While the harmful consequences of these instabilities in novel sequential combustors can be as dramatic as in conventional systems, the associated physics is considerably complexified, because the two flames not only “talk” together via sound waves, but also via entropy waves. In this project, novel active and passive control technologies tailored for this new generation of combustors, have been developped in order to suppress thermoacoustic instabilities. These major achievements have been obtained by solving challenging problems in fluid mechanics, acoustics, combustion, nonlinear dynamics and control theory.
Our project has made significant strides in the field of thermoacoustic instability control and plasma-assisted combustion, achieving several groundbreaking milestones that pave the way of hydrogen gas turbine technologies for sustainable energy networks.
One of our notable accomplishments is the development of the high-pressure test rig "Pele". This state-of-the-art facility, operational since 2023, has been instrumental in conducting advanced experiments, including the first measurements of flame transfer functions of hydrogen flames at elevated pressures.
In our quest to actively control thermoacoustic instabilities in sequential combustors, we have successfully demonstrated the use of ultra-low power cold plasma to eliminate these instabilities under transient operation at high pressure. This achievement, realized in November 2023, is a key milestone of the ERC Consolidator project. To attain this goal, we made pioneering advancements in the understanding of the effects of cold plasma on autoignition in sequential combustors. In 2021, we achieved the first numerical simulation of plasma-assisted sequential combustion at atmospheric conditions, followed by successful experiments on plasma-enhanced self-ignition of hot lean mixtures. Furthermore, we validated the numerical prediction of thermoacoustic stabilization of a sequential combustor via cold plasma discharges at atmospheric conditions at the end of the project.
Our research has also explored the potential of acoustic metamaterials and slow sound burners. Nearly half-way through the project, we designed a slow sound channel and demonstrated its control capabilities on aeroacoustic instabilities. Subsequently, another campaign of experiments showcased the potential of embedding such acoustic metamaterial into a hydrogen burner to passively suppress thermoacoustic instabilities, which led to a patent application.
One of our notable accomplishments is the development of the high-pressure test rig "Pele". This state-of-the-art facility, operational since 2023, has been instrumental in conducting advanced experiments, including the first measurements of flame transfer functions of hydrogen flames at elevated pressures.
In our quest to actively control thermoacoustic instabilities in sequential combustors, we have successfully demonstrated the use of ultra-low power cold plasma to eliminate these instabilities under transient operation at high pressure. This achievement, realized in November 2023, is a key milestone of the ERC Consolidator project. To attain this goal, we made pioneering advancements in the understanding of the effects of cold plasma on autoignition in sequential combustors. In 2021, we achieved the first numerical simulation of plasma-assisted sequential combustion at atmospheric conditions, followed by successful experiments on plasma-enhanced self-ignition of hot lean mixtures. Furthermore, we validated the numerical prediction of thermoacoustic stabilization of a sequential combustor via cold plasma discharges at atmospheric conditions at the end of the project.
Our research has also explored the potential of acoustic metamaterials and slow sound burners. Nearly half-way through the project, we designed a slow sound channel and demonstrated its control capabilities on aeroacoustic instabilities. Subsequently, another campaign of experiments showcased the potential of embedding such acoustic metamaterial into a hydrogen burner to passively suppress thermoacoustic instabilities, which led to a patent application.
We have addressed the problem of controlling the thermoacoutic instabilities at elevated pressure on two fronts:
First, we significantly moved forward the state-of-the-art in passive control of combustion instabilities, by creating acoustic metamaterials with unprecedented thermoacoustic damping properties, and capable of long term operation in harsh environments. A new passive control concept has been developped from scratch and it successfully suppressed thermoacoustic instabilities of pure hydrogen-air flames. The concept is based on the slow-sound effect in the burner channels conveying the hydrogen-air mixture. Theoretical models of the acoustic response of this metaburner and its flames have been developped and validated experimentally. A patent application has also been issued.
Second, we have addressed scientific challenges for achieving active combustion control of thermoacoustic instabilities in sequential combustors, by means of non-equilibrium plasma discharges.
The ultra-low power plasma locally enhance the autoignition chemistry and can modify on-demand the response of the flame to acoustic perturbations. The plasma-based active control has been demonstrated for the first time at high pressure during transient opperation at the end of the project. Furthermore, new models have been developped to predict the dynamics of the autoignition flames subject to these non-equilibrium plasma. The models were implemented in a compressible Large Eddy Simulation solver in order to perfom high fidelity simulations using supercomputers.
First, we significantly moved forward the state-of-the-art in passive control of combustion instabilities, by creating acoustic metamaterials with unprecedented thermoacoustic damping properties, and capable of long term operation in harsh environments. A new passive control concept has been developped from scratch and it successfully suppressed thermoacoustic instabilities of pure hydrogen-air flames. The concept is based on the slow-sound effect in the burner channels conveying the hydrogen-air mixture. Theoretical models of the acoustic response of this metaburner and its flames have been developped and validated experimentally. A patent application has also been issued.
Second, we have addressed scientific challenges for achieving active combustion control of thermoacoustic instabilities in sequential combustors, by means of non-equilibrium plasma discharges.
The ultra-low power plasma locally enhance the autoignition chemistry and can modify on-demand the response of the flame to acoustic perturbations. The plasma-based active control has been demonstrated for the first time at high pressure during transient opperation at the end of the project. Furthermore, new models have been developped to predict the dynamics of the autoignition flames subject to these non-equilibrium plasma. The models were implemented in a compressible Large Eddy Simulation solver in order to perfom high fidelity simulations using supercomputers.