Development of Instability Warning System

by Driek Rouwenhorst, Jakob Hermann and Wolfgang Polifke

Motivation

A major restriction for combustion with minimal emissions of NOx is the danger of thermoacoustic instability. Optimization of the combustion process can be performed by constant monitoring of the system. For this purpose, a stability margin (also called precursor) is required that warns for imminent thermoacoustic instabilities. Typically such a stability margin is estimated from acoustic measurements inside of the combustor.

Host company

This research task is hosted by IfTA GmbH, a company specialized in the monitoring combustion systems. Two test rigs are at one's disposal that are prone to combustion instabilities. In the video below, operation and monitoring of one of the combustors is shown.

Objectives and Strategy

Systematic experiments will be made to investigate any precursors associated with the transition from a stable to an unstable state. Methods based on linear decay rate, modal amplitude as well as nonlinear characteristics are considered. Test data is obtained from a laboratory combustor and simulated time series. In addition thermoacoustic modelling is performed in order to get a better insight in the thermoacoustic behaviour close to instability. Another subject is the prediction of the severity of instability, determined by the nonlinear behaviour manifesting at higher acoustic amplitudes.

On industrial systems, such as gas turbines or furnaces, a proper precursor would allow a systematic investigation of the relevant combustion parameters (e.g. fuel split, ambient conditions etc.) which might lead to combustion instabilities. This analysis can be performed before a critical state is reached. Therefore parameters can be adjusted and a damage to the system prevented.

Acknowledgement

The presented work is part of the Marie Curie Initial Training Network Thermo-acoustic and aero-acoustic nonlinearities in green combustors with orifice structures (TANGO). We gratefully acknowledge the financial support from the European Commission under call FP7-PEOPLE-ITN-2012.