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Cooled Fast-Response Wall Pressure Taps for Combustion Chamber Measurements

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Innovative pressure probes reduce the risk of lean-burn engine failure

An EU-funded project presented improved sensor technology to help overcome a challenge commonly encountered in lean-burn engines: controlling combustion instabilities.

Transport and Mobility icon Transport and Mobility

In the never-ending quest to provide clean transport that will not ultimately poison our world with noxious gases, lean-burn engines promise better fuel economy and reduced greenhouse gas emissions. Unlike conventional combustors, lean-burn, low-nitrogen oxides (NOx) combustors mix more air with fuel in the flame tube of the combustor than is stoichiometrically required, reducing the flame temperature and thus NOx (and other pollutant) generation.

Two major preoccupations: combustion instabilities and noise

Efforts to lower the levels of NOx emissions in lean-burn engines are closer than ever to paying off. “Despite their extremely advanced designs, low-NOx combustors are plagued by reliability issues owing to severe combustion instabilities and noise emissions,” states Julien Clinckemaillie, research engineer at von Karman Institute for Fluid Dynamics and coordinator of the EU-funded FAST TAPS project. Many studies have lately focused on enhancing understanding of the formation mechanisms and dynamics of combustion instabilities as well as the contribution of combustor noise to the overall noise signature of the gas turbine. “Advanced methods for carrying out fast-response pressure measurements in the harsh conditions characterising gas turbine combustors are fundamental for experimentally investigating combustion instabilities and noise,” adds Clinckemaillie.

Advanced technology predicting combustion instabilities and noise

In the framework of the FAST TAPS project, researchers unveiled advanced combustion control system prototypes to extend the knowledge around combustion instabilities and noise in realistic engine conditions. “We successfully produced and qualified eight wall-mounted fast-response pressure taps for use in the primary zone of the combustion chamber of a ground-based turboshaft engine,” highlights Clinckemaillie. The fragile fast-response pressure sensor installed in the cooled probe tip remained around a temperature of 80 °C, despite being immersed in a hot combustion chamber environment that can reach up to 1 600 °C. “Designing an effective and protective cooling layout to keep the fragile sensor cool while maintaining the frequency response of the system as large as possible and the probe intrusiveness as minimal as possible was very challenging,” explains Clinckemaillie. The probe prototype survived four engine starts and 32 minutes of effective testing time in the primary zone of a turboshaft gas turbine running at idle conditions. Tests revealed a weakness in the sensor packaging, which was later addressed by improving the protection of the sensor against the soot deposit.

Technology poised for a big impact

Combustion instabilities are the main roadblock impeding the development of low-emission, lean-burn combustors for next-generation jet engines. By enhancing understanding of combustion instabilities in realistic gas turbine engine conditions, FAST TAPS will ultimately lead to the design of advanced combustion chamber technologies with reduced CO2 and NOx emissions and noise footprint. Project activities will pave the way towards greener and quieter turbine engines in the 1 800–2 000 shaft horsepower class for business aviation and short-range regional applications. “The collaboration between researchers from von Karman Institute and Safran Helicopter Engines has been very fruitful throughout the entire duration of the project and especially during tests on the Safran innovative Bearcat test rig in Bordes (France) which enabled us to challenge and mature the final probe design,” adds Sébastien Detry, project manager for Ardiden 3 & Clean Sky 2. “We now have a fully functional FAST TAPS measurement system. Future tests in engine-representative conditions will allow Safran to further improve design models and combustion performance thanks to the FAST TAPS measurement system capabilities.”

Keywords

FAST TAPS, combustion instabilities, noise, lean-burn engine, combustion chamber, NOx, pressure tap, turboshaft

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