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Japan Aerospace Exploration Agency

Combustion instability control technology

The development of gas-turbine low-emission combustors involves addressing many key technological issues: suppressing combustion instability, preventing flashback, extending blowout limits, preventing over-heating of combustor parts, improving ignition performance, ensuring solid re-ignition performance at high altitudes, and more. Combustion instability, a complex phenomenon with roots in multiple factors, is one of the hardest problems to tackle and one of the pivotal technological challenges in the combustor development.

Developers have conventionally tried to suppress the combustion instability issue with resonators, acoustic liners, and other damping devices, as well as multi-staged fuel injection controls and flow allocation control. Meanwhile, the recent trend of using high-temperature, high-pressure configurations to improve fuel efficiency and the increasingly strict regulations on NOx (nitrogen oxide) emissions are making combustors more susceptible to combustion instability and intensifying the need to develop more radical combustion instability control technologies in addition to conventional oscillation control methods.

The driving sources of combustion instability are the positive interactions among pressure and heat-release fluctuations. JAXA is currently working on a technology that intentionally deforms flame structures to blur the heat-release response against flow disturbances and mitigate the strength of heat-release fluctuations, thereby weakening the primary driving source of combustion instability.

JAXA has already reduced the pressure fluctuation peak value at around 500Hz to 0.5kPa or less in single-sector combustor tests (7 atm). Ultimately, JAXA wants to see such a technology make valuable contributions to the development of combustors for actual jet engines and gas turbine engines.

A pressure spectrum during combustion instability.
This type of oscillation needs to be suppressed.