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Japan Aerospace Exploration Agency

Combustion stability diagnosis using high-speed OH-PLIF measurements

As combustion instability may generate strong, sometimes catastrophic pressure oscillations inside the engine combustion chamber of aircraft and rockets, combustion stability (the suppression or avoidance of combustion instability) is a major technological issue for developers of engine combustors. The most problematic oscillation frequencies in aero-engine combustors are about 100 to 1,000 Hz. Currently, JAXA is developing a combustion diagnosis technology that utilizes the high-speed OH-PLIF (Planar Laser Induced Fluorescence) measurement*1 at a sampling rate of 10,000 Hz in the combustor under high-temperature and high-pressure conditions. This technology analyzes time-series photographs of flame structures to provide indicators for realizing combustion stability.

High- speed OH-PLIF measurement involves capturing photographs of flame structures. In the medical field, doctors treating patients with possible brain abnormalities use X-ray, CT, and MRI scans to take tomograms of the brain and locate problem areas that might be showing bleeding, signs of stroke, or other symptoms. Based on that information, doctors administer drugs or operate to eliminate the problems. Image diagnostic technologies for identifying the locations of problems are vital to proper medical treatment.

Essentially, high-speed OH-PLIF measurement plays the same role as medical image diagnostics in the stabilization of combustion. The OH-PLIF approach uses flame tomograms to locate problems that cause combustion instability, lays out guidelines for suppressing oscillation, and reflects these guidelines to combustor design (by modifying the positions of fuel injection orifices and adjusting swirl vane angles, etc.).

This combustion diagnosis technology holds promise for applications in not only jet and rocket engine combustors but also a vast array of other combustion devices, including land-based gas turbines, automotive engines, boilers, and household gas equipment.

*1 : PLIF (Planar Laser Induced Fluorescence): A method which irradiates the object to be measured with a laser sheet of focused molecule-specific wavelengths, thus exciting the electron energy of the molecules. The photons which are emitted when molecules transition from electric excitation to a ground state are then detected. OH-PLIF refers to PLIF which targets OH radicals which are intermediate products of the combustion reaction.

An overview of the combustion diagnosis process