Session: 05-05: Combustion Measurements 2

Submission Number: 175711

Development and Application of an Optical Duct Segment to Perform Multiple Endoscopic Optical Measurements of Hydrogen Flames in a High Pressure Full Annular Combustor 

Optical detection of passive flame emissions like chemiluminescence can be used to characterize the dynamical properties of a combustion process. With the EU Clean Aviation CAVENDISH project’s goal to develop hydrogen fueled aircrafts, it is vital being able to analyze hydrogen combustions on the way to achieve carbon neutrality in aviation. Performing these measurements on a full annular combustor under full scale conditions poses various challenges for hardware configurations. Optical access cannot be granted by windows or holes in the rig, as this changes the thermal boundary conditions and secondary air flow during testing and therefore perturbates any results. Additionally, the thermal load, vibrations and noise levels during tests can severely damage the sensitive hardware.

An innovative optical duct configuration has been developed by Rolls-Royce to provide a pressure case featuring 3D printed air-cooled adapters for DLR developed advanced endoscopic optical equipment for measuring UV and visible spectral ranges of a flame in a full annular combustor simultaneously. The experiments were conducted at the high-pressure combustion test facility HBK5 of the German Aerospace Center (DLR) in Cologne, Germany on a Rolls-Royce Pearl engine combustor with a hydrogen fuel injector. The resulting chemiluminescence images of the OH-radical are indicative of the effective heat release inside the hydrogen flame and therefore serve as a powerful tool to achieve insights within the dynamic combustion processes.

The optical access to the combustor is realized by a dedicated ring segment in between the combustor exit plane and the rig exhaust. This duct provides mounting inserts for integrating up to 8 endoscopes around the entire circumference of the rig. The inserts can be replaced with blanks such that the rig is functional even without the usage of endoscopes.  

Two endoscope systems were constructed for observing in the UV and visible spectrum respectively. The lightweight CMOS Camera for the visible spectral range is mounted directly onto a rigid endoscopic tube.  It contains a multi-lens system that can observe 3 adjacent burners in the combustion chamber. Due to its size and weight, the UV camera cannot be mounted onto its endoscopic tube directly but is instead enclosed in a sound-damped box next to the test rig. The UV tube instead partially envelopes a 3-lens System and a flexible image fiber bundle with 17.000 single image fibers which transmits the observed light to the UV camera observing one burner and the interaction zone to its adjacent burners.

Both endoscopic tubes are each contained by a cooling jacket in which they are integrated into the optical duct via probe mounts. Water-cooled jackets prevent the tubes from overheating. Additionally, the endoscopes can be inserted and retrieved from the combustor using a pneumatic system.

The results show that the entire measurement system was operating at full function under all conditions up to engine maximum take off conditions. OH-radical chemiluminescence images in the UV were recorded steadily at 70 Hz. The probe tip heads withstood the high thermal load with only minimal wear. In combination with the successful integration of a visual camera the system is ready for future application in EU Clean Aviation Cavendish using both hydrogen and liquid carbon fuels and for further extension by additional endoscopes with additional capabilities.

Presenting Author: Alexander Marzok DLR - German Aerospace Center, Institute of Propulsion Technology

Presenting Author Biography: * Graduated with a Master of Science in geophysics from the University of Cologne, specialized in evaluating spectroscopic space telescope images
* Working as a research scientist at the German Aerospace Center since 2023 in the field of optical combustor diagnostics

Authors:

Alexander Marzok DLR - German Aerospace Center, Institute of Propulsion Technology
Eike Burow DLR - German Aerospace Center, Institute of Propulsion Technology
Armin Weiss DLR - German Aerospace Center, Institute of Propulsion Technology
Martin Müller DLR - German Aerospace Center, Institute of Propulsion Technology
Guido Stockhausen DLR - German Aerospace Center, Institute of Propulsion Technology
Lanz Klein DLR - German Aerospace Center, Institute of Propulsion Technology
Christian Fleing DLR - German Aerospace Center, Institute of Propulsion Technology
Carsten Clemen Rolls-Royce Deutschland Ltd & Co KG
Benno Wurm Rolls-Royce Deutschland Ltd & Co KG