LIQUID FUEL TRANSPORT PHENOMENA IN ROTATING DETONATION ENGINES
Creators: name: Hoeper, Matthew
Publisher: name: Purdue University Graduate School
Year: 2024
Subjects: classificationCode: 401703
subject: Energy generation, conversion and storage (excl. chemical and electrical)
classificationCode: 400106
subject: Hypersonic propulsion and hypersonic aerothermodynamics
classificationCode: 401205
subject: Experimental methods in fluid flow, heat and mass transfer
classificationCode: 401211
subject: Multiphysics flows (incl. multiphase and reacting flows)

description: Interest in using detonation-based combustion cycles for use propulsion and power generation has gained considerable attention in the last 10 years or so. The rotating detonation engine (RDE), in particular, has garnered the most attention as a possible replacement for current generation combustion systems. RDEs are continuous flow devices that typically operate in a non-premixed fashion. Reactants are injected into an annular combustion chamber that is usually several millimeters wide. One or more detonation waves propagate azimuthally around the annulus, consuming the reactants. The products then expand out of the combustor where it can produce thrust or be passed into a turbine. The detonation wave front in RDEs travel at speeds between 1-3 km/s which poses additional complexity beyond traditional combustors. There are large gaps in the research community for RDEs that use one or more liquid based propellants. Questions regarding liquid breakup, atomization, breakup, recovery all remain unanswered both experimentally and numerically. This work seeks to understand these fundamental physical phenomena that drive these devices by applying advanced, high-speed laser and other optical diagnostics. A 120 mm nominal diameter rotating detonation combustor that operates on non-premixed hydrogen-air was modified to remove a hydrogen orifice and was replaced with a single liquid fuel injector. This simple, yet important, modification enables the study of a one-way coupling between a liquid fuel jet and a detonation wave at relevant spatio-temporal scales. Planar laser-induced fluorescence was performed at rates up to 1 MHz to quantify the quasi-steady jet dynamics and the recovery behavior of the single liquid jet. Long-duration PLIF imaging lasting 30-40 detonation periods at 300 kHz was also performed for statistical significance. A diesel liquid-in-crossflow injector was observed to breakup or be removed from the PLIF plane within only a few microseconds. After the detonation wave passes through the spray there is a significant dwell period can last between 20-40% of the detonation period before the new fuel is issued into the channel. The quasi-steady liquid jet trajectory was also compared to a jet-in-crossflow from literature and there is decent agreement in the jet near-field. The same hardware scheme with a different liquid fuel injector was tested in conjunction with an alternative imagine scheme. The first technique was able to capture details in the radial-axial plane but could not resolve any motion in the azimuthal direction. A volume-based illumination scheme was used for LIF to image a liquid fuel jet in the azimuthal-axial plane. For this experiment the location of the liquid fuel jet was moved into a different position and as a result experiences significantly different behavior than the jet in crossflow. The breakup and evaporation process takes place over a much longer period of time and there is no pause of liquid fuel injection. Similarly, LIF was performed at 300 kHz for 30 detonation cycles to enable sadistically quantification and phase averaging. Filtered OH* and CH* chemiluminescence imaging was also performed over the same field of view as the LIF imaging. Estimation of the velocity field was calculated using optical flow from the Jet-A LIF images. The velocity results agree well with the recovery analysis from the PLIF measurements. Using the same liquid fuel injection scheme, Jet-A droplet diameter and velocity was measured <i>in-situ</i> during a hot-fire experiment using phase Doppler interferometry (PDI). Although a point technique, PDI was used to measure thousands of droplets during a single test at multiple locations and with multiple conditions. As a means of comparison, cold flow experiments were performed with water in the exit plume. Droplet diameters were measured between 1-20 µs in both cases. PDI results were compared with the optical flow results and there is agreement in median velocities and some differences in the minimum and maximum velocity values. Possible sources of error in the diameter measurement are discussed as well.