Session: 04-26 Atomization and Spray Combustion II
Paper Number: 125618
125618 - Low Swirl Effect on Compact Spray and Combustion Systems Using Additive Manufactured Dual Airblast Injectors
The wide range of sustainable chemical energy vectors from hydrogen, ammonia to sustainable aviation fuels leads to stringent fuel flexibility requirements of modern gas turbine engines. While the carbon footprint can be mitigated by replacing fossil fuels with green chemical energy vectors, the mitigation of NOX and soot formation require a clean combustion process. The latter is particularly important for the aviation sector, where non-CO2 effects account for up to 75% of its overall anthropogenic climate impact. In order to transfer the excellent fuel flexibility and low emissions of stationary high momentum jet stabilized gas turbines to liquid fuels and compact combustion systems for use in micro gas turbines or hybrid aero-engines, a robust and scalable injection system is indispensable. In a recent development, a dual pressure swirl / airblast injection concept was introduced that readily demonstrated excellent atomization, scalability and the desired liquid fuel flexibility. To further optimize such systems, a understanding of the liquid spray and flame interactions under highly turbulent conditions is pivotal for expanding operational capabilities and achieving emission targets in compact gas turbine designs.
For this purpose, additive manufactured airblast walls are equipped with low swirl vanes with two primary objectives. First, to enhance the fuel distribution and provide a more homogeneously distributed, and thus thinner, wall film and second to utilize the swirling flow to create a more compact flame. The latter facilitates the implementation of the combustion process into a more compact combustor design and is thus pivotal for potential hybrid aero-engine concepts. This study focuses on delineating the low swirl spray interactions of the novel dual pressure swirl / airblast injection system and characterizing the effect of low swirl on the flame dynamics and emission to highlight the potential. The low swirl vane angles are varied from 45 (co-swirling with the liquid pressure swirl) to -45 degrees (counter-swirling) with 15-degree increments. The latter inherently modulates the gas phase turbulence leading to either stabilization or disturbances of the pressure swirl spray, affects the liquid loading on the wall and film homogeneity and ultimate dominates the flame dynamics. In addition to the swirl direction and intensity variation, the air bulk velocity, uj (80 ~ 160 m/s) and the fuel mass flow rate, ml (0.1 ~ 0.5 g/s) supplied by the central pressure swirl injector, is adjusted to delineate the effect of aerodynamic forces and injection momentum. The spray quality is quantified by means of shadowgraphy to visualize primary atomization airblast edge and 3-phase Doppler interferometer (PDI) to measure the droplet velocity and size distribution. The combustion performance is analysed via high speed OH* chemiluminescence imaging at 10 kHz and exhaust gas measurements.
The shadowgraphy results showed that increasing in vane angle in either direction enhances the radial droplet penetration resulting in an expanding spray cone, while no-swirl conditions lead to a collapsing spray cone. Moreover, the fuel accumulation at the airblast wall edge is strongly dependent on all parameters studied, i.e. aerodynamic force, liquid loading, swirl direction and intensity. In the direct proximity of the primary break-up, the PDI measurements show a Sauter mean diameter (d32) that is predominantly below 50 µm for overall conditions. An increase in the vane angle, irrespective of direction, leads to a reduction of the droplet size with negative axial velocities at the centre. With increasing swirl number regardless of the swirl direction, the flame anchors closer to the combustor nozzle and becomes distinctly more compact in comparison to the no-swirl conditions as observed in the high speed OH* chemiluminescence images. However, the co-swirl configuration of the pressure swirl injector / low swirl vanes enhances the homogeneity of the flame noticeably, attributed to the elevated circumferential velocity of the liquid leading to an improved wall film formation. Finally, the exhaust gas measurements illustrate the effect of the highly turbulent yet more compact flame zone due to the introduction of low swirl concepts on the NOX emissions
Presenting Author: Yeonse Kang Institute of Combustion Technology for Aerospace Engineering (IVLR), University of Stuttgart
Presenting Author Biography: 05.2022 ~ Present, Ph. D student; University of Stuttgart.
Authors:
Yeonse Kang Institute of Combustion Technology for Aerospace Engineering (IVLR), University of StuttgartJihwan Ahn Institute of Combustion Technology for Aerospace Engineering (IVLR), University of Stuttgart
Fabian Hampp Institute of Combustion Technology for Aerospace Engineering (IVLR)
Low Swirl Effect on Compact Spray and Combustion Systems Using Additive Manufactured Dual Airblast Injectors
Paper Type
Technical Paper Publication