NON-REACTING SPRAY CHARACTERISTICS OF ALTERNATIVE AVIATION FUELS AT GAS TURBINE ENGINE CONDITIONS
Creators: name: Shin, Dongyun
Publisher: name: Purdue University Graduate School
Year: 2021
Subjects: Aerospace engineering not elsewhere classified
Automotive combustion and fuel engineering

description: The aviation industry is continuously growing amid tight restrictions on global emissionreductions. Alternative aviation fuels have gained attention and developed to replace theconventional petroleum-derived aviation fuels. The replacement of conventional fuels withalternative fuels, which are composed solely of hydrocarbons (non-petroleum), can mitigateimpacts on the environment and diversify the energy supply, potentially reducing fuel costs.To ensure the performance of alternative fuels, extensive laboratory and full-scale enginetestings are required, thereby a lengthy and expensive process. The National Jet Fuel CombustionProgram (NJFCP) proposed a plan to reduce this certification process time andthe cost dramatically by implementing a computational model in the process, which can bereplaced with some of the testings. This requires an understanding of the influence of chemical/physical properties of alternative fuels on combustion performance. The main objectiveof this work is to investigate the spray characteristics of alternative aviation fuels comparedto that of conventional aviation fuels, which have been characterized by different physicalliquid properties at different gas turbine-relevant conditions.The experimental work focuses on the spray characteristics of standard and alternativeaviation fuels at three operating conditions such as near lean blowout (LBO), cold enginestart, and high ambient pressure conditions. The spray generated by a hybrid pressureswirlairblast atomizer was investigated by measuring the drop size and drop velocity ata different axial distance downstream of the injector using a phase Doppler anemometry(PDA) measurement system. This provided an approximate trajectory of the largest dropletas it traveled down from the injector. At LBO conditions, the trend of decreasing drop sizeand increasing drop velocity with an increase in gas pressure drop was observed for bothconventional (A-2) and alternative aviation fuels (C-1, C-5, C-7, and C-8), while the effect offuel injection pressure on the mean drop size and drop velocity was observed to be limited.Moreover, the high-speed shadowgraph images were also taken to investigate the effect ofthe pressure drop and fuel injection pressures on the cone angles. Their effects were foundto be limited on the cone angle.The spray characteristics of standard (A-2 and A-3) and alternative (C-3) fuels wereinvestigated at engine cold-start conditions. At such a crucial condition, sufficient atomizationneeds to be maintained to operate the engine properly. The effect of fuel properties,especially the viscosity, was investigated on spray drop size and drop velocity using bothconventional and alternative aviation fuels. The effect of fuel viscosity was found to be minimaland dominated by the effect of the surface tension, even though it showed a weak trendof increasing drop size with increasing surface tension. The higher swirler pressure dropreduced the drop size and increased drop velocity due to greater inertial force of the gas forboth conventional and alternative aviation fuels at the cold start condition. However, theeffect of pressure drop was observed to be reduced at cold start condition compared to theresults from the LBO condition.The final aspect of experimental work focuses on the effect of ambient pressures on thespray characteristics for both conventional (A-2) and alternative (C-5) aviation fuels. Advancedaviation technology, especially in turbomachinery, has resulted in a greater pressureratio in the compressor; therefore, greater pressure in combustors for better thermal efficiency.The effect of ambient pressure on drop size, drop velocity, and spray cone angle wasinvestigated using the PDA system and simultaneous Planar Laser-Induced Fluorescence(PLIF) and Mie scattering measurement. A significant reduction in mean drop size wasobserved with increasing ambient pressure, up to 5 bar. However, the reduction in the meandrop size was found to be limited with a further increase in the ambient pressure. The effectof the pressure drop across the swirler was observed to be significant at ambient pressure of5 bar. The spray cone angle estimation at near the swirler exit and at 25.4 mm downstreamfrom the swirler exit plane using instantaneous Mie images was found to be independent ofambient pressure. However, the cone angle at measurement plane of 18 mm in the spraywas observed to increase with increasing ambient pressure due to entrainment of smallerdroplets at higher ambient pressure. Furthermore, the fuel droplet and vapor distribution inthe spray were imaged and identified by comparing instantaneous PLIF and Mie images.Lastly, a semi-empirical model was also developed using a phenomenological three-stepapproach for the atomization process of the hybrid pressure-swirl airblast atomizer. Thismodel includes three sub-models: pressure-swirl spray droplet formation, droplet impingement, and film formation, and aerodynamic breakup. The model predicted drop sizes as afunction of ALR, atomizing gas velocity, surface tension, density, and ligament length anddiameter and successfully demonstrated the drop size trend observed with fuel viscosity,surface tension, pressure drop, and ambient pressure. The model provided insights into theeffect of fuel properties and engine operating parameters on the drop size. More experimentalwork is required to validate the model over a wider range of operating conditions andphysical fuel properties.Overall, this work provides valuable information to increase understanding of the spraycharacteristics of conventional and alternative aviation fuels at various engine operatingconditions. This work can provide valuable data for developing an advanced computationalcombustor model, ultimately expediting the certification of new alternative aviation fuels.