Non-Reacting Spray Characteristics of Alternative Aviation Fuels at Gas Turbine Engine Conditions
Abstract
The aviation industry is continuously growing amid tight restrictions on global emission reductions. Alternative aviation fuels have gained attention and developed to replace the conventional petroleum-derived aviation fuels. The replacement of conventional fuels with alternative fuels, which are composed solely of hydrocarbons (non-petroleum), can mitigate impacts on the environment and diversify the energy supply, potentially reducing fuel costs. To ensure the performance of alternative fuels, extensive laboratory and full-scale engine testings are required, thereby a lengthy and expensive process. The National Jet Fuel Combustion Program (NJFCP) proposed a plan to reduce this certification process time and the cost dramatically by implementing a computational model in the process, which can be replaced with some of the testings. This requires an understanding of the influence of chemical/physical properties of alternative fuels on combustion performance. The main objective of this work is to investigate the spray characteristics of alternative aviation fuels compared to that of conventional aviation fuels, which have been characterized by different physical liquid properties at different gas turbine-relevant conditions. The experimental work focuses on the spray characteristics of standard and alternative aviation fuels at three operating conditions such as near lean blowout (LBO), cold engine start, and high ambient pressure conditions. The spray generated by a hybrid pressureswirl airblast atomizer was investigated by measuring the drop size and drop velocity at a different axial distance downstream of the injector using a phase Doppler anemometry (PDA) measurement system. This provided an approximate trajectory of the largest droplet as it traveled down from the injector. At LBO conditions, the trend of decreasing drop size and increasing drop velocity with an increase in gas pressure drop was observed for both conventional (A-2) and alternative aviation fuels (C-1, C-5, C-7, and C-8), while the effect of fuel 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 of the pressure drop and fuel injection pressures on the cone angles. Their effects were found to be limited on the cone angle. The spray characteristics of standard (A-2 and A-3) and alternative (C-3) fuels were investigated at engine cold-start conditions. At such a crucial condition, sufficient atomization needs 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 both conventional and alternative aviation fuels. The effect of fuel viscosity was found to be minimal and dominated by the effect of the surface tension, even though it showed a weak trend of increasing drop size with increasing surface tension. The higher swirler pressure drop reduced the drop size and increased drop velocity due to greater inertial force of the gas for both conventional and alternative aviation fuels at the cold start condition. However, the effect of pressure drop was observed to be reduced at cold start condition compared to the results from the LBO condition. The final aspect of experimental work focuses on the effect of ambient pressures on the spray characteristics for both conventional (A-2) and alternative (C-5) aviation fuels.
Degree
Ph.D.
Advisors
Hasti, Purdue University.
Subject Area
Industrial engineering|Materials science
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