Quantitative analysis of highly transient fuel sprays by time-resolved x-radiography

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Abstract
Microsecond time-resolved synchrotron x-radiography has been used to elucidate the structure and dynamics of optically turbid, multiphase, direct-injection gasoline fuel sprays. The combination of an ultrafast x-ray framing detector and tomographic analysis allowed three-dimensional reconstruction of the dynamics of the entire 1-ms-long injection cycle. Striking, detailed features were observed, including complex traveling density waves, and unexpected axially asymmetric flows. These results will facilitate realistic computational fluid dynamic simulations of high-pressure sprays and combustion. © 2003 American Institute of Physics. @DOI: 10.1063/1.1604161# High-pressure liquid fuel sprays and their atomization and combustion processes are the basis of modern internal combustion engines. Despite decades of intensive experi- mental and theoretical study,1 much is still unknown about fuel injection sprays, largely because the fuel aerosols scatter visible light so strongly that the detailed dynamics of fuel and vapor mass distribution cannot be readily imaged. Un- derstanding of the fuel-spray physics is essential for the de- velopment of improved engines. For example, recently de- veloped gasoline direct injection ~GDI!, which injects fuel into the combustion cylinder ~as opposed to the air intake port!, has greatly improved internal combustion engine per- formance because of the capability of precise control of the injection rate, timing and combustion of the fuel. 2,3 Quanti- tative spray characterization has been difficult because it re- quires microsecond time resolution of submillimeter-scale structures in a complex mixture of liquid and gas. Conven- tional visible light methods are severely limited by optical multiple scattering from the fuel droplets 4 ~see also EPAPS Document #1 for a comparison of visible light shadow graph and x-radiograph of a GDI spray5!. Other techniques, such as patternators, are capable of probing the near-nozzle region, but perturb the spray and have limited spatial and temporal resolution.6 X-radiography is an alternative imaging technique. Re- cently, we used point-by-point measurement of monochro- matic x-ray absorption to quantitatively characterize the dy- namics and structure of high-pressure diesel sprays with unprecedented resolution.8 Point-scanning methods are labo-