Abstract
Fuel spray characteristics directly determine the formation pattern and quality of the fuel/air mixture in an engine, and thus affect the combustion process. For this reason, the improvement and optimization of fuel injection systems is crucial to the development of engine technologies. The fuel jet breakup and atomization process is a complex liquid–gas two-phase turbulent flow system that has not yet been fully elucidated. Owing to the limitations of standard optical measurement techniques, the spray breakup mechanism and its interaction with the nozzle internal flow are still unclear. However, in recent years synchrotron radiation (SR) X-ray imaging technologies have been widely applied in engine fuel injection studies because of the higher energy and brilliance of third-generation SR light sources. This review provides a brief introduction to the development of SR technology and compares the critical parameters of the primary third-generation SR light sources available worldwide. The basic principles and applications of various X-ray imaging technologies with regard to nozzle internal structure measurements, visualization of in-nozzle flow characteristics and quantitative analyses of near-field spray transient dynamics are examined in detail.
Highlights
Synchrotron radiation (SR) is a kind of electromagnetic radiation generated when the direction of movement of electrons traveling at almost light speed is altered by a magnetic field
The electron energy is a crucial factor that reflects the size and cost of the light sources and differentiates these three hard X-ray facilities from other much smaller light sources. All these three facilities have over 30 undulator beamlines open to public use and provide high-energy, high-brilliance and highly penetrating X-ray beams that are ideal for studying the arrangements of molecules and atoms, probing the interfaces where materials meet, determining the interdependent form and function of biological proteins, and tracking chemical processes that occur on the nanoscale
Before X-ray micro-computerized tomography (CT) technique was applied to the assessment of nozzle internal structures, fuel flow simulations were generally based on simplified and idealized geometric models according to the nozzle design parameters, which can be quite different from the actual nozzle structure
Summary
Synchrotron radiation (SR) is a kind of electromagnetic radiation generated when the direction of movement of electrons traveling at almost light speed is altered by a magnetic field. SR has many other advantages, including high brilliance, a broad spectrum, the capacity for a significant level of polarization and collimation, along with high photon flux, low emittance, the potential for pulsed emission, and energy and wavelength tuning For all these reasons, SR has numerous applications in scientific research. SR X-ray imaging technology can be utilized to precisely measure the internal structure of a nozzle, the needle movement, the internal flow and the breakup process of the near-field spray. This review is based on the recent work of the authors as well as other relevant work worldwide This summary of recent research achievements is expected to assist in promoting the application of this advanced technique within the field of spray studies, so as to fully elucidate the spray breakup mechanism
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