Dynamic characteristics of in-nozzle flash boiling bubbles and corresponding temporal responses of external spray
Flash boiling spray is believed to have the potential in further improving the efficiency of practical liquid fuel combustors. However, the complex physics of this transient, multiphase process are not fully understood. Despite improved spray breakup and atomization performance, near-nozzle flash boiling sprays also faced the challenge in cycle-to-cycle variation and fluctuation. This work aims to explore the dynamic formation, development, and aggregation of in-nozzle flash boiling bubbles to establish the connection between bubble features and external spray behaviors. In this investigation, a transparent two-dimensional nozzle was utilized for high-speed shadowgraph visualization and flash boiling sprays at various fuel temperatures (superheat degrees) were measured and investigated. Theoretical analysis was incorporated to interpret the nucleation and growth of the flash boiling bubbles. Near-field external sprays were also captured to reveal the temporal response with regard to in-nozzle flash boiling bubble structures. Results showed that the layered structure inside the nozzle had a direct impact on the oscillation on the external spray. Fast Fourier transform (FFT) was also adopted in quantifying the dominant frequency of the oscillating flash boiling sprays.
This research is sponsored by Ford Motor Company (USA) and National Natural Science Foundation of China (NSFC) under Grant No. 51376119/E060502. It was carried out at the National Engineering Laboratory for Automotive Electronic Control Technology of Shanghai Jiao Tong University.
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