Ultrafast high-repetition imaging of fuel sprays using picosecond fiber laser

• Published in: Optics express 2015-12, Vol.23 (26), p.33396-33407
• Main Authors: Purwar, Harsh, Wang, Hongjie, Tang, Mincheng, Idlahcen, Saïd, Rozé, Claude, Blaisot, Jean-Bernard, Godin, Thomas, Hideur, Ammar
• Format: Article
• Language: English
• Subjects: Engineering Sciences
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.23.033396

Modern diesel injectors operate at very high injection pressures of about 2000 bar resulting in injection velocities as high as 700 m/s near the nozzle outlet. In order to better predict the behavior of the atomization process at such high pressures, high-resolution spray images at high repetition rates must be recorded. However, due to extremely high velocity in the near-nozzle region, high-speed cameras fail to avoid blurring of the structures in the spray images due to their exposure time. Ultrafast imaging featuring ultra-short laser pulses to freeze the motion of the spray appears as an well suited solution to overcome this limitation. However, most commercial high-energy ultrafast sources are limited to a few kHz repetition rates. In the present work, we report the development of a custom-designed picosecond fiber laser generating ∼ 20 ps pulses with an average power of 2.5 W at a repetition rate of 8.2 MHz, suitable for high-speed imaging of high-pressure fuel jets. This fiber source has been proof tested by obtaining backlight images of diesel sprays issued from a single-orifice injector at an injection pressure of 300 bar. We observed a consequent improvement in terms of image resolution compared to standard white-light illumination. In addition, the compactness and stability against perturbations of our fiber laser system makes it particularly suitable for harsh experimental conditions.