High-speed non-intrusive measurements of fuel velocity fields at high-pressure injectors

• Published in: Optics and lasers in engineering 2017-03, Vol.90, p.91-100
• Main Authors: Gürtler, Johannes, Schlüßler, Raimund, Fischer, Andreas, Czarske, Jürgen
• Format: Article
• Language: English
• Subjects: Frequency shift keying; High-speed camera; Nyquist–Shannon sampling theorem; Uncertainty analysis; Velocity measurement
• ISSN: 0143-8166; 1873-0302
• DOI: 10.1016/j.optlaseng.2016.10.003

Using a single high-speed camera and a frequency modulated laser, a novel approach is presented for fast velocity field measurements in unsteady spray flows. The velocity range is from zero up to several 100m/s, which requires a high measurement rate and a large dynamic. Typically, flow measurements require to seed tracer particles to the fluid. A paradigm shift to seeding-free measurements is presented. The light scattered at the phase boundaries of the fluid droplets is evaluated. In order to validate the high-speed measurement system, a detailed uncertainty analysis is performed by means of measurements as well as simulations. Thereby, variations of the scattered light intensity, which are based on the high temporal velocity gradients, are found to be the main contribution to the uncertainty. The eventually measurement results, obtained at a measurement rate of 500kHz, exhibit spray velocities ranging from 0m/s up to 400m/s in less than 1ms, and the detection of unsteady and irregular flow phenomena with a characteristic time of several μs is achieved. This demonstrates the high measurement rate, the high temporal resolution and the large measurement range of the proposed high-speed measurement system. •Seeding-less planar velocity measurements are performed using a high-speed camera.•The system requires only a single camera due to the laser frequency modulation.•As physical limit, the measurement rate is maximized to the half camera frame rate.•The measurement system is validated by means of simulation and experiment.•Measurement rates of 500kHz are demonstrated for fast, highly dynamic sprays.