Simultaneous two-phase flow measurement of spray mixing process by means of high-speed two-color PIV

Abstract

In this article, a novel high-speed two-color PIV optical diagnostic technique has been developed and applied to simultaneously measure the velocity flow-fields of a multi-hole spark-ignition direct injection (SIDI) fuel injector spray and its ambient gas in a high-pressure constant volume chamber. To allow for the phase discrimination between the fuel droplets and ambient gas, a special tracer-filter system was designed. Fluorescent seeding particles with Sauter mean diameter (SMD) of 4.8 µm were used to trace the gas inside the chamber. With a single high-speed Nd:YLF laser sheet (527 nm) as the incident light source, the Mie-scattering signal marked the phase of the fuel spray, while the fluorescent signal generated from the seeding particles tracked the phase of ambient gas. A high-speed camera, with an image-doubler (mounted in front of the camera lens) that divided the camera pixels into two parts focusing on the same field of view, was used to collect the Mie-scattering signal and LIF (laser induced fluorescence) signal simultaneously with two carefully selected optical filters. To accommodate the large dynamic range of velocities in the two phases (1–2 orders of magnitude difference), two separation times (dt) were introduced. This technique was successfully applied to the liquid spray and ambient gas two-phase flow measurement. The measurement accuracy was compared with those from LDV (laser Doppler velocimetry) measurement and good agreement was obtained. Ambient gas motion surrounding the fuel spray was investigated and characterized into three zones. The momentum transfer process between the fuel spray and ambient gas in each zone was analyzed. The two-phase flow interaction under various superheated conditions was investigated. A strengthened momentum transfer from the liquid spray to the ambient was observed with increased superheat degree.

Modulation of integral length scales of turbulence in an optical SI engine by direct injection of gasoline, iso -octane, ethanol and butanol fuels

“…There is very limited information in the existing literature on the application of twophase PIV over a range of conditions and fuel types. Some interesting information can be found in [37] where spray-flow interactions were studied with n-pentane and it was observed that there was stronger momentum transfer from the liquid spray to the ambient with increased fuel superheat. The effect was attributed to the expanded spray plumes of the multihole injector that was used and the smaller droplet sizes, which increased the interaction area between the two phases before the spray collapsed, as well as to the undisturbed velocity core around the injector axis area after the spray had collapsed.…”

Imaging Flow Velocimetry with Laser Mie Scattering

“…PIV spray measurements are described in [195,196]. Zhang et al reported high-speed PIV measurements with 6 kHz using pulsed illumination [197]. Time-resolved DGV spray measurements were performed with continuous-wave illumination by Fischer et al [83].…”

Two-Phase Characterization for Turbulent Dispersion of Sprays: A Review of Optical Techniques

“…An inherent challenge for simultaneous two-phase velocity measurement in this case is due to significantly large velocity difference between the injected droplets and the entrained air flow (for the spray the velocity is of the order of 100 ms −1 in comparison to the gas velocity which is about 1-10 ms −1 ). Accordingly, the laser separation time for PIV application is smaller than 10 µs for the spray, while that for the gas flow lies in the range from tens of microseconds to hundreds of microseconds [65,66,67,68]. The choice of same separation time for both phases can lead to inaccuracy in velocity measurements for both phases.…”