Development of a High-Speed UV Particle Image Velocimetry Technique and Application for Measurements in Internal Combustion Engines.

Abstract

The in-cylinder flow is one of the most influential physical processes in internal combustion (IC) engine operation. It impacts fuel-air mixing, combustion and pollutant emissions. Many flow-related processes occur on a sub-millisecond time-scale. Time-resolved multidimensional flow-velocity data can provide valuable insight into processes relevant to IC engine performance. This document describes the development of a high-speed particle image velocimetry (PIV) technique using a two-laser, single-camera system and the application to a motored and fired stratified spark-ignition, direct-injection (SIDI) engine. The technique is novel in that it (1) achieves unprecedented temporal resolution: one velocity field at every other crank angle at 2000 RPM for approximately 500 consecutive cycles and (2) uses 355 nm (UV) excitation wavelength. Advantages include suppressing the detection of combustion luminosity, capturing the luminosity from the spark discharge, and providing the flexibility to integrate planar laser induced fluorescence (PLIF) of biacetyl for simultaneous velocity and equivalence ratio distribution measurements. Initial PIV experiments conducted in an optical SIDI engine are described and results from the first application of UV PIV in a fired engine at 600 RPM presented. Next, an experiment introducing the simultaneous application of high-speed UV PIV and biacetyl-PLIF is described. The application of UV PIV for velocity measurements in the SIDI engine at 2000 RPM is then presented. Velocity fields are shown for multiple crank angles of motored and fired engine cycles. The action exerted by the post-injection flow field on the spark plasma channel is captured. Results confirm that the ensemble mean kinetic energy decreases as the piston approaches top-dead-center (TDC) and that, under fired conditions, the flow pattern near TDC is dominated by the residual spray momentum. The effect of PIV measurement noise on two-dimensional kinetic energy and dissipation rate spectra of IC engine flows is described. Low-resolution (2 mm) and high-resolution (0.35 mm) measurements show an abrupt increase in energy and dissipation rate spectra at the spatial resolution limit. This increase can be attributed to noise introduced by the PIV interrogation algorithm. A spatial averaging filter removes the spectral peaks, while attenuating kinetic energy and dissipation rate values near the PIV resolution limit.