Molecular Tagging Velocimetry and Its Application to In-Cylinder Flow Measurements

Abstract

This review article provides an overview of the experimental studies of in-cylinder flows using various flow measurement techniques with a focus on molecular tagging velocimetry. It is necessary to understand the evolution of large-scale and small-scale turbulence as prepared during the intake stroke with a cycle resolved quantitative description. Due to the difficulty in obtaining these descriptions, either by modeling or experimentally, they are often characterized with somewhat ambiguous notions of bulk swirl and tumble measurement methods. During the intake stroke, in-cylinder flows are formed in such a manner as to provide advantageous spatial and temporal behavior for mixture formation later during the compression stroke. Understanding the details of how these flows influence fuel-air mixing, the initiation of ignition, combustion, and subsequent flame propagation processes is the primary motivation for the development of the methods described in this paper. The authors provide an introduction to fundamental flow motion inside the engine cylinder and measurement techniques, e.g., hot-wire anemometry, laser Doppler anemometry, and particle image velocimetry. Furthermore, molecular tagging velocimetry is discussed in detail in terms of (i) different mechanisms, (ii) procedure and data reduction methods to obtain the desired flow properties such as velocity, vorticity, and turbulent intensities, and (iii) applications to flow studies in internal combustion engines. Finally, the significance of experimental investigations of in-cylinder flows is discussed along with possible future applications.

Parametric Study to Improve Subpixel Accuracy of Nitric Oxide Tagging Velocimetry with Image Preprocessing

“…However, a study showed that the particles tracked the flow properly even when the value was greater than 0.1 and only failed to follow for measurements in the Taylor length scale [25]. A brief overview with several applications of MTV for engine flow studies is given in [26]. MTV is a flow measurement technique that is based on one of the two luminescence principles: phosphorescence and fluorescence.…”

Vibrationally excited hydroxyl tagging velocimetry

“…In addition, PIV particle seeding can cause rapid obscuration of test section windows and damage the experimental apparatus [3,4]. Therefore, MTV methods that track the flow velocity with molecular grids have been developed for experiments in which the application of PIV is not practical [5,6].…”