Visualization of Diesel Spray Penetration, Cool-Flame, Ignition, High-Temperature Combustion, and Soot Formation Using High-Speed Imaging

Abstract

Shadowgraph/schlieren imaging techniques have often been used for flow visualization of reacting and nonreacting systems. In this paper we show that high-speed shadowgraph visualization in a high-pressure chamber can also be used to identify cool-flame and hightemperature combustion regions of diesel sprays, thereby providing insight into the time sequence of diesel ignition and combustion. When coupled to simultaneous high-speed Mie-scatter imaging, chemiluminescence imaging, pressure measurement, and spatially-integrated jet luminosity measurements by photodiode, the shadowgraph visualization provides further information about spray penetration after vaporization, spatial location of ignition and hightemperature combustion, and inactive combustion regions where problematic unburned hydrocarbons exist. Examples of the joint application of high-speed diagnostics include transient non-reacting and reacting injections, as well as multiple injections. Shadowgraph and schlieren image processing steps required to account for variations of refractive index within the hightemperature combustion vessel gases are also shown.

Experimental characterization of diesel ignition and lift-off length using a single-hole ECN injector

“…As explained by Pickett et al [12], this phenomenon is related to the changes in chemical composition and temperature of the mixture that take place in this early phase of the ignition. The refractive index of the mixture changes and for a transient period is very close to the one of the surrounding gas, becoming then invisible to the Schlieren setup.…”

“…broadband chemiluminescence [7], [10] and the Schlieren imaging [12], [24] both implementable with the use of fast cameras.…”

“…Pickett et al [12], using a Schlieren setup, observed that cool flames onset can be appreciated as a temporal disappearance of the spray in the tip region. As explained by Pickett et al [12], this phenomenon is related to the changes in chemical composition and temperature of the mixture that take place in this early phase of the ignition.…”

“…Moreover, a special effort has been made to study the spray disappearance phenomenon observed when a Schlieren setup is used to study a reacting Diesel spray [7], [12]. A novel processing method has been applied and the results obtained allow to clearly distinguishing the onset of cool flames and the ignition delay (or second stage ignition).…”

Experimental Validation of Combustion Models for Diesel Engines Based on Tabulated Kinetics in a Wide Range of Operating Conditions

“…In particular, the well-known constantvolume spray-A experiment from ECN [28,29,30] Figs. 8 and 9 reports comparison between computed and experimental values of ignition delay and flame lift-off.…”