Assessment of impinged flame structure in high-pressure direct diesel injection

Abstract

Spray impingement often occurs during cold-start in direct-injection diesel engines, affecting the subsequent combustion process by altering the local flow condition. This work has investigated the impinged flame structure by examining local expansion distance and planar curvature of the boundary in details. The experiments were carried out in a constant volume combustion chamber. The injection pressure and ambient density were varied from 120 to 180 MPa and 14.8 to 30.0 kg/m3 under non-vaporizing conditions, respectively. For reacting conditions, the injection pressure and ambient density were fixed at 150 MPa and 22.8 kg/m3 but with different ambient temperatures from 800 to 1000 K. Unlike orthogonal spray impingement, the profile of expansion distance along the radial direction at the 60° impinging angle is non-uniform but the profile is comparable between the non-vaporizing and reacting conditions under the same injection pressure and ambient density. With the help of Intensity-aXial-Time method, the most intensive soot luminosity region and Mie scattering intensity region are identified and the region has been found to be along the impinged spray axial direction. Outmost boundary of an impinged flame is found to have wrinkles attributed to air entrainment. The temporal level of flame wrinkles is higher in reacting conditions than in non-vaporizing conditions. The scatter distribution of the boundary curvature and near-field soot formation illustrates an inverted “S” shape correlation with time. High flame luminosity is found to be formed in concave regions while less soot is formed in convex regions. This inverted S-shape is a new finding of the state relationship at the solid–liquid–gas impinged flame propagation. Finally, heat flux measurement through the plate is examined.

Diesel Spray: Development of Spray in Diesel Engine

“…Table 1 shows the optical diagnostic techniques used for several phenomena capturing. The distribution of liquid and vapor phases in diesel spray has gained great attention [126,189,[203][204][205]. In the last two decades, a new technique called particle image velocimetry (PIV) has successfully advanced the research in mixture formation [206][207][208].…”

Spray-wall interactions in direct-injection engines: An introductory overview

“…Zhao et al 10 report on spray impingement onto a plate, liquid fuel-film behavior, and the structure of a flame impinging onto the liquid film in a constant-volume combustion chamber under conditions of diesel engine cold start. Optical imaging was augmented by heat-flux measurements at several locations on the plate, while film thickness and mass data were taken from earlier RIM measurements in the same experimental rig.…”

“…These studies include numerical simulations 1–3 and measurements 4–8 of SWIs and fuel-film formation and dynamics, as well as measurements of fuel-film combustion and emissions processes. 9–11…”

Visualization of diesel spray and combustion from lateral side of two-dimensional piston cavity in rapid compression and expansion machine, second report: Effects of injection pressure and interval of split injection

“…It is widely known that mixture formation and combustion processes are highly dependent on the impinging spray. 31 However, owing to the limitation of the structure of the piston, visualization was performed mainly in a constant volume chamber and other optical engines with a flat piston wall, which facilitated observation from the top and bottom sides.…”