The application of Flame Image Velocimetry to after-injection effects on flow fields in a small-bore diesel engine

Jinxin Yang, Lingzhe Rao, Charitha De Silva, Sanghoon Kook

Research output: Contribution to journalReview ArticleResearchpeer-review


This study implements Flame Image Velocimetry (FIV), a diagnostic technique based on post-processing of high-speed soot luminosity images, to show the in-flame flow field development impacted by after-injection in a single-cylinder, small-bore optical diesel engine. Two after-injection cases with different dwell times between the main injection and after-injection, namely, close-coupled and long-dwell, as well as a main-injection-only case are compared regarding flow fields, flow vector magnitude, and turbulence intensity distribution. For each case, high-speed soot luminosity movies from 100 individual combustion cycles are recorded at a high frame rate of 45 kHz for FIV processing. The Reynolds decomposition using a spatial filtering method is applied to the obtained flow vectors so that bulk flow structures and turbulence intensity distributions can be discussed. The results show significant after-injection-induced flow structures as a group of vectors travelling back toward the center of the combustion chamber upon the jet impingement on the piston bowl wall and then jet-to-jet collision. Despite higher cyclic variations caused by the after-injection, increased bulk flow magnitude and turbulence intensity upon the after-injection event suggests locally enhanced mixing. Compared to the long-dwell after-injection, the close-coupled after-injection shows more significant turbulence enhancements.

Original languageEnglish
Pages (from-to)322-333
Number of pages13
JournalSAE International Journal of Engines
Issue number3
Publication statusPublished - 2022
Externally publishedYes


  • After-injection
  • Diesel engine
  • Flame image velocimetry (FIV)
  • In-flame flow field
  • Turbulence intensity

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