Near-wall Flame and Flow Measurements in an Optically Accessible SI Engine

Marius Schmidt, Carl-Philipp Ding, Brian Peterson, Andreas Dreizler, Benjamin Boehm

Research output: Contribution to journalArticlepeer-review

Abstract

Near-wall processes in internal combustion engines strongly affect heat transfer and pollutant emissions. With continuously improving capabilities to model near-wall processes, the demand for corresponding measurements increases.
To obtain an in-depth understanding of the near-wall processes within spark-
ignition engines, flame distributions and flow fields were measured simultaneously near the piston surface of an optically accessible engine operating with homogeneous, stoichiometric isooctane-air mixtures. The engine was operated at two engine speeds (800 rpm and 1500 rpm) and two different intake pressures (0:95 bar and 0:4 bar). Flame distributions at high spatial resolution were conducted using high-speed planar laser induced fluorescence of sulfur dioxide (SO2). Particle tracking velocimetry was utilized to measure the
flow field above the piston at high spatial resolution, which enabled the determination of hydrodynamic boundary layer profiles. Flame contours were extracted and statistical distributions of the burnt gas area determined. The burnt gas distributions were compared with the simultaneously recorded high-speed flow field measurements in the unburnt gas. A direct comparison with motored engine operation showed comparable boundary layer profiles until the
flame approaches the wall. Flow acceleration due to flame expansion rapidly increases velocity gradients and the boundary layer development becomes highly transient. The interaction of flame and flow depends on the operating conditions, which results in a different evolution of burnt gas positions
within the field-of-view. This has additional implications on the development of
the velocity boundary layer. Depending on the operating conditions, the flame
strongly affects the velocity boundary layer profiles resulting in boundary layer
thicknesses in the order of the flame thickness (50 µm to 150 µm).
Original languageEnglish
JournalFlow, Turbulence and Combustion
DOIs
Publication statusPublished - 14 May 2020

Keywords

  • Near-wall reacting flows
  • boundary layer flows
  • particle tracking velocimetry
  • Planar laser induced fluorescence

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