Flow and Temperature Distribution in an Experimental Engine: LES Studies and Thermographic Imaging

Temperature stratification plays an important role in HCCI
combustion. The onsets of auto-ignition and combustion
duration are sensitive to the temperature field in the engine
cylinder. Numerical simulations of HCCI engine combustion
are affected by the use of wall boundary conditions,
especially the temperature condition at the cylinder and
piston walls. This paper reports on numerical studies and
experiments of the temperature field in an optical
experimental engine in motored run conditions aiming at
improved understanding of the evolution of temperature
stratification in the cylinder. The simulations were based on
Large-Eddy-Simulation approach which resolves the
unsteady energetic large eddy and large scale swirl and
tumble structures. Two dimensional temperature experiments
were carried out using laser induced phosphorescence with
thermographic phosphors seeded to the gas in the cylinder.
The results revealed different mechanisms for the
development of temperature stratification: intake gas and
residual gas mixing, heat transfer in the wall boundary layer,
compression of the charge, and large scale flow transport.
The sensitivity of LES results to different wall boundary
conditions and inflow conditions was analyzed.