Convective Heat Transfers in the Combustion Chamber of an Internal Combustion Engine Influence of In-Cylinder Aerodynamics

Previous studies of in-cylinder heat transfers give numerous approaches of heat losses modelling principally compression and expansion strokes. These simulation methods are discussed showing that their accuracy during the intake stroke is neglected.

Since most of the modern engines use strong structured air motion during the intake and compression strokes to both reduce consumption and reach different emissions levels targets, one may focus on in-cylinder aerodynamics and convective heat transfer coupling. The experimental velocity data acquired allow us to get an in-depth understanding of the spatial and temporal gradients of measured heat transfers in the cylinder of an internal combustion engine.

Two different experimental methods have been used to investigate the in-cylinder air motion. First, near wall flow has been studied using two component local time-resolved Laser Doppler Anemometry (LDA). Heat transfers are measured by thin-film fast-response heat flux probe constituted of two thermocouples. Velocity and turbulence intensity are analysed by the cycle resolved method. For a global time-resolved analysis of in-cylinder aerodynamics Time Resolved Planar Image Velocimetry (TR-PIV ) fields are analysed. The comparison of the TR-PIV and LDA measurements gives a detailed description of the effect of in cylinder aerodynamics on the near wall flow characteristics. Parametric analysis of the motored optical test-engine conditions effects on heat transfers and flow fields is presented. In parallel to physics understanding, experimental databases built here are then of a great interest to check quality of the different models implemented in CFD software. A first evaluation of a local convection coefficient formula during the intake stroke is then carried out. Thermal experimental data compared to this correlation demonstrate a great underestimation of the simulated coefficient during the intake stroke leading to an underestimation of the heat transfer from the wall to the gas.