Evaluation and Improvement of an Unsteady Heat Transfer Model for Spark Ignition Engines

This study utilized time-resolved heat-flux measurements to assess the applicability of a thermal boundary-layer based heat-transfer model. The model is significant in that it is not based on Nu ∼ Re correlation of the heat transfer in steady incompressible pipe flow as are most heat-transfer models used in quasi-dimensional engine simulations. The model was implemented in a two zone zero-dimensional engine simulation with a κ-ϵ turbulence and turbulent combustion submodels which provide the required inputs for the heat transfer model. The experimental engine had a pent-roof shaped combustion chamber with two intake and two exhaust valves. The primary variable examined was the intake-flow configuration which was varied by means of shrouded intake valves.

The presence of large cycle-to-cycle variations in the measured local heat-flux histories necessitated evaluating the heat-transfer model with information from individual cycle calculations. The model in its original formulation was able to accurately predict the heat transfer if convective effects were negligible. After the model was modified to account for these effects, it showed good agreement with measurements made at a location exposed to a strong convective influence. The model gave significantly improved heat-transfer predictions over the currently available correlations tested.