Convective heat transfer predictions and experiments in an internal combustion engine.

摘要

Knowledge of heat transfer in engines is critical to engine efficiency, hydrocarbon and particulate emissions, engine-component thermal stress analysis, as well as engine cycle simulation accuracy. However, the relationship between pressure, heat-release rate, turbulent flow, and the heat transfer is not known. Previous engine heat-transfer models, including the law-of-the-wall used for multi-dimensional calculations, are based on a steady-state incompressible flow which is not the case in engines.; Accurate prediction of local heat flux requires either complete three-dimensional calculation to the wall, or an appropriate wall model. However, a one-dimensional simulation of compressible turbulent boundary layer flow showed that application of traditional k {dollar}-{dollar} {dollar}varepsilon{dollar} turbulent models to the viscous-dominated region can produce errors in the calculated heat flux and surface friction, and that application of the law-of-the-wall for the thermal boundary layer in an engine is physically incorrect.; A new heat transfer model has been developed which is based on an approximate solution of the linearized and normalized one-dimensional energy equation. An empirical turbulent viscosity relation has been used to include the effects of turbulence. The response of this equation to a unit step function was acquired by multi-parameter fit to the numerical solution. The effects of initial thermal boundary layer formed before compression were also considered.; The proposed heat-transfer model has been extended to include the effects of combustion. Thus, the relationship between pressure variation, spatially-resolved heat-release rate, local flow condition, initial thermal boundary layer, and the surface heat flux and temperature profile has been developed.; To validate the proposed model, a see-through engine experiment has been developed which has full optical access. Velocity in boundary layer was measured by LDV, while surface temperature was measured by surface thermocouple. Comparison of the proposed heat-transfer model with motored-engine experiments showed good agreement.; In the Appendixes, a method to find better initial iteration values for non-linear problems, an approximate analytical solution of the one-dimensional energy equation by a regular perturbation method, a comparison of proposed heat-transfer model with Dao's data, some experimental data in this study, and a computer subroutine of the proposed model are included.