Large Eddy Simulations with Conjugate Heat Transfer (CHT) modeling of Internal Combustion Engines (ICEs)

Angela Wu,Volker Sick,Seunghwan Keum,C Angelberger

doi:10.2516/ogst/2019029

Abstract

In this study, the effects of the thermal boundary conditions at the engine walls on the predictions of Large-Eddy Simulations (LES) of a motored Internal Combustion Engine (ICE) were examined. Two thermal boundary condition cases were simulated. One case used a fixed, uniform wall temperature, which is typically used in conventional LES modeling of ICEs. The second case utilized a Conjugate Heat Transfer (CHT) modeling approach to obtain temporally and spatially varying wall temperature. The CHT approach solves the coupled heat transfer problem between fluid and solid domains. The CHT case included the solid valves, piston, cylinder head, cylinder liner, valve seats, and spark plug geometries. The simulations were validated with measured bulk flow, near-wall flow, surface temperature, and surface heat flux. The LES quality of both simulations was also discussed. The CHT results show substantial spatial, temporal, and cyclic variability of the wall heat transfer. The surface temperature dynamics obtained from the CHT model compared well with measurements during the compression stroke, but the absolute magnitude was 5 K (or 1.4%) off and the prediction of the drop in temperature after top dead center suffered from temporal resolution limitations. Differences in the predicted flow and temperature fields between the uniform surface temperature and CHT simulations show the impact of the surface temperature on bulk behavior.

Highlights

Health and environmental awareness have been driving more stringent Internal Combustion Engine (ICE) regulations on harmful emissions and engine performance
Once more cycles were added to the averaging process, M follows the same trend as the uniT cycle. Since this quality index has the influence of both the ensemble average hU ii and the fluctuating velocity u0i, it can be used as another indicator of statistical convergence of the simulations
The effects of super-cycling on Large-Eddy Simulations (LES)-Conjugate Heat Transfer (CHT) simulations have not been evaluated in this study

Summary

Introduction

Health and environmental awareness have been driving more stringent Internal Combustion Engine (ICE) regulations on harmful emissions and engine performance. To meet such requirements, it is important to increase the ICE efficiency by reducing loss mechanisms, such as thermal loss across the cylinder wall. The boundary layer experiences large thermal gradients, and most of the engine heat transfer occurs over this layer. This wall heat transfer affects the surface temperature and temperature profile in the Near-Wall Region (NWR), and is one of the major contributors to engine efficiency losses. Accurate simulations of ICEs require that the surface temperature and temperature profile in the NWR are predicted correctly

Methods

Results

Conclusion