Evaluation of Wall Heat Flux Models for Full Cycle CFD Simulation of Internal Combustion Engines under Motoring Operation

Abstract

The present work details a study of the heat flux through the walls of an internal combustion engine. The determination of this heat flux is an important aspect in engine optimization, as it influences the power, efficiency and the emissions of the engine. Therefore, a set of simulation tools in the OpenFOAM® software has been developed, that allows the calculation of the heat transfer through engine walls for ICEs. Normal practice in these types of engine simulations is to apply a wall function model to calculate the heat flux, rather than resolving the complete thermo-viscous boundary layer, and perform simulations of the closed engine cycle. When dealing with a complex engine, this methodology will reduce the overall computational cost. It however increases the need to rely on assumptions on both the initial flow field and the behavior in the near-wall region. As the engine studied in the present work, a Cooperative Fuel Research (CFR) engine, is a simple single cylinder pancake engine, it was possible to implement more complex and numerically demanding methodologies, while still maintaining an acceptable computation time. Both closed and full cycle simulations were therefore performed, for which the heat flux was calculated by both implementing various wall function models and by resolving the complete thermo-viscous boundary layer. The results obtained from the different kind of simulations were then compared to experimental heat flux data, which was measured using a thermopile type heat flux sensor in different locations in the CFR engine. By comparing the results from the different types of simulations, a performance evaluation of the used methodology could be carried out. It was found that the heat flux obtained by resolving the thermo-viscous layer was accurate compared to experiments, while the wall functions were not able to correctly capture the heat flux. Full cycle simulations resulted in a slightly improved result, especially when resolving the boundary layer, but due to the increased computational cost, this method does not seem beneficial.

Evaluation of wall heat flux calculation methods for CFD simulations of an internal combustion engine under both motored and HCCI operation

“…tal ones. This method also gave the most accurate heat flux predictions under motored operation, as was reported in a previous work [27]. If a study of the heat transfer is to be performed and RANS simulations using axi-symmetry can be performed, the computational time is still acceptable and this method can still be considered.…”

“…This has been conducted by performing some simulations of other engine geometries, such as the ones described in [7,8], and comparing the results to other published results. This validation aspect has already been reported in a previous work [27]. Furthermore, this previous work also performed a mesh dependency check for the low Reynolds methodology, resulting in an appropriate mesh, which has been used here as well.…”

Validation and Enhancement of a Supermesh Strategy for the CFD Simulation of Four-Stroke Internal Combustion Engines

“…At the walls, a non-slip condition is defined for the velocity, and standard wall-functions are considered for the turbulence variables. On the cylinder, cylinder head, and piston crown, wall temperatures are imposed and set to be equal to the cooling fluid temperature [46]. The walls at the inlet and outlet ports are configured with the atmospheric temperature.…”

Thermodynamic work in inline piston gasoline engines as a function of crank angle

“…As shown by the analysis of open sources of information currently, work in the field of piston engine modeling is underway in the field of: modeling of fuel combustion processes [1,9,19], modeling of gas dynamic processes both inside the cylinder and in the intake and exhaust systems [2-6, 8, 11-13, 15, 16, 30-32], modeling of heat transfer processes inside the cylinder [7,14,18,20,26], modeling of fuel properties [10], modeling of friction processes in cylinder-piston group parts [17], modeling work of fuel systems [21], modeling for optimization purposes the design [22][23][24][25], modeling of shock interaction of the piston [27], modeling of engine cycles [28], modeling of the engine management system [29].…”