In Search of Improvements for the Computational Simulation of Internal Combustion Engines

Abstract

The modeling of internal combustion engines is a multidisciplinary sub-ject that involves chemical thermodynamics, fluid mechanics, turbulence, heattransfer, combustion, and numerical methods. In this chapter, we focus onsome aspects of the computational resolution of the fluid dynamic problem.We present strategies designed in order to improve the simulation tools avail-able today. A Computational Mesh Dynamics (CMD) to solve the movement of themesh is presented. This kind of techniques are useful when an Arbitrary La-grangian Eulerian (ALE) method is applied in the resolution of flows on movingdomains. For in-cylinder flows in internal combustion engines, the domain has avery high relative deformation and even changes on its topology. This demandsa CMD strategy with great robustness to avoid the deterioration of the gridquality and to reduce at minimum possible the number of remeshing needed inthe whole simulation. The CMD strategy proposed is based on an optimizationproblem solved in a global way. The strategy can handle meshes with invertedelements, being a simultaneous mesh untangling and smoothing method. The flow inside of an internal combustion engine is characterized by a lowMach number, except in the early moments in which the exhaust valve (or port)is opened. The numerical methods for compressible flow based on the densityfail when they are applied to flows with low Mach numbers, which is due to theill-conditioning of the system of equations. For this reason, it is necessary toapply a technique that allows the resolution of compressible flows in all the rangeof Mach numbers, especially in the low Mach limit. Here, we apply the method of preconditioning of the equations in conjunction with the dual time steppingtechnique. The preconditioning matrix used was originally designed by Choiand Merkle to solve steady compressible flows with the Finite Volume Method.We adapt this matrix to the unsteady flows case via an eigenvalues analysisof the system. A stabilized Finite Element formulation for the preconditionedsystem of equations is presented. The dynamic boundary conditions on inlet/outlet of the 3D problem areobtained by using a code with thermodynamic (0D) and gas-dynamic (1D)models. Therefore, the need to couple appropriately the solutions obtained inthe computational 1D and 3D domains arises. We propose a coupling strategyof 1D/multi-D domains for compressible flows based on constraints of the stateat the coupling section. Finally, these tools are applied to solve the fluid flow in the novel rotativeengine MRCVC.