Abstract

The numerical simulation of spark ignition engines has uncertainties that compromise the reliability of the results due to the interrelationship between chemical dynamics and flow kinematics within the combustion chamber. This work evaluated the effect of using different reaction mechanisms applied to a G-equation combustion model and its interaction with the velocity field inside the combustion chamber of a CFR engine, which has special technical characteristics (high swirl and low rpm) that allowed the study of this phenomenon. The research was carried out numerically by computational fluid dynamics (CFD) techniques: using a G-equation combustion model (with and without reaction kinetics) and a RANS -k − ϵ- RNG turbulence model. The numerical simulation was compared and validated against reported experimental pressure indicator diagram. The influence of reaction mechanisms and swirl in the development of the flame front and associated variables within the combustion chamber was studied. Finally slight discrepancies were found between reaction mechanisms used in this study that could be important in simulations of spark ignited engines that are different from the one studied. It was noted that an increase in the intensity swirl yields a flame development deviation from the theoretical models. The current codes and simulation techniques require tuning of various parameters, and thus, the validation against experimental data is needed before drawing conclusions from the numerical cases.

Abstract

High-accuracy simulations of internal combustion engines (ICE) allow deep insight into the physical processes of the different phases of the engine cycle: gas exchange, mixture formation, compression, combustion and emission formation. The commercial solvers for ICE simulations provide a full package which covers these areas. However, the user of such software is unable to look into the source code, making it impossible to implement new models or investigate possible implementation errors in the code, and costs arise due to licensing requirements for commercial solvers. Although the open source framework OpenFOAM already includes multiple classes and two solvers dedicated to internal combustion engine simulations, there is no way to move engine valves and piston simultaneously with its standard tools. Thus, this paper presents a new engine library for ICE simulations written for OpenFOAM. The new framework is capable of simulating a complete fired engine cycle. The piston and the valves are moved simultaneously. To address large deformations in the mesh, a methodology to avoid insufficient mesh quality was developed. Ignition and combustion is modeled with standard tools from OpenFOAM. To validate the method, the simulation results for the averaged in-cylinder quantities pressure, temperature and mass are compared with experimental data.

Abstract

Abstract