Metodologia numérica para caracterização da injeção de combustível e formação da mistura para desenvolvimento de motores de combustão interna

Abstract

The growth of the world vehicle fleet generates the increase of the greenhouse gases emissions, which makes necessary to improve the comprehension of the Internal Combustion Engines (ICE) operation, in order to enhance their efficiency. One of the factors that affect the combustion in these engines is the fuel injection, which leads to the mixture formation and influences directly the combustion. This work aims to develop a general methodology in which tridimensional numerical simulations are carried out, using the programa Star-Cd with the modulus es-ice, in order to numerically characterize the fuel injection and the mixture formation in a 2-valve engine under designing step. The methodology consists of two steps, where the first one is to characterize only the injector, installed in an atmospheric chamber, and the results are experimentally validated. On the second step, the validated parameters and conditions for the injector are applied to a complete simulation of the target engine, for different injection conditions, along with the first boundary conditions acquired from experimental procedures. Thus it is possible to study and predict the behavior of important parameters of the fuel injection in the engine during its development step, which can result in improvements on the efficiency of the final product. The proposed methodology presented excellent results for the first step, in which the difference between the experimental and numerical results was only 0.2,%, considering, therefore, the spray characterization as validated. The results of the second step showed many behaviors of the mixture formation for the analyzed conditions, such as fuel loss, incomplete evaporations, poor mixtures, liquid fuel accumulation spots, among other problems that are usually hard to detect in physical experiments, which highlights the importance and relevance of numerical simulations. The models were also capable to well represent the eddy recirculation inside de cylinder and in regions of free shear flow at the valve openings, which makes possible to observe the correlation between parameters such as tumble and swirl during the intake and compression strokes. Considering the results reached in this study, it is possible to adjust some parameters of the design and update the boundary conditions, which makes possible to reach new and more efficient injection conditions, in order to get to more efficient combustions. The present study may be of great relevance for future studies regarding injection and mixture formation studies involving numerical simulations.