Comparação entre resultados experimentais e de simulação numérica de um motor de combustão interna

Abstract

In view of the use of internal combustion engines, currently studies to increase efficiency are increasingly present. With technological advances in computers, there is a trend towards the use of computational resources, which contribute to engine designs. In this context, the present work proposes to carry out a computational simulation of the combustion of an internal combustion engine through a one-dimensional numerical modeling in the GT-POWER program, which uses a Wiebe model to characterize the combustion. The geometric characteristics of the Honda GX35 single-cylinder engine were added as input parameters for a model, operating in the Otto cycle, with a displaced volume of 35.8 cm³, naturally aspirated and with a volumetric compression ratio of 8:1. The numerical simulation was performed assuming a constant temperature of 450K in the cylinder walls, considering methane gas as fuel and rotation of 3600 rpm, at full load. After the simulation, the P-V diagram was obtained, which describes the behavior of the volume and pressure in the system, the absolute pressure curve inside the cylinder, data on the inlet air mass flow, burned mass fraction and temperature inside the cylinder. The results were compared with data from experimental tests taken from works available in the literature. The simulation presented considerably different inlet air mass flow results compared to the experimental results, with a maximum numerical mass flow value of 6.13g/s at 441º, while the maximum experimental value is 4.35g/s at 475º. The absolute pressure curve inside the cylinder and the PV diagram obtained in the simulation reached values close to the experimental values, even with the differences in the inlet air mass flow results, due to an adjustment made in the angles of FMQ 50% (angle at which there is 50% of the mass fraction burned), adjusting the numerical value to 33º, while the experimental value is 41.7º. Thus, the absolute interior pressure inside the cylinder had a maximum value of the numerical curve of 16.47 bar, at 19.8º, while the maximum value of the experimental curve is 16.1 bar, at 17.8º. The numerical model was able to represent an internal combustion engine operating under the specific conditions that were imposed in this study, presenting the greatest differences in the comparison of experimental and numerical values of air mass flow and in the burned mass fraction curve, with a relative percentage error of 20.86% in FMQ 50%.