Análise de temperatura em um motor de combustão com arrefecimento a ar utilizando sensores baseados em redes de Bragg em fibras óticas

Abstract

This study reports the analysis of the temperature in air-cooled internal combustion engines using sensors based on fiber optic Bragg gratings (FBG) as a measuring device to obtain temperature values in different operating conditions of the referred engine. The air-cooled internal combustion engine is considered the simplest and least efficient system model when compared to more complex ones. The fins are important components to promote a more adequate heat transfer. Fin heat transfer does not have a linear coefficient and the temperature distribution on the surface of an air-cooled engine is not uniform, making thermal monitoring more complex. The sensing was performed by an FGB sensor, as it has some advantages over other types of monitoring devices. Among the advantages are that there is no risk of explosions, they do not suffer electrical, magnetic or chemical interference, besides having small dimensions, low weight and being adaptable to more complex contours such as engine cylinders. An analysis of temperature as a function of duration and operating cycle was performed by placing sensors in specific locations in the engine cylinder region. It was possible to obtain the time coefficients through exponential fits and linear fits, by testing at different speeds. It was observed that the longer the time of a step, the greater the exponential value and the decay of the temperature. It was also observed that the higher the temperature reached by the motor, the lower the coefficient and the longer it will take to reach lower temperatures. For cooling, the largest time coefficient observed was 44 s. In the step performed with lower speed, starting at lower temperatures, a speed coefficient value of -0.38 °C/s was obtained. Whereas, in the second test, starting from a higher temperature, even for higher speeds, the decay rate was lower, -0.21 °C/s, showing that the motor temperature has a strong influence on the cooling capacity. The data acquisition was enlightening and presents itself as an interesting alternative for further studies in this area.