The internal combustion engine cooling is very important to its proper functioning, since high temperatures can shorten the durability of internal components and hence increase fuel consumption. In air-cooled engines it is common to use extended surfaces (fins), which provide an increase in the convective and radiative heat exchange. Thus, the present work investigates the phenomenon of convection between the external air and the motor casing through computational simulations. The finite differences method was applied for two fin geometry (annular and rectangular). The temperature distribution and the heat transfer rate in the fin were obtained for different ambient temperatures (20 - 40 °C) and flow rates (0 - 25 m/s). The analysis was based on a typical 150-cylinder motorcycle engine with fins made of 204-aluminum alloy. It was observed that under zero flow conditions and ambient temperature of 30 °C there was a temperature gradient of 38.49 °C on the annular fins and only 7.76 °C on the rectangular ones. For forced convection conditions (at 25 m / s) the gradient on the annular fins was 71.60 °C and on the rectangular ones 41.23 °C. If the ambient temperature is increased by 10 °C there is a decrease in the temperature gradient in the fins. However, decreasing the ambient temperature by 10 °C, the gradient undergoes little variation. Furthermore, although they have higher thermal gradients, the annular fins have had lower thermal exchange values (up to 40% less), because the area in such geometry is somewhat smaller than for the rectangular geometry. Therefore, the present work contributes to the area by providing thermal data to verify the appropriate cooling means, fin geometry and conditions, as well as providing the basis for the indication of the best fin system model to be used.
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