Internal combustion engines that work with fuel at supercritical conditions can benefit from low viscosity, high mass diffusion coefficient, and low surface tension. These properties increase the fuel diffusion and its atomization. Also, heated fluid can improve the engine start and reduce pollutants emissions. However, to achieve these conditions, the fluid needs to be at a reduced temperature and a reduced pressure higher than 1, so it is necessary to heat the compressed fuel. This work concerns the heating of compressed ethanol and its behavior inside a cylindrical heating chamber with a cartridge heater placed concentrically with the chamber. We used the commercial software ANSYS Fluent to simulate the natural convection of ethanol at compressed and supercritical states. The heater works for a given time, about 4 seconds, promoting the increase in the fuel temperature, then it is turned off for 1 second to allow the thermal diffusion in the fluid. All the other walls are adiabatic. We evaluated the fluid behavior and temperature increase for two pressures higher than the critical. The change of thermodynamic properties affects the uniformity of the heated fluid across the heating chamber.