Project of a pressure stabilizing system for fast boiling experiments

The reduction of pollutant emissions and the improvement of cold-phase performance of internal combustion engines can be achieved by heating the liquid fuel prior to its injection into the cylinders. Given the short heating time required as well as the power input, this technique results in the occurrence of boiling on the surface of the heater. With neither the use of pumps (for excessive cost reasons) nor the use of compressed gas (for safety reasons), designing a test bench capable of operating at constant pressure during vaporization of liquids in a closed system is challenging. We present in this paper the step-by-step project of an original pressurization solution for closed systems that has the final purpose of performing pool boiling experiments with water, gasoline, and ethanol at pressures up to 80 bar. The project features a hand-operated pump for initial pressurization and a test section comprised of a representative vehicle fuel gallery operating with a commercial fuel heater. The use of borosilicate glass in the test section, cameras, and adequate lighting make it possible to visualize and film the experiments. A condenser and a spring-piston system were designed externally to the test section as means to decrease the pressure variations during the tests caused by the vaporization of the liquid fuel. One of the major challenges in the modeling is dealing simultaneously with transient boiling and condensation, two phenomena with very different characteristic times ( 10 ms and 1 s, respectively). The simulations performed indicate that the closed system pressure control using these concepts is possible within the required operating ranges. The analysis of the behavior of variables such as the condensation length, spring displacement, and pressure throughout the experiments were used as the basis for dimensioning the piston diameter employed, the spring coefficient of elasticity, and the condenser tube length.