Cavitation in Marine Diesel Applications: Effects of Hydro-erosive Grinding on Flow and Nozzle Geometry

In the recent decades, global warming and climate changes have persuaded engineers to improve the design of internal combustion engines in case of pollutant emissions and efficiency. The injection system is one of the main subsystems which can highly affect the quality of mixing process inside the combustion chamber and result in higher efficiency and lower emission. Winterthur Gas & Diesel, which is a manufacturer of marine diesel engines, has come with an idea to improve injection process. The idea is that to remove sharp edges at the entrance of the nozzle orifice and increase its roundness to improve the discharge coefficient and decreasing the vapor volume, which is formed by cavitation. The roundness of the orifice inlet can be obtained by a hydro-erosive grinding process in which an abrasive fluid with a very high viscosity is extruded through the nozzle orifice and removes the sharp edges and makes a smoother surface. The effect of hydro-erosive grinding on cavitation formation at the entrance of nozzle orifice has been studied in parallel with the following project and the results are published as a licentiate thesis [1]. In the following project, the improvement of the discharge coefficient for three different types of nozzle orifices is investigated by performing several experiments. For this purpose, a literature review has been done to have a suitable theoretical background and to be aware of recent achievements in the relevant fields. The next step is to design and set up test facilities in order to measure the mass flow rate of the nozzle orifices. The system is designed so that water is pressurized to 5 bar by compressed air and is injected through the nozzles over a pre-defined time period. This time period and the pressure inside the pressure vessel are controlled by solenoid valves and a pressure sensor, which are governed by LabVIEW. The discharged mass is weighted and then it is possible to calculate the discharge coefficient. Before doing the main experiments, several sets of experiments are done to understand the optimum condition where the error is minimum. Then, these conditions are chosen for the main experiments. The mass flow rate for each nozzle is measured five times for eight hydro-erosive grinding levels. In the next step, the average discharge coefficient for each level is calculated and reported in tables and graphs. From these results, it has been understood that at the initial levels of hydro-erosive grinding, a relatively large increase in the discharge coefficient is observed, while for the next levels its growth continues linearly but with a lower rate. Another achievement of this project shows the behavior of different types of nozzles. The orifices which are placed in a tangential position to the nozzle, need to be grinded more in comparison to the standard nozzle, which its orifice is placed at the center of the nozzle outlet. Inclination in orifice causes decrease in flow resistance. Therefore, hydro-erosive grinding in this case is not as efficient as in the case, where the orifice is perpendicular to the nozzle.