Spray and Failure Analysis of Porous Injection Nozzles

To improve the mixing of fuel and air in the combustion chamber of current diesel engines, research is carried out regarding injectors with a porous nozzle tip, replacing conventional nozzles with a limited number of holes. Preliminary tests with porous injectors showed that further research concerning spray distribution was necessary due to non-optimal spray shapes and low fuel velocities. Therefore, spray shapes and fuel velocities of porous injectors were examined at atmospheric pressures. These examinations show that the spray shapes can be adjusted by alternating the geometries. Geometrical influences have been studied and compared to conventional injectors, showing that the fuel velocity of the porous injectors has decreased with approximately a factor of 10. Subsequently, research concerning the lifetime of porous nozzles was necessary due to premature failure. Therefore, the micro structure of the porous material has been evaluated using an electron microscope, a micro CT-scanner and a hardness tester. These evaluations show that the current technique to shape the outside of the porous injectors has a negative influence on the lifetime. Furthermore, the relations between subjected materials and corresponding properties have been examined in order to improve the lifetime, resulting in lifetime extension possibilities up to a factor of 5.