Porous Fuel Air Mixing Enhancing Nozzle (PFAMEN)

One of the challenges with conventional diesel engines is the emission of soot. To reduce soot emission whilst maintaining fuel efficiency, an important pathway is to improve the fuel-air mixing process. This can be achieved by creating small droplets in order to enhance evaporation. Furthermore, the distribution of the droplets in the combustion chamber should be optimized, making optimal use of in-cylinder air. To deal with these requirements a new type of injector is proposed, which has a porous nozzle tip with pore diameters between 1 and 50 μm. First, because of the small pore diameters the droplets will also be small. From literature it is known that (almost) no soot is formed when orifice diameters are smaller than 50 μm. Second, the configuration of the nozzle can be chosen such that the whole cylinder can be filled with fine droplets (i.e., spray angle nearly 180°). However, injecting through a porous nozzle is not the same as an infinite number of very small holes, due to the difference in nozzle internal flow. Therefore, the nozzle tip is modeled in COMSOL Multiphysics in order to predict the outflow direction and velocity of the fuel. The Darcy-Forchheimer equation, which follows from the Navier-Stokes equation, is used for this purpose. To validate the model, experiments have been performed in the Eindhoven High Pressure Cell (EHPC) where (for vaporizing sprays) the spray is visually analyzed and (for reacting sprays) the ignition delay has been measured.