Jos Reijnders

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.

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.

Spray analysis of the PFAMEN injector

In an earlier study, a novel type of diesel fuel injector was proposed. This prototype injects fuel via porous (sintered) micro pores instead of via the conventional 6-8 holes. The micro pores are typically 10-50 micrometer in diameter, versus 120-200 micrometer in the conventional case. The expected advantages of the so-called Porous Fuel Air Mixing Enhancing Nozzle (PFAMEN) injector are lower soot- and CO 2 emissions. However, from previous in-house measurements, it has been concluded that the emissions of the porous injector are still not satisfactory. Roughly, this may have multiple reasons. The first one is that the spray distribution is not good enough, the second one is that the droplet sizing is too big due to the lack of droplet breakup. Furthermore air entrainment into the fuel jets might be insufficient. All reasons lead to fuel rich zones and associated soot formation. To acquire more insight into the spray of the porous injector, several PFAMEN nozzles have been produced and investigated. The momentum of the spray was found to be an order of magnitude lower compared to conventional injectors. Afterwards, the porous injector was placed in an optically accessible engine, allowing the analysis of the spray development and combustion process. The main conclusion is that the spray penetration depth is relatively low. Finally, droplet size and velocities are presented using Phase Doppler Anemometry (PDA) and from these measurements it became clear that the droplets of the PFAMEN nozzle are larger compared to conventional injectors. This is believed to be caused by the low exit velocities.

Styrofoam Precursors as Drop-in Diesel Fuel

Styrene, or ethylbenzene, is mainly used as a monomer for the production of polymers, most notably Styrofoam. In the synthetis of styrene, the feedstock of benzene and ethylene is converted into aromatic oxygenates such as benzaldehyde, 2-phenyl ethanol and acetophenone. Benzaldehyde and phenyl ethanol are low value side streams, while acetophenone is a high value intermediate product. The side streams are now principally rejected from the process and burnt for process heat. Previous in-house research has shown that such aromatic oxygenates are suitable as diesel fuel additives and can in some cases improve the soot-NO x trade-off. In this study acetophenone, benzaldehyde and 2-phenyl ethanol are each added to commercial EN590 diesel at a ratio of 1:9, with the goal to ascertain whether or not the lower value benzaldehyde and 2-phenyl ethanol can perform on par with the higher value acetophenone. These compounds are now used in pure form. In future work, real streams, which are rich of these compounds, but contain various other chemicals as well, will be used. Experiments have been performed on a heavy duty (12.6L) diesel engine, of which one cylinder is a dedicated test cylinder. The results demonstrate that the emissions and efficiencies are more or less comparable for all aromatic oxygenates. Afterwards, the results are compared against neat diesel. It was found that, depending on operation conditions, either the efficiency of the oxygenates was higher, while the emissions where comparable to diesel or the emissions decreased dramatically with comparable efficiencies as diesel. Accordingly, compared to neat diesel, both the high- and low-value styrene streams yield overall positive engine behavior in all measured operating conditions.