Development of a cylindrical Diesel evaporator for mobile systems

Fraunhofer ISE has developed and patented an innovative simple process for direct evaporation of diesel by radiative heat exchange with the energy provided by the oxidation of diesel. This novel evaporation process has the remarkable advantage that it can directly vaporize diesel without the formation of coking observed in other diesel evaporators. This process uses the heat generated by the partial oxidation of a portion of the fuel with sub-stoichiometric amounts of air, i.e. it does not rely on external heat sources after the initial heating up to activate the catalyst. The oxidation of a portion of diesel takes place on an alumina wash coat with a noble metal used as a catalyst supported on a catalyst grid. Due to the heat transfer by radiation and convection from the hot catalyst to the thin fuel film, the more volatile components of the fuel evaporate immediately and react with the supplied air. Thus, the fuel on the wall is completely evaporated without forming any residues or coking, since the walls are not heated from the outside and are colder than the fuel, which eliminates the soot formation. The catalyst is not in direct contact with liquid fuels at any time because this would result in an accelerated poisoning of the catalyst. Furthermore, the studies carried out by the institute have shown that the fuel properties change after this simple direct evaporation. In the case of diesel, it has been observed that the fuel vapor obtained has a lower cetane number due to the cracking of the long-chain alkanes and exhibits a composition with a higher octane number. This change makes this fuel suitable for a burner system that is designed by our industrial partner for its utilization in transportation and in domestic applications. In this work, various heating concepts are experimented on for a quicker start-up. The difference between the operations with horizontal and vertical alignment of the evaporator, the extent of the pressure drop across the evaporator and the effect of the variation of diesel inlets and numbers are investigated. The temperature profiles and the gas composition of the evaporated diesel are included when comparisons between different diesel configurations are made. The successful development and characterization of this new cylindrical diesel evaporator with the results aforementioned might not only be an interesting alternative for the industrial burners, but also other various applications, such as steam reformers, particulate filters and motors, which adds up to the attractiveness of the device.