One fundamental subprocess for the utilization of alternative fuels for automotive applications is the in-cylinder mixture formation and therefore the fuel injection, which largely affects the combustion efficiency of internal combustion engines. This study analyzes the influence of the physical properties of various model-fuels on atomization and spray propagation at temperatures and pressures matching the operating conditions of today's gasoline engines. The experiments were carried out using an outwardly opening, piezo-driven gasoline injector. In order to cover a wide range of potential fuels the following liquids were investigated: Alcohols (Ethanol, Butanol and Decanol), alkanes (Iso-Octane, Dodecane and Heptane) and one furane (Tetrahydrofurfuryl Alcohol). The macroscopic spray propagation of the fuels was investigated using shadowgraphy. For complementary spray characterization droplet sizes and velocities were measured using Phase-Doppler Anemometry. These measurements were performed in a heated, pressurized chamber with optical access. Complementary measurements relative to general appearance and fuel mass delivery were done at atmospheric conditions.
Using alternative fuels, earlier studies revealed only a small influence of the fuel's thermophysical properties on spray propagation. In the study considered here, a wide range of physical properties has been examined, revealing a significant influence on atomization and spray propagation. The droplet size, the stationary penetration length of the liquid phase and the total amount of injected mass are especially affected by the fuel properties. Mainly the high-viscosity fuels show different penetration lengths and droplet sizes. Furthermore the macroscopic structure of the hollow cone sprays, in particular the recirculation zone, is highly dependent on the fuel under consideration.