Experimental Determination of Fuel Additive Effects on Leidenfrost Temperature and Deposit Formation

Deposit formation in the induction system of port-fuel-injected engines depends on the fuel-droplet/metal-surface interaction. Previous studies have shown that the metal surface temperature is a critical parameter in deposit formation. Droplet-surface behavior is characterized by the droplet boiling temperature, Nukiyama temperature (at which the droplet has a minimum lifetime), and the Leidenfrost temperature (at which the droplet levitates above the surface on a vapor layer and has a maximum lifetime). In this work, we investigate the effect of fuel additives on deposit formation and on the Leidenfrost temperature. Two experimental apparatuses were used. To determine the temperature range of deposit formation for fuels with different additives, droplets were allowed to impinge upon a heated ramp with a large temperature gradient. The temperature at which the droplets stop sliding and disappear was determined from the position of the residue formation on the ramp. In addition, the Leidenfrost temperature for each additized fuel was directly measured using a high-speed video camera to image the dynamic impact behavior of single falling droplets on a heated metallic surface. The Leidenfrost temperature, defined as the point when the falling droplets no longer recoil as the metallic surface temperature is decreased, was determined for the same additized fuel droplets. The surfactants were found to decrease the Leidenfrost temperature when they were introduced at a concentration above a critical level. The results from these two apparatuses will be compared.