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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.

Technological advances in fast multi-element detectors now permit single-shot temporally and spatially resolved chemiluminescence spectra to be observed from an optically accessible four-stroke single cylinder spark-ignition engine. We demonstrate three techniques using multi-element detectors. First, with a wavelength coverage of 300 - 700 nm, we have observed the chemiluminescence spectra from individual combustion events with a time-gated intensified linear photodiode array. The broad wavelength coverage allows discrete spectral peaks of multiple species (OH, CH, C2, CN, NH) to be observed simultaneously and be distinguished from the continuum luminosity of the spectra. Second, by using a digital streak camera equipped with UV optics, the continuous time evolution of the chemiluminescence spectra was obtained from the spark gap of the engine. The temporal evolution of the plasma spectra from the spark-gap region was observed on short time scales (nanoseconds through microseconds).