Spray evaporation of ethanol-gasoline-like blend and combustion of ethanol-gasoline blend injected by hole-type nozzle for direct-injection spark ignition engines

The spray evaporation and combustion characteristics of ethanol-gasoline blends, which consisted of E0 (100% gasoline), E85 (85% ethanol and 15% gasoline) and E100 (100% ethanol) were investigated using a hole-type nozzle in a high-temperature and high-pressure quiescent constant volume vessel. A dual-wavelength laser absorption scattering (LAS) technique was employed to differentiate the vapor distribution from the liquid phase. The vapor distribution of gasoline was determined by p-xylene, which had similar physical properties to gasoline and high absorption for ultraviolet. Likewise, the vapor behavior of ethanol was determined by methyl ethyl ketone (MEK). To analyze the flame development and combustion intensity, OH* chemiluminescence was examined by using real ethanol-gasoline blend under the same calorific value. The result shows that the ethanol evaporates faster than the gasoline. Due to different boiling points, a distinct stratified vapor ambient-gas mixture is formed in the E85 spray. It implies that the low boiling point (LBP) components in gasoline probably evaporate similar to ethanol which is distributed homogeneously along the spray axis. While those of high boiling point (HBP), which are the heavy components in gasoline, would locate from the middle to downstream of the spray, and hence a dense gasoline vapor region is formed at the spray tip after the end of injection (EOI). The analysis of the combustion intensity indicates this phenomenon is one possible reason that leads to the different combustion behaviors between the E85 and E100. After ethanol is added, the combustion becomes more vigorous due to the increase of oxygen content. In addition, the combustion stability is improved by using the ethanol-gasoline blends, especially when the ignition is started at the advanced timing and the middle region of the spray.