Characterization of Alcohol Sprays from Multi-Hole Injector for DISI Engines through PIV Technique

The use of alcohols as alternative to gasoline for fuelling spark-ignition (SI) engines is widespread. Growing interest is paid for n-butanol because of its characteristics that are similar to gasoline. If compared with other alcohols, n-butanol has higher energy content and miscibility with gasoline, lower hygroscope and corrosive properties making it an attractive solution for gasoline replacement. Even if several studies have been conduced to characterize the n-butanol combustion within Spark Ignition engines, few data are available on atomization and spray behavior. This paper reports the results of an experimental investigation to characterize the velocity vector field of two fuel-sprays injected by a 6-hole nozzle for Direct Injection Spark Ignition (DISI) engine. 2D Mie-scattering and Particle Image Velocimetry (PIV) measurements were carried out in an optically accessible vessel at ambient temperature and pressure. Two different fuels were used: commercial gasoline and pure n-butanol tested at two different injection pressures: 5 and 10 MPa. The comparison between gasoline and n-butanol in terms of liquid spray morphology, tip penetration, cone angle and droplets velocity vector distribution are presented. 2D digital imaging highlighted a slight difference on the spray propagation and dispersion with higher tip penetration lengths and lower jet cone angles provided by the n-butanol. PIV measurements highlighted that the higher viscosity and surface tension of n-butanol bring on an increase in the droplets velocity field. The analysis of the dimensionless groups such as Reynolds, Weber and Ohnesorge number allowed to emphasize the adverse effect of the n-butanol on the breakup and atomization processes.