Nozzle Flow Characteristics of Alternate Fuels for Compression Ignition Engine Applications

Inner nozzle flow characteristics (e.g., cavitation, turbulence, injection velocity) are known to affect spray development and hence combustion and emissions. Our previous studies showed that petrodiesel and biodiesel (soybean-based fuels) had very different cavitation and turbulence characteristics, which caused differences in spray breakup, penetration, dispersion, etc. Specifically, the atomization characteristics of biodiesel were worse than those of diesel; they were a direct consequence of biodiesel’s reduced cavitation and turbulence levels at the nozzle exit. In this study, the nozzle flow characteristics of biodiesel (from different feedstocks like tallow, soy, rapeseed, cuphea, and hydrotreated vegetable oil [HVO]) were compared with those of diesel. The first step was to obtain data on the physical properties of these fuels (e.g., their density, viscosity, surface tension, vapor pressure) at different temperatures. At full-needle open position, the cavitation contours scaled with the vapor pressure and viscosity; hence, methyl esters such as soy (SME), rapeseed (RME), and tallow (TME) exhibited less cavitation. The nozzle discharge coefficient, exit velocity, turbulent kinetic energy, and dissipation rate at the orifice exit were also compared for these fuels. Transient effects due to needle movement upon the inception of cavitation were studied. The effects of different needle-lift profiles (pertaining to various load conditions) on the nozzle flow development of these fuels were also characterized. This study also provides data on the critical boundary conditions for spray simulations from using the Kelvin Helmholtz-aerodynamic cavitation turbulence (KH-ACT) model, which accounts for cavitation and turbulence-induced breakup in addition to aerodynamic breakup.