7. Modeling of Flash Boiling Phenomenon in Internal and Near-Nozzle Flow of Fuel Injectors

Detailed analysis of the internal and the near-nozzle flow of fuel injectors is a necessity for a comprehensive understanding of any internal combustion engine performance. For gasoline direct injection engines, under part-load conditions, the in-cylinder pressure can be subatmospheric when the high-temperature fuel is injected, resulting in flash boiling. Detailed experimental characterization of such complex phenomena is extremely difficult. Three-dimensional computational fluid dynamics (CFD) simulations provide key insights into the flash boiling phenomena. The Spray G injector from Engine Combustion Network (ECN) has been considered for this study, which has eight counter-bored holes. Homogeneous relaxation model is used to capture the rate of phase change. Standard and RNG \(k-\epsilon \) turbulence models have been employed for modeling turbulence effects. Based on apriori thermodynamic estimates, three types of thermodynamic conditions have been explored: non-flashing, moderate flashing, and intense flashing. Numerical analyses showed that with more flashing the spray plumes grow wider due to the volume expansion of the rapidly forming fuel vapor. Mainly single-component fuel is studied in this work. Iso-octane is considered as the gasoline surrogate for this study. Binary component blends of isooctane and ethanol were also tested for blended fuel flashing predictions using the existing numerical setup. After careful estimation of blended fuel saturation properties, the simulations indicated that blended fuels can be more volatile than the individual components and thus exhibit more flashing compared to the cases with single-component fuels.