Gasoline and gasoline-like fuels (naphtha) have high volatility, which results in flash boiling spray in gasoline engines when operated at throttling or low load conditions. Flash boiling can achieve better atomization, thus benefit fuel evaporation and fuel-air mixing. However, when flash boiling occurs, spray morphology, and fuel distribution are dramatically varied from the injectors' intentional design. This difference will affect the performance of combustion and emissions. Thus it is essential to investigate the spray collapse phenomenon regarding varied conditions. The currently developing gasoline compression ignition (GCI) engines, also has throttled stoichiometric spark ignition operation mode, which inevitably has flash boiling possibility. However, there is a lack of research on flash boiling spray with a GCI injector, which has a large designed cone angle. This work aims to understand the spray collapse phenomenon and fill the gap in GCI flash boiling spray. Simultaneous side-view diffused back illumination (DBI) and front-view mie-scattering are used to capture the liquid spray development. Simultaneous shadowgraph from side and front view are used for recording the liquid+vapor phase spray development. Criteria for distinguishing different spray regimes have been established from these results. It shows this GCI injector is more resistant to collapse than the other conventional gasoline direct injection (GDI) injectors reported in the literature. A combination of DBI and space-time tomographic algorithm is validated in this work, achieving 3D reconstruction of the spray volume development from non-flashing to collapsed spray regime at low cost. The 3D results help elucidate the spray collapse procedure and provide validation data for CFD simulation. Structured laser illumination planar imaging (SLIPI) is firstly implemented in flash boiling spray study in this work to suppress the multiple scattering effect. Reconstructed 3D results from slice sweeping by SLIPI methods exposes the hollow structure in the spray's collapsed central jet, which has not been reported previously by other methods. Different spray motion types are summarized for the transitional and collapsed spray regime from the SLIPI slice and confirmed by the particle image velocimetry (PIV) technique.
|Date made available
|KAUST Research Repository