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Author ORCID Identifier



Open Access Dissertation

Document Type


Degree Name

Doctor of Philosophy (PhD)

Degree Program

Mechanical Engineering

Year Degree Awarded


Month Degree Awarded


First Advisor

David P. Schmidt

Subject Categories

Applied Mechanics | Energy Systems | Heat Transfer, Combustion


The early and late portions of transient fuel injection have proven to be a rich area
of research, especially since the end of injection can cause a disproportionate amount
of emissions in direct injection internal combustion engines. While simulating the
internal flow of fuel injectors, valve opening and closing events are the perennial
challenges. A typical adaptive-mesh CFD simulation is extremely computationally
expensive, as the small gap between the needle valve and the seat requires very
small cells to be resolved properly. Capturing complete closure usually involves a
topological change in the computational domain. Furthermore, Internal Combustion
Engines(ICE) operating with Gasoline Direct Injection(GDI) principle are susceptible
to flash boiling due to the volatile nature of the fuel.
The presented work simulates a gasoline direct injector operating under cavitating
conditions by employing a more gradual and easily implemented model of closure that avoids spurious water-hammer effects. The results show cavitation at low valve lift for
both flash boiling and non-flash boiling conditions. Further, this study reveals post-
closure dynamics that result in dribble, which is expected to contribute to unburnt
hydrocarbon emissions. Flashing versus non-flashing conditions are shown to cause
different sac and nozzle behavior after needle closure. In particular, a slowly boiling
sac causes spurious injection behavior.
Furthermore, a qualitative analysis of the injector tip-wetting phenomena under
both flash-boiling and non-flashing conditions are conducted and different wetting
mechanisms are identified. The jet expansion mechanism is observed to dominate the
wetting process during the main injection period, whereas the sac conditions drive the
post-closure wetting phenomena. Additionally, the effect of flash-boiling conditions
on the near-nozzle spray during the quasi-steady period of the injection cycle is explored. The exploration captured hole-to-hole variations in the rate of injection (ROI), rate of momentum (ROM), and hydraulic coefficients of injection. Moreover, it also indicates influences of the in-nozzle variations on the near-nozzle spray behaviors.
Finally, a novel plume-based coupling approach is developed to couple the Eulerian near nozzle simulations with the Lagrangian spray simulations under both non-
flashing and flash-boiling conditions. Predictions from the novel coupling approach
are validated with the experimental observations. This coupling approach requires
running an Eulerian primary atomization model, i.e., the Σ −Y model, to initialize
the Lagrangian parcels for the secondary atomization process. Hence, this coupling
approach does not depend upon the linearized instability models to simulate the dense spray region.