| Precise silicon micro-machining (SMM) technology, encountered in port injector fabrication, have the potential to eliminate the injector-to-injector variability problem that is a major concern for vehicle derivability and hydrocarbon emissions. The new generation of automotive compound injectors (ACI's) utilize turbulence generation mechanisms within the injector body to enhance the atomization process, and multi-hole pattern to better disperse the fuel in the air stream inside the intake port. ACI's have complicated internal geometries, and therefore, are quite fundamental and interesting in themselves since they involve turbulence generation in the fuel line inside the injector, primary turbulent breakup, and secondary aerodynamic breakup mechanism, as well as dispersion and evaporation of multiple fuel jets in the air stream inside the port geometry. However, limited experimental data in the basic atomization processes in this type of injector are available for design purposes. As such, correlation of injector design parameters to its performance is imperative. The steady state and dynamic spray characteristics of various port injectors have been analyzed via non-intrusive laser diagnostics techniques both qualitatively and quantitatively. PLIF and backlighting techniques are employed for visualization purposes, while the distributions of droplet size and velocities and volume flux were measured by the PDPA technique. Detailed evaluation of various port injectors was performed, and a better understanding on the breakup mechanisms and atomization processes involved was achieved. The time-resolved experiments were employed to provide an improved understanding of the transient spray behavior. An integrated approach for ACI's spray simulation was developed interfacing internal and external CFD simulations. The proposed multidimensional CFD methodology was demonstrated and numerically tested and validated against experimental results.; The results of this investigation indicate that spray characteristics can be controlled and optimized, by the nozzle geometry of an ACI injector, to suit different engine and intake port designs. Additionally, the injector internal design can be numerically tested before being manufactured, and as a consequence, the random matching method of injector selection may be eliminated.; Finally, ACI sprays cause much faster degree of flow development, exhibit an improved atomization quality, and result in shorter, or no liquid core, than other production type port injectors. As such, ACI's may be a viable alternative for PFI system. |
