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The objective of this research is to investigate the behavior of interacting sprays, so-called spray clusters, under typical Diesel combustion conditions. Visualizations and Phase-Doppler Anemometry are employed to characterize the macro- and microscopic spray properties. A significant effect of the cluster geometry on spray formation is noticed. Direct spray-spray interaction is found in all cases, with varying intensity depending on the included angle of the orifices within a cluster. The sprays from all investigated cluster nozzles penetrated significantly slower than those of a comparable conventional nozzle. The stability of the sprays is found to be very sensitive to the orientation of the cluster. Depending on this parameter the sprays from one cluster penetrate very similar or exhibit significant instabilities, especially at lower injection pressures.

A three-dimensional homogeneous equilibrium model (HEM) has been developed and implemented into an engine computational fluid dynamics (CFD) code KIVA-3V. The model was applied to simulate cavitating flow within injector nozzle passages. The effects of nozzle passage geometry and injection conditions on the development of cavitation zones and the nozzle discharge coefficient were investigated. Specifically, the effects of nozzle length (L/D ratio), nozzle inlet radius (R/D ratio) and K or KS factor (nozzle passage convergence) were simulated, and the effects of injection and chamber pressures, and time-varying injection pressure were also investigated. These effects are well captured by the nozzle flow model, and the predicted trends are consistent with those from experimental observations and theoretical analyses.

Computational fluid dynamic (CFD) analysis of in-cylinder events in the automotive industry is heavily dependent on spray simulations for almost all advanced engine concepts. As the upper bound of efficiency in these engines is pursued, the accurate prediction of sprays is critical, since the mixture preparation and ignition, whether by spark or auto-ignition, needs to be precisely controlled. While most of the spray literature closely examines various drop processes, especially breakup, comparatively less attention has been focused on the momentum coupling between the liquid and the gas phases, in particular the numerical aspects. In fact, adjusting models for the evolution of drop size has been one of the dominant means of controlling predictions of spray shape and liquid penetration.

Analysis of the cold-starting performance of diesel engines requires the development of advanced models to describe the multicomponent nature of the fuel as well as the spray impingement and wall film behavior. A new approach to modeling the multicomponent nature of commercial fuels was implemented. This model is based on a continuous distribution using a probability density function, rather than the use of discrete components, to capture more accurately the entire range of composition in commercial fuels. The model was applied to single droplet calculations to validate the predictions against experimental results. Previous discrete component wall-film modeling has been extended to include the continuous multicomponent fuel representation. A significant factor that has received little attention in analyzing the cold-start performance of diesel engines is the spray impingement angle and location. This has been investigated using the modified KIVA code.

Various single and split injection schemes are studied to provide a better understanding of fuel distribution during cold starting in DI diesel engines. Improved spray-wall interaction, fuel film and multicomponent vaporization models are used to analyze the combustion processes. Better combustion characteristics are obtained for the split injection schemes than with a single injection. An analysis of the fuel impingement processes identifies the mechanisms involved in producing the differences in vaporization and combustion of the fuel. A greater amount of splashing occurred for the split injections compared to a single injection. This behavior is attributed to the decreased film thickness (less dissipation of impingement energy), the decreased impingement area (obtained by increasing the impingement Weber number), and most importantly, the reduced frequency of drop impingement.

In multidimensional modeling, fuels have been represented predominantly by single components, such as octane for gasoline. Several bicomponent studies have been performed, but these are still limited in their ability to represent real fuels, which are blends of as many as 300 components. This study outlines a method by which the fuel composition is represented by a distribution function of the fuel molecular weight. This allows a much wider range of compositions to be modeled, and only requires including two additional “species” besides the fuel, namely the mean and second moment of the distribution. This approach has been previously presented but is applied here to multidimensional calculations. Results are presented for single component droplet vaporization for comparison with single component fuel predictions, as well as results for a multicomponent gasoline and a diesel droplet.