A detailed understanding of the air–fuel mixing process in gasoline direct injection engines is necessary to avoid soot formation that might result from charge inhomogeneities or liquid fuel impingement on the cylinder walls. Within this context, the use of multidimensional models might be helpful to better understand how spray evolution in cylinder charge motions and combustion chamber design affects the mixture quality at spark-timing. In this work, the authors developed and applied a computational fluid dynamics methodology to simulate gas exchange and air–fuel mixture formation in gasoline direct injection engines. To this end, a suitable set of spray submodels was implemented into an open-source code to properly describe the evolution of gasoline jets emerging from multihole atomizers. Furthermore, the complete liquid film dynamics was also considered. For a proper assessment of the approach, a gasoline direct injection engine running at full load was simulated and effects of spray targeting and engine speed were studied. A detailed postprocessing of the computed data of liquid film mass, homogeneity index and equivalence ratio distributions was performed and correlated with experimental data of particulate emissions. Satisfactory results were achieved, proving the effectiveness of the proposed methodology in predicting the effects of injection system and operating conditions on soot formation.

In this article, a complete and original method to analyse both the epitrochoidal and the hypotrochoidal rotary machines is presented. The internal trochoidal machines consist of two rotors: the first rotor is an envelope of a trochoid, the second rotor is its conjugate. In particular, in this article, the profiles of the trochoidal rotor and its conjugate are expressed by original and particularly synthetic equations using a method based on the theory of gearing. Then the geometry of these machines is completely defined by the choice of four non-dimensional parameters. Once these parameters are selected, the geometric and kinematic characteristics of the rotor profiles are obtained in an original analytic form; hence, the main theoretical performance indexes are computed by a proper method. The results of the analysis allow us to choose the best geometric configuration for a specific application.

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Direct Injection technology for Spark Ignition engines is currently undergoing a significant development process in order to achieve its complete potential in terms of fuel conversion efficiency, while preserving the ability to achieve future, stringent emission limits. In this process, improving the fuel spray analysis capabilities is of primary importance. Among the available experimental techniques, the momentum flux measurement is one of the most interesting approaches as it allows a direct measurement of the spray-air mixing potential and hence it is currently considered an interesting complement to spray imaging and Phase Doppler Anemometry. The aim of the present paper is to investigate the fuel spray evolution when it undergoes flash boiling, a peculiar flow condition occurring when the ambient pressure in which the spray evolves is below the saturation pressure of the injected fluid. These thermodynamic conditions can occur in part load operation for GDI (Gasoline Direct Injection) engines, causing the spray flow structure and hence the mixture formation process to be completely altered with respect to standard flow conditions. To investigate the effects of flash-boiling on the spray evolution, a single-hole GDI research injector designed by Magneti Marelli was analyzed in terms of both global spray shape evolution and of spray momentum flux. A preliminary injection rate analysis was also carried out to investigate the hydraulic behavior of the research injector. The spray tests were executed inside a quiescent vessel at ambient pressure ranging from 40 to 300 kPa. To obtain the flashboiling conditions, both the injector fixture and the test fuel (nheptane) temperatures were set between 30 °C and 120 °C. For the spray momentum flux tests, distances from 5 to 40 mm from the nozzle were used. Aiming to compare the internal spray structure under low and high temperature conditions, momentum spatial distribution was also investigated over planes at different distances from the nozzle. The results of this work, obtained in well-defined conditions in terms of fuel composition and spray configuration (single jet), can assist the development of CFD numerical tools as well as contribute to a better understanding of the flash-boiling phenomenon effect to the spray formation and evolution.