Unconventional gasoline spray injection events: Compared evolution of experimental data and numerical simulations

The current homologation standards in the automotive field impose the manufacturers to develop very efficient and clean engines. Low-Temperature Combustion engines have the potential to simultaneously reduce all the pollutants released while maintaining high efficiency. Among them, in Gasoline Compression Ignition (GCI) combustion technology, multiple injections allow to generate a tailored stratified charge which can auto ignite limiting the rough Pressure Rise Rate (PRR) and heat release rate typical of GCI. Therefore, the three-dimensional local distribution of the mixture becomes the key-point which the engine performance depends on. Due to emphasis on the multi-dimensional and local nature of the mixture formation phenomenon, three-dimensional CFD simulations are a promising and attractive method aiming at the design of the injection event features (timing, pattern, etc.). This paper deals with both experimental and CFD campaign on the evolution of a gasoline spray at ultra high-pressure multiple injection as well as high backpressure, typical of Gasoline Compression Ignition engines. The experimental tests have been conducted on a reference Diesel Common-Rail injector which shots in a constant-volume chamber. The hydraulic behaviour of the injector was characterized by means of the Bosch Tube principle whilst the Mie-scattering technique was used to capture the spray images. The numerical methodology is required to predict the Liquid Length Penetration and the jet morphology features (shape, area). Both experiments and simulations were conducted at different values of injection pressure (350, 500, 700 bar), back pressure (1-8 bar), energizing time (350, 600 & mu;s), according to the operations of a real reference GCI test engine. Furthermore, a dedicated sub-model which takes into consideration the effect of the spray dynamics during the injection transient opening stage has been validated. The importance of this approach when dealing with short energizing time (e.g. 350 & mu;s) is shown. Comparing both the experimental and numerical results, the model has proven to efficiently reproduce the spray penetration and morphology features, also under the hypothesis of injector ballistic phase operations, whose determination is crucial in the early development and sustainability of such combustion concept.