In- and near- nozzle and external flow characterization in Gasoline Direct injection (GDi) engines - A review of latest technologies and trends. Part 1: Experimental background

In an era of increasingly stringent emissions regulations, environmental standards are driving gasoline engine research and development toward more widespread use of direct injection systems. It is also of interest to know what kind of phenomena cause these types of emissions in order to address and reduce them as much as possible. Therefore, it has been considered of interest to summarize in this article the latest research topics related to the gasoline direct injection (GDI) process, providing researchers with a valuable resource to understand the current state of research, the different technologies of gasoline direct injection and the phenomena that take place in this process. Research applied to GDI engines can be approached in several ways. The one chosen for this article is mainly based on separating the relevant processes within the engine with the objective of going deeper into each of them. In this sense, it is proposed to study the injection without taking into account the combustion phenomenon. In the same way, it is suggested to study the injection process in several phases: in- and near-field of the injector and downstream of the injector. Therefore, this work performs an extensive analysis of the experimental techniques employed for the study of each of the phenomena that take place in the injection process. The objective of the research is a better understanding of the phenomena, an improved characterization of the internal flow and spray and consequently the final optimization of the engine design. In a subsequent publication (Part 2), the same literature review will be addressed but only taking into account the computational work carried out in recent years with the same objective of investigating the injection, the mixture formation process, and the associated emissions characterization.