Abstract
The post injection strategy has been one of the most used solutions for reducing pollutant emissions in Diesel engines during the last decade. Many authors have studied the effects of this strategy in the past years. The present research starts with a literature review related to the subject, where it is possible to conclude that the great majority of studies can be considered in a technologic framework where soot reduction associated to the post injection is found as one of the most relevant results. This point of view has as a weakness the lack of scientific perspective. With the aim of avoiding this limitation, the main objective for the current thesis is the contribution for a better comprehension of the physical phenomena involved in the combustion and soot formation processes with the use of post injection strategies.
For achieving the desired objective the research has been scheduled in two stages where experimental facilities have been used in conjunction with theoretical tools. In the first stage an exploratory study of the effects of the post injection strategy on combustion process and emissions has been performed where two important phenomena appear: on the one hand, an acceleration of the final stage of the combustion process and, on the other hand, an apparent disconnection between the combustion of the main injection and the post which is named as split flame phenomenon which can be used for easier explanation of the final soot emissions.
In the second stage each of the phenomena mentioned before have been studied in depth. It was found that the improvement in the mixing process during the initial transient of the injection process induced by the post injection strategy was especially relevant as a physical explanation of the combustion acceleration phenomenon. It was also found that the unburned temperature at the end of the post injection pulse and the ratio between the duration of injection and the apparent combustion time were the physical parameters that explain the soot emissions associated to the post injection.