Three-Zone in-cylinder process model for DI diesel engines

Abstract

The need to reduce harmful emissions to the environment is been addressed on different fronts. Diesel engines, as one of the prime movers in transport industry, has become an active research focus for several years in order to improve their efficiency while keeping the harmful emissions the lowest possible. The inclusion of more stringent regulations and emission control areas such as NECA in the north sea demands for a better understanding of the combustion process in the cylinder in order to reduce emissions. To study such problem an approach is to regard the cylinder as a perfectly mixed volume. This concept is very simple and allows for fast calculations but it lacks the physics and the resolution necessary to study pollutants formation. The main objective of this thesis is to propose a model where the cylinder volume is divided into a few volumes, so the cylinder process can be studied in more detail and some resolution is included to calculate NO emissions. A model with three control volumes, called zones, is introduced. One zone represents the liquid fuel in the cylinder and two zones represent the gas mixture. In one of the gaseous zones the mixture preparation and combustion reaction occur; the second gaseous zone provides the oxidant to the previous zone and the combustion products are further mixed with air. The detailed model and the equations necessary to simulate the process are introduced. The required sub-models are proposed and the implementation of the complete model is done in different steps. First the liquid volume is treated and tested under a set of different conditions. In a second step the gas phase is simulated by neglecting the existence of liquid fuel in the cylinder. Finally, the complete model is assembled and NO formation mechanism is coupled with the model, testing is done allowing to evaluate the concept.