Numerical Investigation on Effects of Combustion Chamber Structure and Oxygen Enriched Air on Combustion and Emission Characteristics of Marine Diesel Engine

摘要

In order to improve the combustion and emissions for high-speed marine diesel engines, numerical investigations on effects of different combustion chamber structures combined with oxygen enriched air have to be conducted. The study uses AVL Fire code to establish three-dimensional combustion model and simulate the in-cylinder flow, air-fuel mixing and combustion process with the flow dynamics metrics such as swirl number and uniformity index, analyze the interactional effects of combustion chamber structures and oxygen enriched air against the experimental data for a part load operation at 1350 r/min, find the optimized way to improve engine performance as well as decrease the NO_x and soot emissions. The novelty is that this study is to combine different oxygen concentration with different combustion chamber structures including the re-entrant chamber, the straight chamber and the open chamber. Results show that the chamber diameter, bowl depth, oxygen enrichment can greatly influence in-cylinder flow, the re-entrant chamber makes a higher power output at the price of a smaller increase of NO_x emissions, meanwhile the chamber combined with suitable oxygen concentration can enhance the in-cylinder peak pressure and temperature, decrease the soot emissions and cause more NO_x emissions. The straight chamber has lower emissions at the same output power level compared with the prototype, the open chamber is found to have a lower output power.