Spray Processes in Optical Diesel Engines - Air-Entrainement and Emissions

Sammanfattning: Internal combustion engines have been an important technological field for more than a century. It has had an important impact on society through improved transportation and industrial applications. However, concerns about environmental effects of exhaust gases and utilization of oil resources have pushed development of combustion engines towards cleaner combustion and higher efficiencies. The diesel engine is today an interesting solution in terms of fuel economy. However, emissions of pollutants such as soot particles are still a major concern for diesel engines. The combustion process in diesel engines is far from fully understood and there are many to questions to be answered about emissions formation and oxidation within the combustion chamber. The objective of this work is it to gain knowledge on in-cylinder processes related to engine-out emissions. More specifically, the focus is set on understanding the connections between spray processes and the formation of pollutants such as soot particles and unburned hydrocarbons by using optical diagnostics. Engines modified for optical studies allowing optical access inside the combustion chamber have been used in the different investigations presented in this thesis. The types of engines concerned here are four-stroke heavy- and light-duty diesel engines. Even though engines are complex systems with interacting sub-systems, such as turbochargers and after-treatment devices, the focus of this work is solely on the in-cylinder processes. The focus of this thesis is fuel-jet mechanisms related to air-entrainment and emission formations. The different investigations conducted in this work can be divided in two main categories. First, air-entrainment in fuel jets and its coupling to emissions formation were studied in different optical engines. Previous results in the field, often obtained in constant volume combustion vessels, were used for prediction calculations and comparison between free jets and jets in engine environment. Second, multiple injection strategies were investigated to reduce engine-out emissions of soot and unburned hydrocarbons and also to stabilize combustion in cold conditions. The results presented in this thesis can be divided in two main categories; air entrainment in fuel jets and multiple injection strategies. The first part regards air entrainment both upstream the lift-off length and in the interaction between adjacent jets. The second part presents multiple injections strategies as a tool for combustion stabilization in cold conditions and emissions reduction