Visualization of the Effects of Post Injection and Swirl on the Combustion Process of a Passenger Car DI Diesel Engine

The effects of variations in injection strategy and swirl on a DI Diesel engine performance and emissions were tested. The cylinder head was fitted with a small diameter endoscope, coupled with a triggered CCD camera, in order to study the effect of these variations on the combustion process. The images that were taken of the combustion process were used to calculate the spatial and temporal distribution of flame temperature and soot kks factor by using the 2-color method.The engine used in the experiments is a single cylinder version of a modern, passenger car type, common rail Diesel engine with a displacement of 480 cc. The fitted endoscope caused very little interference with the combustion chamber due to its small dimensions. The 65 degree angle view of the endoscope allowed coverage of a large portion of the entire combustion chamber. The combustion images and derived temperatures and soot concentrations were used to study the influence of post injection and high swirl.Adding a third (post) injection to the pilot and main injection increases the mixing and the flame temperature during the second half of the combustion process, thereby improving soot oxidation. The fuel efficiency was not negatively affected by the later phasing of part of the heat release. Increased swirl of the intake air was also studied. An 80% increase in swirl-ratio was achieved by closing off one of the two intake ports with a butterfly valve. The improved mixing gave significant reductions in soot emissions, with a small increase in NOx formation