PIV and DBI Experimental Characterization of Air Flow-Spray Interaction and Soot Formation in a Single Cylinder Optical Diesel Engine Using a Real Bowl Geometry Piston 2019-24-0100

With demanding emissions legislations and the need for higher efficiency, new technologies for compression ignition engines are in development. One of them relies on reducing the heat losses of the engine during the combustion process as well as to devise injection strategies that reduce soot formation. Therefore, it is necessary a better comprehension about the turbulent kinetic energy (TKE) distribution inside the cylinder and how it is affected by the interaction between air flow motion and fuel spray. Furthermore, new diesel engines are characterized by massive decrease of NOx emissions. Therefore, considering the well-known NOx-soot trade-off, it is necessary a better comprehension and overall quantification of soot formation and how the different injection strategies can impact it. The present study aims to define a methodology to analyze the velocity field and consequently TKE distribution as well as to characterize soot formation inside of a real bowl geometry considering different operating conditions. For that purpose, two different optical techniques were simultaneously applied in this study. On the one hand, in-cylinder velocity fields were measured by using 2D standard Particle Image Velocimetry (PIV) under injection (non-reactive ambient) and motored conditions by using single injection strategy. On the other hand, soot formation was quantified by Diffused back-illumination imaging technique (DBI) under firing conditions and multiple injection pattern. The experiments were carried out in a single cylinder optical engine based in a commercial GM MDE light duty diesel engine with specific bottom and side optical accesses from the liner and the piston. As the optical piston features the same metal bowl geometry, it was necessary to solve significant hurdles to accurately implement the optical techniques under fully real engine conditions. Injection events for PIV measurements were performed at different laser timings with a vertical laser sheet centered in the middle of the cylinder using a single injection strategy. For the DBI measurements, tests were performed in 3 different firing conditions, using four injection events and three injection pressures. Results indicate that, in comparison with motored condition, fuel spray reduce flow velocity and impact directly on TKE distribution. DBI measurements highlight also that, as the load increases, the KL value increases as well. Furthermore, the results show that the injection timing impacts directly in the KL value.