CFD Study of Heat Transfer Reduction Using Multiple Injectors and Optimized Geometry in a DCEE Concept 2019-01-0246

A study was performed on how multiple injectors can be used to decrease heat transfer losses in a CI engine through a changed flow pattern. Specifically, it was investigated how the geometry can be changed to better suit the multiple injector concept. The primary target for the automotive industry has for many years been the reduction of greenhouse gas emissions. One simple solution for dealing with this is to improve fuel economy through enhanced efficiency. A promising concept in this area is the DCEE concept, showing efficiencies of 56 %. In this concept, the leftover exhaust energy is used for a second expansion. Thus, reducing heat transfer losses becomes increasingly important compared to normal CI engines. It has been proven in earlier studies that reduction of heat losses can be achieved by using multiple injectors placed at the rim of the bowl. This achieves longer distance to the wall as well as sprays aimed into the cylinder as opposed to the centrally mounted injector. However, problems have been found with the typical bowl using a pip shape. Aiming the sprays towards the combustion chamber center will mean that the pip is a target for impingement. In this study, a flat bowl is therefore suggested and investigated. Well-validated RANS CFD simulations were performed using the software Converge on a 2.33 liter Volvo D13 single-cylinder engine. Reference cases with the standard bowl geometry were compared to multiple injector cases using the flat bowl geometry. Also, multiple injector cases from previous studies using the standard bowl were compared to the flat piston cases. Findings showed that the sprays can be directed with more freedom without the pip. This lead to reduced heat transfer losses both compared to the reference case and standard multiple injector case.