Computational study of the multi-injector isobaric combustion concept in a heavy-duty compression ignition engine

Compared to the conventional diesel combustion engine that is equipped with a single centrally installed injector, the multi-injector spray-combustion concept has the potential to achieve higher thermal efficiency. In this work, a numerical study to explore the combustion characteristics of the multi-injector concept on an isobaric combustion compression ignition engine was conducted. The simulation results reveal that, compared to the single-injector case, a significantly lower heat transfer loss was induced using two side injectors owing to the less intense flame-piston interaction. In addition, good fuel flexibility was achieved using multiple injections, which was attributed to the initially generated hot regions downstream of the injection trajectory. To further optimize the engine combustion performance, the effects of several major design parameters such as the injector location and rotation angle, hole number and gap angle, spray angle, and piston geometry were investigated. The results showed that the spray/flame-wall interaction had a significant effect on the development of combustion heat release. Various design parameters showed a significant impact on the combustion heat release during the late combustion period when an intense flame-wall interaction was occurring. To attain a better engine performance, the injector location and nozzle design should be adequately adjusted according to the inner piston radius and depth. The reduction of intake temperature and introduction of an appropriate amount of isochoric combustion process were found to further promote the engine work, making it possible to achieve a thermal efficiency of over 50%.