Applying Advanced CFD Analysis Tools to Study Differences between Start-of-Main and Start-of-Post Injection Flow, Temperature and Chemistry Fields Due to Combustion of Main-Injected Fuel

This paper is part of a larger body of experimental and computational work devoted to studying the role of close-coupled post injections on soot reduction in a heavy-duty optical engine. It is a continuation of an earlier computational paper. The goals of the current work are to develop new CFD analysis tools and methods and apply them to gain a more in depth understanding of the different in-cylinder environments into which fuel from main- and post-injections are injected and to study how the in-cylinder flow, thermal and chemical fields are transformed between start of injection timings. The engine represented in this computational study is a single-cylinder, direct-injection, heavy-duty, low-swirl engine with optical components. It is based on the Cummins N14, has a cylindrical shaped piston bowl and an eight-hole injector that are both centered on the cylinder axis. The fuel used was n-heptane and the engine operating condition was light load at 1200 RPM. The in-cylinder processes investigated are typical and include fuel injection and the subsequent growth of a largely non-combusting fuel-rich vapor jet, pre-mixed burn followed by sharp reductions in fuel and oxygen concentrations, limited air entrainment that coincides with a transition from pre-mixed burn to mixing-controlled burn, and the end of main-injection, after which many in-cylinder processes tend back toward their pre-injection values. What distinguishes the work is the ability to use the newly developed tools and methods so that the aforementioned in-cylinder processes of interest can be linked in a quantifiable and visual way.