In-cylinder swirl analysis of different strategies on over-expanded cyclies

Abstract

Innovative series hybrid vehicles have a small Internal Combustion Engine used as a “range extender”. This engine should work at steady conditions whenever is running. Therefore its development is quite different from engines intended to be driven (unsteady working conditions, such as accelerations). For thıs applicatıon the engine development seeks optimisation on a specified speed/load condition. Previous work proved the concept of over-expansion, as a mean to enhance thermal efficiency of spark ignition engines, even beyond the efficiency of common Diesel engines. There are two ways of performing over-expansion through variation of inlet valve timing: early inlet valve closure (EIVC) and late inlet valve closure (LIVC). To further enhance efficiency, these engines should work with lean or extra lean mixtures. which are very sensitive to in-cylinder charge motion. In order to improve fast burning rates at lean conditions one should optimise turbulence at the end of the compression stroke. A small engine geometry and mesh was created in GAMBIT and later FLUENT was used to perform calculations of the in-cylinder fluid dynamics during intake and compression strokes. These calculations were performed with both described over-expanded valve strategies. The results are compared with engine performance data using the same strategies.