Simulation of exhaust gas residuals in a turbocharged, spark ignition engine

Highly downsized, Direct Injection (DI) engines benefit strongly from cylinder scavenging where possible, to reduce internal residuals thereby reducing the occurrence of knock. Some researchers also suggest that non-homogeneous distribution of internal residuals at high load could contribute to pre-ignition or ‘mega-knock’ with much higher pressure amplitude than that of common knock.

For this reason, a computational study was conducted to assess the residual gas fraction and in-cylinder distribution, using the combustion geometry of the three cylinder, 1.2L MAHLE Downsizing engine, which has proven to be a very robust and reliable research tool into the effects of combustion effects under a number of different operating conditions. This study used a CFD model of the cylinder gas exchange. ES-ICE coupled with STAR-CD was employed for a moving mesh, transient in-cylinder simulation. The boundary conditions were provided by a correlated 1-D (GT-power) model, with several scenarios simulated including engine speed, valve overlap and port geometry. The residual distributions at part load with different inlet ports were also assessed.