The effect of combustion chamber shape on cylinder flow and lean combustion process in a large bore spark-ignition CNG engine

The combustion process and fluid flow in a spark-ignition natural gas engine with three kinds of different combustion chambers are calculated by coupling multi-dimensional computational fluid dynamics (CFD) code AVL FIRE. The calculated results have been validated by experimental results firstly. Through the simulations on three different combustion chambers in this research, it can be found that turbulence intensity has almost no influence on combustion process during the phase of flame kernel development. While turbulence intensity has a direct and obvious influence on flame propagation velocity in rapid combustion period, and the stronger turbulence intensity leaded to a higher flame propagation speed. It can increase the inverse extrusion flow through enlarging the squish area appropriately to improve the turbulent kinetic energy (TKE) in cylinder, and which could promote the flame propagation. Meanwhile, suitable squeeze shape of combustion chamber can achieve the balances of flame propagation and oxides of nitrogen (NOx) emissions.