The effect of combustion chamber geometry on in-cylinder flow and combustion process in a stoichiometric operation natural gas engine with EGR

Abstract

The performances of three representative chamber geometries, i.e. the nebula, cross and reentrant geometries, in a stoichiometric operation natural gas engine with exhaust gas recirculation (EGR) were investigated through experiments and simulations. The results indicate that the cross and reentrant chambers show quite similar performances in improving the combustion and thermal efficiency, followed by the nebula chamber. The asymmetrical turbulence distribution and hence asymmetrical flame propagation, which reduce the flame development in a certain direction, should be one of the main reasons for increasing the combustion duration with nebula chamber. The cross chamber has similar issues; and its grooves could further reduce the flame surface. Its higher combustion rate than that of the nebula chamber can be mainly attributed to the stronger squish effect which results in a stronger turbulence during initial combustion stage. The reentrant chamber has the highest turbulence intensity before top dead center (TDC) and hence a higher flame surface density. Furthermore, it shows a more symmetrical flame propagation, and also a larger flame surface development during the late period of combustion. However, the effect of its turbulence on flame propagation reduces obviously after TDC since the high intensity region rapidly separates from the flame surface.