Large-eddy simulation of flame-turbulence interaction in a spark ignition engine fueled with methane/hydrogen/carbon dioxide

Abstract

A three dimensional large-eddy simulation of in-cylinder charge and combustion process of a spark ignition engine was conducted. Partially stirred reactor combustion model and Arc and kernel tracking ignition model were implemented and applied to capture in-cylinder ignition and turbulent combustion. Interaction between flame and in-cylinder background turbulence for different mixtures of methane, hydrogen and carbon dioxide were studied. When a spark ignition engine is fueled with methane and carbon dioxide, its found that gas heating effect plays a dominant role in flame-induced turbulence. Increase of volume fraction of carbon dioxide has little effect on turbulent flame speed in each combustion phase defined by mean combustion progress variable, but it weakens gas heating effect owing to reduction in burnt temperature. Flame-induced turbulence produces small-scale vortices with high vorticity within gas preheating zone. When engine is fueled with methane, hydrogen and carbon dioxide, large volume fraction of hydrogen leads to high turbulent flame speed, which plays a dominant role in flame-induced turbulence. If volume fraction of hydrogen is small, flame-induced turbulence mainly is determined by gas heating effect due to large volume fraction of carbon dioxide. Flame-induced turbulence produces many vortex-pairs, which are the major sources of wrinkles of flame front. Rotation direction of vortex-pair determines whether the flame front bulges towards unburnt area or burnt area. Level of vorticity value and space size of vortex-pair affect sizes of wrinkles on the flame front.