Correlation between Simulated Volume Fraction Burned Using a Quasi-Dimensional Model and Flame Area Measured in an Optically Accessible SI Engine

Multi-fuel operation is one of the main topics of investigative research in the field of internal combustion engines. Spark ignition (SI) power units are relatively easily adaptable to alternative liquid-as well as gaseous-fuels, with mixture preparation being the main modification required. Numerical simulations are used on an ever wider scale in engine research in order to reduce costs associated with experimental investigations. In this sense, quasi-dimensional models provide acceptable accuracy with reduced computational efforts. Within this context, the present study puts under scrutiny the assumption of spherical flame propagation and how calibration of a two-zone combustion simulation is affected when changing fuel type. A quasi-dimensional model was calibrated based on measured in-cylinder pressure, and numerical results related to the two-zone volumes were compared to recorded flame imaging. Gasoline, ethanol, methane and hydrogen were used as fuels and the aforementioned comparison was performed for each case. In order to identify the influence of specific properties, intake pressure, air-fuel ratio and spark timing were kept constant for al fuel types. Overall the spherical flame assumption was found to ensure acceptable results and the correlation between turbulence intensity and flame propagation emphasized the importance of proper description of localized scales at which chemical reactions occur behind the flame front.