A MEAN VALUE MODEL FOR ESTIMATION OF LAMINAR AND TURBULENT FLAME SPEED IN SPARK-IGNITION ENGINE

Flame velocity is the main parameter for determination of combustion propagation in a spark-ignition engine. The first part of combustion that consists of flame initiation and flame kernel growth has laminar velocity. For a certain radius of kernel growth, transition to turbulent flame occurs; afterwards, the flame can be described as turbulent. This paper investigates the relationship between fuel properties and engine operation parameters, their influence on flame velocity and their ability to calculate the time delay from ignition to 50% mass fraction burned (MFB) that is used for adjusting the spark advance. The GT-Power software is employed to simulate the combustion process of a spark-ignition (SI) engine. The flame speed mean value model is applied to determine the laminar flame speed under different amounts of unburned mixture, temperatures and pressures. The results show that mixture with less than the stoichiometric ratio has the greatest laminar flame speed. At higher temperature, the difference between poor and rich mixture is significant for laminar flame speed. On the other hand, the relationship between turbulence intensity and engine speed is almost linear. The cylinder pattern used to create turbulence during the intake and compression strokes defines the slope between the engine speed and turbulent flame speed. The mean value flame speed model was capable of determining the combustion phasing and predicting spark ignition in advance.