The thermodynamic characteristics of stratified-charge combustion inside a wall-guided gasoline direct injection (GDI) engine are investigated experimentally and the effects of start of injection (SOI) on the combustion stability are studied in this work. Numerical simulation of the gas flow inside the GDI engine starting from the beginning of intake stroke to the point of start of spark ignition (SOS) are conducted. By coupling the heat release rate analysis with the geometry data of gas mixture composition obtained from numerical simulation, substantial insight into the combustion behaviors can be obtained. The effect of cycle-to-cycle variation on the combustion stability can be predicted by the equivalence ratio distribution obtained from numerical simulation. Results show that with the same amount of fuel injected and the same timing of ignition the stratified-charge combustion produces 10% larger imep than that produced by stoichiometric combustion at the expense of an insignificant combustion stability if proper injection timing is adopted. Emission data obtained from the exhaust gas analyzer indirectly confirmed the effects of SOI on the combustion behaviors inside the GDI engine. (C) 2019 Elsevier Ltd. All rights reserved.