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Dogu, Yahya/0000-0003-0474-2899 WOS: 000468368400038 In this study; for a sequential dual ignition gasoline engine, the effects of ignition advance on engine characteristics and in-cylinder flame propagation have been numerically investigated for CNG usage with an in-cylinder combustion model. A CFD model for a single cylinder of the four-cylinder Honda L13A4 i-DSI engine with a sequential dual spark ignition is constructed in STAR-CD software for CNG usage by considering all components related to the combustion chamber (intake-exhaust manifold connections, intake-exhaust valves, cylinder, cylinder head, piston, spark-plugs, etc.). By using the CFD analyses for CNG usage, the optimum ignition advance is determined for the prescribed engine operating conditions of 3000-rpm engine speed, 10.8:1 compression ratio, and 1.2 air-fuel ratio. Analyzes are performed by varying the ignition advance in a wide range (60 degrees-10 degrees CAD and 55 degrees-5 degrees CAD ignition advance for the lst-2nd spark plugs, respectively). For engine operating conditions examined, it has been determined that the 30 degrees-25 degrees CAD advance value for the 1st-2nd spark plug from the top dead point is the optimum ignition advance in terms of engine performance and emission balance. For CNG, ignition advances have increased compared to gasoline. The in-cylinder flame propagation is visualized and evaluated for all investigated conditions.