Karakteristik Pembakaran Bahan Bakar GEM (Gasoline-Ethanol-Methanol) Berdasarkan Data Ignition Delay Time Pada Simulasi Closed Homogeneous Batch Reactor = Combustion Characteristics Testing of GEM (Gasoline-Ethanol-Methanol) Fuels Based on Ignition Delay Time Data in Closed Homogeneous Batch Reactor Simulation