Due to the increase in the greenhouse effect, lowering emissions is becoming a certain issue all over the world. It is a concern to develop alternative options to minimize the spread of exhaust gases. For this purpose, in this study, the plug flow reactor in the system consisting of solid oxide fuel cell, reactor, electric motor, battery, burner, and the heat exchanger is considered. Numerical modeling of hydrogen gas generation in a plug flow reactor is studied. The reactor indicated on-board hydrogen gas generation for an electric motor automobile has not been modeled in the literature yet. Autothermal reforming of isooctane is simulated in the comsol multiphysics software program in the reactor particularly. Conversion of isooctane and H2O is examined at different overall heat transfer coefficients, input temperatures, and steam/carbon ratios. Also, there are certain differences between adiabatic and non-adiabatic conditions. The produced synthesis gas of hydrogen drastically increases in the non-adiabatic case. The obtained results from the model are compared with experimental data obtained from the literature. H2 production at the end of the autothermal reforming process indicates that the power provided from the reactor can operate a motor of an automobile. In this study, the achieved power is 65.8 kW (88 HP) and is sufficient for an automobile. Simulation results show that the reactor volume of 75 L supplies 0.18 mol−1 of H2 and 0.08 mol−1 of CO in the non-adiabatic case.