Modeling and numerical simulation of combustion in the cylinders of spark-ignition and compression-ignition internal combustion engines (ICEs) provide a considerable contribution in engines engineering and the optimization of engines performance, efficiency, and emissions. This chapter demonstrates the application of the reactor approach and the chemical nonequilibrium model (Chapters 1–3) to the simulation of combustion in the cylinder of the spark-ignition ICE aiming to predict the variation in ionized particle concentration as control variables. It is known that the combustion of hydrocarbon fuels with oxidizers at high pressures and temperatures is accompanied by the output of some ionized substances. Research on the ionization in flames was started in the mid-1950s for the purpose of optimization of magnetohydrodynamic generators as well as the study of ionized particle formation in combustion products of propulsion systems, particularly in the thrust chambers and exhaust plumes of rocket engines [1, 160, 215, 227, 228]. This study was later extended to the combustion in the ICE for the purpose of employing empirical and theoretical data on the ionization of combustion products for engine performance control intended for the optimization of the combustion process, the reduction of fuel consumption, the reduction of exhaust gas emission, the optimization of the exhaust gas recirculation (EGR) process, etc. [292–305].