For some time past it has been observed that piston engines of the spark ignition type display wide variations in the combustion process as indicated, e.g., by the pressure development from one cycle to another. These random variations occur although overall engine operating conditions are apparently kept constant. The engine's mechanical (power output) and chemical (exhaust gas emissions) performance are the result of an averaging out of the individual cycles. One of the points in question is the existence of a correlation between the random variations of the combustion process and the exhaust gas emission. A solution to the exhaust emission problem might then be attempted by decreasing the magnitude of the variations. The report tries to establish the relationship to design a system capable of correlating certain parameters of the combustion process.