Complexity Investigation of Cycle to Cycle Pressure Variations in a Spark Ignition Engine with Natural Gas versus Various Equivalence Ratios

In this study, a number of tests are conducted on a four-cylinder spark ignition engine with natural gas and the cycle to cycle variations of peak pressure max P and peak pressure angle Pmax  in the engine are analyzed for nine different equivalence ratios. By using multi scale entropy technique, it is shown that the complexity of peak pressure and peak pressure angle depends on the equivalence ratio variations. Thereby, a limitation is found for optimum equivalence ratios that can be used for controlling the combustion process and improving engine performance.