It is presented a novel theory for designing spark ignition (SI) engines based on tests in three SI engines, three scientific methodologies, and thermodynamics laws applied to Otto cycles. Mathematical modeling used the optimal thermal efficiency for the Otto cycle and data on octane rating for liquid fuels and the methodology for methane number for gaseous fuels. Before, two methodologies had been developed for quantitative estimation of energy quality and exergy efficiency for gaseous fuels in SI engines. Equations are proposed to correlate exergy efficiency, entropy, energy recovered, maximum thermal efficiency, and certain fuel physicochemical properties for SI engines. Also, tests and correlations between fuel properties and octane rating are presented to validate the hypothesis. Besides, it presented the performance data of an SI engine converted and optimized for biogas, which was...

It is presented a novel theory for designing spark ignition (SI) engines based on tests in three SI engines, three scientific methodologies, and thermodynamics laws applied to Otto cycles. Mathematical modeling used the optimal thermal efficiency for the Otto cycle and data on octane rating for liquid fuels and the methodology for methane number for gaseous fuels. Before, two methodologies had been developed for quantitative estimation of energy quality and exergy efficiency for gaseous fuels in SI engines. Equations are proposed to correlate exergy efficiency, entropy, energy recovered, maximum thermal efficiency, and certain fuel physicochemical properties for SI engines. Also, tests and correlations between fuel properties and octane rating are presented to validate the hypothesis. Besides, it presented the performance data of an SI engine converted and optimized for biogas, which was...