The higher H:C ratio (Hydrogen versus Carbon ratio) of 4:1 for Methane, from LNG, compared to 2:1 for Gasoline , Kerosene and Diesel oils (having a C6-20 hydrocarbons chain) determines a 15% higher calorific value per unit of weight and net 25-30% lower emissions of CO2 (assuming same energy efficiency).
LNG is pure Methane, with only marginal quantities of C2-C3, no aromatics, no heavier HC, no sulphur, no heavy metals (no soot), that, instead are present in Petrol. Its combustion is clean, it generates less CO2 and more H2O, giving a quenching effect that substantially reduces by over 85% the formation of NOX. The engines can be operated at lower peak temperatures thanks to the good gas combustion and favourable physical factors, which also means that lower maintenance costs are incurred. The maximum combustion temperature of CH4 is 60 K lower than that of kerosene (CH4 = 2491 K, kerosene = 2550 K).