Investigation of the Effect of Compression Ratio and Different Fuels on CO2 Emissions

Air pollution caused by the exhaust gases of internal combustion engines threatens the future of these machines. CO₂, which is normally non-polluting but causes global warming, has necessitated limiting the emission of this gas. Therefore, reducing CO₂ production at its source is the most effective method. In particular, the use of fuels with a high H/C ratio, such as compressed natural gas (CNG), significantly reduces CO₂ emission. In this study, the contribution of different mechanisms to CO₂ reduction was examined by combining both thermal efficiency and fuel types. Experiments were conducted with gasoline and CNG fuels at different compression ratios and mixtures. When CNG was used instead of gasoline in stoichiometric mixture, CO₂ emission was reduced by 23% at a brake mean effective pression (BMEP) of 5 bar. Approximately 8% less CO₂ was produced when operating with a lean mixture (λ = 1.6) instead of a stoichiometric mixture for both fuels. In the experiments conducted with CNG, CO₂ emission decreased by 1.5% when compression ratio was changed from 10.5 to 14. However, as the compression ratio increased, the volumetric efficiency decreased at constant BMEP. Therefore, the efficiency coefficient, which takes into account the effect of volumetric efficiency, was defined and it was observed that thermal efficiency could increase up to 7% by increasing the compression ratio from 10.5 to 14. Finally, when comparing CNG fuel with a high compression ratio (ε = 14) and ultra-lean mixture, and gasoline fuel with a low compression ratio (ε = 10.5) and stoichiometric mixture, it was observed that CO₂ emission decreased by around 33%.