Various alternative fuels are candidates for partial or total replacement of fossil fuel for spark ignition (SI) engines used in the transport sector. These include ethanol (already in use in blends), compressed natural gas (CNG) (popular in certain markets) and liquid petroleum gas (LPG) (popular in other markets). These fuels are all suitable for use in SI engines, but their physicochemical parameters differ from those of standard petrol. Specifically, their carbon weight fraction and the energy density differ significantly; these two factors (among others) strongly control fuel consumption and exhaust emissions of greenhouse gases (GHG), including carbon dioxide (CO2). This study considers chassis dynamometer data obtained under laboratory conditions. Results from the literature and from experiments conducted by the authors show a range of responses in terms of exhaust emissions of GHG for different fuel types. CNG in particular shows low CO2emissions, but ethanol blends show virtually no change in CO2emissions and an increase in volumetric fuel consumption.
Bielaczyc, P., Woodburn, J., Szczotka, A., & Pajdowski, P. (2015). The Impact of Alternative Fuels on Fuel Consumption and Exhaust Emissions of Greenhouse Gases from Vehicles Featuring SI Engines. In Physics Procedia (Vol. 66, pp. 21–24). Elsevier B.V. https://doi.org/10.1016/j.egypro.2015.02.011