Review and Performance Evaluation of Fifty Alternative Liquid Fuels for Spark-Ignition Engines

The currently discussed alternative fuels for spark-ignition engines are numerous. A total of 50 different liquid fuel compounds were identified from the literature. Using a thermodynamic engine model, which adapts the engine to the fuel and thereby determines the performance potential of a fuel candidate, the different fuel candidates are investigated in terms of efficiency, tank-to-wheel CO2 emissions, and volumetric fuel consumption. Additionally, the particulate matter index (PMI) of each compound is calculated to estimate the soot emissions. Furthermore, possible negative impacts on health and the environment are taken into account. The only compound leading to a volumetric fuel consumption lower than gasoline is found to be anisole (8.0 L/100 km), at the cost of increased CO2 emissions (225 g/km) and PMI levels (2.27 bar(-1)). Minimum tank-to-wheel CO2, emissions are achieved by isopropanol (175 g/km) but at the expense of increasing volumetric fuel consumption (10.2 L/100 km). CO2 reduction potential of 2,2,3-trimethylbutane (180 g/km) is not as significant; in return, the increase in volumetric fuel consumption (8.5 L/100 km) is less pronounced. tert-Butanol and isopropanol result in minimum PMI values (0.04 bar(-1)), while tert-butanol shows a slightly worse performance than isopropanol, with a full load efficiency of 36.8% versus 37.1%, respectively. Although they contain oxygen, levulinates are predicted to form a high amount of particulate matter.