Tank-to-Wheel Greenhouse Gas Emissions of Methanol–Gasoline Blends: Vehicle Emissions and Fuel-Based Emission Factors

Renewable methanol has attracted increasing attention as an alternative fuel for reducing greenhouse gas (GHG) emissions from transport. However, comprehensive evaluations of tank-to-wheel (TTW) GHG emissions, including CO2, CH4, and N2O, from methanol–gasoline blends across wide blend ratios and vehicle operating conditions remain limited. This study investigated the effects of methanol blending and driving conditions on TTW GHG emissions and compared fuel-property-based CO2 emission factors with vehicle-based GHG emission factors. Two conventional internal combustion engine vehicles and one hybrid electric vehicle were tested with M0–M20 over five driving cycles, with city, highway, and combined emissions evaluated using the 5-cycle method. A flex-fuel vehicle was also tested with M0–M100. For low-level blends, CO2 emissions generally decreased with increasing methanol content; among the statistically significant relationships, the regression-predicted reductions at M20 ranged from 1.9% to 6.2% depending on the vehicle and driving cycle. Using the 5-cycle method, the combined TTW GHG emissions of M20 were 3.5%, 4.1%, and 2.6% lower than those of M0 for Vehicles A, B, and C, respectively, while CH4 and N2O showed no consistent trends. In the flex-fuel vehicle, CO2, CH4, and N2O emissions decreased significantly with increasing methanol content, with predicted reductions at M100 relative to M0 of 8.8%, 64.3%, and 58.5%, respectively. Vehicle-based CO2 emission factors were 0.2–0.5% lower than fuel-property-based values, whereas vehicle-based TTW GHG emission factors were 0.1–0.6% higher when CH4 and N2O were included. These findings highlight the importance of considering fuel properties and actual vehicle emissions when evaluating methanol–gasoline blends.