Evaluation of pollutant and greenhouse gas emission reduction effect of vehicles burning neat methanol

Methanol, as a low-carbon vehicle fuel, is a crucial pathway to promote decarbonization of the transportation sector and secure energy sustainability. The exhaust emissions from a state-of-the-art methanol/gasoline bi-fuel sedan were tested over the Worldwide Harmonized Light Vehicles Test Cycle (WLTC) to demonstrate its potential on pollutants, greenhouse, and secondary ozone abatement. The results indicated that compared to gasoline, burning neat methanol managed to reduce carbon monoxide (CO), total hydrocarbons (THC), non-methane hydrocarbons (NMHC), nitrogen oxides (NOX), formaldehyde, and 1,3-butadiene emissions and greenhouse gases (GHGs), namely carbon dioxide (CO2) and methane (CH4), but slightly increased nitrous oxide (N2O). Moreover, methanol fueling significantly reduced the ozone formation potential of exhaust as 1,3-butadiene was largely eliminated. Relative to gasoline, methanol fueling showed evidently lower CO2-equivalent (CO2-eq) primarily due to the much higher H/C ratio of the fuel molecules, as for both fuels, around 99% of CO2-eq was overwhelmed by exhaust CO2 emissions. Meanwhile, methanol fueling also reduced the CO2-eq of CH4 by 73% predominately during the cold-start, warm-up, and after the gasoline-to-methanol fuel-switch. The increase of 4.5% in the CO2-eq of N2O played a less determinative role in GHG calculation. Overall, the environmental risks, including non-regulated and secondary pollutants, of methanol-fueled vehicles are being alleviated with the improvement of emission control, creating a good foundation for future scale application.