Heavy duty vehicle engines currently mainly use diesel and natural gas,and engine companies are developing engines that use methanol fuel.This article investigates the carbon emissions of heavy-duty vehicle engines using different fuels through experiments.Three heavy-duty engines with similar displacements,fueled with diesel,natural gas,and methanol respectively,were subjected to WHTC cold and hot state tests.Based on the emission results and fuel consumption in the operating cycle,the theoretical fuel and specific carbon emissions of pollutants were calculated separately.The results indicate that diesel heavy-duty vehicle engines have the highest combustion thermal efficiency and the lowest specific carbon emissions,while methanol heavy-duty vehicle engines have the lowest combustion thermal efficiency and the highest specific carbon emissions.