A Comparison Between the Gaseous and Particulate Emissions from Diesel and Natural Gas Yard Tractors

We used a heavy-duty chassis dynamometer to measure gaseous and particulate emissions from natural gas and diesel-powered yard tractors tested on different driving cycles, some being representative of typical yard tractor operation. The natural gas yard tractors were operated with fuel blends of varying compositions, including a renewable natural gas (RNG) fuel. Results showed weak fuel compositional effects on gaseous and particulate emissions. Nitrogen oxide (NOx) emissions showed mixed trends between the natural gas and diesel yard tractors, with some test cycles demonstrating important NOx reductions for the natural gas yard tractors. Particulate matter (PM) and black carbon emissions were found at similar levels for the natural gas and diesel vehicles, with the diesel yard tractor showing systematically higher total particle number emissions and solid particle number emissions above and sub 23 nm in diameter. Overall, the greenhouse gas (GHG) and the life cycle GHG emissions for the natural gas vehicles were lower compared to those of the diesel vehicle, suggesting a positive impact of using fossil natural gas and RNG fuels than fossil diesel fuel on a life cycle basis.