Regulated, greenhouse gas, and particulate emissions from lean-burn and stoichiometric natural gas heavy-duty vehicles on different fuel compositions

The gaseous and particulate matter (PM) emissions from three heavy-duty natural gas vehicles, including a lean-burn bus with an oxidation catalyst and two stoichiometric Class 8 trucks with three-way catalysts were evaluated. Testing was performed on a range of three to seven different test fuels with varying Wobbe and methane numbers. The lean-burn vehicle showed general trends of higher emissions of nitrogen oxides (NOx) and non-methane hydrocarbons (NMHC), and lower emissions of total hydrocarbons (THC), methane (CH4), and formaldehyde, and improved fuel economy for the fuels with low methane numbers. The stoichiometric trucks showed some trends toward lower THC, CH4, and NOx emissions with the low methane number fuels, whereas some increases in NMHC, carbon monoxide (CO), and ammonia (NH3) emissions were also observed. Results of the particle size distributions revealed bimodal size distribution profiles for all three vehicles, with a predominant nucleation mode close to 10 nm for the lean-burn bus and one of the stoichiometric trucks.