Regulated and unregulated emissions from Euro VI Diesel and CNG heavy-duty vehicles

This study compares emissions from Euro VI-D Diesel and CNG buses across temperatures from -7 °C to 35 °C. Pollutants including NOx, THC, CH₄, CO, NH₃, N₂O, HCHO, Solid Particle Number larger than 23 nm (SPN23) and larger than 10 nm (SPN10) were measured. Both buses complied with Euro VI-D but exceeded European Commission's proposed Euro 7 limits, notably for NOx and SPN10. The CNG bus also surpassed NH₃, CO, and CH₄ limits, while the Diesel exceeded N₂O limits. High NH₃ emissions were observed from CNG (up to 0.320 g/kWh), with Diesel reporting lower levels (up to 0.021 g/kWh). HCHO emission from both vehicles were very low. SPN23 was under limits, but SPN10 exceeded Euro 7 limits at cold start tests. CNG's CH₄ and N₂O emissions constituted up to 4.6% and 3.5% of CO₂ equivalent, respectively. Diesel bus showed negligible CH₄ but N₂O emissions represented up to 37% of CO₂ equivalent.