NOx Emission Model of Heavy-Duty Diesel Vehicles Considering Exhaust Temperature Under Real-World Driving Conditions

Selective catalytic reduction technology (SCR) is one of the commonly used technologies to reduce nitrogen oxide (NOx) emissions from heavy-duty diesel vehicles. The efficiency of NOx conversion in the SCR system is closely related to the exhaust temperature. However, the existing NOx emission models primarily focus on vehicle driving conditions, neglecting the correlation with exhaust temperature. Thus, it increases the uncertainty of NOx emission measurement results, and challenges the establishment of emission inventory and the assessment of emission reduction policies. This study established a NOx emission rate library and a model based on actual vehicle operating conditions and measured emission data. Subsequently, an exhaust temperature model utilizing vehicle specific power (VSP) and heat loss coefficient was developed. Based on this, based on the chemical reaction principle in the SCR system, a NOx emission model incorporating exhaust temperature was derived. Finally, the proposed NOx model and the MOVES model (MOtor Vehicle Emission Simulator) were employed to estimate NOx emissions, which are then compared and analyzed against actual emissions. Results demonstrate the effectiveness of the proposed NOx emission model in real-world conditions, with relative errors of 9. 1%, 3. 9%, and 3. 3% observed across three heavy-duty diesel buses. These errors represent a reduction of 24. 0, 13. 1, and 16. 3 percentage points, respectively, when compared to the MOVES model. Additionally, analysis of NOx emission characteristics under different operating conditions reveals that the average NOx conversion rate of heavy diesel trucks is 39. 2 percentage points higher than that of diesel buses. © 2024 South China University of Technology. All rights reserved.