Feasibility study on mornitoring NOx emissions of China-VI natural gas engines with the NOx sensor

Based on a heavy-duty stoichiometric natural gas engine which can meet the requirement of China-VI regulations, steady-state and transient cycles were carried out to measure the exhaust NOx concentration out of TWC by a NOx sensor and a gaseous emission analyzer simultaneously. The results show that the measurement results of NOx sensor are relatively higher when the NOx emission concentrations are lower than 50 ppm, and the accuracy is not high enough. Due to the obviously smaller proportion of lower NOx concentrations, especially for the concentrations below 10ppm, the average concentration measured by the NOx sensor was 24.3% higher than the average concentration measured by the emission analyzer during the whole testing process. When the NOx concentrations are higher than 50ppm, the frequency distributions of NOx concentration measured by NOx sensor and emission analyzer are almost the same, and the deviations of average NOx concentrations between these two measurement methods can be within ±4.5%, which represent a significantly high reliability of NOx sensor.