Analyses of Mechanism on Roadside Pollution by on board Emissions Measurement System (Transient Characteristics of NOx Emissions in Vehicles with EGR System in Real Traffic Conditions)

In order to clarify the reason why the NOx emissions factor is higher at vehicle acceleration at intersections etc, two freight vehicles with EGR system for the reduction of NOx were tested by onboard NOx measurement system. Higher NOx emissions factor was observed at lower gear operations in each vehicle. The NOx emissions characteristics were analyzed in the view of engine torque, NOx mass emissions and EGR ratio, considering the rate of engine speed change. As the results, it was found that lower gear operations made the rate of engine speed change higher and also made EGR ratio lower, resulting in higher NOx emissions. This seems to be one of the factors to engender the intensive NOx pollution at roadside.