An experimental study on the NO x emission characteristics of state-IV city bus

Using portable emission measurement system, an experimental study on the emission characteristics of two city buses meeting national stage-IV emission regulation in practical operation are conducted. The results show that NO x emissions from vehicles are greatly affected by vehicle driving cycle: when driving on open road with higher vehicle speed and engine output power, the NO x emission rate is lower, and vice versa; When vehicle speed increases from 15 km/h to 55 km/h, NO x emission rate can be reduced by 70%, while the time proportion of urea injection can rise by 25 percentage points. Hence, raising vehicle speed is one of the effective means for giving full play to the advantage of stage-IV vehicles in emission and improving traffic status.