利用车载排放测试系统对两辆国Ⅳ城市公交车在实际运行时的排放特性进行了试验研究.结果表明,车辆的NOx排放受车辆行驶状况影响较大,当行驶道路畅通,车速较高且输出功率较大时,车辆的NOx排放率较低,反之,NOx排放率较高；当车速由15km/h提高到55km/h以上时,NOx的平均排放率可以降低70％,而尿素喷射时间占比可提高25个百分点.因此,提高车速是充分发挥国Ⅳ车辆排放优势,改善交通的有效手段之一.%Using portable emission measurement system, an experimental study on the emission characteristics of two city buses meeting national stage-]V emission regulation in practical operation are conducted. The results show that NO, 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, emission rate is lower, and vice versa; When vehicle speed increases from 15km/h to 55km/h, N0x 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.
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