Abstract: In order to study the emission assessment method of real road PEMS test of vehicles, one heavy-duty diesel city vehicle is selected and three real road PEMS tests with different loads are carried out. The test results show that the cold start stage and hot stage of the engine are defined by the coolant temperature reaching 30 °C and 70 °C, and from the cumulative emissions, although the maximum proportion of cold start stage time is only 6.8%, NOx emissions reach 23.7%～82.4% in the cold start stage, and its emissions cannot be ignored. The relationship between window power ratio, specific emission and temperature of selective catalytic reduction (SCR) in the cold start stage is analyzed, and the emission calculation method based on the power-based window method of China VIB stage is proposed, the maximum specific emission value in all windows is taken in the cold start stage, the effective window is taken above the 10% power threshold in the hot stage, the 90% quantile value of the effective window ratio emission is taken as the hot stage emission, the weight coefficients of the cold and hot stages are set to 0.14 and 0.86 respectively, and the weighted sum obtains the real road driving ratio emission of the vehicle. Through the analysis of three sets of test results with different emission levels, compared with the power-based window method of setting the power threshold adopted by the current heavy-duty China VI emission standard, the NOx specific emission is increased by more than 25%, so the new emission evaluation method that incorporates cold start into the calculation will increase the difficulty of passing the emission test.

Key words: Heavy-duty diesel urban vehicle; NOx emission; Cold start emission

摘要： 为研究车辆实际道路车载尾气检测设备（PEMS）测试排放评估方法，选取了 1 辆重型 柴油城市车辆，分别进行 3 次不同载荷的实际道路 PEMS 测试。试验结果表明，以冷却液温 度到达 30 ℃、70 ℃界定发动机冷启动和热态，从累计排放量上看，虽然冷启动时长占比最 大仅为 6.8%，但是 NOx 排放在冷启动阶段达 23.7%～82.4%，其排放不可忽略；分析冷启动 阶段的窗口功率比、比排放和选择性催化还原技术（SCR）前温度的关系，提出基于国六 b 阶段的功基窗口法排放计算方法，冷启动阶段取所有窗口中的最大比排放值，热态以 10%功 率阈值以上为有效窗口，取有效窗口比排放的 90%分位值作为热态排放，冷、热态分别设置 权重系数为 0.14 和 0.86，加权求和得到车辆实际道路行驶比排放。通过不同排放水平的 3 组 试验结果分析，相比现行重型国六排放标准采用的设置功率阈值的功基窗口法，NOx 比排放 升高 25%以上，所以将冷启动纳入计算的新的排放评价方法会加大排放测试的通过难度。

关键词: 重型柴油城市车辆；NOx 排放；冷启动；排放特性