试验针对车用发动机在WHTC循环试验中的NOx污染物排放，根据试验程序和测量方法建立了NOx排放的数学计算模型，并通过理论方法对模型中测量重复性、稀释排气流量、排气污染物浓度、NOx湿度校正系数和实际循环功等各种参数的相对标准不确定度进行了分析，最终得到了NOx排放的不确定度评定结果。结果表明，WHTC试验NOx比排放量的合成相对标准不确定度为5%，满足标准法规对NOx测量的精度要求。从不确定度的评定过程可以看出，在试验时要保证发动机和后处理系统状况良好，工作稳定，并在日常保养时加强定容稀释系统、排放分析系统和发动机测功机系统的标定和维护工作。%This test focuses on NOx emissions during the WHTC cycle test from automotive engine. Accord-ing to the test procedure and measurement method, the mathematics model of NOx emissions was estab-lished. Relative standard uncertainty of measurement repeatability, dilute exhaust flow, NOx emissions con-centration, humidity correction coefficient, actual circulation work and so on various parameters were ana-lyzed by means of theoretical model. Finally evaluation results of uncertainty of NOx emissions were ob-tained. Results show that the synthesis of relative standard uncertainty of NOx emissions during WHTC test was 5%, satisfying the requirement of the standards and regulations for NOx measurement precision. Seen from the process of uncertainty evaluation process, the engine and after-treatment system should be in good condition and work stable in the test. The calibration and maintenance work of constant volume dilution system, emission analysis system and engine dynamometer system should also be strengthened during daily maintenance.
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