# Evaluating the Real-World NOx Emission from a China VI Heavy-Duty Diesel Vehicle
###### Abstract  
The manufacturers of China VI heavy-duty vehicles were required to conduct in-service conformity (ISC) tests by using a portable emissions measurement system (PEMS). The moving averaging window (MAW) method was used to evaluate the NOx emission required by the China VI emission standard. This paper presented the results of four PEMS tests of a China VI (step B) N3 category vehicle. Our analyses revealed that the real NOx emission of the test route was much higher than the result evaluated by the MAW method. We also found the data produced during the urban section of a PEMS test was completely excluded from the evaluation based on the current required boundary conditions. Therefore, in order to ensure the objectivity of the evaluation, this paper proposed three different evaluation methods. Method 1 merely set the power threshold as 10% for valid MAWs; Method 2 reclassified the MAWs into \"Urban MAWs\", \"Rural MAWs\" and \"Motorway MAWs\" according to the vehicle speed. Method 3 reclassified the MAWs into \"Hot MAWs\" and \"Cold MAWs\" according to engine coolant temperature. The NOx emission evaluation results for Method 1 were not satisfactory, but those for Method 2 and Method 3 were close to the real NOx emission, the errors were all within \(\pm\)10%. p 2021 11 1335 11.11.11.11.11.11.11.11.11.11.1.11.11.11.1.11.11.11.1.11.11.11.11.11.11.11.11.11.11.11.11.11.11.11.11  
operating conditions than during laboratory certification testing [1, 11, 12]. Under this condition, the real driving emissions (RDE) test (also called PEMS test) protocols using a portable emissions measurement system (PEMS)--which is a compact equipment composed by a portable gas analyzer, a global positioning system (GPS) receiver, a data logging system and so on--had already been adopted by many countries (e.g., Europe, US, Korea) to check the on-road conformity of emissions [5, 13, 14, 15, 16, 17]. In addition, manufacturers were also required to conduct in-service conformity (ISC) testing by using a portable emissions measurement system (PEMS) in China. The PEMS test regulation establishes the requirements for route composition which must cover a wide range of real-world conditions by accounting with defined shares of urban, rural and motorway operation. Other parameters considered are trip duration, ranges of vehicle speed, cumulative work performed by the engine, etc. [18]. Ambient boundary conditions including altitude and ambient temperature for the PEMS test are also involved in the regulation [14]. However, even with all these requirements, repeatability of PEMS tests is hardly achievable, because the boundary conditions are unique for a PEMS test. For instance, it is scarcely possible to guarantee that the trip time and vehicle speed of two PEMS tests are exactly the same on the same test route, needless to say different test routes [14, 19, 20]. Therefore, PEMS tests still have some debatable points (e.g., trip composition, boundary conditions and data analysis methods) required further detailed study [14]. For instance, a study performed by [PERSON] et al. [21] revealed that up to 85% of the NOx emissions measured during the tests performed were not taken into consideration if the boundary conditions for data exclusion set in the current legislation were applied. In order to overcome the repeatability issue of the PEMS tests, many data analysis methods (e.g., the vehicle specific power (VSP) method, the power binning (PB) method, not-to-exceed (NTE) method, moving averaging window (MAW) method, etc.) were introduced for processing the test data [22, 23]. [PERSON] et al. [23] tested three different methods (the MAW, PB and VSP), concluding that there were differences between all methods both for CO2 and NOx emissions estimation due to the statistical and numerical treatment from each method. The current data analysis method regulated by the European Community (EC) and China is the moving average window (MAW) method. This work aims to analyze the data produced during the four PEMS tests.