Real-world Emission Analysis Methods Using Sensor-based Emission Measurement System 2020-01-0381
Every year, due to exhaust gas regulations that are getting stricter, the average air pollution is going to be solved, but the local roadside pollution is still pressing issue. In order to solve this local roadside pollution problem, it is necessary to evaluate and/or predict “where” and “how much” pollutants such as NOx are emitted. In recent years, Real Driving Emission regulations using PEMS (Portable Emission Measurement System) have been introduced mainly in Europe. However, PEMS has a configuration close to 100 kg, and its weight affects the driving conditions of vehicles running on actual roads. In this study, we focused on the analysis of real world emissions using SEMS (Sensor-based / Simple Emission Measurement System). Whereas PEMS is a method of sampling and analyzing exhaust gas, SEMS directly attaches NOx sensor and PM sensor to the exhaust pipe and measures the concentration. Although SEMS has a limited number of items that can be measured compared to PEMS, other analyzes are possible by devising the analysis method. This paper focuses on the analysis method of real world emissions using SEMS, and aims to examine the analysis method of CO2 emission concentration, exhaust gas flowrate, and local roadside emission from the measured value of SEMS. In addition, an example of applying this analysis method using on-road test data of a diesel passenger car acquired with SEMS is shown. The NOx sensor can measure not only the NOx concentration but also the O2 concentration and air-fuel ratio. It is clarified that the CO2 concentration at wet condition can be calculated with high accuracy by using the measured values of the O2 concentration. Also, the exhaust flowrate is obtained by combining the intake air flow rate acquired through the vehicle's OBD and the air-fuel ratio measured by the NOx sensor. At that time, the exhaust gas density is also calculated based on the air-fuel ratio, so that the exhaust flowrate can be calculated with higher accuracy.