Real-World Emission Analysis Methods Using Sensor-Based Emission Measurement System 2020-01-0381
Every year, exhaust gas regulations are getting stricter with the intention to solve the average air pollution problem, however, local roadside pollution is still a 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. To predict the local roadside pollution, it is necessary to collect emissions data from various kinds of vehicles driving on real-world and analyze them. In recent years, Real Driving Emission regulations using PEMS (Portable Emission Measurement System) have been introduced mainly in Europe. A typical PEMS configuration can weigh close to 100 kg however, 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 Emission Measurement System). Whereas PEMS is a method of sampling and analyzing exhaust gas, SEMS directly attaches a 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 analysis is 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 emissions 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 equipped 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.