Advantages of Simultaneous In Situ Multispecies Detection for Portable Emission Measurement Applications

In this work, an in situ multispecies portable emission measurement system (PEMS) is presented. The system is based on tunable diode laser absorption spectroscopy (TDLAS) and is capable of measuring tailpipe emissions without the necessity of online calibration. It is intended for application on passenger cars within the real drive emission (RDE) procedure of the Worldwide Harmonized Light Duty Test Procedure (WLTP). In contrast to the extractive measurement principles of commercially available PEMS, the introduced measurement system does not require gas sampling or preconditioning and thus does not suffer from the same low-pass filter effects on the measurements. These differences are suspected to have an impact on certification-relevant measurement data. Measurements have been conducted on a 3-cylinder 1 liter EURO 6b gasoline engine test bench to investigate the differences between the presented measurement system and a commercially available PEMS. For the WLTP relevant investigation, water (H₂O), carbon dioxide (CO₂), carbon monoxide (CO), nitrogen oxide (NO), ammonia (NH₃), and methane (CH₄) were detected with an effective temporal resolution of 10 Hz by the introduced PEMS. The comparison of CO and NO concentration curves between the two systems show a distinct low-pass filter behavior of the commercially available PEMS. It is shown that the low-pass filter influences the calculation of the certification-relevant cumulative emissions, leading to deviations between both systems. As a result, deviations of up to 12% (CO) and 17% (NO) have been measured within the first 800 s of the Worldwide Harmonized Light Duty Test Cycle (WLTC). Increasing vehicle dynamics (e.g., in RDE application) are expected to lead to even higher deviations