Overcoming Challenges in Motorcycle Exhaust Flow Measurement: A Study on Measurement Accuracy and Systematic Effects of an Annubar-Based Approach

Accurate exhaust mass flow measurement is critical for Real Driving Emission (RDE) assessment, however, it is particularly challenging for motorcycles due to variations in chemical composition, strong pulsations and even reverse flow effects at low engine speeds. Traditional differential pressure-based flow meters often struggle under these conditions, particularly in low-speed and low-load operation. This study evaluates the feasibility and accuracy of an Annubar-based exhaust flow meter (EFM) designed to address these challenges by means of assessing eight motorcycles with single-, two-, and four-cylinder engine configurations. The EFM’s performance is evaluated via correlation analysis with laboratory-grade reference instruments and engine control unit (ECU) data. Additionally, systematic effects such as pulsation behavior, spectrogram analysis, and the influence of engine load and speed are investigated. The results demonstrate a strong correlation between Annubar-based EFM and reference measurements, indicating this EFM as a viable exhaust mass flow measurement solution for this specific application. However, systematic deviations were observed, particularly at low engine speeds and loads, where pulsation effects caused oscillatory measurement behavior. These deviations stem from the interaction between engine-induced pulsations and the EFM response characteristics. To mitigate these effects, advanced filtering techniques and engine-aware compensation strategies, leveraging engine RPM and load data, are proposed to enhance measurement stability and accuracy. These improvements will make Annubar-based EFMs an even more reliable tool for motorcycle RDE assessments, enhancing real-world emission testing methodologies.