Influence of dilution parameters on the internal flow field and dilution ratio of a particulate matter sampling diluter

Abstract

Dilution sampling systems are crucial for obtaining accurate measurements of engine exhaust particulate mass and number. The system design requires a comprehensive understanding of the impact of dilution parameters on its internal flow field and dilution ratio. In this study, a computational fluid dynamics (CFD) model of an ejector diluter was established. This CFD model was validated based on results of experiments conducted on a diesel engine with the self‐designed partial flow sampling system. The discrepancies between the simulation and experimental results of the dilution ratio were acceptable (average error of 7.42% and a minimum error of 0.72%). These errors indicated that the model was suitable for performing numerical simulations. The effects of the dilution parameters, including exhaust gas velocity, exhaust gas temperature, and air velocity, on the internal flow field and dilution ratio of the diluter system were investigated. The results showed that an increase in the exhaust velocity from 0.542 to 1.489 m/s decreased the dilution ratio from 41.31 to 15.98 when the air velocity and pressure were constant at 9.147 m/s and 200 kPa, respectively. A 100 K increase in exhaust temperature increased the dilution ratio by 1.62 on average. When the air velocity was increased from 4.333 to 28.405 m/s, the dilution ratio significantly increased from 10.55 to 64.66 when the exhaust velocity and pressure were constant at 1.083 m/s and 90 kPa, respectively.