Numerical simulation of the influence of the structural parameters of a sampling diluter for particulate matter in diesel engines on the internal flow field and dilution ratio

This study investigated how structural parameters (including injection ducts and exhaust nozzle inner diameters) affect the internal flow field and dilution ratio of diesel particulate sampling diluters. Increasing air injection duct diameter increased the injection chamber pressure and decreased the air velocity peak, mixed gas flow velocity, sample temperature, and mixing rate. Excessively small tube diameters caused uneven and discontinuous flow field distributions, while substantial air blockage rendered the flow state poor. Increasing nozzle inner diameters increased the exhaust flow area and the sample temperature, but decreased the velocity of the exhaust and gas mixtures and the pressure drop. Compared with a 2.0 mm inner diameter, 2.5 and 3.0 mm diameters decreased the peak velocity by 11.18% and 14.41%, respectively, and mixing slowed significantly. Inner nozzle diameters of <1.5 mm increased the pressure drop significantly; the exhaust velocity also increased, exceeding the air velocity at the mixing position. The dilution ratio and relative error decreased with increasing inner nozzle diameter. At an air injection duct and an inner nozzle diameter of 0.1 and 2.0 mm, respectively, the dilutor's flow field distribution improved, the mixed gas flow stabilized, and the dilution ratio and relative error were 21.34% and 6.74%, respectively.