Dilution gas mixing unit and exhaust gas analysis system

A dilution gas mixing unit used in an exhaust gas analysis system that analyzes a mixed gas obtained by diluting an exhaust gas with a dilution gas, the dilution gas mixing unit mixing the dilution gas with the exhaust gas, the dilution gas mixing unit comprising:

• a dilution gas supply pipe connected to an exhaust gas introduction pipe into which the exhaust gas is introduced, the dilution gas supply pipe supplying a dilution gas to the exhaust gas introduction pipe;
• a dilution gas sampling unit that is provided in the dilution gas supply pipe and collects the dilution gas;
• and
• a backflow prevention member provided downstream of the dilution gas sampling unit and upstream of the exhaust gas introduction pipe, in a flow direction of the dilution gas, to prevent the mixed gas from flowing backward in the dilution gas supply pipe, wherein the backflow prevention member includes a through hole through which the dilution gas passes, and is provided along an inner peripheral surface of the dilution gas supply pipe and wherein the dilution gas sampling unit includes an introduction port disposed so as to be positioned in the through hole as viewed from a pipe axis direction in the dilution gas supply pipe, or so as to be positioned inside more than half of an inner diameter from a pipe axis of the dilution gas supply pipe, with the pipe axis being a center.