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This paper describes the development of a dilution mini-tunnel to allow measurement of diesel exhaust particulate emissions in transient operating cycles. The dimensions of the tunnel were 84 mm inner diameter and 1.7 m length. A fraction of the total exhaust gas is drawn into the tunnel by an air ejector. The amount of exhaust gas depends on the flow rate of driving air in the air ejector corresponds to the operating engine speed. Performance of the dilution mini-tunnel system was examined using a light-duty vehicle under steady-state conditions and FTP cycles. A good correlation was found between the particulate emission rates measured in the mini-tunnel system and those measured in a total exhaust dilution tunnel system.