A lean NOx trap (LNT) catalyst has been used to suppress NOx emission from a diesel engine. A need to control the LNT catalyst has helped introduce a hydrocarbon-lean NOx trap (HC-LNT) system. The system has a secondary injector that injects diesel fuel (HQ into an exhaust pipe. A typically high temperature (i.e., 250-350 degrees C in the exhaust pipe affects the spray behavior of the secondary injector. Therefore, in this research, the spray behavior of HC injected into a transparent exhaust manifold was investigated. First, the atmospheric injection characteristic of the secondary injector was analyzed. The injector has a solid-cone-shaped structure that can concentrate the spray along the central axis. The atomization process of the'injector is dominated by the liquid film breakup, which generates many droplets with broad dispersion angle. Additionally, the injector was attached in the transparent exhaust manifold, and experiments were conducted in various conditions of the exhaust gas. The results show that the spray cone angle becomes broad and the breakup length of the liquid sheet becomes short as the ambient temperature increases. As the air mass flow increases, the fuel is curved downward and the spray cone angle is reduced because the centrifugal force affects the flow field in the curved part. Moreover, the droplets are found to be distributed by evaporation as the distance from the nozzle tip increases.