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The worldwide fuel economy compliance level has been tightening, at the same time, LEV-III/Euro-6d/China-6/BS-6 regulations for NMOG and NOx emissions are being introduced or already effective. Therefore, intensive research effort has been conducted in order to improve the fuel efficiency of passenger cars and reduce exhaust emission. In response to these demands, turbocharged gasoline direct injection (TGDI) engine is being introduced for gasoline vehicles in consideration of fuel efficiency improvement, high output and driving performance compared to naturally aspirated (NA) engine. However, due to its larger thermal mass from the turbo hardware in the exhaust, it suffers from the cold-start emission. The main hazardous gases emitted from gasoline vehicles are CO, HC and NOx, and a three-way catalyst (TWC) is installed for the purification of these harmful emissions.

In this study, the effect of the nozzle tip geometry on the nozzle tip wetting and particulate emissions was investigated. Various designs for the injector nozzle hole were newly developed for this study, focusing on the step hole geometry to reduce the nozzle tip wetting. The laser induced fluorescence technique was applied to evaluate the fuel wetting on the nozzle tip. A vehicle test and an emissions measurement in a Chassi-Dynamo were performed to investigate the particulate emission characteristics for injector nozzle designs. In addition, the in-cylinder combustion light signal measurement by the optical fiber sensor was conducted to observe diffusion combustion behavior during the vehicle test. Results showed that the step hole surface area is strongly related to nozzle tip wetting and particulate emissions characteristics. Injectors without the step hole and with a smaller step hole geometry showed significant reduction of nozzle tip wetting and number of particulate emissions.