The effect of fuel injection atomization on engine performance has been known to improve fuel economy and to reduce emissions. Hitachi America, Ltd. Research and Development along with Hitachi Research Laboratory in Japan have studied the effects and the operation of the air assist injection system which was developed and studied to help meet future Low Emission Vehicles (LEV) regulations and also Ultra Low Emission Vehicles (ULEV) regulations.The system consisted of newly designed air assist injectors having a spray angle of 15° at 170 kPa (absolute air pressure) with 370 kPa (absolute fuel pressure). The air assist injector generates highly atomized fuel droplets by swirling the fuel clockwise and the air counterclockwise. The fuel and air flowing in opposite directions collide, thereby producing particles around 30 μm in size at 274 kPa air pressure.These characteristics improve cold start, cold coolant conditions and fully warm engine conditions. HydroCarbons (HC) reduction of up to 40 percent were obtained with certain set engine parameters.