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We have examined a new precise control method of the air fuel ratio during a transient state which provides improved exhaust characteristics of automobile engines. We investigated the measurement method for the mass of fresh air inducted by the cylinder, which is most important for controlling the air fuel ratio. The mass of fresh air must be measured in real time because it changes in each cycle during a transient state. With an conventional systems, it has been difficult to get accurate measurement of this rapidly changing mass of fresh air. The method we studied measures the mass of fresh air by using the intake manifold pressure and air flow sensors. During a transient state, the reverse flow of the residual gas from the cylinder into the intake manifold, which occurs at the first stage of the suction stroke, changes with each cycle. The mass of fresh air changes accordingly.

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.