Mixture formation technology for multipoint fuel injection systems in spark ignition engines has been reviewed regarding reduced exhaust emissions, fuel consumption and improved engine performance. In conventional systems, under light load conditions, the mixture of fuel to suction air is not uniform due to a short injection pulse width against a long duration of suction stroke. Under heavy load conditions, fuel spray is apt to be deflected by the air flow through the intake port and the injected fuel clings and remains onesidely on the cylinder wall during the combustion cycle. Under cold start conditions, the fuel on the intake manifolds and ports is not evaporated quickly enough so that it is evaporated in the cylinder after the temperature rises due to the compression stroke. A lot of fuel is injected to compensate for the small evaporation rate.
To overcome these problems, a new fuel injection system with variable injection pattern control in accordance with engine operating conditions was investigated. The control could optimize mixture formation and reduce HC emissions under a wide range of engine operating conditions. Also, engine speed fluctuations under light load conditions could be minimized, engine response under heavy load conditions could be improved, and fuel economy could be improved due to zero unburned fuel.
The functions of the systems are as follows. Under light load conditions, the fuel mixing time to blast air flow is lengthened to get a uniform mixture as the fuel is injected into swirlers and then it is gradually atomized by the assist air. The spray pattern is widened using swirlers to reduce both spray penetration and impingement on the intake ports and valves. Under heavy load conditions, the fuel is directly injected toward the intake valves and not deflected by the air flow through the intake ports as the blast air flow is minimized. The fuel is mixed uniformly by the air through the intake valves. Under cold start conditions, the duration of blasting fuel against suction air duration is lengthened by using the swirlers and good atomization of fuel is attained with a suitable configuration of the nozzles under conditions where the blast air velocity is not enough to atomize fuel in conventional systems.