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The control strategies of auto-ignition for homogeneous charge compression ignition and controlled auto ignition operations were investigated using a simple engine model. The fluctuations of auto-ignition characteristics during transients in variable timing of exhaust and intake valves were analyzed. When the valve timing changed stepwise, the characteristics fluctuated and differed slightly from these in steady state conditions because combustion in the prior cycle affected the gas exchange in the next cycle. To reduce such fluctuations, the control strategies of cylinder air mass, residual gas mass, fuel mass, air/fuel ratio were investigated for a simple engine dynamic model (a 4-cylinder, 4-stroke engine with total cylinder stroke volume of 2000 cm3), which could simulate the dynamics of gas exchange during transient valve timing in a wide dynamic range.

Generalized models of the air/fuel ratio control using estimated air mass in the cylinder were presented to obtain highly accurate control during transient conditions in high supercharged direct injection systems with a complex air induction system. The air mass change was estimated by using upstream models which estimated the pressure of the intake manifold by introducing the output of the air flow meter and the differential of the output into aerodynamic equations of the intake system. The air mass into the cylinders was estimated at the beginning of the intake stroke under a wide range of driving conditions, without compensating for changes in the downstream parameters of the intake system and engine. Therefore, the upstream models required relatively minor calibration changes for each engine modification to be able to estimate the air mass on a cylinder-by-cylinder basis.

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.

Mixture formation and the ignition process in 4 cycle 4 cylinder spark ignition engines were investigated, using an optical combustion sensor that combines fiber optics with a conventional spark plug. The sensor consists of a 1-mm diameter quartz glass optical fiber cable inserted through the center of a spark plug. The tip of the fiber is machined into a convex shape to provide a 120-degree view of the combustion chamber interior. Light emitted by the spark discharge between spark electrodes and the combustion flames in the cylinder is transmitted by the optical cable to an opto-electric transducer. As a result, the ignition and combustion process which depends on the mixture formation can be easily monitored without installing transparent pistons and cylinders. This sensor can give more accurate information on mixture formation in the cylinders.

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.

Effects of mixture formation of fuel injection systems on gasoline engine performance have been studied. Several fuel injectors which produced various spray diameters and spray patterns were used in engine tests. Spray behavior in an air flow was investigated to clarify the spray distribution through the intake valve. The relationships between the spray distribution near the intake valve and the HC emission or engine response were considered. The amount of HC emissions increased if fuel was injected when the intake valve was open with a heavy load (e.g. an engine speed of 2000 rpm and a manifold pressure of 98 kPa), because fuel would flow into the cylinders one-sidedly, causing a liquid film to form. The amount of HC emissions also increased if fuel was injected when the intake valve was open with a light load (e.g. during idling), because the fuel injection pulse would be short and fuel would flow into the cylinders, but the air-fuel mixing would not be enough to cause a misfire.

Mixture formation technology for gasoline engine multipoint fuel injection systems has been investigated. The fuel injector's spray, the volatility of droplets floating in the air flow, the movement of droplets around the intake valve's upper surface, the volatility of droplets on heated surfaces, and the process of atomizing droplets in the intake valve air flow was analyzed. Droplet diameters and spray patterns for good mixture formation without liquid film in cylinders have been clarified. When sequential injection is used for better responsiveness in fuel injection systems, engine performance may be reduced through increased HC emissions in some conditions. Reducing the diameter of spray droplets and preventing fuel from concentrating in the intake valve promotes vaporization, reduces fuel concentration on cylinder walls, and prevents reductions in engine performance.

Dynamic characteristics of fuel supply system for multi-cylinder gasoline engine was studied analytically and experimentally. We investigaged. (1) The relation between the air flow rate upstream the throttle valve and the air flow rate into the cylinder, when the throttle valve is opened or closed rapidly. (2) The air fuel ratio in the cylinder affected by the above relation. (3) Pmax response affected by the residual fuel in the intake manifold.