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Meeting future exhaust emission and fuel consumption standards for passenger cars will require refinements in how the combustion process is carried out in spark ignition engines. A direct injection system reduces fuel consumption under road load cruising conditions, and stratified charge of the air-fuel mixture is particularly effective for lean combustion. This paper describes an approach to improve combustion stability for direct fuel injection gasoline engines. Effects of spray characteristics (spray pattern and diameter) and air flow motion on the combustion stability were investigated. Spray patterns were observed by the laser sheet scattering method and 3-dimensional laser doppler velocimetry. Mixture behavior in the combustion chamber was observed by the laser-induced fluorescence method using an excimer laser and single cylinder optical engine. It was found that the spray pattern for a pressurized condition affects the combustion stability and smoke generation.

A thermodynamic analysis of mixture formation in cylinders that takes into account mixture inhomogeneity and the wall film is presented. Conditions for obtaining low hydrocarbon emission are clarified analytically as a function of the fuel mass of the wall film and inhomogeneity of the mixture. Optimum processes for atomizing and vaporizing fuel are presented to reduce the inhomogeneity and the fuel mass of the film.

Meeting future exhaust emission and fuel consumption standards for passenger cars will require refinements in how the combustion process is carried out in spark ignition engines. Improvements must be made in the fuel injection device, intake air system, and ignition device based on careful studies of the engine combustion process. Lean burn is preferable to decrease fuel consumption under a road load cruising condition. To achieve stable combustion in a lean air fuel ratio, the in -cylinder air flow must be optimized. Vortex flow in the vertical direction is produced by auxiliary air passages which are located beside the intake air port. The fuel injector has a two-direction spray for the two intake valves. The spray flows into the cylinder uniformly through these two intake valves. Due to effects of air flow from the auxiliary air passages and the two-direction fuel spray, the in -cylinder mixture concentrates around the spark plug.

The relationships between air flow metering and combustion control for spark ignition engines, such as engines with three way catalysts, lean NOx catalysts, two stroke engines and direct fuel injection engines were investigated. The effects of control parameters on combustion were analysed and the relationships between control parameters and air flow metering and roles of the meters in combustion control were clarified. The control strategies adaptable to many types of engines which have a wide control range of the air/fuel mass ratio are classified as (1) air quantity control,(2) fuel quantity control, and (3) exhaust gas recycle quantity control. The control parameters for the three strategies are fuel quantity, air quantity, exhaust gas recycle quantity, exhaust gas temperature, knocking, excess air factor, and mixture quality with additional parameters of swirl ratio, and spark timing for conventional spark ignition engines, two stroke engines and direct injection engines.

Mixture formation technology for a fuel injection system has been investigated. The effects of spray droplet diameter on engine performance were clarified. The combustion light Intensity was measured with a spark plug integrated combustion flame sensor. When sequential injection is used for better responsiveness in fuel injection systems, engine performance may be reduced through increased HC emissions. Reducing the diameter of the spray droplets and preventing fuel from adhering to the intake manifold walls promote vaporization, reduce fuel concentration on the cylinder wall, decrease HC emissions, improve cold start ability, and give good idling performance.

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.

The basic structure of a new engine control system for highly accurate air-fuel ratio control is introduced. Improved engine power and decreased fuel consumption are required for today's engines. Better air-fuel ratio control must be attained to set the air-fuel ratio to that of the maximum power and minimum fuel consumption. In order to enhance the accuracy of the air-fuel ratio control, the air flow meter, air-fuel ratio sensor, and fuel supply device are improved in the new system. Accuracy is lost in conventional system owing to the sensors' deterioration over long-term use. So prevention of air flow meter deterioration and compensation of air-fuel ratio sensor deterioration are taken into consideration. Fuel atomization of the fuel supply device is improved in order to reduce the air-fuel ratio fluctuation in the transient operating state. High power and decreased fuel consumption over long-term use are made possible with the new system.

This paper describes the sensing principle of a new air-fuel ratio sensor, which has the ability to detect air-fuel ratios in rich, stoichiometric and lean ranges. The sensing part is composed of a gas diffusion layer and a zirconia solid electrolyte with a pair of electrodes which function as an anode and a cathode. The anode and the cathode electrodes are exposed to the atmosphere and the exhaust gas, respectively. To obtain the bidirectional pumping current between the two electrodes, the potential of the cathode is held to a constant value higher than the electronic circuit ground. The electromotive force induced between the two electrodes is forcibly controlled to a constant value by the electronic circuit. In this composition, three ranges of air-fuel ratio can be detected by the amount of pumping current.