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The accurate measurement of air volume is one of the critical issues in an LPL-EGR system, which has a large intake volume from the EGR valve to the combustion chamber compared to an HPL-EGR system. This includes the difficulty of measuring the flow rate of the LPL-EGR accurately. In this study, we investigated the EGR rate estimation logic with the cylinder pressure for an LPL-EGR system. This methodology is characterized by an EGR rate estimation, which uses the polytrophic change during the compression stroke, depending on the mixture and EGR rate. The polytrophic index is mainly changed by the EGR rate and the airflow rate. The EGR rate is estimated by the difference between measured pressure with sensors, and referenced pressure, which is calculated by measured parameters before compression with the assumption that the EGR rate is zero. To calculate the exact EGR rate, the influence of the air fuel ratio on the cylinder pressure was also taken into account.

As for homogeneous charge compression ignition (HCCI) combustion, many parameters influence on self-ignition timing. We formulated a self-ignition timing simulation model. A control algorithm for HCCI engine has been formulated on the basis of this self-ignition timing simulation model. And the application of the control algorithm to a 4-cylinder engine provided with an electromagnetic valve train demonstrated that it was possible to control HCCI combustion in response to operating conditions. In addition, when switching between spark ignition and HCCI operation, the control algorithm for HCCI engine compensating for the difference in exhaust temperature and the fuel wall-wetting compensating algorithm have enabled switching without torque shock.

A direct injection gasoline engine featuring a center-injection method that incorporates a high-pressure injector at the top center of the combustion chamber, has been developed. The engine is characterized by a significantly improved fuel economy and emissions performance as the result of the application of direct-injection stratified charge, DISC, which is one of the main features of the direct-injection engine. This paper describes a study on a change control method for switching between DISC and homogeneous charge combustion. The two forms of combustion employed in the new direct-injection engine differ in terms of combustion limits in relation to recirculated exhaust gas and air-fuel ratio. This causes the torque difference which is a specific issue in direct injection gasoline engines. The authors attempted to cope with the issue from the viewpoints of misfire prevention and fuel amount restriction in accordance with the torque required.

The authors developed a direct injection stratified charge engine employing a center-injection system in which a high-pressure fuel injector is located in the center of the combustion chamber and the fuel spray is vertically injected into the cylinder toward the piston bowl. Stratification is controlled by the fuel spray characteristics and the piston-bowl shape which were calibrated using CFD simulations and in-cylinder analyses. The VTEC mechanism is employed to control the burn rate with in-cylinder swirl gas motion, which is generated by one-intake-valve deactivation. Optimization of the mixture preparation and combustion through calibrations of the piston bowl, the fuel spray characteristics of the high pressure injector and the in-cylinder gas motion enabled stable combustion with an ultra lean air-fuel ratio of 65. As a result, this engine has significantly improved fuel economy and emissions.