Development of a High Fuel Economy and Low Emission Four-Valve Direct Injection Engine With a Center-Injection System

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. In addition higher full load performance is attained by applying the i-VTEC mechanism which consists of VTEC as a cam shifter for four-valve operation and a cam phaser to obtain higher volumetric efficiency. In order to meet the rather stringent exhaust emission category in Japan, the authors apply the ultra lean combustion system to mass EGR during lean operation, so that the engine-out NOx emission is reduced by 80%. Furthermore, a newly developed lean NOx catalytic converter system is adopted and a conversion efficiency over 95% is obtained. The integration of the combustion system and the highly efficient lean NOx catalytic converter enables the vehicle with a lean burn direct injection engine to become the first one to achieve the emissions category of 25% of the level stipulated by the Japanese emissions regulations and obtains ULEV certification.