The lean combustion of an SI engine has been recognized as one of the most promising methods for further improvement of fuel economy. There has been, however, difficulty in extending the lean misfire limit enough to realize NOx emission levels below the mandatory level and still keep satisfactory driveability.
A simulation study has been carried out to search for the possibility of getting better fuel economy under the constrainsts of NOx emission and driveability.
To realize the optimum calibration, the lean misfire limit has been extended by the introduction of (1) high swirl and high combustion chamber turbulence through the use of a helical port with an unique swirl control valve, (2) a newly developed ZrO2 lean mixture sensor and (3) the multi-point fuel injection with sophisticated control. A very good fuel economy level of 17.0 km/1 (Japanese 10 mode) has been accomplished while still meeting the NOx emission cycle regulation of 0.25 g/km.
This paper describes the system and its components, the results of the simulation and the experiments on the effects of each component.