1. Field of the Invention
This invention relates to a stratified charge burning internal combustion engine wherein air fuel mixture and air are introduced from intake air ports into a combustion chamber such that they may make laminar tumble swirls in the combustion chamber to effect combustion of the air fuel mixture, and more particularly to a stratified charge burning internal combustion engine with a fuel injection time controlling function wherein the fuel injection end time is set differently depending upon whether or not the operating condition of the engine is in the proximity of a full load operation.
2. Description of the Prior Work
It is effective, as means for enhancing combustion of an internal combustion engine, for example, to produce, at the intake stroke, such vertical whirling flows, i.e., so-called tumble swirls, as shown in FIG. 7 in a cylinder.
FIG. 7 schematically shows structure of a cylinder of an internal combustion engine adapted to produce such tumble swirls Fa and Fm. Referring to FIG. 7, reference numeral 22 denotes a cylinder block, 24 a cylinder bore, 26 a piston, 28 a cylinder head and 30 a combustion chamber. A pentagonal roof 34 is formed at an upper wall of the combustion chamber 30, and a pair of intake ports 40 and 42 for intake air passageways are provided for each cylinder. An intake valve not shown is provided for each of the intake ports 40 and 42.
An injector 66 is disposed in the proximity of the intake port 42 such that fuel is injected from the injector 66 may be mixed into an air flow from the intake port 42 to make air fuel mixture, which is advanced into the combustion chamber 30.
The pentagonal roof 34 has such inclined faces that can guide air and air fuel mixture from the intake ports 40 and 42 downwardly along an inner wall face of the cylinder bore 24 on extension lines of axial lines of the intake ports 40 and 42.
Consequently, the flows of air and air fuel mixture from the intake ports 40 and 42 form, also by the guidance of the pentagonal roof 34, such laminar tumble swirls as indicated by arrow marks Fa and Fm, respectively, in the combustion chamber 30.
As a result, the fuel air mixture is likely burnt completely. Thus, for example, even if the air fuel ratio of the entire air and air fuel mixture is higher than the stoichiometric air fuel ratio, in short, even if the air fuel mixture as a whole is lean, the air fuel mixture can be burnt. Consequently, not only the fuel cost of the engine can be enhanced, but also reduction of hazardous exhaust substances such as CO or NO.sub.x contained in exhaust gas of the engine and prevention of knocking of the engine can be achieved.
However, such a stratified charge burning internal combustion engine as described above is disadvantageous in that, when the air fuel ratio becomes rich upon high load operation or the like, smoke is produced in the exhaust gas. The disadvantage is liable to take place particularly when fuel is injected from only one of a pair of intake ports of an internal combustion engine of the two intake valve type.
While it may seem a promising idea, as means for suppressing production of such smoke, to limit the spraying spreading angle of fuel at an injector so that fuel injected from the injector may not stick to an inner wall of an intake port, since production of smoke depends upon a burning condition of fuel in the combustion chamber, production of smoke can be reduced by a fuel injection time.