(a) Field of the Invention
The present invention relates to an internal combustion engine having a direct injection combustion chamber, and more particularly, to an internal combustion engine in which fuel is directly injected in a center of a combustion chamber and two spark plugs perform ignition, one under an intake port and the other at a periphery of an injector, such that stable combustion of ultra-lean fuel is realized.
(b) Description of the Related Art
The shape of a combustion chamber depends on the shape of the depression in the cylinder head and the shape of the piston head. Combustion is affected to a large extent by the shape of the combustion chamber.
One type of prior combustion chamber design is the open, or direct injection, combustion chamber in which fuel is injected directly into the combustion chamber. In the direct injection combustion chamber, the piston head is designed in various ways to cause turbulence of the air in the cylinder. Different piston head designs used for the open combustion chamber include a flanged-domed design, a dished design with a raised center area, and other irregularly shaped designs. Advantages for the open combustion direct injection design include good fuel economy and simplicity of design.
FIG. 13 shows a sectional view of a conventional direct injection combustion chamber and all related elements, and FIG. 14 shows a sectional view taken along line XIV--XIV of FIG. 13. An injector 4 directly injects fuel in a combustion chamber 2, and a swirl effect of the fuel is achieved as the fuel undergoes compression by a dished portion 6 formed on a head of a piston 8. Further, a spark plug 10 is provided in a center of the combustion chamber 2, the spark plug 10 acting to ignite the fuel fed into the combustion chamber 2 through the fuel injector 4.
In the conventional direct injection combustion chamber structured as in the above, the direction and manner in which the fuel undergoes the swirl effect is dependent upon the shape of the dished portion 6 of the piston 8. However, the swirl effect of the fuel is also affected by the rectilinear motion of the piston 8, and the speed at which the piston 8 undergoes the same (i.e., engine rpm). Accordingly, design of a piston head that minimizes this change in the swirl effect is difficult.