Internal-combustion engines – Precombustion and main combustion chambers in series – Having combustible mixture forming means
Patent
1983-04-04
1985-05-14
Nelli, Raymond A.
Internal-combustion engines
Precombustion and main combustion chambers in series
Having combustible mixture forming means
123262, F02N 1708, F02B 306, F02B 300
Patent
active
045165491
DESCRIPTION:
BRIEF SUMMARY
Technical Field
This invention relates to internal combustion engines, especially compression ignition engines.
Direct injection diesel engines are known with pistons having a combustion bowl recessed in the head of the piston and a local raised projection or pip in the floor of the bowl. This pip is located centrally in the bowl and is considered to have a centring action on the fuel-air charge as it enters the bowl. Fuel is injected into the bowl as a number of jets with a conical spray pattern.
It has also been proposed in German Patent No. 1022415 to locate a pip in the floor of a recessed combustion bowl so that the pip is offset from the centre of the bowl and thereby provides an annular venturi that speeds up the flow of air through the narrow part of the annular bowl as it is swirled in the combustion chamber. A fuel injector is provided to inject fuel into this narrow part of the bowl substantially tangentially of the walls of the pip and bowl so as to wet these walls. The accelerated flow of air enhances evaporation of the fuel from the walls, which then mixes further with the air as it flows into the wider part of the bowl.
Direct injection diesel engines are also known with pistons having a recessed combustion bowl that is of a re-entrant form so as to induce turbulence in the flow of the fuel/air mixture in the bowl. This turbulence increases the rate of fuel/air mixing and hence the speed of heat release, thereby allowing the engine to operate at more retarded fuel injection timings without loss in fuel economy and with improved fuel tolerance, with lower NOx emissions and controlled smoke emission. However, the overhanging lip around the mouth of the re-entrant bowl may need to be strengthened.
DISCLOSURE OF THE INVENTION
The present invention aims to provide a direct injection diesel engine having a piston with a recessed combustion chamber adapted to have performance characteristics similar to a re-entrant bowl, but which is inherently stronger in its design.
This object is achieved according to the present invention by providing a piston having a recessed combustion bowl with a raised projection in the floor of the bowl so as to define an annulus with the sides of the bowl, swirl means to cause the inlet air to rotate about said raised projection, and a fuel injector having orifices that spray a plurality of jets into the annulus at spaced points around the projection, the cross-sectional area of the annulus being such as to vary around the projection and to have a minimum value in a median plane through the axis of the projection, and the injector nozzle being located in a central region of the bowl and having orifices orientated so as to direct jets of fuel both sides of said median plane.
Preferably, the cross-setion area of the annulus is varied by varying the radial width of the annulus, this being achieved conveniently in a circular bowl by offsetting the axis of the projection radially from the axis of the bowl. Both axes then lie on the median plane through the narrowest part of the annulus. Preferably, the injector nozzle is also located along the median plane and directs fuel jets into the four quadrants of the annulus defined by the median plane and perpendicular plane through the axis of the bowl.
DESCRIPTION OF THE DRAWINGS
The invention will now be described by way of example with reference to the accompanying drawings in which:
FIG. 1 is an axial section through the crown of a piston and a four hole fuel injector according to the invention;
FIG. 2 is a plan view of the piston crown and injector of FIG. 1;
FIG. 3 is an axial section through the crown of a known piston with a recessed combustion bowl;
FIG. 4 shows a specific fuel consumption (s.f.c.) and smoke curves for a single cylinder test comparing the combustion system of FIGS. 1 and 2, and that of FIG. 3;
FIG. 5 is a plan view of the piston crown of FIGS. 1 and 2 with a single hole injector;
FIG. 6 shows s.f.c. smoke curves for the combustion system of FIG. 5;
FIG. 7 is a plan view of the piston crown of FIGS. 1
REFERENCES:
patent: 2914044 (1959-11-01), Liobol
patent: 2959161 (1960-11-01), Bottger
patent: 3020898 (1962-02-01), Hardmann
patent: 3144008 (1964-08-01), List
patent: 3814068 (1974-06-01), Kimbara et al.
patent: 3954089 (1976-05-01), Hardesty et al.
patent: 4207843 (1980-06-01), List et al.
patent: 4378702 (1983-01-01), Finsterwalder et al.
Farris Robert L.
Massey-Ferguson-Perkins Limited
Nelli Raymond A.
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