Internal-combustion engines – Precombustion and main combustion chambers in series – Having combustible mixture forming means
Patent
1985-02-11
1986-10-14
Argenbright, Tony M.
Internal-combustion engines
Precombustion and main combustion chambers in series
Having combustible mixture forming means
123279, F02B 1908
Patent
active
046166122
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a piston for an internal combustion engine having a combustion system of the direct injection type.
Diesel engines of the direct injection type are commonly provided with pistons having an open combustion bowl recessed in the crown, and means to produce a swirling motion of the inlet air about the axis of the bowl so as to give improved fuel/air mixing and combustion. It is also known to modify the shape of the combustion bowl in order to induce turbulence in the swirling flow of air and fuel in the bowl, thereby further increasing the rate of air/fuel mixing and hence improving the rate of heat release. This in turn allows the engine to be operated at more retarded fuel injetion timings at which lower oxides of nitrogen emissions are produced, without suffering any serious effect of increased specific fuel consumption or smoke emission.
Bowl shapes have been modified by making them of a reentrant form with an over-hanging lip portion around the mouth of the bowl so as to produce a turbulent squish action beneath the lip of the bowl.
Also, the shape of the bowl in the plane normal to the bowl axis has been made non-circular by forming scallops in the side wall of the bowl or making the bowl of substantially square section. Turbulence is generated in the scallops or corners of the bowl, and fuel jets directed towards these regions are thereby more thoroughly mixed with the air.
U.S. Pat. No. 4,176,628 discloses a piston with a generally toroidal recessed bowl having four recesses in the side wall each to receive one of the four fuel jets. Each recess has a section that extends tangentially of the side wall and joins a semi-circular section, the tangential section lying on the upstream side of the air swirl in the chamber so as to lead air into the recess. The radius of the semi-circular section of the recesses is considered important in order that a large air swirl in the bowl shall induce a desired level of turbulence in the recesses. Preferably the ratio of the radii of the recesses and the bowl is between 1/6 and 1/2. In all the illustrated embodiments the actual depth of the recesses varies greatly and in all cases is relatively large.
U.K. No. 509,838 also discloses a piston with a toroidal recessed bowl having four recesses in the side wall each to receive one of the four fuel jets. Each recess is semi-circular and symmetrical about a bowl radius, and serves to accommodate a longer path length for a corresponding fuel spray directed into the recess. The size of the recesses is not considered important, but in all the illustrated embodiments the recesses are relatively deep in order to give a long fuel spray path length.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a direct injection diesel engine with an improved combustion system that gives improved specific fuel consumption and smoke performance over a wide range of engine speeds.
According to the present invention, a piston for an internal combustion engine has a combustion bowl recessed in the crown of the piston and a plurality of arcuate recesses formed in the side wall of the bowl and spaced apart by arcuate intermediate portions of the side wall, and is characterised in that the ratio of the maximum distance by which each recess extends radially into the side wall compared with the radius of the side wall lies within the range 0.10 to 0.20.
In use swirl means causes the inlet air to rotate about the axis of the bowl, and fuel injection means serves to direct a plurality of fuel jets radially of the bowl each towards a corresponding recess. The recesses are sufficiently deep to produce the required turbulence for air/fuel mixing at all speeds but are not so deep as to have a detrimental affect on the swirling air motion at low engine speeds.
Preferably, the arcs of the recesses are formed on circles with centres lying on a circle coaxial with said intermediate arcuate portions of the side walls.
DESCRIPTION OF THE DRAWINGS
The invention will now be described by way
REFERENCES:
patent: 3374773 (1968-03-01), Scherenberg
patent: 4176628 (1979-12-01), Kanai et al.
patent: 4538566 (1985-09-01), Tsuruoka
Argenbright Tony M.
Farris Robert L.
Perkins Engines Group Limited
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