Combustion chamber and nozzle arrangement for direct fuel injection type diesel engine

A quadrangular combustion cavity V in the crown of a diesel engine piston is offset from the center thereof, and the position of the fuel injector nozzle is also offset relative to the center of the cavity to accomodate enlarged intake and exhaust valves. The rotational orientation of the nozzle and cavity are geometrically determined such that: PA1 A. the fuel distances J.sub.1, J.sub.2 and J.sub.3, J.sub.4 are equal, PA1 B. the angles between a line A connecting the geometric center C.sub.1 of the cavity and the center C.sub.2 of the nozzle, and fuel jet directions J.sub.1 and J.sub.2 are equal, as are the angles between line A and fuel jet directions J.sub.3 and J.sub.4, and PA1 C. the difference between the maximum jet distance J.sub.1 and the minimum jet distance J.sub.3 is minimized The distances from the four fuel impingement points Z.sub.1 - Z.sub.4 on the side walls of the cavity to the respective corners of the cavity are also equal.

BACKGROUND OF THE INVENTION 
This invention relates to a diesel engine wherein an injection nozzle tip 
is offset from the center of an offset quadrangular cavity formed in the 
crown of a piston. 
In U.S. Pat. No. 3,872,841, assigned to the assignee of the present 
invention, the power output and the exhaust emission of a diesel engine 
are improved by obliquely directing fuel jets to the respective inside 
walls of a quadrangular cavity formed in the piston crown, and the engine 
according to this patent has been recognized as yielding very satisfactory 
performance characteristics. In the course of such development it has been 
found that the fuel impingement points at the respective side walls of the 
cavity, the fuel impingement angles, and the fuel travel distances from 
the nozzle orifices to the cavity walls are extremely important factors in 
improving engine output and exhaust emissions. 
In the combustion chamber of the above patent the central axis of the 
quadrangular cavity V", as shown by a solid line in FIG. 1, coincides with 
the center of the piston P, and the fuel injection nozzle N is positioned 
at the center C of the piston. The fuel jets J.sub.1 " to J.sub.4 " 
simultaneously and symmetrically impinge on the cavity walls at 
predetermined points Z.sub.1 " to Z.sub.4 ". Thus, the areas between 
adjacent fuel jets are uniform and each of the jets is uniformly diffused 
in the cavity with the same amount of air between adjacent jets, whereby 
uniform air-fuel mixture and efficient combustion is obtained. 
In a small, high speed engine having a high output, however, the intake 
valve K and exhaust valve H must be enlarged to obtain high intake and 
exhaust efficiency, whereby the cavity V" must be offset from the center 
of the piston in view of air turbulence effects, as shown by the dotted 
lines in FIG. 1. If the intake and exhaust valves are enlarged, however, 
it becomes impossible to position the injection nozzle at the center of 
the piston. The nozzle N must therefore be offset from the center C.sub.1 
of the offset cavity to point C.sub.2 in order to obtain enough space to 
mount the nozzle. That is, if the intake and exhaust valves are enlarged 
the remaining space in the cylinder head is reduced, and the position of 
the injection nozzle must therefore be changed from C.sub.1 to C.sub.2. 
Such nozzle disposition results in unequal fuel impingement lengths and 
different air spaces between adjacent jets, however, whereby the fuel 
distribution and uniformity of the air-fuel mixture is degraged, resulting 
in poorer combustion characteristics. More specifically, the positions of 
C.sub.1 and C.sub.2 are determined in accordance with various engine 
operating conditions, and the fuel impingement points Z.sub.1 ' to Z.sub.4 
' are thus fixed. The distances between the imaginary points a to d 
defined by the corner intersections of the cavity side wall extensions and 
the points Z.sub.1 ' to Z.sub.4 ' are made equal to each other, and the 
four injection nozzle orifices are directed to impinge the fuel jets 
J.sub.1 ' to J.sub.4 ' at points Z.sub.1 ' to Z.sub.4 '. With this 
arrangement the maximum length fuel jet J.sub.1 ' is much longer than the 
minimum length fuel jet J.sub.3 ', however, which degrades the air-fuel 
mixture characteristics. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to overcome the 
above-mentioned drawbacks and to provide an improved combustion chamber 
and nozzle orientation which minimizes the fuel impingement length 
differences from a geometrical stand point. Briefly, and in accordance 
with the present invention, a quadrangular combustion cavity V in the 
crown of a diesel engine piston is offset from the center thereof, and the 
position of the fuel injector nozzle is also offset relative to the center 
of the cavity to accomodate enlarged intake and exhaust valves. The 
rotational orientation of the nozzle and cavity are geometrically 
determined such that: 
a. the two longest and the two shortest fuel jet distances are equal in 
length, 
b. a line connecting the geometric center of the cavity and the center of 
the nozzle bisects the angles between the two longest and the two shortest 
fuel jet directions, and 
c. the difference between the lengths of the longest and shortest fuel jet 
distances is minimized. 
As in the prior art, the distances from the four fuel impingement points on 
the side walls of the cavity to the respective cornners of the cavity are 
equal. 
This arrangement optimizes the fuel distribution and combustion 
characteristics, given the structural necessity of offsetting both the 
cavity and the injector nozzle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to the present invention the differences between the fuel 
impingement lengths, particularly between jets J.sub.1 ', and J.sub.3 ', 
are minimized by a geometric technique as described below. 
First, a line A is drawn in FIG. 2 connecting the geometric center C.sub.1 
of the imaginary cavity V' and the center C.sub.2 of the fuel injection 
nozzle, as shown by a double dotted chain line. 
Second, broken lines D and B are drawn connecting C.sub.1 with Z.sub.1 ' 
and Z.sub.2 ', respectively. 
Third, bisector line E of the angle .theta. between lines B and D is drawn. 
Fourth, the imaginary cavity V' is rotated clockwise through an angle Y 
about point C.sub.1 to superimpose line E on line A, thus obtaining a 
cavity orientation V as shown by the solid line. 
Now if the nozzle center C.sub.2 was positioned on the bisector line E, the 
fuel injection distances from C.sub.2 to Z.sub.1 ' and from C.sub.2 to 
Z.sub.2 ' would obviously be equal. Since the position of point C.sub.2 is 
predetermined by combustion chamber and valve dimensions as well as fuel 
mixture flow parameters, however, the imaginary cavity is instead rotated 
through the angle Y about point C.sub.1. The injector nozzle is then 
similarly rotated such that the respective fuel jets J.sub.1 to J.sub.4 
are directed at points Z.sub.1 to Z.sub.4, which correspond to Z.sub.1 ' 
to Z.sub.4 ' of cavity V', respectively, resulting in a cavity orientation 
and fuel jet directions as shown in FIG. 3. 
With this arrangement the jets J.sub.1, J.sub.2 and J.sub.3, J.sub.4 are 
symmetrical with respect to line A and equal in length. That is, J.sub.1 = 
J.sub.2 and J.sub.3 = J.sub.4. Furthermore, the maximum length J.sub.1 ' 
is reduced to J.sub.1 and the minimum length J.sub.3 ' is increased to 
J.sub.3, whereby the difference between the impingement distances J.sub.1 
and J.sub.3 is minimized. This may easily be visualized by observing that 
if the cavity is rotated more than angle Y, J.sub.1 will continue to 
decrease and J.sub.3 will continue to increase, but now J.sub.2 becomes 
the longest distance and continues to increase while J.sub.4 becomes the 
shortest distance and continues to decrease.