Internal combustion engine

Spark ignited internal combustion engine of the reciprocal piston type, having inlet means 7 for substantially tangentially introducing a combustible mixture into a combustion chamber 6 to generate a swirling motion of the mixture and provided with means 16 for breaking up the swirling motion so as to produce turbulence at or near the end of the compression stroke of the piston 3.

TECHNICAL FIELD 
The invention relates to a spark ignited internal combustion engine, and 
more particularly to a reciprocal piston type internal combustion engine 
with one or more combustion chambers having a shape or being provided with 
means for generating motion of an air/fuel mixture when the piston(s) of 
the internal combustion engine is (are) performing a compression stroke. 
The motion of the air/fuel mixture causes an increase in the rate of 
combustion thereof so that the engine efficiency is advantageously 
influenced. 
PRIOR ART 
In view of the rise in fuel energy prices, especially over the last decade, 
there is a growing interest in increasing the thermal efficiency of 
internal combustion engines. Increase of the thermal efficiency can in 
general be attained via two different ways, viz. the use of higher 
compression ratio and the use of leaner air/fuel mixtures. Both ways, 
however, have their limitations; higher compression ratios are limited by 
knock and lean mixture operation is limited by increasing slowness of 
combustion. Since high compression ratios promote combustion of lean 
mixtures, while lean mixtures are less prone to knock, both trends in 
conjunction will lessen each other's limitations. The slowness of normal 
combustion, however, sets a limitation to progress in both directions. 
If the combustion could be speeded up, there would be less time for knock 
to set in at the higher compression ratios on the one hand, and lean 
mixture combustion would become more satisfactory on the other. The 
crucial factor which determines the duration of combustion is the rate of 
development of flame area from that of the initial flame kernel to that of 
a convoluted flame penetrating through much of the combustion chamber. 
Apart from mixture strength, the most important factor likely to influence 
the duration of combustion significantly is the motion of the air/fuel 
mixture in the combustion chamber. In order to reduce the duration of 
combustion, several methods have been proposed in the past. 
A first known method consists of generating a swirl motion or turbulence in 
an air/fuel mixture in the combustion chamber during introduction of the 
mixture. In a further known method turbulence is generated in the 
combustion chamber for example by the squish action between the cylinder 
head and the piston. 
The above methods, however, have insufficient influence on the duration of 
combustion. In the first method, turbulent motion generated at the time of 
the intake stroke becomes weak during the compression stroke and is likely 
to have decayed greatly by the time the air/fuel mixture is ignited, while 
swirl motion, through continuing, has relatively little effect on the rate 
of combustion. Also turbulence generating devices interfere with the 
breathing of the engine. Turbulence generated by squish, i.e. displacement 
of part of the air/fuel mixture from regions of small piston clearance, at 
the top of the compression stroke is normally produced later than 
desirable. Further, there can be significant losses from thermodynamic 
irreversibility suffered during the process and during the reverse motion 
as the piston descends. 
Another known method consists of generating turbulence by the expansion of 
burning gases during the early stages of combustion through a passage in a 
divided combustion chamber. In this case the turbulence is again generated 
rather late, and is associated with substantial losses due to 
irreversibility as well as with greater heat losses than normal. 
Turbulence generated by simple displacement of the piston in its cylinder 
is too small to effect a significant increase in the rate of combustion. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide an improved internal 
combustion engine capable of burning combustible mixtures significantly 
more rapidly as an aid to improving efficiency. 
According to the invention, an internal combustion engine is provided 
comprising a cylinder block having a cylinder bore therein, a cylinder 
head mounted on said cylinder block, a piston reciprocally movable in said 
cylinder bore, thereby defining a combustion chamber of varying geometry, 
an intake valve movably mounted in said cylinder head and cooperating with 
inlet means for introducing a combustible mixture substantially 
tangentially into said combustion chamber to generate a swirling motion of 
the combustible mixture, an exhaust valve movably mounted in said cylinder 
head and cooperating with outlet means for discharging an exhaust gas from 
the combustion chamber, and a device for producing ignition within said 
combustion chamber, which combustion chamber houses a spoiling device for 
breaking up the swirling motion of the combustible mixture in the 
combustion chamber so as to produce turbulence in the form of small scale 
eddies at or near the end of the compression stroke of the piston. 
The turbulence generated at or near the end of the compression stroke of 
the piston will cause an important increase in the rate of combustion 
compared with the rate of combustion obtainable with the known methods. 
Since small scale eddies decay very rapidly, within a few milliseconds, 
the timing of the induction of turbulence takes on a crucial significance. 
In the internal combustion engine according to the invention the 
production of turbulence is delayed until the end of the compression 
stroke so that a full profit of the turbulence at the moment of the 
ignition is made. Furthermore, the method of producing turbulence in the 
proposed combustion engine does not interfere with the breathing of the 
engine, nor with the expansion of the working fluid during the power 
stroke.

DETAILED DESCRIPTION 
It should be noted that identical elements shown in the drawings have been 
indicated with the same reference numeral. 
Referring to FIGS. 1 and 2, a cylinder block 1 is shown having a cylinder 
bore 2 in which a piston 3 is reciprocally movable. A cylinder head 4 is 
suitably secured onto the cylinder block 1 with a gasket 5 arranged 
therebetween. The cylinder block 1, piston 3 and cylinder head 4 cooperate 
with one another to define a combustion chamber 6 of varying geometry. The 
cylinder head 4 is provided with an inlet conduit 7 having a downstream 
end, with respect to the flow of combustible mixture through the inlet 
conduit, formed with a valve seat 8 of an intake valve 9. The intake valve 
9 is provided with a deflector element 10 for deflecting the flow of the 
combustible mixture in said conduit 7, thereby urging the mixture to enter 
into the cylinder bore 2 in substantially a tangential direction to the 
wall of said bore. The cylinder head 4 is further provided with an outlet 
conduit 11 having an upstream end, with respect to the flow of exhaust gas 
through the outlet conduit, formed with a valve seat 12 of an exhaust 
valve 13. 
In this first shown embodiment according to the invention the piston 3 is 
provided with a substantially flat piston head 14, while the cylinder head 
4 has a recess 15 being substantially coaxial with the cylinder bore 2. In 
order to attain a higher compression ratio the recess 15 has a cross 
sectional area which is substantially smaller than that of the cylinder 
bore 2. The inner wall of the cylinder head 4 forming recess 15 is 
provided with an inwardly extending protrusion or baffle 16. The cylinder 
head 4 is further provided with a spark plug 17 arranged adjacent to 
protrusion 16 and extending into a quiescent zone of the recess 15. 
During operation of the above described cylinder/piston construction of for 
example a four stroke internal combustion engine, an air/fuel mixture from 
a not shown carburettor is sucked into the combustion chamber 6 via inlet 
conduit 7 by opening intake valve 9 and downwardly moving the piston 3. 
From inlet conduit 7 the air/fuel mixture enters the cylinder bore 2 in 
substantially a tangential direction to the wall of said bore. The 
tangential entry of the combustible mixture results in a forced swirl or 
vortex of the mixture within the cylinder bore. As the vortex is largely 
of a rigid type of rotation and is associated with only a rather moderate 
velocity gradient at the cylinder wall it will persist during the downward 
inlet stroke and the consecutive compression stroke of the piston 3. 
During the compression stroke the swirling air/fuel mixture is compressed 
into the upper part of the combustion chamber 6 formed by the relatively 
small recess 15. As a consequence thereof the angular velocity of the 
vortex is accelerated. At the same moment the relatively large vortex is 
broken up into a plurality of small scale eddies, causing a highly seared 
movement of the air/fuel mixture. The greatest mass flow into the recess 
takes place towards the end of the compression stroke, so that turbulence 
is principally generated shortly before the passage of the spark. The 
highly turbulent air/fuel mixture is subsequently ignited by the spark 
plug 17. Due to the heavy turbulence of the combustible mixture the flame 
thus ignited propagates rapidly over the entire space in the recess 15, 
thereby minimizing the risk of knock. The specific arrangement of the 
spark plug 17 near the protrusion 16, facing towards the relatively 
sheltered portion of recess 15 directly sidewards of said protrusion 16 
allows the flame to be less affected by the motion of the mixture during 
the early stages of its growth, after which it is caught up in the highly 
sheared gas movement. The main flow direction in recess 15 has been 
indicated in FIG. 2 by arrow A. 
Reference is now made to FIGS. 3 and 4 showing a second embodiment of an 
internal combustion engine according to the invention. 
The piston 3 shown in FIGS. 3 and 4 is provided with a recess 20 in the 
head thereof. The recess 20 forms the lower part of the combustion chamber 
6, and has a relatively small cross-sectional area compared with the 
cross-sectional area of the cylinder bore 2. In said recess 20 a spoiling 
device 21 is mounted for transforming a swirling movement of the 
combustible mixture into a highly turbulent movement. As shown in FIG. 4, 
the spoiling device 21 has a substantially tapering shape in 
cross-section, allowing transfer of heat to the piston, thereby preventing 
overheating of the spoiling device during combustion. The spark plug 17 is 
arranged in a passage in the cylinder head 4 in such a manner that in the 
upward position of the piston 3 the lower end of spark plug 17 is located 
in a quiescent zone near the spoiling device 21 in recess 20. 
During operation of this cylinder/piston construction shown in FIGS. 3 and 
4, a combustible mixture tangentially enters into the combustion chamber 6 
at the intake stroke of the piston, which results in a forced swirl of the 
mixture within the cylinder bore 2. At the compression stroke of the 
piston the downward swirling movement of the mixture is transformed into 
an upward swirling movement. When the piston has reached a level near to 
the cylinder head the swirling mixture is compressed into the rather small 
recess 20, causing a considerable acceleration of the swirling movement. 
The presence of spoiling device 21 causes a break-up of the swirling 
movement into random vortices resulting in a highly sheared movement of 
the mixture. As a consequence thereof the flame formed via spark plug 17 
propagates rapidly through the whole mixture in recess 20, so that the 
risk of knock is minimized. 
Reference is now made to FIGS. 5 and 6 showing a third embodiment of an 
internal combustion engine according to the invention. In this third 
embodiment the cylinder head 4 has a recess 30 which is eccentric to the 
cylinder bore axis, but is cylindrical and posesses no baffle. The piston 
is provided with a central axial protrusion 31. 
During operation of this cylinder/piston construction, shown in FIGS. 5 and 
6, a combustible mixture tangentially enters the cylinder during the 
intake stroke of the piston. During compression the swirling motion 
continues smoothly within the cylinder bore during the greater part of the 
compression stroke, the rotation accelerating as the mixture enters the 
recess. Since the protrusion 31 is centrally arranged, it does not 
interfere significantly with swirling motion during the greater part of 
the compression stroke. Towards the end of the compression stroke the 
protrusion 31 on the piston enters the off-centre recess 30 in the 
cylinder head and destroys the swirling motion therein, converting it to 
turbulence and causing the flame formed via spark plug 17 to propagate 
rapidly through the whole mixture in recess 30. 
A fourth suitable embodiment of the invention--not shown here--is the 
converse of the third embodiment which was shown in FIGS. 5 and 6. In this 
further arrangement there is a concentric recess in the piston as in FIG. 
3, but with no baffle. The cylinder head is furnished with an eccentric 
protrusion which enters the piston recess towards the end of the 
compression stroke, thereby acting as a spoiler converting swirling motion 
into turbulence. 
It should be noted that the invention is not restricted to the particular 
means shown in the Figures, for causing a tangential entry of gas into the 
combustion chamber 6. 
The inlet conduit itself may be so disposed as to urge the combustible 
mixture to enter into the cylinder bore in a substantially tangential 
direction. A so disposed inlet conduit may be further provided with a 
deflector to enhance this effect. 
The invention is further not restricted to a particular type of spoiling 
device for generating turbulent gas movement. Instead of the baffles shown 
in the Figures, it might for example be possible to use spoiling devices 
formed by eccentrically arranged grids. 
Finally, the invention is not restricted to a particular position of the 
ignition device. Instead of the shown arrangements, in which the ignition 
device protrudes into the combustion chamber, the ignition device may be 
totally arranged outside the combustion chamber.