GB2132263A - Creating turbulence in i.c. engine combustion chambers - Google Patents

Abstract

A squish chamber 14 defined by cooperating profiles on the piston 3 and cylinder head 4 communicates through orifices 16 with a combustion chamber 6 having a spark plug 11 and mixture intake and exhaust valves. Towards the end of compression mixture is compressed in the chamber 14 and flows as jets through the orifices 16 to cause turbulence in the chamber 6. The squish chamber may be annular, (Figs. 3 and 4), circular (Figs. 5 and 6) or comprise a plurality of segments of a circle. <IMAGE>

Description

SPECIFICATION Internal combustion engine The invention relates to a spark ignited internal cornbustion 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 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.

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 ratios 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 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 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 an insufficient influence on the duration of combustion.

In the first method, the turbulent swirl 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, though 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.

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 into said combustion chamber, an exhaust valve movably mounted in said cylinder head and cooperating with outlet means for discharging an exhaust gas from the combustion chamber, a device for producing ignition within said combustion chamber, the cylinder head and the piston having opposite ends being so profiled that during operation near the end of the compression stroke of the piston a squirt chamber is formed, and at least one orifice being provided for discharging combustible mixture from said squirt chamber into the combustion chamber.

The internal combustion engine according to the invention is so constructed that part of the combustible mixture is displaced through one or more orificies from the squirt chamber into the combustion chamber during the last part of the compression stroke, thereby producing high velocity jets into the combustion chamber. These jets will bring the mixture into a highly turbulent motion, thereby advantageously influencing the rate of combustion after ignition. According to the invention the turbulence is generated just before the piston has reached its upper position so that the mixture is highly turbulent in the upper position of the piston. Since the mixture is normaliy ignited at the end of the compression stroke, the invention allows a fully effective use of the generated turbulence.Further the high velocity jets produced during operation of the proposed engine according to the invention freely flows into the combustion chamber not being hampered by adjacent wall surfaces.

The invention will now be described in more detail with reference to the accompanying drawings, wherein Figure 1 is a cross-sectional view of a first embodiment according to the invention; Figure 2 is a cross-sectional view taken along the line Il-Il in Figure 1; Figure 3 is a cross-sectional view of a second embodiment according to the invention; Figure 4 is a cross-sectional view taken along the line IV-lV in Figure 3; Figure 5 is a cross-sectional view of a third embodiment according to the invention; and Figure 6 is a cross-sectional view taken along the line VI--VI in the Figure 5.

It should be noted that identical elements shown in the drawings have been indicated with the same reference number.

Reference is now made to Figures 1 and 2 showing a first embodiment according to the invention. In these Figures a cylinder block 1 of a spark ignited internal combustion engine is shown, said cylinder block 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 inlet means 7 consisting of an inlet conduit 8 and a not shown intake valve, and outlet means 9 consisting of an outlet conduit 10 and a not shown exhaust valve. The cylinder head 4 further houses a spark plug 11, having its lower end arranged within combustion chamber 6.The cylinder head 4 is provided with a downwardly extending portion 12, the free ends of said portion 1 2 comprising a baffle 13 defining a recess. The head of piston 3 is provided with a raised portion 1 5 upwardly projecting from the piston and being so dimensioned as to closely fit in the recess thereby forming a squirt chamber 14 in an upper position of piston 3. For the discharge of combustible mixture from squirt chamber 14 a plurality of orifices 1 6 have been formed in the baffle 13.

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 conduit 8 by opening the accompanying valve and downwardly moving the piston 3. Near the end of the consecutive compression stroke of the piston 3, the raised portion 1 5 on the piston head will enter into the recess, thereby defining the squirt chamber 14 of varying geometry. Upon a further upward motion of the piston the pressure of the air/fuel mixture in the squirt chamber rises more rapidly than the pressure prevailing in the combustion chamber 6.As a result of the generated difference in pressure in and outside said squirt chamber, fluid is displaced from the squirt chamber through the orifices 1 6 in the baffle 13, and enters into the combustion chamber 6 in the form of jets. The so produced jets generate turbulence of the air/fuel mixture just before the end of the compression stroke, so that at the end of the compression stroke the whole mixture has been brought into a highly turbulent motion.

It should be noted that the jets can freely flow into the combustion chamber 6 without the reduction of their intensity by proximity to a wall that would occur in normal squish. Due to the heavy turbulence of the combustible mixture the flame ignited with spark plug 11 propagates rapidly over the combustion chamber 6, so that the risk of knock is minimized.

Reference is now made to Figures 3 and 4 showing a second embodiment of a cylinder/piston construction of an internal combustion engine according to the invention. The piston 3 shown in Figures 3 and 4 is provided with an annular raised portion 20. The cylinder head 4 is provided with a downwardly extending raised portion 21 having at its inner side a downwardly extending annular baffle 22 forming with the wall of the cylinder bore 2 an annular recess, in which the raised portion 20 closely fits thereby forming an annular squirt chamber 23 in an upper position of piston 3. Said baffle is provided with orifices 24 distributed over the periphery thereof.

In operation the raised portion 20 on the piston enters the recess at the last part of the compression stroke, so that upon further movement of the piston the pressure in the squirt chamber 23 will rise more rapidly than the pressure in the combustion chamber 6. As a consequence of this difference in pressure rise the combustible mixture caught in the squirt chamber 23 will be ejected into the combustion chamber 6 via the orifices 24. In this manner a high turbulence in the mixture in combustion chamber is generated, resulting in a rapid propagation of the flame ignited by spark plug 11.

Instead of the arrangement shown in Figures 3 and 4 with a central combustion chamber and an annular squirt chamber 23 the inverse arrangement with an annular combustion chamber and a central squirt chamber may be applied as shown in Figures 5 and 6. This central squirt chamber, indicated by reference numeral 30, is formed by a central downwardly extending protrusion 31 having its lower part formed by an annular baffle 32 provided with fluid discharge orifices 33 and cooperating with a central protrusion 34 on top of the piston 3.

It should be noted that the invention is not restricted to the particular arrangements of recesses and raised portions described with reference to the Figures. Instead of the arrangement shown in Figures 1 and 2, with one recess in the form of a segment of a circle, a plurality of rece'sses with accompanying raised portions may be applied, each being for example in the form of a segment of a circle.

The invention is further not restricted to a particular number of orifices for introducing fluid in the form of jets into the combustion chamber. It should be noted that the pattern of the jets depends on the size and distribution of the orifices. Smaller orifices will generate more intensive jets. The orifices should preferably be so distributed that shearing motion is induced throughout the combustion space, but less intensively in the neighbourhood of the sparking plug.

Claims (9)

1. Internal combustion engine 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 into said combustion chamber, an exhaust valve movably mounted in said cylinder head and cooperating with outlet means for discharging an exhaust gas from the combustion chamber, a device for producinq ignition within said combustion chamber, the cylinder head and the piston having opposite ends being so profiled that during operation near the end of the compression stroke of the piston a squirt chamber is formed, and at least one orifice being provided for discharging combustible mixture from said squirt chamber into the combustion chamber.

2. Internal combustion engine as claimed in claim 1, wherein the cylinder head is provided with a raised portion downwardly projecting from the cylinder head and defining a recess cooperating with a raised portion upwardly projecting from the piston to form said squirt chamber.

3. Internal combustion engine as claimed in claim 2, wherein the recess and the raised portion fitting in said recess are substantially annularly shaped.

4. Internal combustion engine as claimed in claim 2, wherein the recess and the raised portion fitting in said recess are each substantially in the form of a segment of a circle.

5. Internal combustion engine as claimed in any one of the claims 2--4, being provided with a plurality of recesses and raised portions each fitting in an accompanying recess, thereby forming a plurality of squirt chambers.

6. Internal combustion engine as claimed in claim 2, wherein the recess and the raised portion fitting in said recess are substantially centrally arranged with respect to the cylinder bore.

7. Internal combustion engine as claimed in any one of the claims 1-6, comprising a plurality of orifices distributed over the squirt chamber(s) for discharging combustible mixture therefrom.

8. Internal combustion engine as claimed in any one of the claims 1-7, wherein the orifice(s) are arranged in a baffle-shaped element.

9. Internal combustion engine substantially as described in the specification with particular reference to the accompanying drawings.