SE522254C2 - Working cycle and internal combustion engine compresses inlet air in two parts to different pressures and adds fuel to lower pressure air before mixing and expanding burning fuel and air in cylinder - Google Patents

Abstract

The engine inlet air is divided into two sections that are compressed to different pressures. Fuel is added and ignited in only the lower pressure portion then the two portions are combined and expanded together Independent claims are also included for (a) A working cycle for an internal combustion engine (b) The internal combustion engine using the cycle

Description

25 30 I ø | o v: o 522 2fâ4 There are many reasons for this, and among these is a desire to reduce engine fuel consumption, thereby reducing operating costs, and also a desire to reduce emissions of harmful residues from combustion to nature.

One way to increase the thermal efficiency of an internal combustion engine is, as can be seen above, to increase the compression ratio in the engine. However, there are some limitations to this, as a high compression ratio gives a high pressure in the combustion chamber of the engine cylinder or cylinders at the end of the compression.

During combustion, the stresses on the engine, especially the moving parts, then become very high. In order to obtain sufficient strength, the dimensions of the parts must be increased, which means increased weight and increased internal friction and lowers the mechanical efficiency. High pressures also lead to problems in controlling the ignition of the fuel, and this is especially the case for engines with spark ignition of the fuel, i.e. engines operating according to the Otto cycle, but also engines with compression ignition, i.e. Engines operating according to the Diesel cycle will face problems if the pressure in the combustion core is very high at the end of the compression- IIBII.

SUMMARY OF THE INVENTION An object of the present invention is to provide a duty cycle for a heat engine, which duty cycle enables an increase in the thermal efficiency of the engine compared with previously known heat engines. This object is achieved by a work cycle according to claim 1.

Another object of the present invention is to provide a duty cycle for a piston type internal combustion engine, which duty cycle enables an increase in the thermal efficiency of the engine as compared with a conventional engine, which duty cycle is applicable to both spark ignition engines and compression ignition engines of both and four-stroke type. This is achieved by a duty cycle as defined above, which duty cycle is characterized by the features defined in claim 2.

Another object of the present invention is to provide an internal combustion engine with increased thermal efficiency compared to a conventional engine, which engine in the present invention is either a spark ignition or compression ignition engine of the two- or four-stroke type.

This is achieved by an internal combustion engine of the initially defined type, which engine is characterized by the features defined in claim 9.

Preferred embodiments of the work cycle and the motor are defined in the independent claims.

Description of the drawings The invention will now be described in more detail below, with reference to the accompanying drawings, of which Fig. 1 is a temperature / entropy diagram for the work cycle according to the invention, Fig. 2 is a pressure / volume diagram for a work cycle according to Fig. 1, Figs. 3a-e are highly schematic longitudinal cross-sections through a motor operating according to a work cycle according to the present invention in different stages of the work cycle, Fig. 4 is a temperature / entropy diagram for a work cycle according to a second embodiment. Fig. 5 is a pressure / volume diagram of the working cycle according to a second embodiment of the invention, Figs.

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Figs. 6a-c 8a-e 9 522 254 fn in 4 show diagrams of pressure against crankshaft angle for cycle processes A and B and the combined working cycle according to the second embodiment of the present invention, is a pressure / volume diagram for the compression stroke in the working cycle according to the second embodiment of the invention, is a highly schematic longitudinal cross-section through a motor operating after the working cycle according to the second embodiment of the invention in different stages of the working cycle, is a pressure / crankshaft angle diagram for a motor according to Figs. 10-133, 10-13 shows a cross section through an internal combustion engine according to the invention in different stages of the working cycle, 11a, 12a, and 13a shows enlarged parts of Figs. 11, 12 and 13, 14 14a 14b 15 16 16a respectively with the piston in its upper dead center position. shows a cross-section along the line XIV-XIV in Fig. 14, shows an enlarged cross-section of a part of an engine according to Fig. 14, with the piston approximately 10 crankshaft degrees before the upper dead center position, shows a cross-section through another internal combustion engine according to the invention, which engine is of the two-stroke type with spark ignition, at the beginning of the compression stroke, shows a cross section corresponding to Fig. 15 but with the engine in a position below the last part of the compression stroke, is an enlarged view of the marked area in Fig. 16. 17, 17a show cross section through a four-stroke engine according to a further modified embodiment of the present invention in positions initially respectively towards the end of the compression stroke, shows a cross-section through a modified four-stroke engine according to the invention, and "i" shows a cross-section through a further modified four-stroke engine according to recovery. Detailed Description of Preferred Embodiments Reference will first be made to Figs. 1-3, which relate to a substantially theoretical side of the invention. Fig. 1 shows a temperature / entropy diagram for a work cycle according to the invention. The curves marked A and B respectively refer to sub-processes performed in different parts of an internal combustion engine, which will be described in more detail below. The numbers in circles mark specific points and are used as an index in the description below.

As can be seen in Figs. 1 and 2, process A comprises a compression from point 1 to point 3 comprising supplying QaddA compression heat, while process B comprises a compression from point 1 to point 2, which is significantly less than the compression according to process A. Thereafter, process B comprises a pressure increase by supplying heat Qaddß, so that processes A and B meet at point 3. From that point it is a common expansion to point 4, where the remaining heat Qdiss is diverted from point 4 to point 1 , whereupon the process restarts from the beginning.

The ternary efficiency of the work cycle described above, as for all friend motors, is calculated as now, = (Qadd - Qdiss) / Qadd, where Qadd = supplied heat = m - cv (T3-T2) and Qdíss = dissipated heat = m - cv (T4 - TI). Thus now, = 1- (T4- TI) / (T3 - T2) = 1 - T] / Tz. The index figures correspond to the conditions in the specific points in Figs. 1 and 2 mentioned above. About TI / T; = sm, it is concluded that now, = l- aw, where the compression ratio is defined as s = (VC + VS) / VC, where VC is the compression volume and VS is the engine stroke volume. This means that for the work cycle described above, a = (VCA + VCB + VSA + VSB) / (VGA + VCB), where indices A and B refer to process A and B, respectively, as described above.

Fig. 3a-e shows very schematically the order of the work cycle according to the present invention. If one starts in Fig. 3a, a heat engine is shown in the form of a very schematic internal combustion engine 1 having two cylinders 2 and 3, in which pistons 4 and 5, respectively, are movable in an upward direction. and down. The pistons 4, 5 are by means of connecting rods 6 and 7, respectively, connected to a crankshaft 8 in the lower part of the engine. A cylinder head 9 is shown which shuts off the upper part of the cylinders 2, 3.

There is also shown a connecting channel 10 between the cylinders 2, 3 and a flap or valve 11, which can open or close the connecting channel 10.

In the mode illustrated in Fig. 3a, the pistons 4, 5 are shown as they start their upward movement in the cylinders 2 and 3, respectively. As soon as the pistons move upwards, a compression stroke starts.

The flap 11 is in its closed position, as shown in Fig. 3b, so that the connecting channel 10 is closed. The gas trapped in the cylinder 2 above the piston 4 will be compressed separately from the gas trapped in the cylinder 3 above the piston 5. As can be seen in Fig. 3b, the two amounts of gas in the cylinders 2, 3 will be compressed differently. The compression ratio in cylinder 2 will be significantly higher than the compression ratio of the gas in cylinder 3, which can be seen in Fig. 3c, i.e. the compression volume VCB in cylinder 2 is smaller than the compression volume VGA in cylinder 3.

In the position indicated in Fig. 3c, the pistons are located at their upper dead center positions in the cylinders 2 and 3, respectively. The flap 11 is opened and heat is supplied, which is indicated by the arrow 12. This means that the temperature and pressure in the compression chamber two volumes of VGA and VCB increase significantly. The pistons 4, 5 will begin their downward movement under the influence of enthalpy of the gas in the compression chamber 13. This is indicated by the arrows 14 in Figs. 3d. The movement of the pistons 4, 5 is transmitted through the connecting rods 6, 7 to the crankshaft 8.

When the pistons 4, 5 reach the position illustrated in Fig. 3e, heat is dissipated as indicated by the arrow 15, after which the situation is the same as in Fig. 3a. 1/10 15 20 25 30 o o v u aa u 7 The above description with reference to Figs. 3a-e is mainly theoretical and has therefore been illustrated with a cross section through a motor, which is shown very schematically and only with the parts necessary for the understanding of the invention.

Reference will thus be made to Figs. 4-8, which relate to a second embodiment of the work cycle according to the invention. This embodiment is also highly theoretical and the engine is shown in Figs. 8a-e are very schematically illustrated. In Figs. 4-8, the same reference numerals are used as in Figs. 1-3, with reference numerals added for parts having no equivalent in Figs. 1-3.

As can be seen in Figs. 4 and 5, process A, as before, comprises a compression from point 1 to point ls and on to point 3, while process B comprises a compression from point 1 to point ls, and thence to point 2. From point 1 to point 1s the two processes A and B are parallel, but from point 1s the two processes are separate, and, as can be seen, the compression according to process B from point 1s to point 2 gives a much lower compression than the compression according to the process A. This means that after point 2, the process B comprises an increasing pressure through an additional vein, as described above in connection with Figs. 1-3. From point 3, processes A and B are performed together as a process in the same manner as described above in connection with Figs. 1-3.

Figs. 6a-c show pressure / piston position diagrams for process A, process B and the combination of the two processes, respectively.

Fig. 7 shows a pressure / volume diagram for the compression stroke of the work cycle. Points 1, 2 and 3 are the same as before, but F ig. 7 shows an example where the compression ratio from point 1 to point 2 is s = 10, while the compression ratio from point 1 to point 3 is a = 36: An imaginary curve 16 is also shown, which represents the adiabatic compression to a compression ratio at s = 20, which represents the nominal compression ratio of the motor when the compression ratios in points 2 and 3 are s = 10 and s = 36, respectively. These values are applicable to the example illustrated in Fig. 7, but depending on the physical configuration of the engine, a predetermined value of the nominal compression ratio can be obtained with other values of the compression ratios for process A and process B. Curves 17 and 18 are also shown in Fig. 7, which represent the adiabatic compression to the compression ratio s = 36 and a, respectively. = 10.

Figs. 8a-e show very schematically an internal combustion engine in which the working cycle according to Figs. 4-7 is performed. The reference numerals used in Figs. 8a-e are the same as those used in Figs. 3a-e, but additional numbers are used for elements not found in Figs. 3a-e. Starting in Fig. 8a, pistons 4, 5 in cylinders 2, 3 are in a position to expose inlet 19 and outlet 20, so that gas exchange can take place in the engine. The flap or valve ll is open. From that point on, there will be a common compression of the gas in cylinders 2, 3 during a part of the stroke of the pistons 4, 5 along the adiabate corresponding to the nominal compression ratio of the engine. When the pistons 4, 5 reach the position shown in Fig. 8b, the flap 11 is moved to its closed position, so that their connecting channel 10 is closed. From that point and up to the point shown in Fig. 8c, the gas parts in cylinders 2, 3 will be compressed separately to different compression conditions, as shown in Figs. 4-7.

Fuel is then supplied to the gas in cylinder 3 above piston 5 by means of a fuel injector 21, whereupon the fuel / gas mixture is ignited by means of a spark plug 22.

Then, the valve 11, as shown in Fig. 8e, is opened so that the gas parts will be mixed in the compression volume corresponding to the nominal compression ratio of the engine and will then expand together, as shown by the arrows.

When the expansion is completed, the pistons 4, 5 have reached a position for exposing the inlets 19 and the outlets 20, so that gas exchange can be performed again. Then the process is repeated. 10 15 20 25 30 ø. v n nu 522 254 9 With reference to F ig. 9-13a, a working cycle of an internal combustion engine will be described, and the engine according to these figures represents what is ideally possible to achieve in operation.

Fig. 9 shows a pressure / crankshaft angle diagram of the working cycle of the motor according to Figs. 10-13a. As can be seen, it is first a common compression from the lower dead center position to point 1s. Thereafter, the gas is divided into two parts, one of which is compressed to a high compression ratio, while the second gas part is supplied with fuel which is ignited in order to raise the compression pressure to substantially the same level as for the first gas part. At a point just before the upper dead center position, designated 23 in Fig. 9 and called the tap point, some gas from the highly compressed gas portion is allowed to flow into the other gas portion in order to improve the mixture of gas and fuel, which will be described in more detail below. . Also shown in Fig. 9 is a curve 24, which relates to adiabatic compression according to the nominal compression ratio of the motor. The process after upper dead center position is essentially as described above, i.e. the two gas parts are expanded together to produce work.

The engine illustrated in Figs. 10-13a has an engine block 25 and a crankcase 25a. A cylinder liner 26 is inserted into the engine block 25, in which a piston 27 is movable up and down.

The piston 27 is connected by means of a connecting rod 28 to a crankshaft 29, which runs in bearings (not shown) in the engine block 25 and the crankcase 25a. An inlet 30 and an outlet 31 are provided in the engine block 25 and the cylinder liner 26, but for the sake of clarity no inlet or outlet systems are shown, as they may be of conventional type and do not form part of the invention. From the position of the inlet 30 and the outlet 31, it is clear that the motor operates according to the two-stroke operating cycle.

At the upper end of the cylinder liner 26 there is a cylinder head 32 which closes the upper end of the cylinder liner 26. In the cylinder head 32 there is indicated a fuel injector 33 for injecting fuel into the engine combustion chamber. It can also be seen in the drawings that the cylinder head 32 is an insert which is inserted into the upper part of the engine block 25. Cooling passages 34 and 35 are arranged both in the cylinder head 32 and in the engine block 25 around the upper part of the cylinder liner 26.

The upper surface of the piston 27 and the lower surface of the cylinder head 32 define, together with the peripheral wall of the cylinder liner 26, the combustion chamber. When the piston 27 is in its lower dead center position, as shown in Fig. 10, the combustion chamber 36 is connected to the inlet 30 and the outlet 31, so that gas exchange can be performed in the combustion chamber 36.

On its upper surface, which delimits the combustion canary 36, the piston 27 is provided with a projection 37. The projection 37 is coaxial with the piston 27 and substantially cylindrical and provided with a slightly concave upper surface 38. However, the surface 38 may have other shapes, e.g. . flat or convex. The projection 37 is peripherally delimited by a substantially cylindrical peripheral surface 39, and radially outside the peripheral surface 39 there is an annular surface 40, which in the embodiment shown is designed as a truncated cone with a large apex angle. The projection 37 can of course be designed differently. Its cross-sectional shape may be other than circular-cylindrical, and it may be placed armor-like rather than centrally on the piston 27. Furthermore, the annular surface may be flat or shaped in a reinforced manner.

The inside of the cylinder head 32 is formed with a cylindrical surface 41 and an annular surface 42 for co-operation with the peripheral surface 39 and the annular surface of the piston 27, which will be described in more detail below. Above the annular surface 42, the cylinder head is formed with a recess 43 defined by the cylindrical surface 41 and the inside of the cylinder head 32 above the cylindrical surface 41.

The fuel injector 33 extends into the recess 43.

When the crankshaft 29 rotates from / the position in Fig. 10, the piston 27 will be moved upwards in the cylinder by means of the connecting rod 28. When the piston, after a short movement, has closed the inlet 30 and the outlet 31, the air found in the combustion chamber 36 that 10 15 20 25 30 Q »n - .o 522 254 11 is compressed during the compression stroke. When the piston 27 has reached the position in Fig. 11, the projection 37 will start to enter the recess 43 in the cylinder head 32. As can be seen in Fig. 11 and in more detail in Fig. 11a, the peripheral surface 39 of the projection 37 fits with a relatively small gap against the cylindrical surface 41 in the recess 43. This means that the combustion chamber 36 is divided into two parts, where one part is the recess 43 and the other part is an annular chamber 44 between the annular surfaces 40 and 42 (see Fig. lla). It can also be seen that the inside of the cylinder head 32 along the surfaces 41 and 42 is provided with a protective surface coating, e.g. of a heat-resistant material, such as a ceramic material. The reason for this is to enable the use of higher temperatures during operation of the engine. For the same reason, the annular surface 40 and the peripheral surface 39 of the piston 27 are provided with a protective surface coating 46. As can be seen in e.g. Fig. 1a extends the protective coating 45 of the cylinder head a short distance down into the cylinder.

During continued rotation of the crankshaft 29, further compression will take place.

During this period, the compression of the air in the recess 43 is relatively low compared to the compression of the air in the annular chamber 44.

When the piston reaches the position shown in Figs. 12 and 12a, and the crankshaft 29 continues its rotation, a narrow gap is formed between the peripheral surface 39 and the cylindrical surface 41, due to the fact that the peripheral surface 39 has a section 39a with reduced diameter. This gap is clearly seen in Figs. 13 and 13a, which show the piston 27 in its upper dead center position.

This small gap 47 will allow some of the highly compressed gas in the annular chamber 44 to flow through the gap 47 and into the recess 43. In this way, some of the gas from the chamber 44, which is very highly compressed and very hot, can da blown through the gap 47 into the recess 43 to improve the combustion in the recess 43. In the position shown in Figs. 43. During the movement of the piston 27 from the position shown in Figs. 13 and 13a, it will reach the positions shown in Figs. 12 and 12a, and 11 and 11a, whereupon the remaining combustion and expansion will take place. throughout the combustion chamber 36.

Figs. 14, 14a and 14b show a piston 48 and a cylinder head 49, which are slightly modified in relation to the corresponding parts according to Figs. 10-13a. In the piston 48, the projection 50 is formed as an insert which is welded in the lq-one of the piston. This allows the use of another material for the projection 50 and for the rest of the piston 48. Furthermore, the cylinder head 49 is provided with a cutter 51 which extends along a part of the cylinder surface 52 and which is intended to create a controlled gas flow through the gap 47, described in connection with Figs. 10-13a. In this way, it is possible to further improve the mixture of gas and fuel in the recess 43 in order to obtain a better combustion. By varying the shape and size of the groove 51, it is possible to create different fl fate patterns to suit different circumstances.

Figs. 15, 16 and 16a show another embodiment of an internal combustion engine according to the invention. The engine comprises an engine block 53, a crankcase 54 and a cylinder head 55. In the crankcase 54, a crankshaft 56 is rotatably mounted. The crankshaft 56 carries a connecting rod 57, on the other end of which a piston 58 is arranged. The cylinder head 55 is provided with a spark plug 59 and a fuel injector 60.

The upper surface of the piston 58 and the lower surface of the cylinder head 55 defined, together with the peripheral cylinder wall, a combustion chamber 61. When the piston is in its lower dead center position, as shown in Fig. 15, the combustion chamber 61 is connected by a inlet duct 62 to an air supply device 63 and through an outlet duct 64 to an exhaust system 65.

The upper surface of the piston 58 is provided with a projection 66 which is coaxial with the piston 58 and is provided with a substantially flat upper surface 67. The projection 66 is defined peripherally by a substantially cylindrical peripheral surface 68, and radially outside this. 52 2 2 5 4 i Es. 13 surface there is an annular surface 69, which in the embodiment shown is designed as a truncated cone with a large top angle.

The inside of the cylinder head 55 has a cylindrical surface 70 and an annular surface 71 for cooperating with the peripheral surface 68 and the annular surface 69 of the piston 58. Above the cylindrical surface 70 the cylinder head 55 has a recess 72, into which the spark plug 59 and the fuel injector 60 extend. .

When the crankshaft 56 rotates from the position in Fig. 15, the piston 58 will be moved upwards in the cylinder by means of the connecting rod 57. When the inlet duct 62 and the outlet duct 64 have been closed by the piston, the air in the combustion chamber 61 will be compressed. When the piston 58 has reached the position in Fig. 16, the projection v66 will begin to enter the recess 72 in the cylinder head 55. As can be seen in Figs. 16 and in more detail in Fig. 16a, the peripheral surface 68 of the projection 72 fits with a small gap against the cylindrical surface 70 of the recess 72. This means that the pre-combustion core 61 is divided into two parts, one part being the recess 72 and the the second part is an annular chamber 73 between the annular surfaces 69 and 71.

During continued rotation of the crankshaft 56, further compression will take place until the piston reaches its upper dead center position. During this period, the compression of the air in the recess 72 is relatively low in iron with the compression of the air in the annular chamber 73. As an example, the compression ratio of the air in the recess 72, from the position according to Figs. 6 and 6a to the piston 58 dead center position, be 1.3, while the compression ratio of the air in the ring-shaped frame 73 during the same period may be 5.

When the piston 58 has reached the upper dead center position, or just before this position, fuel is injected into the recess 72 by means of the fuel injector 60, whereupon the fuel / air mixture is ignited by means of the spark plug 59. After this the process will be substantially the same as described above with reference to Figs. 10-13a, with the exception that since the peripheral surface 68 has no section of reduced diameter, there will be no or very little air flow from the annular chamber 73 to the recess 72.

Reference is made to Figs. 17 and 17a, which show parts of an internal combustion engine of the four-stroke type, which means that the engine comprises an inlet valve 74 and an outlet valve 75. It should also be noted that in this embodiment the position of the recess and the protrusion have been replaced. . In this embodiment, the piston 76 is provided with a recess 77, while the cylinder head 78 is provided with a projection 79. This shows that a four-stroke engine is possible according to the invention, and Figs. 17 and 17a also show that the piston may have the recess while the cylinder head is provided with the protrusion. The function and duty cycle of the engine according to this embodiment is analogous to what has been described previously with respect to Figs. 10-16.

F ig. 18 shows an internal combustion engine of the four-stroke diesel type. In this case, the upper surface of the piston 80 is flat and the recess 81 has a conical shape. A fuel injector 82 extends into the recess 81, and in this case the compression ratio has been selected relatively high, so that the pressure and temperature after compression in the recess 81 are high enough to cause self-ignition in the recess 81. e F ig. 19 shows a further modified internal combustion engine according to the invention. This engine is of the four-stroke Ottotype, and in this embodiment the piston 83 has an upper surface which consists of different parts. The upper surface of the protrusion 84 consists of two surfaces 84a and 84b, which are flat surfaces inclined towards each other. In a similar manner, the annular surface 85, which surrounds the projection 84, consists of two flat parts 85a, 85b, which are inclined towards each other. Otherwise, the motor in Fig. 19 largely corresponds to the motors described above, and also the work cycle performed in the motor according to Fig. 19 corresponds to the work cycle performed in the motors according to the previously described embodiments. o o | | The invention is not limited to what has been described above, but the person skilled in the art can modify the invention within the scope of the appended claims.

Claims (23)

10 15 20 25 522 254 16 Patent claims 1. A working cycle for a heat engine, in particular of a piston type, which engine has a gas as the working medium, the working cycle comprising the following steps: isentropic compression of the gas (P2, P3), isocortical supply of heat to the gas (Qaddß), isentropic expansion of the gas (P4), isocortical return of the gas to its original state (Qm), characterized in that the gas before or during the compression is divided into a first and a second part (A, B), that the parts of the gas are compressed to different levels (P2 , P3), that the supply (Qom) of heat is carried out only or mainly to the part of the gas which is compressed to the lowest level, after which the two parts of the gas are brought into communication with each other and expanded together (P4). Work cycle of a piston-type internal combustion engine, having an internal combustion chamber (36, 61) and a cylinder head (9, 32, 49, 55, 78), characterized by the following steps: entering a quantity of gas into the combustion chamber ( 36, 61), dividing the gas into a first and a second part, compression (P2) of the first part of the gas to a first predetermined compression ratio, compression (P3) of the second part of the gas into a second, higher compression ratio holding, introducing a predetermined amount of fuel into the first part of the gas, igniting the fuel in the first part of the gas (Qaddß), connecting the first and the second part of the gas, expanding the first and the second part of the gas together (P4), and outflow of the expanded gas from the combustion chamber (36, 61). 10 15 20 25 30 522 254 17 Operating cycle for a heat engine according to claim 1 or 2, characterized in that the nominal compression ratio s for the motor is: 8 = (VGA + VcB + VsA + Vsß) / (VCA + VCB), where VCA = the compression volume of the first gas part, VCE = the compression volume of the second gas part, VSA = the stroke volume of the first gas part, and VSB = the stroke volume of the second gas part. Work cycle according to one of Claims 1 to 3, characterized in that the division of the amount of gas into a first and a second part is carried out after a primary compression (P4) of the entire amount of gas. Work cycle according to one of Claims 2 to 4, characterized in that! of fuel being introduced into the first part of the gas during the last part of the compression and / or the first part of the expansion. Work cycle according to one of Claims 4 or 5, characterized in that the division of the amount of gas is carried out when the piston (27, 48, 58, 76, 80, 83) has reached a predetermined position in the cylinder. Work cycle according to one of Claims 2 to 6, characterized in that a connection (47) between the two parts of the gas is opened during the last part of the compression, which connection (47) has a limited cross-sectional area. Working cycle according to Claim 7, characterized in that the cross-sectional area of the connection (47) is varied depending on the position of the piston in the cylinder. A piston-type internal combustion engine, in which the piston (27, 48, 58, 76, 80, 83) defines a combustion chamber (36, 61) together with the walls of the cylinder in which the piston (27, 48, 58, 76, 80, 83) is movable back and forth, and a cylinder head (9, 32, 49, 55, 78) closing one end of the cylinder, characterized in that the combustion chamber (36, 61) is provided with means (37, 50, 66, 79, 84, 43, 72, 77, 81) for dividing the combustion core (36, 61) into two parts, which give different compression ratios when the piston (27, 48, 58 , 76, 80, 83) performs a compression stroke in the cylinder. Internal combustion engine according to Claim 9, characterized in that means (33, 60, 82) for introducing fuel and means (59) for igniting the fuel are arranged in the part of the combustion chamber (36, 61) which has the lowest compression ratio. . Internal combustion engine according to claims 9-10, characterized in that the end surface of the piston (27, 48, 58, 76, 80, 83) on the combustion gas side or the cylinder head (9, 32, 49, 55, 78) is provided with a projection (37, 50, 66, 79, 84) for cooperating with a recess (43, 72, 77, 81) in the surface of the cylinder head (9, 32, 49, 55, 78) or the piston (27, 48, 58 , 76, 80, 83) for the purpose of dividing the combustion chamber (36, 61) into two parts, the dimensions of the cross section of the projection and the recess being such that the projection (37, 50, 66, 79, 84) fits into the recess (43, 72, 77, 81) with a predetermined margin between the two. Internal combustion engine according to one of Claims 9 to 11, characterized in that the projections (37, 50, 66, 79, 84) and the recess (43, 72, 77, 81) are located substantially centrally on or in the piston (27). , 48, 58, 76, 80, 83) and the cylinder head (9, 32, 49, 55, 7 8). Internal combustion engine according to one of Claims 9 to 12, characterized in that the height of the projection (37, 50, 66, 79, 84) in the direction of the cylinder axis is substantially less than the corresponding height of the recess (43, 72, 77, 81). 10 15 20 25 30 522 254 19 Internal combustion engine according to one of Claims 9 to 13, characterized in that the end surface of the projection (66, 79) is substantially flat. Internal combustion engine according to one of Claims 9 to 13, characterized in that the end surface of the projection (37, 50, 66, 79, 84) is provided with a cavity. Internal combustion engine according to one of Claims 9 to 15, characterized in that the cross sections of the projections (37, 50, 66, 79, 84) and the recess (43, 72, 77, 81) are substantially circular. Internal combustion engine according to one of Claims 9 to 16, characterized in that the piston (27, 48, 58, 76, 80, 83) has an annular surface (40, 69) which surrounds the projection (37, 50, 66, 79, 84 ) or the recess (43, 72, 77, 81), which annular surface (40, 69) is preferably substantially frustoconical with a large apex angle. Internal combustion engine according to claim 17, characterized in that the cylinder head (9, 32, 49, 55, 78) has an annular surface (42, 71) surrounding the recess (43, 72, 77, 81) or the projection (37, 50, 66, 79, 84), which annular surface (42, 71) is preferably substantially frustoconical with a large apex angle. Internal combustion engine according to one of Claims 9 to 16, characterized in that the piston (83) and the cylinder head have an annular surface (85a, 85b) which surrounds the projection and the recess, respectively, which annular surface (85a, 85b) comprises two substantially flat lower surfaces (85 a, 85b), which are inclined at a large angle to each other. Internal combustion engine according to one of Claims 9 to 19, characterized in that the cylinder head (9, 32, 49, 55, 78) is provided with an insert which supports the projection (37, 50, 66, 79, 84) or the recess. (43, 72, 77, 81) and made of materials with high thermal resistance properties, and low thermal conductivity. 10 522 254 20 Internal combustion engine according to claim 20, characterized in that the insert in the cylinder head (9, 32, 49, 55, 78) is provided with a collar which extends into the cylinder and forms the upper part of the wall of the cylinder. Internal combustion engine according to claim 20 or 21, characterized in that the insert in the cylinder head (9, 32, 49, 55, 78) is uncooled or arranged for cooling only to a limited extent. Internal combustion engine according to one of Claims 9 to 22, characterized in that the upper part of the piston (27, 48, 58, 76, 80, 83), which comprises the recess (43, 72, 77, 81) or the projection (37, 50, 66, 79, 84), is made of a material with high heat resistance properties and low thermal conductivity.