Abstract:
The present invention relates to a working cycle for a heat engine, especially of the reciprocating piston type, having a gas as working medium, including the steps of isentropic compression of the gas, isochoric addition of heat to the gas, isentropic expansion of the gas, and isochoric return of the gas to its initial condition. The invention is characterized in that the gas, before or during the compression, is divided into two portions, that the gas portions are compressed to different degrees, that heat is added only or mainly to the gas portion compressed to the lowest degree, and that the two gas portions are brought into connection with each other and are expanded together.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a working cycle for a heat engine, especially an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     Heat engines, e.g. internal combustion engines of the reciprocating piston type, have been used extensively for a long time for driving a wide range of machinery, both stationary, e.g. generators, pumps, and compressors, and movable, e.g. land, sea, and aerial vehicles. In the technology of internal combustion engines the two principal working cycles are the Otto cycle and the Diesel cycle. Both these cycles have been used in both two- and four-stroke variants. 
     In heat engines of the type referred to above, the principal, ideal working cycle includes isentropic compression of the gas, isochoric addition of heat to the gas, isentropic expansion of the gas, and isochoric return of the gas to its condition at the start of the working cycle. 
     This ideal cycle is only possible under certain conditions, i.e. the working medium is an ideal gas having constant specific heats c p , c v , there are no heat, gas or flow losses, the addition and dissipation of heat is instantaneous, and there is no residual gas. 
     In the internal combustion engine technology it is desirable to achieve as high efficiency as possible, and this is true for both the mechanical and the thermal efficiency. There are many reasons for this, and among these there is a desire to reduce the fuel consumption of the engine, and thereby to reduce the operation costs, and also a desire to reduce the emission of harmful residues from the combustion to the environment. 
     One way to increase the thermal efficiency of an internal combustion engine is, as can be seen above, to raise the compression ratio of the engine. However, there are certain limitations to this, because a high compression ratio gives a high pressure in the combustion chamber in the cylinder or cylinders of the engine at the end of the compression. During combustion, the stresses of the engine, especially the moving parts, then become very high. In order to get sufficient strength, the dimensions of the parts have to be increased, which means increased weight and increased internal friction and lowers the mechanical efficiency. High pressures also lead to problems regarding control of the ignition of the fuel, and this is particularly the case for spark ignition engines, i.e. engines working according to the Otto working cycle, but also compression ignition engines, i.e. engines working according to the Diesel working cycle, will encounter problems if the pressure in the combustion chamber is very high at the end of the compression. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a working cycle for a heat engine, said working cycle enabling an increase in the thermal efficiency of the engine in comparison to previously known heat engines. 
     Another object of the present invention is to provide a working cycle for an internal combustion engine of the reciprocating piston type, said working cycle enabling an increase of the thermal efficiency of the engine in comparison to a conventional engine, said working cycle being applicable to both spark ignition and compression ignition engines of both two- and four-stroke types. 
     This is achieved by a working cycle as defined above. 
     Another object of the present invention is to provide an internal combustion engine having increased thermal efficiency compared to a conventional engine, said engine of the present invention being either a spark ignition or a compression ignition engine of the two- or four-stroke type. 
     This is achieved by an internal combustion engine of the initially defined type. 
     Preferable embodiments of the working cycle and the engine are defined in the depending claims. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention will be described in more detail below with reference to the enclosed drawings, in which 
     FIG. 1 is a temperature-entropy diagram for the working cycle according to the invention, 
     FIG. 2 is a pressure-volume diagram for a working cycle according to FIG. 1, 
     FIG. 3 a-e  are highly schematic longitudinal sections through an engine working according to the working cycle of the present invention in various stages of the working cycle, 
     FIG. 4 is a temperature-entropy diagram for a working cycle according to a second embodiment of the invention, 
     FIG. 5 is a pressure-volume diagram for the working cycle according to the second embodiment of the invention, 
     FIG. 6 a-c  show diagrams of pressure vs. crankshaft angle for cycle processes A and B and the combined working cycle according to the second embodiment of the present invention, 
     FIG. 7 is a pressure-volume diagram of the compression stroke of the working cycle of the second embodiment of the invention, 
     FIGS. 8 a-e  are highly schematic longitudinal sections through an engine working according to the working cycle of the second embodiment of the invention in different stages of the working cycle, 
     FIG. 9 is a pressure-crankshaft angle diagram for an engine in accordance with FIGS. 10-13 a,    
     FIGS. 10-13 show cross sections through an internal combustion engine according to the invention in different stages of the working cycle, 
     FIGS. 11 a ,  12   a  and  13   a  show enlarged portions of FIGS. 11,  12 , and  13 , respectively, 
     FIG. 14 shows a section through a modified embodiment of an engine according to the present invention, with the piston in its top dead centre position, 
     FIG. 14 a  shows a section along the line XIV—XIV in FIG. 14, 
     FIG. 14 b  shows an enlarged section of a part of the engine according to FIG. 14, with the piston approx. 10 crankshaft degrees before top dead centre position, 
     FIG. 15 shows a section through another internal combustion engine according to the invention, said engine being of the two-stroke type with spark ignition, at the beginning of the compression stroke, 
     FIG. 16 shows a section corresponding to FIG. 15 but with the engine in a position during the last part of the compression stroke, 
     FIG. 16 a  is an enlarged view of the marked area in FIG. 16, 
     FIGS. 17,  17   a  show sections through a four-stroke engine according to a further modified embodiment of the present invention in positions at the beginning and towards the end of the compression stroke, respectively, 
     FIG. 18 shows a cross section through a modified four-stroke engine according to the invention, and 
     FIG. 19 shows a cross section through a further modified four-stroke engine according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will first be made to FIGS. 1-3, which relate to a mostly theoretical aspect of the invention. FIG. 1 shows a temperature-entropy diagram of a working cycle according to the invention. The curves marked A and B, respectively, refer to part processes performed in different parts of an internal combustion engine, as will be described in more detail below. The numbers in circles denote specific points and are used as indexes in the description below. 
     As can be seen from FIGS. 1 and 2, the process A includes a compression from point  1  to point  3  including addition of compression heat Q addA , whereas the process B includes a compression from point  1  to point  2 , which is considerably less than the compression according to process A. Thereafter, the process B includes an increase in pressure by addition of heat Q addB , so that the processes A and B meet at the point  3 . From that point there is a common expansion to point  4 , where the remaining heat Q diss  is dissipated from point  4  to point  1 , whereupon the processes start all over again. 
     The thermal efficiency of the working cycle described above, as of all heat engines, is calculated as η th =(Q add −Q diss )/Q add , where Q add =added heat=m c v (T 3 −T 2 ) and Q diss =dissipated heat=m c v (T 4 −T 1 ). Therefore, η th =1−(T 4 −T 1 )/(T 3 −T 2 )=1−T 1 /T 2 . The index numbers correspond to the conditions in the specific points in FIGS. 1 and 2 as mentioned above. If T 1 /T 2 =ε k−1 , we will arrive at the η th =1−ε k−1 , we will arrive at η th =1−ε k−1 , where the compression ratio is defined as ε=(V c +V s )/V c , where V c  is the compression volume and V s  is the displacement of the engine. This means that for the working cycle described above, ε=(V cA +V cB +V sA +V sB )/(V cA +V cB ), where the indexes A and B refer to processes A and B, respectively, as described above. 
     In FIGS. 3 a-e , there is shown very schematically the sequence of the working cycle according to the present invention. Starting in FIG. 3 a , there is shown a heat engine 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 and downward direction. 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 closing off the upper portion of cylinders  2 ,  3 . There is also a connection channel  10  between the cylinders  2 ,  3 , and a flap or valve  11 , which is able to open or close the connection channel  10 . 
     In the position illustrated in FIG. 3 a , the pistons  4 ,  5  are shown as they start their movement upwards in cylinders  2 ,  3 , respectively. As soon as the pistons  4 ,  5  move upwardly a compression stroke starts. The flap  11  is in its closed position, as shown in FIG. 3 b , so that the connection channel  10  is closed. The gas enclosed in cylinder  2  above piston  4  will be compressed separately from the gas enclosed in the cylinder  3  above piston  5 . As can be seen in FIG. 3 b , the two masses of gas in the cylinders  2 ,  3  will be compressed differently. The compression ratio in cylinder  2  will be substantially higher than the compression ratio of the gas in cylinder  3 , as can be seen in FIG. 3 c , i.e. the compression volume V cB  in cylinder  2  is smaller than the compression volume V cA  in cylinder  3 . 
     In the position indicated in FIG. 3 c , the pistons  4 ,  5  are situated at their top dead centres in cylinders  2 ,  3 , respectively. The flap  11  is opened and heat is added, as indicated by the arrow  12 . This means that the temperature and the pressure in the compression chamber  13  formed by the two volumes V cA  and V cB  increase substantially. The pistons  4 ,  5  will start their downward movement under the influence of the entalphy of the gas in the compression chamber  13 . This is indicated by the arrows  14  in FIG. 3 d . The movement of the pistons  4 ,  5  is transmitted through the connecting rods  6 ,  7  to the crank shaft  8 . 
     When the pistons  4 ,  5  reach the position illustrated in FIG. 3 e , heat is dissipated, as indicated by the arrow  15 , whereafter the situation is the same as in FIG. 3 a.    
     The description above with reference to FIGS. 3 a-e  is mainly theoretical and has therefore been illustrated by sections through an engine, which is shown very schematically and only with the parts necessary for an understanding of the invention. 
     Reference will then be made to FIGS. 4-8, which relate to a second embodiment of the working cycle according to the invention. This embodiment is also mostly theoretical, and the engine shown in FIG. 8 a-e  is very schematically illustrated. In FIGS. 4-8, the same reference numerals are used as in FIGS. 1-3, with reference numerals added for elements not having any correspondence in FIGS. 1-3. 
     As can be seen from FIGS. 4 and 5, the process A includes, as before, a compression from point  1  to point  1   s  and further to point  3 , whereas the process B includes a compression from point  1  to point  1   s , and from there to point  2 . From point  1  to point  1   s  the two processes A and B are parallel, but from point  1   s  the two processes are separate, and, as can be seen, the compression according to the process B from point  1   s  to point  2  gives a considerably lower compression than the compression according to process A. This means that after point  2 , the process B includes an increasing pressure by additional heat, as described above in connection with FIGS. 1-3. From point  3 , the processes A and B are performed together as one process in the same manner as described above in connection with FIGS. 1-3. 
     FIGS. 6 a-c  show pressure-piston position diagrams for the process A, the process B and the combination of the two processes, respectively. 
     FIG. 7 shows a pressure-volume diagram of the compression stroke of the working cycle. Points  1 ,  2  and  3  are the same as before, but FIG. 7 shows an example where the compression ratio from point  1  to point  2  is ε=10, whereas the compression ratio from point  1  to point  3  is ε=36. There is also shown an imaginary curve  16 , which represents the adiabatic compression to a compression ratio of ε=20, which represents the nominal compression ratio of the engine when the compression ratios in points  2  and  3  are ε=10 and ε=36, respectively. These values apply to the example illustrated in FIG. 7, but depending on the physical configuration of the engine, a predetermined value of the nominal compression ratio may be achieved with other values of the compression ratios for process A and process B. Also shown in FIG. 7 are curves  17  and  18 , which represent the adiabatic compression to compression ratio ε=36 and ε=10, respectively. 
     In FIGS. 8 a-e , there is shown very schematically an internal combustion engine in which the working cycle according to FIGS. 4-7 is performed. The reference numerals used in FIGS. 8 a-e  are the same as used in FIGS. 3 a-e , but extra numerals are used for elements not found in FIGS. 3 a-e . Starting in FIG. 8 a , pistons  4 ,  5  in cylinders  2 ,  3  are situated in a position to uncover inlets  19  and outlets  20 , so that gas change can take place in the engine. The flap or valve  11  is open. From that point, there will be a common compression of the gas in cylinders  2 ,  3  during a portion if the stroke of pistons  4 ,  5  along the adiabat corresponding to the nominal compression ratio of the engine. When the pistons  4 , 5  reach the position shown in FIG. 8 b , the flap  11  is moved to its closed position, so that their connection channel  10  is closed. From that point and up to the point shown in FIG. 8 c , the gas portions in cylinders  2 ,  3  will be compressed separately to different compression ratios, as shown in FIGS. 4-7. 
     Fuel is then added 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 . 
     Thereafter the valve  11  is opened, as shown in FIG. 8 e , so that the gas portions will be mixed, in the compression volume corresponding to the nominal compression ratio of the engine and will then expand together, as show with the arrows. 
     When the expansion is completed, the pistons  4 ,  5  have reached a position to uncover the inlets  19  and the outlets  20 , so that gas change can be performed again. Thereafter the sequence is repeated. 
     With reference to FIGS. 9-13 a , a working cycle in an internal combustion engine will be described, and the engine according to these figures represent what is ideally possible to achieve in operation. 
     In FIG. 9, there is shown a pressure-crankshaft angle diagram over the working cycle of the engine of FIGS. 10-13 a . As can be seen, there is first a common compression from bottom dead centre to the point  1   s . Thereafter the gas is divided into two portions, one of which is compressed to a high compression ratio, whereas the other gas portion is provided with fuel that is ignited in order to raise the compression pressure at substantially the same rate as for the first gas portion. At a point shortly before top dead centre, designated  23  in FIG.  9  and called the release point, some gas from the highly compressed gas portion is allowed to flow into the second gas portion in order to enhance the mixture of gas and fuel, as will be described in more detail below. Also shown in FIG. 9 is a curve  24 , which relates adiabatic compression according to the nominal compression ratio of the engine. The process after top dead centre is substantially as described above, i.e. the two gas portions are expanded together in order to produce work. 
     The engine illustrated in FIGS. 10-13 a  has an engine block  25  and a crankcase  25   a . In the engine block  25  is inserted a cylinder liner  26 , in which a piston  27  is movable up and down. The piston  27  is, by means of a connecting rod  28 , connected to a crankshaft  29 , which is running in bearings (not shown) in the engine block  25  and the crankcase  25   a . An inlet  30  and an outlet  31  are arranged in the engine block  25  and the cylinder liner  26 , but, for the sake of clarity, no inlet system or outlet system is shown, as they may be of conventional type and do not form any part of the invention. From the position of the inlet  30  and the outlet  31  it is clear that the engine is working according to the two-stroke working cycle. 
     In the upper end of the cylinder liner  26  there is a cylinder head  32  closing 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 combustion chamber of the engine. It can also be seen from 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 portion 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  36 . When the piston  27  is situated in its bottom dead centre as shown in FIG. 10, the combustion chamber  36  is connected to the inlet  30  and the outlet  31 , so that gas change can be performed in the combustion chamber  36 . 
     On its upper surface, which defines the combustion chamber  36 , the piston  27  is provided with a protrusion  37 . The protrusion  37  is coaxial to 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 protrusion  37  is defined peripherally by a substantially cylindrical peripheral surface  39 , and radially outside the peripheral surface  39  there is a ring shaped surface  40 , which in the shown embodiment is shaped as a truncated cone having a large top angle. The protrusion  37  may, of course, be differently shaped. Its cross section shape may be other than circular-cylindric, and it may be placed differently from centrally on the piston  27 . Further, the ring-shaped surface  40  may be flat or shaped in a different way. 
     The inside of the cylinder head  32  is formed with a cylindrical surface  41  and a ring-shaped surface  42  for cooperation with the peripheral surface  39  and the ring-shaped surface  40  of the piston  27 , as will be described in more detail below. Above the ring-shaped surface  42 , the cylinder head  32  is shaped with a recess  43 , which is 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 of FIG. 10, the piston  27  will be moved upwardly 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 present in the combustion chamber  36  will be compressed during the compression stroke. When the piston  27  has reached the position of FIG. 11, the protrusion  37  will begin to enter the recess  43  in the cylinder head  32 . As can be seen in FIG.  11  and in more detail in FIG. 11 a , the peripheral surface  39  of the protrusion  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 portions, where one portion is the recess  43  and the other portion is a ring-shaped chamber  44  between the ring-shaped surfaces  40  and  42  (see FIG. 11 a ). It can also be seen that the inside of the cylinder head  32  along the surfaces  41  and  42  is provided with a protective coating  45 , e.g. made of a heat-resistant material, such as a ceramic material. The reason for this is to make it possible to use higher temperatures during the operation of the engine. For the same reason, the ring-shaped surface  40  and the peripheral surface  39  of the piston  27  are provided with a protective coating  46 . As can be seen from e.g. FIG. 11 a , the protective coating  45  of the cylinder head extends a short distance down into the cylinder. 
     During continued rotation of the crankshaft  29 , a further compression will take place. During this period the compression of the air in the recess  43  is relatively low in comparison with the compression of the air in the ring-shaped chamber  44 . 
     When the piston reaches the position shown in FIGS. 12 and 12 a , and the crankshaft  29  continues its rotation, a narrow gap will be formed between the peripheral surface  39  and the cylindrical surface  41 , due to the fact that the peripheral surface  39  has a portion  39   a  having a reduced diameter. This gap can be clearly seen in FIGS. 13 and 13 a , which show the piston  27  in its top dead centre. This small gap  47  will allow some of the highly compressed gas in the ring-shaped 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, may flow through the gap  47  into the recess  43  in order to enhance the combustion in recess  43 . hi the position shown in FIGS. 13 and 13 a , the combustion has already started in recess  43 , and the piston  27  will start its downward motion under the influence of the pressure of the combustion gases in the recess  43 . 
     During the movement of the piston  27  from the position shown in FIGS. 13 and 13 a , it will reach the positions shown in FIGS. 12 and 12 a , and  11  and  11   a , whereupon the remaining combustion and expansion will take place in all of the combustion chamber  36 . 
     FIGS. 14,  14   a , and  14   b  show a piston  48  and a cylinder head  49 , which are slightly modified in relation to the corresponding parts according to FIGS. 10-13 a . In the piston  48  the protrusion  50  is shaped as an insert that is welded into the crown of the piston. This makes it possible to use another material for the protrusion  50  and for the rest of the piston  48 . Further, the cylinder head  49  is provided with a groove  51  which extends along a part of the cylindrical surface  52  and which is intended to create a guided flow of gas through the gap  47 , described in connection with FIGS. 10-13 a . In this way it is possible to further enhance the mixing of gas and fuel in the recess  43 , in order to get a better combustion. By varying the shape and size of the groove  51  it is possible to create different flow patterns to suit different circumstances. 
     FIGS. 15,  16 , and  16   a  show another embodiment of an internal combustion engine according to the invention. The engine includes an engine block  53 , a crankcase  54  and a cylinder head  55 . In the crankcase  54 , a crankshaft  56  is rotatably supported. The crankshaft  56  carries a connecting rod  57 , at the other end of which a piston  58  is arranged. The cylinder head  55  is provided with a sparkplug  59  and a fuel injector  60 . 
     The upper surface of the piston  58  and the lower surface of the cylinder head  55  define, together with the peripheral wall of the cylinder, a combustion chamber  61 . When the piston  58  is situated in its bottom dead centre, as shown in FIG. 15, the combustion chamber  61  is connected by an inlet channel  62  to an air supply device  63  and by an outlet channel  64  to an exhaust system  65 . 
     The upper surface of the piston  58  is provided with a protrusion  66 , which is coaxial to the piston  58  and is provided with a substantially flat upper surface  67 . The protrusion  66  is defined peripherally by a substantially cylindrical peripheral surface  68 , and radially outside this surface there is a ring-shaped surface  69 , which in the embodiment shown is shaped as a truncated cone having a large top angle. 
     The inside of the cylinder head  55  has a cylindrical surface  70  and a ring-shaped surface  71  for cooperation with the peripheral surface  68  and the ring-shaped surface  69  of the piston  58 . Above the cylindrical surface  70  the cylinder head  55  has a recess  72  into which the sparkplug  59  and fuel injector  60  extend. 
     When the crankshaft  56  rotates from the position of FIG. 15, the piston  58  will be moved upwardly in the cylinder by means of the connecting rod  57 . When the inlet channel  62  and the outlet channel  64  have been closed by the piston, the air present in the combustion chamber  61  will be compressed. When the piston  58  has reached the position of FIG. 16, the protrusion  66  will begin to enter the recess  72  in the cylinder head  55 . As can be seen in FIG.  16  and in more detail in FIG. 16 a , the peripheral surface  68  of the protrusion  72  fits with a small gap against the cylindrical surface  70  in the recess  72 . This means that the combustion chamber  61  is divided into two portions, where one portion is the recess  72  and the other portion is a ring-shaped chamber  73  between the ring-shaped surfaces  69  and  71 . 
     During continued rotation of the crankshaft  56 , a further compression will take place until the piston reaches its top dead centre. During this period the compression of the air in the recess  72  is relatively low in comparison with the compression of the air in the ring-shaped chamber  73 . As an example, the compression ratio for the air in the recess  72 , from the position according to FIGS. 6 and 6 a  to the top dead centre of the piston  58 , may be 1.3, while the compression ratio for the air in the ring-shaped chamber  73  during the same period may be  5 . 
     When the piston  58  has reached top dead centre, or shortly 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 sparkplug  59 . After this the process will be substantially the same as described above with reference to FIGS. 10-13 a , with the exception that, as the peripheral surface  68  has no portion with reduced diameter, there will be no or very little flow of air from the ring-shaped chamber  73  to the recess  72 . 
     Reference is then made to FIGS. 17 and 17 a , which show parts of an internal combustion engine of the four-stroke type, which means that the engine includes and inlet valve  74  and an outlet valve  75 . It should also be noted that in this embodiment the location of the recess and the protrusion has been exchanged. In this embodiment the piston  76  is provided with a recess  77 , while the cylinder head  78  is provided with a protrusion  79 . This shows that an engine of the four-stroke type is possible in accordance with the invention, and FIGS. 17 and 17 a  also show that the piston may have the recess while the cylinder head is provided with the protrusion. The function and the working cycle of the engine according to this embodiment is analogue to what has been described previously in relation to FIGS. 10-16. 
     FIG. 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 chosen comparatively high so that the pressure and temperature after compression in the recess  81  is high enough to cause self-ignition in the recess  81 . 
     FIG. 19 shows a further modified internal combustion engine according to the invention. This engine is of the four-stroke Otto-type, and in this embodiment the piston  83  has an upper surface consisting of different parts. The upper surface of the protrusion  84  consists of two surfaces  84   a  and  84   b , which are flat surfaces that are inclined to each other. In a similar manner the ring-shaped surface  85  surrounding the protrusion  84  consists of two flat portions  85   a ,  85   b , which are inclined in relation to each other. Otherwise the engine shown in FIG. 19 corresponds closely to the engines described above, and also the working cycle performed in the engine according to FIG. 19 corresponds to the working cycle performed in the engines according to the previously described embodiments. 
     The invention is not restricted to what is described above, but the skilled person may modify the invention within the scope of the appended claims.