Field of the Invention

The present invention concerns a free-piston engine with a linear power generator and a least one engine arrangement including:

- a linear chamber with a longitudinal direction and at a first end with a first housing with a first reaction chamber, a first chamber port and a first intermediate chamber port, and at a second end with a second housing with a second reaction chamber, a second chamber port and a second intermediate chamber port, and between the first and second housing an intermediate housing with an intermediate chamber around which is provided

- a coil arrangement with at least one coil in connection with at least one first magnetic flux arrangement;

- a piston with a first working face facing the first end and oppositely a second working face facing the second end, the piston provided for a linear reciprocating movement in the linear chamber, the piston having at least one second magnetic flux arrangement for interacting with the at least one first magnetic flux arrangement;

- where the first reaction chamber has a first chamber end face facing the first working face of the piston, and the second reaction chamber has a second chamber end face facing the second working face of the piston, and where the first chamber end face in the first housing has a connection to a first actuator for a first displacement in the first reaction chamber, and the second chamber end face in the second housing has a connection to a second actuator for a second displacement in the second reaction chamber. Background of the Invention

In US patent 1,167,366 with the title "Dynamo-Electric Machine" issued 1916, Fessen describes an oscillating dynamo which is regarded as a generator, with means for producing a magnetic field, a primary coil disposed in the magnetic field and a secondary short-circuited coil which is also disposed in the magnetic field and inductively interacting with the primary coil in order thereby to neutralise the self- induction in the primary coil. The coils are rigidly connected via a tube to a piston working in a combustion chamber. In US Patent 1,657,641 issued to Pescara in 1928, a "Motor Compressor Apparatus" is disclosed. This document is known as a first introduction of a freely movable piston in a cylinder with a combustion chamber at one end and compression chamber at the other end for compressing gases.

Pescara follows later with a European application which is issued later in 1940 with US Patent 2,189,497 which is immediately accessible today, in which a "Free-Piston Machine" is disclosed. In this patent, the compressed gas and the heat are utilised for driving a machine which originally is a turbine.

GB patent 1,005,922 discloses a generator system designed with a free-piston engine in one chamber and with a movable piston at each end connected by a rod to accessories which in turn are linearly movable in a generator unit. The combustion chamber is thus at the centre at the chamber, and the generators at respective ends of the chamber.

In US patent 3,234,395 with the title "Free-Piston Electric Generator" issued in 1966, S.A. Colgate describes a cylinder closed at the ends with a central combustion chamber and with a free piston of iron at each end of the cylinder. Each end of the cylinder has a coil surrounding the axis of the cylinder. By combustion or explosion in the combustion chamber, a pressure is built up at the centre which will press the free pistons of iron through the coils at each end, and a current is induced. The free pistons compress air at the end of the cylinder whereby they are braked, and the pressure delivers a force directed toward the centre, which force, as the pressure is released by venting at the centre, presses the free pistons of iron through the coils, and a current is induced. The process is continued in the same way by supplying new fuel.

US patent 3,465,161 discloses a reciprocating combustion engine power generator with one housing with a central chamber with a displaceable coil arrangement therein which at each side facing the ends of the housing is integrated with a rod which is finished at each end with a piston acting as a combustion chamber. Between the chambers there are duct systems and valve systems, and in the piston there is also a valve by which the structure is cooled as the movement of the coil arrangement results in a flow which then circulates and cools. In US patent 5,788,003 with the title "Electrically Powered Motor Vehicle with Linear Generator" issued in 1998, Spiers discloses a linear engine with a reciprocating first ring coil disposed on a piston rod with a piston head at each end, where each piston head is embedded in a combustion chamber, and where the first coil is surrounded by an outer annular coil. The patent also describes the complicated control devices for the interaction of the engine with a vehicle.

In US patent 5,850,111 with the title "Free-Piston Variable-Stroke Linear-Alternator Generator" issued in 1998, Haaland discloses a linear generator, where a magnetic device interacts with a coil device which is mounted on a flying turnbuckle which at each end is connected to a piston rod with a piston disposed in a combustion chamber.

In the publication WO 0055482, a combustion engine with a linear AC-generator is disclosed. The AC-generator consists of at least one module including two oppositely disposed cylinders as the structural units of the module, the cylinders containing pistons that are rigidly connected by a central chamber in which runs a rod with windings that interact with windings outside the central chamber. As a structural part, the AC generator also includes a controller controlling the fuel supply for providing an AC generator with desired phase and frequency.

In US patent 6,199,519 with the title "Free-Piston Engine" issued in 2001, Van Blarigan discloses a combustion system consisting of a linear chamber which at each end has a combustion chamber, and which has a double-ended free piston which can be moved between the two combustion chambers. The double-ended free piston is provided with magnets that interact with an electric generator. The described generator functions as a two-stroke engine with self-ignition. The invention is characterised by having great thermal efficiency and low NO _x -emissions. It is also noted that the invention is described in connection with various fuels. In US patent 6,541,875 with the title "Free-Piston Engine with Electric Power Output" issued in 2001, Berlinger et al discloses one free piston, the piston rod being provided with at least one magnet which is moved in a surrounding coil device connected to a condenser in an electric device connected with a battery, driving a load which is typically motors in a vehicle. The free-piston engines disclosed before the present invention and with special reference to US patent 6,199,519 are, however, disadvantageous for the reason that the free-piston engines have one chamber which at one end - and most often both ends - has a combustion chamber which is the same as the chamber in which the piston with magnets are moving for inducing a current in the surrounding coils.

The existing free-piston engines thereby originate in a technique which primarily originates from combustion engines and processes and materials thereof. Prior art seeks to adapt electrodynamic technique to combustion engine technique which of course limits optimisation of combustion technique as well as electrodynamic technique.

Object of the Invention

The object of the invention is to provide a technical device which compared to existing free-piston engines is a more efficient engine.

It is a further object to provide a technical device which can operate at a lower temperature than existing free-piston engines.

It is a further object to provide a technical device which can operate when using several different fuels without large changes.

It is a further object to provide a technical device which can operate quietly as compared with existing engines.

Description of the Invention

One or more objects are achieved by the present free-piston engine with a linear power generator and a least one engine arrangement including:

- a linear chamber with a longitudinal direction and at a first end with a first housing with a first reaction chamber, a first chamber port and a first intermediate chamber port, and at a second end with a second housing with a second reaction chamber, a second chamber port and a second intermediate chamber port, and between the first and second housing an intermediate housing with an intermediate chamber around which is provided - a coil arrangement with at least one coil in connection with at least one first magnetic flux arrangement;

- a piston with a first working face facing the first end and oppositely a second working face facing the second end, the piston provided for a linear reciprocating movement in the linear chamber, the piston having at least one second magnetic flux arrangement for interacting with the at least one first magnetic flux arrangement;

- where the first reaction chamber has a first chamber end face facing the first working face of the piston, and the second reaction chamber has a second chamber end face facing the second working face of the piston; and wherein

- the first chamber end face in the first housing has a connection to a first actuator for a first displacement in the first reaction chamber, and the second chamber end face in the second housing has a connection to a second actuator for a second displacement in the second reaction chamber. It is understood that each reaction chamber is provided for reactions between reactants whereby energy stored in the reactants are transformed into heat and/or movement which is transmitted to the piston, which in turn delivers its kinetic energy to the coil arrangement and thereby to the power generator. The reactions between the reactants result in one or more reaction products.

Thereby, in connection with each reaction chamber there is provided a technical device resulting in that the volume of the reactin chamber can be varied, as it is understood that the volume in the widest sense is defined by being delimited by the working face of the piston at one side, a chamber end face at the other side, and the wall defining the chamber in radial direction about the longitudinal direction.

The volume can be zero when the chamber end face abuts on the working face of the piston. The volume can be zero when the chamber end face abuts on an inserted face.

The volume can be infinite in the sense that there may be an opening, e.g. through a port, to the surroundings. The volume can be changed continuously by displacement of the chamber end face.

By displacement of the chamber end face at appropriate low speed and regularly, the chamber end face will move a matter in the reaction chamber as a unified mass.

By a displacement of the chamber end face at high speed or suitably irregularly, the chamber end face will move matter in the reaction chamber in a turbulent way.

The heat distribution in the matter can thereby be changed, and the heat exchange between the matter and the housing itself can be changed.

By displacing the chamber end face past a port or an adjacent space, the volume will be changed discontinuously. According to one or more embodiments, the chamber end face and the actuator are incorporated by reference to the patent application DK PA 2009 70096.

According to an embodiment, the chamber end face, the actuator and the housing are provided with a rod that acts as a passage through the end of the housing, the rod end interacting with the actuator outside the chamber.

According to an embodiment, the actuator consists of at least a first arrangement of magnets with at least one magnet mounted on the rod, the first arrangement of magnets interacting with at least one second arrangement of magnets with at least one magnet.

According to further embodiments, by a magnet is understood a magnetic field which can be a permanent magnet, a ferromagnetic material or an electromagnet. According to an embodiment, the at least one arrangement of magnets interacts with a controller.

According to an embodiment, the position of the chamber end face in the reaction chamber is coordinated via a coupling to the position of the piston. According to a further embodiment, the actuator is surrounded by a vacuum chamber which is optionally connected with a vacuum pump.

By the invention there is provided a free-piston engine with a power generator which is more efficient than previously known free-piston engines as inter alia it is possible to vary the expansion ratio independently of the compression ratio, which will be exemplified below.

Furthermore, by the invention there is provided a free-piston engine which can operate at a lower temperature as the energy released from the reactants to a higher degree is transformed to kinetic energy of the piston. In the following, it will be elaborated how the free-piston engine can operate more efficiently at a lower mean temperature..

Moreover, by the invention there is provided a free-piston engine which can use various reactants, fuels and/or oxidants, as the displacement of the chamber end face can efficiently suck reactants and expel reaction products, particularly as the volume of the reaction chamber can be varied freely between zero, or a minimum, and the maximum volume contained in the housing around the reaction chamber. Moreover, by the invention there is provided a free-piston engine which at the passage of the piston in the intermediate chamber past the intermediate chamber port results in an exhaust of reaction products that is quiet as the pressure in the reaction chamber at that point can be equal to the pressure of the surroundings, here particularly at atmospheric pressure.

According to a further embodiment, the free-piston engine with linear power generator is peculiar in that in a first cross-section of the longitudinal direction through the chamber and between the first reaction chamber and the intermediate chamber there is provided a first lock gate, and in a second cross-section of the longitudinal direction through the chamber between the second reaction chamber and the intermediate chamber there is provided a second lock gate. Hereby is provided a port between each reaction chamber and the intermediate chamber such that reactants can be introduced in the reaction chamber as well as reaction products can be removed from the reaction chamber. According to a preferred embodiment the lock gate is peculiar by being designed as a disc with a preferably circular cross-section.

At one position, each lock gate thus provides a port or aperture between the reaction chamber and the intermediate chamber such that the piston can pass between the reaction chamber and the intermediate chamber.

In a further position, each lock gate thus provides a passage between the reaction chamber and the intermediate chamber, a passage for exhaust of reaction products. In a further position, each lock gate thus provides a passage through the injection port between the reaction chamber and the surroundings for suction of reactants, the reactants containing oxidants, preferably being atmospheric air.

According to a further embodiment, the free-piston engine with linear power generator is peculiar in that around the centre, each lock gate has a lock gate aperture for a lock gate shaft, preferably in parallel with the longitudinal direction, and with a lock gate periphery which by rotation of the lock gate around the lock gate shaft surrounds the cross-section of the chamber. According to a preferred embodiment, the lock gate has the form of a rotatable disc.

Each lock gate is hereby provided for rotation preferably perpendicularly to the longitudinal direction, whereby the previously mentioned positions of the lock gate are achieved by rotating the lock gate around the lock gate shaft.

According to a preferred embodiment, the free-piston engine with linear power generator is peculiar in that the lock gate periphery of the lock gate is complementary in the form of the hole of the chamber port in the housing for a free but tight rotation of the lock gate periphery immediately inside the chamber port. According to a further embodiment, the free-piston engine with linear power generator is peculiar in that each lock gate has at least one lock opening for passage of the piston in longitudinal direction between the intermediate chamber and respective reaction chambers.

The piston can hereby pass between the intermediate chamber and the reaction chamber as the lock gate opening and the piston are matched to size. It is within the scope that the shape of the lock gate opening and thereby the shape of the piston can be selected among several geometric shapes.

According to a preferred embodiment, the lock gate opening appears in that the cross- section in longitudinal direction of the piston is used as a shape which is turned over a lock gate opening angle around the lock gate shaft whereby a banana-shaped opening appears in the lock gate.

According to a preferred embodiment, the cross-section of the piston in longitudinal direction is circular.

According to alternative embodiments, the cross-section of the piston is a polygon.

The piston can thereby pass between the intermediate chamber and the reaction chamber in a given period of time as the lock gate is turned around the lock gate shaft.

It is within the scope of the invention to do experiments with the rotational speed of the lock gate around the lock gate shaft as well as the size of the lock gate angle in order to adjust the period in which the piston can pass between the intermediate chamber and the reaction chamber.

According to a further embodiment, the free-piston engine with linear power generator is peculiar in that each lock gate has a recess in a surface facing the reaction chamber, initiating around the centre and preferably radially opening towards the lock periphery of the lock gate. Thereby is achieved that the lock gate through the recess at a position provides a connection from a chamber port to a reaction port, whereby at least one reactant, which is an oxidant like atmospheric air, can be sucked in from the surroundings of the free-piston engine to a reaction chamber.

By a recess is meant a groove or a depression in the lock gate. The lock gate with the shape of a disc will thus have a recess having a preferred embodiment as a fan radiating from a area close to the centre of the disc and towards the periphery of the disc.

According to a further embodiment, the recess is peculiar by being narrowest in longitudinal direction at the centre of the lock disc and deepest at the periphery of the disc. According to a further embodiment, the free-piston engine with linear power generator is peculiar in each lock gate is connected to a lock gate motor via a lock gate shaft.

Hereby is provided an arrangement by which one or more lock gates can be rotated such that the lock gate opening and the recess in the lock gate can assume different positions in relation to the intermediate chamber and/or the reaction chambers.

According to a preferred embodiment of the free-piston engine, there is a common lock gate shaft for one or more lock gate ports. According to an alternative embodiment, for every lock gate or every pair of lock gates for every engine arrangement there is a lock gate shaft driven by a lock gate motor.

According to a further embodiment, each lock gate is driven by a lock gate motor as the forces from the lock gate motor is transmitted at the periphery of each lock gate, e.g. in that each lock gate is applied a gear wheel arrangement at the periphery or by an electromotoric arrangement. According to a further embodiment, the free-piston engine with linear power generator is peculiar in that the lock gate motor is a step motor with a step division of 360 degrees, the steps being aligned with positions of the piston in the longitudinal direction between extreme positions near a reaction position at the first end and the second end, respectively.

According to an embodiment, in connection with the free-piston engine there is provided a device along each chamber giving the position of the piston in the chamber. The device can be a simple detector or a signal from the coil arrangement.

According to a preferred embodiment, the lock gate motor interacts via the lock gate shaft with the position of the piston such that the lock gate opening is in a position by which there is passage between the reaction chamber and the intermediate chamber when the piston is on its way towards or is in the vicinity of the lock gate.

According to a preferred embodiment, the step motor is an electromagnetic motor with a response time between each step which is adjusted to the speeds of the piston in the chamber. According to a further embodiment, the free-piston engine with linear power generator is peculiar in that means are provided for injecting at least one reactant, the means being connected to either the chamber ports and/or the injection ports.

The means for injection are nozzles, sprayers or similar means for injecting a liquid from a container. In special embodiments, the means are provided with an atomizer that either provides a fixed particle size or a variable particle size.

According to a further embodiment, the free-piston engine with linear power generator is peculiar in that at least one heat exchanger is provided in connection with the intermediate chamber port for preheating at least one reactant and preferably a liquid, like water, for injection into the reaction chamber.

Thereby heat from the reaction products from the reactions is recycled and reintroduced in the subsequent reactions, increasing the efficiency. In addition, the housing is cooled around the reaction chambers, whereby external cooling devices can be omitted entirely or partially.

Since the free-piston engine as described has two opposing reaction chambers, there will be a waiting period at a reaction chamber while the other reaction chamber is activated. In the waiting period, there will be possibility of an efficient heat transmission for this reason only. Thereby is achieved a further evening of the temperature and a lowering of the mean temperature whereby external cooling can be omitted entirely.

According to a further embodiment, the free-piston engine with linear power generator is peculiar by consisting of at least one pair of engine arrangements arranged in a frame. According to an embodiment, a pair of the engine arrangements is arranged in that each motor arrangement is equidistantly displaced radially from the lock gate shaft and preferably with an engine arrangement opposite another engine arrangement relative to the lock gate shaft. Hereby, each pair uses a common lock gate shaft and each lock gate operates in several engine arrangements.

According to an embodiment, a pair of engine arrangements is disposed in continuation of each other with a common longitudinal axis. In a preferred embodiment thereof, the piston in each engine arrangement runs in opposite phase whereby no torque arises about the longitudinal direction.

According to a particularly simple embodiment, the free-piston engine is provided with a pair of engine arrangements displaced radially from the lock gate shaft with common lock gates and a corresponding arrangement with a pair of engine arrangements disposed in continuation in the longitudinal direction, but with the pistons running in opposite phase. According to a further method, the free-piston engine with a linear power generator is peculiar by being capable of being used for partial converting chemical energy stored in reactants into kinetic energy in a piston in a reaction chamber, described as a cycle in an equilibrium diagram and including one or more of the following processes: - process C-D with adiabatic compression of a least one reactant, preferably an oxidant like air, followed by injection of a reactant, preferably a fuel, at the condition D;

- optionally a process D-Dl with injection and expansion of heated high-pressure liquid, preferably water, at a constant pressure;

- process Dl-A with reaction or combustion at a constant pressure with a rise in temperature;

- process A-B with adiabatic expansion of reaction products whereby pressure and temperature drop, and whereby the more substantial work is performed and transferred to kinetic energy of the piston;

- process B-Cl with lowering of the pressure to the initial state, C, at constant volume by decreasing temperature;

- process Cl-C with replacement of hot reaction products with fresh reactant, preferably with an oxidant like air, while the volume of the reaction chamber is adjusted to the initial state, C, at a constant pressure.

According to a further method, the free-piston engine with a linear power generator is peculiar by being capable of being used for converting chemical energy stored in reactants into kinetic energy in a piston to electric energy in a power generator by using a free-piston engine according to a preceding embodiment, where at least one cycle consists of:

- a partial conversion of chemical energy stored in reactants into kinetic energy of the piston occurs according to the preceding processes (C-D, ...Cl-C) and followed by

- a partial conversion of kinetic energy in the piston into electric energy in a power generator.

According to a further method, the free-piston engine with a linear power generator is peculiar by being capable of being used such that after passing through the intermediate chamber, the piston has residual kinetic energy which is used for compressing one or more reactants in the reaction chamber. Description of the Drawing

The invention will hereafter be explained in more detail with reference to the Figures below, in which: Figure 1 shows central elements of the free-piston engine with linear power generator in an embodiment with two linear chambers, preferably acting in opposite phase;

Figure 2 shows an isometric view of an embodiment of a lock for disposition between a reaction chamber and an intermediate chamber in a free-piston engine with linear power generator; and

Figure 3 shows an ideal PV diagram for a reaction cycle in a reaction chamber in the free-piston engine. Compared with the PV diagram in Figure 3, the individual steps or positions of the elements in the design of the free-piston engine on Figure 1 are elaborated in the following Figures as the individual elements are described in Figure 1, and only the various stages in the cycle are described in detail and such that Figure 4 is identical to Figure 1, and with reference to the preceding Figures, Figure 4 shows the more important condition C;

Figure 5 shows the cycle immediately around condition C and towards condition D; Figure 6 shows the cycle in continuation of Figure 5 and immediately around condition C and towards condition D;

Figure 7 shows the cycle which compared to Figure 6 is still under way from condition C to condition D;

Figure 8 shows the cycle 100 around condition D;

Figure 9 shows the reaction between the reactants 50, 50', ..., Figure 10 shows the end of the process A-B which is the expansion phase;

Figure 11 shows part of the process B-Cl closest to the condition B;

Figure 12 shows part of the process B-Cl closest to the condition CI;

Figure 13 shows a stage of the process Cl-C where the second lock gate is in a position where the recess forms an open connection between the second chamber port to the second reaction chamber;

Figure 14 shows in continuation of Figure 13 a stage of the process Cl-C;

Figure 15 shows in continuation of Figure 14 that the second chamber end face is maintained in the waiting position while the second lock gate continues rotating;

Figure 16 shows, like Figure 15, how the second chamber end face is kept in the waiting position while the pistons act in the other reaction chambers;

Figure 17 shows, like Figure 16, how the second lock gate by continued rotation now is in a position where the end of the recess begins to close the opening from the second reaction chamber and to the second chamber port;

Figure 18 shows corresponding to Figure 17 how the turning of the second lock gate continues to close the opening between the second chamber port and the second reaction chamber;

Figure 19 shows interrelated PV and TV equilibrium diagrams for a basic embodiment of the free-piston engine; and Figure 20 shows interrelated PV and TV equilibrium diagrams for an optimised embodiment of the free-piston engine. Detailed Description of Embodiments of the Invention

DA #

Free-piston engine 1

Power generator 2

Engine arrangement 3

Linear chamber 4

Longitudinal direction 5

First end 6

First housing 7

First reaction chamber 8

First chamber port 9

First intermediate chamber port 10

Second end 11

Second housing 12

Second reaction chamber 13

Second chamber port 14

Second intermediate chamber port 15

Intermediate chamber 16

Intermediate housing 16A

Coil arrangement 17

Coil 18

First magnetic flux arrangement 19

Piston 20

First working face 21

Second working face 22

Second magnetic flux arrangement 23

First chamber end face 24

Second chamber end face 25

First actuator 26

Second actuator 27

First displacement 28

Second displacement 29

First lock gate 30 Second lock gate 31

Lock gate shaft 32

Lock gate motor 33

Frame 34

First injection port 35

Second injection port 36

Lock gate opening 37

Recess = niche 38

Lock gate shaft hole 39

Degree marking 40

Lock gate periphery 41

Lock gate opening diameter 42

Lock gate opening angle 43

Recess angle 44

Reactant 50

First reactant = Oxidant 50'

Second reactant = Fuel 50"

Reaction product 51

Guide 52

Scavenging position 60

Reaction position 61

Waiting position 62

Cycle 100

Condition D 101

Condition Dl 102

Condition A 103

Condition B 104

Condition CI 105

Condition C 106

Process D-Dl 110

Process Dl-A 111

Process A-B 112

Process B-Cl 113 Process Cl-C 1 14

Process C-D 115

A particular embodiment of the free-piston engine will be described below with reference to the above reference numbers. For the sake of clarity, it has been decided initially to describe the most essential components and subsequently introduce components which are relevant for a special position or part process of the free-piston engine.

Figure 1 thus shows an embodiment of a free-piston engine 1 with a power generator 2. The free-piston engine 1 consists of at least one engine arrangement 3, and in the actual embodiment engine arrangements 3, 3'. Each engine arrangement 3 has basically identical components which, however, can be located and arranged differently as the case is about symmetrical or assymmetrical dispositions and lateral reversals being trivial to the skilled in the art, however. Below, the upper engine arrangement 3 is described on the drawing, and it is understood that the elements of the lower engine arrangement 3' are designated with -', if necessary.

The engine arrangement 3 has preferably a linear chamber 4 which is oriented in a longitudinal direction 5. The chamber 4 has a first end 6 with a first housing 7 with a first reaction chamber 8 to which there is provided a first suction port 9. Also, at the first end 6 there is a first intermediate chamber port 10.

Opposite the first end 6, the chamber 4 has a second end 11 with a second housing 12 with a second reaction chamber 13 to which there is provided a second suction port 14. Also, at the second end 11 there is a second intermediate chamber port 15.

Between the first reaction chamber 8 and the second reaction chamber 13 there is provided an intermediate chamber 16, the three chambers substantially constituting the chamber 4.

The intermediate chamber 16 is defined by an intermediate housing 16 A. Around the chamber 4 and mainly around the intermediate chamber 16 in the vicinity thereof there is at least one coil arrangement 17 having at least one coil 18 and at least one first magnetic flux arrangement 19. In the shown embodiment, the coil arrangement 17 of the engine arrangement 3 is connected to the coil arrangement 17' of the second engine arrangement 3', and the two coil arrangements 17, 17' are connected to the power generator 2.

In the chamber 4, there is a piston 20 having a cross-section adapted to the cross- section of the chamber 4 for a back-and-forth or reciprocating movement in the chamber 4 from the first reaction chamber 8 through the intermediate chamber 16 and to the second reaction chamber 13 and back to the first reaction chamber 8.

The piston 20 has a first working face 21 facing the first end 6 and a second working face 22 facing the second end 11 as the piston 20 is located in the intermediate chamber 16.

The piston 20 furthermore has at least one second magnetic flux arrangement 23 which in the shown embodiment is a magnet oriented N-S for optimal interaction with a first magnetic flux arrangement 19 at the passage of the travel of the piston 20 through the intermediate chamber 16.

In the first reaction chamber 8 there is a first chamber end face 24 facing the first working face 21 of the piston 20. The first chamber end face 24 defines the end in longitudinal direction 5 of the chamber 4 at the first end 6.

In the second reaction chamber 13 there is a second chamber end face 25 facing the second working face 22 of the piston 20. The second chamber end face 25 defines the end in longitudinal direction 5 of the chamber 4 at the second end 11.

The first chamber end face 24 is connected to a first actuator 26 operating through the first housing 7. The second chamber end face 25 is connected to a second actuator 27 operating through the second housing 12.

The first actuator 26 can be displaced outside the first housing 7, resulting in a first displacement 28 of the first chamber end face 24 in the first reaction chamber 8 and thereby a change of the length of the chamber 4.

Also, the first displacement 28 provides that the volume between the first chamber end face 24 and the first working face 21 in the first reaction chamber 8 by the presence of the piston 20 herein is variable, depending on the position of the piston 20 and relative to the position of the first chamber end face 24 subject to the action of first actuator 26 and forces from the latter.

The second actuator 27 can be displaced outside the second housing 12, resulting in a second displacement 29 of the second chamber end face 25 in the second reaction chamber 13 and thereby a change of the length of the chamber 4.

Also, the second displacement 29 provides that the volume between the second chamber end face 25 and the second working face 22 in the second reaction chamber 13 by the presence of the piston 20 herein is variable depending on the position of the piston 20 and relative to the position of the second chamber end face 25 subject to the action of second 27 actuator and forces from the latter.

Between the first reaction chamber 8 and the intermediate chamber 16 there is a first lock gate 30. Between the second reaction chamber 13 and the intermediate chamber 16 there is a second lock gate 31.

In the shown embodiment, the first lock gate 30 and the second lock gate 31 are mounted on a common lock gate shaft 32 which is substantially in parallel with the longitudinal direction 5.

The lock gate shaft 32 is connected with a lock gate motor 33 whereby the first lock gate 30 and the second lock gate 31 can be rotated perpendicularly to the chamber 4 such that the first lock gate 30 rotates between the first reaction chamber 8 and the intermediate chamber 16 and the second lock gate 31 rotates between the second reaction chamber 13 and the intermediate 16.

In Figure 1 is also shown a cross-section through the free-piston engine 1 through a frame 34 supporting the two engine arrangements 3, 3', and as shown here the intermediate chamber 16 as seen from the other end 11. In the shown cross-section, the second lock gate 31 with the lock gate shaft 32 is centered between the intermediate chambers 16, 16' and so that the lock gate 31 by rotation around the lock gate shaft 32 surrounds the intermediate chambers 16, 16', and here the second reaction chamber 13, 13'.

Similarly, the second chamber port 14 is seen in the cross-section.

Corresponding cross-sections through the frame 34 and the engine arrangements 3, 3' will apply for the first lock gate 30 at the first end 6.

The first lock gate 30 and the second lock gate 31 are identical in the actual embodiment, but can be made as a lateral reversals of each other. Figure 2 shows and embodiment of the first lock gate 30 and the second lock gate 31 which is here described as the lock gate 30, as the two lock gates can be identical or just differ by being a simple lateral reversal or other obvious transformations of the features described below. Similarly, where necessary, the features below find subsequent application in connection with references associated with the first lock gate 30 as well as with the second lock gate 31.

The lock gate 30 is here designed with circular shape, having a lock gate opening 37 in one half and a recess 38 in the opposite half. The lock gate 30 has a lock gate shaft hole 39 through the centre of the lock gate 30 for fitting with the lock gate shaft 32. The lock gate shaft hole 39 is provided with a degree marking 40 for disposition of the lock gate 30 in a matched angle.

The lock gate 30 extends radially from the lock gate shaft hole 39 and ends at lock gate port periphery 41, here circular in shape. In the shown embodiment, the lock gate opening 37 is produced as a perforation of the lock gate 30, 31, consisting of a drilling with a lock gate opening diameter 42 which is matched with the diameter of the piston 20, as the diameter is understood broadly as the radial dimension of the piston 20 in such a way that the piston 20 can pass through the lock gate opening 37 and furthermore such that the drilling is performed in a lock gate opening angle 43 so that the piston 20 can pass through the lock gate opening 37 as the lock gate 30 is rotated.

In the actual embodiment of the lock gate 30, in the half opposite the lock gate opening 38 there is the recess 38 which is designed as a fan radiating radially over a recess angle 44 from the area around the lock gate shaft hole 39.

Figure 3 shows a cycle 100 in a Pressure- Volume (PV) diageram referring to the pressure in and volume of a reaction chamber 8, 13, in the actual embodiment a reaction chamber 8, 13 in the free-piston engine 1.

The individual conditions in the cycle 100 in relation to the free-piston engine 1 are to be understood in the context of the subsequent Figures where each condition and process between the conditions will be exemplified.

The cycle 100 is naturally running in a Temperature-Volume (TV) diagram corresponding to the PV diagram and/or a Temperature-Pressure (TP) diagram as it is supposed that a skilled in the art can change and understand the embodiment on the basis of such equilibrium diagrams.

The cycle 100 is to be understood as an ideal cycle 100 consisting of processes between the conditions D 101, an alternative or optional condition Dl 102, a condition A 103, a condition B 104, a condition CI 105 and a condition C 106. Between the conditions there are following processes: process D-Dl 110, process Dl- A 111, process A-B 112, process B-Cl 113, process Cl-C 114 and process C-D 115.

In the following Figures, it is elaborated how the cycle 100 proceeds ideally in the free-piston engine 1. However, it is understood that a skilled in the art can disregard the ideal cycle 100 and perform adjustments with regard to obvious deviations in a real process compared with the ideal cycle 100. It may thus be the case that conditions are coincident or omitted. The condition Dl 102 may thus be omitted whereby the process D-Dl 1 10 and the process Dl-A 111 become one and the same process D-A.

Figure 4 is identical to Figure 1, and with reference to the preceding Figures, Figure 4 shows substantially the condition C 106 as reference is made to the second reaction chamber 13' of the engine arrangement 3' at the other end 1 1.

In the actual embodiment, the process proceeds asymmetrically in the engine arrangement 3 such that the facts described by the second reaction chamber 13' at the second end 11 applies essentially to the first reaction chamber 8 at the first end 6 as well.

In the following, it is understood that in a reaction chamber 8, 8, 13, 13' a process runs in or between one or more reactants 50.

In the shown embodiment, a first reactant 50' is substantially an oxidant 50' which in the actual case is oxygen in atmospheric air.

In the following, the result of a reaction in or between one or more reactants is termed a reaction product 51. The piston 20' is located in the intermediate chamber 16' in a guide 52' in the intermediate chamber housing 16A'. The piston 20' is travelling on its way from the first end 6 towards the second end 11.

The kinetic energy of the piston 20' is transformed into electric energy by the travel of the piston 20' through the intermediate chamber 16' as the second magnetic flux arrangement 23 movement past the first magnetic flux arrangement 19 gives rise to an induced current in the coils 18. At the second reaction chamber 13', the second lock gate 31 is in a position where the lock gate opening 37 provides an opening between the second reaction chamber 13' and the intermediate chamber 16'. The second lock gate 31 turns so that the lock gate opening 37 provides free passage for the piston 20' from the intermediate chamber 16' to the second reaction chamber 13 when the piston 20' is present at the second lock gate 31.

Similar to Figure 1, the position of the second lock gate 31 is furthermore shown in a cross-section through the free-piston engine 1. In the subsequent Figures, the position of the lock gate 31 is most correctly represented in the sectional views perpendicular to the longitudinal direction 5, as the positions depicted in the cross-section in longitudinal direction 5 relative to the reaction chamber 13' and the intermediate chamber 16' is indicated as either the lock gate opening 37 or as the recess 38. In continuation of Figure 1, while looking at the direction of rotation 45 around the lock gate shaft 32, the lock gate opening 37 appears to be at the beginning of its overlap of an opening between the second reaction chamber 13' and the intermediate chamber 16'. The position of the chamber end faces 24, 25 in the reaction chambers 8, 13 can be varied by a first and a second displacement 28, 29.

For the sake of clarity, reference is made to the second chamber end face 25 which by the second displacement 29 is located between the two extreme positions, where one extreme position is a scavenging position 60 and the other extreme position is a reaction position 61.

At the scavenging position 60, the second chamber end face 25 is located at the opening of the second reaction chamber 13 or the transition to the second lock gate 31. The volume of the second reaction chamber 13 is ideally zero or at minimum at the scavenging position 60. Between the scavenging position 60 and the reaction position 61, the second chamber end face 25 is a waiting position 62 which is the position at which the second chamber end face 25 is seen in the Figure. Figures 5 to 7 show the free-piston engine 1 from the condition C 106 on the way to the condition D 101.

The piston 20' has given off the greater part of the kinetic energy of the piston 20', and the remaining kinetic energy is used for compressing the reactants 50 in the second reaction chamber 13'.

In Figure 5 the cycle 100 is immediately around condition C 106 and on the way to condition D 101. The lock disc 31 is rotated compared with Figure 4, and the piston 20' is passing freely from the intermediate chamber 16' to the second reaction chamber 13'.

The second working face 22' of the piston 20' has passed the lock opening 37 and is just inside the second reaction chamber 13' whereby the reactant 50', here in the form of atmospheric air, is contained between the second working face 22' of the piston 20' and the second chamber end face 25' in the vicinity of the waiting position 62'.

The second chamber end face 25' interacts with the second actuator 27' via a rod through the end of the second housing 12. In the shown embodiment, on the rod outside the second house 12 there is applied a permanent magnet that interacts with an arrangement of electromagnets by which the position of the chamber end face 25' can be varied.

In immediate continuation of Figure 5, Figure 6 shows the cycle 100 about condition C 106 and towards condition D 101.

The piston 20' is inside the second reaction chamber 13' and the second chamber end face 25' is moved under control in direction towards the second end 1 1 such that the pressure of the reactant 50' is not appreciably increased compared with the condition shown in Figure 5.

The second lock gate 31 is further rotated in that it appears that the lock gate opening 37 still provides free communication between the second reaction chamber 13' and the intermediate chamber 16.

In Figure 7, the cycle 100 is still under way from condition C 106 to condition Dl 101, as the compression of the reactant 50' has begun since the second chamber end face 25' is now in the reaction position 61 ' where the structure forming the second chamber end face 25' is bearing against the interior of the end itself of the second housing towards the second end 11.

The second chamber end face 25' in the reaction position 61 ' provides access for the second injection port 36' to the second reaction chamber 13'.

Figure 8 shows the cycle 100 around the condition D 101 where through the second injection port 36' there is injected a reactant 50 which is the fuel itself, in the present case diesel.

According to a further embodiment, after condition D 101 there is injected a high pressure liquid, as e.g. high-pressure water, at constant pressure, as the temperature is kept constant, rises or drops, depending on the temperature and the amount of high- pressure liquid. The cycle 100 thereby arrives at the condition Dl 102.

If a further reactant 50"', which is a high-pressure liquid, is not injected the conditions D 101 and Dl 102 coincide.

Figure 9 shows the reaction itself between the reactants 50, 50', ... which then in the actual case is the combustion of diesel. The reactions between the reactants 50, 50', or in short the combustion, occurs at constant pressure whereby the cycle 100 goes from condition Dl 102, or D 101, to the condition A 103. In the actual case, the reaction or combustion starts by self-ignition, but by using alternative reactants the reaction can be started with an ignition matching the fuel.

The piston 20' hereby commences its travel from the second end 11 towards the first end 6 as the second lock gate 31 is still in a position where the lock gate opening 37 is still entirely open to passage of the piston 20' from the second reaction chamber 13' to the intermediate chamber 16.

The second chamber end face 25' is in the reaction position 61 during the reaction.

Figure 10 shows the end of the process A-B 112 which is the expansion phase, which ideally is adiabatic, from the condition A 101 in Figure 9 to around condition B 104. In the process A-B 112, the pressure P and the temperature T drop, and during the process the more substantial work is performed whereby the piston 20' transmits part of the released energy from the reactants 50, and the piston 20' thus has a certain kinetic energy.

The second reaction chamber 13' is now filled with reaction products 51. The second chamber end face 25' is still in the reaction position 61 '.

The second lock gate 31 is still in a position where the lock gate opening 37' is completely open for passage of the piston 20' between the second reaction chamber 13' and the intermediate chamber 16'. Figure 1 1 shows part of the process B-Cl 113 closer to the condition B 104 where the piston 20' is in the intermediate chamber 15' and entirely or partially past the intermediate chamber port 15' and with the lock gate 31 in a position where the lock port opening 37 entirely or partially forms an opening between the reaction chamber 13' and the intermediate chamber 16'. The reaction products 51 will thus, partly as a pressure relief, leave the reaction chamber 13' out through the intermediate chamber port 15', and partly as the second chamber end face 25' commences a displacement in the reaction chamber 13' against the intermediate chamber port 15'. Figure 12 shows part of the process B-Cl 113 closer to the condition CI 105 where the piston 20' is in the intermediate chamber 16', and where the second chamber end face 25' is displaced to the scavenging position 60' whereby the reaction chamber 13' is emptied of reaction products 51.

Compared with the beginning of the process B-Cl 113, the lock gate 31 is further rotated and in a position where the lock gate opening 37 goes from forming an opening to the intermediate chamber 16' to the area of the lock gate 31 between the lock gate opening 37 and the recess 38 closing periodically between the intermediate chamber 16 ' and the reaction chamber 13'.

Figure 13 shows a stage of the process Cl-C 114 where the second lock gate 31 is in a position where the recess 38 forms an open connection between the second chamber port 14' and the second reaction chamber 13', the volume of which ideally being zero or relatively small as the second chamber end face 25' is in the scavenging position 60.

The reactant 50,' which in the actual embodiment is oxygen from atmospheric air as the oxidant, is ready to be sucked in through the chamber port 14'.

In continuation of Figure 13, Figure 14 shows a stage of the process Cl-C 114 where the second chamber end face 25' is moved from the scavenging position 60 to the waiting position 62 by the second displacement 29 of the chamber end face 25' in such a way that the reactant 50, here atmospheric air, is introduced in the second reaction chamber 13'.

Suction of the reactant 50 can occur by an even and slow displacement 29 of the second chamber end face 25' towards the second end 11 whereby a preferably laminar flow can be achieved, or the suction can occur by a more rapid displacement 29 of the second chamber end face 25 whereby a preferably turbulent suction is achieved.

The heat exchange between the reactant 50 and the housing 12 itself can be varied or adjusted hereby. In continuation of Figure 14, Figure 15 shows that the second chamber end face 25' is kept in the waiting position 62 while the second lock port 31 is still turned. The suction of the reactant 50 is finished, and the reactant 50 is stabilised in the second reaction chamber 13'.

As in Figure 15, Figure 16 shows how the second chamber end face 25' is held in the waiting position 62 while the pistons 20', 20 work in the reaction chambers 8', 13, respectively. Figure 17 shows a situation similar to Figure 16 while noting that the second lock gate 31 by the continued rotation is now in a position where the end of the recess 38 viewed relative to the rotation begins to close the opening from the second reaction chamber 13 'and to the second chamber port 14'. Figure 18 shows corresponding to Figure 17 how the rotation of the second lock gate 31 continues closing the opening between the second chamber port 14' and the second reaction chamber 13'.

Figures 16 to 18 thus shows how the cycle 100 runs in the other reaction chambers 8, 8' and 13 while the second chamber end face 25' is in the waiting position 62'.

In total, the Figures 4 to 18 thus present an approximately complete course of the actual four cycles 100 in the reaction chambers 8,8,13,13', and how the two engine arrangements 3, 3' interact with the two lock gates 30, 31 by the common lock gate shaft 32.

It is within the scope of the present description of the free-piston engine 1 to change the number of engine arrangements 3, 3' as it is obvious to increase the number to two pairs of engine arrangements 3, 3", and in the cross-section of the longitudinal direction 5 to dispose the second pair perpendicularly to the first pair, and at the same instance provide the lock gates 30, 31 with a pair of recesses 38 and a pair of lock port openings 37. Figure 19 shows the cycle 100 of a basic embodiment of the free-piston engine 1. The cycle 100 with the conditions cf. Figure 3 for the basic embodiment is depicted in a PV diagram and an associated TV diagram. In the above, the cycle 100 with conditions is outlined in relation to the free-piston engine 1. In the following, an actual example will be described with a starting point in a standard reference work which is available for a skilled in the art, which inter alia can be J.M. Smidt et al, "Introduction to Chemical Engineering Thermodynamics", 7th ed; McGraw-Hill; Singapore 2005.

The precondition is that all gases are regarded as ideal gases irrespective of pressure and temperature, and that the free-piston engine is mechanically reversible in the sense that friction of the mechanical components of the free-piston engine is disregarded.

It is within the scope of the present description to extend the standard ideal gas model such that the heat capacity of reactants 50 is expanded from being constant to being temperature dependent. It is within the scope to use the above mentioned assumptions as it becomes possible thereby to compare different types of engines, and it is thus understood that results from the calculations cannot be expected in a physical realisation, but the results from the model can be used for relative comparisons between engines and for optimisation of the free-piston engine 1 as described here.

It is thus within the scope of the present free-piston engine 1 to start with a set of design parameters, as e.g. the volume of the reaction chambers 8,8', 13, 13' in various conditions while observing the positions of the chamber end faces 24,24',25,25, including particularly the scavenging position 60, the reaction position 61 and the waiting position 62, and within the scope of the ideal model to freely choose or determine one or more parameters, free parameters, and by the ideal model calculate the dependent parameters. The free-piston engine 1 with one or more of the displaceable chamber end faces 24,24',25,25', the lock gates 30,31, the chamber ports 9,9', 10,10', the intermediate chamber ports 14,14', 15, 15' together with the dynamics of the actuators 26,26', 27,27', the lock gate motor 33 and the travel of the piston 20, 20' in the chamber 4, 4' provide that the parameters given in Table 1 can be determined as a basic embodiment.

It is noted that the ideal gas parameters T, P and V - temperature, pressure and volume - in the various conditions 101-106 in the cycle 100 are represented by an index indicating the condition A 103, B 104 , CI 105, C 106 or D 101.

Table 1

It is noted that V _B =Vc, whereby the basic version of the free-piston engine 1 is identical to a standard air-based diesel engine, and the conditions C 106 and CI 105 coincide.

On the background of the parameters determined for the free-piston engine 1 and the choice of reactants 50 as diesel and atmospheric air with oxygen (21 %) and nitrogen (79 %), the extended ideal model is used in which the applied heat capacities are temperature dependent for calculating the conditions in the cycle 100. Thermal and physical data for the reactants 50 from e.g. data sources like National Institute of Standards and Technology (NIST) are used.

Thereby, the values indicated in Table 2 appear for the basic case of the cycle 100 for the free-piston engine 1 with the conditions C 106, D 101, Dl 102, A 103, B 104 and CI 106.

Table 2

The resulting cycle 100 for the basic version is shown in Figure 19 with the interrelated PV and TV diagrams on the basis of Table 2.

In Table 3 and on the basis of the conditions indicated in Table 2, there are the related energy changes in the form of work and heat for the processes between the conditions. On this background, the efficiency of the cycle 100 for the basic version will appear.

On the basis of the modified ideal gas model, the efficiency of the basic version is found to be η=52 %. To this is noted that this efficiency of course appears on the basis of idealised assumptions and preconditions. However, the result and the methodology can be used as a starting point as the same modified model can be used for characterising the free-piston engine 1 in further - and improved - embodiments whereby a comparison will be possible.

As a result of the basic version, a compression ratio R=20, an expansion ratio r _e =5.7 and a mean temperature for the cycle 100 T _av =1025 ^o C are attained. Table 3

Figure 20 shows the cycle 100 of an improved embodiment of the free-piston engine 1 compared with the basic embodiment. The cycle 100 with the conditions cf. Figure 3 for the improved embodiment of the free-piston engine 1 is depicted in a PV diagram and an associated TV diagram.

It is within the scope of the described features of the free-piston engine 1 to vary the parameters in order to improve the free-piston engine 1.

Hereby is meant that a skilled in the art may choose various parameters, and by the indicated modified ideal model calculate the other parameters in order thereby to be able to design improved versions of the free-piston engine 1.

By improved versions are meant embodiments having greater efficiency in relation to the basic embodiment of the free-piston engine 1.

By improved versions are meant embodiments having lower average temperature in the cycle 100 in relation to the basic embodiment of the free-piston engine 1 .

By improved versions are meant embodiments having both greater efficiency and a lower temperature in the cycle 100 than the basic embodiment of the free-piston engine 1.

By improved versions are meant embodiments which are quiet in relation to existing engines, including free-piston engines. An improved version of the free-piston engine can readily be achieved by proceeding through one or more of three steps:

A step where the compression ratio is varied followed by

a step where the expansion ration is varied, and finally and optionally a step where the amount and temperature of injected water is varied.

In the step where the compression ratio is varied, the starting point is a volume of the reaction chamber 8', 13' of Vc=500 ml. With an upper practical limit of the pressure, P _D , in the condition D 101 of 250 bar, the volume at the condition D 101 is V _D =9 ml. For this intermediate step of the embodiment, the efficiency is increased from 52% to 68%.

As a result of this intermediate step, a compression ratio R=55.6, an expansion ratio r _e =19.6 and a mean temperature for the cyclelOO T _av =861 ⁰ C are attained.

In the step where the expansion ratio is varied, and this is just possible in the free- piston engine 1 as described, independent of the compression ratio, a further improvement of the efficiency is achieved, from 68% in the first step to 76%.

This occurs by varying the volume of the reaction chamber 8', 13' in the condition B 104, VB, while the volume in the condition D 101, V _D , like the volume in the condition C 106, V _c , is kept constant. Se particularly the Figures 5 and 6. As the piston 20' travels from the reaction chamber 13' to the intermediate chamber 16' - see particularly Figures 10 and 11 - a free passage from the reaction chamber 13' to the surroundings is provided via the intermediate chamber port 15', whereby the pressure in condition B 104 is equalised to atmospheric pressure, or to the pressure in the surroundings; hence as the pressure at the condition B 104, P _B , is kept just over 1 bar, an optimal expansion condition of r _e =66.8 is attained, which for a volume in condition B 104 is V _B =1700 ml. A further result of this is that the embodiment of the free-piston engine hereby becomes quiet as by the exhaust no great pressure equalisation occurs as otherwise known with the associated bang.

As a result of this step, in total a compression ratio R=55.6, an expansion ratio r _e =66.8 and a mean temperature for the cycle 100 T _av ^: =670 ^o C are attained.

Starting with the embodiment of the free-piston engine 1 on the basis of the two steps, a further improvement is achieved in that in the reaction chamber 13', a liquid like water is injected.

By using a heat exchanger connected in continuation of the intermediate chamber port 15' and the means for injecting the reactant 50, in this case water, and under the assumption that the reaction products 51 can be cooled to 150°C, in the condition B 104 is then obtained the following: The temperature of the reaction products 51, TB, is to be higher than the temperature of the injected water, and the amount of heat of the reaction products 51 cooled to 150°C is to be greater than the amount of energy required to heat the water, resulting in that the optimal amount of water is Vw=0.08 ml per reaction at a water temperature of Tw ⁼ 525°C.

Hereby, energy is circulated in the reaction, and the mean temperature 100 is lowered. The total result is an efficiency of 80% and a mean cycle temperature of 546°C.

The total data for the improved embodiment of the free-piston engine 1 are gathered in Table 4 and Table 5. Data from Table 4 are graphically represented in Figure 20.

Table 4

Table 5

It is noted that the cycle 100 concerns a reaction chamber 13', and since every cylinder block 2 in the free-piston engine 1 has a reaction chamber 8', 13' at each end 6, 11, the assumptions regarding the mean temperature in the cycle 100 are simplified. A more detailed review of the kinetics of the piston 20' travel in the chamber 4' is therefore required in principle.

Since the piston 20' runs in the intermediate chamber 16' and since there is a waiting period in a reaction chamber 13', 8' as the piston 20' is in an opposite reaction chamber 8', 13', all things being equal, the mean temperature will be lower. The cycle 100 in the condition C 106 will thus have a waiting time, see particularly the Figures 12 to 18.

On the basis of the improved embodiment summed up in Tables 4 and 5 and with a cylindric piston 20' with a mass of 500g and a diameter of 0.10 m, whereby the reaction chamber 8', 13' also have a diameter of 0.10 m, it is estimated that the mean temperature by 3000 cycles 100 per minute will be T _av =210 ^o C.

By these final and estimated rough calculations of the kinetics of the piston 20', the parameters and results for the basic embodiment and the improved free-piston engines, respectively, are summed up in Table 6. Table 6

Within the scope of hte present invention it is possible freely to select reactants 50 among known fuels, such as petrol, DME, hydrogen or any other fuel, together with oxidants like pure oxygen, mixtures with oxygen or chemically bonded oxygen. The above methodology can thus be used as long as the thermo-chemical properties of the reactants 50 can be found or obtained.

Applications

In the following, a number of configurations and connections in which the free-piston engine 1 can be used are described. The examples are only illustrative in order to show the versatility as well as the efficiency of the invention.

Hydrogen-powered hybrid electric automobile

The described power generator particularly finds application in hybrid electric and hybrid cars which are characterised by having an electric drive system which typically includes a battery storage, and often a condenser as well, which act as energy stores and not the least energy buffers for variation between consumption and production of electric energy. For pure electric vehicles with batteries, the driving range is still a problem compared with e.g. petrol-powered cars as well as the charging time is still longer than the time used for filling fuel. Although cars with fuel cells and hydrogen and methanol have been demonstrated experimentally with potentially high efficiency, the service life of these components is limiting.

The free-piston engine with the power generator may supply electric energy in an efficient way to the electric system in an hybrid electric car as the load in that case is supposed to be dimensioned to balance the power generator with the electric drive system in the car.

In a preferred embodiment, the free-piston engine will operate at a constant rotational speed, and the hybrid electric system with batteries etc. will cover peak loads.

A super condenser will basically absorb transient currents from the power generator and balance brief variations with the battery storage which in addition can be charged during driving as well as during stops.

During steady driving, the power generator will supply a constant amount of electric energy which by suitable equalisation is delivered almost directly to the electric motors of the vehicle.

During acceleration, the free-piston engine with the power generator can increase its output, but energy will also be stored in the super condenser and the battery so that rapid acceleration is possible for a short, but still sufficiently long period of time.

By braking and deceleration the power generator can reduce its power production as the super condenser and the battery storage will receive the energy which is excessive in relation to the consumption in the electric motor. From descriptions of fuel cell cars and systems it is well-known that fuel cell systems can function as so-called micro-powerplants which are connected to the network.

The described free-piston engine with power generator can also, and in connection with the battery storage in particular, be connected to the network. Here it is noted that the energy efficiency of the described generator is close to the efficiency of fuel cells operating in practice, why the system advantages of the described power generator will elevate the power generator to a level with or above an electro-chemical power generator.

Regarding fuel for the power generator for use in a hybrid electric vehicle, the existing infrastructure with petrol and diesel will be immediately available.

The free-piston engine with the power generator will operate with these fuels as the reaction chambers will act as a combustion chamber with a spark plug by using petrol and air as reactants. By using diesel, the reaction chambers and the strokes will be adapted to self-ignition in connection with the compression stroke.

Establishing a so-called hydrogen infrastructure is not excluded why the use of hydrogen as reactant is relevant. Hydrogen reacts strongly with oxygen by combustion which occurs explosively and compared with diesel without large liberation of heat. The free-piston configuration is particularly suited for such a combustion.

It is noted here that combustion of hydrogen with air occurs almost emission-free at the combustion site, and the injection/ejection piston is only to be adapted for exhaust of water vapours and small amounts of NO _x .

Stand-alone diesel hybrid generator

The described free-piston engine with power generator finds equal application in stationary systems that include houses connected to the network and houses or technical facilities operating isolated from a network.

The free-piston engine with the power generator will here operate with the consumption through a battery storage in the preferred realisation, since part of the load can be provided as condenser and solid-electric components balancing the power generator with the battery storage and the consumption.

The free-piston engine with the power generator can be configured to operate in connection with a network such that it can supply energy to the household, but which in principle may also act as a micro-generator for supplying electric power to the network. In such cases there will be immediate access to fuels like petrol and to a greater extent bio-fuels. A particular stationary application is found in connection with remote technical facilities where the diesel is often used as the standard fuel.

In that case the power generator will be configured to use diesel and to exhaust diesel combustion products. Moreover, the power generator will be connected to a load balancing the power generator with the direct consumption, and a battery storage. By using diesel as fuel, there will be a relatively high operating temperature. In that case it will be possible that particularly the cylinder chambers, but also the intermediate chamber, interact with a heat exchanger, liquid- or air-based, which operates with a heat storage in the form of e.g. a hotwater tank.

Generator for use under oxygen-free and gravity-free conditions

The free-piston engine with the power generator is particularly suited for working under extreme conditions which is the case where no oxygen is present, or where oxygen is a very limited ressource. Use in space is particularly such a place where there are often gravity-free conditions.

The free-piston engine with the power generator with the displaceable chamber end face find application here as reactants in e.g. powder form can be used. Immediate examples are so-called metal fuels based on iron, aluminium or boron whre these are provided as nanoparticles. The oxidant is here provided e.g. bonded with another metal and can be part of a combined structure of nanoparticles or -clusters.

The displaceable chamber end face will provide for a complete emptying of the reaction chamber for reaction products, and when applied under conditions without gravity, the displaceable chamber end face will furthermore by suction efficiently distribute reactants in the reaction chamber.