Abstract:
A four-stoke reciprocating internal combustion engine includes the capability to change the distance between the crankshaft axis and the big end of the connecting rod and hence the maximum cylinder displacement within a combustion cycle. This provides for a given inducted volume of gases to be expanded over a greater volume. An exhaust gas aperture is uncovered by the piston towards the end of the expansion stroke. The piston and crankcase space serves as a pre-compression space for supercharging air to be inducted into the cylinder via ducts. A unitary valve device sliding axially co-operates with intake and exhaust apertures of the combustion cylinder. The unitary device extends at times into a recess in the head of the piston. A diffuse ignition source is provided. A fuel pump is operated by action of the piston.

Description:
[0001]    The present invention relates to improvements to reciprocating machines such as pumps, compressors, gas or fluid driven motors and internal combustion engines. 
         [0002]    The basic design of the reciprocating internal combustion engine has remained relatively unchanged for over a century. Typically, a connecting rod connects a piston, which moves linearly in a cylinder, to the offset throw of a crankshaft arranged at 90° to the travel of the piston. This arrangement translates the linear movement of the piston into a rotational movement of the crankshaft via the interaction of the connecting rod and a sliding ‘big end’ bearing mounted between the connecting rod and the offset throw of the crankshaft. Thus, each stroke of the piston is translated into a semi-circular rotation of the crankshaft and by geometrical symmetry the crankshaft then completes its full cycle and reciprocates an equal but opposite stroke to the piston. The stroking movement of the piston within the cylinder therefore occurs over a fixed distance in both directions of travel during each complete cycle of the crankshaft. Energy to induce this movement is provided by the introduction and subsequent compression and combustion of mixed gases within the cylinder. The resulting expansion under combustion causes a rise in pressure which forces the piston linearly towards the crankshaft end of the cylinder. This movement is then reciprocated in the opposite direction by the interaction of the crankshaft and connecting rod and stored energy in the crankshaft arrangement. 
         [0003]    Over the years, improvements in the efficiency of the internal combustion engine have been achieved by several means. Such means have included more accurate control of the timing, the atomisation and amount of fuel being input to the cylinder by means of pressurised fuel injection, electronic mapping of the engine&#39;s operating parameters to optimise power/efficiency and achieving more complete combustion (thereby reducing toxic emissions), increasing the amount of combustion air being induced by multi-valving, by forced induction (turbocharging or supercharging), or by various combinations of these. 
         [0004]    Nevertheless, the depressingly inflexible laws of thermodynamics govern the performance of all heat engines. The CARNOT cycle describes these limits for ideal gases operating within a closed chamber. On a more practical level, the interaction between pressure and volume resulting in work done on and by a gas within an internal combustion heat engine are described by the OTTO (spark ignition) and DIESEL (compression ignition) cycles. 
         [0005]    These pressure/volume diagrams have been approximated and combined within  FIG. 15  which shows the four stroke cycle of both spark and compression ignition internal combustion engines. 
         [0006]    The area under each curve, calculated by changes in pressure and volume (displacement of the piston) within the closed cylinder, represents a measure of the work done. Causing the curves to move up the diagram by increasing pressure during the compression stroke (a higher compression ratio) will indeed cause a higher pressure curve after combustion. This has been shown to improve thermal efficiency and hence work output. However, since it is the area between the power and compression curves which gives a measure of work done during the cycles, an increase in compression ratio will also require a higher work input, and in any case is limited by pre-ignition problems due to the detonation properties of the hydrocarbon based fuels. 
         [0007]    It is interesting to note that—although not clear from this diagram—the DIESEL compression ignition cycle approaches closer to the efficiency limits of the ideal CARNOT cycle than does the OTTO spark ignition cycle. This is partly due, as explained above, to the inherently higher compression ratio allowable (and in fact necessary) to compression detonate the less volatile fuel oil within Diesel cycle engines. It is also due to the less abrupt ‘burn period’ which maintains a higher mean pressure for more of the power stroke. 
         [0008]    Due to these factors, Diesel cycle engines subsequently deliver a higher torque—albeit over a lower and more restricted speed range—than Otto cycle engines. This is one of the reasons which make Diesel engines ideal for marine propulsion applications where high torque at low engine speed is desirable to initiate propulsion and during manoeuvring. The disadvantage of this limited speed range is more pronounced when Diesel cycle engines are used in road vehicle applications, which demand a large speed range, and the problem is overcome by introducing additional gear ratios. Even so the Diesel cycle in its current form is not a universally ideal internal combustion engine. 
         [0009]    The main problem in achieving an increase in expansion within traditional reciprocating engines is just that—they are indeed reciprocating. The geometry between crank, connecting rod and piston dictates that their swept volume during the induction stroke is equal to that during the expansion or power stroke. 
         [0010]    A further inherent problem with traditional engines, which is often overlooked, is that the residual combustion gases from the previous cycle remain in the un-swept volume of the combustion chamber to contaminate the next charge of air and fuel. This degrades the speed and efficiency of the combustion process in several ways, and leads to secondary exhaust products which are major contributors to toxic pollution. 
         [0011]    In order to improve specific power outputs, it has been long recognised that supercharging of the incoming combustion air provides a major improvement to output—especially in the case of diesel engines where a lack of rotational speed can be compensated for by increased torque as mentioned. Supercharging is achieved by various methods, but each results in an increase in complexity. 
         [0012]    Likewise, highly pressurised fuel injection systems which have been deployed to improve combustion efficiency also result in a more complex fuel supply and distribution system. 
         [0013]    Mindful of the above limitations and the general desire to achieve ever greater efficiency of operation and a reduction of toxic waste products, the present inventor has devised various improvements applicable in internal combustion engines and other reciprocating machines, which are now presented as aspects of the present invention. 
         [0014]    In accordance with a first aspect of the invention, there is provided apparatus for changing a maximum cylinder displacement in an internal combustion engine having a combustion cycle of at least four strokes, the apparatus comprising: 
         [0015]    a crankshaft rotatable about a crankshaft axis, 
         [0016]    a connecting rod in engagement towards a first end with a throw of the crankshaft and configured to couple towards a second end to a piston in a cylinder of the internal combustion engine, 
         [0017]    wherein the apparatus is configured to change, when in use, a distance between the crankshaft axis and the second end of the connecting rod from a point during a revolution of the crankshaft to the same point during a subsequent revolution of the crankshaft. 
         [0018]    The capability to change the distance between the crankshaft axis and the second end of the connecting rod and hence the maximum cylinder displacement within a combustion cycle can have the advantage of providing for more efficient operation of an internal combustion engine. More specifically, this provides for a given inducted volume of gases to be expanded over a greater volume. This can have significant thermodynamic and combustion chemistry benefits and can lead to a significantly more thermally efficient and hence economical engine with cleaner toxic omissions. In addition, a mechanical advantage can be provided because the moment arm of the connecting rod and crankshaft arrangement can be greater during the power stroke when it is most beneficial. This increase in expansion of combusted gases coupled with an increase in piston movement and torque applied to the crankshaft can increase the amount of power extracted from the induced gas charge. In addition, the arrangement permits the induced gas charge to execute a more complete ‘burn’ during the extended combustion stroke. 
         [0019]    In relation to conventional four-stroke internal combustion operation the minimum cylinder displacement may be caused to occur during the first revolution of the crankshaft during the transition from the suction stroke to the compression stroke. The maximum cylinder displacement during the second revolution of the crankshaft may be caused to occur during the transition from the expansion stroke to the exhaust stroke. 
         [0020]    More specifically, the distance between the crankshaft axis and the second end of the connecting rod may be greater at a point (e.g. the transition from the suction stroke to the compression stroke) during the first revolution of the crankshaft than at the same point (e.g. the transition from the expansion stroke to the exhaust stroke) during the second revolution of the crankshaft. Thus, the maximum cylinder displacement may be greater during the third and fourth strokes than during the first and second strokes within a four stroke combustion cycle. Having a piston travel a shorter distance during the pre-combustion first and second strokes thus inducing a prescribed quantity of combustion gases then expanding the combusted gases over a greater piston travel during the energy producing third stroke can provide for more energy efficient operation. 
         [0021]    In addition, having a changing length of piston travel from one part of the combustion cycle to the next can provide for improved operation and/or variation as regards, for example, exhaust gas scavenging and induction of combustion gases. 
         [0022]    Alternatively or in addition, the apparatus may be configured to change from a point during a revolution of the crankshaft to the same point during a subsequent revolution of the crankshaft a location on at least one of the connecting rod and the throw of the crankshaft at which the first end of the connecting rod and the throw of the crankshaft engage with each other. 
         [0023]    More specifically, the apparatus may be configured to change from a point during a revolution of the crankshaft to the same point during a subsequent revolution of the crankshaft a location on the connecting rod at which the first end of the connecting rod and the throw of the crankshaft engage with each other. 
         [0024]    Alternatively or in addition, the change in the distance between the crankshaft axis and the second end of the connecting rod from a point during a revolution of the crankshaft to the same point during a subsequent revolution of the crankshaft may be progressive. 
         [0025]    More specifically, the apparatus may comprise an eccentric coupling between the crankshaft and the connecting rod, the eccentric coupling being operative to provide the progressive change in distance. 
         [0026]    According to a first form of the invention, the apparatus may comprise an epicyclic gear means for coupling movement of the first end of the connecting rod to the throw of the crankshaft. 
         [0027]    More specifically, the epicyclic gear means may be provided on the throw of the crankshaft. 
         [0028]    Alternatively or in addition, the connecting rod may define an aperture the geometric centre of which is offset from a centre of the first end of the connecting rod and with which the throw of the crankshaft rotatably engages. 
         [0029]    More specifically, the throw of the crankshaft may travel around an internal circumference of the aperture. 
         [0030]    More specifically, the aperture and the throw of the crankshaft may comprise respective teethed portions which engage with each other during travel of the throw around the internal circumference. 
         [0031]    Alternatively or in addition, the connecting rod may comprise a connecting rod gear, which defines the aperture and which is rotatably located on the connecting rod such that, in use, it moves generally to and fro on the connecting rod as the throw of the crankshaft travels around the circumference of the aperture. 
         [0032]    More specifically, the first end of the connecting rod may define a connecting rod gear receiving aperture in which the connecting rod gear is rotatably located. 
         [0033]    Alternatively or in addition, the epicyclic gear means may comprise a fixed gear fixedly located on the throw and a plurality of rotatable gears spaced apart around the fixed gear, and, in use, the aperture defined by the connecting rod cooperates with the rotatable gears, which in turn cooperate with the fixed gear, whereby movement of the connecting rod is coupled to movement of the crankshaft. 
         [0034]    More specifically, the plurality of rotatable gears may comprise three rotatable gears spaced apart equally around the fixed gear. 
         [0035]    Alternatively or in addition, the fixed gear and the plurality of rotatable gears may comprise toothed portions for engagement of the fixed gear with the rotatable gears. 
         [0036]    Alternatively or in addition, the epicyclic gear means may be configured such that the throw of the crankshaft describes a substantially complete revolution within the circumference of the aperture each combustion cycle. 
         [0037]    According to a second form of the invention, the first end of the connecting rod may comprise a connecting rod gear and the throw of the crankshaft may comprise a throw gear, the connecting rod gear and the throw gear being of relative dimensions such that, in use, they cooperate to provide progressively for a change in distance between the crankshaft axis and the second end of the connecting rod from a point during a revolution of the crankshaft to the same point during a subsequent revolution of the crankshaft. 
         [0038]    More specifically, the connecting rod gear may be of greater diameter than the throw gear such that as the throw gear travels on a circumference of the connecting rod gear there is a progressive variation in the extent to which the throw gear (and hence the throw) is offset laterally of a centre line of the first end of the connecting rod during a combustion cycle. 
         [0039]    During a four stroke combustion cycle the apparatus may be operative such that the throw gear lies on the centre line of the first end of the connecting rod at two points. For example, when the piston is at its minimum lowest location during the first half of the cycle and a full half cycle later during the second half of the cycle when the piston is at its maximum lowest location. 
         [0040]    More specifically, the connecting rod gear may define an aperture having a geometric centre substantially concentric with the first end of the connecting rod and the throw gear may be operative to travel on the internal circumference of the aperture. 
         [0041]    More specifically, the throw gear may be mounted concentrically on a crank pin of the crankshaft and the connecting rod gear may be mounted eccentrically on the crank pin. The connecting rod gear may be comprised in the connecting rod in the sense that they mechanically cooperate, e.g. by the connecting rod gear being received in a connecting rod gear receiving aperture, whereby movement of the connecting rod is imparted to the connecting rod gear. 
         [0042]    The mounting of the throw gear and the connecting rod gear on the crank pin in this way can hold the throw gear in its proper location in relation to the connecting rod gear to provide for the requisite eccentric movement. 
         [0043]    Alternatively or in addition, the connecting rod gear and the throw gear may comprise respective toothed portions which in use engage with each other. 
         [0044]    Alternatively or in addition, the connecting rod gear may be mounted on the first end of the connecting rod such that, in use, the connecting rod gear moves generally to and fro on the first end during a combustion cycle. 
         [0045]    More specifically, the first end of the connecting rod may define a connecting rod gear receiving aperture in which the connecting rod gear is rotatably located. 
         [0046]    Alternatively or in addition, the throw gear may be rotatably mounted on the throw of the crankshaft. 
         [0047]    More specifically, the throw gear may be concentric with the crank pin. 
         [0048]    According to a third form of the invention, the first end of the connecting rod may comprise a connecting rod gear and the crankshaft may comprise a crankshaft gear, the connecting rod gear and the crankshaft gear being located on the apparatus such that, in use, they cooperate to provide progressively for the change in distance between the crankshaft axis and the second end of the connecting rod from a point during a revolution of the crankshaft to the same point during a subsequent revolution of the crankshaft. 
         [0049]    More specifically, the connecting rod gear may be mounted eccentrically on the connecting rod to thereby provide progressively for the change in distance. 
         [0050]    More specifically, the crankshaft gear may be mounted concentrically with the crankshaft axis. 
         [0051]    Alternatively or in addition, the connecting rod gear may be mounted on a bearing provided on the first end of the connecting rod. 
         [0052]    Alternatively or in addition, the connecting rod gear may be of greater diameter than the crankshaft gear. 
         [0053]    Alternatively or in addition, the crankshaft gear may be fixedly mounted on the crankshaft and the connecting rod gear may be rotatably mounted on the first end of the connecting rod. 
         [0054]    Alternatively or in addition, the connecting rod gear and the crankshaft gear may comprise respective toothed portions which in use engage with each other. 
         [0055]    The third form of the invention may be used alone or in conjunction with one or other of the first and second forms of the invention. 
         [0056]    In the third form of the invention, the apparatus may further comprise control means configured to provide for cooperative movement of the connecting rod gear and the crankshaft gear that is independent of the cooperative movement of the connecting rod gear and the crankshaft gear associated with rotation of the crankshaft about the crankshaft axis. 
         [0057]    The independent cooperative movement of the connecting rod gear and the crankshaft gear can allow for an advance or a delay of the particular point during a combustion cycle at which the piston is at its minimum and/or maximum lowest location during the combustion cycle. For example, in a four-stroke internal combustion operation the maximum cylinder displacement may be caused to occur slightly in advance of or after the transition from the suction stroke to the compression stroke. 
         [0058]    Thus, the control means may be used to provide independent cooperative movement of the connecting rod gear and the crankshaft gear at any point during a combustion cycle. 
         [0059]    An application of the independent movement achievable with the control means is to alter the timing of any one of the four strokes within a four stroke cycle or to provide different compression ratios or swept volumes within a combustion cycle. This can bring benefits in economy, e.g. where the engine is part-loaded, and longevity of the related moving parts of the engine. 
         [0060]    More specifically, the control means may be controllable externally of an internal combustion engine incorporating the invention, e.g. by a user of the internal combustion engine. 
         [0061]    More specifically, the control means may be controllable externally by electrical and/or mechanical means. 
         [0062]    Alternatively or in addition, control means may comprise a crankshaft having a bore and a member passing through the bore, in which a first end of the member is coupled to external control means and a second, opposite end of the member is coupled to the crankshaft gear. 
         [0063]    More specifically and in an internal combustion engine having two or more cylinders each having a crankshaft and connecting rod pair the control means may be configured to provide for independent control of each crankshaft and connecting rod pair. 
         [0064]    More specifically, independent control of a first crankshaft and connecting rod pair may be coupled mechanically to the second crankshaft and connecting rod pair. 
         [0065]    More specifically, the control means may comprise a second pair of crankshaft and connecting rod gears provided on an opposite of the side of the connecting rod to the first pair of crankshaft and connecting rod gears. 
         [0066]    More specifically, opposing connecting rod gears of each crankshaft and connecting rod pair may be coupled to each other (e.g. via the connecting rod) and adjacent crankshaft gears of adjacent crankshaft and connecting rod pairs may be coupled to each other, whereby movement of a crankshaft gear of a first crankshaft and connecting rod pair is coupled to crankshaft gears of successive crankshaft and connecting rod pairs. 
         [0067]    More specifically, adjacent crankshaft cog means of adjacent crankshaft and connecting rod pairs may be coupled to each other by means of a further member passing through a bore in a section of crankshaft between the adjacent crankshaft and connecting rod pairs. 
         [0068]    In accordance with another aspect of the invention, there is provided apparatus for changing a maximum cylinder displacement in an internal combustion engine having a combustion cycle of at least four strokes, the apparatus comprising: a crankshaft rotatable about a crankshaft axis, a connecting rod in engagement towards a first end with a throw of the crankshaft and configured to couple towards a second end to a piston in a cylinder of the internal combustion engine, wherein the apparatus is configured to change, when in use, a distance traveled by the piston within the cylinder during the course of a combustion cycle. 
         [0069]    In accordance with a second aspect of the invention, there is provided a method of changing a maximum cylinder displacement in an internal combustion engine, the method comprising: 
         [0070]    engaging a throw of a crankshaft towards a first end of a connecting rod, the crankshaft being rotatable about a crankshaft axis, coupling a piston of an internal combustion engine towards a second end of the connecting rod, and 
         [0071]    configuring the crankshaft and connecting rod to change, when in use, a distance between the crankshaft axis and the second end of the connecting rod from a point during a revolution of the crankshaft to the same point during a subsequent revolution of the crankshaft. 
         [0072]    Further embodiments of the second aspect of the present invention may comprise one or more features described above according to the first aspect of the present invention. 
         [0073]    According to a third aspect of the present invention, there is provided an internal combustion engine having a combustion cycle of at least four strokes comprising an arrangement according to the first aspect of the present invention. 
         [0074]    More specifically in a reciprocating four stroke internal combustion arrangement, the internal combustion engine may comprise an exhaust gas aperture provided in a cylinder of the internal combustion engine, the internal combustion engine being configured to close the exhaust gas aperture during at least a compression stroke of the cycle and to open the exhaust gas aperture towards the end of an expansion stroke of the cycle, and wherein the exhaust gas aperture is in the vicinity of the piston when the piston is situated in the cylinder towards the end of the expansion stroke. 
         [0075]    More specifically, the internal combustion engine may be configured such that the exhaust gas aperture is opened and closed by movement of the piston in the cylinder during the course of the cycle. 
         [0076]    More specifically, the exhaust gas aperture may be operative to open during a longer length of stroke of the piston and to remain closed during a shorter length of stroke of the piston during the cycle. 
         [0077]    Alternatively or in addition, the internal combustion engine may further comprise an exhaust port located towards a top of the cylinder which is operable in accordance with conventional practice of an internal combustion engine. 
         [0078]    Alternatively or in addition, the internal combustion engine may further comprise a substantially air-tight space defined by a part of the internal combustion engine, the space being in fluid communication with a piston moveably situated in a cylinder such that, in use, air within the space is compressed as the piston moves toward the open end of the cylinder, and at least one of the piston and the part of the internal combustion engine is configured to open an aperture to the space after compression of the air, the aperture being in fluid communication with an air intake to the cylinder, whereby compressed air is released from the space to the cylinder. 
         [0079]    More specifically, at least one of the piston and the part of the internal combustion engine may be configured to open the aperture by movement of the piston in the cylinder during the course of a cycle. 
         [0080]    More specifically, the piston may define a conduit which is open at an end to the space and is in fluid communication at another end with the aperture during part of the movement of the piston in the cylinder. 
         [0081]    Alternatively or in addition, at least one of the piston and the part of the internal combustion engine may be configured to open a further aperture to the space before compression of the air, whereby air (e.g. atmospheric air) is admitted to the space prior to compression. 
         [0082]    More specifically, at least one of the piston and the part of the internal combustion engine may be configured to open the further aperture by movement of the piston in the cylinder. 
         [0083]    More specifically, the piston may define a further conduit which is open at an end to the space and is in fluid communication at another end with the further aperture during part of the movement of the piston in the cylinder. 
         [0084]    Alternatively or in addition, the space defined by the part of the internal combustion engine may comprise a crankcase, e.g. a crankcase of a conventional internal combustion engine. 
         [0085]    More specifically, the internal combustion engine may further comprise a dry sump. 
         [0086]    Alternatively or in addition, the internal combustion engine may further comprise a trap for trapping oil vapour contained within the air compressed within the crankcase. 
         [0087]    More specifically, the trap may be located between the aperture and the air intake to the cylinder. 
         [0088]    Alternatively or in addition, the internal combustion engine may comprise a plurality of cylinders each cylinder having a substantially air-tight space associated with it and an aperture for releasing compressed air to an air intake of the cylinder. 
         [0089]    Alternatively or in addition, fluid communication between the aperture and the air intake may be by means of an air intake conduit. 
         [0090]    More specifically, where the air intake to the cylinder is a combustion air intake, at least one of the piston and the part of the internal combustion engine may be configured to open the aperture at about the transition between the suction and compression strokes. 
         [0091]    More specifically, where the internal combustion engine comprises a further aperture, at least one of the piston and the part of the internal combustion engine may be configured to open the further aperture at about the transition between the compression and expansion strokes. 
         [0092]    Alternatively or in addition, the internal combustion engine may further comprise a unitary device comprising a fluid intake valve and an fluid outlet valve, the unitary valve being operable during an operating cycle of the internal combustion engine to move in relation to a cylinder of the internal combustion engine to open a fluid intake aperture to the cylinder and to open a fluid outlet aperture to the cylinder. 
         [0093]    More specifically, the unitary device may be operable to move to a first position at which neither the fluid intake aperture nor the fluid outlet aperture is open, to a second position at which the fluid intake aperture is open and the fluid outlet aperture is closed and to a third position at which the fluid intake aperture is closed and the fluid outlet aperture is open. 
         [0094]    More specifically, the unitary device may be operable to move from one of the three positions to another by substantially linear movement in relation to the cylinder. 
         [0095]    Alternatively or in addition, the unitary device may be operable to move substantially in a direction of a longitudinal axis of the bore of the cylinder. 
         [0096]    Alternatively or in addition, the unitary device may define at least one conduit for each of fluid intake and fluid expulsion, each conduit being brought into fluid communication with the cylinder during the course of a cycle. 
         [0097]    Alternatively or in addition, the cylinder and the unitary device may be configured for movement of at least part of the unitary device into the cylinder bore during the cycle. 
         [0098]    More specifically, the unitary device may be moveable to a first position in the cylinder bore at which the fluid intake aperture is opened. 
         [0099]    More specifically, the unitary device may be moveable to a second position in the cylinder bore at which the fluid outlet aperture is opened. 
         [0100]    More specifically, the unitary device may be operable to reach further into the bore at the second position than at the first position. 
         [0101]    Alternatively or in addition, the piston and unitary device may be configured such that part of one is received in the other during the course of the cycle. 
         [0102]    More specifically, the piston may define a recess configured to receive at least a part of the unitary device. 
         [0103]    More specifically, the unitary device and piston may be operative such that the part of the unitary device is received in the recess in the piston towards the end of an exhaust stroke of the cycle. 
         [0104]    More specifically, the unitary device may be configured to substantially fill the recess in the piston. 
         [0105]    Alternatively or in addition, the unitary device may be actuated by means of at least one solenoid. 
         [0106]    More specifically, the solenoid may be controlled to provide for synchronisation with an operating cycle of the internal combustion engine. 
         [0107]    Alternatively or in addition, the internal combustion engine may further comprise a fluid injection pump comprising a pump member operative to pump fluid by moving within a housing of the fluid injection pump, in which a piston situated in a cylinder of the internal combustion engine cooperates, when in use, with the pump member to actuate the pump member as the piston moves in the cylinder. 
         [0108]    More specifically, the housing may define a space and the pump member may be operative to move bodily within the space. 
         [0109]    More specifically, the pump member and housing may be configured to create a fluid tight seal between the housing and the pump member as the pump member moves. 
         [0110]    Alternatively or in addition, the internal combustion engine may be configured to synchronise movement of the pump member within the housing with a combustion cycle. 
         [0111]    In a form of the present invention, the space may comprise a priming portion and an injecting portion and the pump member may be operative to move between the priming portion and the injecting portion. 
         [0112]    More specifically, the housing may define a fluid inlet, the fluid inlet being closed when the pump member is situated in the priming portion and being open when the pump member is situated in the injecting portion. 
         [0113]    More specifically, the fluid injection pump may be configured to create a vacuum as the pump member moves from the priming portion to the injecting portion. 
         [0114]    Alternatively or in addition, the internal combustion engine may further comprise fluid metering means. The fluid metering means may be operative to provide a predetermined, perhaps controllable measure of fluid to the fluid injection device. 
         [0115]    Alternatively or in addition, the fluid metering means may be operative to pump fluid from a fluid supply to the fluid injection pump. 
         [0116]    Alternatively or in addition, the fluid injection pump may be configured to transfer fluid from the priming portion to the injecting portion as the pump member moves from the injecting portion to the priming portion. 
         [0117]    More specifically, movement of the pump member may actuate the transfer of fluid from the priming portion to the injecting portion. 
         [0118]    More specifically, the fluid injection pump may comprise a fluid conduit between the priming portion and the injecting portion and the pump member and housing may be configured to form a fluid tight seal with the housing as the pump member moves. 
         [0119]    Alternatively or in addition, the internal combustion engine may further comprise at least one fluid outlet to the cylinder, the fluid outlet being in fluid communication with the injecting portion, and the pump member and housing may be configured to form a fluid tight seal with each other as the pump member moves from the priming portion to the injecting portion. 
         [0120]    In a further form of the present invention, the fluid injection pump may be provided in the piston. 
         [0121]    More specifically, the body of the piston may define the housing of the fluid injection pump. 
         [0122]    More specifically, the housing and the pump member may be configured to constrain movement of the pump member within the housing in a direction substantially in line with a longitudinal axis of the bore of the cylinder. 
         [0123]    Alternatively or in addition, the internal combustion engine may further comprise a plurality of fluid outlets to the cylinder, the fluid outlets being in fluid communication with the fluid injection pump and configured to provide a dispersion of fluid within the cylinder. 
         [0124]    Alternatively or in addition, the fluid injection pump may be configured to pump combustion fuel. 
         [0125]    Alternatively or in addition, the internal combustion engine may comprise combustion ignition means operative to generate a source of ignition within a cylinder of the internal combustion engine, in which the combustion ignition means is configured to generate a diffuse source of ignition. 
         [0126]    More specifically, the combustion ignition means may comprise an optical energy generator for generating optical energy as the source of ignition. 
         [0127]    More specifically, the optical energy generator may comprise a laser. 
         [0128]    Alternatively or in addition, the combustion ignition means may comprise an energy conductor (e.g. a fibre optic cable) for conveying the source of ignition from the optical energy generator to the cylinder. 
         [0129]    Alternatively or in addition, the combustion ignition means may comprise diffusion means for converting a point source of ignition to a diffuse source of ignition. 
         [0130]    Alternatively or in addition, where the internal combustion engine comprises a unitary device comprising an air intake valve and an exhaust valve, the combustion ignition means may be provided in the unitary device. 
         [0131]    Alternatively or in addition, the internal combustion engine may further comprise combustion ignition means operative to generate a source of ignition within a cylinder of the internal combustion engine, in which the combustion ignition means comprises a laser and the source of ignition is laser light. 
         [0132]    Alternatively or in addition, the internal combustion engine may further comprise combustion ignition means operative to generate a source of ignition within a cylinder of the internal combustion engine, in which the combustion ignition is configured to generate a diffuse source of ignition. 
         [0133]    Alternatively or in addition, the internal combustion engine may comprise a petrol engine or a compression-ignition engine, such as a diesel engine, or indeed a gas engine. 
         [0134]    The present applicant has realised that providing an exhaust gas aperture in the vicinity of the piston when the piston is situated in the cylinder towards the end of the expansion stroke has wider application than hitherto described. 
         [0135]    Therefore, according to a fourth aspect of the present invention there is provided an internal combustion engine having a combustion cycle of at least four strokes comprising an exhaust gas aperture provided in a cylinder of the internal combustion engine, 
         [0136]    the internal combustion engine being configured to close the exhaust gas aperture at least during a compression stroke of a cycle and to open the exhaust gas aperture towards the end of an expansion stroke of the cycle as a piston moves in the cylinder, 
         [0137]    wherein the exhaust gas aperture is in the vicinity of the piston when the piston is towards the end of the expansion stroke. 
         [0138]    Conventionally, combustion products are exhausted from a cylinder by opening an exhaust port located towards the top of the cylinder when the piston reaches the end of the expansion stroke. Opening an exhaust gas aperture that is in the vicinity of the piston towards the end of the expansion stroke according to the invention can relieve the pressure of combustion gases in the cylinder. This may have the advantage of reducing resistance encountered by the piston as it moves on its return stroke after completion of the expansion stroke. Also, exhaust valves can be exposed to significantly lower temperature and/or pressure gases than in conventional arrangements. 
         [0139]    More specifically, the internal combustion engine may be configured such that the exhaust gas aperture is opened and closed by movement of the piston in the cylinder during the course of the cycle. 
         [0140]    More specifically, the piston may be operative to move from a position at which it covers the exhaust gas aperture to another position at which it uncovers the exhaust gas aperture. 
         [0141]    Alternatively or in addition, the internal combustion engine may be configured to change a length of a stroke of the piston in the cylinder from one stroke to another during a cycle, the exhaust gas aperture opening during a longer length of stroke of the piston. 
         [0142]    More specifically, the internal combustion engine may be operative according to a four stroke cycle and may further comprise a crankshaft rotatable about a crankshaft axis, a connecting rod in engagement towards a first end with a throw of the crankshaft and coupling towards a second end to the piston, in which the connecting rod and crankshaft are configured to change a distance between the crankshaft axis and the piston from a point during a revolution of the crankshaft within a combustion cycle to the same point during a subsequent revolution of the crankshaft within the combustion cycle. 
         [0143]    Alternatively or in addition, the internal combustion engine may further comprise an exhaust port located towards a top of the cylinder which is operable in accordance with conventional practice. 
         [0144]    Further forms of the fourth aspect of the present invention may comprise one or more features of one or more other aspects of the present invention. 
         [0145]    According to a fifth aspect of the present invention there is provided a method of relieving exhaust gas pressure in a cylinder of an internal combustion engine having a combustion cycle of at least four strokes comprising: 
         [0146]    providing an exhaust gas aperture in the cylinder such that it is in the vicinity of a piston when the piston is situated in the cylinder towards the end of an expansion stroke of a cycle, and 
         [0147]    configuring the internal combustion engine to close the exhaust gas aperture at least during a compression stroke of the cycle and to open the exhaust gas aperture towards the end of an expansion stroke of the cycle. 
         [0148]    Forms of the fifth aspect of the present invention may comprise one or more features described above in respect of the fourth aspect. 
         [0149]    The present applicant has realised that using the piston to compress air for use in combustion has wider application than hitherto described. 
         [0150]    Therefore, according to a sixth aspect of the present invention there is provided an internal combustion engine having a combustion cycle of at least four strokes comprising: 
         [0151]    a substantially air-tight space defined by a part of the internal combustion engine, the space being in fluid communication with a piston moveably situated in a cylinder of the internal combustion engine such that, in use, air within the space is compressed as the piston moves toward the open end of the cylinder, and the internal combustion engine is configured to open an aperture to the space after compression of the air, the aperture being in fluid communication with an air intake to the cylinder, whereby compressed air is released from the space to the cylinder. 
         [0152]    Compression by the piston of air contained within the space can provide for injection of air, e.g. combustion air, into the cylinder without having to rely on conventional means, such as a turbocharger or supercharger. Thus, the present approach can make fuller use of energy released during a combustion cycle and may therefore provide for more efficient engine operation. In addition, increasing the density of the intake charge and hence the power output of the engine can lead to one or more of smaller engine size, lighter engine weight and a less expensive engine for a required power output. 
         [0153]    More specifically, the internal combustion engine may be configured to open the aperture by movement of the piston in the cylinder during the course of a cycle, e.g. a combustion cycle. 
         [0154]    More specifically, the piston may be operative to move from a position at which it covers the aperture to another position at which it uncovers the aperture. 
         [0155]    Alternatively or in addition, the piston may define a conduit which is open to the space at an end and is in fluid communication at another end with the aperture during part of the movement of the piston in the cylinder. 
         [0156]    Alternatively or in addition, the internal combustion engine may be configured to open a further aperture to the space before air is compressed in the space. Thus, air (e.g. atmospheric air) may be admitted to the space prior to compression. 
         [0157]    More specifically, the internal combustion engine may be configured to open the further aperture by movement of the piston in the cylinder. 
         [0158]    More specifically, the piston may operative to move from a position at which it covers the further aperture to another position at which it uncovers the further aperture. 
         [0159]    More specifically, the piston may define a further conduit which is open to the space at an end and is in fluid communication at another end with the further aperture during part of the movement of the piston in the cylinder. 
         [0160]    Alternatively or in addition, the space defined by the part of the internal combustion engine may comprise a crankcase. 
         [0161]    Typically, the bottom of a crankcase contains oil for machine lubrication. The applicant has realised that under certain circumstances the oil may release a vapour which may contaminate the air compressed in the crankcase. Therefore and more specifically, the internal combustion engine may further comprise a dry sump. A dry sump is a sump which does not contain lubrication oil. Alternatively or in addition, the internal combustion engine may further comprise a trap for trapping oil vapour contained within air compressed within the crankcase. More specifically, the trap may be located between the aperture and the air intake to the cylinder. 
         [0162]    Alternatively or in addition, the internal combustion engine may comprise a plurality of cylinders each cylinder having a substantially air-tight space associated with it and an aperture for releasing compressed air to an air intake of the cylinder. 
         [0163]    Alternatively or in addition, fluid communication between the aperture and the air intake may be by means of an air intake conduit. More specifically, the air intake conduit may comprise an air-to-air intercooler chamber external to the chamber block. Alternatively or in addition, the air intake may comprise a non-return valve, such as a pressure differential flapper or reed valve. 
         [0164]    Alternatively or in addition, the internal combustion engine may be configured to change a length of a stroke of the piston in the cylinder from one stroke to another during a cycle, the air in the space being compressed to a higher pressure during a longer length of stroke of the piston. 
         [0165]    Alternatively or in addition, the internal combustion engine may comprise a non-return valve for trapping air compressed in the space. 
         [0166]    More specifically, the non-return valve may be configured to release compressed air from the space. For example, compressed air may be released for induction into the cylinder. 
         [0167]    Alternatively or in addition, the internal combustion engine may comprise an internal combustion engine in which the air intake to the cylinder is a combustion air intake. 
         [0168]    More specifically, the internal combustion engine may comprise a petrol engine or a compression-ignition engine, such as a diesel engine. 
         [0169]    Alternatively or in addition, the internal combustion engine may be operative to perform a four stroke combustion cycle. 
         [0170]    More specifically, at least one of the piston and the part of the internal combustion engine may be configured to open the aperture at about the transition between the suction and compression strokes. 
         [0171]    More specifically where the internal combustion engine comprises a further aperture, at least one of the piston and the part of the internal combustion engine may be configured to open the further aperture at about the transition between the compression and expansion strokes. 
         [0172]    Forms of the sixth aspect of the present invention may comprise one or more features described in respect of one or more other aspects of the present invention. 
         [0173]    According to a seventh aspect of the present invention there is provided a method of injecting air into a cylinder of an internal combustion engine having a combustion cycle of at least four strokes comprising: 
         [0174]    providing a substantially air-tight space defined by a part of the internal combustion engine, the space being in fluid communication with a piston moveably located in the cylinder such that, in use, air within the space is compressed as the piston moves toward the open end of the cylinder, and 
         [0175]    configuring the internal combustion engine to open an aperture to the space after compression of the air, the aperture being in fluid communication with an air intake on the cylinder, thereby releasing compressed air from the space to the cylinder. 
         [0176]    Forms of the seventh aspect of the present invention may comprise one or more features defined in respect of the sixth aspect of the present invention. 
         [0177]    The present applicant has realised that a unitary device comprising an air intake valve and an exhaust valve has wider application than hitherto described. 
         [0178]    Therefore, according to an eighth aspect of the present invention, there is provided a reciprocating machine comprising a unitary device comprising a fluid intake valve and a fluid outlet valve, the unitary device being operable during an operating cycle of the reciprocating machine to move in relation to a cylinder of the reciprocating machine to open a fluid intake aperture to the cylinder and to open a fluid outlet aperture to the cylinder. 
         [0179]    The unitary device of the present invention may confer advantages, e.g. over the conventional rocker arm and separate intake valve and exhaust valve arrangement of an internal combustion engine, by simplifying the valve structure, which in turn may provide for ease of manufacture and lower cost. 
         [0180]    More specifically, the unitary device may be operable to move to a first position at which neither the fluid intake aperture nor the fluid outlet aperture is open, to a second position at which the fluid intake aperture is open and the fluid outlet aperture is closed and to a third position at which the fluid intake aperture is closed and the fluid outlet aperture is open. 
         [0181]    More specifically, the unitary device may be operable to move from one of the three positions to another by substantially linear movement in relation to the cylinder. 
         [0182]    Alternatively or in addition, the unitary device may be configured to prevent the unitary device falling into the cylinder. This feature may be useful in the event of an electrical power failure or electronic control failure. 
         [0183]    Alternatively or in addition, the unitary device may be operable to move substantially in a direction of a longitudinal axis of a bore of the cylinder. 
         [0184]    Alternatively or in addition, the unitary device may define at least one conduit for each of fluid intake and fluid expulsion, each conduit being brought into fluid communication with the cylinder during the course of the operating cycle of the reciprocating machine. 
         [0185]    Alternatively or in addition, the cylinder and the unitary device may be configured for movement of at least part of the unitary device into the cylinder bore during the cycle. 
         [0186]    More specifically, the unitary device may be moveable to a first position in the cylinder bore at which the fluid intake aperture is opened. 
         [0187]    More specifically, the unitary device may be moveable to a second position in the cylinder bore at which the fluid outlet aperture is opened. 
         [0188]    More specifically, the unitary device may be operable to reach further into the bore at the second position than at the first position. 
         [0189]    Alternatively or in addition, the piston and unitary device may be configured such that part of one is received in the other during the course of the cycle. 
         [0190]    More specifically, the piston may define a recess configured to receive at least a part of the unitary device. This feature allows for the recess to be of such a volume to provide a desired compressed volume. This can address the infinite compression ratio problem encountered during the following compression stroke. In addition, the presence of the recess can prevent contact between the piston and the unitary device in the event of a failure, such as electrical power, solenoid or control electronics failure. 
         [0191]    More specifically, the unitary device and piston may be operative such that the part of the unitary device is received in the recess in the piston towards the end of an exhaust stroke of the cycle. Where the reciprocating machine is an internal combustion engine this can aid more complete scavenging of exhaust gases from the cylinder. 
         [0192]    More specifically, the unitary device may be configured to substantially fill the recess in the piston. 
         [0193]    Alternatively or in addition, the unitary device may be actuated by means of at least one solenoid. 
         [0194]    More specifically, the solenoid may be controlled to provide for synchronisation with the operating cycle of the reciprocating machine. 
         [0195]    Alternatively or in addition, the unitary device may be controlled in dependence upon engine speed and/or load demand, e.g. by means of the engine&#39;s electronic management system. Controlling the speed and or degree of opening of the unitary device during the intake cycle to correctly match the intake volume with the fuel charge supply can avoid there being too lean an air-fuel mixture and subsequent excessive combustion temperatures. 
         [0196]    Alternatively or in addition, the fluid intake valve and a fluid outlet valve may be configured to utilise circular porting for both inlet and outlet movements. This can provide for thermal symmetry and even radial expansion which allows the unitary device to have a light and robust structure. 
         [0197]    Alternatively or in addition, the unitary device may be configured such that its valve porting and/or its passage geometry provides for release of exhaust gas contained within the unitary device. 
         [0198]    Alternatively or in addition, the reciprocating machine may comprise an internal combustion engine in which the fluid intake valve is an air intake valve, the fluid outlet valve is an exhaust valve, the fluid intake aperture is a fluid intake aperture and the fluid outlet aperture is an exhaust gas aperture. 
         [0199]    This aspect of the invention may also be applicable to pumps as well as motors, such as the internal combustion engine. Indeed this aspect may be applicable to any apparatus involving valve/porting in the control of movement of fluids and/or gases. Thus, the reciprocating machine may alternatively comprise a pump. 
         [0200]    Further forms of the eighth aspect of the invention may comprise one or more features described in respect of one or more of the other aspects of the present invention. 
         [0201]    The present applicant has realised that having a pump member which is actuated by movement of a piston of an internal combustion engine has wider application than hitherto described. 
         [0202]    Therefore, according to a ninth aspect of the present invention there is provided an internal combustion engine having a combustion cycle of at least two strokes comprising: 
         [0203]    a fluid injection pump comprising a pump member operative to pump fluid by moving within a housing of the fluid injection pump, 
         [0204]    in which a piston situated in a cylinder of the internal combustion engine cooperates mechanically, when in use, with the pump member to actuate the pump member as the piston moves in the cylinder. 
         [0205]    Making use of the movement of the piston as it moves to and fro within the cylinder to actuate the fluid injection pump can be more efficient than the conventional approach of actuating a fluid injection pump by dedicated means, such as an electricity supply. 
         [0206]    More specifically, the housing may define a space and the pump member may be operative to move bodily within the space. 
         [0207]    More specifically, the pump member and housing may be configured to create a fluid tight seal between the housing and the pump member as the pump member moves. 
         [0208]    Alternatively or in addition, the internal combustion engine may be configured to synchronise movement of the pump member within the housing with a combustion cycle. 
         [0209]    In a form of the present invention, the space may comprise a priming portion and an injecting portion and the pump member may be operative to move between the priming portion and the injecting portion. 
         [0210]    More specifically, the housing may define a fluid inlet, the fluid inlet being closed when the pump member is situated in the priming portion and being open when the pump member is situated in the injecting portion. Thus, fluid can be admitted to the fluid injection pump prior to injection. 
         [0211]    More specifically, the fluid injection pump may be configured to create a vacuum as the pump member moves from the priming portion to the injecting portion. The vacuum can help draw fluid into the fluid injection pump. 
         [0212]    Alternatively or in addition, the internal combustion engine may further comprise fluid metering means. The fluid metering means may be operative to provide a predetermined, perhaps controllable measure of fluid to the fluid injection device. Alternatively or in addition, the fluid metering means may be operative to pump fluid from a fluid supply to the fluid injection pump. 
         [0213]    Alternatively or in addition, the fluid injection pump may be configured to transfer fluid from the priming portion to the injecting portion as the pump member moves from the injecting portion to the priming portion. 
         [0214]    More specifically, movement of the pump member may actuate the transfer of fluid from the priming portion to the injecting portion. 
         [0215]    More specifically, the fluid injection pump may comprise a fluid conduit between the priming portion and the injecting portion and the pump member and housing may be configured to form a fluid tight seal with the housing as the pump member moves. Thus, movement of the pump member from the injecting portion to the priming portion may pump fluid from the priming portion to the injecting portion via the fluid conduit. 
         [0216]    Alternatively or in addition, the internal combustion engine may further comprise at least one fluid outlet to the cylinder, the fluid outlet being in fluid communication with the injecting portion, and the pump member and housing being configured to form a fluid tight seal with each other as the pump member moves from the priming portion to the injecting portion. Thus, fluid may be injected from the injecting portion into the cylinder by movement of the pump member within the housing. 
         [0217]    In a further form of the present invention, the fluid injection pump may be provided in the piston. 
         [0218]    More specifically, a body of the piston may define the housing of the fluid injection pump. 
         [0219]    More specifically, the housing and the pump member may be configured to constrain movement of the pump member within the housing in a direction substantially in line with a longitudinal axis of the bore of the cylinder. Thus, the pump member may be thrown to and fro within the housing as the piston moves to and fro within the cylinder. 
         [0220]    Alternatively or in addition, the internal combustion engine may further comprise a plurality of fluid outlets to the cylinder, the fluid outlets being in fluid communication with the fluid injection pump and being configured to provide a dispersion of fluid within the cylinder. The plurality of fluid outlets can provide for the injection of an atomised charge of fuel into the cylinder thereby setting up an advantageous combustion environment in the cylinder. 
         [0221]    Alternatively or in addition, the fluid injection pump may be configured to pump combustion fuel. 
         [0222]    More specifically, the fluid injection pump may be configured to alternately pump combustion fuel and air. This can reduce leakage of fuel down the cylinder wall into the crankcase. 
         [0223]    Movement of the pump member towards the end of the exhaust stroke/beginning of the intake stroke can purge the fluid injection pump of combustion fuel, e.g. fuel that has leaked back into the fluid injection pump after injection of fuel by the pump into the cylinder. 
         [0224]    Alternatively or in addition, the internal combustion engine may be a petrol engine or a compression-ignition engine, such as a diesel engine. 
         [0225]    Further forms of the ninth aspect of the present invention may comprise one or more features of one or more of the other aspects of the present invention. 
         [0226]    According to a tenth aspect of the present invention, there is provided a method of actuating a fluid injection pump in an internal combustion engine having a combustion cycle of at least two strokes, the method comprising: 
         [0227]    providing a fluid injection pump comprising a pump member operative to pump fluid by moving within a housing of the fluid injection pump, and 
         [0228]    configuring a piston situated in a cylinder of the internal combustion engine to cooperate mechanically, when in use, with the pump member to actuate the pump member as the piston moves in the cylinder. 
         [0229]    Further forms of the tenth aspect of the present invention may comprise one or more features of the ninth aspect of the present invention. 
         [0230]    The present applicant has realised that using a diffuse source of ignition in an internal combustion engine has wider application than hitherto described. 
         [0231]    Therefore, according to an eleventh aspect of the present invention there is provided a reciprocating internal combustion engine having a combustion cycle of at least two strokes comprising combustion ignition means operative to generate a source of ignition within a cylinder of the internal combustion engine, in which the combustion ignition means is configured to generate a diffuse source of ignition. 
         [0232]    Igniting an air-fuel mixture in a cylinder by means of a diffuse source of ignition can provide for more effective combustion and/or a reduction on stresses exerted on the internal combustion engine. This is because an efficient and ‘clean burn’ of combustion gases can be achieved by providing a large flame front during burn. In a conventional internal combustion engine the flame front originates from (one or more) electrical discharge spark plugs which must be located centrally within the cylinder head for maximum effect. The spark plug and the associated electrical control and distribution system can be a major source of maintenance failure (e.g. dampness problems at high tension connectors and insulators) and limited life on account of contamination of insulators and continual and progressive electrical erosion of the spark gap. This in turn can weaken the spark density and cause a minute delay in optimal ‘timing’ of the spark discharge. In addition, ignition using the conventional spark plug can cause a combustion ripple though the cylinder which may provide for less effective combustion and generate undesirable stresses. 
         [0233]    More specifically, the combustion ignition means may comprise an optical energy generator for generating optical energy as the source of ignition. 
         [0234]    More specifically, the optical energy generator may comprise a laser. 
         [0235]    Alternatively or in addition, the combustion ignition means may comprise an energy conductor (e.g. a fibre optic cable) for conveying the source of ignition from the optical energy generator to the cylinder. 
         [0236]    More specifically, the optical energy generator may comprise a sealed maintenance laser energy source. 
         [0237]    Alternatively or in addition, the combustion ignition means may comprise diffusion means for converting a point source of ignition to a diffuse source of ignition. 
         [0238]    Alternatively or in addition, the diffusion means may be located in the wall of the cylinder. 
         [0239]    More specifically, the diffusion means may be located such that it is swept by the piston as it moves within the cylinder. Thus, the diffusion means can be self cleaning. 
         [0240]    Alternatively or in addition, the source of ignition may be configured to discharge radially into the bore of the cylinder. Thus, the flame front can accelerate through the bore of the cylinder to provide for full and relatively instantaneous combustion. 
         [0241]    Alternatively or in addition, the laser light may be configured to impinge directly on the air-fuel mixture. 
         [0242]    Alternatively or in addition, the internal combustion engine may be a petrol engine or a compression-ignition engine, such as a diesel engine. 
         [0243]    Where the internal combustion engine is a compression-ignition engine, e.g. a diesel engine, the combustion ignition means may be operative to generate a source of ignition during cranking of the engine. 
         [0244]    Thus, the combustion ignition means can perform the function of conventional means of ignition, such as the glow plug. 
         [0245]    Alternatively or in addition, where the internal combustion engine is a compression-ignition engine the combustion ignition means may be operative to generate a source of ignition during running of the engine after the cranking phase is complete. 
         [0246]    A combustion ignition means according to the two immediately preceding paragraphs may be independently controllable of a combustion cycle of the internal combustion engine. 
         [0247]    Thus, operation of the combustion ignition means need not depend directly on the combustion cycle. This can be advantageous in a compression-ignition engine. A conventional means of ignition in a compression-ignition engine normally involves injection of fuel, such as diesel, into the cylinder at around the top of the compression stroke. When the fuel is injected it vaporises and ignites due to the heat created by compression of the air in the cylinder. Thus, ignition timing may be non-optimal because of its direct dependence on the combustion cycle. 
         [0248]    The combustion ignition means can provide further benefits. For example, where the combustion ignition means comprises a laser the laser&#39;s inherent controllability can provide for improved heat switch on and switch off characteristics. Also, the ability to direct laser light within the cylinder can provide for improved flame front characteristics thereby providing for more efficient and a cleaner burn of combustion gases. 
         [0249]    The combustion ignition means may provide the sole means of ignition or may reduce reliance on or improve upon conventional means of ignition by being provided in addition to such conventional means. 
         [0250]    Alternatively or in addition, the internal combustion engine may further comprise a unitary device comprising an air intake valve and an exhaust valve according to another aspect of the present invention, and the combustion ignition means may be provided in the unitary device. 
         [0251]    Forms of the eleventh aspect of the present invention may comprise one or more features of one or more of the other aspects of the present invention. 
         [0252]    According to a twelfth aspect of the present invention, there is provided a reciprocating internal combustion engine having a combustion cycle of at least two strokes comprising combustion ignition means operative to generate a source of ignition within a cylinder of the internal combustion engine, in which the combustion ignition means comprises a laser and the source of ignition is laser light. 
         [0253]    Forms of the twelfth aspect of the present invention may comprise one or more features of one or more of the other aspects of the present invention. 
         [0254]    According to a further aspect of the present invention, there is provided a vehicle comprising an internal combustion engine according to any of the previous aspects of the present invention. 
         [0255]    For the avoidance of doubt references herein to internal combustion engines are not to be considered as relating to petrol or diesel engines alone but should be considered to include internal combustion engines operating on other appropriate fuels, such as gas. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0256]    Specific embodiments of the present invention will now be described by way of example only and with reference to the following drawings, in which: 
           [0257]      FIG. 1  is a schematic view of an internal combustion engine in accordance with the present invention and during a suction stroke; 
           [0258]      FIG. 2  is a schematic view of the engine of  FIG. 1  during a compression stroke; 
           [0259]      FIG. 3  is a schematic view of the engine of  FIG. 1  during an expansion stroke; 
           [0260]      FIG. 4  is a schematic view of the engine of  FIG. 1  during an exhaust stroke; 
           [0261]      FIG. 5  is a detailed view of the crankcase of  FIG. 1  as the piston approaches the transition between a suction stroke and a compression stroke; 
           [0262]      FIG. 6  is a detailed view of the crankcase of  FIG. 1  as the piston approaches the transition between an expansion stroke and an exhaust stroke; and 
           [0263]      FIGS. 7   a  to  7   c  provide detailed views and illustrate the operation of the epicyclic gear means of  FIGS. 1 to 6 ; 
           [0264]      FIGS. 8   a  to  8   c  provide detailed views and illustrate the operation of an alternative embodiment to that of  FIGS. 1 to 7   c;    
           [0265]      FIGS. 9   a  to  9   c  provide further detailed views of the embodiment of  FIGS. 8   a  to  8   c;    
           [0266]      FIGS. 10   a  to  10   c  provide detailed views and illustrate the operation of a further alternative embodiment to those of  FIGS. 1 to 9   c;    
           [0267]      FIG. 11  illustrates a means of external independent control in the embodiment of  FIGS. 10   a  to  10   c;    
           [0268]      FIG. 12  is a schematic view of an internal combustion engine during a suction stroke and corresponding to that shown in  FIG. 1  but having an alternative embodiment of combustion ignition means; 
           [0269]      FIGS. 13   a  and  13   b  are transverse and axial schematic views of a further alternative embodiment; 
           [0270]      FIG. 14  depicts a path of the big end in the embodiment of  FIGS. 13   a ,  13   b ; and 
           [0271]      FIG. 15  is a graph illustrating thermodynamic principles of internal combustion engines and illustrating the additional useful work which the novel engines having an eccentric expansion stroke make available. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0272]    Referring now to the drawings,  FIG. 1  provides a schematic view of an internal combustion engine  10  in accordance with the present invention and during a suction stroke during a combustion cycle. The internal combustion engine comprises a crankshaft  12  rotatable about a crankshaft axis  14 . A connecting rod  16  engages towards a first end  18  with a throw  20  of the crankshaft  12  and couples towards a second end  22  to a piston  24 . The first end  18  of the connecting rod  16  engages with the throw  20  by epicyclic gear means  26 . 
         [0273]    The first end of the connecting rod  16  comprises a connecting rod gear  28  around which the epicyclic gear means  26  and hence the throw  20  of the crankshaft travels. The operation of the epicyclic gear means  26  is described in greater detail below with reference to  FIG. 7 . 
         [0274]    The internal combustion engine  10  of  FIG. 1  also comprises an exhaust gas aperture  30  provided in a cylinder  32  of the internal combustion engine. An exhaust gas port  34  is located towards the top of the cylinder. 
         [0275]    In addition, the internal combustion engine comprises a crankcase  36  (which constitutes an air-tight space defined by part of the internal combustion engine), within which the crankshaft  12  is situated. The piston  24  defines a first conduit  38  for release of compressed air from the crankcase  36  to the cylinder  32  and a second conduit  40  for admitting atmospheric air to the crankcase. An air intake conduit  42  provides for conveyance of compressed air from the first conduit  38  to the cylinder. A trap  44  is provided in the air intake conduit. 
         [0276]    The internal combustion engine  10  also comprises a unitary device  46  comprising an air intake valve  48  and an exhaust valve  50 . A leading p art  52  of the unitary device is shown in  FIG. 1  in the bore  54  of the cylinder  32 . The piston has a recess  56  in its leading face opposing the unitary device. A solenoid (not shown) is used to move the unitary device  46 . 
         [0277]    The internal combustion engine also comprises a combustion fuel injection pump  60  (which constitutes a fluid injection pump), which comprises a pump member  62  in a housing  64  of the pump, and which is defined within the body of the piston  24 . The pump member  62  creates a fluid tight seal with the housing  64  as it moves. The space defined by the housing  64  comprises a priming portion  66  and an injecting portion  68  (shown in  FIG. 4  only). The housing  64  defines a fluid inlet  70 , which registers at a point during the combustion cycle with a further fluid inlet  71  defined in the body of the internal combustion engine. In addition, a fuel metering means  72  is connected to the further fluid inlet  71 . A fluid conduit  74  connects the priming portion  66  and the injecting portion  68 . A plurality of fluid outlets  76  convey fuel from the injecting portion  68  to the bore  54  of the cylinder. 
         [0278]    Combustion ignition means  78  is provided in the unitary device  46 . The combustion ignition means  78  comprises a laser  80  (which constitutes an optical energy generator) connected to a fibre optic cable  82  (which constitutes an energy conductor) which in turn is connected to diffusion means  84 . 
         [0279]      FIG. 1  shows the internal combustion engine during a suction stroke of a four stroke combustion cycle. 
         [0280]    Turning now to  FIG. 2 , an internal combustion engine  10  is shown during a compression stroke of a four stroke combustion cycle. The internal combustion engine  10  of  FIG. 2  has the same components as  FIG. 1  and thus reference should be made to the description given with reference to  FIG. 1 . 
         [0281]    Turning now to  FIG. 3 , an internal combustion engine  10  is shown during an expansion stroke of a four stroke combustion cycle. The internal combustion engine  10  of  FIG. 3  has the same components as  FIG. 1  and thus reference should be made to the description given with reference to  FIG. 1 . 
         [0282]    Turning now to  FIG. 4 , an internal combustion engine  10  is shown during an exhaust stroke of a four stroke combustion cycle. The internal combustion engine  10  of  FIG. 4  has the same components as  FIG. 1  and thus reference should be made to the description given with reference to  FIG. 1 . 
         [0283]      FIGS. 1 to 4  will be referred below when the operation of the internal combustion engine is described. 
         [0284]      FIGS. 5 and 6  provide detailed schematic views of the internal combustion engine of  FIGS. 1 to 4  at particular stages during a combustion cycle. The internal combustion engine  10  of  FIGS. 5 and 6  have the same components as  FIG. 1  and thus reference should be made to the description given with reference to  FIG. 1 . More specifically,  FIG. 5  shows the piston  24  as it approaches the transition from the suction stroke to the compression stroke and  FIG. 6  shows the piston  24  as it approaches the transition from the expansion stroke to the exhaust stroke. 
         [0285]    The operation of the invention will now be described with reference to  FIGS. 1 to 6 . 
         [0286]    During a suction stroke, as shown in  FIG. 1 , the unitary device  46  is at a position in which the air intake valve  48  is open to admit air from the air intake conduit  42  to the cylinder bore  54 . As the piston drops in the cylinder, air within the crankcase is pressurised. Upon movement of the piston slightly further down in the cylinder beyond the position shown in  FIG. 1 , the first conduit  38  in the piston aligns with the air intake conduit  42  to allow compressed air to be released from the crankcase into the air intake conduit. As the piston drops in the cylinder the suction thereby created helps draw combustion air into the cylinder. At the end of the stroke, the arrested movement of the piston  24  throws the pump member  62  from the injecting portion  68  to the priming portion  66 , whereby fuel contained within the priming portion is pumped from the priming portion to the injecting portion by way of the fluid conduit  74 . 
         [0287]    At the bottom of the suction stroke the cooperative action of the crankshaft  12  and connecting rod  16  cause the piston to perform an upstroke, i.e. compression stroke. At the start of the compression stroke, the unitary device  46  rises in the cylinder to shut off the air intake and to seal the cylinder as shown in  FIG. 2 .  FIG. 2  shows the internal combustion engine  10  towards the end of the compression stroke, which as regards compression of the cylinder contents is similar to that of a conventional internal combustion engine. As the piston reaches the end of the compression stroke, the second conduit  40  in the piston aligns with an air intake  41  of the engine to admit air, e.g. atmospheric air, to the crankcase. In addition, the pump member  62  is thrown by the arrested movement of the piston  24  from the priming portion  66  to the injecting portion  68 , whereby fuel contained within the injecting portion is injected into the bore  54  cylinder by way of the plurality of fluid outlets  76 . Movement of the pump member  62  also draws a fresh charge of air into the priming portion  66  of the fuel injection pump. 
         [0288]    At the end of the compression stroke, the combustion ignition means  78  operates to ignite the air-fuel mixture contained in the bore  54  of the cylinder and the piston is thrown downwards on its expansion stroke.  FIG. 3  shows the piston  24  towards the end of the expansion stroke. As the piston  24  reaches the end of the stroke (i.e. a little further beyond the position shown in  FIG. 3 ) the exhaust gas aperture  30  opens to release combustion products from the cylinder. This relieves the pressure that has built up in the cylinder as a result of combustion. In addition, the pump member  62  is thrown by the arrested movement of the piston from the injecting portion  66  to the priming portion  68 . 
         [0289]    At the start of the exhaust stroke, the unitary device  46  drops into the cylinder to take up the position shown in  FIG. 4 , at which the exhaust valve  50  is opened.  FIG. 4  shows the internal combustion engine  10  towards the end of the exhaust cycle. As can be seen from  FIG. 4 , the unitary device is received within the recess  56  in the piston  24  to provide for more complete exhaust gas scavenging. As the piston  24  progresses beyond the position shown in  FIG. 4 , the second conduit  40  in the piston aligns with an air intake  41  of the engine to admit air, e.g. atmospheric air, to the crankcase. In addition, the fluid inlet  70  registers with the further fluid inlet  71  to admit a charge of fuel from the fuel metering means  72  to the priming portion  66  of the fuel injection pump  60 . This completes a combustion cycle in a four-stroke internal combustion engine. 
         [0290]    For each complete combustion cycle, the epicyclic gear means  26  and hence the throw  20  performs one complete progression around the connecting rod gear  28 . This means that at the transition between the suction and compression strokes, as shown in  FIG. 5 , the lower edge of the piston drops to the level indicated by the term ‘min’. In contrast, at the transition between the expansion and exhaust strokes, as shown in  FIG. 6 , the lower edge of the piston drops to the level indicated by the term ‘max’. Thus, the cylinder displacement is greater during the power producing second half of the combustion cycle than during the first half of the combustion cycle. 
         [0291]      FIGS. 7   a ,  7   b  and  7   c  provide detailed views and illustrate the operation of the epicyclic gear means of  FIGS. 1 to 6 . With the exception of the specific detail of the epicyclic gear means  26  and the connecting rod gear  28 , the parts of the apparatus shown in  FIGS. 7   a ,  7   b  and  7   c  are the same as is described above with reference to  FIGS. 1 to 6 . 
         [0292]    As can be seen from  FIGS. 7   a  to  7   c , the epicyclic gear means  26  is located on the throw of the crankshaft and comprises a fixed gear  92  fixedly mounted on the throw and three rotatable gears  94  spaced equally apart around the fixed gear. The fixed gear  92  and the rotatable gears  94  have toothed portions with the toothed portions of the fixed gear engaging with the toothed portions of the rotatable gears. The connecting rod gear  28  defines an aperture  96 , the geometric centre of which is offset from the centre of the first end of the connecting rod. It is this offset that provides for the eccentric behaviour of the coupling between the crankshaft and the connecting rod. The internal circumference of the aperture  96  is toothed, with the teeth of the rotatable gears  94  engaging with the teeth of the internal circumference. 
         [0293]    The first end of the connecting rod defines a connecting rod gear receiving aperture  98  in which the connecting rod gear  28  is rotatably located. 
         [0294]    The operation of the arrangement of  FIGS. 7   a  to  7   c  will now be described.  FIG. 7   a  shows the arrangement in much the same condition as shown in  FIG. 5 , i.e. when the piston  24  is at the transition from the suction stroke to the compression stroke at which the lower edge of the piston drops in the crankcase  36  to the minimum level. At this position, the connecting rod gear  28  is oriented in the connecting rod gear receiving aperture  98  such that the aperture  96  is towards the foot of the crankcase, thereby effectively shortening the connecting rod. 
         [0295]    As the combustion cycle progresses the arrangement passes through the condition shown in  FIG. 7   b , in which the connecting rod gear  28  has been rotated in the connecting rod gear receiving aperture  98  by the cooperative action of the fixed gear  92  and the rotatable gears  94 , and the cooperative action of the rotatable gears  94  and the toothed aperture  96  of the connecting rod gear  28 . 
         [0296]    At half a complete combustion cycle from the position shown in  FIG. 7   a  the arrangement is in the condition shown in  FIG. 7   c , which corresponds to the condition shown in  FIG. 6 . In this condition the piston  24  is at the transition from the expansion stroke to the exhaust stroke at which the lower edge of the piston drops in the crankcase  36  to the maximum level. At this position, the connecting rod gear  28  is oriented in the connecting rod gear receiving aperture  98  such that the aperture  96  is located towards the piston  24 , thereby effectively lengthening the connecting rod. 
         [0297]      FIGS. 8   a  to  8   c  provide detailed views and illustrate the operation of an alternative embodiment to the epicyclic gear means described above with reference to  FIGS. 1 to 7   c . With the exception of the specific detail of the coupling between the connecting rod and the crankshaft, the parts of the apparatus shown in  FIGS. 8   a  to  8   c  are the same as is described above with reference to  FIGS. 1 to 6 . 
         [0298]    As can be seen from  FIGS. 8   a  to  8   c , the first end of the connecting rod  16  comprises a connecting rod gear  102 . The connecting rod gear defines an aperture  106  having a toothed circumference and which is concentric with the first end of the connecting rod  16 . In addition, the connecting rod gear  102  is mounted so as to allow for its to and fro rotary movement in relation to the first end of the connecting rod. A toothed throw gear  104  is rotatably mounted on the throw  20 . The teeth of the throw gear  104  and of the aperture  106  cooperate mechanically. 
         [0299]    The operation of the arrangement of  FIGS. 8   a  to  8   c  will now be described. 
         [0300]      FIG. 8   a  shows the arrangement in much the same condition as shown in  FIG. 5 , i.e. when the piston  24  is at the transition from the suction stroke to the compression stroke at which the lower edge of the piston drops in the crankcase  36  to the minimum level. At this position, the throw gear  104  has traveled around the toothed aperture  106  such that the throw gear  104  is towards the foot of the crankcase, thereby effectively shortening the connecting rod. 
         [0301]    As the combustion cycle progresses the arrangement passes through the condition shown in  FIG. 8   b , at which the throw gear  104  has traveled some distance around the internal circumference of the toothed aperture  106 . 
         [0302]    At half a complete combustion cycle from the position shown in  FIG. 8   a  the arrangement is in the condition shown in  FIG. 8   c , which corresponds to the condition shown in  FIG. 6 . In this condition the piston  24  is at the transition from the expansion stroke to the exhaust stroke at which the lower edge of the piston drops in the crankcase  36  to the maximum level. At this position, the throw gear  104  has traveled around the internal circumference of the toothed aperture  106  such that the throw gear  104  is located towards the piston  24 , thereby effectively lengthening the connecting rod. 
         [0303]    The means by which the throw gear  104  maintains its position in relation to the connecting rod gear  102  during a combustion cycle will now be described with reference to  FIGS. 9   a  to  9   c . A crankshaft  110  is shown in  FIGS. 9   a  to  9   c , having a crankshaft  112  and a throw  114 . In between the arms of the throw is provided the crank pin  116 . The crank pin  116  is configured as shown in  FIG. 9   a  to provide two bearings  118 ,  120 . The first bearing  118  is concentric with the crank pin  116  and the second bearing  120  is eccentric to the crank pin  116 . The throw gear (not shown) is mounted on the first bearing  118  and the connecting rod gear (not shown) is mounted on the second bearing  120 .  FIGS. 9   b  and  9   c  show movement of the eccentric bearing  120  about the axis of the crank pin at two different crank positions during a combustion cycle. 
         [0304]      FIGS. 10   a  to  10   c  provide detailed views and illustrate the operation of a further alternative embodiment to the epicyclic gear means described above with reference to  FIGS. 1 to 7   c  and to the embodiment described above with reference to  FIGS. 8   a  to  9   c . With the exception of the specific detail of the coupling between the connecting rod and the crankshaft, the parts of the apparatus shown in  FIGS. 10   a  to  10   c  are the same as is described above with reference to  FIGS. 1 to 6 . 
         [0305]    As can be seen from  FIGS. 10   a  to  10   c , a toothed crankshaft gear  122  is mounted fixedly and concentrically with the crankshaft axis  14 . A toothed connecting rod gear  124 , which is of greater diameter than the crankshaft gear  122 , is mounted rotatably and eccentrically on the first end of the connecting rod  16 . The teeth of the crankshaft gear  122  and of the connecting rod gear  124  engage with each other. 
         [0306]    The operation of the arrangement of  FIGS. 10   a  to  10   c  will now be described.  FIG. 10   a  shows the arrangement in much the same condition as shown in  FIG. 5 , i.e. when the piston  24  is at the transition from the suction stroke to the compression stroke at which the lower edge of the piston drops in the crankcase  36  to the minimum level. At this position the connecting rod gear  124  has traveled around the crankshaft gear  122  such that the effective length of the connecting rod is at a minimum by virtue of the eccentric position of the connecting rod gear  124  on the connecting rod  16 . 
         [0307]    As the combustion cycle progresses the arrangement passes through the condition shown in  FIG. 10   b , at which the connecting rod gear  124  has traveled some distance around the external circumference of the crankshaft gear  122 . 
         [0308]    At half a complete combustion cycle from the position shown in  FIG. 10   a  the arrangement is in the condition shown in  FIG. 10   c , which corresponds to the condition shown in  FIG. 6 . In this condition the piston  24  is at the transition from the expansion stroke to the exhaust stroke at which the lower edge of the piston drops in the crankcase  36  to the maximum level. At this position, the connecting rod gear  124  has traveled around the external circumference of the crankshaft gear  122  to a position at which the effective length of the connecting rod is at a maximum by virtue of the eccentric position of the connecting rod gear  124  on the connecting rod  16 . 
         [0309]    The embodiment of  FIGS. 10   a  to  10   c  can be used alone or in conjunction with either of the first two embodiments. 
         [0310]      FIG. 11  is an illustration of a modification of the embodiment of  FIGS. 10   a  to  10   c .  FIG. 11  shows a piston  24 , which is connected to a connecting rod  16 , a crankshaft  12  rotatable around a crankshaft axis  14  and a crankshaft throw  20 .  FIG. 11  also shows the connecting rod gear  124  and the crankshaft gear  122  of  FIGS. 10   a  to  10   c . The crankshaft has a bore in which a control member  126  is rotatably located. The control member  126  is coupled to the crankshaft gear  122  at one end and is connected at its other end to a mechanical or electro-mechanical actuator (not shown). Operation of the actuator causes rotation of the control member  126 , which rotates the crankshaft gear  122 , which in turn rotates the connecting rod gear  124 . Thus, cooperative movement of the crankshaft gear  122  and the connecting rod gear  124  can be provided independently of movement provided by operation as described above with reference to  FIGS. 10   a  to  10   c.    
         [0311]    The control member  126  can be rotated in either direction thereby providing for an advance or a delay of the particular point during a combustion cycle at which the piston is at its minimum and/or maximum lowest location in the crankcase during a combustion cycle. 
         [0312]    To provide for transmission of an advance or a delay as described in the immediately preceding two paragraphs in an engine having more than one cylinder, a further pair of crankshaft and connecting rod gears  122 ,  124  (not shown) can be provided on the opposite side of the connecting rod and crankshaft section to the first pair shown in  FIG. 11 . Also, each further cylinder in the engine has the same arrangement of opposing pairs of crankshaft and connecting rod gears  122 ,  124 . Opposing connecting rod gears  122  of a cylinder are coupled to each other via the connecting rod and adjacent crankshaft gears  124  of neighbouring cylinders are coupled to each other to transmit the advance or the delay from one cylinder to the next. Adjacent crankshaft gears  124  of neighbouring cylinders are coupled to each other by a further control member (like control member  126  of  FIG. 11 ), which passes though a bore provided in the section of crankshaft between the neighbouring cylinders. 
         [0313]      FIG. 12  provides a schematic view of an internal combustion engine during a suction stroke.  FIG. 12  corresponds to  FIG. 1  with the exception of an alternative embodiment of combustion ignition means  150 . Accordingly reference should be made to the description given above with reference to  FIG. 1  for a description of the component parts and operation that the present embodiment has in common with the previous embodiment. 
         [0314]    In  FIG. 12  the combustion ignition means  150  is located in the wall of the cylinder and comprises a laser  152  (which constitutes an optical energy generator) connected to a fibre optic cable  154  (which constitutes an energy conductor) which in turn is connected to diffusion means  156 . Diffusion means  156  is of cylindrical form and extends around inside of the upper end of the cylinder. Such an arrangement of diffusion means can provide for an annular flame front that progresses towards the piston/cylinder centre. An advantage of locating the diffusion means  156  in the cylinder wall is that the diffusion means  156  can be swept and thus cleaned by the upper end of the piston during the course of a combustion cycle. In addition, the depth of the recess  56  provided in the leading face of the piston opposing the unitary device is reduced as shown in  FIG. 12 . During the exhaust stroke the piston moves to the very top of the cylinder. During the compression/ignition stroke the piston moves to within a predetermined distance to provide a workable compression space, thereby taking account of the reduction in the recess  56 . 
         [0315]      FIG. 13   a  shows in partial cross-section a further alternative arrangement for regulating the path of the big end of the connecting rod  16  so as to vary the displacement of the piston  24  in alternate revolutions of the crankshaft  14 . Crank arms  20  in this case are provided with a slot  130  which receives pin  132  (and incorporated bearings) attached to big end of the connecting rod  16 .  FIG. 13   b  is a view of the crank arm and pin in an axial direction. In this way, the big end is forced to rotate about the crank axis while being permitted to move radially relative to crankshaft  14 . Opposite ends of the pin  132  are constrained by fixed plates  134 , which surround the crankshaft  14  and have channels cut in them to define paths of the form shown schematically in  FIG. 14 . 
         [0316]    Referring to  FIG. 14 , the locus of the axis of pin  132  is shown on a graph, with the crankshaft axis at its origin. The different extents of the intake, compression, power and exhaust parts of the cycle can clearly be seen. Furthermore, it can be seen that the path in the power stroke is essentially a semi-circle, while the path in the other strokes is more elliptical. This channeled path embodiment accordingly allows a more complex curve to be followed by the big end than can be achieved by the simple gear arrangements described already. This facility allows piston acceleration and decelerations to be reduced. If advancing or retarding the relationship between the paths and the crankshaft (via mechanical or electro-mechanical means) is of interest, it can be envisaged that the plates  134  be mounted so as to be rotatable in advance or retard controlled by electronic means to achieve a variation or optimisation of the path and it&#39;s timing, resulting in optimised engine performance and reduced emissions. 
       Modifications and Variations 
       [0317]    The examples described above are illustrative only and many variations are possible within the spirit and scope of the invention as defined by the appended claims, and each aspect of the invention can be adopted alone or in combination with the others. For example: ignition by laser can be replaced by more conventional spark or compression ignition arrangements; fuel injection by piston action can be replaced by more conventional aspiration or injection arrangements and the unitary valve device can be replaced by more conventional valves. Several aspects of the invention are not limited in application to four-stroke engines, but can be applied for example in two-stroke engines, where a complete combustion cycle occurs in a single revolution of the crankshaft, as well as in pumps, compressors, hydraulic motors and other reciprocating machines. 
       Overview of Features and Benefits 
       [0318]    In answer to the elements of an ‘ideal’ reciprocating internal combustion engine mentioned in the introduction, the novel engines provide several new features and benefits of a subsidiary nature. The skilled person can select which of these features and benefits are important in a given application engine or machine, and they are presented above in combination for illustrative purposes only. 
         [0000]    a) Thermodynamics: 
         [0319]    More heat energy can be extracted as useable work by allowing the engine to vary its capacity cyclically between induction and expansion strokes. Consider the idealised situation whereby an engine induces 100 units of fuel/air mixture—but expands the combustion products through for example 130 units (a bit like the compound steam engine which extracts heat energy via an HP/IP/LP chain of expansions). With reference to  FIG. 15  and the resulting extension of the power or expansion curve to include the shaded area, we have seen that a significant increase in power would result from each marginal increase in piston movement. 
         [0320]    The novel engines described above achieve this varying capacity automatically and cyclically by adjusting the ‘throw’ of the crankshaft via an eccentrically pivoted big end bearing and driving arrangement introduced between the crank pin and the connecting rod big end bearing. 
         [0321]    It should be noticed that a further benefit is derived from the increased moment arm of the crank during this eccentric motion—which results in a useful increase in engine torque during the power stroke. 
         [0000]    b) Exhaust: 
         [0322]    Since the piston extends to a lower bottom dead centre (BDC) at completion of the expansion stroke it is possible to incorporate a simple cylinder wall exhaust port (similar to that found on a two-stroke engine). Due to the eccentric feature, this port is only uncovered once during the four-stroke cycle. The bulk of exhaust gases can therefore be discharged through this porting arrangement. The traditional cylinder head mounted exhaust valve and port are subjected to considerably lower mass flows of hot exhaust gases—and a more thermally balanced engine block and exhaust valve environment results. 
         [0000]    c) Purging and Valving: 
         [0323]    As noted above, since the mass of exhaust gases left in the cylinder after BDC is significantly reduced by the action of the exhaust port arrangement, the function of the upper exhaust valve becomes one of purging only the remainder of these gases during the exhaust stroke. This reduction in thermal loading on the exhaust valve and its immediate downstream environment improves the conditions under which a combined inlet and exhaust valve becomes more feasible. By incorporating these functions into a single, optimally positioned and liberally sized poppet valve—with appropriate inlet and exhaust porting indexed to variable valve opening positions—the use of alternative valve materials such as ceramics, and more highly variable and energy efficient operating mechanisms such as magnetic induction—become more feasible. 
         [0324]    To ensure complete purging of the exhaust gases, it is further arranged that the piston moves almost completely to cylinder head at top dead centre (TDC) with each stroke. The combustion chamber is located within the piston bowl—which in turn allows the combined inlet/exhaust valve to displace fully into this chamber at completion of the exhaust stroke to achieve a high gas discharge coefficient and fully purging the engine before a fresh intake of air passes through and cools the combined valve. These parts are shown with a rectangular cross-section for convenience only and can be shaped differently to improve mixing and combustion in practice. 
         [0325]    It should be noted that by achieving a very high level of exhaust gas purging the secondary burning of previously combusted exhaust gases is largely avoided and the associate creation of undesirable oxides of nitrogen is greatly reduced. This also has benefits in the fact that the induced fresh charge has a high purity. 
         [0000]    d) Supercharging: 
         [0326]    The induction process was examined, and it was concluded that the displacement of the piston into a sealed crankcase provides a readily available method of positive displacement supercharging. The induction gases are forced into a crankcase port by atmospheric pressure during each upward displacement of the piston, and compressed by each downward movement. It is intended that a lower piston ring arrangement is provided to ensure gas tight sealing. Since this event happens twice during the four-stroke cycle (and in fact this displacement is even greater in the novel engine during the power/exhaust stroke sequence due to the eccentric effect described above), a viable source of effective supercharging can be exploited with a minimum of additional moving parts. The piston skirt area is arranged to provide both a passage for the inducted air into the crankcase and of the supercharged air into an intermediate chamber. Each of these functions is once again operated by the interaction of the piston and static ports in the cylinder wall—prior to the inlet valve opening to transfer this pressurised store of air into the engine.