GB1559995A - Low emission compound combustion engine - Google Patents

Description

(54) LOW EMISSION COMPOUND COhlBUSTION ENGINE (71) I, FRASER ATKINSON HURD, a citizen of the United States of America, of 103 Fifth Street, Liverpool, New York 13088, United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be part:cularly described in and by the following statement: The present invention relates to an internal combustion engine which produces low emission of harmful exhaust gases and converts to useful work a great portion of the energy of combustion.

A great deal of research effort and money has been directed toward a suitable power system for automotive and other types of vehicles wherein the by-products of the energy source are ecologically acceptable.

Automotive vehicles comprise a large share of the atmospheric pollution sources due to the level of nitrous oxides, carbon monoxide and unburned hydrocarbons contained in the exhaust gases of the engines used in the enormous number of such vehicles. Virtually all automotive engines in current use are of the internal combustion type and burn a fuel mixture of air and gasoline, or other petroleum type fuel. It is generally regarded as economically unfeasible to change in a short time from conventional mechanical engine designs to radically different types of power plants. Accordingly, those efforts which have received the greatest attention from a commercial standpoint are those which involve modification of existing equipment by adding fillers, reactors, etc., to reduce harmful emissions.

Unfortunately, the devices which have thus far been put into commcrcial use, and others which appear effective to produce acceptable emmission levels from more or less standard engines tend to decrease substantially the efficiency in terms of power output per unit of fuel consumed. There is, therefore, a conflict between the use of presently acceptable anti-pollution devices and conservation of basic energy sources.

In accordance with the invention an eight -event, compound cycled internal combustion engine comprises first and second enclosed power chambers each having therein a movable element to create an alternately increas in and decreasing enclosed volume; inlet meons associated with each of the chambers; exhaust means to the atmosphere only through the second chamber; retractable wall means between the first and second chambers movable between retracted and closed positions and through which the enclosed volumes of the first and second power chambers directly communicate when the wall means is in the retracted position, thereby forming a common chamber; means for introducing a fuel-rich, oxygen-lean first charge through the inlet means to the first power chamber; means for igniting the first charge to provide a power impulse to the movable element within the first chamber; means for introducing a fuel-lean, oxygenrich second chamber through the inlet means to the second power chamber; and means for opening the retractable wall means subsequent to the power impulse within tlie first chamber and introducing the second charge, thereby creating a combustible mixture within the common chamber of the second charge with the by-products of the first charge's partial combustion.

The invention also includes an eight-event method of operating a series compound internal combustion engine having a pair of adjacent enclosed chambers of differential volume, each having a movable element to create therein alternately increasing and decreasing differential enclosed volumes, the method comprising introducing a fuel-rich, oxygen-lean first stage charge into the first stage chamber, by increasing volume thereof; exhausting gases of a prior cycle from the second stage chamber, by decreasing the volume thereof to the atmosphere concurrently with introducing the first stage charge; compressing the first stage charge by decreasing the volume within the first stage chamber; introducing a fuel-lean, oxygen-rich second stage charge into the second stage by increasing the volume thereof concurrently with compressing the first stage charge; igniting and partially burning the first stage charge for power expansion within the first stage chamber; compressing the second stage charge by decreasing the volume within the second stage chamber concurrently with power expansion within the first stage chamber: causing the first and second stage chambers to directly communicate and form a common enclosed volume, thereby allowing the second stage charge to mix with the byproducts of partially burning the first stage charge, and causing the resulting mixture to extend and sustain continuity of combustion substantially uninterrupted to complete the burning of combustible elements thereof, for second stage power expansion by differential displacement within the chamber; and transferring gases from the first stage, by decreasing the volume thereof, to the second stage chamber concurrently with power expansion by differential displacement within the chambers to provide power impulse to the movable element within the second stage chamber.

The new engine thus includes means defining at least one pair of undulating (constantly either increasing or decreasing) volumes, which, in the most familiar form, may be pistons reciprocating within cylinders. The cylinders of each pair are usually arranged side-by-side, with first and second stage in juxtaposition for differentially compound expansion, with axes parallel and in close proximity. An inlet valve may be arranged in or near the top of each paired cylinder, and suitable atomizing means for preparing externally of the combustion chamber a charge of proper fuel-air ratio are associated with the inlet valve specifically of the first stage and optionally of the second stage, depending on the type of service.A valve is provided to allow direct communication between the paired differential displacement chambers at selected times in the operational cycle, and a valve for exhaust to the atmosphere is provided in only the second stage cylinder, thereby allowing extended expansion of the second stage and scavenging of the first stage therethrough.

A total of eight indentifiable events are associated with one complete operational cycle of the cylinders paired for compound differential displacement. These events occur in four essentially concurrent pairs, as follows: first stage cylinder intake, or reception of a fuel-rich, oxygen-lean charge simultaneously with its second stage mated cylinder exhausting to atmosphere; first stage compression and second stage intake of a fuellean, oxygen-rich charge which charge could contain zero fuel; first stage combustion and power stroke concurrently with second stage compression; and, upon the timed opening of the valve so that the two chambers communicate to form a common combustion volume with the first and second stage pistons near the bottom and top of their respective strokes, second stage combustion and differential power stroke, with the smaller first stage discharging and scavenging itself into the substantially larger second stage. The second stage displacement is preferably significantly larger than the first to effectively extract additional work from the greatly extended expansion with final exhaust pressure so close to atmospheric as to allow replacement of the power robbing muffler with a non-restricting resonator.

An example of an engine constructed in accordance with the invention is illustrated in the accompanying drawings, in which: Figures 1 to 4 are fragmentary, partly diagrammatic, elevational views in vertical section, illustrating in extremely simplified form the functional sequence of engine operation; and, Figure 5 is a somewhat more detailed elevational view, in half-section, of the engine.

The illustrated engine is disclosed in somewhat diagrammatic form, the elemental parts selected for ease of disclosure being of a general type which has undergone nearly a century of refinement and experience in the context of automotive power plants.

Therefore, these elements and the many alternative embodiments thereof are familiar to those skilled in the art and are not described in detail herein. The illustrated mechanical elements are more indicative of function than appearance, and the scope of the invention is not intended to be limited to the particular form chosen for discussion.

The simplified form of engine shown in Figures 1--4 includes the usual frame or block 10 wherein the cylinders are formed.

Pistons 12 and 14, having rods 16 and 18, respectively, associated therewith in the usual manner, are arranged to reciprocate within the two illustrated cylinders. Both rods are connected to crankshaft 20, which would actually extend transversely of the two cylinders, but is shown rotated 90" and separately for each cylinder in order to indicate in each view the position and direction of movement of the respective rod ends 22 and 24 which are linked to crankshaft 20.

Henceforth, the cylinder including piston 12, and parts and events associated therewith, will be termed "first stage", and those associated with the cylinder including piston 14 will be termed, "second stage". First state fuel mixing means 26, having the usual valves, ports, etc., including throttle valve 28, is arranged to provide an atomized combustible charge through inlet valve 30 to the first stage cylinder. The charge comprises a mixture in predetermined ratio of liquid fuel and air, such ratio appropriately being relatively rich in fuel and lean oxygen in order to achieve the desired result, as described more fully hereinafter.

The second stage may be provided with similar fuel mixing means 32, having throttle valve 34, inlet valve 36 and exhaust valve 38. It will be noted that the wall separating the first and second stage cylinders, denoted by reference numeral 40, terminates short of the upper cylinder head, providing a space for direct communication between the two cylinders. In one or the other of the paired cylinders, optionally in the second stage cy'inder, as shown, a vertically slideable sleeve valve 42 is provided. The valve may, of course, take other forms such cs a sliding plate valve with its own type of movement, and is opened at selected times in the operating cycle to provide communication between the first and second stage displacement chambers, thereby forming a common combustion chamber at such times.

As pictured in the sequence of pictorial diagrams 1 to 4, the first events to occur are intake or ingestion of the fuel charge into the first stage concurrently with exhaust from the second stage. As shown, first stage inlet valve 30 is open, piston 22 is moving downward, second stage inlet 36 is closed, exhaust 38 is open, piston 13 is moving upward, and valve 42 is closed. Final exhaust from the second stage to the atmosphere takes place through manifold 44.

Since Figures 2 to 4, are merely illustrative of additional functions, only those portions operationally associated with such functions are shown. In Figure 2, first stage compression occurs as piston 12 moves upwardly with inlet valve 30 and valve 42 closed. At the same time, second stage piston 14 moves downwardly to draw in a fresh air charge, which may or may not include an atomized fuel, or catalyst through inlet valve 36, exhaust valve 38 now being closed. For reasons which will presently be apparent, the quantity of oxygen in the lean charge ingested by the second stage during any one cycle is appropriately equal to or in excess of that required for complete combustion of both the by-products from the first stage together with any fuel which may have been ingested by the second stage.That is, the second stane charge is oxygen-rich, fuel-lean and may, in fact. include no fuel at all depending on conditions associated with the first stage burn, and the power demand at that time. At any rate, second stage fuel mixture and throttling, or other intake control, are preferably automated to the throttled variability of the first stage. and for engines proposed to be operated continuously at a fixed speed and load, throttle valve 34, or its equivalent, may be omitted, with preference given to a fixed type orifice of appropriate proportions.

The elements are pictured in Figure 3 just after combustion of the first stage charge by igniter 46. The heat energy generated by the combustion, resulting in rapid pressure increase of the gas within the first stage cylinder, provides power to move piston 12 downwardly and turn crankshaft 20. At the same time, piston 14 is moving upwardly within the second stage cylinder with valves 36, 38 and 42 closed, thereby compressing the charge in the second stage cylinder.

It is anticipated that many variations and refinements such as combustion chamber contouring, timing, valving, porting, and tun- ing of the engine will be possible. It is assumed for purposes of the present discussion, however, that since in the preferred arrangement, volumetric displacement of the second stage cylinder is substantially greater than that of the first stage to effect final power expansion most efficiently by differential displacement, that likewise the theoretical compression ratio of second stage be greater than first stage to permit a relationship of volume to area within the first stage most favourable for minimal heat loss to the cooling medium without jeopardizing total overall expansion efficiency, and that for normal operation the sleeve valve 42 separating the stages begins to open at some point in advance of pistons 12 and 14 reaching their bottom and top dead centres, respectively, viz: at a point between the positions of the elements shown in Figures 3 and 4. It is deemed desirable to have the ascending pressure of the second stage on compression at about the same level as that of the descending, end pressure of the first stage while still on power, when valve 42 begins to open in order to avoid erosion of the valve seal by wire drawing.Also, it is a preferred feature that not only the displacement ratio be substantially greater but likewise the concomitant rate of compression of second stage exceed that of first stage so that the second stage's compression pressure peaks at a faster rate than the first stage's rate of pressure depletion, this makes the second stage dominant, and the first stage submissive, in that the pressure within the second stage while each is approaching their respective dead centres, be somewhat, although not excessively, in excess of that within the first stage to the degree that there is an initial "backwash" of an oxygen rich charge from second stage into first stage to mix with the hot byproduct gases thereof to initiate second stage combustion as an afterburn with its flame front properly in advance of second stage power expansion whereby to effect complete stoichiometric and final combustion early in the second stage stroke for maximum power impulse from the expanding gases. This advanced "backwashing" makes for more thorough mixing of the first and second stage gases while sharing the same combustion space, and provides for valve 42 an initial bathing of the sealing surfaces by the fresh air charge from the second stage as the valve first cracks open, rather than being immediately subjected to the severe heat, velocity and eroding turbulence of gases transposed from the first stage.

The second combustion is an afterburn and is final, taking place internally for additional work expansion and not externally as with retrofit devices, and is appropriately timed preferably just prior to the instant pistons 12 and 14 reach their bottom and top dead centres, respectively. This second combustion preferably occurs spontaneously from the copulative "backwash" mixing of the hot byproduct gases, not fully expanded and still under pressure, of first stage wiili that of second stage's oxygen rich charge which by compression is at some lesser temperature but similar pressure. Except for warmup or special conditions any further aid of igniter 46, or its equivalent such as a supplementary glow plug, hot bulb, etc., for second stage burn is not deemed necessary.Opening of valve 42, normally initiates second stage combustion as a spontaneous afterburn and with the second stage's higher displacement and compression ratio causing pressure in the second stage cylinder to peak rapidly and reach a pressure complementing that for the first stage, before their respective dead centres, as just described, allows ample time for improved advance mixing of the fresh, oxygen rich charge from the second stage cylinder with the by-product of incomplete first stage combustion.The common combustion chamber shared by the first and second stage cylinders at the time of initiating the second burn, receives a second charge which this time is intentionally rich in oxygen, a condition most compatible with power efficiency and a clean exhaust; oxygen is intentionally in short supply during the high temperature first burn to minimize NOX and is ample at the lower temperature second burn to eliminate HC and CO.

The elements are pictured in Figure 4 just after the second stage burn, after pistons 12 and 14 have begun upward and downward movement, respectively. This is the power stroke of piston 14, imparting mechanical energy to crankshaft 20, through differential displacement of the second over the first stage as piston 12 moves upward to evacuate the gases from the first into the second stage cylinder through open valve 42.

The operational cycle is then complete and begins again as the elements return to the position of Figure 1.

In Figure 5 is shown a four cylinder, opposed piston, pancake-type engine. This design may be exnanded to eiht, or more cylinders with fully opposed, V-type and other cylinder configurations which are also practical, but with lower performance potential than the fully opposed configuration.

The numeral 48 denotes a first crankcase sealed volume defined by the walls of the crankcase and first stage cylinders 50, and the opposing sides of first stage pistons 52.

Tne same reference numerals are used to cic.:ote iaLentical portions of each of the two opposed first stages, as well as to identical elements of the opposed second stages. First stage pistons 52 are connected to crankshaft 54 by suitable bearings on the ends of connecting rods 56. Conventional bearings 57 and seals 59 are also provided where the shaft extends through the crankcase inner and outer walls.

Second stage pistons 58 reciprocate within cylinders 60 toward and away from one another to alternately compress and expand second crankcase volume 62. As pistons 58 diverge to expand volume 62, an air charge is drawn through inlet means 64, having any Venturi restrictions and the like which may be found desirable, and including main throttle valve 66 which primarily controls engine output. Flapper valve 68, or equivalent, is opened as the air charge is drawn into volume 62 and closed as pistons 58 converge to decrease the volume of this space, thereby compressing the air charge.

It is to be noted that second stage pistons 58 function, on the crankcase side, as first stage pre-compression pistons. If desired a supply of lubricating oil may be provided through opening 69 to form a lubricating mist in the air entering the crankcase. Con ventional lubricating systems may, of course, be provided in the usual manner.

The initially compressed air passes through opening 70 in the wall separating crankcase volumes a8 and 62, this opening also being provided with a flapper-type check valve 72, or equivalent. Converging movement of pistons 52 produces further compression of the air charge within volume 48, and movement thereof through openings 74 having flapper valves 76, or equivalent, into inlet manifolds 78. As the compressed air charge moves through manifolds 78 a fuel charge is metered through openings 79 for mixing in proper proportion with the air. The fuel-air mixture, which at this point is fuel-rich, oxygen-lean is introduced for charging first stage cylinders 50 through inlet valves 80.

Continued operation of each paired set of first and second stage cylinders within each bank of cylinders from this point is essentially identical to that described in con nectio'i with Figures 1 > . After first stage reception of the combustible charge through inlet valves 80, the valves close and pistons 52 diverge to compreqq the charge for the final time within cylinders 50, two stages of crankcase pre-compression having already been accomplished. Igniters 82 then produce combustion within cylinders 50. It should be understood at this point that as pistons 52 move toward one another, one cylinder is on the intake cycle of event as the other is on its power stroke.Likewise, as pistons 52 move apart, one is compressing the fuelair mixture prior to ignition while the other is discharging the gases from the first stage to the second stage cylinders.

As explained in connection with Figures 1--4, the fuel charge provided to the first stage cylinders is of a mixture ratio, appropriately fuel-rich, oxygen-lean, whereby the temperature and pressure of combustion are compatible with producing low amounts of oxides of nitrogen. Besides control by mixture ratio, peak temperature is controlled by the isothermal pre-compression and the evaporative cooling effect to the fuel-rich charge. After first stage combustion provides the power stroke of the first stage pistons, the second stage burn occurs, with sleeve valves 84 of second stage -cylinders 60 open to provide a common, or communicating combustion chamber between the paired first and second stage cylinders.At this time inlet and exhaust valves 86 and 88 respectively, of the second stage cylinders are closed, and the power stroke of pistons 58 moves them to the position shown. As pistons 52 move to the top of their respective cylinders with sleeve valves 84 open and all other valves closed, during the second stage power stroke, gases from the first stage cylinders are transferred to the second. Exhaust valves 88 then open and the next diverging stroke of pistons 58 expels the gases to the atmosphere.

Second stage inlet valves 86 then open, exhaust and sleeve valves 88 and 84, res- pectively, closing, and a fresh air charge Is ingested into the second stage cylinders.

This charge may or- may not have atomized fuel included therein, depending on the composition of the gases after first stage combustion, and the type of engine application.

That is, with the fuel rich mixture indicated, first stage combustion will leave unburned hydrocarbons and carbon monoxide which may be combustible in the second stage burn without mixing additional fuel therewith. Metering valve 87 in the intake line to the second stage, may be provided if required and suitably automated to throttle valve 66 to attain optimum engine performance. At any rate, the conditions of the second stage burn will be such as to reduce to an acceptably low level the HC and CO without producing additional NO, in objectional quantities.

As previously mentioned in connection with the first stage cylinders, although the cycle of events has been described as it occurs through the engine, it is again pointed out that opposed cylinders of the same stage are not undergoing the same event at the same time. As pistons 58 move toward one another, to the position shown in Figure 5, one is on its power stroke as gases from the first stage are discharged into the second, while the other is on its intake stroke, receiving a fresh charge through intake valve 86.

As shown in Figure 5, second stage piston 58 on the left has just completed its power stroke with inlet valve 86 closed. Exhaust valve 88 has just opened to atmosphere.

Complete release of pressure from first stage cylinders 50 may take place by opening exhaust valve 88 while valve 84 is still open, as shown in Figure 5, or, as an optional refinement, valve 84 may close substantially s:multaneously with exhaust valve 88 opening, since it has been noted that a residue of the combustion products carried over into the subsequent cycle has been beneficial for further minimizing NOx. At the same time, the second stage piston on the right has just completed the intake of fresh air charge (with or without additional fuel or catalyst) through open valve 86, exhaust valve 88 and valve 84 being in the closed positions.

Although the foregoing description has concentrated principally upon the function and operation of the eight-event engine, multiple structural embodiments based on these operating principles will be apparent to those skilled in the art. In fact, one of the major advantages of the invention is the wide range of design options and continued refinements in the area of piston engines which are made possible within the framework of an engine having low emission, high performance and high efficiency potential.

WHAT I CLAIM IS:- 1. An eight-event, compound cycled internal combustion engine comprising first and second enclosed power chambers each hav int therein a movable element to create an alternately increasing and decreasing enclosed volume; inlet means associated with each of the chambers; exhaust means to the atmosphere only through the second chamber; retractable wall means between the first and second chambers movable between - re- tracted and closed positions and through which the enclosed volumes of the first and second power chambers directly communicate when the wall means is in the retracted position, thereby forming a common chamber; means for introducing a fuel-rich, oxygen-lean first charge through the inlet means to the first power chamber; means for igniting the first charge to provide a power impulse to the movable element within the first chamber; means for introducing a fuel-lean, oxygen-rich second charge through the inlet means to the second power

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (20)

**WARNING** start of CLMS field may overlap end of DESC **. been accomplished. Igniters 82 then produce combustion within cylinders 50. It should be understood at this point that as pistons 52 move toward one another, one cylinder is on the intake cycle of event as the other is on its power stroke. Likewise, as pistons 52 move apart, one is compressing the fuelair mixture prior to ignition while the other is discharging the gases from the first stage to the second stage cylinders. As explained in connection with Figures 1--4, the fuel charge provided to the first stage cylinders is of a mixture ratio, appropriately fuel-rich, oxygen-lean, whereby the temperature and pressure of combustion are compatible with producing low amounts of oxides of nitrogen. Besides control by mixture ratio, peak temperature is controlled by the isothermal pre-compression and the evaporative cooling effect to the fuel-rich charge. After first stage combustion provides the power stroke of the first stage pistons, the second stage burn occurs, with sleeve valves 84 of second stage -cylinders 60 open to provide a common, or communicating combustion chamber between the paired first and second stage cylinders.At this time inlet and exhaust valves 86 and 88 respectively, of the second stage cylinders are closed, and the power stroke of pistons 58 moves them to the position shown. As pistons 52 move to the top of their respective cylinders with sleeve valves 84 open and all other valves closed, during the second stage power stroke, gases from the first stage cylinders are transferred to the second. Exhaust valves 88 then open and the next diverging stroke of pistons 58 expels the gases to the atmosphere. Second stage inlet valves 86 then open, exhaust and sleeve valves 88 and 84, res- pectively, closing, and a fresh air charge Is ingested into the second stage cylinders. This charge may or- may not have atomized fuel included therein, depending on the composition of the gases after first stage combustion, and the type of engine application. That is, with the fuel rich mixture indicated, first stage combustion will leave unburned hydrocarbons and carbon monoxide which may be combustible in the second stage burn without mixing additional fuel therewith. Metering valve 87 in the intake line to the second stage, may be provided if required and suitably automated to throttle valve 66 to attain optimum engine performance. At any rate, the conditions of the second stage burn will be such as to reduce to an acceptably low level the HC and CO without producing additional NO, in objectional quantities. As previously mentioned in connection with the first stage cylinders, although the cycle of events has been described as it occurs through the engine, it is again pointed out that opposed cylinders of the same stage are not undergoing the same event at the same time. As pistons 58 move toward one another, to the position shown in Figure 5, one is on its power stroke as gases from the first stage are discharged into the second, while the other is on its intake stroke, receiving a fresh charge through intake valve 86. As shown in Figure 5, second stage piston 58 on the left has just completed its power stroke with inlet valve 86 closed. Exhaust valve 88 has just opened to atmosphere. Complete release of pressure from first stage cylinders 50 may take place by opening exhaust valve 88 while valve 84 is still open, as shown in Figure 5, or, as an optional refinement, valve 84 may close substantially s:multaneously with exhaust valve 88 opening, since it has been noted that a residue of the combustion products carried over into the subsequent cycle has been beneficial for further minimizing NOx. At the same time, the second stage piston on the right has just completed the intake of fresh air charge (with or without additional fuel or catalyst) through open valve 86, exhaust valve 88 and valve 84 being in the closed positions. Although the foregoing description has concentrated principally upon the function and operation of the eight-event engine, multiple structural embodiments based on these operating principles will be apparent to those skilled in the art. In fact, one of the major advantages of the invention is the wide range of design options and continued refinements in the area of piston engines which are made possible within the framework of an engine having low emission, high performance and high efficiency potential. WHAT I CLAIM IS:-

1. An eight-event, compound cycled internal combustion engine comprising first and second enclosed power chambers each hav int therein a movable element to create an alternately increasing and decreasing enclosed volume; inlet means associated with each of the chambers; exhaust means to the atmosphere only through the second chamber; retractable wall means between the first and second chambers movable between - re- tracted and closed positions and through which the enclosed volumes of the first and second power chambers directly communicate when the wall means is in the retracted position, thereby forming a common chamber; means for introducing a fuel-rich, oxygen-lean first charge through the inlet means to the first power chamber; means for igniting the first charge to provide a power impulse to the movable element within the first chamber; means for introducing a fuel-lean, oxygen-rich second charge through the inlet means to the second power

chamber; and means for opening the retractable wall means subsequent to the power impulse within the first chamber and introducing the second charge, thereby creating a combustible mixture within the common chamber of the second charge with the byproducts of the first charge's partial combustion.

2. An engine according to claim 1, wherein the volume of displacement of the movable element within the second power chamber is significantly greater than the volume of displacement of the movable element within the first power chamber.

3. An engine according to claim 1 or claim 2, wherein the movable elements are pistons, and the first and second power chambers are portions of cylinders on the inlet sides of the pistons.

4. An engine according to claim 3, wherein the cylinders are arranged side-byside, in close proximity, with parallel axes.

5. An engine according to claim 4, wherein the retractable wall means is arranged in a wall separating the cylinders at their inlet ends.

6. An engine according to claim 3, further including third and fourth cylinders, of which the fourth cylinder has a maximum volume significantly greater than the third cylinder, and a common crankshaft to which all four of the cylinders are connected.

7. An engine according to claim 6, further including a crankcase wherein the crankshaft is at least partially enclosed, the crankcase having one enclosed volume variable by reciprocating movement of the first and third pistons, and another enclosed volume variable by reciprocating movement of the second and fourth pistons, air inlet means into the other volume for compression within the crankcase, and means for introducing the air compressed within the crankcase through the inlet means to the first and third power cylinders.

8. An engine according to claim 7, further including fuel inlet means for mixing a fuel charge with the compressed air between the crankcase and the first and third power cylinders.

9. An engine according to claim 1, substantially as described with reference to the accompanying drawings.

10. An eight-event method of operating a series compound internal combustion engine having a pair of adiacent enclosed chambers of differential volume, each having a movable element to create therein alternately increasing and decreasing differential enclosed volumes, the method comprising introducing a fuel-rich, oxygen-lean first stage charge into the first stage chamber, by increasing volume thereof; exhausting gases of a prior cycle from the second stage chamber, by decreasing the volume thereof to the atmosphere concurrently with introducing the first stage charge; compressing the first stage charge by decreasing the volume within the first stage chamber; introducing a fuel-lean, oxygen-rich second stage charge into the second stage by increasing the volume thereof concurrently with compressing the first stage charge; igniting and partially burning the first stage charge for power expansion within the first stage chamber; compressing the second stage charge by decreasing the volume within the second stage chamber concurrently with power expansion within the first stage chamber; causing the first and second stage chambers to directly communicate and form a common enclosed volume, thereby allowing the second stage charge to mix with the by-products of partially burning the first stage charge, and causing the resulting mixture to extend and sustain continuity of combustion substantially uninterrupted to complete the burning of combustible elements thereof, for second stage power expansion by differential displacement within the chambers; and transferring gases from the first stage by decreasing the volume thereof, to the second stage chamber concurrently with power expansion by differential displacement within the chambers to provide power impulse to the movable element within the second stage chamber.

11. A method according to claim 10, wherein the pressure created by decreasing the volume within the second stage chamber is made to increase by compression to approximate that within the first stage chamber at the time the chambers are caused to directly communicate.

12. A method according to claim 10 or claim 11, wherein the second stage charge is at least partially transferred to the first stage chamber upon causing of the first and second stage chambers to directly communicate.

13. A method according to any one of claims 10 to 12, wherein the composition of the first stage charge, and the temperature and pressure resulting from ignition of the first stage charge are such as to minimize forming of oxides of nitrogen as a product of partially burning the first charge.

14. A method according to any one of claims 10 to 13, wherein the composition of the mixture and the temperature and pressure at which the mixture is burned are such as to maximize oxidation of carbon monoxide and unburned hydrocarbons resulting from the partial burning of the first stage charge

15. A method according to any one of claims 10 to 14, wherein the composition of the by-products of partially burning the first stage charge and that of the second stage charge, and the temperature and pres sure of the by-products and the second stage charge at the time the first and second stage chambers are caused to directly communicate are such that combustion is sustained spontaneously.

16. A method according to any one of claims 10 to 15, and including the further step of pre-compressing the first stage charge, prior to introducing the latter into the first stage power chamber.

17. A method according to any one of claims 10 to 16, wherein the second stage charge consists essentially entirely of air, with no fuel added thereto.

18. A method according to any one of claims 10 to 16, wherein the second charge includes air with a fuel mixed therein.

19. A method according to any one of claims 10 to 18, wherein the second stage charge includes a catalyst.

20. A method according to claim 10, substantially as described with reference to the accompanying drawings.