FIELD OF THE INVENTION
This invention relates to combustion engines and, more particularly, to engines having positive displacement means for compression and expansion of the working charge, combined with dual combustion phases, including initial combustion at constant volume, followed by final combustion at constant pressure.
SUMMARY OF THE INVENTION
The present invention provides an improvement in combustion engines which combines the constant volume burning of the Otto cycle with the constant pressure burning of the Brayton cycle to yield a dual combustion cycle engine utilizing positive displacement means for compression and expansion of the working charge. The invention takes advantage of the improved combustion control and emission characteristics possible in a fixed volume constant pressure burner while retaining in part the advantage of the higher efficiency of constant volume combustion for heating and compressing the charge.
Numerous variations of engine physical arrangements, components and cycle variations are possible within the scope of the overall fuel combustion concept. However, a preferred embodiment involves the use of interconnected piston-cylinder arrangements for positive displacement, compression and expansion of the working charge. Additional satellite expansion cylinders may be utilized to partially expand a charge following constant volume combustion, after which constant pressure combustion and final expansion occur. Alternatively, the satellite cylinders may be deleted and the engine arranged for a lower initial compression ratio with constant volume combustion in the compression and combustion cylinders, being directly followed by constant pressure combustion in the fixed volume combustion chamber.
These and other features and advantages of the invention will be more clearly understood from the following description of certain preferred embodiments, chosen for purposes of illustration, taken together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a diagrammatic cross sectional view illustrating the arrangement of one embodiment of an engine according to the invention;
FIG. 2 is a cross sectional view of a combustion cylinder of the engine of FIG. 1 taken in the plane generally indicated by the line 2--2 of FIG. 1 and showing the location of the fuel injection and ignition means;
FIG. 3 is a longitudinal cross sectional view showing diagrammatically the relations of elements of an alternative embodiment of engine, according to the invention;
FIG. 4 is a transverse cross sectional view showing other constructional aspects of the engine of FIG. 3; and
FIGS. 5 and 6 are graphical presentations of pressure-volume diagrams comparing the cycle differences of the embodiments disclosed in the drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIGS. 1 and 2 of the drawings, numeral 10 generally indicates a dual combustion engine formed according to the invention. Engine 10 includes a cylinder block 12 having a plurality of cylinders, including combustion cylinders 13, satellite cylinders 14 and expansion cylinders 15. The various cylinders are arranged in three banks, each made up of a plurality of the same type of cylinder and each preferably having at least three cylinders, only one of which is shown.
Cylinders 13, 14, 15 are each provided with reciprocable pistons 17, 18, 19, respectively, which are connected with one of the throws of the engine crankshaft 20 by means of connecting rods 22, 23, 24, respectively. In this manner, reciprocation of the pistons on a predetermined cycle relative to one another is provided.
Combustion cylinders 13 and pistons 17 together define variable volume working or combustion chambers 25, which are provided with inlet and outlet ports 27, 28 controlled by inlet and outlet valves 29, 30, respectively. Inlet port 27 connects through passage means 32 controlled by a throttle 33 with a source of air, not shown.
Satellite cylinders 14 and their respective pistons 18 together define working chambers 34 having inlet and outlet ports 35, 37, controlled by inlet and outlet valves 38, 39, respectively. Inlet ports 35 of the satellite cylinders connect through transfer passages 40 with the outlet ports 28 of their respective combustion cylinders.
Expansion cylinders 15 and their respective pistons 19 together define expansion chambers 42, having inlet and outlet ports 43, 44 controlled by inlet and outlet valves 45, 46, respectively. Outlet ports 44 communicate with an exhaust passage 48 which may be connected with suitable muffling and/or exhaust treatment means, not shown.
Intermediate the cylinder banks containing the satellite cylinders 14 and the expansion cylinders 15, there is provided a walled enclosure 49 defining a fixed volume combustion chamber 50. Combustion chamber 50 includes a plurality of inlet ports 52, which connect through transfer passage means 53 with the outlet ports 37 of the respective satellite cylinders. The combustion chamber 50 has at the end opposite the inlet ports, a plurality of outlet ports 54 which connect through suitable transfer passages 55 with the inlet ports 43 of the respective expansion cylinders 15.
Fuel supply means and ignition means are provided for both the combustion chambers of cylinders 13 and the fixed volume combustion chamber 50. These include injection nozzles 57 and spark plugs 58, located in the walls of the respective combustion chambers 25 and fuel injection nozzle 59 and spark plug 60 located in the wall 49 of the fixed volume combustion chamber 50. In each case, the fuel injection nozzles and the spark plugs from the respective chambers are located such that a relatively small fuel spray from the injection nozzles will form a locally rich fuel mixture that may be ignited by the spark plug, regardless of the amount of fuel present in the remaining portions of the combustion chamber.
Although not shown, it should be understood that the engine further includes suitable means for operating the various fuel supply means and ignition means in timed relation with the movement of the engine pistons in order to carry out the intended operating cycle of the engine, as will be subsequently fully described.
In operation, the various pistons, inlet and exhaust valves, and fuel injection and ignition means are operated in timed relation upon rotation of the crankshaft 20. Upon the downward motion of each piston 17, its inlet valve 29 opens, permitting a charge of air to be drawn into the combustion chamber 25 through the inlet passage means 32. Valve 29 then closes and piston 17 moves upwardly, compressing the air charge until the piston reaches a position near top dead center. A small charge of fuel is then injected into the combustion chamber 25, forming a combustible mixture which is ignited by the spark plug 58. The burning of the fuel-air mixture further compresses and heats the charge. However, the amount of fuel injected is sufficient to combine with only a small part of the air in the charge so that a mixture of excess air and combustion products is formed by the combustion in cylinder 25.
Following and/or during the combustion, which occurs in chamber 25 at approximately constant volume, the exhaust valve 30 is opened, allowing the heated and compressed charge of air and combustion products to escape through a transfer passage 40, passing through the then open inlet valve 38 into the relatively large clearance space forming the working chamber 34 of the associated satellite cylinder 14. Valves 30 and 38 then close and the gases in chamber 34 are partially expanded as the satellite piston 18 moves downwardly. It will be noted that the satellite cylinders and their respective pistons are smaller in diameter than the associated combustion cylinders and pistons in order to provide for this partial expansion of the charge. At the end of the downward stroke of piston 18, the outlet valve 39 is opened. The charge is exhausted from each satellite cylinder on the upward stroke of its respective pistons, passing through the respective transfer passage 53 and port 52 into the fixed volume combustion chamber 50.
Preferably, the combustion chamber 50 will be supplied by at least three satellite cylinders, each associated with a combustion cylinder and the pistons of these satellite and combustion cylinders will be sequentially timed so that the admission of air and combustion products into the combustion chamber 50 is more or less continuous. In the combustion chamber 50, additional fuel is admitted to the working charge through the fuel nozzle 59 and the mixture formed is ignited by spark plug 60 and burned at constant pressure, further heating and expanding the charge.
From the fixed volume combustion chamber 50, the gases then pass through the various expansion cylinders, to which they are admitted by the opening of the respective inlet valves 45 when the pistons 19 are near their respective top dead center positions. The products are then expanded by the downward motion of the pistons 19 in the expansion cylinders, with the admission of gases being cut off by closing of the inlet valves at a suitable point in the expansion stroke, which may, if desirable, be made adjustable in much the same manner as the cutoff point of the steam engine inlet valve may be made variable. When each piston 19 reaches its downward position, the respective exhaust valve 46 is opened and the piston moves upwardly, forcing out the expanded combustion products.
It should be noted that the partial expansion of the charge in the satellite cylinders and the final expansion of the gases in the expansion cylinders both result in the development of useful work which is transmitted to the engine crankshaft in conventional fashion, some of this work being absorbed in the operation of the combustion pistons 17, as well as the other engine components.
In FIG. 5 there is shown a pressure-volume diagram which illustrates the operation of the above-described cycle of the embodiment of FIGS. 1 and 2. Line 1-2 represents the compression of the charge in cylinders 13. Line 2-3 represents theoretical adiabatic constant volume combustion in these cylinders with line 2 - 3' indicating the curve as modified by heat losses. Line 3'-4 represents the partial expansion of the charge in satellite cylinders 14. Line 4-5 represents the constant pressure combustion in chamber 50, while line 5-6 represents the final expansion of the gases in the expansion cylinders. Line 6-1, of course, represents the return to atmospheric pressure due to the exhausting of the charge and intake of a fresh air charge.
In FIGS. 3 and 4, there is illustrated an alternative embodiment of dual combustion engine, which is generally indicated by numeral 10'. While the arrangement of the components in engine 10' varies in a number of ways from the arrangement of similar components in the embodiment of FIGS. 1 and 2, the use and operation of the components present is sufficiently similar to those of the first embodiment that it is necessary to discuss only the differences in construction and operation between the two embodiments. Accordingly, primed numerals have been utilized in FIGS. 3 and 4 to indicate components corresponding in operation and function to like elements of the embodiment of FIGS. 1 and 2.
The construction of engine 10' differs from that previously described in that the two cylinder banks each contain both a combustion cylinder 13' and an expansion cylinder 15'. It should also be noted that the satellite cylinders are completely eliminated and the longitudinally extending fixed volume combustion chamber 50' communicates directly with the combustion chambers 25' of the combustion cylinders 13' through transfer passages 62, which are controlled by spring-biased check valves 63. The compression ratio of the combustion cylinders is reduced in view of the absence of satellite cylinders. Another variation in design is that the inlet valves 64 of expansion cylinders 15' are arranged to open outwardly in the fashion of a steam engine. Rocker means 65 are illustrated for actuating the inlet and exhaust valves of the combustion and expansion cylinders, respectively.
The operation of the alternative embodiment is like that of the embodiment first described in many respects. A charge of air is drawn into the combustion cylinders 13' and compressed, followed by the injection of a small amount of fuel and burning of the charge at substantially constant volume conditions. This causes further heating and compression, forcing the charge out through check valve 63 and into the fixed volume combustion chamber 50', at which point additional fuel is added and the mixture is ignited for burning at constant pressure. The remaining gases are then transferred into the expansion cylinders 15' and expanded in the manner previously described, with the resultant work output.
FIG. 6 shows a pressure-volume diagram illustrating the cycle of the alternative embodiment of FIGS. 3 and 4. Line 1'-2' represents the compression of the charge in cylinders 13'. Line 2'-3' represents constant volume combustion in these cylinders. Line 3'-4' shows constant pressure combustion in chamber 50'. Line 4'-5' illustrates expansion of the gases in the expansion cylinders 15' and Line 5'-1' shows the return to atmospheric pressure through exhausting of the charge.
While the invention has been described by reference to certain preferred embodiments, it should be apparent that numerous changes could be made in the manner of utilizing the inventive concepts disclosed in the arrangement and construction of combustion engines. Accordingly, it is intended that the invention not be limited except by the language of the following claims.