Internal-combustion engines – Multiple piston – common nonrestrictive combustion chamber – Four-cycle
Reexamination Certificate
1998-12-24
2001-02-06
Kwon, John (Department: 3747)
Internal-combustion engines
Multiple piston, common nonrestrictive combustion chamber
Four-cycle
C123S0510BA
Reexamination Certificate
active
06182619
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a two-stroke cycle diesel engine having improved performance characteristics. More particularly, the present invention relates to an opposed piston, two-stroke cycle diesel engine which is adapted for use in small, unmanned aircraft.
BACKGROUND
Opposed piston, two-stroke cycle diesel engines have been in development for a number of years. Theoretically, due to its configuration, an opposed piston, two-stroke cycle diesel engine should generate more power than a comparable sized four-stroke diesel engine. This is so because the two-stroke cycle engine has twice as many power cycles per revolution as does the four-stroke cycle engine.
In order to maximize the benefit of an opposed piston, two-stroke cycle diesel engine, it is desirable to make the engine as compact as possible. As a high output engine is made very compact, however, cooling becomes difficult and can pose serious concerns. This happens because an excessive amount of heat is generated within a confined area, and there is very little room in this confined area for coolant to pass through the engine. Furthermore, if the cooling system design is compromised as a trade-off to compactness, uneven cooling or inadequate cooling can result and lead to premature failure of the engine.
In order to maximize thermal efficiency, in addition to effective cooling, it is also desirable to reduce heat transfer and thereby retain as much heat as possible in the exhaust stream. This is particularly desirable when heat in the exhaust stream can be subsequently used to maximize turbocharger output. The reduction of heat transfer is more difficult in the opposed piston engine than in the more conventional four-stroke engine because the exhaust ports are located all around the cylinder chamber. The exhaust gases must therefore be redirected in order to exit the engine block on the sides. Redirecting the flow without some means of minimizing heat transfer, however, will increase the cooling problem previously mentioned and simultaneously reduce the amount of heat retained for transfer to the turbocharger.
It is also of some concern that, present opposed piston, two-stroke diesel engines suffer from incomplete fuel combustion within the cylinder chamber. Because of the opposed piston design, the fuel injector is not able to inject the combustion fuel to the top center of the pistons. Instead, the fuel injectors must inject from a cylinder wall. Presently, existing designs are not able to effectively mix and/or distribute the fuel within the cylinder chamber. Frequently, in order to improve the fuel combustion, some existing diesel two-stroke engines are initiating a strong swirl within the cylinder chamber to enhance the removal of the exhaust fluid from the cylinder chamber. However, the strong swirl can subsequently inhibit the propagation of the diesel within the cylinder chamber and cause incomplete fuel combustion within the cylinder chamber. This has minimized the efficiency of these engines.
In light of the above, it is an object of the present invention to provide an opposed piston, two-stroke cycle diesel engine which operates more efficiently, is more durable and is more reliable than existing engines. Another object of the present invention is to provide an opposed piston, two-stroke cycle diesel engine having an improved cooling system and thermal shields which allow the engine to operate at a cooler temperature. Still another object of the present invention is to provide a two-stroke diesel engine having improved fuel ignition and combustion characteristics.
SUMMARY
The present invention is directed to an engine which satisfies these needs. In one embodiment, the engine includes a tubular cylinder housing which is formed with a plurality of exhaust ports. The cylinder housing itself is mounted in an engine block which at least partly encircles the cylinder housing. First and second axially opposed pistons are positioned in the cylinder housing, and a thermal shield surrounds the exhaust ports to at least partly shield the engine block from exhaust fluid as it exits from the cylinder housing through the exhaust ports. As provided in detail below, because the thermal shield acts to isolate the engine block from the exhaust fluid, the engine block operates at a cooler temperature and requires less cooling. Further, this allows the exhaust fluid to be transferred to a turbocharger at a hotter temperature.
In more detail, the cylinder housing includes a cylinder wall which defines a cylinder chamber. The plurality of exhaust ports are arranged circumferentially and extend through the cylinder wall to release the exhaust fluid from the cylinder chamber. As intended for the present invention, the opposed pistons are adapted to move axially within the cylinder chamber between a first configuration in which the pistons are spaced apart from each other, and a second configuration in which the pistons are proximate each other. In the second configuration the exhaust ports are closed and the pistons act to compress air in the cylinder between the pistons. The compressed air thereby ignites fuel as it is injected into the cylinder between the pistons. The resultant ignition then drives the pistons to the first configuration wherein the exhaust ports are opened. It is while the pistons are in this first configuration that air is forced into the cylinder chamber to replenish air in the chamber and to drive exhaust fluids out of the cylinder chamber through the exhaust ports. The pistons then return to the second configuration and the cycle is repeated.
In order to help isolate the engine block from the heat of the exhaust fluid, the thermal shield is positioned to at least partly encircle the cylinder housing around the exhaust ports. Specifically, the thermal shield is positioned between at least one of the exhaust ports and the engine block to thermally shield the engine block from the exhaust fluid. Preferably, the thermal shield is positioned between substantially all of the exhaust ports and the engine block to thermally shield the engine block from the exhaust fluids. This minimizes the heat transfer from the exhaust fluid to the engine block and allows the engine block to operate at a cooler temperature with less requirement for cooling.
As intended for the present invention, the engine includes a sealed fluid gap which is located between the thermal shield and the engine block to reduce heat transfer from the exhaust to the engine block. The sealed fluid gap substantially encircles the cylinder housing and the thermal shield.
In order to provide efficient cooling for the engine, the engine can include cooling passageways which are substantially annular and engineered to effectively encircle each cylinder housing. As provided herein, each cooling passageway around each cylinder housing can be divided into annular sections. These include: a first cooling section, a grooved cooling section, and a second cooling section. Importantly, each of these cooling sections includes at least one cooling fluid inlet which delivers a cooling fluid to the respective cooling sections from a direction that is substantially tangential to the cylinder housing. As provided herein, because each cooling section is annular and the cooling inlet delivers the cooling fluid substantially tangentially, the cooling fluid encircles and spins around the cylinder housing. This promotes uniform cooling, minimizes areas of flow separation, and enhances the heat exchange between the cylinder housing and the cooling fluid.
Preferably, each cooling section also includes at least one cooling fluid outlet which is adapted and oriented to receive the cooling fluid for removal from the respective cooling section in a direction that is substantially tangential to the cylinder housing. This allows for a smooth transition of the spinning cooling fluid out the respective cooling sections.
As intended for the present invention, the first and second cooling sections are essentially unobstructed fluid channels which allow the
Manzke Clifford A.
Spitzer Jeffrey J.
General Atomics Aeronautical Systems, Inc.
Kwon John
Nydegger & Associates
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