Marine propulsion – Means for accomodating or moving engine fluids – Means for handling exhaust gas
Reexamination Certificate
2002-10-17
2004-01-06
Morano, S. Joseph (Department: 3617)
Marine propulsion
Means for accomodating or moving engine fluids
Means for handling exhaust gas
C440S08800J, C060S312000, C123S041080, C123S041440
Reexamination Certificate
active
06672919
ABSTRACT:
BACKGROUND
Under certain operating conditions, mostly at or near idle engine speed, in a four cycle reciprocating marine engine, liquid water can run backward in the marine exhaust system, whereby liquid water flows backward from the exhaust system into the engine cylinders.
Specifically, the invention addresses such marine engine/exhaust assemblies wherein cooling water flows through a water jacket in the exhaust system, to quickly cool the exhaust gases soon after the exhaust gases leave the engine exhaust ports. Typically, such cooling water is directed through a water jacket on the exhaust manifold, or whatever other structure first receives the exhaust gases from the engine. After circulating through the water jacket, the cooling water is injected into the exhaust gas stream, downstream from the water jacket.
Such injected water mixes with the exhaust gases, thus to further cool the exhaust gases. The mixture of exhaust gases and water then travel together to the exit of the exhaust system. The primary reason for mixing the liquid water with the exhaust gases is to cool the exhaust gases sufficiently that rubber components of the exhaust system not be damaged by the exhaust gases.
A first source of the condensed liquid water of concern is the hot exhaust gas which comes into contact with a colder surface of the metal exhaust manifold, where the metal exhaust manifold has a temperature cold enough to condense water vapor out of the exhaust gases. Water vapor, which is a primary component of the engine exhaust gases, condenses out of the exhaust gases onto the exhaust manifold walls, flows downwardly, and accumulates on a lower surface of the exhaust manifold. In some instances, such condensation takes place downstream of the exhaust manifold, in an exhaust pipe, wherein the condensed liquid water accumulates on a lower surface of the exhaust pipe.
A second source of water accumulation on a lower surface of the exhaust manifold or exhaust pipe is based on a phenomenon known as reversion. Reversion occurs when, in operation of the intake valves and the exhaust valves, both an intake valve and an exhaust valve are momentarily open at the same time. Specifically, the engine/exhaust combination is most susceptible to reversion when a piston is positioned between near and approaching top dead center, and near and just after top dead center, during the transition from the upward exhaust cycle to the downward intake cycle. This momentary valve-timing occurrence is known as valve overlap.
When valve overlap occurs, the high negative pressure of the intake plenum can cause the direction of flow of exhaust gases in the exhaust manifold and the down stream exhaust conduit pipe to momentarily be reversed. This reverse direction of flow of exhaust gases, known as reversion, can carry with it any of the liquid cooling water which is injected into the exhaust gas stream. The reverse direction flow of exhaust gases can cause the injected liquid water to be pulled, or walked backward, into the exhaust manifold or other water-jacketed exhaust system component. After a period of operation under such reverse direction flow conditions, this water can accumulate on the floor or other lower surface of the respective exhaust system component.
When this water, either exhaust gas condensate, or reversion in injected water, or both, accumulates in quantity large enough to flow backward into an engine cylinder at the respective exhaust port, either by gravity or by further operation of reverse exhaust gas flow of the reversion process, such flow does occur, whereby the liquid water flows back into a respective cylinder.
When the liquid water, which is essentially incompressible, flows into the engine cylinder in sufficient quantity, the piston is prevented from moving through the compression stroke when the piston reduces the cylinder volume to essentially the volume of the water in the cylinder, before the piston completes the compression stroke. When that happens, the engine is stopped dead. The engine cannot turn further because completion of the compression stroke of the piston requires further reduction of the space in the cylinder, but the liquid water in the cylinder cannot compress and there is no path by which the water can quickly escape. Thus, the piston movement is blocked by the incompressible water. While the water can be removed by removing the spark plug, the only full cure for the water in the cylinder is to disassemble the engine in order to repair the damage done by the water.
Even if the quantity of water entering the engine is not great enough to stop the engine from running, such water ingestion can cause other problems. For example, any quantity of liquid water in the engine can cause corrosion. In addition, under certain conditions, the water can, over time, leak past the piston rings, and thereby enter the underlying oil reservoir, commonly known as the lubricating oil reservoir, or the oil crank case. In the crank case, the water becomes entrained with the engine lubricating oil, and is thus distributed throughout the engine as the oil is pumped through the oil passages, and onto all parts which are lubricated by the oil. The presence of the water in such loci, even though carried by oil, works to initiate corrosion in respective ones of the engine parts and areas so exposed to the water.
The resulting corrosion can occur throughout all areas, and in all parts, of the engine to which the oil flows because all the contaminated oil, which is pumped to all areas of the engine, is contaminated. The most predominant place for corrosion to occur is on the cylinder walls, which is the first area to see the ingested water. In some instances, the corrosion can become severe enough to cause engine components, which are supposed to slide with respect to each other, to freeze together. The greatest risk of corrosion, and the most rapid spread of corrosion, typically occur where the boat is being used in salt water, whereby salt water is being used as the cooling water.
The condensation portion of the above described problem occurs in all internal combustion reciprocating engines when a given engine is cold. For engines which are not used in a marine application, when the engine starts operating, the heat of the exhaust gases rapidly heats up the walls of the exhaust conduit system to the point where water vapor stops condensing, and any already-condensed water is either evaporated and carried out of the exhaust system as vapor, or the liquid water is physically entrained in the exhaust gases by the force of flow of the exhaust gases. Such non-marine engine/exhaust assemblies are so exposed to ambient air that heat build-up is of less concern, and since cooling water is not so available as in a boat, such water-jacketed exhaust systems are typically not used, whereby condensate and reversion in the exhaust system, near the engine, typically do not occur.
The phenomenon of condensed water leaving the exhaust system can be observed in colder climates in non-marine applications where, for a short period after an engine is started, water can be seen dripping out of the tailpipe of the exhaust system. The liquid water stops dripping after a short period of running time as the exhaust system heats up and maintains the exhaust gas water vapor, in the vapor state.
The problem of condensed, liquid water entering the engine block through the exhaust ports, and thereby causing engine damage or engine failure is generally confined to marine engines where cooling water is necessarily used to cool the exhaust system. Namely, fresh or salt sea water, depending on the body of water involved, is pumped through water jackets which surround the exhaust pipes which carry exhaust gases away from the engine. Typically, after the sea water traverses the water jacket, that same sea water is injected into the exhaust gas flow stream in the main exhaust-carrying conduit or chamber of the exhaust pipe. Thus, in the exhaust system, the sea water first passes through a water jacket which extends around the exhaust p
Morano S. Joseph
Olson Lars A.
Wilhelm Thomas D.
Wilhelm Law Service
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