Internal-combustion engines – Water and hydrocarbon
Reexamination Certificate
1998-06-26
2001-01-09
Dolinar, Andrew M. (Department: 3747)
Internal-combustion engines
Water and hydrocarbon
C123S668000
Reexamination Certificate
active
06170441
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a highly efficient engine employing an unsymmetrical expansion and compression cycle along with the use of a supercritical mixture of fuel and water.
The operation of internal combustion engines is generally a trade-off between efficiency of the engine and cleanliness of the exhaust. For example, diesel engines provide high efficiency but the exhaust usually includes particulate matter (PM) such as soot and nitric oxide (NO
x
). In general, internal combustion engines, whether spark ignition or diesel, operate on a symmetrical cycle. That is, compression volume equals expansion volume. Ralph Miller in U.S. Pat. No. 2,670,595 was the first to describe an engine operating on an unsymmetrical cycle. He recognized that closing intake valves either before or after bottom dead center (BDC) could change the “effective” compression ratio in an engine.
For example, by doubling the length of the stroke of the engine and closing the intake valve early when the piston is halfway down toward bottom dead center (BDC), the amount of compressed air is reduced by one-half, giving the same effective compression ratio as the original engine. No work is done on the air inside the cylinder during expansion to bottom dead center and subsequent compression back to atmospheric pressure. At the same fuel-air ratio the same peak pressures will be felt by the engine components. If the expansion ratio is left unchanged, then the combusting gases can expand to twice the volume. This increased expansion reduces heat loss to the exhaust and allows the combustion products to do additional work by reaching a lower temperature prior to opening of the exhaust valve(s). Thereby, the engine extracts more useful mechanical energy.
Historically, this unsymmetrical cycle innovation went largely unnoticed because it called for an increase in size and weight for the engine providing the same power. This size and weight penalty was unacceptable to the engine industry of the 1950's and 1960's during which time the single most important figure of merit was horsepower/cubic inch of engine displacement. Also, Miller's proposed mechanism for variable valve timing was cumbersome and did not provide as much valve timing angle variation as desired.
In 1992 Ozawa (see U.S. Pat. No. 5,682,854) discussed ways of overcoming this deficiency in power output by developing a variable compression/expansion ratio. His system used a planetary gear drive designed to alter the position of the intake valve camshaft. Mechanical actuators on the planet carrier physically rotated the camshaft forward or backward in response to the engine's need for power at the expense of engine cycle efficiency. Ozawa's innovation has been commercially realized in vehicles built by the Mazda Corporation. In particular, the Mazda Millennia, introduced in 1994, employs a continuously variable cam component to combine high power capability with high efficiency.
Engines generally use solid metal pistons and cylinder heads and because of the solid metal, the a thermal diffusivity is high. The thermal diffusivity is selected so that the surface temperature of the pistons and cylinder heads remain low enough to avoid thermal stress cracking of the surface under the repeated cyclic heating resulting from engine combustion. This avoidance of thermal stress cracking requires relatively low operating temperatures (300° F.-500° F.) for aluminum pistons and heads. This temperature is maintained by the engine cooling system removing the heat transferred by the combustion process. Of course, such heat is not available for conversion to work in the engine expansion cycle. Thus, heat transfer through solid metal pistons and heads results in loss of efficiency. A reduction in such heat transfer through pistons and cylinder heads will therefore improve the overall thermal efficiency of the engine.
Copending U.S. patent application Ser. No. 08/992,983 filed on Dec. 18, 1997 discloses a supercritical water/fuel composition and combustion system in which a mixture of water and a hydrocarbon fuel is maintained near or above the thermodynamic critical point such that the mixture is a homogeneous single phase. As taught in that application, because the water/hydrocarbon fuel mixture is maintained as a homogeneous isotropic single phase it will combust more completely when introduced into a combustion chamber.
It is well known in the engine system art that liquid fuel combustion relies on spray atomization followed by fuel droplet evaporation and finally on the combustion reaction sequence. Smaller droplets favor more complete and cleaner combustion. Prior art approaches used extremely high injection pressures to minimize the droplet diameters. Fuel preheating and chemical surfactants produce smaller droplets, but such fuel preheating and chemical surfactants produce only modest reductions in droplet size and heating is only effective up to 150° C. to 200° C. Above these temperatures excessive coke, gum, and tar formation blocks operating flow channels in the fuel delivery system.
It is therefore desirable to create a highly efficient engine system by combining an unsymmetrical cycle with a supercritical water/fuel mixture along with controlled thermal diffusivity in the piston and cylinder head.
SUMMARY OF THE INVENTION
In one aspect, the engine system of the invention includes an internal combustion engine having at least one piston in a cylinder, the cylinder including a cylinder head. Apparatus cooperating with the piston creates an unsymmetrical expansion and compression cycle wherein the expansion portion of the cycle is greater than the compression portion of the cycle. An insulating material having a selected thermal diffusivity is applied to a surface of the piston and the cylinder head to reduce heat transfer therethrough. In one embodiment apparatus is provided for injecting a supercritical mixture of fuel and water into the cylinder for combustion. In another embodiment, the expansion portion of the cycle is greater than the compression portion of the cycle by a factor in the range of 1.3:1 to 2.5:1. The unsymmetrical cycle may be achieved through an increased stroke length. Alternatively, the unsymmetrical cycle can be achieved by decreasing the enclosed volume at the top of the compression stroke combined with early closing of the engine intake valve. While late closing of the air intake valve can accomplish the unsymmetrical compression, this operation involves additional pumping work in first drawing in the full charge and then pumping half of it back out. Thus, the early closing is to be preferred on a thermodynamic cycle basis.
In other embodiments of the invention the injection apparatus injects the supercritical water/fuel mixture near the top of the compression stroke such as near top dead center. The invention also includes a heat exchanger for using engine waste heat to heat the supercritical mixture of fuel and water. A pump is provided for pressurizing the water/fuel mixture up to a pressure as high as 4000 psi before introduction into the heat exchanger. The heat exchanger may be thermally coupled to the exhaust from the engine.
In yet another embodiment, electrical preheating is provided for the water/fuel mixture. This preheating may be needed during start up or whenever exhaust temperature is below a desired preheating level. This electrical preheating may also include feedback control apparatus for controlling the preheating. It is preferred that the supercritical mixture be at approximately 4000 psi and approximately 400° C.
The engine system of the present invention is highly efficient. The unsymmetrical Miller cycle reduces heat loss to the exhaust. The insulating material lining the head and piston reduces heat loss to the engine coolant. Further, water and fuel are preheated by exchanging heat with the engine cooling and/or exhaust streams to result in a supercritical mixture of water and fuel. The addition of water enables the heating of the supercritical water/fuel mixt
Ahern Brian S.
Haldeman Charles W.
Choate Hall & Stewart
Dolinar Andrew M.
Huynh Hai
Quantum Energy Technologies
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