Internal-combustion engines – Water and hydrocarbon
Reexamination Certificate
2000-08-30
2002-01-22
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Water and hydrocarbon
C123S07000R, C123S543000, C123S559100, C060S712000
Reexamination Certificate
active
06340004
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of internal combustion engines, and in particular the improvement of their efficiency by using a regenerator. The engine of the present invention represents a combination of elements, which combined yield an engine with a brake efficiency of greater than 50%, which is competitive with fuel cells and other advanced movers.
BACKGROUND OF THE INVENTION
The fuel economy of vehicles primarily depends on the efficiency of the mover that drives the vehicle. It is well recognized that the current generation of internal combustion (IC) engines lacks the efficiency needed to compete with fuel cells and other alternative vehicle movers. At least one study has recommended that auto manufacturers cease development of new IC engines, as they may be compared to steam engines—they are obsolete. The present invention is directed to an IC engine that is competitive with fuel cells in efficiency.
The following principles must be embodied in one engine in order for the engine to achieve maximum efficiency.
1) Variable fuel ratio and flame temperature
For ideal Carnot cycle efficiency:
n=
(
T
h
−T
l
)/
T
h
Where
T
h
=highest temperature
T
l
=lowest temperature (usually ambient temperature)
n=thermal efficiency
shows that the higher the temperature, T
h
, the higher the engine efficiency. This is not the case in real-world conditions. The basic cause of the breakdown in the Carnot cycle rule is due to the fact that the properties of air change as the temperature increases. In partcular, C
V
, the constant volume specific heat, and C
p
, the constant pressure specific heat, increase as the temperature increases. The ratio k, on the other hand, decreases with increasing temperature. To heat 1 lb of air at constant volume by 100 degrees F. requires 20 BTU at 1000 degrees F., but 22.7 BTU at 3000 degrees F. The extra 2.7 BTU is essentially wasted. At the same time, each increment of T
h
adds less and less to the overall efficiency. If T
l
is 600 R, and T
h
is 1800 R (1340 degrees F.), n=0.66666. At T
h
=3600 (3140 degrees F.), n=0.83333, and at T
h
=5400 R (4940 degrees F.), n=0.88888. In the first instance, going from 1800 R to 3600 R netted an increase in n of 0.16666, whereas going from 3600 R to 5400 R netted only an increase in n of 0.0555, or ⅓ of the first increase. At the same time, the specific heat of air is a monotonic function of temperature, so at some point the efficiency gains from higher temperatures are offset by losses due to higher specific heats. This point is reached at around 4000 R.
The most efficient diesels are large, low swirl DI (direct injection) turbocharged 2-strokes. These are low speed engines (<400 rpm) and typically have 100%-200% excess air.
The combustion temperature is proportional to the fuel ratio. A CI (compression ignition) engine will have a theoretical flame temperature of 3000-4000 R, as opposed to the SI (spark ignition) engine, which has a theoretical flame temperature of 5000 R. Note also that the reason the specific heat is increased is due to increased dissociation of the air molecules. This dissociation leads to increased exhaust pollution.
Ricardo increased the indicated efficiency of an SI engine by using hydrogen and reducing the fuel ratio to 0.5. The efficiency increased from 30% to 40%.
Hydrogen is the only fuel which can be used in this fashion. There are 2 basic types of ignition—spark and compression. This engine proposes to use hot air ignition (HAI), which allows variation in the fuel ratio similar to CI, but with the additional advantage that HAI does not require the engine do work to bring the air up to the temperature where it can be fired. All engines which claim to be efficient must use an ignition system which allows wide variations in the fuel ratio. An incidental advantage of this design is that because molecular dissociation is much less at lower temperatures, the resulting exhaust pollution (species such as nitrous oxide, ozone, etc) is also lessened.
2) Uniflow Design
Uniflow design, although it is more critical to a Rankine cycle engine, such as the Stumpf Unaflow steam engine, is also of importance to an IC engine. Generally speaking, in a uniflow design, the motion of the working fluid into and out of the cylinder does not cause degradation of the cycle efficiency. The uniflow design minimizes unwanted heat transfer between engine surfaces and the working fluid. Only two-stroke cycle IC engines can claim some kind of uniflow design.
Consider the typical four-stroke cycle Diesel engine:
1) Intake—Air picks up heat from the intake valve and from the hot head, piston and cylinder. Generally speaking, the air heats up from 100-200 F.
2) Compression—The air continues picking up heat, in addition to the work done on it by the engine.
3) Power—Air is hot after firing, and begins to lose heat to the walls. Luminosity of the diesel combustion process accounts for much of the heat lost. The short cycle time of a high speed Diesel engine holds these heat losses by conduction to a minimum.
4) Exhaust—During the blowdown, heat is transferred to the exhaust valve, and hence to the cylinder head.
The engine of the present invention has separate cylinders for intake/compression and for power/exhaust. The intake/compression cylinder is cool, and in fact during the intake and compression process, efforts can be made to create a nearly isothermal compression process by adding water droplets to the intake air. Addition of water droplets is optional and is not essential to the design, which has had its efficiency calculations performed without taking water droplet addition into account.
Addition of water droplets, of course, is impossible with a Diesel engine. A variation on this is used in SI engines, where the heat of vaporization of the fuel keeps the temperature down during compression. This is one reason why methanol, which has a high heat of vaporization, is used in some high performance engines.
The power/exhaust cylinder is the ‘hot’ cylinder, with typical head and piston temperatures in the range of 1000-1100 F. This necessitates the use of 18/8 (SAE 300 series) stainless steels for the head and piston, and superalloys for the valves. Any other suitable high temperature material, such as ceramics, can also be used in the application. Combustion 22 temperatures are in the neighborhood of 2000-3000 F. The high heat of the combustion chamber prior to combustion reduces the heat transfer from the working fluid to the chamber during the power stroke. It also reduces the radiant heat transfer, however the larger reduction in radiant heat transfer comes from keeping the maximum temperature below 3000 F.
Thus, unwanted heat transfer is minimized in the engine of the present invention.
There are several dissociation reactions which become important absorbers of heat above 3000 F. The two most important are:
2CO
2
⇄2CO+O
2
a)
2H
2
O⇄2H
2
+O
2
b)
The production of CO, carbon monoxide, is particular undesirable, as it is a regulated pollutant. All of these reactions also reduce the engine efficiency.
3) Regenerator
In the use of a regenerator, the state of the art is not yet commercially feasible.
The principle of using a regenerator is not new. Siemens (1881) patented an engine design which was a forerunner of the engine of the present invention. It had a compressor, the air traveling from the compressor through the regenerator and into the combustion chamber. There are, however, some basic differences between the Siemens engine and the engine of the present invention:
1) Siemens proposed using the crankcase, rather than a separate cylinder, to compress the air. The engine appears to be a variation of Clerk's two-stroke cycle engine (1878). The engine features are:
a) All of the compression occurs in the crankcase
b) Max compression occurs at the wrong time on the stroke. It should occur at piston TDC, not BDC. This is remedied by use of a reservoir. This greatl
Kamen Noah P.
Roberts Abokhair & Mardula LLC
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