Patent Application
20210239039
We on earth (7.8 billion people in 2021) are destroying our planet by wasteful use of resources, and in particular by wasting energy. Of all the vast production of energy on the planet, now at over 600×1015 BTUs (630 EJ) per year, about 80% is from burning fossil fuels at very low efficiency. Renewable energy sources are beginning to replace fossil fuel use, but the best solution in the near term, to meet our energy needs with far less dependence on fossil fuels, is to improve energy efficiency of fuel use. Our invention—a high efficiency engine—is directed to that purpose. It is particularly useful for combined heat and power applications where a combined efficiency of 90% or more may be achieved. Our engine, or engines, are ideally suited for use with renewable fuels.
The scientific principles of operation of internal combustion engines have been known for approximately 130 years, after Rudolph Diesel first applied the concept of the thermodynamic cycle in 1892, just 16 years after the foundation concepts were introduced by Willard Gibbs. Modern theory of the thermodynamic cycles of internal combustion engines began with Diesel's work. In Diesel's U.S. Pat. No. 608,845, he presents what has become known as the “Diesel cycle.” Today, the five well-known internal-combustion engine cycles are represented by standard reversible forms composed of isentropic, isochoric, and isobaric process steps. Those five cycles are: Diesel cycle, Otto cycle, dual cycle, Brayton cycle, and the Atkinson (or Miller) cycle. It was not generally known until recently that a sixth comprehensive standard thermodynamic cycle includes and extends the five prior cycles—we refer to this improved cycle as The General Cycle. A thorough description of the General Cycle is provided in the reference:
Our invention concerns the design and application of internal combustion engines having optimum efficiency, operating generally in accordance with a thermodynamic cycle called the General Cycle, and at prescribed products of Atkinson ratio and compression ratio (ARC). An engine constructed in accordance with our invention having the required optimal conditions of RC and prescribed ARC comprises a multiplicity of volumes with enclosing structures, which volumes generally are of cylindrical form, each volume with an enclosed compressible fluid, or gas, that is cyclically compressed from a first volume to a second volume, heated by combustion, and expanded from the second volume to a third volume. These operations are performed by operation of mechanisms having parts such as pistons and valves, such that the ratio of the first volume to the second volume equals RC, which is the compression ratio, and the ratio of the third volume to the first volume equals A, which is defined as the Atkinson ratio. As used to produce combined heat and power, our inventive engines produce electricity at near 60% efficiency while also providing an additional 30% or more of the input energy as high-quality heat.
In order to describe our invention, it will be necessary to review the scientific principles pertaining to it and to define terms. As currently practiced, our invention is a two-stroke direct-injected piston engine that is represented by the General Cycle, which is explained below.
The General Cycle is an idealized thermodynamic cycle that can represent most, if not all, common internal combustion engines. Usually it is analyzed as a sequence of reversible steps performed on a compressible working fluid. In a real engine, this compressible fluid is a gas comprising oxygen with any amount of other gases, such as air or a gas composed of air, fuel, or combustion products. The General Cycle is best understood by reference to the P-V diagram of
I. Starting at point 1, a fresh charge of compressible fluid is compressed from volume V1 to volume V2. The compression ratio is RC=V1/V2. Pressure increases from P1 to P2. The compression work from point 1 to point 2, defined as W12, is negative.
II. Beginning at point 2, a first heat input Q1 from fuel raises the pressure from P2 to P3, at constant volume. This P3 is the maximum pressure, and V3=V2.
III. Beginning at point 3, a second heat input Q2 is added at constant pressure as the piston moves outward from V3 to V4. Fuel had begun to burn at point 2, and burning is complete at point 4. The total heat input is QIN=Q1+Q2. The expansion work from 3 to 4 is W34.
IV. After the hot compressible fluid (combustion gas) expands from point 3 to point 4, it continues to expand to V5 without further heat input. The power stroke is complete at point 5. In our engines, point 5 is at a substantially greater volume than point 1. The expansion ratio is defined as RE=V5/V2 and exceeds the compression ratio by the factor A=V5/V1. A is called the Atkinson ratio. It is equivalent to A=RE/RC. The work from 4 to 5 is W45.
V. Valves open at point 5 and remain open as the piston returns to 1, the starting point. A fresh charge of compressible fluid enters as the piston moves from V5 to V1, then the valves close and a new cycle begins. This recharge step is inherently irreversible and represents a departure from the fully reversible cycle model. Opening the cycle causes a loss of work against the atmosphere. The work against the atmosphere, Watm, is negative. The total work of this cycle is W=W12+W34+W45+Watm. The efficiency of the cycle is obtained by dividing the total work W by total heat input QIN.
We caution that while the above explanation of the General Cycle is of great benefit for understanding our invention, it represents a particular example and only approximates processes that may occur in a real engine built according to the invention. One may, for example, program the rate of heat input Q2 so as to restrain the maximum gas temperature (rather than maintaining constant pressure as described above) and thereby prevent formation of nitrogen oxides by nitrogen and oxygen molecules present in the combustion gas. Such a useful variation from the General Cycle should be understood to fall within the scope of our invention.
We have found that a two-stroke, direct-injected engine generally working in accordance with the General Cycle is superior to all other engines regarding the combined properties of efficiency, power density, and ease of construction. And we have for the first time found the optimum design conditions providing best efficiency for a two-stroke, direct-injected engine operating substantially in accordance with the General Cycle. Our invention concerns the application of these conditions to the construction of efficient engines. We will now describe the optimum conditions and show how they may be applied in novel, high-efficiency engine constructions.
We have found in our work that a practical upper limit of efficiency exists for internal combustion engines. For those engines of most efficient design, such as two-stroke, direct-injected engines, best efficiency lies in the general range of 60 to 65 percent brake efficiency, depending on the fuel used. In order to obtain such an optimum brake efficiency of approximately 60 percent or greater the following inequality must be satisfied:
ARC≥36.33+8788e−0.375 Rc (1)
For these highly efficient engines, the most desirable values of compression ratio, RC, are in the range from 19 to 30, as there is no practical benefit of a compression ratio greater than 30. The design property of Inequality 1 determines highly desired values for ARC (the product of Atkinson ratio, A, and compression ratio, RC, and also equal to the expansion ratio, RE). The following Table 1 illustrates minimum values of ARC satisfying the Inequality 1 for whole number compression ratios from 19 to 30.
Referring to
ARC≥36. (2)
Although deviations in construction of a practical engine which do not quite satisfy the original inequality may result in an engine with slightly less efficiency than 60%, it will be apparent to those skilled in the art that such an engine would still be highly efficient, and would exceed the efficiency of any practical engines known heretofore. Therefore, it should be considered that any such engine making use of the theoretical principles in its design and construction as herein set forth falls within the scope of our invention, regardless of the actual efficiency. Moreover, any engine which substantially approaches the design constraints herein set forth also falls within the scope of our invention.
We will now describe example constructions of engines designed in accordance with the principles that have been presented. In doing so we will describe per example only one cylinder and its accompanying structure, but it will be appreciated by one skilled in the art that engines are commonly composed of multiples of such similar cylinders and parts, and such constructions are within the scope of our present invention.
A First Example Engine Construction Having Backstroke Compression and a Shaft Linkage and/or Articulated Connection
We will now show a preferred engine construction that uses piston motions to inject air into the engine, and to compress and expand the gas as performed in the General Cycle. This particular example is presented in
During the recharge portion at the end of each cycle and before the beginning of the next cycle, piston 24 is in a position outward from wall port 26 so that wall port 26 is in communication with cylinder volume 22. A gas or compressible fluid such as air is introduced into cylinder volume 22 through wall port 26. This gas is obtained from a gas supply 33. The gas flows from gas supply 33 to reservoir 34, then through wall port 26 into the cylinder volume 22. An optional check valve, such as a reed valve (not shown), may be placed between the gas supply 33 and reservoir 34. This check valve can optionally serve to prevent gas from flowing back toward the gas supply 33 as the piston moves outward, reducing the back volume 25. As the piston moves outward, gas in the back volume 25 is forced out through wall port 26 and a back port 37. The back port 37, which provides for final discharge of gas from the back volume 25, may be either situated in the end portion of the engine body 27 or adjacent to the shaft bearing 36 in bearing housing 38, as shown in
Additional parts connected to the combustion chamber 23 are an exhaust port 40 with a valve 41, and a fuel injector 42. Port 40 with valve 41 form a closable opening to selectably permit transfer of the fluid out of the cylinder. Fuel injector 42 receives fuel from a fuel supply system 43 to provide a heat input means to increase the internal energy of the fluid by combustion of an injected fuel.
The beginning of a cycle as defined here occurs at the time that the valve 41 is closed in the exhaust port 40 and the piston then begins to compress gas in the cylinder volume 22. However, this does not occur at the time that the piston is near to the far outward position, called bottom dead center (BDC). Rather, the piston 24 moves inward from BDC with the exhaust valve 41 open until a position is reached where the cylinder volume 22 has been reduced by a factor of 1/A from the substantially greater value V5 referred to above in describing the General Cycle and further described below. A is the Atkinson ratio. (In the present example, A has a value of 1.4 and the desired compression ratio is RC=27.)
At the time that the valve 41 is fully closed, the value of cylinder volume 22 is V1. All valves are closed and compression of the gas, or air, in the cylinder volume 22 begins as piston 24 continues to move inward toward top dead center (TDC) position, which is the point of least cylinder volume referred to as V2 in the above General Cycle description. This least cylinder volume is substantially the chamber volume 23. As the piston 24 arrives at substantially the TDC position, heat is added to the gas in the cylinder volume 22 (presently equal to chamber volume 23) by the injection and burning of fuel. This process continues for a short time, initially raising the gas temperature and pressure at a near-constant-volume condition, and for a brief additional time as the piston moves outward, then fuel cutoff occurs. At fuel cutoff, the cylinder volume 22 will have increased in volume to a value V4 as described in the above General Cycle description. The heated gas, at a very substantial pressure, drives the piston farther thus sending power via the piston shaft 28, through power link 30, and to the power transfer means 32. This continues until the piston reaches an outward position approaching BDC, at which point exhaust valve 41 opens to discharge burnt gases from the cylinder volume 22. At the effective time of valve 41 opening, the volume of cylinder volume 22 is substantially equal to V5. Shortly after, the pressure in cylinder volume 22 falls below the pressure of the gas in gas reservoir 34. As the piston 24 continues to move outward, it uncovers wall port 26. Then a fresh charge of gas displaces remaining burnt gas in the volume 22 and fills the volume 22 with a fresh charge of gas. The replenishing of the cylinder volume 22 with fresh gas continues for a length of time while the piston 24 completes its travel to BDC and where it then reverses direction, and covers the wall port 26 again by its inward motion. The valve 41 remains open for a further time as the piston continues to move inward. The valve 41 closes at the point where the cylinder volume 22 has returned to the value V1. This is the point of beginning of a new cycle.
This two-stroke engine operating at an effective input pressure P1=115 kPa (1.15 bar) and having a compression ratio of RC=27 has excellent fuel utilization for a broad range of renewable and fossil fuels. It gives good specific power and substantially 60% brake efficiency or greater, depending on the fuel that is used. The engine has the following operating characteristics operating on No. 2 diesel fuel (ASTM D975-19a, 2-D (S-15) at 70% of stoichiometric mixture:
As an example, this small engine has dimensions of:
At 1200 RPM, a mean piston speed of 8.0 meters per second.
Other fuels are also being evaluated:
Eli) gasoline (ASTM D4814-19, 10% ethanol)—efficiency is 60%
Fuel methanol (ASTM D5797, M100)—efficiency is above 64%
The above small engine shown in
Fuel flexibility is an important benefit of our high-compression, high-efficiency engines. Except for changes in fuel injection means, the engine of
An especially preferred engine for cogeneration of heat and electric power, and satisfying Inequality 1, is shown in
A ceramic face 18 is applied to each of the pistons 2. This ceramic material is applied by plasma or flame spraying or other means and in a sufficient thickness to substantially reduce heat transfer from the hot gases to the piston bodies. The combination of the ceramic combustion chamber 16 and the ceramic piston faces 18 is an important optional aspect of our invention as it greatly reduces energy loss by heat transfer.
In the first portion of the engine cycle, the pistons 2 move toward the partition 14, approaching it very closely as they reach their top dead center (TDC) positions. In so doing, they compress a compressible fluid or gas 19 into the combustion chamber 16. This gas 19 may comprise oxygen, air, combustible gas or vapor, or any combination of suitable gases. Heat is introduced into the combustion chamber 16 by injection of fuel through fuel injector 7, which fuel almost immediately commences burning in cooperation with the compressed gas 19, thus forming a combusted gas at high temperature and pressure. In the next portion of the cycle, the pistons 2 move outward, transferring energy to crankshafts 4 by means of connecting rods 3. This is the power stroke of the engine. The two rotatable crankshafts are mounted in relation to the engine body, and the connecting rods or linkages between each crankshaft and its associated piston drive the pistons or extract energy from the movement of the pistons. The crankshafts are timed to advance the pistons at substantially the same time. The power stroke ends as the pistons 2 draw near to uncovering wall inlet ports 9. The exhaust port with valve 6 opens at the end of the power stroke, and combusted gas is discharged from the cylinder volume. This cylinder volume is composed of combined volumes 12 and chamber 16. The combusted gas is discharged through an exhaust manifold system 8. Shortly afterward, the pistons 2 pass outward sufficiently to uncover wall intake ports 9. While the pistons 2 are outward past the wall ports 9, gas 19 enters through the wall ports 9 and displaces remaining burnt gas within the cylinder volumes 12 and chamber 16. As the pistons 2 reach BDC, they reverse their direction of motion and begin to move inward again.
A third portion of the cycle comprises the operation of the engine between the time of beginning of inward motion of the pistons 2 and the time at which the engine again begins to compress gas for a new cycle. During this time interval, the pistons move a substantial distance inward. The end of the interval is defined by the effective closure of the exhaust valve 6. A key aspect of our invention concerns the positions of pistons 2 and the total operating volume of the engine at the times of opening and closing of the exhaust valve 6. The total operating volume is equal to the volume of the combustion chamber 16 plus the combined volumes of the two volumes 12. This total operating volume will now be referred to simply as “V” with a designating subscript that indicates the value of V at a particular point in the engine's cycle. With reference to the P-V diagram of
V
2
/V
1
=R
C
V
5
/V
1
=A
And ARC≥36.33+8788 e−0.375 Rc as has been discussed in detail above.
This second preferred engine construction is considered to be of great value for use in distributed power generation. The engine is imagined to be coupled to one or more electric generators of any desired type. In addition, the waste energy is to be collected at available locations. Approximately 60% of the energy in the engine fuel will be delivered as work to the electrical generator(s). Of that work, as much as 96% to 98% may be converted to electrical energy. The waste energy comprises approximately 40% of the energy in the engine's fuel. A portion of that energy may be collected in the form of high-quality heat. The efficiency of collection and transfer of this heat may be in the general range of 75% to 80%. The heat is referred to as being of high quality because it can be collected at a very substantial temperature, in the general range of 100 degrees Celsius to as much as 300 degrees to 400 degrees Celsius. High-quality heat has great practical value for heating, producing hot water or steam, and for industrial process heat. Combining the two system efficiencies, the engine's efficiency of producing electrical power with the efficiency of collection and use of heat, provides an overall system efficiency of approximately 90%. In this fashion, our invention can be of immense value in reducing dependence on fossil fuels, or fuels of any kind. Our engines may use any of several suitable fuels such as natural gas or biomethane, dimethyl ether, methanol, diesel fuel, gasoline, or a combination of fuels. Some of these fuels may be obtained from renewable as well as geologic sources. Basic physical properties and design parameters of the above example engine are:
As mentioned, our cogeneration engine described above can provide both heat and electricity with a combined efficiency of 90% or greater, and causes no net increase in atmospheric greenhouse gas (e.g., CO2) in its operation when using a renewable fuel. This engine combined with a synchronous generator has a fuel consumption of approximately 0.148 kg/kWh when operating on ultra-low-sulfur diesel fuel. Electrical generation is at approximately 57% efficiency. Thus, our new engine technology represents a great advance toward reduction of global warming and climate change.
| Number | Date | Country | |
|---|---|---|---|
| 62969090 | Feb 2020 | US |
