An internally cooled internal combustion piston engine and method of operating a piston engine is provided, with the combination of liquid water injection, higher compression ratios than conventional engines, and leaner air fuel mixtures than conventional engines. The effective compression ratio of the engines herein is greater than 13:1. The engines may employ gasoline or natural gas and use spark ignition, or the engines may employ a diesel-type fuel and use compression ignition. The liquid water injection provides internal cooling, reducing or eliminating the heat rejection to the radiator, reduces engine knock, and reduces NOx emissions. The method of engine operation using internal cooling with liquid water injection, high compression ratio and lean air fuel mixture allow for more complete and efficient combustion and therefore better thermal efficiency as compared to conventional engines.
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1. A method of operating an internal combustion engine for use with a hydrocarbon fuel, said engine having at least one cylinder and a reciprocating piston therein, at least one air intake valve, at least one exhaust valve, and a fuel handling system with at least one fuel injector, said method comprising, at each engine cycle:
injecting, from a water injector coupled to a water source, liquid water into the cylinder any time from about 180° to about and 30° before TDC of said piston during a compression stroke, wherein the amount of water injected is greater than the amount of water that is present at the saturation point of water vapor in the ambient air in before the ambient air is taken into the cylinder and up through the at least one air intake valve, wherein the amount of water is in the range of about 105% to about 800% w/w of the amount of fuel being injected in the engine cylinder;
wherein a ratio of air to fuel provided to said at least one cylinder is greater than stoichiometric, and the engine has an effective volume compression ratio greater than about 13:1.
19. A method of operating an internal combustion engine, said engine using a hydrocarbon fuel with at least one cylinder and a reciprocating piston therein, an intake manifold with at least one air intake valve, at least one exhaust valve in fluid communication with an exhaust manifold, and a fuel handling system with at least one fuel injector, said method comprising:
injecting, via a water injector coupled to a water source, a predetermined quantity of liquid water into the cylinder at any time ranging from about 180° to about 30° before TDC of said piston during a compression stroke, wherein the amount of water injected is greater than the amount of water that is present at the saturation point of water vapor in the ambient air in that is taken into the cylinder and up through the at least one air intake valve, wherein the amount of water is in the range of about 105% to about 800% w/w of the amount of fuel being injected in the engine cylinder;
adjustably modulating, via a turbocharger or supercharger, a quantity of air forced into the intake manifold or cylinder during said compression stroke;
wherein a ratio of air to fuel provided to said at least one cylinder is greater than stoichiometric,
and the engine has an effective volume compression ratio greater than about 13:1.
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sensing, via a temperature sensor in the cylinder coupled to a control device, a real-time temperature value in said cylinder;
sensing, via a temperature sensor in the exhaust manifold coupled to a control device, a real-time temperature value of combustion exhaust products;
receiving, at said control device, one or more real-time temperature values from said temperature sensor; and
responsively adjusting, via a programmed control device, the amounts of water injected and the air to fuel ratio provided to the said at least one cylinder.
21. The method of
0. 22. The method according to claim 19 wherein the liquid water is injected in the cylinder as a continuous stream, as intermittent injection, or as an atomized spray, said atomized spray being finally atomized or coarsely atomized.
0. 23. The method according to claim 19 wherein the air to fuel ratio greater than stoichiometric is expressed as a value or λ said λ being about 1.2 or greater.
0. 24. The method according to claim 23 wherein λ is greater than about 1.5.
0. 25. The method according to claim 23 wherein λ ranges from about 1.2 to about 8.0.
0. 26. The method according to claim 1, wherein the fuel is gasoline and the air to gasoline fuel is about 14.7:1 w/w.
0. 27. The method according to claim 1 wherein the amount of water injected ranges from 110% to 800% of the amount of fuel being injected.
0. 28. The method according to claim 1 wherein the amount of water injected ranges from 125% to 800% of the amount of fuel being injected.
0. 29. The method according to claim 19 wherein the amount of water injected ranges from 110% to 800% of the amount of fuel being injected.
0. 30. The method according to claim 19 wherein the amount of water injected ranges from 125% to 800% of the amount of fuel being injected.
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This application
where Qin is thermal energy put into the engine, and mechanical energy, or work is Wout. A cyclic heat engine, even in the ideal limit, cannot completely convert the net heat input into work output, so some of the input heat energy has to be dissipated into the environment as waste heat Qout. The thermal efficiency of a cyclic heat engine is defined as:
where ηth is a dimensionless efficiency factor. This is a performance measure of a device that uses thermal energy, such as an internal combustion engine.
The theoretical maximum efficiency of any heat engine is given by the Carnot theorem, which posits that the theoretical maximum efficiency of any heat engine depends on the difference between hot and cold temperature reservoirs in an ideal thermodynamically reversible engine. This maximum efficiency in a Carnot engine is defined to be:
where TC is the absolute temperature of the cold reservoir, and TH is the absolute temperature of the hot reservoir. Therefore, efficiency in a Carnot engine is a factor of the temperature gradient between the hot and cold reservoirs.
The Otto cycle is another ideal thermodynamic cycle that relates engine efficiency of internal combustion spark-ignition engines to compression ratio. The geometry of Otto cycle employs two adiabatic and two constant volume processes. Otto cycle efficiency, which assumes perfect gas law behavior, can be expressed as:
where r is the volume compression ratio, and γ=Cp/Cv, the specific heat ratio, of heat capacity at constant pressure (CP) to heat capacity at constant volume (CV). A similar formula for diesel engines relates compression ratio (and combustion expansion ratio) to efficiency in diesel (compression ignition) engines. The specific heat ratio is also known as the “isentropic expansion factor.” The specific heat ratio of the air-fuel mixture γ varies with temperature and the heat capacity of the fuel vapor, but is generally close to the air value of 1.4. When using this standard value, the cycle is called an “air-standard cycle.” Because γ is always greater than 1, engine efficiency in the Otto cycle is directly related to compression ratio. Therefore, high compression ratio engines will operate more efficiently than a lower compression ratio engine, all other factors being equal.
Temperature control in engines is also an important factor affecting engine efficiency. The Carnot cycle suggests that the higher the temperature after the ignition at top dead center (TDC) of the piston in the cylinder (i.e., the highest temperature in the engine), the larger the temperature differential will be, which leads to greater efficiency. However, real world inefficiencies include the lack of complete mixing of the fuel with air, the rate of combustion, and the air/fuel ratio required for effective ignition. Most engines operate at a near stoichiometric air/fuel ratio. Combustion under these conditions creates excess heat that is not converted into mechanical work. This excess heat must be rejected using a radiator or through the exhaust. The high combustion temperatures created also create undesirable NOx emissions.
Temperature control in modern engines is usually accomplished by a cooling jacket surrounding the engine, transporting heat to a heat exchanger (radiator) that rejects excess heat to the environment and maintains the engine within operating temperature limits. The use of a conventional radiator in such a fashion is termed herein as external cooling. Most modern internal combustion engines are liquid (or water) cooled (externally cooled) using either water or some other liquid coolant, which circulates through the engine and runs through the heat exchanger. Alternatively, some engines are characterized as “air cooled,” typically because they lack a radiator. Instead, most air cooled engines have additional fins integral with the engine block or cylinders to convect and radiate heat away from the engine.
Even in the most efficient liquid or air cooled conventional engines, the requirement to shed heat through the cooling system significantly decreases engine efficiency. Approximately 40% of engine heat is dissipated in the radiator or cooling fins, which is lost energy, some part of which could still theoretically be useable as mechanical energy. Thus, reducing this heat loss, and converting excess heat to useful mechanical energy, is an important unmet need in engine design. Conventional automobiles are only about 20% efficient at converting the energy in gasoline to mechanical energy. The remaining 80% or so of the energy in the fuel is lost to the environment through the cooling system and heat exchanger (radiator) and as exhaust heat. Thus, if the heat loss through the radiator (or otherwise dissipated to the environment) could be substantially reduced, engine efficiency could be substantially improved.
The compression ratio in engines which use fuels like gasoline or natural gas is limited by the need to control engine knock, which is caused by pre(auto)-ignition of the fuel prior to the desired ignition from firing of the spark plug. During pre-ignition, fuel ignites during the compression stroke in an uncontrolled fashion due to the high temperatures generated in the cylinder during compression. Such pre-ignition wastes energy and could lead to engine damage if uncontrolled. To avoid engine knock, conventional spark ignition engines are generally limited to an effective compression ratio of about 10:1, with up to 12:1 possible with more expensive high octane fuel.
An additional factor affecting engine performance is the air (oxygen) to fuel ratio. Stoichiometric air provides one mole of molecular oxygen per mole of carbon and 0.5 mole of molecular oxygen per mole of hydrogen in the fuel. The amount of air for true stoichiometric oxygen is dependent on the exact chemical makeup of the fuel, but is approximately 14.7:1 weight/weight (w/w) for gasoline and diesel engines (i.e., 1 gram of fuel to 14.7 grams of air). Engines are typically run rich during cold start and high load operation, but when run rich, there will be non-combusted fuel and thus wasted energy and additional air pollution. Engines normally run most efficiently at about a stoichiometric mixture, but there are theoretical bases for efficient engine operation under lean conditions, of greater than stoichiometric oxygen.
In one aspect, there is provided a system and method for operating a spark or compression-ignition engine at elevated compression ratios compared to conventional engines, using lean air fuel ratios and liquid water injection to control the temperature inside the cylinder during both the compression and power strokes. The higher compression allows for higher thermal efficiency in accordance with the Otto or compression ignition (diesel) ideal engine cycles, and also allows for reliable ignition of leaner fuel mixtures. The liquid water injection reduces the work during compression by reduction in pressure, controls knock and provides temperature control. The liquid water injection also reduces the need for external cooling leading to less heat loss to the radiator and thus higher efficiency. The combination of liquid water injection and other heat management features, including using very lean air/fuel mixtures, can eliminate totally or substantially reduce the need for a radiator (i.e., a smaller radiator can be employed) than conventional engines, and have substantially lower heat losses to the environment. Engines described herein therefore produce much higher thermal efficiency compared to conventional engines, as well as lower emissions.
According to one embodiment, there is provided an internal combustion engine for use with a hydrocarbon fuel, with at least one cylinder and a reciprocating piston therein, at least one air intake valve providing air into the at least one cylinder, at least one exhaust valve, and a fuel handling system with a fuel injector providing fuel into the at least one cylinder, comprising a water injector coupled to a liquid water source for injecting liquid water (by direct injection) into the cylinder at any time from about 180° to about 30° before TDC during a compression stroke of the piston, wherein the amount of liquid water injected is greater than the amount of water that is present at the saturation point of water vapor in the ambient air in the cylinder. Alternatively, the engine may be provided with an air intake manifold in fluid communication with water or fuel injectors or both, such that the water or fuel or both are port injected into the intake manifold rather than directly into the cylinder. In this port injection embodiment, the water injector will be controlled to inject liquid water at a somewhat earlier time in the cycle, typically from about 300° to about 180° before TDC when the intake valve is still open. The engines have a ratio of air to fuel provided to the at least one cylinder that is greater than stoichiometric.
The engines have an effective compression ratio greater than 13:1. In an embodiment, the engine has an effective compression ratio greater than 15:1. In an embodiment, the compression ratio can be as high as 20:1, or higher. For example, in spark-ignition engines typically operating on gasoline (petrol) ethanol or natural gas, the compression ratio ranges from about 13:1 to about 25:1 and in another embodiment, from about 13:1 to about 20:1. In other embodiments, it is, about 16:1 or about 17:1 or about 18:1 or about 19:1 or about 20:1 or about 21:1 or about 22:1 or about 23:1 or about 24:1 or about 25:1. In diesel fuel engines, in an embodiment the compression ratio may be lower, for example, from about 12:1 or about 13:1, including all of the ranges and values described herein above, but, in addition, in other embodiments it is higher, e.g., it may range up to about 35:1 or higher, for example, about 25:1, or about 26:1 or about 27:1 or about 28:1 or about 29:1 or about 30:1 or about 31:1, or about 32:1, or about 33:1, or about 34:1 or about 35:1.
In an embodiment, when liquid water is directly injected into the cylinder, the injection is timed to occur at from about 180° to about 30° before TDC during a compression stroke of the piston. The internal combustion engine of the present invention includes, in one embodiment, a water injector for direct injection into the cylinder, and in another embodiment water injector for port injection into the cylinder, and in another embodiment two water injectors, one directly into the cylinder and the other through a port. It is to be understood that direct water injection can occur at any time during the cycle from about 180° to about 30° before TDC during a compression stroke of the piston. Moreover the water injection may be at the same or at a different position in the compression stroke of the piston, from cycle to cycle of the compression stroke. For example in one stroke, it may be at position of about 60° before TDC, and in another cycle at about 90° before TDC, the timing and the amount being controlled, as described herein below. In an embodiment, the water injection may range from about 90° to about 60° before TDC, for example, when the water is directly injected into the cylinder.
The above-description is also applicable when the liquid water is port injected. In an embodiment when port injected; however, the liquid water can be port injected at a value outside of 30° to 180° before TDC, such as, for example, at about 300° to about 180° before TDC.
Further in an embodiment, an amount of liquid water injected in an engine cycle ranges at about 1.05 to about 10 times the amount of water vapor carried by air saturated with water vapor at ambient temperature of 25° C. at the engine intake.
Alternately, in another embodiment, an amount of liquid water injected in an engine cycle is about 20% to about 800% w/w of the amount of fuel being injected in the engine cycle. In one embodiment, controls are implemented such that at higher compression ratios, the greater is this % difference. The controls implemented maintain compression end temperature at specified value. As in-cylinder temperature is not measured, the control may be implemented through ambient pressure, temperature, humidity and in-cylinder pressure relative to engine load and engine RPM (rotations per minute).
According to a further aspect, there is provided a method of operating an internal combustion engine for use with a hydrocarbon fuel, the engine having at least one cylinder and a reciprocating piston therein, at least one air intake valve providing air into the at least one cylinder, at least one exhaust valve, and a fuel handling system with a fuel injector providing fuel into the at least one cylinder. The method comprises: injecting liquid water into the cylinder at any time from about 180° to about 30° before TDC of the piston during compression, wherein the amount of liquid water injected is greater than the amount of water that is present at the saturation point of water vapor in the ambient air in the cylinder; wherein a ratio of air to fuel provided to the at least one cylinder is greater than stoichiometric; and, wherein the engine operates at an effective compression ratio of greater than 13:1.
Further to this embodiment, the method includes injecting an amount of liquid water in an engine cycle of about 1.05 to about 10 times an amount of water vapor carried by air saturated with water vapor at ambient temperature of 25° C. at the engine intake.
Further to this embodiment, the method includes injecting an amount of liquid water in an engine cycle of about 20% to about 800% w/w of the amount of fuel in the engine cycle.
As described herein in an embodiment the liquid water is injected into the cylinder any time from about 180° to about 30° before TDC. In another embodiment, water is injected any time from about 45° to about 120° before TDC, and in another embodiment, from about 60° to about 90° before TDC. It is understood that any value or range from about 180° to about 30° before TDC is contemplated, for example, 180°, 179°, 178°, 177°, 176°, 175°, 174°, 173°, 172°, 171°, 170°, 169°, 168°, 167°, 166°, 165°, 164°, 163°, 162°, 161°, 160°, 159°, 158°, 157°, 156°, 155°, 154°, 153°, 152°, 151°, 150°, 149°, 148°, 147°, 146°, 145°, 144°, 143°, 142°, 141°, 140°, 139°, 138°, 137°, 136°, 135°, 134°, 133°, 132°, 131°, 130°, 129°, 128°, 127°, 126°, 125°, 124°, 123°, 122°, 121°, 120°, 119°, 118°, 117°, 116°, 115°, 114°, 113°, 112°, 111°, 110°, 109°, 108°, 107°, 106°, 105°, 104°, 103°, 102°, 101°, 100°, 99°, 98°, 97°, 96°, 95°, 94°, 93°, 92°, 91°, 90°, 89°, 88°, 87°, 86°, 85°, 84°, 83°, 82°, 81°, 80°, 79°, 78°, 77°, 76°, 75°, 74°, 73°, 72°, 71°, 70°, 69°, 68°, 67°, 66°, 65°, 64°, 63°, 62°, 61°, 60°, 59°, 58°, 57°, 56°, 55°, 54°, 53°, 52°, 51°, 50°, 49°, 48°, 47°, 46°, 45°, 44°, 43°, 42°, 41°, 40°, 39°, 38°, 37°, 36°, 35°, 34°, 33°, 32°, 31°, 30°, before TDC.
If the water is port injected, the injection may occur from about 300° to about 180° before TDC. It is understood that any value or range from about 180° to about 300° before TDC is contemplated, for example, 300°, 299°, 298°, 297°, 296°, 295°, 294°, 293°, 292°, 291°, 290°, 289°, 288°, 287°, 286°, 285°, 284°, 283°, 282°, 281°, 280°, 279°, 278°, 277°, 276°, 275°, 274°, 273°, 272°, 271°, 270°, 269°, 268°, 267°, 266°, 265°, 264°, 263°, 262°, 261°, 260°, 259°, 258°, 257°, 256°, 255°, 254°, 253°, 252°, 251°, 250°, 249°, 248°, 247°, 246°, 245°, 244°, 243°, 242°, 241°, 240°, 239°, 238°, 237°, 236°, 235°, 234°, 233°, 232°, 231°, 230°, 229°, 228°, 227°, 226°, 225°, 224°, 223°, 222°, 221°, 220°, 219°, 218°, 217°, 216°, 215°, 214°, 213°, 212°, 211°, 210°, 209°, 208°, 207°, 206°, 205°, 204°, 203°, 202°, 201°, 200°, 199°, 198°, 197°, 196°, 195°, 194°, 193°, 192°, 191°, 190°, 189°, 188°, 187°, 186°, 185°, 184°, 183°, 182°, 181°, or 180° before TDC.
As defined hereinabove, in an embodiment, the amount of liquid water injected ranges from about 1.05 times to about 10 times the amount of water vapor carried by air saturated with water vapor at ambient temperature of 25° C. at the engine intake. Thus for example, in various embodiments, the amount of water injected may be at any values in the range described hereinabove or may range from about 1.05 to about 10 times the amount of water vapor carried by air saturated by water vapor at ambient temperature at the engine intake such as, for example, 1.25, 1.50, 1.75, 2.00, 2.25, 2.50, 2.75, 3.00, 3.25, 3.50, 3.75, 4.00, 4.25, 4.50, 4.75, 5.00, 5.25, 5.50, 5.75, 6.00, 6.25, 6.50, 6.75, 7.00, 7.25, 7.50, 7.75, 8.00, 8.25, 8.50, 8.75, 9.00, 9.25, 9.50, 9.75, or 10.00. times the amount of water vapor carried by air saturated by water vapor at ambient temperature of 25° C. at the engine intake.
In alternative embodiment, the amount of water injected ranges from about 20% to about 800% w/w of the fuel. Any range or value from about 20% to about 800° w/w fuel can be utilized, e.g., 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115%, 120%, 125%, 130%, 135%, 140%, 145%, 150%, 155%, 160%, 165%, 170%, 175%, 180%, 185%, 190%, 195%, 200%, 205%, 210%, 215%, 220%, 225%, 230%, 235%, 240%, 245%, 250%, 255%, 260%, 265%, 270%, 275%, 280%, 285%, 290%, 295%, 300%, 305%, 310%, 315%, 320%, 325%, 330%, 335%, 340%, 345%, 350%, 355%, 360%, 365%, 370%, 375%, 380%, 385%, 390%, 395%, 400%, 405%, 410%, 415%, 420%, 425%, 430%, 435%, 440%, 445%, 450%, 455%, 460%, 465%, 470%, 475%, 480%, 485%, 490%, 495%, 500%, 505%, 510%, 515%, 520%, 525%, 530%, 535%, 540%, 545%, 550%, 555%, 560%, 565%, 570%, 575%, 580%, 585%, 590%, 595%, 600%, 605%, 610%, 615%, 620%, 625%, 630%, 635%, 640%, 645%, 650%, 655%, 660%, 665%, 670%, 675%, 680%, 685%, 690%, 695%, 700%, 705%, 710%, 715%, 720%, 725%, 730%, 735%, 740%, 745%, 750%, 755%, 760%, 765%, 770%, 775%, 780%, 785%, 790%, 795%, or 800%.
In another embodiment, the amount of water injected range from about 40% to about 400% (w/w) of the amount of fuel being injected in the engine cylinder.
In another embodiment, the amount of water injected range from about 50% to about 300% (w/w) of the amount of fuel being injected in the engine cylinder.
In still another embodiment, the amount ranges from about 60% to about 200% (w/w) of the amount of fuel being injected in the engine cylinder.
The loss of dissipated heat in the internal combustion engine is minimized by utilizing water injection in which the amount of liquid water injected is greater that in conventional combustion engines.
The objects, features and advantages will become apparent to one ordinary skill in the art, in view of the following detailed description taken in combination with the attached drawings, in which
This disclosure provides two-stroke or four-stroke, or higher stroke combustion engines with at least one cylinder employing direct liquid water cylinder injection and/or port injection features to regulate the temperature of the combustion process, as the combustion is in progress. The engine may thus include a spark plug, or a glow plug, a plasma igniter, or a laser igniter providing for spark ignition, plasma ignition, pilot ignition, laser ignition, free radical ignition or spark assist compression ignition and operate with gasoline (petrol), alcohol or combination thereof or natural gas as fuel. Alternatively, the engine may employ compression ignition, such as a diesel (kerosene) powered engine with or without additional assistance of spark, plasma or laser.
Referring to
In
In the embodiment of
In a further embodiment, shown in
As shown in the embodiment of engine 50 in
Further, in the embodiment of the engine 50 of
A further embodiment is shown in
In another embodiment,
A further embodiment is shown in
In the engine 450 of
Referring to matrix 500 of
The engines of the matrix 500 of
The engines of the matrix 500 of
Further, in the engines of the matrix 500 of
The sum of these features results in engines 50, 150, 250, 350, 450, of
Further, in the engines of the matrix 500 of
In one embodiment, the amount of water to be injected per cycle is controlled in relation to inlet pressure, temperature, relative humidity and current engine operating parameters as compression end pressure, load and rpm. The microcontroller described below with respect to
Water Injection
One factor allowing for greater compression in each of the engine embodiments is internal cooling during the compression cycle by the addition of liquid water in the engine's cylinder(s) during the compression stroke. Injecting liquid water into the engine cylinder performs several important functions. The liquid water internally cools the interior of the cylinder during compression by absorbing the heat produced during the compression. This internal cooling has the effect of reducing the work required for compression, and also has the effect of allowing greater compression ratios without engine knock.
The amount of liquid water injected into the engine cylinder during a compression cycle is a function of the saturated water vapor capacity of ambient air, or a function of fuel on a weight basis. In an embodiment, the amount of liquid water injected per cycle is greater than the amount that is required to saturate air at 20° C. Alternatively, the amount of liquid water injected per cycle may be about 1.05 to about 10 times the amount of water vapor carried in ambient air in the engine inlet. Alternatively, the amount of liquid water may range from about 20% to about 800% w/w of the amount of fuel injected per compression stroke. The amount of liquid water injected may be metered to optimize internal cooling, minimization of work required during compression, minimization of engine knock, and to provide or prevent liquid water droplets mixed with gases at the moment of ignition. The control of the liquid water injection may be based on pressure and temperature sensors in the engine that are coupled to a computer control system that controls the water injection system as described below with respect to
A direct liquid water injector 46 may inject liquid water into the cylinder as a liquid droplet stream, either continuously, intermittently, or as a pulsed stream. In another embodiment, the liquid water may be injected as a “coarse” spray or an atomized flow. In another embodiment, the liquid water may be injected as a stream directed to cool internal surfaces of the cylinder head and piston top. In yet another embodiment, the liquid water is port injected as an atomized spray into the intake manifold. Any combination of these embodiments may be used and other embodiments of injecting liquid water are also possible and within the scope of this concept. In one aspect, the size of liquid droplets will determine rate of heat transfer as the interface area will increase with decrease in droplet size. The size of the droplets is controlled by the liquid water injector settings (and other factors such as timing and metering) and will be controlled according to the required rate of heat absorption (evaporation) as dictated by compression temperature rise (sensed through pressure). In one embodiment, the smaller the required rate of heat absorption, the coarser (less atomized) could be the injected water spray. In one embodiment, the size of the average liquid water droplets are spherical-like in a “fine” size ranges from about 0.5 μm to about 25 μm in diameter while the size of the average liquid water droplets in a “coarse” size range may be from about 25 μm to about 100 μm.
In several of the engine embodiments, at least a portion of the liquid water is injected into the cylinder (by a water injection direct in the cylinder or in the air intake) during the first part of the compression stroke, between about bottom dead center (BDC) (i.e., about 180° before TDC) and about 30° before TDC. The presence of liquid water during the compression stroke will reduce the work required in the compression stroke, as the liquid water will absorb latent heat from hot air during compression and thus reduce its temperature. The enthalpy of vaporization, (Δvap) of water at standard pressure is about 40.7 kJ/mol, equivalent to about 2250 J/g. This is the energy required to convert liquid water to steam. The enthalpy of vaporization of liquid water depends on pressure and reduces to zero at the critical point, 374.4° C. at 22242 kPa (about 222 bar). For pressures of 10, 30, 50, or 100 bar, the enthalpy of vaporization is about 2015, 1796, 1640, or 1317 J/g respectively, which is still substantial. As pressure is related to temperature, the pressure will be proportionally reduced in spite of small increases in mass and the gas constant R. The reduction in pressure during compression will therefore reduce the work necessary to achieve compression. The work required for compression depends only on pressure as a given volume is fixed (δW=P·dV), where W is the work, P is Pressure, and dV is volume differential.
Another effect of added liquid water during the compression stroke is to reduce or eliminate the need for external jacket cooling. The need for external cooling arises due to very high gas temperatures and inevitable heat transfer to internal surfaces in the cylinder, particularly the cylinder head, but also the piston face. The injected liquid water may form droplets in the cylinder that cools the gases in the cylinder during compression.
Alternatively, liquid water injection may be configured to spray and cool internal surfaces of the engine (cylinder head and piston head) rather than directly cool the gases in the cylinder. In one embodiment, the fuel is expected to be injected predominantly in radial direction and water predominantly in axial direction such that these may not interfere substantially. An embodiment of this concept is shown in
In operation, some of the liquid water injected may remain unevaporated as liquid droplets mixed with other gases in the cylinder at the moment of ignition. This liquid water converts to steam after the ignition. Thus, there is provided a higher density medium before the ignition and substantially greater expansion of the water droplets leading to higher efficiency. This embodiment is based on the principle that liquid water expands in volume about 1600-fold when converted to steam (at 100° C. at standard pressure). Furthermore, the vaporization of liquid water during combustion will provide a denser medium and enhanced expansion pressure, from the greater volumetric expansion of water to steam as compared to other gases in the cylinder during combustion. This embodiment may also allow for cooler exhaust gases due to the high latent heat of vaporization (enthalpy of vaporization) water. In this case, less heat would need to be rejected to keep the engine temperature within its operating limits.
In an alternative embodiment, whether directly input to the port or cylinder, the amount of liquid water added during the compression stroke is metered to minimize the presence of liquid water when combustion is initiated. This addresses the concern that liquid water present at the beginning of ignition will absorb heat from the combustion gases, reducing both temperature and pressure in the power stroke, for the same reasons that the work required during compression will be reduced when liquid water is present—pressure and temperature are reduced from the latent heat of vaporization as liquid water is vaporized.
In another embodiment, whether directly input to the port or cylinder, the metered amount of liquid water may be injected into the cylinder at a time ranging from about 180 to about 30 degrees before TDC. In the embodiment shown in
In a further embodiment, the engines employ a mixture of liquid water with an alcohol, or other additives that are commonly added to water in engines to lower the freezing point of liquid water, such as, e.g., methanol, ethanol, isopropanol. The use of such an alcohol additive prevents the liquid from freezing in cold weather, which is an important consideration in for example, automotive applications in cold climates. The liquid water-alcohol mixture ratio may range from about 0% to about 50% by weight. As used herein, with respect to the water-alcohol mixture ratio, it is understood that ranging from about 0% means that an amount of alcohol (or like additive) is present.
Lean Fuel Mixture
In combination with various embodiments of the engines as described herein is the use of lean air/fuel mixtures. That is, the fuel is injected either into the inlet air stream or injected directly into the cylinder with a fuel injector. The amount of fuel is adjusted to keep the air/fuel mixture lean. This means that a molar excess of oxygen, in air, is employed in the engines. Stoichiometric air to gasoline fuel is approximately 14.7:1 (w/w). The ratio of actual amount of air to stoichiometric air for the injected fuel is expressed as λ (i.e., the relative air fuel ratio), where λ=1 is defined as stoichiometric air. This is referred to in the engine literature as the relative air fuel ratio. As defined herein, λ>1 is a lean ratio, and λ<1 is a rich (oxygen deficient) ratio.
Combustion efficiency may increase with lean mixtures, because the limiting reagent is air rather than fuel. At rich mixtures, there will be non-combusted fuel in the exhaust, which is wasted energy. Combustion temperatures are also lower with lean mixtures, leading to reduced heat losses. Of course, there is an optimal air-fuel ratio that depends on the fuel, temperature, and pressure at the moment of ignition. A key feature of the engines described herein is that λ can be increased far more than in conventional spark ignition engines because the instant engine is capable of operating at much higher compression ratios than conventional engines.
In one aspect, liquid water injection in the amounts and timing relative to TDC as described herein achieves more uniform mixing of fuel and air than in conventional engines. In another aspect, the high compression, along with excess oxygen (air) allow for higher temperature and pressure prior to ignition leading to higher rate and extent of combustion and consequent higher efficiency. Thus, lean mixtures are expected to decrease engine knock by increasing the auto ignition temperature. Conventionally, gasoline engines will not operate reliably at λ>1.5, but the engines described herein are expected to operate efficiently at λ>1.5 to as much as about λ=8. In an embodiment, the engines described herein operate with the air to fuel ratio λ greater than about 1.2; in another embodiment, the air to fuel ratio λ is greater than about 1.5. In another embodiment, the air to fuel ratio λ is greater than about 2.0. In another embodiment, λ is greater than about 4.0. In another embodiment, the air to fuel ratio λ is greater than about 6.0. In an embodiment, the air to fuel ratio is in a range of about λ≥1.2 to about λ≤8.0; or about about λ≥2.5 to about λ≤5.5; or about λ≥3.5 to about λ≤5.0.
The inlet air or fuel or air/fuel mixture may be heated individually or together prior to injection or inspiration into the cylinder. Heating the air or fuel or air fuel mixture can transfer useful energy from the exhaust back to the engine. Furthermore, heating the air/fuel mixture provides better and more efficient mixing of air and fuel in the cylinder, and heated liquid fuels at or below the critical state are expected to evaporate more efficiently and mix better with air. Supercritical liquid fuels will flash into vapor and mix very readily with air. In such an embodiment, a liquid fuel may be subject to a temperature and pressure condition above its critical point, where distinct liquid and gas phases do not exist. Supercritical fluids having properties between those of a gas and a liquid for use with combustion and/or compression stroke engines include, but are not limited to: Methane, Ethane, Propane, Ethylene, Propylene, Methanol, Ethanol and Acetone. The air or fuel (or both) may therefore be heated to a temperature selected from about 30° C. to about 150° C. In a further embodiment, the fuel/air mixture at the air to fuel ratio is heated before the injection of water to a value ranging from about 30° C. to about 80° C. or ranging from about 40° C. to about 80° C., or ranging from about 50° C. to about 80° C., or to a value of about 80° C. or greater before the injection of water.
Engine Temperature Control
If an embodiment where air or fuel is heated, the heat is supplied from a heat exchanger 71 or like device that captures heat from the exhaust and transfers some of the exhaust heat to the air or fuel. This is an aspect that transfers heat that would otherwise be wasted and lost to the environment to useful work. Inlet air may also be preheated in cold start conditions.
In order to control the amount of cooling affected by added liquid water during the compression stroke, the engines may employ one or more temperature and pressure sensors at various locations. As shown in
The amount of cooling required is based on the maximum operating temperature of the various components of the engine, above which some part will melt or deform or lubrication may fail. The conventional solution to engine temperature control is a heat exchanger (radiator) with a fluid (engine coolant) that circulates through the engine and conveys excess heat out of the engine into the environment via the radiator. In practice, the amount of wasted heat in conventional engines as typically at least 40%. From the Carnot theorem, some of this wasted heat theoretically is thermodynamically available for conversion to mechanical energy.
Thus, in an embodiment, the engines additionally employ sufficient liquid water added during the compression stroke to cool the engine to the point that a radiator will not be necessary. In a further embodiment, the combustion engines described herein provides a method to reduce or eliminate waste heat that needs to be rejected to the environment, because of the liquid water injected into the cylinder. The amount of liquid water would be metered according to data provided by the temperature and pressure sensors. In an embodiment, the liquid water injected into the engine may be preheated by circulation from within the engine, thereby reducing heat losses to the environment. As noted elsewhere, the liquid water may be heated to about 80° C. or even higher in high pressure environments. Further features that are expected to assist in cooler internal temperatures are the lean fuel mixtures (λ>1.5), and also the high effective compression ratios. By the term “internal temperature” is meant the temperature at the cylinder head, which is typically the warmest part of an engine. The high effective compression ratios are expected to produce a cooling effect due to the greater volumetric expansion of the cylinder during the power stroke as compared to conventional lower compression ratio engines.
If the engines employ a radiator (e.g., a heat exchanger) and liquid coolant for external cooling, the amount of liquid water injection and other cooling features of the engines are expected to reduce by at least 20% the amount of cooling (heat rejected to the coolant) required as compared to conventional engines. In other embodiments, the amount of heat rejection by the coolant is reduced by at least 40% by liquid water injection as compared to an engine without liquid water injection. In other embodiments, the amount of heat rejection by the coolant is reduced by at least 60% by liquid water injection as compared to an engine without liquid water injection. In other embodiments, the amount of heat rejection by the coolant is reduced by at least 80% by liquid water injection as compared to an engine without liquid water injection. In another embodiment, a coolant is employed with higher boiling point, e.g. using higher amounts of glycol or operating the cooling loop at higher pressures to allow for a cycle running at higher temperature.
In an embodiment, the engines may further require no external means of cooling. In another embodiment, the engines may be air-cooled, lacking a heat exchanger entirely. The amount of air cooling may be controlled by either controlling speed or intermittency of an electrically powered fan or by other means such as controlling operation of a flap. For example, a flap may control the flow of air, either actively using a flap and a fan or passively by controlling the surface areas exposed and flow controlled by opening of the inlet of air and exhaust. Another way to cool the engine and recover some of the waste heat is by circulating inlet air around the engine.
In alternative embodiments, the engines may be designed to operate at a higher temperature than conventional engines. Conventional engines are typically set to run at an internal temperature of about 91° C. (195° F.), but the engines of matrix 500 described herein may be set to run at an internal temperature of 100° C. to 175° C. with suitable changes in lubricant specifications. In one embodiment, the engine operates at a cylinder temperature ranging from about 85° C. to about 175° C. (i.e., the external temperature of the engine walls that the coolant or radiator water would experience when a cooling system is employed). In combination with the additional heat management features described herein, the engine requires no external means of cooling, but optionally, can include an exhaust radiator. For example, the engine operates at an external temperature ranging from about 85° C. to about 100° C. or ranging from about 85° C. to about 120° C., or ranging from about 85° C. to about 140° C., or ranging from about 85° C. to about 150° C. and the engine requires no external means of cooling.
In alternative embodiments, the engines may be insulated to minimize environmental heat loss, with cooling only coming from the injected water, and optionally, from heat captured in the exhaust for heating air and fuel. In this embodiment, the engine will be designed to run at a higher internal temperature than a normal engine. In one embodiment, the combustion chamber or cylinder, or a portion of the engine housing the combustion chamber, or the entire engine, is optionally heat insulated by a heat insulator 90 known to one of ordinary skill in the art.
In alternative embodiments, the engines recover heat in the exhaust or engine head by a heat exchanger 70 that transfers heat from the exhaust or engine head or both to pre-heating of liquid water, fuel and inlet air. If the engine has no other external cooling apparatus, such as a radiator, or if the engine is insulated to minimize environmental heat loss, pre-heating of the fuel and liquid water can be a means to transfer heat that would otherwise be lost to the environment through the exhaust to useful mechanical energy.
As a result of the cooling measures that control the temperature in the cylinder during the compression stroke, including liquid water injection and lean fuel mixtures, greater compression ratios are possible than with conventional engines. The engines of the present disclosure have an effective compression ratio greater than 13:1, but more preferably will have an effective compression ratio of greater than 15:1, or greater than 20:1 or greater than 25:1, or greater than 30:1 and can be as high as 40:1. The higher compression ratios achievable by the engines will be more efficient than conventional engines in part because of the higher compression ratios available by the apparatus and methods. According to the Otto cycle (or diesel cycle in the case of compression ignition engines), higher compression ratios theoretically will result in greater thermal efficiencies.
The fuel used by the engines may be a low alkane, such as natural gas, methane, ethane, n-propane, or isopropane, or lower alkyl aldehyde or lower alkyl ketone, wherein lower alkyl contains 1-6 carbon atoms (e.g., acetone), or a mixture thereof. Alternatively, the fuel may be gasoline (petrol) optionally mixed with an alcohol, e.g., ethanol. Other hydrocarbons may be used as fuels in the engines, such as other C4-C15 alkanes or mixtures thereof, or diesel (kerosene) fuels. Gasoline and low alkane fuels normally will likely require spark ignition. Diesel fuels are compression ignited and the engines may use a fuel mixture based on a diesel-like fuel, e.g., Diesel, Biodiesel, Kerosene, JP-8, JP-A and other Kerosene type fuels. Both types of fuels and ignition methods are compatible with the embodiments described. In an embodiment, the fuel may be a mixture of natural gas and a diesel-like fuel, wherein the diesel-like fuel causes ignition by compression but the bulk of the charge is from natural gas.
Ignition in the engines is from a spark plug, from compression ignition or the combination or another other means such as plasma discharge or laser. In the case of spark ignition, the timing may be varied depending upon the fuel, air fuel ratio, and amount of liquid water being injected or any combination thereof. Ignition is timed to be initiated prior to TDC because the entire fuel charge does not ignite instantaneously. The process of combustion once ignition is initiated takes time, as the flame front formed on ignition moves through the cylinder. For this reason, ignition, however initiated, is timed (e.g. under computer system control), to ensure that the maximum pressure from combustion occurs at or slightly after TDC. In spark ignition engines, “spark advance” (timing of the spark) is adjusted to optimize ignition timing to maximize efficiency. The engines described herein operating with lean fuel mixtures and high compression ratios may require less spark advance, due to better and more uniform mixing of fuel and a smaller combustion compartment, so that maximum pressure from combustion will be achieved more quickly than in conventional lower compression ratio engines.
Compression ignition engines, which have no spark ignition, will typically require adjustment of the timing of the fuel being injected into the cylinder because of the water cooling in the inventive engine. Thus, with higher λ values and more water injection, which equates to cooler internal temperatures, a computer control system described herein is operated to inject a diesel-type fuel in a compression ignition engine earlier in the compression stroke in order to get appropriately timed ignition and complete combustion.
For example, operating engine parameters may be dynamically adjusted according to power/speed output requirements of the engine (e.g., engine load) and temperature cooling targets in which the programmed microprocessor or programmable logic controller element 105 is responsive to the power setting (load) 113, e.g. such as indicated by engine RPM, and one or more engine operating conditions. For example, messages or information indicating engine operating conditions are continually sensed by sensor devices and communicate real-time values that are input to the programmable logic controller element 105 include, but are not limited to: a first temperature T1 value of the cylinder, a second temperature T2 of the cylinder at the exhaust manifold, and piston cylinder pressures P to determine the parameters for operation of the engine at a next cycle, e.g., parameters for providing control of air intake valves and/or fuel injector control and parameters for controlling liquid water injector/variable pump control.
As described herein, the amount of water injected is an amount that is greater than the amount of water that is present at the saturation point of water vapor in the ambient air in the cylinder. This amount is determinable by a skilled artisan. Standard textbooks of Thermodynamics contain a chapter/section on Humid Air. Saturation vapor mass can be approximately calculated by using ideal gas laws and Saturation Steam tables.
The amount of water vapor is constrained by the restrictions of partial pressures and temperature. Dew point temperature and relative humidity act as guidelines for the process of water vapor in the water cycle. The balance between condensation and evaporation gives the quantity called vapor partial pressure.
The maximum partial pressure (saturation pressure) of water vapor in air varies with temperature of the air and water vapor mixture. A variety of empirical formulas exist for this quantity; the most used reference formula is the Goff-Gratch equation:
where T, the temperature of the moist air, is given in units of Kelvin, and “p” the partial pressure of water, is given in units of millibars (hectopascals). Thus, at various temperatures, the partial pressure of water when the air is fully saturated can be determined using this formula. The amount that is injected is greater than that amount “p” calculated by this equation. For example, at 101.33 kPa and 20° C. air can have a maximum of about 1.5% vapor mass as compared to about 6.8% stoichiometric fuel mass. At 25° C. it is about 2%. In an embodiment, for example, the amount of water injected ranges from about 1.05 to about 10 times an amount of water vapor carried by air saturated with water vapor at ambient temperature of about 25° C. Thus, whatever value of “p” is calculated from the equation such as that given hereinabove, in this embodiment, the amount of water vapor injected is about 1.05 to about 10 times that value. This amount can then be converted to the amount of liquid water to be added by determining the number of moles this amount in vapor represents from the ideal gas law equation, PV=nRT, where P is the partial pressure of water to be added, V is the volume of the cylinder, T is the temperature in Kelvin, R is the ideal gas constant and n is the number of moles. Based on the number of moles of water calculated, one can calculate the amount of water to be injected in grams of water, since water has a molecular weight of 18 grams/mole. Since water has a density of about 1 gm/mL, one can then calculate the amount of liquid water to add in milliliters.
As described herein above, the optimal amount of water to be injected into the engine is calculated, for example, by the ECU (Engine Control Unit) via one or more equivalency tables. The equivalency tables contain information regarding how much water to inject into the engine under different operating conditions. One example of an equivalency table is “Water injection amount VS Intake Air Temperature (IAT) Multiplier”. This is very similar to the “Ignition Timing Retard VS IAT multiplier” table electronically controlled engines have, which retard the spark timing with increasing intake air temperatures to suppress detonation, except that in the present case, the water injection amount is multiplied by a small positive number that grows with increasing IATs in order to account for the increased charge cooling demand of a hotter intake charge taking into consideration various parameters, such as the rpm of the engine, the load, the temperature, pressure, fuel, and the like. Any other factor that has an impact on the propensity of knock to occur will have a table for it in the ECU that looks at the increase in the property, and counter it by retarding spark timing, increasing fueling, and increasing/decreasing the amount of water. The primary water injection equivalency table co-relates the amount of water, fuel, and engine load.
The water injection equivalency table is generated experimentally by running injection sweeps (holding the engine at a constant speed and load and varying the amount of water injection from 0 to 100%) at various speeds and loads so that the optimum amount of water is identified under most operating conditions. Data is interpolated in between test results to produce a full matrix for the points that sit in between actual test points, so when the engine runs through various loads and speeds the ECU knows exactly how much water it needs to inject in order to keep it running optimally.
More specifically, a method 200 for determining an optimal amount of water to inject for each piston per engine cycle is described in
Then, continuing to 225, there is determined via equivalency look-up tables a base water injection amount to inject based on the determined fuel mass. As described herein, the base water amount injected, as described hereinabove, is an amount of water injected that is greater than the amount of water that is present at the saturation point of water vapor in the ambient air in the cylinder. An example method to calculate a water injection amount is described herein above.
Continuing, in
Continuing to
That is, referring back to
It is understood, that the monitoring and control of the engine operations at any particular cycle of operation of the engine may be adjusted based on the operation during the prior cycle (including time average of a few prior cycles) to ensure ignition and water injections occurs at the proper crankshaft angle(s) in a stable manner.
Among other benefits, liquid water in the combustion chamber of an internal combustion engine reduce the internal temperature, which allows higher compression engines to operate without knock, thus allowing lower octane fuel to be used in higher compression and more efficient engines. The lower internal temperatures can also avoid and/or reduce NOx emissions, which increase with increased internal temperature. In addition, the engines described herein exhibit decreased amount of carbon monoxide relative to that produced by conventional engines.
As used herein, a top dead center (TDC) point of each cylinder corresponds to an orientation of the piston as at a point furthest away from the crankshaft within the cylinder. Measured in degrees, a crank angle (referring to the position of an engine's crankshaft in relation to the piston as it travels within the cylinder) for a piston that is at top dead center (TDC) of its compression stroke is zero crankshaft angle degrees. As used herein, a bottom dead center point (BDC) of each cylinder corresponds to an orientation of the piston closest to the crankshaft. A crank angle measured in degrees for a piston that is at bottom dead center (TDC) of its compression stroke is at 180 crankshaft angle degrees.
Unless indicated to the contrary, the temperatures used herein refer to ° C.
As referred herein, “ambient” is defined as the conditions of temperature and pressure outside of the energy storage system, e.g., about 25 degrees C. and 1 atm.
As used herein, the term “hydrocarbon fuel” refers to a fuel comprised substantially of hydrocarbons (more than 80% hydrocarbons by weight), but may additionally include other additives, such as alcohols, e.g., ethanol.
As used herein, the plural connotes the singular, and vice versa, the singular connotes the plural.
The following non-limiting examples are illustrative.
The electrical output shown is a direct measure of the efficiency of the engine at the various operating parameters. Efficiency was calculated by dividing measured electrical output by the thermal energy content (heat of combustion) of the fuel injected. Fuel was ULSD ultra low sulfur diesel. Particularly,
TABLE 1
Data for test engine with water injection and
supercharging, plotted in FIG. 10
Engine Load
Electrical
Water/Fuel
(Watts)
efficiency
ratio
λ
15 PSI Air Injection
1008
18.2
2.4
7.57
2055
32.0
2.1
6.54
3016
38.7
1.7
5.22
3920
44.4
1.6
4.51
3938
43.9
2.1
4.46
5037
55.3
1.5
4.46
5020
54.7
2.1
4.38
10 PSI Air Injection
1031
15.0
2.0
5.72
2021
25.8
1.8
4.74
3045
38.3
1.7
4.89
3976
46.1
1.6
4.32
4785
47.4
1.4
3.65
5 PSI Air Injection
1006
11.2
1.5
4.35
2021
19.0
1.3
3.65
3065
24.3
1.1
3.05
3065
24.5
1.5
3.05
4138
27.0
0.9
2.45
4145
26.7
1.2
2.43
4956
27.4
0.8
2.02
TABLE 2
Data for test engine with at various loads and constant air
pressure, without and without water injection (FIG. 11)
Engine Load
Electrical
Water/Fuel
(Watts)
efficiency
ratio
λ
10 PSI Water Injection
3045
38.3
1.7
4.89
3976
46.1
1.6
4.32
4785
47.4
1.4
3.65
No Water Injection
3044
32.8
0
6.09
4050
32.2
0
4.97
5000
31.5
0
3.84
As the engines described herein may be embodied in different forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any one of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within the spirit and scope, as defined in the appended claims. Therefore, all changes and modifications that fall within the metes and bounds of the claims or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.
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