Cracking of fuel for combustion engines

Abstract

Combustion engine system (10) comprising: a motor (12) comprising: a combustion chamber (20) for burning a fuel to produce work; a fuel injection system (18) for supplying a mixture of fuel and air to the combustion chamber (20); a fuel supply (16); and a fuel conditioning system (14) comprising: a heat circuit (28) and an additional heat circuit (32) for absorbing heat energy; a cracking vessel (24) for receiving fuel from the fuel supply (16) and for cracking carbon-carbon bonds of fuel hydrocarbons using the thermal energy obtained from the thermal cycle to produce cracked fuel; a fuel supply line (26) for supplying the cracked fuel to the engine (12); wherein the heat circuit (28) is designed to receive heat energy from the engine (12) and to transfer it to the cracking vessel (24) by means of a heat exchange fluid, the cracking vessel heating the fuel, and wherein the additional heat circuit (32) is designed to receive heat energy from an additional heat source (30), and to transfer it to the cracking vessel (24) by means of an additional heat exchange fluid, the cracking vessel heating the fuel, wherein the additional heat source is configured to provide heat energy until the engine (12) alone provides sufficient heat energy to break the carbon bonds of the fuel hydrocarbons; and further comprising a control system (34) for controlling the amount of heat energy, which the heat circuit (28, 32) receives from the engine (12) and the additional heat source (30).

Description

[0001] In an internal combustion engine, combustion occurs after a mixture of fuel and air is compressed upward during the stroke of a piston in a cylinder. A spark ignites a flame front that travels through the mixture, increasing its temperature and pressure, which drives the piston downward. At the top of the stroke, the fuel and air are compressed to a predetermined volume to ensure optimal engine performance and efficiency. The higher the compression, the more energy and power are obtained from a given amount of fuel.

[0002] The flame front, which travels through the fuel / air mixture, does not always advance smoothly and steadily. In some situations, one or more pockets of the mixture explode before they are reached by the flame front, terminating the optimal combustion process and creating a shock wave that dramatically increases pressure within the cylinder. This phenomenon is known as "knock" or "pinging." Engine knock can lead to engine wear and engine failure. To reduce engine knock, engine designers generally modify engine variables, including the compression ratio, fuel octane rating, and ignition timing.

[0003] Reducing an engine's compression ratio can reduce engine knock. The compression ratio is the ratio of the volume of a combustion chamber at its largest capacity to the volume of the combustion chamber at its smallest capacity. However, an engine's compression ratio is usually determined early in the design process based on efficiency goals and experience. Reducing the compression ratio generally reduces engine efficiency and fuel economy. Increasing the octane rating of the fuel used in the engine can reduce engine knock. Most fuel sold in the United States has an octane rating between 87 and 93. The tendency toward engine knock can be reduced by using a fuel with a higher octane rating.However, switching from a fuel with an 89 or 93 octane rating to one with a higher octane rating (e.g., 100 octane aviation gasoline) is costly. Higher octane fuel is also not always readily available. Delaying the initiation of the spark used during combustion can also reduce engine knock. However, this delay comes at the expense of the power obtained on the downstroke.

[0004] US 5,794,601 A discloses an internal combustion engine system with an engine, two tanks containing different fuels, and a fuel conditioning system. One of the fuels is regular gasoline, while the other fuel is inherently unsuitable for operating the internal combustion engine. This unsuitable fuel undergoes pretreatment in a cracking vessel so that it becomes suitable for operating the internal combustion engine. The heat for cracking is provided by the internal combustion engine. When the internal combustion engine is started, if the engine does not yet provide sufficient energy to crack the unsuitable fuel, the engine is operated with the other fuel, i.e., regular gasoline.

[0005] US 4,070,993 A discloses using heat energy from an additional heat source to split fuel hydrocarbons when the engine does not provide sufficient heat energy for this purpose.

[0006] DE 3422784 A1 discloses a fuel conditioning system in which carbon-carbon bonds of fuel hydrocarbons are broken down. The need for a cracking catalyst is not mentioned.

[0007] WO 2009 / 102500 A2 discloses an internal combustion engine system comprising an engine, a fuel supply to the engine, and a heat circuit including a fuel reservoir, a fuel cracking vessel, and an engine exhaust recirculation cooler. The fuel can be heated by means of the exhaust recirculation cooler, by means of an auxiliary heater in the heat circuit, and / or by means of an auxiliary heater directly at the cracking vessel. A control system regulates the use of the auxiliary heater. The internal combustion engine system has a single heat circuit that includes the fuel reservoir.

[0008] The present invention provides a high compression ratio internal combustion engine that reduces knock without resorting to high octane fuels or ignition retardation.

[0009] A fuel conditioning system includes a fuel reservoir, a cracking vessel, a heat source, a fuel supply line, a supplemental heat source, and a control system. The cracking vessel receives fuel from the fuel reservoir and cracks carbon-carbon bonds of hydrocarbons contained in the fuel. The heat source and the supplemental heat source provide heat energy to the cracking vessel to crack the carbon-carbon bonds of the fuel hydrocarbons. The control system controls the amount of heat energy the cracking vessel receives from the heat source and the supplemental heat source. The fuel supply line supplies cracked fuel to an internal combustion engine.

[0010] An internal combustion engine system includes an engine, a fuel supply, a fuel conditioning system, and a fuel delivery system. The engine has a combustion chamber for burning a fuel to generate work, and a fuel injection system for delivering a mixture of fuel and air to the combustion chamber. The fuel conditioning system includes a thermal cycle that absorbs thermal energy, a cracking vessel that receives fuel from the fuel supply and cracks carbon-carbon bonds of fuel hydrocarbons using the thermal energy absorbed by the thermal cycle, a supplemental heat source, and a control system. The fuel delivery system supplies cracked fuel to the engine.The thermal circuit is designed to receive thermal energy from the additional heat source, and the control system controls the amount of thermal energy the thermal circuit receives from the engine and the additional heat source.

[0011] A method for operating an internal combustion engine includes supplying a fuel to a cracking vessel, thermally cracking the fuel in the cracking vessel, supplying cracked fuel to an engine, and combusting the cracked fuel. The heat used to thermally crack the fuel is supplied from a heating fluid generated by burning the cracked fuel in the internal combustion engine or from a supplemental heat source, and a control system controls the amount of heat energy supplied to the heating fluid from the engine and the supplemental heat source.

[0012] The supply of heat energy to the cracking vessel occurs either via a heat cycle with a heat exchange fluid heated by the combustion engine or via an additional heat cycle with an additional heat exchange fluid heated by an additional heat source.

[0013] The drawings show: Fig. 1 a simplified schematic representation of an internal combustion engine system, Fig. 2 a simplified schematic representation of an internal combustion engine system according to the invention, and Fig. 3 a method for operating an internal combustion engine.

[0014] The present invention relates to an internal combustion engine system having the features as set out in independent claim 1.

[0015] The present invention also relates to a fuel conditioning system having the features as set out in independent claim 5.

[0016] The present invention further relates to a method for operating an internal combustion engine having the features as specified in independent claim 8.

[0017] Specific embodiments of the invention are set out in the respective dependent claims.

[0018] The present invention describes pre-combustion fuel cracking. Pre-combustion fuel cracking reduces the tendency toward engine knock and allows the engine to operate at a higher compression ratio. When cracked fuel is combusted in a combustion chamber, the flame front in the combustion chamber burns quickly and evenly, preventing pockets of the fuel / air mixture from detonating.

[0019] Fig. Figure 1 illustrates a simplified schematic diagram of an internal combustion engine system. The internal combustion engine system 10 includes an engine 12, a fuel conditioning system 14, and a fuel supply 16. The engine 12 is any type of internal combustion engine, including two-stroke, four-stroke, and six-stroke piston engines and rotary engines. The engine 12 includes a fuel injection system 18 and a combustion chamber 20. The fuel injection system 18 receives fuel and distributes the fuel to the combustion chamber 20 to form the fuel / air mixture that is combusted in the combustion chamber 20.

[0020] The fuel supply 16 supplies uncracked fuel, such as gasoline, to the fuel conditioning system 14. The uncracked fuel typically contains hydrocarbon components with multiple carbon atoms. For example, most of the hydrocarbons present in gasoline contain between approximately 4 and 12 carbon atoms. The fuel conditioning system 14 conditions, or processes, the uncracked fuel by cracking the fuel before it is burned in the combustion chamber 20. The fuel conditioning system 14 includes a fuel inlet line 22, a cracking vessel 24, a fuel supply line 26, and a thermal circuit 28. Uncracked fuel from the fuel supply 16 flows through the fuel inlet line 22 to the cracking vessel 24. The fuel is cracked in the cracking vessel 24. The cracked fuel exits the cracking vessel 24 and flows through the fuel supply line 26.The heat circuit 28 establishes a connection between the cracking vessel 24 and a heat source by means of a heat exchange fluid.

[0021] Inside the cracking vessel 24, the fuel is exposed to thermal energy to facilitate cracking of the fuel. The heat source heats the heat exchange fluid. The heated fluid moves from the heat source through the thermal circuit 28 to the cracking vessel 24. In exemplary embodiments, the heat source produces a heated fluid having a temperature between about 370°C (700°F) and about 815°C (1500°F).

[0022] Thermal energy from the heat exchange fluid is transferred to the cracking vessel 24, where the thermal energy breaks carbon-carbon bonds of the fuel hydrocarbons, reducing the size of the fuel hydrocarbons and producing small hydrocarbons such as methane and ethane. For example, the C4 to C12 fuel hydrocarbons present in raw gasoline are cracked in the cracking vessel 24 to produce fuel hydrocarbons with shorter carbon chains, increasing the overall volatility of the fuel and producing fuel hydrocarbons that burn more steadily in the combustion chamber 20. In exemplary embodiments, the heat exchange fluid heats the cracking vessel 24 and its contents to a temperature between about 260°C (500°F) and about 595°C (1100°F). As the temperature of the cracking vessel 24 increases, the pressure within the cracking vessel 24 also increases.The increased pressure in cracking vessel 24 also contributes to the cleavage of carbon-carbon bonds in the fuel hydrocarbons. In exemplary embodiments, the pressure in cracking vessel 24 is between about 345 kPa (50 psi) and about 620 kPa (90 psi). In exemplary embodiments, cracking vessel 24 does not contain a catalyst used for catalytic cracking of fuel, but instead relies on the heat energy and pressure within cracking vessel 24.

[0023] Cracked fuel exits cracking vessel 24 through fuel supply line 26. Fuel supply line 26 supplies the cracked fuel to fuel injection system 18, which then produces the fuel / air mixture that is combusted in combustion chamber 20. Due to the elevated temperature of cracking vessel 24 and the increased pressure within cracking vessel 24, the cracked fuel supplied through fuel supply line 26 has an elevated temperature and pressure. The elevated temperature and pressure of the cracked fuel provide benefits to internal combustion engine system 10. For example, the elevated temperature of the cracked fuel better prepares the fuel for combustion by increasing the fuel's vapor pressure. Increasing the fuel's vapor pressure reduces the likelihood of pockets of the fuel / air mixture forming and detonating prior to combustion.The increased pressure of the cracked fuel also reduces the pumping force required to deliver the cracked fuel from the fuel conditioning system 14 to the fuel injection system 18. Additionally, the critical pressure of the cracked fuel is lower than that of standard (uncracked) fuel. The increased pressure of the cracked fuel leaving the cracking vessel 24 and the reduced critical pressure of the cracked fuel can reduce the pressure required to deliver the cracked fuel to the combustion chamber 20 by as much as 100 kPa (15 psi).

[0024] The cracked fuel is burned in the combustion chamber 20. At the time of combustion, the fuel hydrocarbons present in the cracked fuel have shorter chain lengths than the fuel supplied to the cracking vessel 24 from the fuel supply 16. The cracked fuel contains more short-chain and volatile hydrocarbons, such as methane and ethane. For a fuel to burn properly, the fuel must vaporize and break down into short-chain hydrocarbons. The increased concentration of short-chain hydrocarbons allows the flame front generated during combustion to travel more quickly through the combustion chamber 20, burning the cracked fuel before any pockets of the fuel / air mixture have a chance to prematurely detonate. The smaller the hydrocarbon chain lengths, the faster the flame front advances through the fuel / air mixture in the combustion chamber 20.The flame front advances faster in cracked fuel than in uncracked fuel. The increased flame front velocity in cracked fuel allows the engine 12 to have a higher compression ratio than a comparable engine burning uncracked fuel. An engine 12 with the fuel conditioning system 14 may have a compression ratio about 60% higher than other engines using the same fuel source. In exemplary embodiments, the engine 12 has a compression ratio between about 14:1 and about 18:1.

[0025] In the Fig. In the embodiment illustrated in Figure 1, the engine 12 serves as the heat source. The engine 12 generates heat during operation. The burning of fuel in the combustion chamber 20 generates energy. Some of this energy is extracted from the engine 12 to generate motion. However, much of this energy is released as heat. In embodiments where the engine 12 serves as the heat source for the thermal cycle 28, the heat released by the engine 12 during combustion is used to provide the heat energy needed to crack the fuel in the cracking vessel 24.

[0026] Fig. Figure 2 illustrates a simplified schematic diagram of an internal combustion engine system according to the present invention. The internal combustion engine system 10A includes the elements of the internal combustion engine system 10 described above, in addition to an auxiliary heat source 30, a secondary heat circuit 32, and a control system 34. The operation of the internal combustion engine system 10 is described with respect to fuel conditioning during the steady-state engine operating condition (after the engine 12 has been started and begun combusting fuel). When the engine 12 first begins operating and combusting fuel, the engine 12 cannot provide the heat energy required to raise the temperature of the cracking vessel 24 so that fuel cracking can occur.Until the engine 12 produces enough heat to provide sufficiently heated heat exchange fluid through the heat loop 28, the cracking vessel 24 requires heat energy from a separate heat source. The auxiliary heat source 30 heats a second heat exchange fluid that is supplied to the cracking vessel 24 through the second heat loop 32. The additional heat source, or auxiliary heat source 30, provides the heat energy necessary to crack the fuel until the engine 12 reaches steady-state operation. The control system 34 determines and controls which heat source (12 or 30) supplies heat exchange fluid to the cracking vessel 24. The control system 34 receives inputs from temperature and / or pressure sensors in the engine 12. When the engine 12 is not operating at a steady-state operation, the control system 34 allows the auxiliary heat source 30 to supply heat energy to the cracking vessel 24 via the second heat loop 32.When the engine 12 is operating in steady-state mode, the control system 34 allows the engine 12 to supply heat energy to the cracking vessel 24 via the heat circuit 28 and shuts off the auxiliary heat source 30 to conserve energy. The control system 34 may also allow the simultaneous transfer of heat energy from both the engine 12 and the auxiliary heat source 30 to the cracking vessel 24.

[0027] Fig.3 illustrates a method for operating the internal combustion engine systems 10 and 10A described above. The method 36 includes supplying a fuel to a cracking vessel (step 38), thermally cracking the fuel in the cracking vessel (step 40), supplying the cracked fuel to an engine (step 42), and combusting the cracked fuel (step 44). In step 38, uncracked fuel is supplied from the fuel supply 16 to the cracking vessel 24. In step 40, thermal energy is used to crack the fuel in the cracking vessel 24. The thermal energy used to crack the fuel is provided by a heat source, such as an engine 12 or an auxiliary heat source 30. A heat exchange fluid is circulated between the engine and the cracking vessel. The engine heats the fluid using the heat released by fuel combustion in the engine.Once heated, the fluid is fed to the cracking vessel 24 to provide heat energy. The fluid is then returned to the engine 12 so that it can be reheated and the process repeated. Cracking the fuel reduces the carbon chain lengths of hydrocarbons present in the fuel, producing the short-chain hydrocarbons methane and ethane and increasing fuel vaporization. In exemplary embodiments, the fuel is cracked at a temperature between about 260°C (500°F) and about 595°C (1100°F) and at a pressure between about 345 kPa (50 psi) and about 620 kPa (90 psi) without the use of catalysts.

[0028] In step 42, the cracked fuel is delivered to the engine 12. In exemplary embodiments, the cracked fuel is delivered to an injection system in the engine 12 at a pressure between about 275 kPa (40 psi) and about 550 kPa (80 psi), which reduces the power required for any fuel pumps or eliminates their need altogether. The cracked fuel is mixed with air to form a fuel / air mixture. In step 44, the fuel / air mixture is burned to produce work. The method 36 is performed in a single internal combustion engine system (i.e., the fuel is not cracked at a location separate from the engine and then added to an engine fuel supply). The steps of the method 36 are performed in a short period of time, nearly simultaneously.Method 36 provides for combustion engine operation that allows for an increased compression ratio without subjecting the engine operation to increased engine knock.

[0029] Cracking the fuel in a cracking vessel immediately before fuel combustion promotes proper fuel combustion. Reducing the carbon chain lengths of fuel hydrocarbons increases the flame front speed during combustion, which reduces the tendency for engine knock. The increased flame speed allows internal combustion to operate at a higher compression ratio without increasing the tendency for engine knock.

[0030] While the invention has been described with reference to exemplary embodiments, those skilled in the art will understand that various modifications may be made and equivalents may be substituted for elements of the embodiments without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its essential scope. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

[1] Internal combustion engine system (10) comprising: a motor (12) comprising: a combustion chamber (20) for burning a fuel to produce work; a fuel injection system (18) for supplying a mixture of fuel and air to the combustion chamber (20); a fuel supply (16); and a fuel conditioning system (14) comprising: a heat circuit (28) and an additional heat circuit (32) for absorbing heat energy; a cracking vessel (24) for receiving fuel from the fuel supply (16) and for cracking carbon-carbon bonds of fuel hydrocarbons using the thermal energy obtained from the thermal cycle to produce cracked fuel; a fuel supply line (26) for supplying the cracked fuel to the engine (12); wherein the heat circuit (28) is designed to receive heat energy from the engine (12) and to transfer it to the cracking vessel (24) by means of a heat exchange fluid, the cracking vessel heating the fuel, and wherein the additional heat circuit (32) is designed to receive heat energy from an additional heat source (30), and to transfer it to the cracking vessel (24) by means of an additional heat exchange fluid, the cracking vessel heating the fuel, wherein the additional heat source is configured to provide heat energy until the engine (12) alone provides sufficient heat energy to break the carbon bonds of the fuel hydrocarbons; and further comprising a control system (34) for controlling the amount of heat energy, which the heat circuit (28, 32) receives from the engine (12) and the additional heat source (30). [2] The internal combustion engine system (10) of claim 1, wherein no catalyst is present in the cracking vessel (24). [3] The internal combustion engine system (10) of claim 1 or 2, wherein the engine (12) has a compression ratio between about 14:1 and about 18:

1. [4] The internal combustion engine system (10) of any one of claims 1 to 3, wherein the fuel supply line (26) is configured to supply fuel to the fuel injection system (18) at a pressure between about 275 kPa (40 psi) and about 550 kPa (80 psi). [5] Fuel conditioning system (14) comprising: a fuel supply (16) for providing a fuel; a heat circuit (28) and an additional heat circuit (32) for absorbing heat energy; a cracking vessel (24) for receiving the fuel from the fuel supply (16) and for cracking carbon-carbon bonds of hydrocarbons present in the fuel to produce cracked fuel; a fuel supply line (26) for supplying the cracked fuel to an internal combustion engine (20); wherein the heat circuit (28) is designed to receive heat energy from a heat source (12) and to transfer it to the cracking vessel (24) by means of a heat exchange fluid, wherein the cracking vessel heats the fuel, and wherein the additional heat circuit (32) is designed to obtaining heat energy from an additional heat source (30) and transferring it to the cracking vessel (24) by means of an additional heat exchange fluid, the cracking vessel heating the fuel; wherein the additional heat source (30) is designed to supply the cracking vessel (24) with heat energy until the heat source alone provides sufficient heat energy to cleave the carbon-carbon bonds of the fuel hydrocarbons; and a control system (34) for controlling the amount of heat energy that the cracking vessel (24) receives from the heat source (12) and the additional heat source (30). [6] A fuel conditioning system (14) according to claim 5, wherein the heat source is the internal combustion engine (12) receiving the cracked fuel. [7] A fuel conditioning system (14) according to claim 5 or 6, wherein no catalyst is present in the cracking vessel (24). [8] A method for operating an internal combustion engine (12), the method comprising: Supplying a fuel to a cracking vessel (24); thermally cracking the fuel in the cracking vessel (24) to produce cracked fuel; Supplying the cracked fuel to the internal combustion engine (12); and Combustion of the cracked fuel in the internal combustion engine (12), wherein the heat used for thermal cracking of the fuel in the cracking vessel (24) is supplied by a heat exchange fluid of a heat circuit (28) and / or an additional heat circuit (32), wherein the heat circuit (28) receives heat energy from the engine (12) and transfers it to the cracking vessel (24) by means of the heat exchange fluid, wherein the cracking vessel heats the fuel, and wherein the additional heat circuit (32) receives heat energy from an additional heat source (30) and transfers it to the cracking vessel (24) by means of the additional heat exchange fluid, wherein the cracking vessel heats the fuel, and wherein a control system (34) controls the amount of heat energy that the heating fluid receives from the internal combustion engine (12) and the additional heat source (30). [9] A process according to claim 8, wherein no catalysts are used to crack the fuel in the cracking vessel (24). [10] A process according to any one of claims 8 or 9, wherein the fuel is cracked at a temperature between about 260°C (500°F) and about 595°C (1100°F) and at a pressure between about 345 kPa (50 psi) and about 620 kPa (90 psi). [11] A method according to any one of claims 8 to 10, wherein the cracked fuel is supplied to an injection system (18) of the internal combustion engine (12) at a pressure between about 275 kPa (40 psi) and about 550 kPa (80 psi). [12] A process according to any one of claims 8 to 11, wherein thermal cracking of the fuel produces methane and ethane and increases the vaporization of the fuel.

Images