Ammonia on-line cracking device capable of recovering exhaust heat energy and rotor engine system

Abstract

The invention discloses an ammonia online cracking device capable of recovering exhaust heat energy and a rotor engine system, and aims to overcome the defects that a rotor engine is low in combustion heat efficiency and low in fuel combustion activity and a traditional ammonia cracking system exists in the prior art. The device comprises a liquid ammonia storage device, a preheating chamber, a core reaction chamber and a nitrogen-hydrogen separation chamber which are sequentially communicated, sleeving holes are formed in the preheating chamber, the core reaction chamber and the nitrogen-hydrogen separation chamber and used for being arranged on an exhaust pipeline of the rotary engine in a sleeving mode, an auxiliary heating device is arranged outside the core reaction chamber, and the nitrogen-hydrogen separation chamber is provided with an exhaust part. The device is arranged on an engine exhaust pipeline in a sleeving mode, high-temperature waste heat of tail gas is used for driving ammonia gas to absorb heat and decompose, generated hydrogen is introduced into a combustion chamber to be coupled with fuel oil to form a hydrogen-oil mixed fuel system, gradient utilization of waste heat and safe and efficient utilization of ammonia fuel are achieved, the combustion efficiency of the whole machine is improved, and structural support is provided for zero carbonization of a rotor engine; and the method has high engineering application value.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of aerospace power engineering and clean energy utilization, and relates to an online ammonia cracking device for exhaust heat recovery and a rotary engine system. Background Technology

[0002] The rotary engine is an internal combustion engine that outputs power through internal combustion. Compared to traditional reciprocating piston engines, its core characteristic is the absence of complex crankshaft and connecting rod mechanisms and valve trains, resulting in advantages such as fewer parts, a compact structure, a high power-to-weight ratio, smooth operation, and low vibration and noise. Against the backdrop of vigorously promoting "dual-carbon" goals, the rotary engine's fuel system is undergoing a transformation towards cleaner and lower-carbon technologies. Currently, leveraging its unique advantages, it is being explored for applications in fields such as aerospace power (e.g., small unmanned aerial vehicles) and vehicle power (e.g., range extenders for new energy vehicles), becoming a key low-carbon power solution. Research institutions and enterprises are investing resources in fuel innovation and performance optimization research.

[0003] Despite the numerous structural advantages of rotary engines and their alignment with the dual-carbon trend, significant challenges remain in practical applications, hindering their low-carbon development and large-scale adoption. Currently, mainstream rotary engines primarily rely on fossil fuels such as gasoline, diesel, and natural gas for power. These fuels, with their elongated combustion chambers, exhibit slow flame propagation and incomplete combustion, producing pollutants like nitrogen oxides (NOx) and carbon monoxide (CO), contradicting the dual-carbon reduction and pollution control requirements. Furthermore, their effective thermal efficiency is only about 20%, resulting in substantial waste heat emissions with the exhaust, leading to energy waste and increased costs. Addressing these issues is a key bottleneck in their adaptation to dual-carbon goals.

[0004] Addressing the issues of rotary engines' dependence on fossil fuels, high pollution, and low energy efficiency, systems based on exhaust gas-driven online ammonia cracking to generate zero-carbon fuel possess significant application potential. Although industrial ammonia cracking for hydrogen production is mature and this approach effectively addresses the core pain points of rotary engines, existing conventional exhaust gas direct-drive cracking structures still face several technical bottlenecks in practical applications: First, poor integration and adaptability; existing devices struggle to flexibly adapt to exhaust heat energy under varying engine operating conditions, resulting in low waste heat recovery efficiency and large fluctuations in ammonia conversion rate. Second, slow cold start response; during initial startup, the exhaust temperature does not reach the catalyst ignition temperature, leading to delayed hydrogen supply and continued reliance on auxiliary fuel. Third, combustion deterioration and corrosion risks; directly introducing crude cracked gas into the cylinder not only fails to fully leverage the coupling advantages of hydrogen's high diffusivity and nitrogen's NOx suppression but also easily induces combustion instability and engine component corrosion. In summary, existing solutions have significant shortcomings, necessitating in-depth optimization of system structure and operating mechanisms. Summary of the Invention

[0005] This invention provides an online ammonia pyrolysis device and a rotary engine system for exhaust heat recovery. Addressing the pain points of low combustion thermal efficiency and low fuel combustion activity in rotary engines, it innovatively proposes a technical solution integrating multi-stage preheating, high-efficiency online pyrolysis, and membrane separation purification. The online ammonia pyrolysis device is integrated into the engine exhaust pipe, directly utilizing the high-temperature waste heat of the exhaust gas to drive the endothermic decomposition reaction of ammonia. The generated hydrogen is introduced into the combustion chamber and coupled with fuel to form a hydrogen-oil mixed fuel system. The high diffusivity and wide combustibility of hydrogen improve fuel combustion activity, achieving cascade utilization of waste heat and improved overall engine combustion efficiency. Simultaneously, it solves problems such as poor quality of traditional pyrolysis gas, poor adaptability to varying operating conditions, low thermal efficiency, slow cold start, and unstable operation, achieving safe and efficient utilization of ammonia fuel and providing substantial structural support for the zero-carbonization of rotary engines.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an online ammonia cracking device for exhaust heat recovery, comprising a liquid ammonia storage device, a preheating chamber, a core reaction chamber, and a nitrogen-hydrogen separation chamber connected in sequence, wherein the preheating chamber, the core reaction chamber, and the nitrogen-hydrogen separation chamber are all provided with sleeve holes for sleeved onto the exhaust pipe of a rotary engine, an auxiliary heating device is provided outside the core reaction chamber, and the nitrogen-hydrogen separation chamber is provided with an exhaust section.

[0007] Furthermore, the liquid ammonia storage device includes an ammonia storage tank, a connecting pipe, and a square flange. One end of the connecting pipe is connected to the outlet of the ammonia storage tank, and the other end is connected to the square flange. The square flange is used to achieve a sealed connection between the connecting pipe and the preheating chamber. Heat dissipation fins are evenly distributed around the outside of the connecting pipe to form a thermal resistance barrier, blocking the high temperature of the preheating chamber from being conducted to the ammonia storage tank. Liquid ammonia is sprayed out under high pressure through the connecting pipe and the square flange.

[0008] Furthermore, the preheating chamber is equipped with spiral guide fins to absorb exhaust heat energy and achieve phase change vaporization of liquid ammonia from liquid to gas.

[0009] Furthermore, a spiral pipe is installed in the core reaction chamber 8, and there are cross-distributed fins inside the spiral pipe. The surface of the fins is coated with a ruthenium-based catalyst.

[0010] Furthermore, auxiliary heating devices are arranged in a ring array outside the core reaction chamber to raise the temperature of the core reaction chamber to the operating temperature.

[0011] Furthermore, the nitrogen-hydrogen separation chamber is equipped with an annular palladium membrane tube array for separating pure hydrogen from the reaction products.

[0012] Furthermore, it also includes a fixing device, which includes mounting ears and annular T-shaped clamps. The mounting ears are located outside the auxiliary heating device for connecting the online ammonia cracking device to the engine housing; the annular T-shaped clamps are located at the end of the nitrogen-hydrogen separation chamber away from the core reaction chamber for locking one side of the nitrogen-hydrogen separation chamber to the rotary engine exhaust pipe.

[0013] Furthermore, the exhaust section of the nitrogen-hydrogen separation chamber includes an exhaust port and a hydrogen outlet. The exhaust port is used to discharge the remaining nitrogen, and the hydrogen outlet is used to introduce pure hydrogen into the rotary engine combustion chamber through a hydrogen conduit.

[0014] The present invention also provides a rotary engine system, wherein the exhaust pipe of the rotary engine is connected to the above-mentioned online ammonia cracking device for exhaust heat recovery.

[0015] Furthermore, the online ammonia cracking device is installed on the exhaust pipe of the rotary engine, and the hydrogen outlet of the online ammonia cracking device is connected to the combustion chamber of the rotary engine through a hydrogen conduit.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: This invention provides an online ammonia cracking device for exhaust heat recovery. A liquid ammonia storage device, a preheating chamber, a core reaction chamber, and a nitrogen-hydrogen separation chamber are sequentially connected. The preheating chamber, core reaction chamber, and nitrogen-hydrogen separation chamber are all fitted onto the exhaust pipe of a rotary engine through internal sleeve holes. This allows direct use of the high-temperature waste heat from the engine exhaust to drive the endothermic decomposition reaction of ammonia, eliminating the need for additional external energy consumption. This successfully achieves the cascaded recovery and efficient utilization of exhaust heat from the rotary engine, effectively improving the overall thermal efficiency and solving the problem of severe heat waste in traditional rotary engines. The auxiliary heating device can quickly raise the temperature of the core reaction chamber to the catalyst operating temperature during cold start conditions, effectively compensating for insufficient exhaust waste heat in the initial cold start phase. This ensures stable operation of the device under various conditions and improves its adaptability to changing operating conditions.

[0017] Furthermore, the device, through a unique design of spiral guide fins and spiral pipes, significantly increases the heat exchange area and ammonia reaction residence time within a limited installation space, substantially improving ammonia cracking efficiency and ensuring complete decomposition of ammonia fuel to provide a sufficient hydrogen source for subsequent combustion gains. In addition, the circumferentially distributed heat dissipation fins on the outer side of the connecting pipes form an effective thermal resistance barrier, efficiently preventing the high temperature of the preheating chamber from being conducted to the ammonia storage tank. This fundamentally ensures the safety of the liquid ammonia storage and supply process, avoids safety hazards caused by high-temperature backflow, and further enhances the reliability of the device operation.

[0018] Furthermore, the annular palladium membrane tube array installed in the nitrogen-hydrogen separation chamber can efficiently and selectively separate the gases generated by pyrolysis, accurately separating pure hydrogen and nitrogen. The separated pure hydrogen is directly introduced into the combustion chamber and coupled with fuel to form a hydrogen-oil mixed fuel system. With the help of the high diffusivity and wide combustibility of hydrogen, the combustion activity of fuel is significantly improved, further enhancing the combustion efficiency of the rotary engine. At the same time, the low-pressure environment formed when nitrogen is discharged through the exhaust section promotes the continuous and efficient ammonia pyrolysis reaction from a thermodynamic perspective.

[0019] Furthermore, the design of locking on one side and floating on the other end enables thermal expansion compensation of the device, preventing thermal stress caused by temperature changes during engine operation from damaging the device structure and extending its service life. Overall, this technical solution not only achieves efficient utilization of waste heat from exhaust gas and in-situ preparation of zero-carbon fuel, but also takes into account the safety, stability, and efficiency of the device operation, effectively solving many problems existing in the prior art, and has extremely high engineering application value and promotion prospects. Attached Figure Description

[0020] Figure 1 : Schematic diagram of an online ammonia cracking device for exhaust heat recovery according to the present invention.

[0021] Figure 2 : Schematic diagram of the location of the auxiliary heating device on the online ammonia cracking unit of the present invention.

[0022] Figure 3 Cross-sectional view of the preheating chamber, core reaction chamber, ammonia-hydrogen separation chamber, and annular clamp of this invention.

[0023] Figure 4 : Schematic diagram of the assembly of the online ammonia cracking device of the present invention.

[0024] Figure 5 : Temperature field cloud map of the initial stage of the core reaction chamber of this invention.

[0025] Figure 6 : Temperature field cloud map of the stable stage of the core reaction chamber of this invention.

[0026] Figure 7 : Cloud map of pressure field changes in the core reaction chamber of this invention.

[0027] Figure 8 The curve showing the change in ammonia mass in the core reaction chamber over time.

[0028] In the attached diagram: 1. Ammonia storage tank; 2. Connecting pipe; 3. Square flange; 4. Circular flange; 5. Spiral guide fins; 6. Preheating chamber; 7. Trapezoidal mounting lug; 8. Core reaction chamber; 9. Nitrogen-hydrogen separation chamber; 10. Exhaust port; 11. Hydrogen conduit; 12. Annular T-shaped clamp; 13. Annular palladium membrane tube array; 14. M6 threaded hole; 15. Auxiliary heating device; 16. Exhaust pipeline. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] This invention provides a rotary engine system, including an online ammonia cracking device. The inlet of the online ammonia cracking device is connected to an ammonia source to receive ammonia gas supplied by the ammonia source, providing raw materials for the ammonia cracking reaction. Simultaneously, the exhaust pipe of the rotary engine forms a heat exchange connection with the online ammonia cracking device (sleeved onto the exhaust pipe), providing the necessary heat energy for the endothermic decomposition reaction of ammonia gas, thus realizing the recovery and utilization of exhaust waste heat. The outlet of the online ammonia cracking device is connected to the combustion chamber of the rotary engine. Hydrogen gas produced by the endothermic decomposition reaction of ammonia gas in the online ammonia cracking device is directly introduced into the combustion chamber of the rotary engine through the outlet pipe, coupling with fuel to form a hydrogen-fuel mixture system, participating in the engine combustion process. The remaining exhaust gas after the ammonia cracking reaction is discharged through a corresponding pipe; the low-pressure environment created during its release process can further promote the forward ammonia cracking reaction.

[0031] In summary, the online ammonia cracking device achieves waste heat recovery through heat exchange connection with the engine exhaust pipe, and completes ammonia input, hydrogen output and combustion utilization through pipeline connection with ammonia source and engine combustion chamber, ultimately achieving the invention objective of waste heat cascade utilization and overall combustion efficiency improvement.

[0032] Furthermore, the structure of the online ammonia cracking device of the present invention includes, in sequence, an ammonia source, a front-end preheating section, a middle cracking section, and a rear-end separation and fixing device, as detailed below: The front-end preheating section includes a preheating chamber with spiral guide fins installed inside. The preheating chamber is fitted and integrated on the outside of the exhaust pipe. Liquid ammonia output from the ammonia source is injected into the preheating chamber and fully absorbs the exhaust heat energy under the action of the spiral guide fins, realizing phase change vaporization from liquid to gas.

[0033] The central pyrolysis section includes a core reaction chamber and an auxiliary heating device. The core reaction chamber 8 is equipped with a spiral pipe with fins distributed inside. The fins are coated with a catalyst. After liquid ammonia is vaporized, it enters the core reaction chamber 8 and undergoes an endothermic decomposition reaction in the high-temperature environment provided by the catalyst and exhaust gas to generate a nitrogen-hydrogen mixture. The auxiliary heating device is distributed in a ring array outside the core reaction chamber 8. The auxiliary heating device is used to compensate for the heat energy during the cold start of the engine and ensure that the reactor can quickly reach the reaction temperature.

[0034] The rear-end separation section includes a nitrogen-hydrogen separation chamber and an exhaust section. The nitrogen-hydrogen separation chamber is equipped with an annular palladium membrane tube array. The tail end of the core reaction chamber is directly connected to the nitrogen-hydrogen separation chamber. The palladium membrane tube array selectively separates pure hydrogen from the reaction products, and then introduces the pure hydrogen into the rotary engine combustion chamber, achieving a hydrogen enhancement effect. The exhaust section includes an exhaust port and a hydrogen outlet. The exhaust port is used to discharge residual nitrogen, and the low-pressure environment created during this discharge further promotes the ammonia cracking reaction from a thermodynamic perspective. The hydrogen outlet is used to introduce pure hydrogen into the rotary engine combustion chamber through a hydrogen conduit, coupling it with fuel to form a hydrogen-oil dual-fuel system. The high diffusivity and wide flammability range of hydrogen significantly improve combustion activity and stability.

[0035] The mounting device includes mounting ears and annular T-shaped clamps. The mounting ears are located outside the auxiliary heating device to connect the online ammonia cracking device to the engine housing. The annular T-shaped clamps are located at the end of the nitrogen-hydrogen separation chamber away from the core reaction chamber and are fixed to the exhaust pipe by the annular T-shaped clamps, locking one side of the nitrogen-hydrogen separation chamber to the rotary engine exhaust pipe, while the other side remains floating to provide thermal expansion compensation.

[0036] Example 1 like Figures 1-4 As shown, an online ammonia cracking device for exhaust heat recovery according to the present invention includes an ammonia storage tank 1, a connecting pipe 2, a square flange 3, a circular flange 4, spiral guide fins 5, a preheating chamber 6, a trapezoidal mounting lug 7, a core reaction chamber 8, a nitrogen-hydrogen separation chamber 9, an exhaust port 10, a hydrogen conduit 11, an annular T-shaped clamp 12, an annular palladium membrane tube array 13, an M6 threaded hole 14, and an auxiliary heating device 15, wherein: The online ammonia cracking unit is mounted on the exhaust pipe 16 and secured by annular T-shaped clamps 12. It is connected to the engine casing via trapezoidal mounting ears 7 on the outer wall of the core reaction chamber 8. Liquid ammonia is stored in the ammonia storage tank 1, which features hemispherical end caps to optimize stress distribution. Liquid ammonia is ejected under high pressure via connecting pipe 2 and square flange 3. Heat dissipation fins are evenly distributed around the outer circumference of connecting pipe 2, forming a thermal resistance barrier that effectively prevents the high temperature of the preheating chamber 6 from being conducted to the ammonia storage tank 1, ensuring safe storage and supply. The square flange 3 and the round flange 4 on the preheating chamber 6 are fixedly connected through the M6 ​​threaded hole 14 to achieve a sealed connection between the connecting pipe 2 and the preheating chamber 6, ensuring the sealing performance during the high-pressure injection of liquid ammonia and preventing ammonia leakage. After the liquid ammonia is injected into the preheating chamber 6, it is heated and vaporized under the guidance of the spiral guide fins 5. The temperature of the preheating chamber 6 is maintained at about 300℃ to ensure that the liquid ammonia can be vaporized in a short time. The spiral guide fins 5 are used to prevent the accumulation of liquid and fluid pulsation in the gas-liquid two-phase flow, creating conditions for the subsequent ammonia cracking reaction.

[0037] The vaporized ammonia enters the core reaction chamber 8, which employs a spiral tube arrangement to extend the residence time of the reactants and increase the heat exchange area, enabling the cascade utilization of exhaust heat energy. In the core reaction chamber 8, a ruthenium-based catalyst (in this example, a commercially available supported ruthenium catalyst) is coated on the surface of cross-distributed fins. The turbulence effect generated by the cross-structure ensures sufficient contact between the ammonia and the catalyst, resulting in a highly efficient endothermic decomposition reaction of the ammonia at 450°C and low pressure.

[0038] like Figure 2 As shown, an auxiliary heating device is configured for cold start conditions of the engine. The auxiliary heating device is distributed in a ring array outside the core reaction chamber 8, and consists of 8 heating units with a single unit power of 300W, with a total power of 2400W. This device can quickly raise the temperature of the core reaction chamber 8 to about 450°C in the early stage of the rotary engine start-up, make up for the heat energy gap, and ensure that the rotary engine can obtain hydrogen gain in time when burning aviation fuel.

[0039] Hydrogen and nitrogen generated from the cracking in the core reaction chamber 8 enter the nitrogen-hydrogen separation chamber 9. A ring-shaped palladium membrane array 13 uses high selectivity to separate pure hydrogen, which is then directly introduced into the combustion chamber via hydrogen conduit 11, coupling with aviation fuel to form a hydrogen-oil dual-fuel system. The high diffusivity and wide flammability of hydrogen significantly improve combustion activity and stability. The remaining nitrogen is discharged through exhaust port 10; the low-pressure environment created during its release further promotes the ammonia cracking reaction from a thermodynamic perspective.

[0040] Example 2 (suitable for small rotary engines, power 50~80kW) This embodiment is adapted to a small rotary engine, with a compact size. Specific parameters are as follows: The device is mounted on a DN80 exhaust pipe 16, which is made of 310S stainless steel with a wall thickness of 4mm. The device is fixed by a BH-T80 type annular T-shaped clamp, which is made of 304 stainless steel and has a width of 40mm. The device is connected to the engine housing via an AZ-100 type trapezoidal mounting ear, which is made of Q235B material and hot-dip galvanized, with dimensions of 100mm × 50mm × 15mm. The ammonia storage tank 1 is a CGA-330B model with a volume of 5L. It features hemispherical end caps made of 304 stainless steel, a design pressure of 4.0MPa, and a working pressure of 2.5~3.0MPa. It contains a level sensor and a safety valve. Liquid ammonia is ejected under high pressure through a DN15 connecting pipe and a custom square flange. The connecting pipe is made of 304 stainless steel, measuring 21.3mm × 3.0mm and 50mm in length, with 12 heat dissipation fins evenly distributed around its outer circumference. The custom square flange measures 80mm × 80mm × 10mm. The square flange is fixedly connected to a DN15 round flange via M6 × 1.0 threaded holes with a depth of 15mm. The liquid ammonia enters preheating chamber 6, which is adapted to a DN80 exhaust pipe. Preheating chamber 6 has external dimensions of 120mm outer diameter × 85mm inner diameter × 250mm length, is made of 310S material, and operates at a temperature maintained between 280~320℃. The liquid ammonia vaporizes under the guidance of spiral guide fins. The spiral guide fins are also made of 310S material, with a height of 17mm and a pitch of 25mm. The vaporized ammonia gas enters the core reaction chamber, which contains a DN25×3mm spiral tube coated with a Ru / Al2O3-0.5% ruthenium-based catalyst. The ammonia gas undergoes a cracking reaction at 450℃ and 0.1~0.3MPa. The auxiliary heating device consists of eight 300W heating units, with a total power of 2400W, using the JH-300 model, which can rapidly raise the core reaction chamber temperature to 450℃. The cracked gas then enters a nitrogen-hydrogen separation chamber adapted to the core reaction chamber. This separation chamber has external dimensions of 150mm outer diameter × 105mm inner diameter × 300mm length. Hydrogen is separated internally by a PD-10 type annular palladium membrane tube array, which contains 10 palladium membrane tubes made of Pd-Ag 77 / 23 alloy. The separated pure hydrogen gas is introduced into the combustion chamber through a DN10 hydrogen conduit, which measures 14mm × 2.5mm and is 400mm long. The remaining nitrogen gas is discharged through exhaust ports, which have a diameter of 12mm and are set in four in total. The nitrogen gas discharge process can promote the continuous ammonia cracking reaction.

[0041] Example 3 (suitable for medium-sized rotary engines, power 80~120kW) This embodiment is adapted to a medium-sized rotary engine, balancing efficiency and stability. Specific parameters are as follows: The device is mounted on a DN100 exhaust pipe 16, which is made of 310S stainless steel with a wall thickness of 5mm. The device is fixed using a BH-T100 type annular T-shaped clamp, which is 45mm wide. The device is connected to the engine housing via an AZ-120 type trapezoidal mounting ear, which measures 120mm × 60mm × 18mm. The ammonia storage tank 1 is a CGA-340 model with a volume of 8L; other parameters are consistent with Embodiment 1. Liquid ammonia is ejected through a DN20 connecting pipe and a custom square flange. The connecting pipe measures 27.3mm × 3.5mm, is 50mm long, and has 16 fins evenly distributed around its outer circumference. The custom square flange measures 100mm × 100mm × 12mm. The square flange is fixedly connected to a DN20 type circular flange. The preheating chamber 6 is adapted to a DN100 exhaust pipe, with external dimensions of 140mm outer diameter × 105mm inner diameter × 350mm length. The internal spiral guide fins have a height of 20mm and a pitch of 35mm. The core reaction chamber's spiral tube is DN32 × 3.5mm, with the inner fin surface coated with a Ru / Al2O3-1.0% ruthenium-based catalyst. The parameters of the auxiliary heating device are the same as in Example 1. The nitrogen-hydrogen separation chamber is adapted to the core reaction chamber, with external dimensions of 170mm outer diameter × 130mm inner diameter × 400mm length. Internally, hydrogen is separated by a PD-12 type annular palladium membrane tube array, which contains 12 palladium membrane tubes. The separated hydrogen is introduced into the combustion chamber through a DN12 hydrogen conduit, with dimensions of 16mm × 2.5mm and a length of 500mm; the remaining nitrogen is discharged through a 15mm diameter exhaust port.

[0042] Example 4 (suitable for large rotary engines, power 120~150kW) This embodiment is adapted to a large rotary engine, focusing on efficient heat exchange and hydrogen production. Specific parameters are as follows: The device is mounted on a DN125 exhaust pipe 16, which is made of 310S stainless steel with a wall thickness of 6mm. The device is fixed using a BH-T125 type annular T-shaped clamp, which is 50mm wide. The device is connected to the engine housing using AZ-120 type trapezoidal mounting ears. The ammonia storage tank 1 is a CGA-350 model with a volume of 12L; other parameters are the same as in Embodiment 1. Liquid ammonia is sprayed out through a DN20 connecting pipe and a custom square flange; the connecting pipe is 90mm long. The square flange is fixedly connected to a DN20 type round flange. The preheating chamber 6 is adapted to the DN125 exhaust pipe, with external dimensions of 160mm outer diameter × 125mm inner diameter × 450mm length. The internal spiral guide fins have a height of 25mm and a pitch of 40mm. The core reaction chamber's spiral tube has a specification of DN40×4mm, and the inner fin surface is coated with a Ru / ZrO2-0.8% ruthenium-based catalyst. The auxiliary heating device consists of 10 sets of 300W heating units, with a total power of 3000W. The nitrogen-hydrogen separation chamber is adapted to the core reaction chamber, with external dimensions of 190mm outer diameter × 150mm inner diameter × 500mm length. Internally, hydrogen is separated by a PD-15 type annular palladium membrane tube array, which contains 15 palladium membrane tubes. The separated hydrogen gas is introduced into the combustion chamber through a DN15 hydrogen conduit, with dimensions of 21.3mm × 2.5mm and a length of 600mm; the remaining nitrogen gas is discharged through an 18mm diameter exhaust port.

[0043] Based on transient CFD calculations using CONVERGE software and Tecplot post-processed cloud plots, the dynamic evolution of temperature, pressure, and ammonia component mass in the core reaction chamber of an online ammonia cracking unit driven by exhaust waste heat was systematically analyzed within a time window of 0 to 0.2 s. This reaction chamber employs a helical tube structure and cross-distributed fins, aiming to efficiently utilize engine waste heat to drive the ammonia cracking reaction within a limited time and space.

[0044] like Figure 5 , Figure 6 As shown, from the temperature field evolution perspective, the initial stage of the reaction chamber is filled with preheated ammonia gas at approximately 600K, and the heating wall is set at 850K to simulate a high-temperature exhaust pipe. As time progresses, the high-temperature region rapidly expands from the wall towards the center of the spiral tube, the 600K low-temperature region is rapidly compressed, and the bulk fluid temperature rises to over 750K, demonstrating excellent heat transfer efficiency. The secondary flow induced by the spiral flow effectively promotes radial heat exchange, breaks the laminar boundary layer, and enhances the mixing of the high-temperature gas and the central fluid. The cross-fins not only provide the catalytic surface area but also act as a thermally conductive framework, rapidly transferring heat to the deeper layers of the flow field. Under the synergistic effect of secondary flow convection heat transfer and fin thermal conduction, the reaction chamber completes the thermal field construction within 0.2s, laying the thermodynamic foundation for the efficient operation of the ruthenium catalyst.

[0045] like Figure 7 As shown, the evolution of the pressure field also exhibits a clear pattern. With the inlet pressure set at approximately 108,000 Pa, the pressure gradually decreases to approximately 100,500 Pa at the outlet as the fluid moves downstream along the helical tube, forming a stable pressure gradient. This distribution aligns with fluid dynamics expectations: ammonia gas must overcome pipe wall friction and local fin resistance during flow, leading to a continuous decrease in static pressure; simultaneously, the gas density decreases and the flow velocity increases after heating, increasing dynamic pressure and further lowering static pressure. The low-pressure environment at the outlet is thermodynamically beneficial in suppressing the reverse reaction, promoting forward ammonia cracking, and improving the single-pass conversion efficiency.

[0046] like Figure 8 As shown, the evolution of temperature and pressure fields jointly affects the mass change of ammonia components. Within 0 to 0.2 s, the total mass of ammonia in the reaction chamber decreases non-linearly from an initial 0.00039 kg to approximately 0.00019 kg. The initial mass decrease is relatively slow because heat has not yet fully penetrated, and the catalyst activity is not fully activated. Subsequently, the slope of the curve increases, and the mass decreases significantly. This stage is mainly driven by the dual effects of thermal expansion and catalytic cracking. The high-temperature, low-pressure coupled environment significantly increases the cracking reaction rate. By 0.2 s, the ammonia mass tends to stabilize, indicating that the system has entered a dynamic equilibrium state: the inlet ammonia supply, catalytic consumption, and unreacted ammonia discharge reach a relatively stable state.

[0047] In summary, the spiral tubular reaction chamber is rationally designed and can establish a stable thermal and flow field in a very short time, providing strong support for the engine to achieve efficient and timely hydrogen supply.

Claims

1. An ammonia on-line cracking device with exhaust heat energy recovery, characterized in that, It includes a liquid ammonia storage device, a preheating chamber, a core reaction chamber, and a nitrogen-hydrogen separation chamber connected in sequence. The preheating chamber, the core reaction chamber, and the nitrogen-hydrogen separation chamber are all provided with sleeve holes for sleeved onto the exhaust pipe of the rotor engine. An auxiliary heating device is provided on the outside of the core reaction chamber, and the nitrogen-hydrogen separation chamber is provided with an exhaust section.

2. The online ammonia cracking device for exhaust heat recovery according to claim 1, characterized in that, The liquid ammonia storage device includes an ammonia storage tank, a connecting pipe, and a square flange. One end of the connecting pipe is connected to the outlet of the ammonia storage tank, and the other end is connected to the square flange. The square flange is used to achieve a sealed connection between the connecting pipe and the preheating chamber. Heat dissipation fins are evenly distributed around the outside of the connecting pipe to form a thermal resistance barrier, blocking the high temperature of the preheating chamber from being conducted to the ammonia storage tank. Liquid ammonia is sprayed out under high pressure through the connecting pipe and the square flange.

3. The online ammonia cracking device for exhaust heat recovery according to claim 1, characterized in that, The preheating chamber is equipped with spiral guide fins to absorb exhaust heat energy and achieve phase change vaporization of liquid ammonia from liquid to gas.

4. The online ammonia cracking device for exhaust heat recovery according to claim 1, characterized in that, The core reaction chamber 8 is equipped with a spiral pipe with fins arranged in a cross pattern inside the spiral pipe. The surface of the fins is coated with a ruthenium-based catalyst.

5. The online ammonia cracking device for exhaust heat recovery according to claim 1, characterized in that, The auxiliary heating devices are arranged in a ring array outside the core reaction chamber to raise the temperature of the core reaction chamber to the operating temperature.

6. The online ammonia cracking device for exhaust heat recovery according to claim 1, characterized in that, The nitrogen-hydrogen separation chamber is equipped with a ring-shaped palladium membrane tube array, which is used to separate pure hydrogen from the reaction products.

7. The online ammonia cracking device for exhaust heat recovery according to claim 1, characterized in that, It also includes a fixing device, which includes mounting ears and annular T-shaped clamps. The mounting ears are located outside the auxiliary heating device to connect the online ammonia cracking device to the engine housing. The annular T-shaped clamps are located at the end of the nitrogen-hydrogen separation chamber away from the core reaction chamber to lock one side of the nitrogen-hydrogen separation chamber to the rotary engine exhaust pipe.

8. The online ammonia cracking device for exhaust heat recovery according to claim 1, characterized in that, The exhaust section of the nitrogen-hydrogen separation chamber includes an exhaust port and a hydrogen outlet. The exhaust port is used to discharge the remaining nitrogen, and the hydrogen outlet is used to introduce pure hydrogen into the rotary engine combustion chamber through a hydrogen conduit.

9. A rotary engine system, characterized in that, The exhaust pipe of the rotary engine is connected to an online ammonia cracking device for exhaust heat recovery, as described in any one of claims 1 to 8, via a heat exchange connection.

10. A rotary engine system according to claim 9, characterized in that, The online ammonia cracking device is installed on the exhaust pipe of the rotary engine, and the hydrogen outlet of the online ammonia cracking device is connected to the combustion chamber of the rotary engine through a hydrogen conduit.

Images