Turbofan and engine for lowering turbine inlet temperature and increasing thrust

Abstract

To develop a cycle that lowers a turbine inlet temperature and increases thrust, and create a new field of aircraft engines that goes beyond the scope of conventional turbofan cycles.SOLUTION: Two exhaust nozzle areas are enlarged, a wide main jet nozzle increases a core flow rate to lower a fuel-air ratio, at the same time, an engine back pressure is reduced to increase a turbine expansion ratio and absorb and utilize some of the residual exhaust energy, thereby increasing a flow rate per engine frontal area, so that a wide fan bypass nozzle increases BPR and increases thrust.EFFECT: By improving SFC, a CO2 emission can be reduced, and low TIT reduces generation of NOx, and a turbine service life can be extended, so that it is possible to achieve both economical and environmental benefits.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention is a turbofan cycle that increases thrust by lowering the temperature at the turbine inlet and outlet, and aims to create a new field in aircraft engines. [Background technology]

[0002] Passenger aircraft turbofan engines, which require high takeoff thrust and economical cruising performance, have continuously pursued higher temperatures and pressures to improve performance. Jet engine thrust is governed by the turbine inlet temperature (TIT), which is limited by the material's melting point. This has led to the development of advanced turbine air-cooling technologies and innovative heat-resistant materials. However, higher temperatures shorten turbine life. Furthermore, if too much cooling air is used to prevent this, the performance improvement achieved by higher temperatures will be outweighed by cycle losses due to excess cooling air. Furthermore, as flame temperature in the combustor increases, NOx (nitrogen oxide) emissions increase exponentially. NOx is a greenhouse gas. Thus, achieving high performance while conserving resources and protecting the environment is difficult, making aircraft engines an extremely challenging field in terms of environmental and noise control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent application 2023-120299 [Non-patent literature]

[0004] [Non-Patent Document 1] Mitsuo Morita and Shizuo Sekine, "Off-Design Performance of a Multi-Shaft Turbofan Engine," National Aerospace Laboratory Report No. 347 Summary of the Invention [Problem to be solved by the invention]

[0005] The trend in turbofan technology development has been toward higher bypass ratios to improve propulsion efficiency. However, increasing the bypass ratio requires increasing TIT, which increases the work done by the low-pressure system. Increasing TIT, as mentioned above, creates numerous problems and does not necessarily lead to environmental benefits. In light of these issues, Patent Document 1 developed an original technical concept that increases the work done by the low-pressure turbine and fan system within a realistic temperature range without increasing TIT, thereby increasing engine airflow and maintaining thrust. However, for aircraft engines, which require light weight, compactness, and high thrust, improving thrust is essential, even if it means creating a new field where TIT can be reduced and thrust can be maintained.

[0006] Therefore, the present invention aims to solve the problem of evolving the "cycle that reduces TIT without reducing thrust (Patent Document 1)" into "a cycle that can reduce TIT and increase thrust." [Means for solving the problem]

[0007] A conceptual diagram of this engine is shown in Figure 1. This engine has larger main jet nozzle and fan bypass nozzle outlet areas than a normal turbofan with the same fan front area. Increasing the main jet nozzle area reduces resistance behind the high-pressure compressor (HPC), shifting the HPC operating line toward the choke. When the HPC flow rate increases due to the shift in operating point, the fuel-air mixture ratio decreases, lowering TIT. In addition, a larger main jet nozzle area reduces engine back pressure P7 and increases the expansion ratio of the low-pressure turbine (LPT), which drives the fan, thereby increasing the amount of air suctioned into the fan.

[0008] By increasing the fan bypass nozzle area, the distribution of the fan intake airflow to the bypass flow increases. As the expansion ratio increases, the LPT absorbs some of the available energy contained in the exhaust of the main jet nozzle, generating work to increase the bypass flow and increasing the bypass ratio (BPR). In other words, as the fuel-air ratio decreases, the specific enthalpy decreases, but as the flow rate of the core engine increases, the total enthalpy increases, raising the BPR, and thereby increasing thrust.

[0009] To increase thrust, TIT must be increased. To increase BPR, TIT must also be increased. This is common knowledge for turbofans. However, this invention can increase thrust by lowering TIT and increasing BPR. The reason for this is explained below.

[0010] Figure 2 shows the T-s diagram for just the core side of a typical (fan + HPC) type turbofan engine. This diagram shows the case where the cycle pressure ratio (CPR) is held constant and the TIT is varied. Increasing the TIT while keeping the CPR constant increases the amount of thermal energy that can be used as core thrust. This is similar to the turbojet cycle, and although this type of engine increases thrust, the core exhaust velocity increases, which can cause noise problems during takeoff.

[0011] The solution is to increase the BPR of the fan when increasing the TIT, so that the excess heat energy released into the exhaust is absorbed by the LPT with an increased number of stages, thereby increasing the thrust on the bypass side. Since the increase in thrust is an increase in the flow rate rather than the flow velocity at the nozzle exit, noise issues are also reduced.

[0012] The primary objective of this invention is to lower the maximum temperature from the perspectives of environmental conservation, resource conservation, and lifecycle cost reduction. Therefore, lowering the TIT (Figure 2) with a constant CPR reduces the amount of thermal energy available for core thrust, resulting in a decrease in thrust per unit flow rate. Therefore, the main jet nozzle area is increased, further increasing the expansion ratio of the LPT (fan-drive turbine) and increasing the fan work. Furthermore, the fan bypass nozzle area is increased to increase the bypass flow rate, thereby increasing the BPR without increasing the TIT, thereby increasing the engine flow rate and increasing thrust per unit time. This is the operating principle of this invention and the means to solve the problem. [Effects of the Invention]

[0013] The cycle effects achieved by the concept of the present invention described above will now be explained. Table 1 shows six cases in which the BPR to be calculated is changed. A is a conventional turbofan with a normal exhaust nozzle area. A8, A9, and A10 have a fan relative corrected rotation speed Nfc = 1 and TIT = 1820K. The BPR is 8 for A8, 9 for A9, and 10 for A10. B is the case of the present invention, where the fan, low-pressure compressor (LPC), and HPC are the same hardware as conventional type A. Nfc for B is 1.03, TIT = 1690K, and the relative corrected flow rate is also 1.03 compared to 1 for conventional type A. Since the core flow rate of present invention B is higher than that of conventional type A, the BPR is lower than that of A. Note that in both conventional type A and present invention B, the core engine size remains unchanged, but the fan area is increased to increase the BPR.

[0014] Figures 3 and 4 show the results of calculations to determine which of the six cases in which the BPR was changed in Table 1, conventional type A or present invention B, was more effective in extracting useful energy from the exhaust. Figure 3 shows the relationship between BPR and thrust increase, and Figure 4 shows the relationship between BPR and SFC (specific fuel consumption). Table 1 and Figures 3 and 4 show that the present invention's B10 has a TIT 130 degrees lower than the conventional type A8, which was used as the basis for this calculation, and has a 13.9% increase in thrust and a 19% reduction in SFC. The area ratios in Table 1 are calculated by dividing the area of ​​each main jet nozzle by the nozzle area of ​​A8.

[0015] [Table 1] [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a conceptual diagram of the turbofan engine of the present invention. [Figure 2] This is a T-s diagram in which TIT is varied while CPR is constant. [Figure 3] A diagram showing the relationship between TIT, BPR, and thrust in this cycle. [Figure 4] FIG. 10 is a diagram showing the relationship between TIT, BPR, and SFC in this cycle. [Figure 5] This is the fan operation map. [Figure 6] This is the LPC operation map. [Figure 7] This is the HPC operation map. [Figure 8] Turbine flow characteristic curves. Example 1 is HPT, Example 2 is LPT (solid line is the present invention, dotted line is a conventional engine). DETAILED DESCRIPTION OF THE INVENTION

[0017] The core exhaust nozzle controls the HPC operating line of the turbofan engine of this invention, and the expansion ratio of both the HPT and LPT must not exceed the choke value so that the operating conditions of the downstream exhaust nozzle are transmitted to the upstream HPC. From Figure 1, the present invention appears to be mechanically identical to a conventional turbofan, but the technological concept of lowering the TIT and increasing thrust is completely different from conventional technology. Lowering the TIT necessarily results in a decrease in thrust (output). This was the common knowledge with gas turbines.

[0018] Aiming to create a new field for aero engines, this invention has a different goal from the conventional technological trend of pursuing higher temperatures and higher bypass ratios, and its cycle is a method of increasing BPR and boosting thrust through a high LPT expansion ratio, despite the low specific entropy generated by the core engine, as explained in Figure 2. In other words, the novelty and inventiveness of this invention lie not in the newness of the mechanism or structure, but in the conceptual design, that is, in the software rather than the hardware.

[0019] As shown in Figure 1, the present invention features larger main jet nozzle and fan bypass nozzle exit areas and a larger turbine capacity than conventional turbofans. The larger main jet nozzle exit area increases core flow, lowering the fuel-air ratio and TIT. Furthermore, engine backpressure decreases, increasing the LPT expansion ratio. The larger fan bypass nozzle exit area also increases bypass flow, enhancing BPR and increasing thrust. However, mechanical changes alone do not generate thrust. Increasing flow and thrust requires increased thermal energy. In this invention, the heat supplied to the engine is not only the fuel flow rate in the combustor, but also the LPT absorbs and utilizes a portion of the available energy remaining in the core exhaust, thereby increasing the work of the low-pressure shaft. The two arrows in Figure 1 indicate this energy transfer. From the above, this engine configuration transcends the boundaries of conventional turbofan cycles and creates the technological concept of "reducing TIT and increasing thrust." [Example]

[0020] As an example, we will use conventional engine A8 and present invention B8 in Table 1 to explain the differences in the cycles. Figures 5, 6, and 7 show operating maps for the FAN, LPC, and HPC. Figure 8 is a turbine flow characteristic curve diagram. Example 1 in Figure 8 is a characteristic curve diagram for the high-pressure turbine HPT, and Example 2 is a characteristic curve diagram for the low-pressure turbine LPT. In the diagram, the solid line is the flow characteristic curve for the present invention, and the dotted line is the conventional engine. The black dots at the ends of the characteristic curves are the turbine choke points for each. As is clear from the diagram, the conventional engine and present invention being compared here have the same hardware for the FAN, LPC, and HPC, but different turbine hardware.

[0021] In Figures 5 to 7, point A is the aerodynamic design point (ADP) for the conventional engine and this engine, and the corrected relative fan speed Nfc = 1. The operating point for the conventional takeoff rating is point A, and the conventional TIT at point A is 1820K (1547°C), the fan flow rate is 9kg / s, the core flow rate is 1kg / s, and the BPR is 8. In this calculation, 1820K is used as the upper limit temperature for the TIT for an engine for a small or medium-sized aircraft.

[0022] Point B is an operating point where the relative corrected fan speed is increased to Nfc = 1.03 on the same operating line as the conventional engine, and is the operating point at the takeoff rating of this engine. The TIT at point B of this invention is 1690K (1417°C), which is 130 degrees lower than the TIT of the conventional engine at point A. The thrust at point A of the conventional engine and the thrust at point B of this engine are almost the same, as shown in Table 1. The main jet nozzle area ratio in this calculation between the conventional engine and this invention is approximately 1 to 1.235.

[0023] When the relative corrected fan speed of invention B8 is increased from 1 to 1.03, the LPC is coaxial with the fan, so the mechanical speed is the same but the inlet temperature is higher than the fan, and the relative corrected speed decreases as shown in Figure 6. The relative corrected flow rate of 1.02 at the HPC inlet obtained from the LPC outlet condition is shown by the vertical dotted line in Figure 7 of the HPC map.

[0024] In this engine, the nozzle area A7 is set wider than in a normal conventional engine, so if the HPT and LPT do not exceed their choke points, the resistance downstream of the HPC decreases, and as shown in Figure 7, the HPC operating line moves toward the choke side, increasing the flow rate at operating point B and lowering the pressure ratio HPR. Here, the HPT, LPT, and nozzle are all choked. In other words, in Examples 1 and 2 in Figure 8, which show the turbine flow characteristics, the choke point for the conventional engine is A, and the choke point for this invention is B. The turbine nozzle area for both the HPT and LPT is set to the minimum area that allows the HPC operating line to move.

[0025] These are the key points and inventive steps of this invention. Until now, no one had realized that lowering the TIT and widening the core exhaust nozzle area would produce a large LPT expansion ratio, as shown in Figure 8, and increase the BPR. Furthermore, no one had ever thought that lowering the TIT, increasing the airflow per frontal area, and increasing the BPR would reduce fuel consumption per thrust. In other words, the technical concept of this invention is not something that even experts can easily come up with, and had been completely unknown until now.

[0026] The difference between conventional thinking about methods for improving engine performance and the thinking (point of view) of this invention has led to the inventive step of this invention. Performance indicators for gas turbines include specific power (specific impulse) and thermal efficiency. To increase specific impulse, the maximum temperature is raised, and to improve thermal efficiency, the pressure ratio is increased. However, in this invention, the TIT is lowered while the pressure ratio remains roughly constant.

[0027] The novelty and inventive step of this invention is that it has focused on this point and created a new cycle. By widening the core exhaust nozzle and reducing back pressure, the invention increases fan flow without increasing fuel flow, going beyond the boundaries of conventional turbofans, lowering the temperatures at the turbine inlet and engine outlet, further increasing the LPT expansion ratio, recovering some of the exhaust heat, and increasing the flow rate per frontal area, thereby increasing thrust. [Industrial Applicability]

[0028] Increasing the BPR of the proposed B-type engine (Table 1) to 14.5 would result in a 37.7% increase in thrust and a 32.9% reduction in SFC compared to the conventional A8 engine, which was the basis for this calculation. This invention, which aims to create a new field for aircraft engines, reduces CO2 emissions by lowering SFC and NOx emissions by lowering combustion gas temperatures. Furthermore, as a means of improving economic efficiency, it lowers turbine inlet temperatures to increase thrust, extending turbine life and reducing lifecycle costs, thereby achieving both environmental and economic benefits. Furthermore, it could contribute to the future realization of hydrogen-fueled turbofan engines by suppressing NOx generation, a weakness of hydrogen combustion. For turbofans, which have traditionally prioritized high temperature and pressure, this cycle opens up a new world of improved performance at lower temperatures. [Explanation of symbols]

[0029] A: Operating point or area of ​​relative corrected rotation speed Nfc=1 ADP Aerodynamic design point BPR Bypass ratio COMB Combustor FAN Fan G Actual flow rate HPC High pressure compressor HPT High Pressure Turbine LPC Low Pressure Compressor LPT Low Pressure Turbine M Mach Number NFC Fan Relative Correction Speed numbers 0. Atmosphere 1. Fan inlet 22. Fan outlet 2. LPC outlet 3. HPC outlet (combustor inlet) 4. Combustor outlet (HPT inlet) 5.LPT inlet 6.LPT outlet 7. Core nozzle outlet 8. Bypass nozzle outlet

Claims

[Claim 1] The present invention sets the core main jet nozzle and fan bypass nozzle area wider than that of a normal turbofan; 1) The wide main jet nozzle area increases the core flow rate, lowering the fuel-air mixture ratio and reducing the turbine inlet temperature (TIT). 2) The wide main jet nozzle area also reduces engine back pressure, increasing the expansion ratio of the low-pressure turbine (LPT), which drives the fan, and increasing the fan intake air flow rate. 3) A larger fan bypass nozzle area increases the bypass flow rate, increasing the bypass ratio (BPR) and increasing thrust. 4) The thermal energy required to increase BPR and thrust is not only provided by the fuel supplied to the combustor, but also by absorbing some of the available energy contained in the core engine exhaust gas through the LPT, which has an increased expansion ratio. 5) In other words, as the fuel-air ratio decreases, the specific enthalpy decreases, but as the flow rate of the core engine increases, the total enthalpy increases, allowing for an increase in BPR and thrust. As mentioned above, the turbofan cycle reduces TIT and engine outlet temperature to increase thrust.

Images