JP2024007302A - Low-entropy engine compatibly attaining environmental conservation and economical efficiency - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower a turbine intake temperature (TIT) without reducing a thrust by employing a variable mechanism for an exhaust nozzle of a core and widening a variable core nozzle (VCN) at a take-off rating, and to reduce a specific propellant consumption (SFC) by controlling a thrust by reducing a fuel flow rate, without lowering a fan rotating speed in cruising.

SOLUTION: A take-off rating at which a fan rotating speed is maximum is defined as an aerodynamic design point (ADP), it is made possible to choke a high-pressure turbine (HPT), a low-pressure turbine (LPT), and a nozzle of a VCN at the ADP, and then increase a low-pressure shaft rotating speed without increasing a high-pressure shaft rotating speed when the VCN is opened, and new "TIT-flow rate-thrust" relation for a turbofan engine for subsonic aircraft is thus created to solve the problem to be solved.

EFFECT: Heat efficiency is enhanced through low-entropy cycles to reduce an SFC and decrease a CO2 discharge amount, and a discharge amount of NOX is reduced with a low TIT to prolong a turbine lifetime, thereby compatibly attaining economic efficiency and environment adaptability.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a variable cycle engine (VCE) in which a core exhaust nozzle is a variable mechanism. This invention relates to environmental measures for turbofan engines, and is a low entropy engine that reduces greenhouse gas emissions and reduces engine life cycle costs.

The independent variable that can be manipulated in conventional fixed cycle turbofans is fuel flow. The fuel flow rate, that is, the turbine inlet temperature (TIT) determines the rotational speed of the compressor and the fan, and also determines the thrust force. In this way, the thrust of a jet engine is controlled by the TIT, and the TIT is limited by the melting point of the material. Therefore, advanced turbine air cooling technology and innovative materials technologies have been developed. However, if the amount of cooling air is too large, the performance improvement due to higher temperature will be outweighed by the cycle loss due to excess cooling air. Furthermore, as the flame temperature inside the combustion machine increases, the amount of NOx (nitrogen oxide) emissions, which are greenhouse gases, increases exponentially.

Mitsuo Morita and Shizuo Sekine “Performance beyond design point of multi-shaft turbofan engine” Aerospace Technology Research Institute Report No. 347

Keizo Hatta “Gas Turbines and Jet Engines” Kyoritsu Publishing Co., Ltd.

Conventionally, the direction of technological development of turbofan engines has been to increase the difference between the maximum cycle temperature (turbine inlet temperature TIT) and the minimum temperature (atmospheric temperature Ta) with the aim of making them compact, lightweight, and high in thrust. The problem to be solved by the present invention, on the contrary, is to suppress the rise in TIT and maximize the thrust to TIT.

To explain the above issues separately for the ground and the air, the first is to lower the TIT without reducing the thrust at the takeoff rating. Generally speaking, lowering TIT will reduce thrust. Second, during cruising, the thrust is controlled by reducing the fuel flow rate while maintaining the engine flow rate to reduce specific fuel consumption (SFC). Generally speaking, if the fuel flow rate is reduced, the fan rotation speed will decrease and the engine flow rate will also decrease.

In order to solve the above problem, it is sufficient to create a system that increases the rotation speed of the low-pressure shaft without increasing the rotation speed of the high-pressure shaft. The means are;
1) Install a variable core exhaust nozzle (VCN) to increase the number of independent variables that can be manipulated to two.
2) The takeoff rating at which the fan rotation speed is maximum is the aerodynamic design point (ADP).
3) Let ADP be the choke point of the high pressure turbine (HPT) and the low pressure turbine (LPT).
4) By widening VCN, the operating line of the high pressure compressor (HPC) is moved to the high flow rate side at the choke point ADP, the flow rate at the operating point is increased, and the pressure ratio (HPR) is increased. The nozzle areas and expansion ratios of the HPT, LPT, and VCN on the downstream side are set so as to decrease (details will be explained in the "Details of the Invention" section).

The effects of the invention are to reduce CO2 emissions by reducing SFC and NOx emissions by reducing TIT, extend the life of the turbine by lowering the temperature of TIT, reduce life cycle costs, and reduce global warming. The aim is to strike a balance between countermeasures and economic efficiency.

Basic configuration of the low entropy engine of the present invention. FAN operation map. LPC operation map. HPC operation map. The flow rate characteristic curve diagram of the turbine, the solid line in the figure is the present invention, and the dotted line is the conventional engine (Example 1 is HPT, Example 2 is LPT). Comparison of turbine inlet temperature and thrust at takeoff rating for the present invention and conventional engines. A diagram showing the relationship between relative thrust (F)/(F)des and SFC (Example 3 is stationary on the ground, Example 4 is when cruising). Turbine characteristic curve diagram showing the aerodynamic connection between HPT and LPT (Example 5 is stationary on the ground, Example 6 is when cruising). A diagram showing the relationship between the flow rate of the turbine part of a fixed cycle engine. Comparison of entropy changes at takeoff rating for the present invention and conventional engines.

The basic configuration of the low entropy engine of the present invention is shown in FIG. The mechanism is a variable cycle engine with a variable core nozzle. In the figure, FAN is a fan, LPC is a low pressure compressor, HPC is a high pressure compressor, COMB is a combustor, HPT is a high pressure turbine, LPT is a low pressure turbine, and VCN is a variable core nozzle. The numbers also represent engine position numbers.

An easy way to explain the cycle characteristics and effects of the low entropy engine of the present invention is to compare and show the differences between a conventional fixed cycle engine with the same engine front area and the present invention equipped with a variable core nozzle. Therefore, in this operational description, two engines with equal fan front areas and the same FAN, LPC, and HPC geometries are used: a conventional turbofan with a fixed core exhaust nozzle, and a variable cycle engine equipped with a VCN (the present invention). Calculate and compare the takeoff rating and operation at cruise (same flight conditions).

Figures 2, 3, and 4 show operational maps of FAN, LPC, and HPC. These are based on the map published in Aerospace Technology Research Institute Report No. 347 (Non-Patent Document 1), and the flow rate characteristics with respect to the rotation speed are reproduced by a method of parabolic approximation to the flow rate, and each calculated on the operating line. The operating points are plotted. FIG. 5 is a diagram depicting a turbine flow rate characteristic curve using Equation 1, which will be described later. Example 1 is a characteristic curve of the high pressure turbine HPT, and Example 2 is a characteristic curve of the low pressure turbine LPT. In the figure, the solid line is the flow characteristic curve of the present invention, and the dotted line is the flow characteristic curve of the conventional type. As is clear from the figure, in the conventional type and the present invention compared here, the FAN, LPC, and HPC are the same hardware, but the turbine is different hardware. Note that Aeronautical Engineering Research Report No. 347 was written in the engineering unit system, and this specification also follows that system.

First, as "Example 1", setting values of basic specifications of the engine will be shown, and a calculation method will be explained. It also shows the difference between the operation of the present invention and the conventional type based on calculations. In FIGS. 2 to 5, point A is the aerodynamic design point (ADP) of a conventional engine with a fixed exhaust nozzle, where the fan relative corrected rotation speed Nfc=100% and TIT=2000K. For simplicity, it is assumed that the conventional HPT and LPT are choked at point A.

Point TS (Top speed) is an operating point where the fan rotation speed is increased to Nfc=105% on the same operating line as the conventional type. The TS point is the ADP of the present invention, the relative corrected rotation speed of the fan is 105%, and the TIT is 1773K. In the present invention, both HPT and LPT are choked at point TS. Further, in this case, when the relative correction rotation speed is 100%, TIT=1614.6K.

Calculation of the takeoff rating proves that the thrust at point A of the conventional model is almost equal to the thrust at point TS of the present invention, which opens the VCN, increases the fan relative corrected rotation speed to 105%, and lowers the TIT by 227 degrees. . The conventional calculation method at point A is a normal design point performance calculation.

The calculation method of the present invention at point TS will be explained. If the fan corrected rotation speed is increased to 105%, the mechanical rotation speed is the same since the LPC is coaxial with the fan, but the inlet temperature is higher than that of the fan, so the corrected rotation speed becomes as low as 99.5%. When a constant rotation speed curve with Nlc=99.5% is drawn on the LPC map, the intersection of the curve and the LPC operating line is the LPC operating point TS of the present invention. Therefore, since the LPC corrected flow rate and pressure ratio can be obtained, the HPC inlet corrected flow rate can be determined from the LPC outlet conditions. The HPC inlet relative corrected flow rate of 1.026 is shown as a dotted line on the HPC map in FIG.

The intersection of the dotted line indicating the HPC corrected flow rate and the HPC operating line is the HPC operating point when the fuel flow rate is increased and the fan rotation speed Nfc is increased from 100% to 105% in the conventional fixed cycle, HPR = 9.015, TIT = 2088K, which exceeds the limit and makes it impossible to operate. Therefore, a turbine and VCN design is required to lower the TIT to 1773K.

In NAL Report No. 347 (Non-Patent Document 1), the turbine flow rate characteristics are approximated by an elliptic equation shown in Equation 1. In Equation 1, i is the entrance and e is the exit. In the takeoff rating calculation, G*Sqrtθi/δi is the corrected flow rate at the aerodynamic design point, and Pi/Pe is the expansion ratio at the aerodynamic design point. If i=4 and e=5, the left side of Equation 1 represents the HPT inlet corrected flow rate. Next, the corrected flow rate at the combustor outlet with TIT specified as 1773K is shown in Equation 2.

Here, ε is the combustor total pressure loss coefficient. In order to avoid choking of the HPT at the initial stage of calculation, the choke values of the corrected flow rate and expansion ratio in Equation 1 are assumed to be large, and the second term on the right side of Equation 2, the denominator HPR = P03/P02, is By performing various calculations and matching the combustor outlet corrected flow rate on the left side with the HPT inlet corrected flow rate on the left side of Equation 1, the HPR value at the point TS shown in FIG. 4 can be found. This HPR value is the value when the VCN is expanded, and is a state in which the operating conditions of the VCN are transmitted to the upstream HPC, and at this calculation stage, it is the VCN that controls the operating line of the HPC.

In other words, the HPC downstream throttle is opened and the HPC operating line is moved to the high flow rate side, and the value at the intersection of the operating line and the HPC corrected flow rate derived from the LPC exit conditions becomes the HPR. Therefore, a matching calculation is performed in which the core flow rate Ghc increases and the HPC outlet pressure P03 does not rise excessively. When the left sides of Equation 1 and Equation 2 become equal, if the choke values of the corrected flow rate and expansion ratio of Equation 1 are made to match the calculated values, the HPT of the present invention can be calculated from the point TS of Example 1 in Figure 5 (ADP of the present invention). ).

Next, the LPT characteristics can be obtained by replacing the engine position number in Equation 1 with the LPT inlet and outlet position numbers 5 and 6, and matching the HPT outlet corrected flow rate with the LPT inlet corrected flow rate. Here again, the choke values of the corrected inlet flow rate and expansion ratio of the LPT are set to values that do not prevent the operating conditions of the VCN from being transmitted upstream, and after calculation, the choke values are made to match the calculated values. In other words, LPT is also choked at point TS. Therefore, the choke value of both HPT and LPT becomes the minimum area that allows the above-mentioned HPC operation. Note that the method for calculating the balance between flow rate and work is already known and will therefore be omitted.

From the matching calculations described above, in the present invention, by widening the core exhaust nozzle, the fan flow rate increases without increasing the fuel flow rate, and both the core flow rate and the bypass flow rate increase, so it is possible to lower the TIT without reducing thrust. I can do it. Table 1 shows the relationship between the flow rate, TIT, and thrust. Further, FIG. 6 shows a comparison of the turbine inlet temperature and thrust of the present invention and the conventional engine at takeoff rating. The VCN area of the present invention at takeoff rating is 1.355 times that of the conventional type. It can be seen from Table 1 and FIG. 6 that with this setting, the present invention can lower TIT by 227 degrees than the conventional type without reducing thrust.

Next, the partial load performance while stationary on the ground is shown in Example 3 of FIG. 7, and the cruise performance at an altitude of 10 km and a flight Mach number of 0.9 is shown in Example 4 of FIG. Example 3 compares the partial load performance of a conventional turbofan with a fixed core nozzle (Conventional TF) and this engine VCE in a stationary state on the ground. The SFC at the two operating points connected by dotted lines in the figure is 0.387 for the conventional engine and 0.32 for the present engine, and the present invention is able to reduce the SFC by approximately 17%. Example 4 is a comparison of cruise performance under the same conditions at an altitude of 10 km and a flight Mach number of 0.9. The SFC at the two operating points connected by dotted lines in the figure is 0.804 for the conventional type and 0.7 for the present invention. The present invention in which the VCN is opened can improve the SFC at the dotted line position during cruising by approximately 13% over the conventional type.

Next, two new theories of this cycle will be shown as "Example 2". First, the first theory of this cycle is that the relationship between HPT and LPT in this cycle is different from the energy distribution of a normal two-shaft series free turbine. A turbine characteristic curve diagram showing the aerodynamic connection between the HPT and LPT of the present invention is shown in FIG. Example 5 in FIG. 8 is a state where the aircraft is stationary on the ground, and Example 6 is a state where the aircraft is cruising (altitude 10 km, flight Mach number 0.9). As can be seen from the figure, when the VCN is opened and the TIT is lowered, the LPT expansion ratio increases while the HPT expansion ratio remains constant. This is completely different from the partial load expansion ratio distribution when turbines are connected in series in conventional fixed cycle engines.

FIG. 9 shows a flow rate relationship diagram of the turbine section of a conventional turbo fan with a fixed core nozzle. As can be seen from Figure 9, at the design point, the relationship between both turbines is connected as shown by the solid line, but when the total expansion ratio decreases at partial load, it becomes like the dotted line. Decrease. That is, when the TIT is lowered, the ratio between the work of the HPT and the work of the LPT increases, and the output of the LPT rapidly decreases (from Non-Patent Document 2, page 26).

What should be noted in FIGS. 8 and 9 is that the directions of the arrows indicating increases and decreases in the LPT expansion ratio are completely opposite. The operation of the present invention shown in FIG. 8 is an unprecedented novel phenomenon that breaks the conventional aerodynamic law connecting two turbines. The operations of Examples 5 and 6 in FIG. 8 embody the ``system for increasing the low-pressure shaft rotation speed without increasing the high-pressure shaft rotation speed'' described in ``Means for Solving the Problem.'' This system creates a new theory for turbines. This phenomenon, brought about by the large VCN area, is logical and central to this cycle, and represents the inventive step of the present invention.

Variable exhaust nozzles for aircraft engines have been around for a long time. The world's first mass-produced engine, the Yumo 004B engine, had a variable exhaust nozzle to maintain a constant TIT during high-speed operation. Currently, VCN is used in supersonic military aircraft, and the VCN is opened when using After Banner. However, the purpose of use was completely different from that of the present invention, and the turbine coupling characteristics shown in FIG. 8 did not yet exist in this world.

Next, as theory 2 of this cycle, it will be shown that this cycle is a low entropy cycle, and therefore has high thermal efficiency. In the comparison between the present invention and the conventional type in Example 3 of FIG. 7, the propulsion efficiency is not relevant because the vehicle is stationary on the ground. A T-s diagram for the core engine during takeoff was created from the calculation results of the takeoff rating in Example 3. The diagram is shown in FIG. In FIG. 10, the outer area represents the amount of work of the core engine at point A of the conventional type, and the inner area represents the amount of work (heat amount) of the core engine at point TS of the present invention. The present invention, in which the temperature difference between the combustor inlet 3 and the combustor outlet 4 is small, is a low entropy cycle. It is clear from the figure that the low entropy cycle produces less work per unit flow rate of the core engine. However, Table 1 clearly shows that the thrust is maintained by increasing the engine flow rate.

If the temperature rise when an amount of heat dQ is applied to an object having a weight of G [kgf] is dt [° C.], Δt is proportional to ΔQ and inversely proportional to the weight G. Δt∝ΔQ/G. This engine is a device that increases G without increasing Q during takeoff, where G is the core flow rate Ghp + Gf and the gas generator flow rate. That is, in terms of work efficiency, the power of the engine at point A and point TS is almost the same (see Table 1). The characteristics of this engine are: 1) the temperature difference in the heat receiving process and the heat radiation process is small; 2) the temperature difference in the adiabatic expansion process is large (the turbine expansion ratio is large); these two points make this cycle a low entropy cycle. I can say that. The reason why the power can be maintained without increasing the amount of fuel is that the exhaust residual energy becomes smaller, as is clear from FIG.

In this variable cycle engine, when the VCN is widened to increase the fan speed and increase the fan suction flow rate, not only the bypass flow rate but also the core flow rate increases. Therefore, the bypass ratio is rather reduced. The reason why this engine's SFC is higher than the conventional type when stationary on the ground is due in part to improved thermal efficiency (however, propulsion efficiency improves when cruising). This is a feature of this cycle.

The aviation industry accounts for 2.6% of global CO2 emissions and emits large amounts of carbon dioxide (CO2). Jet fuel is a serious source of air pollution, and the aviation industry is under strong pressure to take steps to reduce greenhouse gas emissions. On the other hand, adding costs to environmental measures increases development costs, soars airfares, and impedes economic activity. Achieving both economic efficiency and environmental conservation is essential to realizing sustainable aircraft engines.

The theory of this cycle is that, first, the characteristics of the turbine are different from the work distribution of a conventional two-shaft series free turbine, and the LPT expansion ratio can be increased without changing the HPT expansion ratio. Second, the temperature difference between the combustor inlet and outlet is small, resulting in a low entropy cycle, which increases thermal efficiency. From these theories, we will create a new relationship between TIT, flow rate, and thrust.

As an environmental measure, the low entropy engine of the present invention reduces CO2 emissions by reducing SFC and reduces NOx emissions by lowering combustion gas temperature. Furthermore, as a measure to improve economic efficiency, it is possible to lower the turbine inlet temperature without reducing the thrust, extend the life of the turbine, and reduce life cycle costs, achieving both the environment and the economy. Probability is high.

A Area ADP Aerodynamic design point BPR Bypass ratio COMB Combustor Cpt Constant-pressure specific heat of turbine part FAN Fan f Fuel-air mixture ratio G Actual flow rate HPC High-pressure compressor HPT High-pressure turbine LPC Low-pressure compressor LPT Low-pressure turbine M Mach number N Rotation speed Nfc Fan relative Corrected rotational speed Nlc LPC relative corrected rotational speed s Entropy Sqrt() Square root SLS Stationary state on sea surface TS High speed rotation range (top speed)
VCN Variable core nozzle (G√θi/δi)/(G√θi/δi) des Relative correction flow rate δ P/Ps ε Total pressure loss coefficient θ T/Ts
Number a. Atmosphere 1. Fan inlet 22. Fan outlet 2. LPC exit 3. HPC outlet (combustor inlet) 4. Combustor outlet (HPT inlet)
5. LPT entrance 6. LPT exit7. Core nozzle outlet 8. Bypass nozzle outlet

Claims (1)

The present invention provides a mechanism for a variable cycle turbofan engine: 1) The core exhaust nozzle is a variable nozzle (VCN).
2) The takeoff rating at which the fan rotation speed is maximum is the aerodynamic design point (ADP).
3) Let ADP be the choke point of the high pressure turbine (HPT) and low pressure turbine (LPT).
As an inventive step, 4) the operating line of the high pressure compressor (HPC) is moved to the choke side at the choke point ADP, and the nozzle areas and expansion ratios of the downstream HPT, LPT, and VCN are set so that the HPC pressure ratio decreases.
As its operation,
5) When the VCN is opened, the engine back pressure decreases, the LPT expansion ratio increases, the fan rotation speed increases, and both the core flow rate and bypass flow rate increase without increasing the fuel flow rate.
6) Due to the increase in core flow rate, the fuel-air ratio decreases and the turbine inlet temperature (TIT) decreases.
7) By increasing the bypass flow rate, the thrust on the bypass side is increased and the total thrust is maintained.
As a new regulation for turbine characteristics, 8) By opening the VCN, the LPT expansion ratio is increased while the HPT expansion ratio is constant, creating turbine characteristics that overturn the work distribution law of conventional 2-shaft series free turbines.
9) Increase the low pressure shaft rotation speed without increasing the high pressure shaft rotation speed.
New regulations regarding cycle characteristics include 10) Forming a low-entropy cycle in which the temperature rise in the combustion process is small and the temperature difference in the expansion process is large, increasing thermal efficiency through the low-entropy cycle.
11) Create a new TIT, flow rate, and thrust relationship for subsonic aircraft.
Effect: 12) If the VCN is opened at takeoff rating, TIT can be lowered without reducing thrust.
13) Also, during cruising, the VCN can be opened and the fuel flow rate can be reduced without lowering the fan speed to control the thrust and reduce the fuel consumption rate (SFC).
Industrial applicability: 14) Reduces CO2 emissions by reducing SFC, reduces NOx emissions by lowering combustion gas temperature, extends turbine life and saves life cycle costs.
Thanks to the above cycle effects, this low entropy engine achieves both environmental conservation and economic efficiency.

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