JPH045436A - Method for improving thermal efficiency of jet engine - Google Patents

Abstract

PURPOSE:To improve the thermal efficiency of a jet engine by mixing fine drops of water into compressed air for cooling the blades, and raising the temperature of combustion gas while suppressing the temperature rise of the blades. CONSTITUTION:A water tank 10 is installed in a jet aircraft in which compressed air is used to cool the blades 5 of an engine, and fine drops of water are mixed into the compressed air for cooling the blades 5. The latent heat of evaporation of these water drops is utilized to increase the heat conductivity on the side faces of the blades 5, which is cooled to a high degree to improve the thermal efficiency of the engine.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention improves the thermal efficiency of a jet engine by cooling the nozzle and blades of a jet engine installed in a jet aircraft and recovering exhaust heat from the engine. This invention can be used for.

(Prior Art) A jet aircraft is equipped with a turbofan engine as illustrated in FIG. This engine sends air compressed by a rotary first-stage compressor la and a second-stage compressor 1b to a burner 2, and combusts fuel separately supplied to the burner to generate high-temperature combustion gas. A compressor 1a fixed to the shaft 6 rotates the rotor 4 and its shaft 6 by injecting air through a blade-shaped nozzle 3 onto a plate 5 planted around the rotor 4;
1b and the fan 7 are rotated, and the combustion gas exiting the final stage of the blades 5 is ejected rearward from the ejection port 8 to generate thrust. FIG. 5 illustrates the gas flow in this case along with temperature changes. Much of the force that moves the aircraft forward comes from fan 7.
The thrust generated by the ejected gas is small.

The nozzle 3 and blade 5 (hereinafter, both will be collectively referred to as blades because they have the same structure) exposed to the high-temperature combustion gas become extremely hot.

The thermal efficiency of a jet engine is similar to that of a gas turbine.
The higher the temperature of the acting combustion gas, the higher the temperature, but because there is a limit to the heat resistance temperature of the blade material, it cannot be made extremely high, and currently it is set at 860° C. or lower.

Conventionally, as a means of suppressing the temperature rise of the blade, the blade was made hollow and had many pores that allowed communication between the inside and outside.
Sending compressed air into the blade to cool the plate from the inside, and cooling the blade from the outside by flowing an air flow jetting out of the blade from the pores along the outer surface of the blade,
At the same time, a heat shielding film made of air was formed on the outer surface of the plate to reduce the degree to which the blades were heated by the combustion gas.

As a result, it was possible to raise the surface temperature of the plate to 850°C, which is at the very limit of the heat resistance of the materials used, and to raise the combustion gas temperature to 1350°C.

In addition, water has a higher specific heat than air and can absorb a large amount of latent heat during evaporation, so the inventor filed a patent application for the idea of using water to cool gas turbine blades. No. 1982-251429, JP-A-2-55
No. 802, No. 2-55837, Patent Application No. 63-3129
No. 14, Patent Application No. 1-84696, No. 1-260599
No. 1-265039, etc.).

Conventionally, the following methods have been used to suppress the temperature rise of jet engine plates using water. In other words, - During the short period of time when a jet aircraft takes off and climbs, when a large amount of power is required, water is injected into the burner of the jet engine to lower the temperature of the combustion gas, and instead, the amount of fuel supplied is increased to save time. The system increases engine output, and when the aircraft shifts to horizontal cruising, water injection is stopped and normal combustion occurs. However, this method significantly deteriorates thermal efficiency and is different from the above-mentioned previous invention of the present inventor.

(Problem to be Solved by the Invention) Jet engines installed in jet aircraft have plates that are exposed to high-temperature combustion gas, similar to gas turbines, so cooling them with water will reduce the temperature of the combustion gas that acts on them. However, jet engines differ from general ground-based gas turbines (for example, for power generation) in that the thrust generated by the jet exhaust gas is used to propel the jet aircraft.

The present invention aims to provide a method for improving the thermal efficiency of a jet engine by utilizing cooling of the blades by cooling air containing fine water droplets and further recovering engine exhaust heat.

(Means for Solving the Problems) The first aspect of the present invention is to equip a jet aircraft that uses compressed air to cool engine blades with a water tank, and to mix fine water droplets into the compressed air for plate cooling. The aim is to utilize this latent heat of vaporization to increase the heat transfer coefficient on the inner surface of the blade, thereby cooling the blade to a high degree and improving the thermal efficiency of the jet engine.

The second point of the present invention is to recover the heat of the jet engine exhaust gas to heat the compressed air exiting the compressor and send it to the burner, thereby reducing the amount of fuel used and improving the thermal efficiency of the jet engine. It is something.

(Function) To explain the -th point, as shown in Fig. 1, the temperature of the combustion gas flowing along the outer surface of the hollow plate 1 is
, the temperature of the plate wall is Tw, the temperature of the cooling compressed air blown into the blade is Tc, and the heat transfer coefficient from the combustion gas to the blade wall is α. , if αco is the heat transfer coefficient from the blade wall to the cooling air that does not mix with water droplets inside the plate, then
Since the amount of heat passing through is equal, (TG − Tw ) Qa = (Tw − Tc ) α
It can be seen as o0. For example, Tw”850°C, To = 1350°C, Tc =
When the temperature is 350°C, fine water droplets are mixed into the cooling compressed air to increase the heat transfer coefficient αco from the blade wall, and this is made twice the heat transfer coefficient αG from the combustion gas to the blade wall (TO- 7,)Qa = (Tw T()X 2a
.

T a ; 3T w 2T c = 1850°C, and the combustion gas temperature has been reduced from the conventional 1350°C to 1850°C.
As a result, the output and thermal efficiency of the jet engine can be increased. This can be done by mixing minute water droplets into the cooling air sent into the blades to achieve good cooling.

In order to cool the blades using water in this way,
It is necessary to equip a jet aircraft with a water tank 10 (Fig. 342), but since jet aircraft often fly in extremely low temperature airspace, the tank should have an insulated structure to prevent the water from freezing, and a heating device should be installed to control the water temperature. The temperature shall be maintained at 20-80°C.

Next, to explain the second point, in current jet engines, only the exhaust gas at about 1000°C is used to generate thrust by the jet flow, and the I¥! Abandoned.

As schematically shown in FIG. 2, the present invention provides a circular heat exchanger 9 in the gas flow path leading to the jet engine jet nozzle 8, and compresses approximately 350° C. discharged from the compressor 1b by the engine exhaust gas. Air is heated to about 900°C and supplied to burner 2.

In the burner 2, the compressed air is used to combust fuel to produce combustion gas at about 1350°C, which is blown onto the plates to rotate the rotor 4.

The amount of heat QA required to raise the temperature of air at 350°C to 1350'e as in the conventional method is QA = Cp (1350350) ” 1000, assuming that the specific heat at this point is c.
When the air temperature is set to 900°C by the c p heat exchanger 9, the amount of heat QB required to produce combustion gas at 1350°C is Qa = Cp (1350900) = 450c p
Therefore, the required fuel will be 45% of the conventional amount.

However, since the thrust of a jet engine is proportional to the absolute temperature of the exhaust gas, the temperature of the gas discharged from the heat exchanger should be 100°C lower than the temperature of the compressed air discharged from the compressor, which is 350°C.
If the temperature is higher than 450 degrees Celsius, the ratio of the thrust of the exhaust gas at this time to the thrust without water cooling will be, and with water cooling, the thrust of the engine will be reduced by about half.

However, in modern turbojet engines, most of the thrust is generated by the fan 7, so if 80% of the thrust comes from the fan 7, the thrust of the fan will not change at all even if water is cooled as described above. Therefore, even if the thrust of the engine exhaust is reduced to 57% of the conventional one, the thrust of the entire engine is 80 + 20 x 0.57 = 91%, so the reduction in thrust is only about 10% of the conventional one. Since fuel consumption is significantly reduced, thermal efficiency is significantly improved.

FIG. 3 shows the flow of gas acting in this way together with temperature changes, and shows whether the temperature tB of the combustion residue exiting the burner 2 is set to 1350° C., which is the same as in the conventional case, or The thermal efficiency of jet engines can be further increased by increasing the temperature of the combustion gas by utilizing the improved cooling effect caused by points.

For example, in a current turbofan jet engine that does not use the heat exchanger 9, the atmospheric temperature is 15°C and the burner 2
Calculating as the temperature of the waste left out tB = 1177°C and the pressure ratio 21.7, the pressure QB = 69.4 kcal/kgA
ir, thermal efficiency 27th = 0.360, but the pressure ratio is the same 21.7, and the gas temperature exiting the burner tB = 165
Calculated as 0℃, output Q = 164 kcal
/kgAir, thermal efficiency n th = 0494.

Furthermore, if heat exchanger 9 is used for this, the output Q = 164
kcal/kgAir, thermal efficiency 7) th=0.562, and the thermal efficiency becomes even higher.

(Effects of the Invention) (11) By mixing fine water droplets into the compressed air that cools the blades, it is possible to increase the temperature of the combustion gas while suppressing the temperature rise of the blades.

Therefore, even if the heat resistance of the blade material remains as it is, the thermal efficiency of the jet engine can be increased.

(2) Fuel consumption can be reduced by recovering a portion of engine exhaust heat.

(3) Even if the thrust from the exhaust gas is reduced due to exhaust heat recovery from the engine, the thermal efficiency can be increased due to the reduction in the amount of fuel used, and the subtractive gain will be larger.

[Brief explanation of drawings]

'tS1 is a cross-sectional view of the blade showing the transfer of heat during cooling of the hollow blade, Figure 2 is a cross-sectional view showing the state in which a turbojet engine is equipped with a heat exchanger, and Figure 3 is a cross-sectional view showing the heat exchanger installed in the turbojet engine. Fig. 4 is a cross-sectional view similar to Fig. 2 showing a conventional turbojet engine, and Fig. 5 is a schematic diagram showing the gas flow and temperature changes in this engine. . 1a - 1st stage compressor, 1b: i 2nd stage compressor, 2: burner, 3: nozzle, 4. Rotor, 5, blade, 6: shaft, 7: fan, 8: spout, 9: heat exchanger, 1
0: Water tank.

Claims (1)

[Claims] 1) A cooling water tank in a jet aircraft using a jet engine that cools the nozzles and blades by blowing compressed air into the nozzles and blades having a similar structure in which the inside and outside are communicated through a number of hollow pores. A method for improving the thermal efficiency of a jet engine, which comprises equipping an aircraft with fine water droplets in the compressed air for cooling to strengthen nozzle and blade cooling. 2) A method for improving the thermal efficiency of a jet engine, comprising providing a heat exchanger that heats compressed air for burning fuel in a burner of the jet engine using exhaust gas from the jet engine.