Aeronautics and astronautics – Aircraft power plants
Reexamination Certificate
2000-03-06
2001-10-30
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Aircraft power plants
C239S127100, C060S039500
Reexamination Certificate
active
06308914
ABSTRACT:
BACKGROUND TO THE INVENTION
This invention relates to an apparatus for the suppression of infra red emissions from a jet engine, and more particularly but not exclusively to such an apparatus for the suppression of infra red emissions from a gas turbine engine of an aircraft such as a helicopter.
Helicopter gas turbine engines generate significant amounts of waste thermal energy. Upon exit from the exhaust pipe of the engine, infra red emissions in this waste energy are readily observable by thermal imaging means as an exhaust plume and thus may be used in the targeting of the aircraft by enemy weapon systems. Also hot exhaust plumes can interact with the fuselage, thus heating the fuselage and causing the fuselage to radiate infra red energy.
DESCRIPTION OF THE PRIOR ART
It is known to suppress the infra red emissions in the exhaust and to cool the exhaust by mixing the hot exhaust gases with a substantial volume of ambient temperature air within a suppressor body located such that the exhaust gases from the exhaust of the engine pass into the suppressor body. Thus substantially cooled exhaust gases are ejected from the helicopter. The greater the cooling efficiency of the suppressor system, the greater the survival probability of the helicopter.
Known suppressor systems are however inefficient at mixing the hot exhaust gases and the cooling air whilst maintaining the suppressor body of an acceptably light and small construction, resulting in only a low reduction of the overall temperature of the exhaust plume. Larger heavier structures which are more efficient at exhaust gas temperature reduction produce large associated engine installation losses and can affect helicopter performance.
Various proposals have been put forward for improving the efficiency of infra red suppression systems, such as described in GB-A-2100798, or EP-A0286800. Such prior proposals have however concentrated solely on the configuration of the suppressor body to improve reduction of engine exhaust gas temperatures.
SUMMARY OF THE INVENTION
According to a first aspect of the invention we provide an apparatus for the suppression of infra red emissions from an engine including a suppressor body through which pass exhaust gases from the engine, the suppressor body having an inlet means for air which is mixed within the suppressor body with the hot exhaust gases to cool the exhaust gases before final exhaustion, characterised in that means are provided to apply within the suppressor body, sonic or supersonic energy to enhance the efficiency of infra red suppression.
Thus in an apparatus in accordance with the invention although the design and configuration of the suppressor body is obviously important improvements in the efficiency of infra red suppression may be achieved in a novel and inventive manner as the flow direction and properties of, particularly but not exclusively, a gas turbine engine exhaust, may be altered by the application of sonic or supersonic energy.
In a typical arrangement, and preferably in an apparatus in accordance with the invention the suppressor body at least substantially surrounds the engine exhaust pipe, and provides a duct between the engine exhaust pipe and suppressor body which duct provides the air inlet means. Thus the ambient temperature air is drawn into the suppressor body for mixing with the hot exhaust gases from the exhaust pipe of the engine.
In such an arrangement, the exhaust plume which is ejected from the suppressor body is of generally conical configuration. To enhance mixing of the hot engine exhaust gases and the ambient air, the cone angle generated within the suppressor body needs to be as wide as possible and widening of the cone may be achieved by the application of sonic or supersonic energy. Thus in one embodiment, the sonic or supersonic energy may be applied by actuator means provided on the engine exhaust pipe within the suppressor body. The precise frequency or frequencies of vibration may be determined theoretically, or by experiment such as by placing a probe within the suppressor body and applying different frequencies to achieve optimum cone widening. The edge of the core flow is characterised by the presence of a strong shear layer which divides the hot exhaust gases from the surrounding cool air flow. The presence of the shear layer acts to reduce the rate of mixing between the hot exhaust gases and the surrounding cool air. The application of sonic or supersonic energy serves to disrupt or weaken the shear layer and significantly enhance the rate of mixing between the hot exhaust gases and the surrounding cold air.
In another embodiment sonic or supersonic energy is applied to promote attachment of a boundary layer flow at an internal surface of the suppressor body. This is desirable both to reduce engine installation losses as a result of separation of flow at the surface due to boundary layer flow being slowed at the surface and thus tending to separate away from the surface, and to maintain efficient cooling of the surface itself to enhance infra red suppression. Thus the sonic energy may be applied by actuator means provided on the surface of the suppressor body, for example on an external surface of the suppressor body.
It has been found that this improves airflow, over the internal surface hence heating of the surface, is minimised or prevented altogether. This is important since it prevents the suppressor body itself from becoming warm and thereby becoming a source of radiant energy which could be detected.
In each case, the actuator means may include a plurality of high frequency response actuators, such as piezo-ceramic actuators, which may be controlled by a control means which applies a signal of a desired frequency to the actuators.
Although the invention may be applied to engines generally, preferably the apparatus is adapted for use with a gas turbine engine or the like.
According to a second aspect of the invention we provide an engine and an apparatus for the suppression of infra red emissions from the engine characterised in that the apparatus for the suppression of infra red emissions is an apparatus according to the first aspect of the invention.
According to a third aspect of the invention we provide a vehicle having an engine and an apparatus for the suppression of infra red emissions from the engine according to the second aspect of the invention.
The vehicle may be an aircraft e.g. a helicopter.
According to a fourth aspect of the invention we provide a method of enhancing the efficiency of the suppression of infra red emissions from an engine including the steps of providing a suppressor body for the passage of exhaust gases from the engine, the suppressor body having an inlet means for air which is mixed within the suppressor body with the hot exhaust gases to cool the exhaust gases before final exhaustion, characterised in that the method includes applying within the suppressor body, sonic or supersonic energy.
REFERENCES:
patent: 4026472 (1977-05-01), Rabone
patent: 4290262 (1981-09-01), Wynosky et al.
patent: 5044464 (1991-09-01), Bremigan
patent: 5088575 (1992-02-01), Eriksson
patent: 5775589 (1998-07-01), Vdoviak et al.
patent: 5799874 (1998-09-01), Eigenbrode et al.
patent: 6112513 (2000-09-01), Catt et al.
patent: 1456018 (1976-11-01), None
Kokkalis Anastasios
Spurway Simon Peter
Barefoot Galen L.
GKn Westland Helicopters Limited
Larson & Taylor PLC
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