WO2005068796A1

WO2005068796A1 - Exhaust gas temperature moderator

Info

Publication number: WO2005068796A1
Application number: PCT/AU2005/000019
Authority: WO
Inventors: Roger Clyde Webb
Original assignee: Poly Systems Pty Limited
Priority date: 2004-01-14
Filing date: 2005-01-11
Publication date: 2005-07-28

Abstract

An exhaust gas temperature moderator (1) including a substantially tubular body (2) extending from an inlet end (4) adapted for receiving exhaust gases expelled from an engine and an outlet end (5) disposed adjacent an ambient environment. The moderator (1) also includes at least one liquid gas source port (20) in communication with a source of liquid gas (6), the liquid gas source port (20) disposed adjacent the body (2) and downstream of the inlet end (4). The source of liquid gas (6) being adapted to inject liquid gas into the body (2) via the port (20) at a predetermined flow rate such that exhaust gases entering the inlet end (4) are temperature moderated along the body (2) by mixing with the liquid gas.

Description

EXHATTST GAS TEMPERATURE MODERATOR

TECHNICAL FIELD

The invention relates to gas temperature moderation and, in particular, to temperature moderation of exhaust gas from rotary and fixed wing aircraft and terrestrial and marine vehicles.

The invention has been developed primarily with respect to vehicles having internal combustion and gas turbine engines and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to these particular fields of use and includes any vehicle engine having exhaust gases being hotter than an ambient temperature to which they are emitted.

BACKGROUND

Vehicle engines, especially internal combustion and gas turbine engines, emit exhaust gases that are substantially hotter than an ambient air temperature. The higher the rate of fuel being consumed by the vehicle the more gases are emitted. In the case of these engines for example, the controlled expansion of combusted fuel is used to provide thrust to power a vehicle. This gas is generally expelled via an exhaust outlet and part of the exhaust may be used to drive a turbo charger.

The exhaust gases are expelled into an ambient environment typically the atmosphere or a chamber adjacent the atmosphere. As exhaust gases from gas turbine and internal combustion engines can be of the order of many hundreds of degrees Celsius which is significantly hotter than the atmosphere. This provides a 'heat signature' which is comprised of the gases themselves and sometimes about the area of the exhaust outlet.

Military vehicles and commercial vehicles operating in potentially hostile territory are extremely vulnerable against attack from remotely fired missiles and projectiles that track an infra-red or heat source of a target. The significant difference in temperature between the exhaust gases and the atmosphere provides a high contrast source for such missiles to lock onto.

The heat of the engines themselves can also provide a substantial heat signature having a contrast sufficient to be targeted by a missile, however, engine cover-plates or fairings are generally used to remove this source.

Some military craft are known to spread the exhaust outlet over a greater area in order to maximise the volume of atmosphere the exhausted gases are expelled into. Although useful in reducing the temperature differential and hence heat signature, the reduction is limited by vehicle size and in the case of aircraft aerodynamic constraints. Therefore, vehicles having spread exhaust outlets are still very vulnerable to attack from infra-red targeting missiles.

It is an object of the invention to provide an exhaust gas temperature moderator that will substantially eliminate or minimise a craft heat signature, or to provide a useful alternative.

SUMMARY OF INVENTION

According to a first aspect of the invention there is provided an exhaust gas temperature moderator including: a substantially tubular body extending from an inlet end adapted for receiving exhaust gases expelled from an engine and an outlet end disposed adjacent an ambient environment; and at least one liquid gas source port in communication with a source of liquid gas, said liquid gas source port disposed adjacent said body and downstream of said inlet end, said source of liquid gas being adapted to inject liquid gas into said body via said port at a predetermined flow rate such that exhaust gases entering said inlet end are temperature moderated along said body by mixing with said liquid gas. In preferred embodiments of the invention, a cyclonic inducer disposed intermediate said liquid gas source port to receive liquid gas and said inlet end, said cyclonic inducer configured to cyclonically introduce liquid gas into said tubular body.

Preferably, a water vapour source port disposed adjacent said liquid gas source port and in communication with a water reservoir wherein water is vaporised into the path of liquid gas from said liquid gas source port.

Preferably, a pressurised air source port disposed adjacent said liquid gas source port and in communication with a source of pressurised air wherein pressurised air is injected into the path of liquid gas from said liquid gas source port. Preferably, the mixed exhaust and liquid gases are emitted from said outlet end at a substantially ambient temperature.

Preferably, a scroll duct disposed in said tubular body, said scroll duct extending substantially between said inlet end and said outlet end, the scroll duct configured to induce cyclonic motion of said exhaust gas and said injected gas. Preferably, the pressurised air source port gas flow rate is dependent on the exhaust and liquid gas flow rates.

Preferably, said at least one liquid gas source part is a plurality of spaced apart liquid gas source ports.

In preferred embodiments of the invention, said tubular body includes a port sleeve disposed near said inlet end and being radially intermediate said tubular body and said liquid gas source ports, said port sleeve being movable between a closed position in which liquid gas is blocked from entering said tubular body and an open position in which liquid gas and ambient environment gases can enter said tubular body.

Preferably, said liquid gas source ports are injection nozzles each being in fluid communication with the source of liquid gas via a liquid gas regulator disposed therebetween.

Preferably, an outer wall surrounds said tubular body along at least a portion thereof, and a cavity is disposed between said outer wall and said tubular body and extends from adjacent said port sleeve to said outlet end, said cavity adapted to receive exhaust gas, ambient environment gas and liquid gas; and a control flap disposed in said cavity near said port sleeve, said control flap adapted to be moved in response to the liquid gas injection controller to vary the inlet size of said cavity.

Preferably, the exhaust gas temperature moderator includes: a plurality of spaced apart exhaust temperature sensors disposed in said tubular body intermediate the body inlet and outlet ends; and a liquid gas injection controller in communication with the temperature sensors.

Preferably, said cavity extends from said inlet end and envelops said port sleeve, said cavity having a second ambient environment gas inlet disposed adjacent said inlet end. Preferably, the liquid gas injection controller is in communication with a sleeve actuator for controlling movement of the sleeve between the open and closed positions, the liquid gas injection controller including a microprocessor.

Preferably, the liquid gas is CO₂ or other inert gas.

Preferably, said engine is a vehicle engine. According to a second aspect of the invention there is provided an exhaust gas temperature moderator including: a substantially tubular body extending from an inlet end adapted for receiving exhaust gases and an outlet end disposed adjacent an ambient environment; and at least one liquid gas source port in communication with a source of liquid gas, said liquid gas source port disposed adjacent said body and downstream of said inlet end, said source of liquid gas being adapted to inject liquid gas into said body via said port at a predetermined flow rate such that exhaust gases entering said inlet end are temperature moderated along said body by mixing with said liquid gas.

According to a third aspect of the invention there is provided a method of moderating exhaust gas from an engine, the method including the steps of: injecting liquid gas into the engine exhaust gas stream at a predetermined rate from liquid gas source ports disposed adjacent thereto between the engine exhaust outlet and an ambient environment such that the exhaust gases are temperature moderated via mixing with the liquid gas; and emitting the moderated gases into the ambient environment.

Preferably, the step of inducing a cyclonic motion to said injected liquid gas. Preferably, the step of introducing vaporised water into the path of liquid gas.

Preferably, the step of injecting pressurised air into the path of said liquid gas.

BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: FIG. 1 is a partial sectional view of an exhaust gas temperature moderator according to a first embodiment; FIG. 2 shows the moderator of FIG. 1 having a sleeve in an open position; FIG. 3 shows the moderator of FIG. 2 schematically showing gas flow; FIG. 4 shows an partial enlarged view of the moderator of FIG. 1; FIG. 5 shows an partial enlarged view of the moderator of FIGS. 2 and 3; FIG. 6 shows the moderator of FIG. 5 with the control flap in a different position; FIG. 7 shows a partial end view of the moderator of FIG. 1 depicting the spaced apart liquid gas nozzles; FIG. 8 shows an end view of the moderator of FIG. 1; FIG. 9(a) shows a schematic sectional side view of an exhaust gas temperature moderator in accordance to a second embodiment; FIG. 9(b) shows the end view of exhaust gas moderator shown in Fig. 9(a); FIG. 10(a) shows the moderator of FIG. 9 with the cyclonic inducer shown enlarged; FIG. 10(b) shows a schematic cross sectional view of the cyclonic inducer shown in FIG. 10(a). FIG. 11 schematically shows a part of the moderator of FIG. 9; FIG. 12 is a schematic side view of a Chinook helicopter engine; FIG. 13 is a Chinook helicopter engine with a gas temperature moderator in accordance with the second embodiment; FIG. 14 is a schematic side view of a Hercules engine; FIG. 15 is a side view of a Hercules engine with a gas temperature moderator according to the second embodiment; FIG. 16 shows the flow of air through the embodiment of FIG. 15; and FIG. 17 shows an enlarged view of FIG. 16.

BEST MODE OF CARRYING OUT INVENTION

Referring to the FIGS. 1 to 8 generally, where like reference numerals denote like parts, there is shown an exhaust gas temperature moderator 1. The moderator 1 includes a tubular body 2 having a bore 3 extending from an inlet end 4 configured for receiving exhaust gases expelled from a vehicle engine (not shown) and a moderator body outlet end 5 disposed adjacent an ambient environment in the form of the atmosphere. The tubular body 2 is flared such that outlet end 5 is greater in diameter than inlet end 4. A tubular outer wall 50 spaced apart from body 2 extends along a portion thereof.

The moderator 1 shown is configured for use with the exhaust of a gas turbine powered helicopter engine, however, the moderator 1 can be used with the exhaust from any fixed wing aircraft or terrestrial or marine vehicle.

A plurality of liquid gas sources in the form of eight injector nozzles 6 are disposed in fluid communication with bore 3 adjacent the inlet end 4. The nozzles 6 are configured to inject liquid gas into the bore 3 adjacent the inlet end 4 via liquid gas source ports 20 at a predetermined rate such that the exhaust gases emitted from the outlet end 5 are temperature moderated by the liquid gas. The moderator 1 further includes an ambient environment gas port 25 being disposed adjacent each liquid gas source 6.

The mixed liquid ambient environment and exhaust gases are emitted from the outlet end 5 at substantially the same temperature as the ambient environment, or such that the emitted gases do not form a temperature differential large enough with the ambient environment for detection by a infra-red or heat seeking missiles.

The moderator 1 includes a plurality of spaced apart exhaust gas temperature sensors 7 disposed along bore 3 and outer wall 50 intermediate the inlet end 4 and outlet end 5. The temperature sensors 7 are in communication with a liquid gas injection controller 8. The controller 8 is also in communication with the liquid gas sources 6 and is configured to control the rate of flow of the liquid gases from the sources in response to the sensed temperature.

The exhaust gas temperature moderator 1 further includes a cavity 9 concentrically disposed between the body 2 and outer wall 50 wherein the cavity 9 extends from the port sleeve 11 to the outlet end 5. The cavity 9 is configured for receiving exhaust gas, ambient environment gas and injected liquid gas from the nozzles 6. An annular control flap 10 is disposed across cavity 9 and is movable to control the flow of mixed gases through the cavity 9. That is, the control flap 10 is opened or closed to allow a predetermined flow of exhaust gas, ambient environment gas and liquid gas through the cavity 9. The control flap 10 is controlled by an actuator 26 in response to signals from the controller 8 to open or close the flap 10 and thereby increase or decrease gas flow through the cavity 9.

Port sleeve 11 is disposed about the body 2 over gas ports 20 and 25, and adjacent the inlet end 4 and the outlet end 5. The port sleeve 11 is also disposed intermediate the nozzles 6 and the body 2. The sleeve 11 is movable between a closed position (FIG. 1) in which liquid gas and ambient environment gases are blocked from entering the bore 3, and an open position (FIG. 3) in which liquid gas and ambient environment gas can enter the bore 3.

The cavity 9 also envelops the port sleeve 11. The cavity 9 includes a second ambient environment gas inlet 12 disposed adjacent the body inlet end 4 for receiving ambient environment gas when the sleeve 11 is in the open position and /or control flap 10 is in an open position. The liquid gas injection controller 8 controls the movement of the sleeve 11 between the open and closed position in response to temperatures sensed by the temperature sensors 7.

As is shown in the FIGS, there is provided a plurality of spacers 13 disposed in cavity 9 between the body 2 and outer wall 50.

The nozzles 6 are in communication with a liquid gas source (not shown) via a regulator (not shown) disposed intermediate to regulate the flow of the liquid gas through the nozzles 6. The liquid gas controller 8 causes a liquid gas source valve (not shown) to open so as to inject liquid gas into the bore 3 and, if the control flap 10 is open, also into cavity 9 in response to sensed temperature.

Liquid gas is injected by the valves via a tube 14 through a cavity 15 so as to cause ambient environment gas to be drawn also through the tube via port 25 and into bore 3 and, if open, cavity 9. The liquid gas is preferably liquid carbon dioxide (CO₂), however, any preferred inert liquid gas can be used. When the liquid CO is injected, the highly dense liquid gas comes into contact with exhaust gases exiting the gas turbine engine (not shown) exhaust and into moderator inlet end 4. The use of liquid CO₂ gas at approximately -78C violently combines with the exhaust gas and a rapid expansion of the liquid CO₂ occurs so as to cause all exhaust gases to rapidly reduce in temperature as they flow along the bore 3 towards the outlet end 5.

Referring now to FIGS. 4, 5 and 6, there is shown a partial expanded view about the moderator 1 adjacent the inlet end 4. It is shown in FIG. 4 that when the port sleeve 11 is in the closed position, the vehicle exhaust gases flow straight through bore 3 and out the outlet end 5. FIGS. 5 and 6 show the case where the port sleeve 11 is open and a portion of the liquid CO₂ is directed by control flap 10 (and accompanying mechanical means 20) through the cavity 9 in combination with exhaust and ambient environment gases.

As a portion of the liquid CO₂ is channelled via external cavity 9, ambient air G_M is drawn into a cavity 17 disposed between inlet 4 and port sleeve 11, in communication with the second ambient environment gas inlet 12 having the effect of reducing the gas temperature in the cavity 9 and the cavity 14 adjacent the second ambient environment gas inlet.

The controller 8 thereby controls the regulation of the temperature of incoming, passing through and outgoing gases through the bore 3 and cavity 9 by altering the flow of liquid CO₂ through nozzles 6 and variable flow control flap 10 mechanism, so as to process exhaust gases to a near ambient temperature upon reaching the ambient atmosphere at the outlet end 5. An external cover panel 45 encasing the exhaust gas temperature moderator 1 is provided. In some embodiments an additional temperature sensor (not shown) may be disposed on the inside of the cover panel 45 to monitor the ambient temperature.

Turning now to FIGS. 7 and 8, there is shown the array of eight nozzles 6 circumferentially disposed equidistantly about port sleeve 11.

With reference particularly to FIG. 3, exhaust gases G_E of the embodiment shown enter the exhaust gas temperature moderator 1 at the inlet end 4 at approximately 800°C with an ambient environment temperature of 15°C, however, both of these values are arbitrarily chosen for the sake of a description of the preferred embodiment. It is noted in FIG. 3 that the liquid CO₂, depicted as G being injected from nozzles 6 is at approximately -78°C and, once mixed with predetermined volumes of inlet ambient environment gas G_M and exhaust gases G_E, reduce from approximately 100°C just downstream of the port sleeve 11 depicted as G_A, to 40°C further along body 2 depicted as Gβ, through to the ambient air temperature of 15°C at the moderator outlet end 5 depicted as Gc.

It is noted that the port sleeve 11 is movable by means of a pair of actuators 18 and 19 disposed adjacent the sleeve. The actuators 18 and 19 are movable in response to a signal from the controller 8 and the wall 51 intermediate the inlet end 4 and port sleeve 11 further acts as a source of cooling and heat shielding due to ambient environment gas flow through the second ambient environment gas port 12. Referring to FIGS. 1 and 2 particularly, liquid CO₂ injector valves is shown. A substantially cylindrical support body 16 includes a plurality of radially inwardly extending support arms 21 which are configured to support the liquid CO₂ nozzles 6.

Referring now to the FIGS. 9 (a)-(b) and 10 (a)-(b), again where like reference numerals denote like parts, there is shown a second embodiment of an exhaust gas temperature moderator 1. In this embodiment, a cyclonic inducer 30 is disposed intermediate the nozzle 6 to receive liquid gas and the bore 3 through which exhaust gases flow. The cyclonic inducer 30 is configured to cyclonically introduce the injected liquid gas into the bore 3.

A fluted scroll duct 31 is disposed in the bore 3 and configured to receive exhaust gases as well as the injected liquid gas. The scroll duct 31 is configured to cause both of the exhaust and injected gases from the cyclonic inducer 30 to move in a circular turbulent motion. By the induction of these air flow conditions, the exhaust gas temperature moderator 1 significantly increases the mixing and distribution process between the injected liquid gases and hot exhaust gases.

The cyclonic inducer 30 includes an inlet 32 for receiving charged air to assist in the creation of the cyclonic turbulence within the cyclonic inducer 1. The cyclonic induction of the charged air (and/or the injected gas mixture) is configured to substantially match the cyclonic motion of the exhaust gas induced by the scroll duct 31 to improve mixing.

It is noted that although illustrated, the fluted scroll duct 31 can be removed or replaced by an equivalent component, or a second scroll duct can be used either in the bore 3 or cyclonic inducer 30.

The exhaust gas temperature moderator 1 further includes a water vapour source port 35 disposed adjacent one or more of the nozzles 6 and is in communication with a water reservoir (not illustrated). Water vapour is injected from the water vapour source port 35 and the vaporised water is injected into the path of the liquid gas from the one or more liquid gas nozzles 6 within the cyclonic inducer 30.

As noted with respect to the first embodiment described with reference to FIGS. 1 to 8, ambient atmospheric air is drawn into the bore 3 to assist with cooling the exhaust gases. In this second embodiment, the heated exhaust gases enter the temperature moderator 1 at the body inlet end 4 and a sensor 7 disposed adjacent detects the gas temperature thereabout. The hot gas flows through to port sleeve 11 where ambient air is also allowed to be drawn through the scroll duct 31 to assist with the primary cooling by supporting the induction of cyclonic motion of the exhaust gas.

Charged air is blown into the cyclonic inducer 30 at inlet 32 and atomised/vaporised water and/or liquid gases in the form of carbon dioxide is injected via nozzle 6 and 35 into the charged air flow entering the cyclonic inducer at 31. At temperature sensor 7 detects the temperature adjacent a liquid gas source port 6.

The vaporised/atomised water injected at 35 is injected into the flow of liquid gas from the source port 6 at a temperate of approximately -78C. The result of this reaction is small water ice particles, dry ice, cold CO gas and air existing at varying temperatures typically from between -20C to -78C. The combined solid particles of gas and air are rotated and mixed in the cyclonic inducer 30 in a cyclonic inducer chamber 36 and then mixed with the exhaust through the scroll duct 31.

Although not illustrated, it is noted that directional blades may be incorporated into the cyclonic inducer chamber 36 to regulate the flow of gases through the exhaust gas temperature moderator 1. A baffle 37 is provided and allows approximately 20% of the cold liquid gas/water vapour/ air mixture to enter the cavity 9 to promote the cooling of an exhaust gas outlet external housing 38. A pair of temperature sensors 7 are located at each end of the cavity 9 to sense temperature differentials. For example, it may be advantageous to allow more or less than approximately 20% of the cold gas/water mixture to flow through the cavity 9 to provide a shield or barrier of cold gas/water to circulate around any exhaust plume existing at outlet end 5. The remaining approximately 80% of the cold gas/water mixture in the cyclonic inducer chamber 36 is directed through ports 20 to mix with hot exhaust gases. As stated above, a fluted scroll duct 31 is employed in this area to improve gas mixing.

It should be understood that heat is removed from the exhaust gases as various phase changes occur with the liquid gas and water and pressurised air, as well as the heat absorption of expanding gases. Temperature sensors 7 are disposed at each end of the bore 3 to measure temperature differentials.

Referring now to FIG. 11, there is shown a schematic illustration of part of the exhaust gas temperature moderator 1 of FIG. 9. It can be seen that charged air enters the cyclonic inducer via charged air entry 32 which mixes with liquid gas injected via nozzle 6 and water vapour injected at port 35 in inducer chamber 36. This is then mixed with the hot exhaust gas via scroll duct 31. The liquid gas may preferably be injected at a pressure of about 850psi, whilst the water vapour injected at port 35 may typically be injected at 2000psi. As the water may typically vapour and liquid gas mix, the resultant mixture may comprise solid and gaseous CO₂, snow/ice and air.

It can be seen that the exhaust gas temperature moderator 1 of this second embodiment is particularly advantageous in reducing the heat signature of an engine. The flow of cold/pressurised air, liquid gas and water vapour/ice injected into the cyclonic inducer and the exhaust plume downstream of the rear engine turbine rotor creates a visual barrier (or cloud) as well as a cold gas air mass which prevents a heat seeking missile from 'seeing' and targeting the hot rotor, as can commonly occur. Thus, in use, the moderator 1 provides a cloaking effect.

Referring to FIG. 12, there is shown a side view of a Chinook helicopter gas turbine engine 150. In this embodiment, exhaust gases exit the exhaust stack 151 unmoderated into the atmosphere. This provides a relatively high contrast heat signature. FIG. 13 shows the exhaust gas temperature moderator 1 of the second embodiment as applied to the Chinook engine of FIG. 12. Air enters the gas turbine engine 150 at inlet 152. It can be seen that the cyclonic inducer inlet 32 provides the liquid gas/water/air mixture to the cyclonic inducer 30. The mixture is then passed through the cavity 9 and the bore 3 via the scroll duct 31 , then exits at outlet end 5.

FIG. 14 shows a side view of a Hercules aircraft engine 160 in which exhaust gases are expelled from the exhaust stack 161 and tail cone assembly unmoderated.

FIG. 15 shows a Hercules engine 160 with an exhaust gas temperature moderator 1 applied. It is noted that in such fixed wing aircraft an engine cowling pod is provided to collect and channel charged air to the gas temperature moderator 1 and to allow the exhaust plume to exit well below the underside of a wing to which the engine is attached.

It is noted that liquid gas injection, CO₂ for example, is only required to substantially moderate to ambient the exhaust gas temperature for take offs and landings or when under attack from heat seeking or other infra-red seeking missiles. It is noted that approximately 50% of the gas temperature moderation can be achieved only with charged air/water vapour mixture provided by the cyclonic inducer 30.

As with the moderator 1 of the first embodiment, the gas temperature moderator 1 is electronically managed to inject liquid gas, water vapour and charged air injected into the cyclonic inducer 30 to provide an exiting exhaust plume temperature being substantially equal to ambient at varying altitudes and in vary weather conditions.

FIG. 16 shows a close up of the engine of FIG. 15 where charged air flow is ducted through an engine cowling as well as the exhaust gas temperature moderator 1 at charged air entry 32. FIG. 17 shows a wing disrupting air flow aerofoil 38 to minimise any heat transfer to the underside of the aircraft wing. The disrupting air flow aerofoil 38 is disposed at the rear of the exhaust gas temperature moderator cowling.

It is noted that the moderator 1 can be used to cool the gearbox on turbo propeller engines to remove a heat source for a missile to target. As the gearboxes typically run relatively hot and provide a high contrast signature for a missile, a temperature moderator 1 can be disposed adjacent to cool the gearbox by mixing injected liquid gas and/or water vapour and pressurised air and passing this about the gearbox or through an outer skin. It can be seen that the temperature moderator 1 can cool heated components, whether vehicular or otherwise, in combination with an air source.

Detailed below is a sample calculation in respect of the exhaust gas temperature moderator as applied to an engine. For given exhaust properties: mass flow, me = 11.5kg s static temp, te = 850k (577°C) specific heat Cpe (tl) = 1.145kj/kg @ 850k specific heat Cpe2 (t2) = 1.033kj/kg @ 373k 100°C average specific heat capacity = 1.09kj/kg

Heat removed from exhaust in cooling from 850k to 373k.

{amount of heat gained or lost} = {mass of substance} x {specific heat capacity} x

{change in temperature] =11.5 x 1.09 x [tl 850 ~ t2 373] = 5979kj

Air cooling

To remove 50% of heat from 11.5 kg/s air mass a reduction of 2989.5 kJ/s needs to be removed by air to air cooling. Mass flow of me is unknown and the average specific heat ofair = 1.09kj/kg

So, 2989.5/ [1.09 x (tl 850 - 12 611.5] = 2989.5 = 11.5kg/s To move 11.5kg/s of air with a high performance fan 15hp (11.25kW) would be consumed. The fan volume versus horsepower information was sourced from Dependable Distributors, South Australia. To remove remaining 50% of heat, 2989.5 kJ/s by water cooling 2989.5 / 4.192 x (100-15) + 2257 = 2989.5 = 1.14kg s

The calculations above are at sea level with the air temperature @ 15°C and @ lbar. As altitude increases and air temperature plus pressure decreases and significant increase in efficiency is gained.

Consideration for improving cooling efficiency At an altitude of 10,000ft air temperature is commonly -20°C (efficiency gain). Average specific heat capacity of air is 1.03 kg/kg 11.5 l.03 x [ ti l5 - t2 -20] = 414.5kj/s

Additional air cooling via the gas temperature moderator 414.5 / [4.192 35 + 2257 = 414.5 2403.72 = 0.172kg/s reduction in water cooling volume 1.14 - 0.172 = 0.968 kg/s water cooling flow Liquid CO? cooling

After 50% moderation via air cooling 2989.5 [0.8625 x (178.5) + 571.3] 725.25 = 4.12 kg/s

The calculations above indicate water cooling is far more efficient than CO₂ cooling. In the changes of state and latent heats of water-solid and water-liquid more than 4 times as much heat is absorbed to force a phase change of solid to liquid.

Mass of Air = 11.5kg/s Mass of Water = 0.372kg/s Mass ofCO2 = 1.65kg/s

In more analytic terms and referring to known physical properties of CO₂ and state changes of substances, the above example can be expressed as follows: kJ=1000J t_t= 85 OK (Exhaust temperature) t₂=473K (Final Temperature of 100C) t₃=611.5K (Intermediate Temperature) C_PCO₂=0.8625 kJ/kg (Heat capacity of CO₂) Cw=1.033 kJ/kg (Heat capacity of water) C_Pair⁼ 1.09 kJ/kg (Average heat capacity of air) Sub= 571.3 kJ/kg (Latent heat of fusion of CO₂) Sub2= 2257 kJ kg (Latent heat of fusion water) Sub3= 334 kJ/kg (Latent heat of fusion ice) m_e=l 1.5kg (mass flow per second) - 1₂)

For 50% temperature reduction by air from 850K to 661.5K, Q₂=Q/2 Q=2.363X10³ KkJ. mass= [Q/(ti - t₃)]/C_pair mass=l 1.5kg

To remove the remaining approximately 50% from approximately 611.5K to 373K by the injection of water vapour, where the full sublimation to vapour is assumed to occur:

Q₃ = Q₂ and Q₃=2.363X10³KkJ.

When the water is injected at a temperature of 40C, for example, Q₃= (heat energy of ice from -40C to 0C + latent heat of fusion) + (heat energy of water from 0C to 100C) + (latent heat of fusion) such that Q₃ =[m(40C_w + Sub3) + m(l 00C_W + Sub2)] .

It follows that m= Q₃/[(40C_W + Sub3) + (100C_W + Sub2)] = 0.744kgK

The amount of liquid CO₂ required to reduce the water temperature to -40C where the final 50% reduction in temperature from 661.5K to 473K, assuming the full sublimation to vapour, is: Q_w == 40mC_w + m Sub3 = 373.014KkJ, being the amount of energy that must be extracted from the liquid CO₂. Thus, the mass of CO₂ required to effect this cooling of the water is:

Q_w=m(C_PCO₂) At + (571.3)m Thus, m= Q_w / [2.30CpCO₂ + Sub] m= 0.625kgK

It can be seen that the total mass of CO₂ and H₂O required is (0.625+0.744)kgs^_1 = 1.369 kgs^"1. Given that 300 to 400 kg of additional weight can be added to an aircraft, the moderator can be used for approximately 15 seconds during take-off and landing, for example, and consume only 41.07 kg of CO₂ and H₂O.

Whilst the abovementioned preferred embodiments relate to exhaust gas temperature moderators for vehicles such as helicopters and fixed wing aircraft, it should be understood the present invention has applications in other vehicles. It should also be understood that the present invention may also have applications in stationary engines used for military and commercial purposes, for instance the exhaust gas temperature moderator of the present invention can be used for commercial cooling of hot gases and as a condenser for use in industry.

The foregoing describes only a preferred embodiment of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-

1. An exhaust gas temperature moderator including: a substantially tubular body extending from an inlet end adapted for receiving exhaust gases expelled from an engine and an outlet end disposed adjacent an ambient environment; and at least one liquid gas source port in communication with a source of liquid gas, said liquid gas source port disposed adjacent said body and downstream of said inlet end, said source of liquid gas being adapted to inject liquid gas into said body via said port at a predetermined flow rate such that exhaust gases entering said inlet end are temperature moderated along said body by mixing with said liquid gas.

2. An exhaust gas temperature moderator as claimed in claim 1 including a cyclonic inducer disposed intermediate said liquid gas source port to receive liquid gas and said inlet end, said cyclonic inducer configured to cyclonically introduce liquid gas into said tubular body.

3. An exhaust gas temperature moderator as claimed in claims 1 or 2 including a water vapour source port disposed adjacent said liquid gas source port and in communication with a water reservoir wherein water is vaporised into the path of liquid gas from said liquid gas source port.

4. An exhaust gas temperature moderator as claimed in any one of claims 1 to 3 including a pressurised air source port disposed adjacent said liquid gas source port and in communication with a source of pressurised air wherein pressurised air is injected into the path of liquid gas from said liquid gas source port.

5. An exhaust gas temperature moderator as claimed in any one of claims 1 to 4 wherein the mixed exhaust and liquid gases are emitted from said outlet end at a substantially ambient temperature.

6. An exhaust gas temperature moderator as claimed in any one of claims 1 to 5 including a scroll duct disposed in said tubular body, said scroll duct extending substantially between said inlet end and said outlet end, the scroll duct configured to induce cyclonic motion of said exhaust gas and said injected gas.

7. An exhaust gas temperature moderator as claimed in claim 4 wherein the pressurised air source port gas flow rate is dependent on the exhaust and liquid gas flow rates.

8. An exhaust gas temperature moderator as claimed in any one of claims 1 to 7 wherein said at least one liquid gas source part is a plurality of spaced apart liquid gas source ports.

9. An exhaust gas temperature moderator as claimed in claim 8 wherein said tubular body includes a port sleeve disposed near said inlet end and being radially intermediate said tubular body and said liquid gas source ports, said port sleeve being movable between a closed position in which liquid gas is blocked from entering said tubular body and an open position in which liquid gas and ambient environment gases can enter said tubular body.

10. An exhaust gas temperature moderator as claimed in claim 8 or 9 wherein said liquid gas source ports are injection nozzles each being in fluid communication with the source of liquid gas via a liquid gas regulator disposed therebetween.

11. An exhaust gas temperature moderator as claimed in claim 9, wherein an outer wall surrounds said tubular body along at least a portion thereof, and a cavity is disposed between said outer wall and said tubular body and extends from adjacent said port sleeve to said outlet end, said cavity adapted to receive exhaust gas, ambient environment gas and liquid gas; and a control flap disposed in said cavity near said port sleeve, said control flap adapted to be moved in response to the liquid gas injection controller to vary the inlet size of said cavity.

12. An exhaust gas temperature moderator as claimed in any one of claims 1 to 10 including: a plurality of spaced apart exhaust temperature sensors disposed in said tubular body intermediate the body inlet and outlet ends; and a liquid gas injection controller in communication with the temperature sensors.

13. An exhaust gas temperature moderator as claimed in claim 11 wherein said cavity extends from said inlet end and envelops said port sleeve, said cavity having a second ambient environment gas inlet disposed adjacent said inlet end.

14. An exhaust gas temperature moderator as claimed in claim 11 or 13 wherein the liquid gas injection controller is in communication with a sleeve actuator for controlling movement of the sleeve between the open and closed positions, the liquid gas injection controller including a microprocessor.

15. An exhaust gas temperature moderator as claimed in any one of claims 1 to 14 wherein the liquid gas is CO₂ or other inert gas.

16. An exhaust gas temperature moderator as claimed in any one of claims 1 to 15 wherein said engine is a vehicle engine.

17. An exhaust gas temperature moderator including: a substantially tubular body extending from an inlet end adapted for receiving exhaust gases and an outlet end disposed adjacent an ambient environment; and at least one liquid gas source port in communication with a source of liquid gas, said liquid gas source port disposed adjacent said body and downstream of said inlet end, said source of liquid gas being adapted to inject liquid gas into said body via said port at a predetermined flow rate such that exhaust gases entering said inlet end are temperature moderated along said body by mixing with said liquid gas.

18. A method of moderating exhaust gas from an engine, the method including the steps of: injecting liquid gas into the engine exhaust gas stream at a predetermined rate from liquid gas source ports disposed adjacent thereto between the engine exhaust outlet and an ambient environment such that the exhaust gases are temperature moderated via mixing with the liquid gas; and emitting the moderated gases into the ambient environment.

19. A method as claimed in claim 18 including the step of inducing a cyclonic motion to said injected liquid gas.

20. A method as claimed in claim 18 or 19 including the step of introducing vaporised water into the path of liquid gas.

21. A method as claimed in any one of claims 18 to 20 including the step of injecting pressurised air into the path of said liquid gas.

22. An exhaust gas temperature moderator being substantially as herein described with reference to FIGS. 1 to 11, 13 and 15 to 17.

23. A method of moderating exhaust gas from an engine, the method being substantially as herein described with reference to FIGS. 1 to 11, 13 and 15 to 17.