GB2274881A

GB2274881A - Jet propulsion engine

Info

Publication number: GB2274881A
Application number: GB9401592A
Authority: GB
Inventors: Clotilde Pauron; David Tonon; Eric Hermant
Original assignee: Societe Europeenne de Propulsion SEP SA
Current assignee: Societe Europeenne de Propulsion SEP SA
Priority date: 1993-02-05
Filing date: 1994-01-27
Publication date: 1994-08-10
Anticipated expiration: 2014-01-27
Also published as: GB9401592D0; RU94003399A; JPH06241119A; FR2701293A1; DE4402941A1; DE4402941B4; GB2274881B; FR2701293B1

Description

2274881 A MULTI-MODE ENGINE INTEGRATING THE FOLLOWING MODES: EJECTOR USING

LIQUEFIED OR COOLED TURBOCOMPRESSED AIR; RAMJET, AND SUPER RAMJET The present invention relates to a multi-mode engine integrating at least the following modes: an ejectoraccelerator mode using liquefied or cooled turbo-compressed air; a ramjet mode using subsonic combustion; and a super ramjet mode using supersonic combustion; with such a multi- mode engine being applicable to an air-breathing hypersonic vehicle making it possible for a single stage to go from altitude Z=0 to a speed of Mach 15 and then to achieve orbit.

is In an article by Nobuhiro, Tanatsugu published in Apr.

1990 in SAE Technical Paper Series, and entitled "Development study on expander cycle air turbo-ramjet with intake air cooler for space plane" proposals have already been made for an engine constituting the first stage of a two-stage multi-mode propulsion vehicle. That article describes, in particular, a turbo-ramjet type engine using cooled air,'with thp presence of a heat exchanger in the combustion chamber. Such an engine does not demonstrate a combination of at least three different successive operating modes integrated within a one-stage space plane.

Proposals have already been made in an air breathing space plane to cool intake air by heat exchange with liquid hydrogen during acceleration.

An object of the present invention is to provide a multi-mode engine i.e. a combined propulsion system whose architecture is optimized and in which the various operating modes are fully integrated.

The invention also seeks to implement a multi-mode engine of bulk and mass that remain relatively small.

These objects are achieved by means of a multi-mode engine integrating the following modes: an ejector mode 2 using cooled or liquefied turbocompressed air; a ramjet mode; and a super ramjet mode; the engine being characterized in that it comprises a main stream fitted with an air intake, a main combustion chamber, and a main exhaust nozzle, a secondary stream outside the main stream and having moving vanes disposed at the inlet thereto, which vanes themselves convey circuits for cooling or liquefying air, the vanes being selectively placeable in different positions for adjusting the rate of air flow into the secondary stream, and including a totally closed position, the secondary stream comprising a low temperature compressor receiving the cooled or liquefied air applied to the inlet of the secondary stream, an ejector combustion chamber fed with fuel and with cooled or liquefied air compressed by the low temperature compressor, a turbine for driving the low temperature compressor and fed with the combustion gases which are produced in the ejector combustion chamber and which, after leaving the turbine, are ejected through a set of nozzles in the main combustion chamber of the main stream, the multi-mode engine thus being capable of operating successively in ejector mode using cooled or liquefied turbocompressed air passing via the secondary stream, the moving vanes being in the open position, in ramjet mode using subsonic combustion via the main stream with the moving vanes being capable of passing from an open position to a closed position, and in a super ramjet mode using supersonic combustion via the main stream, the moving vanes being in the closed position.

The circuits for cooling or liquefying the air passing through the moving vanes are fed with fuel from a tank, the fuel leaving the cooling circuits being used for feeding the ejector combustion chamber with fuel in the ejector mode using cooled or liquefied turbo- compressed air.

In an operating mode of the ramjet type using subsonic combustion, means are provided for keeping the 3 moving vanes open, and for liquefying and storing in an intermediate tank the cooled air injected into the inlet of the secondary stream via the moving vanes, the fuel that leaves the cooling circuits serving to feed fuel to 5 the main combustion chamber.

Advantageously, in the ejector mode using cooled or liquefied turbocompressed air, the combustion gases formed in the ejector combustion chamber are injected into the main stream via nozzles received in retractable spacers that are retracted, at least in part, during the period of ramjet operation using supersonic combustion.

Similarly, in ramjet mode using subsonic combustion, fuel is injected into the main stream via nozzles housed in retractable spacers that are retracted at least in part during the period of ramjet operation using supersonic combustion.

The moving vanes are staged and disposed upstream from the throat of the air intake into the main stream.

The ejector combustion chamber is disposed between the low temperature compressor and the turbine.

The multi-mode engine may include an additional heat exchanger disposed in the secondary stream downstream from the moving vanes and comprising fuel-conveying circuits for cooling or liquefying air.

Preferably, the cooling circuits of the additional heat exchanger are fed with fuel coming from the circuits for cooling the air passing through the moving vanes.

The multi-mode engine may also include at least one conventional rocket engine fed with liquid propellant components from tanks and comprising a divergent portion of a nozzle opening out into the diverging portion of the exhaust nozzle of the main stream.

Optionally, the multi-mode engine may include a tank for liquid oxygen taken on board before departure for injecting an additional flow of oxygen into the ejector combustion chamber in the ejector mode using cooled or liquefied turbocompressed air, for injecting an 4 additional flow of oxygen into the main combustion chamber in the super ramjet mode, and optionally for injecting a flow of oxygen into the conventional rocket engine. 5 Means may be provided for injecting fuel into the main combustion chamber both axially and orthogonally during super ramjet mode. By way of example, the multi-mode engine may operate in ejector mode using cooled or liquefied turbocompressed air between about Mach 0 and about Mach 2, in ramjet mode using subsonic combustion between about Mach 2 and about Mach 6, and in super.ramjet mode between about Mach 6 and about Mach 15, and optionally in rocket mode beyond Mach 15.

It will be observed that because a secondary stream is present with a forebody and moving vanes that are actively cooled during the air-breathing period by the fuel that is subsequently burnt either in the injectors that use air or else in a main stream, the following are obtained simultaneously: an increase in the air intake flow rate, a reduction in external drag, and an increase in thrust.

Given the coupling achieved between the members that ensure operation in ejector mode, and the main stream that is used during operation in ramjet mode, bulk and mass are smaller than they would be with totally separate assemblies.

Other characteristics and advantages of the invention appear from the detailed description of particular embodiments given by way of non-limiting example and made with reference to the accompanying drawings, in which:

Figure 1 is a block diagram showing the various essential component elements of a multi-mode engine of the invention; and Figure 2 is a diagram showing one example of how the various component elements of a multi-mode engine of the invention may be installed.

Figure 1 shows the general organization of the main component elements of a multi-mode engine of the invention, while Figure 2 shows the positions of tChe various component elements relative to one another.

The multi-mode engine of the invention which is fully integrated and comprises a single main exhaust nozzle makes it possible with a single stage to go from the ground to orbit about the Earth.

Operation of the multi-mode engine comprises a first accele2ation period that takes place for speeds lying in the range Mach 0 to about Mach-6, and is itself subdivided into two modes:

a) a rocket mode using liquefied or cooled air (also referred to as an "ejector" mode using liquefied or cooled turbocompressed air) operating in parallel with a single ramjet mode using subsonic combustion, for speeds lying in the range Mach 0 to about Mach 2.5; and b) a pure ramjet mode using subsonic combustion for speeds lying between about Mach 2.5 and Mach 6.

The acceleration period is followed by a period of operation in ramjet mode using supersonic combustion (or super ramjet mode) for speeds lying in the range about Mach 6 to Mach 15.

A conventional rocket period using liquid propellants (e.g. liquid oxygen and a fuel) may take over from the super ramjet period by means of a conventional rocket engine 300 associated with the multi-mode engine 100 for speeds above Mach 15 and into orbit.

With reference to Figures 1 and 2, it can be seen that the multi-mode engine essentially comprises a main stream 1 used both for subsonic combustion ramjet mode and for supersonic combustion ramjet mode, and a 6 secondary stream 2 used for ejector mode using liquefied or cooled turbocompressed air.

The main stream 1 comprises an air intake 110, a main combustion chamber 120, and an exhaust nozzle 130.

The internal portion of the air intake 110 has a converging portion 111 and terminates in a throat 112.

The secondary stream 2 is outside the main stream 1 and has a forebody 181 which co-operates with the outside wall of the air intake 110 to define an air intake 180 for the secondary stream. The air fraction taken in the main stream 1 through the converging portion 111 of the air intake 110 is injected into the secondary stream 2 via openings 113 formed through the converging portion 111 of the air intake 110. The openings 113 may be partially or totally closed by a set 160 of moving vanes 161 that pivot about axes 162 perpendicular to the longitudinal axis X1X of the main stream 1. The vanes 161 are controlled by rodding that is not shown in the figures. Cooling circuits, or where appropriate air liquefying circuits 163, comprise a set of tubes associated with the vanes 161 to cool both the vanes 161 and the air in the main stream as taken via the openings 113 for the purpose of feeding the secondary stream 2. The cooling circuits 163 are advantageously cooled with fuel fed from a tank 140.

The fuel coming from the cooling circuits 163 in the set 160 of moving vanes 161 may be conveyed by a line 145 to an additional heat exchanger 170 disposed in the secondary stream 2 downstream from the moving vanes 161 and placed at the inlet 180 of the secondary stream 2 for the purpose of further cooling the air injected into the secondary stream or for the purpose of liquefying it, prior to said air reaching a low-temperature compressor 210, itself driven by a turbine 270 fed by the combustion gases produced in an ejector combustion chamber 220 interposed between the compressor 210 and the turbine 230.

7 The air as turbocompressed by the low temperature compressor 210 is thus either cooled to a very low temperature or else is liquefied by the heat exchangers 160, 170 prior to passing into the low temperature compressor 210.

The air picked up may also be enriched by passing through a separator 190 enabling nitrogen molecules to be extracted from the air, thus obtaining air having a higher concentration of oxygen. The separator 190 may be placed, for example, between the heat exchangers 160 and 170.

The ejector combustion chamber 220 is fed with fuel via a line 149 coming from the cooling circuits-113, and with liquefied or cooling air from the low temperature compressor 210. When an additional heat exchanger 170 is used, the fuel from said additional heat exchanger 170 may also be used to feed the ejector combustion chamber 220 via the ducts 146 and 147.

Where necessary, liquid oxygen from a tank 152 may also be injected into the ejector combustion chamber 220 via a pipe 155.

The gas at the outlet from the turbine 230 is applied via a duct 231 to a buffer chamber 243 and is then ejected through a set 240 of nozzles 242 in the main combustion chamber of the main stream 1.

The buffer chamber 243 may also be fed with fuel either directly from the tank 140 via the pipe 142, or else via the pipe 148 from the cooling circuits 113 and the additional heat exchanger 170.

The gas or the fuel injected into the buffer chamber 243 is ejected into the main combustion chamber 120 of the main stream 1 that is fed with air from the air intake 110, ejection taking place through the set 240 of nozzles 242 which is preferably mounted on retractable spacers 241 enabling the nozzles 242 either to be fully extended in the main stream 1, or else to be partially or 8 fully retracted into the housing that is constituted by the buffer chamber 243.

A small independent nozzle 250 fed with fuel by the pipe 143 serves to inject the fuel axially into the main combustion chamber 120 at the beginning of the diverging portion of the nozzle 130, independently from or in combination with the set 240 of retractable nozzles 242, depending on the particular period of operation.

Naturally, it is possible to implement a plurality of ejectors fed via a plurality of secondary streams 2 in alignment over one or more main streams 1. Under such circumstances, the various ejectors comprise, in particular, respective turbocompressors 210, 230 and ejector combustion chambers 220 that may be identical in structure and function, such that reference is made below to one ejector only. A conventional rocket engine 300 may optionally be associated with the multi-mode engine of the invention. Such a rocket engine 300 comprises a combustion chamber 20 310 and a nozzle having a sonic throat 320 and a diverging portion 330 which is integrated in the rear body of the vehicle and which opens out into the diverging portion of the main nozzle 130. The rocket engine 300 is fed with fuel from the tank 140 via the pipe 144, and with liquid oxygen from a group of tanks 150. The group of tanks 150 may comprise a tank 151 for containing the liquid air formed in the secondary stream 2 after passing through the heat exchanger 160 constituted by the cooled vanes 161 and the additional heat exchanger 170, together with a tank 152 containing liquid oxygen loaded on board before departure. The liquid oxygen is applied to the injector of the combustion chamber 310 of the rocket engine 300 via pipes 153 and 154 coming from the tanks 151 and 152.

The fuel may be liquid hydrogen or a hydrogen slurry known as "hydrogen slush".

9 The operation of the multi-mode engine of the invention is described below in each of its various modes of operation.

When operating in acceleration mode, during a first period, the moving vanes 161 of the secondary stream 2 are in the open position (Mach 0 to about Mach 2.5). A fraction of the air picked up by the air intake 110 therefore passes into the secondary stream 2.

The main heat exchangers 163 housed in the moving vanes 161 cool this flow of air. If necessary, an additional heat exchanger 170 is integrated in the secondary stream 2 for the purpose of reducing the temperature of the air picked up down to a required level, or for liquefying the air. 15 The air cooled or liquefied in this way is then compressed in the low temperature compressor 210 and is injected into the ejector combustion chamber 220 where it is burnt with the fuel that has been used for cooling or liquefying the air in the heat exchangers 160, 170. 20 As mentioned above, it is also possible to inject a flow of oxygen into the chamber 220 via the pipe 155 for burning with the air and the fuel in order to gain possible thrust increase. The combustion gases are then allowed to expand in part in the turbine 230 that drives the low temperature air compressor 210 using an expander type cycle, after which said gases are ejected into the main stream 1 (ramjet stream) via the nozzles 242 housed in the retractable spacers 241. 30 The flow of air picked up by the main stream 1 is burnt in the ramjet main combustion chamber 120 together with the gases coming from the ejector of the secondary stream 2, and optionally together with additional fuel. At around Mach 2.5, the cooled or liquefied air ejector of the secondary stream 2 is extinguished, feed to the ejector combustion chamber 220 no longer being provided, and the engine operates in subsonic combustion ramjet mode.

Two options are then possible.

In the first case, the moving vanes 161 are closed and all the air picked up in the air intake 110 participates in the combustion in the main stream of fuel that is injected via the nozzles 242 housed in the retractable spacers 241.

In the second case, the moving vanes 161 remain open during the period of operation as a subsonic combustion ramjet.

The flow of air picked up in the secondary stream 2 is then cooled and liquefied for storage in an intermediate tank 151 and it is used as oxidizer in the rocket engine 300 during the period of operation in pure rocket mode.

The remainder of the flow of air picked up in the air intake 110 participates in the combustion in the main stream of the fuel that has already been used for liquefying the air in the secondary stream 2 and that is injected via the nozzles 242 housed in the retractable spacers 241.

In both cases, the period of operation in subsonic combustion ramjet mode continues up to around Mach 6.

From about Mach 6, operation switches to supersonic combustion ramjet mode (referred to as "super ramjeC mode). If the moving vanes 161 have remained open, they are closed at this stage.

In order to facilitate the beginning of operation in the super ramjet period, it is possible to use a pilot flame obtained by the following means:

A pre-burned mixture of fuel and of H20 is ejected via injectors; injection is performed by means of small rocket engines; the high temperature of the injected gases (> 1000 K) and the presence of radicals (OH-) makes it possible to initiate air/fuel combustion.

11 Nevertheless, this method requires the presence of oxygen (tank 152), which oxygen is also used for rocket mode operation at the end of a mission.

Thermal self-ignition of a fuel mixture depends essentially on the temperature and the pressure of the mixture, and also on its richness. A mixture of air and fuel will ignite spontaneously if it is possible to raise it locally to its thermal self-ignition temperature, which temperature is generally easy to achieve downstream from a shockwave. The drawback of that method is the loss of total pressure caused by shockwaves. In order to limit influence on performance, shockwave formation must be local and it may be achieved by a Mach effect by means of a Mach disk producing very considerable speed reduction in the flow of air, at least in a central zone.

The temperature and the pressure of the flow are then sufficiently great to stabilize combustion locally.

The reactive zone acts as a pilot flame for the remainder of the flow.

When the stop temperature on the spacers 241 becomes too great for the strength thereof, they are retracted in part while retaining a peripheral injection point for fuel.

This injection point makes it possible to achieve stable supersonic combustion regardless of flow speed, particularly at high Mach numbers.

The supersonic combustion ramjet period continues up to around Mach 15.

Air flow increases with flight Mach number. For constant richness, it is therefore necessary for fuel flow rate to increase with flight Mach number.

At low flight Mach number, since the richness of the mixture is close to unity, it is possible to burn all of the injected fuel. Better combustion efficiency is obtained by orthogonal injection (which improves the quality of mixing).

12 In contrast, at high Mach numbers, only a fraction of the injected fuel will be oxidized. The remainder does not participate in combustion phenomena and behaves like an inert species. The temperature at the inlet to the burn zone is high and numerous dissociation phenomena (endothermal reactions) appear within the flow during combustion.

The mean speed of the gas within the burn zone is high, so transit time is short. This reduces combustion efficiency.

Under such conditions, orthogonal injection that enables good mixing and combustion conditions to be achieved is no longer necessary. Axial injection then makes it possible to take advantage of the axial injection speed of the fuel.

Nevertheless, it should be observed that a fraction of the fuel may be injected orthogonally (stoiechiometric flow) while the remainder is injected axially.

Above Mach 15, if the supersonic combustion ramjet continues to provide thrust, it propels the vehicle into orbit.

Another option is to inject oxygen during the end of the air-breathing period.

This injection of oxygen from the tank 152 makes it possible to do without a rocket engine, that might otherwise be necessary at the end of a mission. It enables the air-breathing engine to operate in the very low density layers of the atmosphere.

In addition, oxygen stored at a low temperature (91 K) makes it possible to cool air that is admitted. Since the temperature of combustion is lower, dissociation phenomena are less marked, so combustion efficiency is increased.

Should it be necessary, a conventional fuel and liquid oxygen (LOX) rocket engine is used at the end of the trajectory from Mach 15 to orbit.

13 It will be observed that throughout the airbreathing period, the forebody and the air inlet (set 160 of vanes 161) are actively cooled by using the fuel which is subsequently burned either in the air ejector combustion chamber 220 or else in the main stream 1.

Such cooling makes it possible to increase the flow rate of air that is picked up, to reduce external drag by reducing the thickness of the boundary layer and by retarding the laminar-to-turbulent transition, to increase the total enthalpy of the fuel, thereby making it possible by suitable expansion to increase the momentum of the fuel on injection and consequently to increase the thrust.

14

Claims

CLAIMS l/ A multi-mode engine integrating the following modes:

an ejector mode using cooled or liquefied turbocompressed air; a ramjet mode; and a super ramjet mode; the engine being characterized in that it comprises a main stream (1) fitted with an air intake (110), a main combustion chamber (120), and a main exhaust nozzle (130), a secondary stream (2) outside the main stream (1) and having moving vanes (161) disposed at the inlet (180) thereto, which vanes themselves convey circuits (163) for cooling or liquefying air, the vanes being selectively placeable in different positions for adjusting the rate of air flow into the secondary stream (2), and including a totally closed position, the secondary stream (2) comprising a low temperature compressor (210) receiving the cooled or liquefied air applied to the inlet (180) of the secondary stream (2), an ejector combustion chamber (220) fed with fuel and with cooled or liquefied air compressed by the low temperature compressor (210), a turbine (230) for driving the low temperature compressor (210) and fed with the combustion gases which are produced in the ejector combustion chamber (220) and which, after leaving the turbine (230), are ejected through a set of nozzles (240) in the main combustion chamber (120) of the main stream (1), the multi-mode engine thus being capable of operating successively in ejector mode using cooled or liquefied turbocompressed air passing via the secondary stream (2), the moving vanes (161) being in the open position, in ramjet mode using subsonic combustion via the main stream (1) with the moving vanes (161) being capable of passing from an open position to a closed position, and in a super ramjet mode using supersonic combustion via the main stream (1), the moving vanes (161) being in the closed position.

2/ A multi-mode engine according to claim 1, characterized in that the circuits (163) for cooling or liquefying the air passing through the moving vanes (161) are fed with fuel from a tank (140), the fuel leaving the cooling circuits (163) being used for feeding the ejector combustion chamber (220) with fuel in the ejector mode using cooled or liquefied turbocompressed air.

3/ A multi-mode engine according to claim 2, characterized in that in an operating mode of the ramjet type using subsonic combustion, means are provided for keeping the moving vanes (161) open, and for liquefying and storing in an intermediate tank (151), the cooled air injected into the inlet of the secondary stream (2) via the moving vanes (161), the fuel that leaves the cooling circuits (163) serving to feed fuel to the main combustion chamber (120).

4/ A multi-mode engine according to any one of claims 1 to 3, characterized in that in the ejector mode using cooled or liquefied turbocompressed air, the combustion gases formed in the ejector combustion chamber (220) are injected into the main stream (1) via nozzles (242) received in retractable spacers (241) that are retracted, at least in part,.during the period of ramjet operation using supersonic combustion.

5/ A multi-mode engine according to any one of claims 1 to 4, characterized in that in ramjet mode using subsonic combustion, fuel is injected into the main stream (1) via nozzles (242) housed in retractable spacers (241) that are retracted at least in part during the period of ramjet operation using supersonic combustion.

6/ A multi-mode engine according to any one of claims 1 to 5, characterized in that the moving vanes (161) are staged and disposed upstream from the throat (112) of the air intake (110) into the main stream (1).

16 7/ A multi-mode engine according to any one of claims 1 to 6, characterized in that the ejector combustion chamber (220) is disposed between the low temperature compressor (210) and the turbine (230). 5 8/ A multi-mode engine according to any one of claims 1 to 7, characterized in that it includes an additional heat exchanger (170) disposed in the secondary stream (2) downstream from the moving vanes (161) and comprising fuel-conveying circuits for cooling or liquefying air.

g/ A multi-mode engine according to claim 8 and claim 2 or 3, characterized in that the cooling circuits of the additional heat exchanger (170) are fed with fuel coming from the circuits (163) for cooling the air passing through the moving vanes (161).

10/ A multi-mode engine according to any one of claims 1 to 9, characterized in that it further includes at least one conventional rocket engine (300) fed with liquid propellant components from tanks (140, 151, 152) and comprising a divergent portion (330) of a nozzle opening out into the diverging portion of the exhaust nozzle (130) of the main stream (1).

11/ A multi-mode engine according to any one of claims 1 to 10, characterized in that it includes a tank (152) for liquid oxygen taken on board before departure for the purpose of injecting an additional flow of oxygen into the ejector combustion chamber (220) in ejector mode using cooled or liquefied turbocompressed air, for injecting an additional flow of oxygen into the main combustion chamber (120) in the super ramjet mode, and optionally for injecting a flow of oxygen into the conventional rocket engine (300).

17 12/ A multi-mode engine according to any one of claims 1 to 11, characterized in that it includes means (240, 250) for injecting fuel into the main combustion chamber (120) both axially and orthogonally during super ramjet mode. 5 13/ A multi-mode engine according to any one of claims 1 to 12, characterized in that it operates in ejector mode using cooled or liquefied turbocompressed air between about Mach 0 and about Mach 2, in ramjet mode using subsonic combustion between about Mach 2 and about Mach 6, and in super ramjet mode between about Mach 6 and about Mach 15, and optionally in rocket mode beyond Mach 15.

14/ A multi-mode engine according to claim 1, substantially as described with reference to the accompanying drawings.