GB2191821A

GB2191821A - Fuel preheater for an integrated rocket/ramjet engine

Info

Publication number: GB2191821A
Application number: GB07847539A
Authority: GB
Inventors: Harold Alan Scrace
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1978-12-07
Filing date: 1978-12-07
Publication date: 1987-12-23
Also published as: GB2191821B

Abstract

In an integrated rocket/ramjet engine the ramjet fuel is preheated to some extent by a heat exchanger (20) mounted in the rocket propellant combustion chamber (21). Cold ramjet fuel is pumped from the fuel tank (11) through the heat exchanger (20) and back to the tank (11) whereby the heat generated by rocket propellant combustion is utilised to heat a portion of the ramjet fuel which in turn heats the remainder of the fuel in the tank. The fuel is pumped by a turbopump (14) driven by ram air derived from the engine intake during the rocket boost mode of operation of the engine. <IMAGE>

Description

SPECIFICATION A fuel pre-heater suitable for an integrated rocket/ramjet engine This invention relates to a fuel preheater suitable for an integrated rocket/ramjet engine.

Integrated rocket/ramjet engines are utilised as propulsive power units in such vehicles as missiles. Typically such engines are initially propelled by a solid rocket fuel until the vehicle velocity is high enough to enable the ram jet mode of operation of the engine to be initiated and sustained. The fuel required for the ram jet operation of the engine usually has a high calorific value per unit volume if the vehicle is required to have a long operational range. Such fuels have high molecular weights and are consequentiy of high viscosity, particularly at low temperatures. This can present serious operational problems if the vehicle is subjected to low temperatures prior to use.

Thus for instance the vehicle may be positioned prior to use in environments where low temperatures are consistently encountered. If engine operation is intiated under such conditions, ignition of the solid rocket fuel seldom presents any problems. However when the time comes to initiated ram jet mode of operation, the cold fuel is sometimes too viscous to be effectively metered to the ramjet combustion zone of the engine. With the failure of an adequate fuel flow, loss of ram jet operation is likely with consequent failure of the vehicle to reach its destination.

It is an object of the present invention to provide a fuel preheater suitable for an integrated rocket/ramjet engine whereby fuel for the ramjet operation of the engine is preheated prior to its combustion.

According to the present invention, a fuel preheater suitable for an integrated rocket/ramjet engine comprises at least one heat exchanger adapted in operation to be supplied with at least a portion of the fuel intended for the ramjet mode of operation of said engine, said at least one heat exchanger being adapted to be heated during the rocket mode of operation of said engine by the combustion products of said rocket mode of operation whereby said ramjet fuel supplied to said heat exchanger is preheated thereby.

By preheating the ramjet fuel in this manner, its viscosity is reduced, thereby ensuring its effective metering to the ramjet combustion zone of the engine.

The at least one heat exchanger is preferably adapted to be positioned within the combustor wherein combustion for the rocket mode of operation of the engine occurs..

Pump means are preferably provided to supply said ramjet fuel to said at least one heat exchanger.

Said pump means is preferably adapted in operation to pump said ramjet fuel from its storage tank, through said at least one heat exchanger and subsequently back into said storage tank whereby ramjet fuel contained within said storage tank is preheated.

Said fuel preheater may be provided with valve means operable upon the initiation of the ramjet mode of operation of said engine, said valve means being adapted when operated, to supply said peheated fuel contained within said storage tank to the ramjet combustion zone of said engine.

Said pump means is preferably adapted in operation to supply said preheated fuel contained within said storage tank to said valve means.

Said pump means may be driven in operation by an air turbine driven in turn by ram air derived from the air intake of said engine.

The invention will now be described by way of example with reference to the accompanying drawing which is a sectional side view of part of an integrated rocket/ramjet engine provided with a fuel preheater in accordance with the present invention.

With reference to the drawing, a fuel preheater generally indicated at 10 is positioned partially within the ramjet fuel tank 11 of an integrated rocket/ramjet engine 12. The fuel preheater 10 comprises a manifold 13 through which fuel contained in the tank 11 is fed to a turbo pump 14. The turbo pump 14 is driven by an air turbine 15 which is driven in turn by ram air derived from the air intake of the engine 12 through a duct 16. Exhaust air from the air turbine 15 is ducted away from the fuel preheater 10 through an exhaust duct 17.

The ramjet fuel supplied to the turbo pump 14 through the manifold 13 is pumped through a divded duct 19 and into a heat exchanger 20. The heat exchanger 20 is positioned within the combustor 21 of the rocket/ramjet engine 12. The fuel then passes back up through the divided duct 19, through a metered bleed 21 and orifices 22, provided in an annular chamber 18 surrounding the manifold 13 and back into the tank 11. A pressure relief valve 23 provided adjacent the annular chamber 18 ensures that if the pressure of the fuel is excessive, the metered bleed 21 is by-passed.

Initially, the rocket/ramjet engine 12 operates in the rocket mode. Thus solid rocket fuel contained within the combustor 21 is combusted and propels the vehicle containing the engine 12 up to a velocity high enough for the initiation of the ram jet mode of operation of the engine 12. As the solid rocket fuel is combusted, the resultant combustion products heat up the heat exchanger 20 and consequently the ramjet fuel passing through it. Thus as the rocket mode of operation of the engine 12 proceeds, the ram jet fuel contained within the tank 11 is progressively heated up with a consequent reduction in its viscosity.

It will be appreciated that not all of the ramjet fuel contained within tank 11 is preheated by being passed through the heat exchanger 20. Thus fuel which has been preheated by the heat exchanger 20 and passed back into the tank 11 itself preheats the fuel contained within the tank 11 to a certain extent.

When all of the rocket fuel contained within the combustor has been combusted and the vehicle containing the engine 12 is travelling at a velocity high enough to initiate and sustain ram jet operation, a valve 23 located on the exhaust side of the heat exchanger 20 is operated by the firing of a gas cartridge 24.

This exposes a large diameter duct 25 which leads to a fuel/air ratio controller and the ramjet combustion zone (not shown). Since the duct 25 offers less flow resistance than the metered bleed 21, the ramjet fuel pumped from the tank 11 by the turbo pump 14 is preferentially pumped through the duct 25 instead of back into the tank 11. The preheated (and thus low viscosity) ramjet fuel is thus pumped to the ramjet combustion zone where its combustion takes place.

Although the present invention has been described with reference to a fuel preheater provided with one heat exchanger, it will be appreciated that more than one heat exchanger could be utilised.

Claims

1. A fuel preheater suitable for an integrated rocket/ramjet engine comprises a heat exchanger adapted in operation to be supplied with at least a portion of the fuel intended for the ramjet mode of operation of the engine, the heat exchanger being adapted to be heated during the rocket mode of operation of the engine by the combustion products of said rocket mode of operation whereby ramjet fuel supplied to the heat exchanger is preheated thereby.

2. A fuel preheater as claimed in claim 1 and wherein the heat exchanger is positioned within the combustor region of the engine wherein combustion for the rocket mode of operation of the engine occurs.

3. A fuel preheater as claimed in claim 1 or claim 2 and further comprising a pump, adapted in operation to pump said ramjet fuel from a storage tank, through the heat exchanger and back to the storage tank whereby ramjet fuel contained within the storage tank is preheated.

4. A fuel preheater as claimed in claim 3 and wherein valve means are provided operable upon initiation of the ramjet mode of operation of the engine to open a passage. for supplying said preheated fuel contained within the storage tank to the ramjet combustion zone of the engine.

5. A fuel preheater as claimed in claim 3 and wherein an air turbine driven by ram air derived from the air intake of the engine is connected to drive the pump.

6. A fuel preheater substantially as hereinbefore described with reference to the accompanying drawings.