GB1605334A - Gas turbine engines - Google Patents

Description

(54) GAS TURBINE ENGINES We, ROLLS-ROYCE LIMITED a British Company of 65, Buckingham Gate, London SWIE 6AT, formerly ROLLS-ROYCE (1971) LIMITED of Noribik House. St. James' Square.

London, SW I Y 4JR, do hereby declare the inv ntion, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to gas turbine engines, and relates in particular to a novel gas turbine engine cycle.

It is known to provide a gas turbine engine in which flow through a low pressure compressor is split, part of the flow passing down a by-pass duct, and the remainder being further compressed by a further compressor. Fuel is burned in the higher pressure air flow and the flows are then re-combined downstream of the last turbine stage before being ejected to atmosphere through a propulsion nozzle. Such engines are known as by-pass gas turbine engines. It is also known for example, from U.K. specitication No. 1.069.033, to burn fuel in the low pressure by-pass stream to produce greater thrust from the engine.

The amount of thrust available from these known engines is limited. inter alia. by the temperature at which the turbine blades may be operated, and although techniques have been devised for cooling turbines blades they still remain the major limiting factor in the operating temperature of the engine.

The present invention seeks to provide a gas turbine engine cycle which improves upon the performance of a conventional by-pass engine with by-pass duct burning.

According to the present invention there is provided a by-pass gas turbine engine having at least one compressor and In which the air flowing through the compressor, or the highest pressure compressor is split into two streams, the inner one of which passes through both combustion equipment and at least one turbine for driving said at least one compressor, and the outer one of which enters a by-pass duct which by-passes the turbines and In which further fuel is burned, the inner stream being fed into the bypass stream through nozzles projecting into the by-pass stream so that the by-pass stream flowing around the nozzles creates a low pressure zone within the by-pass stream at the exit plane of the nozzles and enables the inner stream to flow into the by-pass stream.

By this means. the fuel burned in the by-pass stream can be bumed at a significantly higher temperature than that in the conventional combustion equipment because the by-pass stream does not pass through any turbine blading.

and since it is a high pressure air stream the cycle efficiency which can be produced by by-pass stream burning is significantly greater than hitherto.

The at least one compressor may be the high pressure compressor of a two shaft gas turbine engine.

The nozzles into which the inner stream is fed may comprise a plurality of separate nozzles which extend into the outer stream.

The invention will now be more particularly described with reference to the accompanying drawing which illustrates a two shaft gas turbine engine constructed according to the invention.

Referring now to the drawing there is shown a gas turbine engine having a first. or low pressure.

compressor 1 which supplies compressed air to a second. or high pressure, compressor 2. The flow from the high pressure compressor 7 is split at the downstream thereof into two streams. The inner stream passes through conventional combustion equipment 3 which includes fuel bumers 4 and then passes through a high pressure turbine 5 which is mounted on a shaft 6 and drives the high pressure compressor 2. From the high pressure turbine the flow passes to a low pressure turbine 7 which is mounted on a shaft 8, which is disposed concentrically within the shaft 6. and which drives the low pressure compressor 1.

The outer stream forms a by-pass stream in the by-pass duct 10 which is equipped a flame tube 11 and fuel burners 12 so that additional fuel may be burned in the stream.

Since there is no turbine blading in the bypass stream fuel may be burned in the by-pass duct at any desired temperature. provided of course, that the materials of the flame tube are chosen to withstand the temperature. or are adequately supplied with cooling air bled from the compressor.

The higher the pressure of the by-pass stream the higher is the efficiency of the combustion cycle involved in burning fuel in the by-pass duct. The two turbines 5 and 7 are therefore adapted to extract the maximum amount of energy from the inner gas stream emerging from the combustion equipment 3 so as to put as much work as possible into the compressors 1 and 2 in order to achieve the greatest pressure rise through the compressors that is possible.

The result of this is that the gas effluent from the low pressure turbine 7 is at a very much lower total pressure than that of the by-pass flow, and the two flows are mixed by means of the ejector nozzles indicated at 15. The hot gases from the inner flow passage are passed into individual nozzles 15 in the by-pass duct 10 causing a contraction in the flow area of the bypass duct. This causes an acceleration in the bypass flow and a reduction in static pressure in the by-pass duct 10 at the outlet plane of the nozzles 15. This "ejector effort" will enable the lower pressure stream from the L.P. turbine to pass from the nozzles into the by-pass duct 10, from whence the mixed stream passes to atmosphere through a final propulsion nozzles 17.

Thus an engine having the cycle abovedescribed is capable of producing more thrust than a conventional by-pass engine of the same size even including by-pass duct buming because, the high pressure by-pass flow of the present engine can be heated to a greater temperature than the high pressure flow passing through the turbine blades.

The engine described has low and high pressure compressors. Clearly, the same cycle may be employed using the high pressure delivery of a single compressor, or of a high pressure compressor of a two or three shaft ducted fan engine.

Also, the various elements of the engine described are not limiting on the invention since for example the nozzles may be of variable area, the turbines may be of more than one stage, and any other variations of design as used in conventional gas turbine engines or by-pass engines may be included in this engine.

WHAT WE CLAIM IS: 1. A by-pass gas turbine engine having at least one compressor and in which the air flowing through the compressor, or the highest pressure compressor is split into two streams. the inner one of which passes through both combustion equipment and at least one turbine for driving said at least one compressor, and the outer one of which enters a by-pass duct which by-passes the turbines and in which further fuel is burned, the inner stream being fed into the bypass stream through nozzles projecting into the by-pass stream so that the by-pass stream flowing around the nozzles creates a low pressure zone within the by-pass stream at the exit plane of the nozzles and enables the inner stream to flow into the by-pass stream.

2. A by-pass gas turbine engine as claimed in claim 1 in which said at least one compressor comprises the high pressure compressor of a two shaft gas turbine engine.

3. A by-pass gas turbine engine as claimed in claim 1 in which the nozzles into which the inner stream is fed comprise a plurality of separate nozzles which extend into the outer stream.

4. A by-pass gas turbine engine as claimed in any preceeding claim substantially as herein described by way of example only and with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. work as possible into the compressors 1 and 2 in order to achieve the greatest pressure rise through the compressors that is possible. The result of this is that the gas effluent from the low pressure turbine 7 is at a very much lower total pressure than that of the by-pass flow, and the two flows are mixed by means of the ejector nozzles indicated at 15. The hot gases from the inner flow passage are passed into individual nozzles 15 in the by-pass duct 10 causing a contraction in the flow area of the bypass duct. This causes an acceleration in the bypass flow and a reduction in static pressure in the by-pass duct 10 at the outlet plane of the nozzles 15. This "ejector effort" will enable the lower pressure stream from the L.P. turbine to pass from the nozzles into the by-pass duct 10, from whence the mixed stream passes to atmosphere through a final propulsion nozzles 17. Thus an engine having the cycle abovedescribed is capable of producing more thrust than a conventional by-pass engine of the same size even including by-pass duct buming because, the high pressure by-pass flow of the present engine can be heated to a greater temperature than the high pressure flow passing through the turbine blades. The engine described has low and high pressure compressors. Clearly, the same cycle may be employed using the high pressure delivery of a single compressor, or of a high pressure compressor of a two or three shaft ducted fan engine. Also, the various elements of the engine described are not limiting on the invention since for example the nozzles may be of variable area, the turbines may be of more than one stage, and any other variations of design as used in conventional gas turbine engines or by-pass engines may be included in this engine. WHAT WE CLAIM IS:

1. A by-pass gas turbine engine having at least one compressor and in which the air flowing through the compressor, or the highest pressure compressor is split into two streams. the inner one of which passes through both combustion equipment and at least one turbine for driving said at least one compressor, and the outer one of which enters a by-pass duct which by-passes the turbines and in which further fuel is burned, the inner stream being fed into the bypass stream through nozzles projecting into the by-pass stream so that the by-pass stream flowing around the nozzles creates a low pressure zone within the by-pass stream at the exit plane of the nozzles and enables the inner stream to flow into the by-pass stream.

2. A by-pass gas turbine engine as claimed in claim 1 in which said at least one compressor comprises the high pressure compressor of a two shaft gas turbine engine.

3. A by-pass gas turbine engine as claimed in claim 1 in which the nozzles into which the inner stream is fed comprise a plurality of separate nozzles which extend into the outer stream.

4. A by-pass gas turbine engine as claimed in any preceeding claim substantially as herein described by way of example only and with reference to the accompanying drawing.