GB2404226A - Accelerating a turbine from rest - Google Patents

Abstract

A method of accelerating a turbine 1 from rest, the turbine comprising an intake housing 5, having steps of introducing fuel, preferably via an injector 55, and air, preferably via an intake 75, into the housing to form an air/fuel mixture to be ignited, preferably by spark ignition 70, to accelerate the turbine wheel 10. The fuel may be gaseous, preferably propane. The turbine may drive a gas boost compressor for compressing gaseous fuel supplied to a gas turbine engine (fig. 2), or a turbocharger. The turbine may also be part of a gas turbine engine. There is preferably a shaft 15 extending through the housing on which the turbine is mounted, and fuel injection may be controlled by valve 62.

Description

A METHOD OF STARTING A TURBINE FROM REST

The present invention relates to a method of accelerating a turbine from rest, and more particularly but not exclusively to a method of accelerating a turbine for a gas boost compressor from rest.

Gas boost compressors are often used to raise low-pressure fuel supplies to the operating pressure of an engine, such as a gas turbine engine. Gas boost compressors may be driven electrically, or they may be driven by utilising the high temperature exhaust of the engine to drive an expansion turbine stage attached to the compressor. In the latter case, a minimum exhaust gas temperature is normally required before efficient fuel compression can be achieved, meaning that the turbine must normally be running for a certain time period before it can drive the gas boost compressor. Start-up may therefore be difficult, requiring an alternative means of fuelling the engine is required, adding cost and complexity to the engine.

Known turbochargers used in motor sport inject air into a fuel rich exhaust within a turbocharger intake manifold to assist the transient performance of the turbine at times when there is a lower mass flow rate of exhaust gases to power the turbine than is desired. Another known turbocharger has liquid fuel injected into the turbine inlet to assist the transient performance of the turbine.

However, these methods are for use at transient stages of the engine cycle and may be used only after the engine has been running long enough for the exhaust gas temperature to auto-ignite the air/fuel mixture in the intake and they are used in reciprocating engines which have a very different start cycle to gas turbines. A method of obtaining adequate fuel compression is still required at an earlier stage in the engine cycle so that an alternative means of fuelling the engine becomes unnecessary, especially for gas turbines.

It is an aim of the present invention to alleviate this problem in a simple yet effective manner. The invention is as set out in the independent claims.

Preferred features are set out in the dependent claims.

In overview, the invention may provide a method of accelerating a turbine for a gas boost compressor from rest. Air supplied through an inlet in the turbine intake housing preferably mixes with fuel that is injected into the intake housing. A spark electrode preferably ignites the air/fuel mixture such that the temperature rise results in a very rapid acceleration of the turbine from rest to the desired operating speed. The rapid acceleration of the turbine may advantageously lead to the rapid acceleration of the gas boost compressor, enabling adequate fuel compression at a very early stage in the engine cycle.

This alleviates the need for an alternative means of fuelling the engine prior to the exhaust gas reaching a high temperature.

An advantage of using gaseous fuel is that it is easier to light than liquid fuel.

Liquid fuel would require atomising prior to ignition. Propane is the preferred fuel as it ignites easily and quickly in air. Spark ignition is preferred, as the method does not rely on high gas temperatures prior to ignition as is the case with the prior art auto-ignition method. Thus the ignition of the fuel/air mixture may occur at a much earlier stage in the engine cycle than has been previously known. Preferably, fuel is injected into the turbine housing as this method allows accurate fuel metering.

An advantage of the air inlet, fuel introducer and ignition device being disposed in close proximity to and orthogonal to each other is that the arrangement promotes good mixing of the fuel and air as they cross paths.

Similarly, the spark of the spark igniter is generated in a path that passes directly through the mixing area for rapid ignition of the air/fuel mixture.

In a preferred embodiment, gaseous fuel is burnt in the intake manifold of a gas boost compressor turbine stage to aid rapid acceleration of the gas boost compressor to its operating speed when starting from cold and stationary to provide adequate compression to an engine fuel supply early in the engine cycle. The method may minimise the time required for a gas boost compressor to reach operating speed, hence maximising compression effect.

An exemplary embodiment of the present invention will now be explained in more detail by the following non-limiting description and with reference to the accompanying drawings, in which: Fig. 1 is a schematic of a turbine for a gas boost compressor according to the invention; Fig. 2 is a schematic of a gas turbine engine incorporating the turbine of Fig. 1.

Figure 1 shows an embodiment of a turbine 1 for use with a gas boost compressor, the turbine 1 comprising an intake housing 5 and a turbine wheel lO. The turbine wheel 10 is mounted on a shaft 15 for co-rotation with the gas boost compressor. The intake housing 5 consists of a boxlike casing fitted over the shaft 15 and turbine wheel 10, the casing comprising a front wall 25, top wall 30, bottom wall 35, back wall 40 and sidewall 45. The shaft 15 extends through the centre of the front wall 25 and back wall 40 of the intake housing 5. The turbine wheel lO lies close to the front wall 25, inside of the intake housing 5. The back wall 40 includes an inwardly extending portion 50, forming a collar around the shaft 15 and providing guide vanes 20 surrounding the turbine wheel 10. The turbine is a single stage radial inlet/axial outlet flow type turbine.

A fuel injector 55 is disposed in the top wall 30 of the intake housing 5, at the end furthest away from the turbine wheel 10. The fuel injector 55 is connected to a fuel supply conduit 60 outside of the intake housing 5. A fuel control valve 62 is disposed along the fuel supply conduit 60 for controlling the fuel entering the intake housing 1. The valve 62 allows the control of fuel through the fuel supply conduit 60. A spark igniter 70 is disposed through back wall 40, close to and approximately 90 degrees to the fuel injector 55. The spark igniter 70 comprises a miniature spark electrode 72 for ignition of air and fuel in the intake housing 5. A circular air inlet 75 is disposed in the sidewall 45 for the supply of air, which may be vitiated air, tangentially into the intake housing.

Walls 25, 30, 35, 40 and 45 of the housing may form a substantially enclosed cylinder and the tangential air flow from inlet 75 may thus produce swirl at the upstream side of the turbine wheel 10. The air inlet 75 is disposed in the vicinity of the fuel injector 55 and spark igniter 70, such the fuel injector 55, the air inlet 75 and the spark igniter are all in close proximity to and perpendicular to each other.

Figure 2 shows a schematic of a gas turbine apparatus 100 incorporating the turbine 1. The gas turbine 100 includes a main compressor 105, main turbine 110 and combustor 115. The main compressor 105 and main turbine 110 are mounted on the same shaft 120 for co-rotation thereof. An air supply conduit provides air to the low-pressure side of the main compressor 105.

Compressed air exiting the high-pressure side of the main compressor 105 passes through the 'cold' side of a recuperator 130 and into an inlet of the combustor 115. A turbine-inlet conduit 150 provides fluid communication between an exit of the combustor 115 and an inlet of the turbine 110.

A bleed point 140 is provided at the high-pressure side of the main compressor 105. The bleed point 140 allows bleed air to pass along a cooling flow path 145 through a control valve 151, heat exchanger 152 (which may cool the flow) and into air inlet 75 of turbine 1. Upon exiting the turbine 1, the air, for cooling purposes, passes through a generator 154 (powered by turbine 110) and power conditioning unit 156.

The turbine I is connected by a shaft 160 to a secondary compressor 170. The construction of the secondary compressor 170 and turbine 1 thus resembles a turbocharger. The secondary compressor 170 may be a single stage axial inlet/radial outlet compressor. The secondary, or gas boost compressor 170 is adapted to compress natural gas fuel supplied from a fuel source 172 and provide a fuel flow through a fuel control valve 174 to the combustor 115, for combustion with the air supplied by the main compressor 105. With the fuel control valve 174 on the high pressure side of the secondary compressor 170, a pressure relief/regulator valve 176 is preferably provided, having a return line 178 to the low-pressure side of the secondary compressor. The valve 176 assists in preventing the secondary compressor 170 from entering a surge condition at low flows. Alternatively, valves 174 and 176 are omitted and, instead, a fuel flow control valve 180 is provided on the low-pressure side of the secondary compressor 170.

In use, the gas turbine 100 is started using generator/alternator 154 as a motor, air is supplied to the main compressor 105 and then a portion of the air is bled at bleed point 140 through cooling path 145 to the air inlet 75 of turbine 1.

Meanwhile, propane gas is supplied through fuel supply conduit 60 for fuel injection into the turbine 1 via fuel injector 55. The air/fuel mixture in the intake housing 5 is ignited using the spark igniter 70. The large temperature rise of the ignited mixture causes the turbine wheel lO to rapidly accelerate from its rest position, causing it to rapidly rotate together with the shaft 15 and the gas boost compressor 170. The gas boost compressor 170 is thus able to supply compressed fuel to the gas turbine combustor 115 very quickly after the engine has been started, alleviating the need for an alternative means of Quelling the engine whilst the turbine 1 is accelerated. The propane supply may then be switched off and the gas boost compressor driven purely by the bleed from the engine. This bleed may alternatively be taken from another point on the main engine such as from the exhaust flow from the turbine 110. A non return valve 182 may be optionally provided. Instead of passing the exhaust of turbine 1 through the generator 154, the exhaust may pass to the atmosphere or to power other equipment or be used for other purposes.

The turbine 1 fuel is propane, however the engine fuel can be any appropriate fuel. Liquid propane may be utilised in place of gaseous propane. If liquid propane is to be used it should preferably be atomised. The fuel may be introduced into the turbine housing using a valve rather than via fuel injection.

The gas boost compressor may have one or two stage compression or a greater number of stages. With, for example, two stage compression, it is important to achieve full volumetric flow at the inlet of the turbine 1 in order to spin up the secondary shaft. The turbine 1 may thus drive a primary shaft of the gas boost compressor, with the exhaust from the turbine 1 driving a second turbine (for two stage expansion/compression).

Various modifications may be made to the embodiment described without departing from the invention as defined by the claims.

Claims (18)

1. A method of accelerating a turbine from rest, the turbine comprising an intake housing and a turbine wheel, the method having the steps of introducing fuel into the intake housing, supplying air into the intake housing to form an air/fuel mixture and igniting the air/fuel mixture for acceleration of the turbine wheel.

2. A method as claimed in claim 1 wherein the air/fuel mixture is ignited by spark ignition.

3. A method as claimed in claim 1 or claim 2 wherein the fuel is gaseous fuel.

4. A method as claimed in claim 1 or claim 2 or claim 3 wherein the fuel is 1 5 propane.

5. A method as claimed in claim 1 wherein the fuel is injected into the intake housing using a fuel injector.

6. A turbine for a gas boost compressor, comprising a turbine wheel housed in an intake housing, an air inlet for the introduction of air into the intake housing, a fuel introducer for introducing fuel into the intake housing to create an air/fuel mixture and an ignition device for ignition of the air/fuel mixture prior to its entry into the turbine wheel.

7. A turbine as claimed in claim 6 wherein the ignition device is a spark igniter.

8. A turbine as claimed in claim 6 or claim 7 wherein the fuel introducer is a fuel injector.

9. A turbine as claimed in claim 6 wherein the fuel is gaseous fuel.

10. A turbine as claimed in any of claims 6 to 9 wherein the fuel is propane.

11. A turbine as claimed in claim 6 wherein the air inlet is disposed in a first wall of the intake housing and the fuel introducer is disposed in a second wall of the intake housing wall that is perpendicular to the first.

12.A turbine as claimed in claim 11 wherein the air inlet, fuel introducer and ignition device are positioned substantially orthogonally to each other.

13.A turbocharger having a turbine as claimed in any of claims 6 to 12 and a fuel compressor driven by the turbine.

14. A gas boost compressor having a turbine as claimed in any of claims 6 to 12 and a fuel compressor driven by the turbine.

15. A gas turbine engine having a turbine according to any of claims 6 to 12.

16.A method substantially as described herein and by the accompanying drawings.

17. A turbine substantially as described herein and by the accompanying drawings.

18.A gas boost compressor substantially as described herein and by the accompanying drawings.

l9.A turbocharger substantially as described herein and by the accompanying drawings.