WO2005075891A1

WO2005075891A1 - Pre-heating unit for a turbine and turbine comprising said pre-heating unit

Info

Publication number: WO2005075891A1
Application number: PCT/IT2004/000043
Authority: WO
Inventors: Santino Genovese
Original assignee: Santino Genovese
Priority date: 2004-02-06
Filing date: 2004-02-06
Publication date: 2005-08-18

Abstract

A pre-heating unit for a liquid fuel turbine for model aircraft comprises: - a body (14) which can be inserted by at least one of its ends in a combustion chamber of a turbine, and in which there is determined a fuel path which is determined between a fuel intake aperture (5) and a fuel outlet aperture (16), the said fuel intake aperture being in fluid communication with means to feed pressurized liquid fuel, and the said outlet aperture being positioned inside the combustion chamber of the turbine; - glow means (18) which are positioned along the said fuel path in order to heat the fuel to above its ignition temperature; and - nebulisation means (19) which are positioned along the said fuel path in order to obtain discharge of nebulised fuel from the said outlet aperture. Advantageously, the said preheating unit makes it possible to carry out starting of the turbine without requiring the use of gas or another fuel, other than that used for normal functioning of the turbine.

Description

DESCRIPTION "Pre-heating unit for a turbine and turbine comprising said pre-heating unit"

The present invention relates to a preheating unit for a turbine according to the preamble of claim 1, and in particular a kerosene turbine with limited dimensions, since it is designed to be used in the model aircraft field.

The invention also relates to a turbine of the aforementioned type, comprising the said ignition device.

In the context of models, it is well known to use turbines to be utilised as propulsion means for aircraft and the like. For this purpose, at present there are commercially available many turbines with reduced dimensions such that they can be fitted on board a model . Purely by way of example, the length of these turbines in the axial direction is approximately 20-30 cm.

Turbines of the above-described type are supplied with kerosene, and are provided with a gas preheating unit suitable for permitting starting. In fact, within the context of models, and in particular of model aircraft, to which reference is made for the sake of simplicity of depiction in the present description, the turbine start up cannot be carried out as for the turbines of an aircraft, since this starting procedure requires the use of pumps which can work at a pressure of approximately 300 bars .

Gas ignition units involve the presence inside the combustion chamber of ducts to feed the gas, as well as of an electric glow plug which, by making a platinum filament incandescent, can trigger the ignition of the gas inside the combustion chamber.

Although the said gas ignition units are now widely used, it should be stated that they have many disadvantages, such as those described hereinafter: the presence on board the vehicle of a small gas cylinder and the corresponding system inevitably involve problems of size and weight, as well as increased complication of the layout of the parts on board the vehicle; the density of the gas and consequently the quantity of gas admitted into the combustion chamber varies significantly according to variation of the external temperature and ambient pressure, thus creating problems of starting in winter and in summer, or on high-altitude flying fields; the quality of the gas used can vary from one supplier to another, and a few months apart can vary even for the same supplier; starting the turbines with gas preheating can give rise to considerable deterioration of the turbines. In fact, during starting of the turbine, and in particular during the initial stage of preheating, for the above- described reasons it becomes difficult to control the correct quantity of gas to be introduced into the combustion chamber, which is necessary in order to develop the minimum preheating temperature. For this reason, during the simultaneous injection of gas and kerosene, the temperature often rises well above that permitted by the electronic control systems, causing aborted starts and thermal stress of the turbine materials, and in particular the bearings, the nozzle guide vane and the rotor.

The problem on which the present invention is based is that of devising and making available a preheating unit for a turbine, and in particular a liquid fuel turbine for model aircraft and similar fields, which has functional and structural features such as to make it possible to start the turbine easily, without the occurrence of the disadvantages described with reference to the known art.

This problem is solved by a preheating unit for a turbine, according to claim 1.

According to a further aspect, this problem is solved by a turbine according to claim 12 and by the method for starting a turbine according to claim 18.

Further features and advantages of the preheating unit according to the present invention, as well as of a turbine comprising the said preheating unit, will become apparent from the following description of some preferred embodiments, provided by way of indicative and non-limiting example, with reference to the attached figures, in which: figure 1 represents a schematic perspective view of a preheating unit for a turbine according to the present invention; figure 2 represents a view which is not to scale, in axial cross-section, of the preheating unit of figure 1; figure 3 represents a perspective view, which is not to scale and is in cross-section, of the preheating unit of figure 1; figure 4 represents a perspective view of a turbine according to the invention, comprising the preheating unit of figure 1; figure 5 represents a view in axial cross-section of the turbine of figure 4; figure 6 represents an exploded perspective view of the turbine of figure 4 ; figure 7 represents a perspective view of a detail of the turbine of figure 4; and figure 8 represents a detail of the preheating unit of figure 1, according to a variant embodiment.

With reference to the attached figures, 1 represents as a whole a preheating unit for a turbine 2 , and in this specific case a liquid fuel turbine which is designed to be used in the model aircraft field.

Preferably, the liquid fuel for supplying to the turbine is kerosene for aeronautical use.

The turbine 2 comprises an outer casing 3, which has a circular cylindrical form, in the interior of which a rotational shaft 4 extends axially and is supported such as to rotate. In particular, the turbine extends in the axial direction X-X between a front end, at which there is a front aperture I which can permit intake of the air sucked in, and an opposite, rear end, at which there is a rear aperture O for discharge of the burnt gases .

In a conventional manner, the turbine 2 comprises in order, starting from the front end towards the rear end: an electric motor 5 which can be connected to the rotational shaft 4 of the turbine, such as to rotate it in the stage of starting the turbine itself, as will become more apparent hereinafter in the description; a conveyor 6 to convey the air towards the intake aperture I ; a centrifugal compressor comprising a rotor 7 which is keyed onto the shaft of the turbine 2 and an air flow rectifier 8 which is positioned upstream from the rotor 7 in order to supply the rotor itself with a flow of tangential air at an increased pressure; an annular combustion chamber 9 ; a flow rectifier (NGV) 10 for the flow of burnt gases ; a rotor 11 of the turbine in which the burnt gases are made to expand and a discharge cone which is disposed outside the rear aperture O.

The annular combustion chamber 9 comprises a plurality of holes through which the air obtained from the centrifugal compressor is admitted into the combustion chamber itself. In particular, some of these holes are swirl holes 12 which can impart swirl motion to the air which enters the combustion chamber 9. The swirl holes 12 are provided in the cylindrical lateral shell of the combustion chamber 9 in the vicinity of the front end of the combustion chamber 9, i.e. the end which faces the front aperture I of the turbine 2.

The turbine 2 is also provided with a primary fuel circuit (not illustrated) which can assure the supply of fuel to the combustion chamber during regular functioning of the turbine. In particular, the intake of fuel into the combustion chamber 9 takes place through corresponding channels which extend in the combustion chamber itself, from the rear end towards the free front end, such that the fuel is admitted into the area of the combustion chamber in which the vortex of air generated by the swirl holes 12 is generated.

Advantageously, with the turbine 2 there is associated the said preheating unit 1, which comprises a body 14 which can be inserted in the outer casing 3 of the turbine 2 until its free end portion projects into the combustion chamber 9 of the turbine 2. For this purpose, the outer casing 3 of the turbine and the combustion chamber 9 are provided with respective insertion holes 13 which correspond with one another. Advantageously, the preheating unit 1 has dimensions and proportions such that it can be inserted in the holes which are designed to accommodate the glow plug for ignition of the gas present in turbines with gas preheating, which are currently commercially available, for model aircraft .

The preheating unit 1 is secured to the outer casing 3 of the turbine 2 by a threaded connection, a connection for form coupling, or another type of functionally equivalent connection. There is also interposition of sealing means of a known type, such as, for example, silicon mastic, seals and the like, in order to assure sealing from the interior to the exterior of the turbine .

Advantageously, the preheating unit 1 is secured to the turbine 2 in a detachable manner, such as to make it possible to have dismantling carried out for the usual operations of overhaul, cleaning or replacement of the heater unit itself.

In the body 14 of the preheating unit 1 there is defined a fuel path which is determined between a fuel intake aperture 15 and a fuel outlet aperture 16.

The fuel intake aperture 15 is in fluid communication with pressurised liquid fuel feed means, whereas the aperture 16 is positioned inside the combustion chamber 9, at the area in which the vortex of air generated by the swirl holes 12 is formed. The preheating unit 1 also comprises glow means 18 which are positioned along the said fuel path and can heat the fuel to above its ignition temperature, and nebulisation means 19 which are positioned along the said fuel path in order to obtain emission of nebulised fuel from the outlet aperture 16.

In the example, the free end portion of the body 14 of the preheating unit 1 is in the form of a hollow cylindrical body, preferably with a circular cross-section, which extends according to a prevalently axial direction G-G. Inside the said hollow cylindrical body there are positioned the glow means 18, and the fuel path is also defined inside it.

According to a preferred embodiment, the nebulisation means 19 take the form of a calibrated passage with dimensions such as to give rise to nebulisation of the pressurised fuel which passes through it. Substantially, before the pressurised liquid fuel can be discharged from the outlet aperture 16, it is forced to pass through a narrow calibrated passage which gives rise to its nebulisation, in other words it must undergo an actual phenomenon of vaporisation or atomisation. As a consequence of this, the fuel emerges from the outlet aperture 16 after having been reduced to extremely minute particles . In the example, the glow means 18 are formed such that they can be inserted in the hollow cylindrical body, so as to leave only one free section, i.e. a minimal opening in relation to the inner wall of the hollow cylindrical body, the said limited free section constituting the said calibrated passage in which the nebulisation of the pressurised liquid fuel takes place.

Preferably, the glow means are in the form of a cylindrical element with a prismatic, elliptical or circular cross- section or the like, with dimensions which are such that they can be inserted coaxially in the hollow cylindrical body in the manner previously described.

It should be noted that there are commercially available at present, glow means which can reach temperatures of approximately 1000°C or more when they are supplied with a 12 Volt voltage, and which have an electrical impedance value which is inversely correlated to their temperature. Consequently, the current which is necessary in order to heat the said glow means is, for a very short initial period approximately 20-25 Amps, and this is then reduced drastically as the temperature of the means increases . In view of the foregoing information, it is apparent that the said glow means can easily be supplied with power by an accumulator with limited dimensions, such as those which are normally installed on board model aircraft with a turbine .

In order to be able to make the said glow means 18 incandescent, the latter are provided with electrical contacts 20 which are accessible from the exterior of the turbine 2, for wiring to a source of energy, for example an accumulator .

According to a preferred embodiment, the preheating unit 1 comprises anti-turbulence means 21 which are positioned in the vicinity of the said outlet aperture 16, such as to determine in the combustion chamber 9 of the turbine 2 an area in which the mixing of the nebulised fuel with the comburent, i.e. with the air, takes place in a manner which is protected against the turbulence caused by the swirl motion of the air in the combustion chamber 9.

In the present example, the anti-turbulence means 21 are determined by an end portion of the hollow cylindrical body which extends such as to project beyond the glow means 18, as illustrated in figures 2 and 3.

According to a further advantageous aspect, in the said end portion of the hollow cylindrical body which projects beyond the glow means, there are present calibrated holes which form a reticulated structure as illustrated in figure 8.

As an alternative to the foregoing arrangement, the anti- turbulence means can be formed differently, and, for example, it is possible to introduce the presence of a baffle plate or another element which is functionally equivalent to that previously described.

With reference to the anti-turbulence means, it should be noted that even in the absence of the latter, the preheating unit according to the invention can function, i.e. the flame can be ignited inside the combustion chamber, although with longer preheating times and at the expense of greater consumption of electrical energy.

The turbine 2 is provided with means to intercept the flow of fuel conveyed to the fuel path of the preheating unit 1, for example with a solenoid valve, which can be activated in alternating mode between an open configuration and a closed configuration in which these means respectively permit and prevent the passage of fuel .

The functioning of the preheating unit 1 is very simple. In fact, in order to obtain ignition of the flame, it is sufficient, for example by means of a 12 Volt accumulator, to supply power to the electrical contacts 20 which are connected to the glow means 18. As soon as the latter have heated up until they are incandescent, for example to a temperature of approximately 1000°C, which moreover can easily be determined in view of the reduction in the current absorbed, it is sufficient to supply with the pressurised liquid fuel the fuel passage which exists inside the body 14 of the preheating unit 1. By this means, the liquid fuel is in direct contact with the glow means, and heats up until it surpasses its own ignition temperature. Whilst passing through the narrow calibrated passage which exists between the glow means 18 and the inner wall of the hollow cylindrical body 14, the liquid fuel is forced to be nebulised. As soon as the nebulised fuel is discharged from the outlet aperture 16, it is mixed thoroughly with the air, and ignites immediately.

The ignition of the nebulised fuel is made more efficient by the presence of the anti-turbulence means, particularly if these are provided with the calibrated holes which form the reticulated structure previously described.

It should be noted that until the nebulised fuel is discharged from the outlet aperture 16, it cannot ignite, even if it is nebulised and heated to a temperature which is higher than its ignition temperature, since it is not in contact with the comburent, i.e. the air.

Starting with an initial configuration in which the turbine 2 is closed and the preheating unit 1 is switched off, in order to start up the turbine 2 it is necessary to carry out the following operations : supply the glow means 18 with current; by means of activation of the electric motor, rotate the shaft 4 of the turbine 2, such that the centrifugal compressor assures intake into the combustion chamber 9 of a quantity of air which is at least equal to that which is necessary in order to keep the flame generated by the preheating unit 1 ignited; - supply the said fuel path of the preheating unit 1 with pressurised liquid fuel, such as to generate a flame inside the combustion chamber 9 of the turbine 2; wait for the combustion chamber 9 to heat up; increase the number of revolutions of the turbine shaft 4 by increasing the number of revolutions of the electric motor; and reduce progressively the supply of fuel to the preheating unit until it is interrupted, and simultaneously start to supply with liquid fuel the primary fuel circuit which can supply the combustion chamber during functioning of the turbine, such as to allow the turbine to reach the minimum number of revolutions which are necessary in order for its functioning to be maintained automatically.

Preferably, the said stage of rotating the shaft 4 of the turbine 2 takes place a few seconds in advance of the stage of ignition of the flame generated by the preheating unit 1.

As can be appreciated from the foregoing description, the preheating unit according to the invention makes it possible to be able to carry out starting of a turbine using only an electric accumulator, which is usually already present on board model aircraft, and the same liquid fuel used by the turbine itself during its normal functioning. In fact, the preheating unit according to the invention does not require the use of a gas to generate the flame necessary to preheat the combustion chamber of the turbine. Consequently, the preheating unit according to the invention makes it possible to eliminate the disadvantages referred to in the introductory part of the present description.

A further advantage of the preheating unit according to the invention consists in its structural simplicity and in the possibility of being easy to dismantle in order to make it possible to carry out occasional operations of maintenance and replacement, as well as being easy to dismantle from the turbine .

A further advantage of the preheating unit according to the invention consists in the possibility of being able to be used also in existing turbines which are designed to be started by gas, without the latter needing to be modified. In fact, for this purpose, it is sufficient to replace the electric glow plug which is present currently in these turbines, by the preheating unit according to the invention.

It will be appreciated that, in order to meet specific and contingent requirements, a person skilled in the art will be able to make many modifications and variations to the above-described preheating unit, all of which however come within the scope of protection of the invention as defined by the following claims .

Claims

1. Preheating unit for a turbine, in particular a liquid fuel turbine for model aircraft, comprising: a body which can be inserted by at least one of its ends in a combustion chamber of a turbine, and in which there is determined a fuel path which is determined between a fuel intake aperture and a fuel outlet aperture, the said fuel intake aperture being in fluid communication with means to feed pressurised liquid fuel, and the said outlet aperture being positioned inside the combustion chamber of the turbine; glow means which are positioned along the said fuel path in order to heat the fuel to above its ignition temperature; and - nebulisation means which are positioned along the said fuel path in order to obtain discharge of nebulised fuel from the said outlet aperture .

2. Preheating unit according to claim 1, wherein the said nebulisation means comprise a calibrated passage.

3. Preheating unit according to claim 1 or claim 2, wherein the said fuel path is determined in the free section determined between the said glow means and the said hollow cylindrical body.

4. Preheating unit according to any one of claims 1 to 3 , wherein the said body comprises a hollow cylindrical section, which extends according to a prevalently axial direction, in the interior of which there extend the said glow means .

5. Preheating unit according to claim 4, wherein the said glow means are formed such as to be inserted in the said hollow cylindrical section, such as to leave only a minimal free section in relation to the inner wall of the said hollow cylindrical body, the said limited free section constituting a calibrated passage in which the pressurised liquid fuel can be nebulised.

6. Preheating unit according to any one of claims 1 to 5, wherein the said glow means are in the form of a cylindrical element.

7. Preheating unit according to any one of claims 1 to 6, wherein the said glow means are provided with electrical contacts for wiring to an energy source .

8. Preheating unit according to any one of claims 1 to 5, comprising anti-turbulence means which are positioned in the vicinity of the said outlet aperture, such as to determine in the combustion chamber of the turbine an area in which the mixing of the nebulised fuel with the comburent takes place in a manner which is protected against the air turbulences.

9. Preheating unit according to claims 4 and 8, wherein the said hollow cylindrical section of the said body extends at the said outlet aperture, such as to project beyond the glow means in order to define the said anti- turbulence means .

10. Preheating unit according to claim 8 or claim 9, wherein the said anti-turbulence means have a plurality of calibrated holes.

11. Preheating unit according to any one of claims 1 to 10, the said glow means of which are selected from the group with the electrical impedance value which is inversely correlated to their temperature .

12. Liquid fuel turbine, in particular for model aircraft, comprising a combustion chamber, characterised in that it comprises a preheating unit according to any one of claims 1 to 11.

13. Turbine according to claim 12, wherein the said preheating unit is inserted in a hole provided in the combustion chamber, such as to project inside the said combustion chamber.

14. Turbine according to claim 12, wherein the said hole is positioned at the portion of the combustion chamber in which there are present swirl holes which can impart swirl motion to the air which enters the combustion chamber.

15. Turbine according to any one of claims 12 to 14, comprising a primary fuel circuit which can assure the supply of fuel to the combustion chamber during regular functioning of the turbine.

16. Turbine according to any one of claims 12 to 15, comprising means to intercept the flow of fuel conveyed to the said fuel path of the preheating unit .

17. Turbine according to claim 16, wherein the said means for intercepting the flow of fuel comprise a solenoid valve which can be activated in an alternating manner between an open configuration and a closed configuration in which it respectively permits and prevents the passage of fuel .

18. Method for starting a turbine according to any one of claims 12 to 17, and comprising a rotational shaft, an intake aperture for the air and a discharge aperture for the burnt gases at the opposite head ends of the turbine, and a compressor which is keyed onto the rotational shaft in order to convey a flow of pressurised air to the combustion chamber of the turbine, the method being characterised in that it comprises the stages of: supplying the glow means with power; rotating the shaft of the turbine, such that the compressor assures intake into the combustion chamber of a quantity of air which is at least equal to that which is necessary in order to keep the flame generated by the preheating unit ignited; supplying the said fuel path of the preheating unit with pressurised liquid fuel, such as to generate a flame inside the combustion chamber of the turbine; - waiting for the combustion chamber to heat up; increasing the number of revolutions of the turbine; and reducing progressively the supply of fuel to the preheating unit until it is interrupted, and simultaneously starting to supply with liquid fuel a primary fuel circuit which can supply the combustion chamber during functioning of the turbine, such as to allow the turbine to reach the minimum number of revolutions which are necessary in order for its functioning to be maintained automatically.

19. Method according to claim 18, wherein the said stage of rotating the shaft of the turbine takes place a limited predetermined period of time in advance of the stage of ignition of the flame generated by the preheating unit.

20. Method according to claim 18 or claim 19, wherein the said stage of supplying pressurised liquid fuel to the said fuel path takes place according to a predetermined frequency of injection.