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Title:
FUEL MIXTURE AND USES THEREOF
Document Type and Number:
WIPO Patent Application WO/2011/138395
Kind Code:
A2
Abstract:
A fuel mixture comprises tert-butyl peroxybenzoate in an amount of 30 % by wt. to 70 % by wt. and kerosene in an amount of 70 % by wt. to 30 % by wt.

Inventors:
MISHRA, Kirti Bhushan (Dominicusstr. 18, Berlin, 10823, DE)
WEHRSTEDT, Klaus-Dieter (Am Weinberg 26, Mittenwalde, 15749, DE)
Application Number:
EP2011/057205
Publication Date:
November 10, 2011
Filing Date:
May 05, 2011
Export Citation:
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Assignee:
Bundesanstalt für Materialforschung und -prüfung (BAM) (Unter den Eichen 87, Berlin, 12205, DE)
MISHRA, Kirti Bhushan (Dominicusstr. 18, Berlin, 10823, DE)
WEHRSTEDT, Klaus-Dieter (Am Weinberg 26, Mittenwalde, 15749, DE)
International Classes:
C10L1/02
Domestic Patent References:
2010-10-14
Foreign References:
US4298351A1981-11-03
US20070028593A12007-02-08
Other References:
"Two-stroke engine oil contg. organic peroxides - gives exhaust gas with reduced smoke content", WPI / THOMSON,, vol. 1977, no. 27, 26 May 1977 (1977-05-26), XP002612360, -& JP 52 063905 A (SUZUKI MOTOR CO) 26 May 1977 (1977-05-26)
CHUN H ET AL: "Thermal radiation of di-tert-butyl peroxide pool fires-Experimental investigation and CFD simulation", JOURNAL OF HAZARDOUS MATERIALS 20090815 ELSEVIER NLD LNKD- DOI:10.1016/J.JHAZMAT.2008.12.088, vol. 167, no. 1-3, 15 August 2009 (2009-08-15), pages 105-113, XP002655149, ISSN: 0304-3894
MISHRA K B ET AL: "Radiative characteristics of large pool fires of organic peroxides", PROCEEDINGS / 4TH EUROPEAN COMBUSTION MEETING : VIENNA UNIVERSITY OF TECHNOLOGY : 14TH - 17TH APRIL 2009, VIENNA, AUSTRIA, VIENNA, 17 April 2009 (2009-04-17), pages 1-6, XP009141865, ISBN: 978-3-902655-06-6
MISHRA K B ET AL: "Prediction of burning rate of an accidentally release flammable fuel by means of CFD simulation", PROCEEDINGS OF THE SEVENTH INTERNATIONAL CONFERENCE ON CFD IN THE MINERALS AND PROCESS INDUSTRIES , CSIRO, MELBOURNE, AUSTRALIA, 9-11 DECEMBER 2009, CSIRO, AU, 9 November 2009 (2009-11-09), pages 1-8, XP002593231,
Attorney, Agent or Firm:
ZIMMERMANN, Gerd et al. (Zimmermann & Partner, Josephspitalstr. 15, Munich, 80331, DE)
Download PDF:
Claims:
CLAIMS

1. A fuel mixture comprising tert-butyl peroxybenzoate in an amount of 30 % by wt . to 70 % by wt . and kerosene in an amount of 70 % by wt . to 30 % by wt .

2. The fuel mixture according to claim 1, comprising tert-butyl peroxybenzoate in an amount of 40 % by wt . to 60 % by wt . and kerosene in an amount of 60 % by wt . to 40 % by wt .

3. The fuel mixture according to either claim 1 or claim 2, comprising tert-butyl peroxy benzoate in an amount of 50 % by wt . and kerosene in an amount of 50 % by wt.

4. The fuel mixture according to any one of the preceding claims, consisting of tert-butyl peroxybenzoate in an amount of 30 % by wt . to 70 % by wt . and kerosene in an amount of 70 % by wt . to 30 % by wt.

5. The fuel mixture according to claim 4, consisting of tert-butyl peroxy benzoate in an amount of 50 % by wt . and kerosene in an amount of 50 % by wt .

6. An industrial dryer which is equipped to be operated in pulse combustion mode with a fuel mixture according to any one of the preceding claims.

7. The industrial dryer according to claim 6, wherein the industrial dryer does not comprise a device for an oscillating fuel supply and does not comprise a baffle valve or an explosion chamber.

8. A gas turbine which is equipped to be operated in pulse combustion mode with a fuel mixture according to any one of claims 1 to 5.

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9. The gas turbine according to claim 8, wherein the gas turbine does not comprise a device for an oscillating fuel supply.

10. The gas turbine according to either claim 8 or claim 9, wherein an injection system of the gas turbine is equipped to provide at least two different injection opening diameters so as to control a pulsation frequency of the pulse combustion.

11. An engine, in particular an aircraft engine, which is equipped to be operated in pulse combustion mode with a fuel mixture according to any one of claims 1 to 5.

12. The engine according to claim 11, wherein the engine does not comprise an active control for noise reduction .

13. The engine according to either claim 11 or claim 12, wherein the engine comprises pulse ducts of different diameter, wherein the respective diameters of the pulse ducts are selected in such a way that the pressure wave generated during pulse combustion of the fuel mixture in a respective pulse duct is out of phase with a pressure wave generated in another pulse duct.

14. A drying method comprising the following steps

(a) providing an industrial dryer according to either claim 6 or claim 7;

(b) drying a material located in the industrial dryer, the heat required for drying being provided by means of combustion of a fuel mixture according to any one of claims 1 to 5.

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15. A method for operating a gas turbine, comprising the following steps

(a) feeding a fuel mixture according to any one of claims 1 to 5 to an injection device; and

(b) injecting the fuel mixture into a combustion chamber, an injection opening diameter of the injection device being set or selected so as to control a pulsation frequency of the pulse combustion .

16. A use of a fuel mixture according to any one of claims 1 to 5 in an industrial dryer for noise reduction in an engine, in particular an aircraft engine, or in a gas turbine.

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Description:
FUEL MIXTURE AND USES THEREOF

The present invention relates to a fuel mixture and to the use of this fuel mixture in industrial dryers, in gas turbines or for noise reduction in engines.

Combustion is one of the most important chemical processes used by mankind. Over time, different fuels have therefore been discovered or developed for the various applications of combustion processes, the properties of which fuels are optimised for the specific applications.

One of the main uses of combustion processes is heat generation, whether for industrial use, electricity generation or for heating purposes. A further important field of application of combustion processes is mobility, since the vast majority of all vehicles are currently driven with the aid of internal combustion engines. Furthermore, combustion processes are also used for the thermal utilisation of waste materials or to render toxic substances unharmful by means of combustion.

For example, combustion processes are frequently used in the drying of moist materials and substances. Drying is an important process within the chemical industry, paper production and also within the food industry. It is known that pulse combustion is more effective compared to continuous combustion. What are known as 'baffle valves' and/or 'explosion chambers' are therefore provided in industrial dryers in order to ensure such a pulse combustion process. During the explosion of conventional fuels in the air or oxygen, the sound produced during this process results in a considerable level of noise which has to be counteracted by costly sound insulation measures. The costs of the drying process are considerably increased by these measures. Another use of combustion processes occurs in turbomachinery and turbines. Turbomachinery and turbines are used, in particular, for power generation and movement, for example in aircraft. It is known that 'pulse combustion' is particularly effective for this purpose. With pulse combustion a flow pulse generator for example is used in order to generate a pulsating flow of hot gases from conventional fuels (for example diesel or gasoline) in a subsequent combustion chamber. The injection line 100 of such a conventional turbine is shown in Fig. 4. In this instance the injection line 100 comprises a fuel reservoir 110 which contains the fuel. The fuel is then fed via a fuel feed pump 120 to a distributor 130. The distributor 130 then divides the fuel flow over two branches, each branch comprising a flow pulse generator 140, 142. For example the flow pulse generator 140, 142 may comprise electronically controlled valves, by means of which the flow rate of the fuel is controlled in an oscillating manner. This oscillating fuel flow is now fed into a combustion chamber (not shown) of the turbine via injectors 150, 152. The combustion of the fuel then takes place in the combustion chamber, more specifically as pulse combustion owing to the oscillating fuel supply. However, the flow pulse generator and high-power fuel feed pumps are cost-intensive and it is difficult to control the pulse frequency. The high feed pressures but low mass combustion rates of conventional fuels further result in incomplete combustion, which leads to a high level of discharge of pollutants and increased fuel consumption.

Another use of combustion processes occurs in engines, for example in aircraft engines. Conventional aircraft engines generate their thrust by discharging hot gases at high speed. This involves a high level of noise, which represents a heavy encumbrance, in particular for those people living close to the airport. It is therefore constantly attempted to reduce the noise level of such engines. For this purpose the engines are generally provided with additional devices for noise reduction. For example US 2007/0028593 describes a device for noise reduction, as is shown in Fig. 6. In this instance an engine 50 comprises a combustion chamber 52, from which a plurality of pulse ducts 54, 56, 58, 60 lead out. The hot gases F generated in the combustion chamber 52 are fed via the pulse ducts 54, 56, 58, 60 to an ejector 64 comprising a plurality of chambers 22. A regulator 55 is arranged between the combustion chamber 52 and pulse ducts 54, 56, 58, 60 and is controlled by a processor 68. The regulator 55 is equipped to route the respective mass flow of the hot gas F to a respective one of the pulse ducts 54, 56, 58, 60. In accordance with US 2007/0028593 a reduction in noise of the engine is now achieved in that the processor 68 routes the respective mass flow into the pulse ducts 54, 56, 58, 60 in such a way that the pressure wave propagating through a respective pulse duct is out of phase with the pressure waves in the other pulse ducts.

It is further common to all combustion processes that the emissions produced during the process, in particular Ox, CO and soot, are precarious in terms of health and environment. It is therefore desirable to provide fuels and combustion processes in which such emissions are reduced. Furthermore, an increased combustion efficiency is desired in order to reduce, inter alia, fuel consumption.

In particular the burning behaviour depends on the properties of the fuel used, the atmosphere in which the combustion process takes place, the burner design and the desired heat transfer rate of the flame. For example burners in smelting furnaces in the glass or steel industries therefore use methane jet flames, oil or coal in order to obtain the desired heat transfer by means of radiation. In order to achieve a comparatively greater transfer in this instance, the fuel should burn more quickly, generate bigger flames, have a higher flame temperature and produce fewer combustion end products, such as NOx and CO.

It is virtually impossible to ensure the accomplishment of this and other objectives with the combustion of conventional hydrocarbon fuels under normal conditions, since these fuels burn relatively slowly under normal conditions and generate abundant soot and other emissions. Methods such as the injection of gas jets in air or in a partially mixed state, or the injection of atomised oil jets in air are therefore typically used for the combustion of conventional hydrocarbon fuels. However, these methods generate large bright flames and therefore more soot. Furthermore, owing to the incomplete combustion many pollutants, such as COx and NOx are also produced. Moreover, these methods require the addition of oxidants in order to improve the completeness of the combustion process .

In view of the above, the present invention proposes a fuel mixture according to claim 1, an industrial dryer according to claim 6, a gas turbine according to claim 8, an engine according to claim 11, a drying method according to claim

14, a method for operating a gas turbine according to claim

15, and uses of the fuel mixture according to claim 16.

In accordance with one embodiment a fuel mixture comprises tert-butyl peroxybenzoate in an amount of 30 % by wt . to 70 % by wt . and kerosene in an amount of 70 % by wt . to 30 % by wt . In particular, the fuel mixture may comprise tert- butyl peroxybenzoate in an amount of 40 % by wt . to 60 % by wt . and kerosene in an amount of 60 % by wt . to 40 % by wt . , and in particular may comprise tert-butyl peroxybenzoate in an amount of 50 % by wt . and kerosene in an amount of 50 % by wt . In accordance with a development the fuel mixture may even consist of tert-butyl peroxybenzoate in an amount of 40 % by wt . to 60 % by wt . and kerosene in an amount of 60 % by wt . to 40 % by wt . In particular, the fuel mixture may consist of tert-butyl peroxybenzoate in an amount of 50 % by wt . and kerosene in an amount of 50 % by wt .

Owing to its high content of tert-butyl peroxybenzoate the fuel mixture described surprisingly exhibits an approximately periodic pulsing of the relative flame length. The fuel mixture itself thus provides a pulsed combustion, in this instance it being possible to adjust the frequency of the pulsation, for example by the mixing ratio between kerosene and tert-butyl peroxybenzoate or else by geometric parameters, such as the diameter of a burner opening, etc. In this way the described fuel mixtures render superfluous the measures previously required to produce pulse combustion.

In accordance with another embodiment an industrial dryer is provided which is equipped to be operated in pulse combustion mode with one of the fuel mixtures described above. In particular, such an industrial dryer no longer requires a device for an oscillating fuel supply and no longer requires a baffle valve or explosion chamber, since the pulse combustion is generated by the fuel mixture itself owing to the high content of tert-butyl peroxybenzoate .

The fuel mixture and the industrial dryer may advantageously be used in a drying process. In this instance the drying process includes the steps of providing an industrial dryer and drying a material located in the industrial dryer, the heat required for drying being provided by means of combustion of the fuel mixture according to the invention. The drying method thus carried out is considerably more efficient and also produces fewer emissions than conventional drying methods.

A further development of the invention relates to the use of the fuel mixture according to the invention in an industrial dryer, a fuel mixture of the composition comprising 50 percent by weight of tert-butyl peroxybenzoate and 50 percent by weight of kerosene being used in particular.

In accordance with another embodiment a gas turbine is provided which is equipped to be operated in pulse combustion mode with one of the fuel mixtures described above. In particular, such a gas turbine no longer requires a device for an oscillating fuel supply, since the pulse combustion is produced by the fuel mixture itself owing to the high content of tert-butyl peroxybenzoate.

For example the fuel mixture and the gas turbine can advantageously be used in power generation. Power generation by means of such a gas turbine which is operated with the described fuel mixture is considerably more efficient and also produces fewer emissions than conventional methods.

A further development of the invention relates to the use of the fuel mixture according to the invention in a gas turbine .

Yet another development of the invention relates to the use of the fuel mixture according to the invention in an engine, in particular an aircraft engine, for noise reduction .

In accordance with an associated embodiment an engine is provided which is equipped to be operated in pulse combustion mode with one of the fuel mixtures described above. In particular, the engine may comprise pulse ducts of different diameter, the respective diameter of the pulse ducts being selected in such a way that the pressure wave generated during pulse combustion of the fuel mixture in a respective pulse duct is out of phase with a pressure wave generated in another pulse duct. In particular such an engine no longer requires an additional active control for the mass flow, since merely the geometric shaping of the pulse ducts causes the pressure waves propagating in the pulse ducts to be out of phase. The same noise-reducing effect as in US 2007/0028593 can thus be achieved, moreover without the costly mechanical and electronic control of US 2007/0028593.

If the geometry of pulse ducts of an engine is set in such a way that different pulsation frequencies of the fuel mixture are produced, the measures previously required for noise reduction, in particular the regulator 55 and the processor 68 according to US 2007/0028593, can thus be rendered superfluous.

In addition to the noise reduction, aircraft which are driven by means of such an engine which is operated with the fuel mixture described are also considerably more efficient and also produce fewer emissions than conventional aircraft.

The fuel mixture and the engine may advantageously be used, for example, in aviation. One embodiment of the invention relates to the use of a fuel mixture of the composition comprising 60 percent by weight of tert-butyl peroxybenzoate and 40 percent by weight of kerosene in an aircraft engine.

Further advantageous configurations, details, aspects and features of the present invention emerge from the dependent claims, the description and the accompanying drawings, in which :

Fig. 1 shows the course over time of the relative flame length of a tert-butyl peroxybenzoate pool flame;

Fig. 2 shows the course over time of the relative flame length of a pool flame of a mixture of 50 % tert-butyl peroxybenzoate and 50 % kerosene;

Fig. 3 shows measured mass combustion rates of tert- butyl peroxybenzoate and kerosene as well as further organic peroxides as a function of pool diameter;

Fig. 4 is a schematic view of a conventional fuel feed line of a gas turbine with pulse combustion;

Fig. 5 is a schematic view of a fuel feed line of a gas turbine in accordance with an embodiment of the present invention;

Fig. 6 is a schematic view of a conventional engine with an electronic control device for noise reduction;

Fig. 7 is a schematic view of an engine in accordance with an embodiment of the present invention.

In accordance with a first embodiment a fuel mixture is used in a self-sustaining, pulsating combustion process in an industrial dryer and comprises tert-butyl peroxybenzoate (TBPB) in an amount of 30 % by wt . to 70 % by wt . and kerosene in an amount of 70 % by wt . to 30 % by wt .

In accordance with a further embodiment a fuel mixture is used in a self-sustaining, pulsating combustion process in an industrial dryer and comprises tert-butyl peroxybenzoate (TBPB) in an amount of 40 % by wt . to 60 % by wt . and kerosene in an amount of 60 % by wt . to 40 % by wt .

In accordance with another embodiment a fuel mixture is used in a pulsating combustion process in a gas turbine and comprises tert-butyl peroxybenzoate (TBPB) in an amount of 30 % by wt . to 70 % by wt . and kerosene in an amount of 70 % by wt. to 30 % by wt .

In accordance with yet a further embodiment a fuel mixture is used in a pulsating combustion process in an engine, in particular an aircraft engine, and comprises tert-butyl peroxybenzoate (TBPB) in an amount of 30 % by wt . to 70 % by wt . and kerosene in an amount of 70 % by wt . to 30 % by wt .

In accordance with another embodiment a fuel mixture is used in a pulsating combustion process in an engine, in particular an aircraft engine, and comprises tert-butyl peroxybenzoate (TBPB) in an amount of 40 % by wt . to 60 % by wt . and kerosene in an amount of 60 % by wt . to 40 % by wt . In particular the fuel mixture may consist of TBPB in an amount of 50 % by wt . and kerosene in an amount of 50 % by wt .

The organic peroxide tert-butyl peroxybenzoate comprises the following structure:

Organic peroxides, in particular peroxyesters including TBPB, are known as radical starters for the polymerisation of different monomers. However, a use of this substance class as a primary constituent in fuel mixtures in self- sustaining, pulsating oxygen-fuel combustion processes is not generally known.

In accordance with a further embodiment the pool flame of the fuel mixture has a Froude number which is 20 times to 100 times greater than the Froude number of a pool flame of kerosene alone. In accordance with a development the Froude number in this instance may be 50 times to 80 times greater than the Froude number of kerosene alone. In this case a 'pool flame' is generally understood to mean a turbulent diffusion flame, of which the liquid fuel is spread horizontally. For example, pool flames are a type of frequently occurring destructive flame which may be produced, for example, during storage, transport and processing of liquid fuels. The Froude number characterises the initial pulse of the flame, rather low Froude numbers being typical for pool flames since the flow rate basically results from the buoyancy of the combustion. On the whole, the fundamental chemical and physical principles of pool flames have been studied in detail and will not be described further here.

Fuel mixtures according to the above-described embodiments and their developments reveal a previously unknown and surprising burning behaviour. Fig. 1 thus shows the course over time of the relative flame length of a pool flame of tert-butyl peroxybenzoate . The relative flame length is given as the ratio H/d of the flame length H to the diameter d of the fuel pool. In this instance the flame length H is defined as a maximum visible length of the flame, i.e. in the wavelength range between 380 nm < λ < 750 nm. Typical values for the relative flame length H/d of conventional fuels, such as liquefied natural gas (LNG) or kerosene lie in the range between 0.8 and 4. By contrast, Fig. 1 shows that the relative flame length H/d for tert- butyl peroxybenzoate can increase up to 18 over the course of time. In other words, the tert-butyl peroxybenzoate flame has a relative flame length up to 18 times the pool diameter. However, the relative flame length of the tert- butyl peroxybenzoate pool flame also decreases down to low values of H/d ~ 2.

This variation of the relative flame length is not unusual per se and is also observed for other fuels. However, what is surprising in the case of the fuels described in this instance is both the wide variation in the relative flame length by one order of magnitude and the regularity of this variation. The fuels thus exhibits an approximately periodic pulsing of the relative flame length, which is also referred to in the diagram (see Fig. 1) as the y W- effect' owing to its appearance. In other words, fuel mixtures of the type described exhibit a substantially regular change over time of the relative flame length in pool flames by a factor of 2 or more. In this contextit is not absolute regularity within the sense of a strict time periodicity which is meant, but instead a similarity between the respective time intervals of large or small relative flame length as well as a similarity between the respective increase or decrease in the relative flame length between such time intervals.

In this regard it should be noted that the frequency f of the pulsation is given by

f ~ (Fr t T ! ' 2 ,

wherein Fr f is the Froude number of the pool flame of the fuel mixture. Since the Froude number of the described fuel mixture is 20 times to 100 times greater than that of kerosene alone, the pulsation frequency f thereof is accordingly 4 times to 10 times lower than that of kerosene alone. Furthermore, the combustion rate of the fuels described in the present case is typically 40 times to 120 times greater than that of kerosene alone. The oscillation of the pool flame can be approximated by a sine wave as follows:

>

d \,a / w wherein (H/d) o is the average flame height, A is amplitude, w is the half period and t c is the phase shift. By comparison, a similar measurement is plotted in Fig. 2, in this case however a fuel mixture according to an embodiment of the present invention comprising 50 % by wt . TBPB and 50 % by wt . commercial kerosene having been burnt off. In this case, too, a sine wave for the flame height was also adapted in accordance with the equation above. The results of the comparison between pure TBPB and a 50:50 mixture of TBPB and kerosene are summarised in Table 1.

Table 1

It surprisingly emerges that the average relative flame height (H/d) o for the mixture is considerably greater than for TBPB alone. Furthermore, the period of the oscillation for the fuel mixture decreases to approximately one quarter of the value for pure TBPB. This is an unexpected effect, namely that in a mixture of TBPB with conventional kerosene the fuel mixture exhibits a considerably quicker oscillation with a simultaneously larger flame and a higher heat release rate compared to pure TBPB.

In Fig. 3 a comparison between the mass combustion rates for pool flames of TBPB and kerosene is plotted in a log- log manner for different pool diameters. It can be seen that TBPB has a natural mass combustion rate which is greater than kerosene by two orders of magnitude. Fig. 3 also shows the mass combustion rates for further peroxy fuels, namely di-tert-butyl peroxide (DTBP for short), tert-butyl peroxy-2-ethylhexanoate (TBPEH for short), diisononanoyl peroxide (INP for short) and tert-butyl hydroperoxide (TBHP for short) . However, none of these peroxy fuels exhibits the W-effect which is so pronounced with TBPB. In this respect it is the specific selection of TBPB together with the relatively high content in the fuel mixture which makes the fuel mixture particularly adapted for the present application in industrial dryers, for the present application in gas turbines, or for the noise reduction in engines.

The specific advantage of the fuel mixture of TBPB and kerosene described in this instance compared to TBPB alone lies in the fact that it has a shorter period of the sine ¬ like flame pulsation with a simultaneously larger flame height. The pulse combustion can be better controlled by means of this shorter period and the relatively larger flame height. The parameters of pulse combustion can be adjusted within a wide range by the mixing ratio between TBPB and kerosene.

The natural pulsing of the above-described fuel mixtures is used in a combustion process, as a result of which the drying heat is provided in an industrial dryer. The natural pulsing of the above-described fuel mixtures can also be used in a combustion process, as a result of which a gas turbine can be operated in a particularly efficient, low- polluting manner and with low consumption. Furthermore, the natural pulsing of the above-described fuel mixtures can be used in a combustion process, as a result of which an engine can be operated in a particularly efficient, low- polluting manner and with low consumption. Furthermore, the pulsation frequency can also be affected by the geometry of the burner, in particular by the diameter of its outlet opening. The pulse combustion process can thus be controlled by the mixing ratio and the burner geometry without having to provide additional means, such as baffle valves or the like.

In particular, in accordance with one embodiment the mixing ratio between TBPB and kerosene can also be changed during the combustion process. In accordance with one embodiment TBPB and kerosene can be mixed in a mixing chamber at the desired ratio. In accordance with another example TBPB and/or kerosene can be added to an initial mixture of TBPB and kerosene, for example a 50:50 mixture, in order to alter the mixing ratio.

For example, dryers are known in the prior art in which a pulsating combustion process takes place. The pulsation of the combustion process is generated in this instance, for example, by a specifically equipped valve. The valve controls the fuel supply to the burner, it being possible to alter the fuel rate in an oscillating manner. The valve is connected to a computer-controlled control which comprises a complex logic unit. In other known industrial dryers 'baffle valves' and/or 'explosion chambers' are provided in order to ensure pulse combustion.

If the fuel mixtures described in the present instance, which exhibit a natural pulsation behaviour, are used instead, the advantages of pulsating combustion processes can be obtained without having to provide additional means, such as baffle valves, explosion chambers or complex injection devices. This not only reduces the costs, but also allows relatively compact constructions of the industrial dryers. As described at the outset, gas turbines for example are known in which a pulsating combustion process takes place. In this case the pulsation of the combustion process is generated, for example, by a specifically equipped valve - the flow pulse generator. The valve controls the fuel supply to the burner, it being possible to control the fuel rate in an oscillating manner. The valve is connected to a computer-controlled control which comprises a complex logic unit .

If the fuel mixtures described in the present instance, which exhibit a natural pulsation behaviour, are used instead, the advantages of pulsating combustion processes can be obtained without having to provide additional means, such as complex injection devices. This not only reduces the costs, but also allows relatively compact constructions of the gas turbines.

A schematic view of a fuel feed line or injection line 400 of a gas turbine in accordance with an embodiment of the present invention is shown in Fig. 5. In this case the injection line 400 comprises a fuel reservoir 410 which contains the fuel. The fuel is then fed via a fuel feed pump 420 to a distributor 430. The distributor 430 then divides the fuel flow over two branches, in which the fuel flow is fed into a combustion chamber (not shown) of the turbine via injectors 450, 480. In contrast to the conventional injection line 100 of a conventional turbine shown in Fig. 4, in this case the flow pulse generator is completely omitted. Instead, the pulsating combustion is provided merely by the fed fuel mixture. Furthermore, the (electric) pump power of the pump 420 can also be considerably lower than that of the pump 120 in conventional injection lines. Owing to the high mass combustion rates of the TBPB and its high content in the fuel mixture, the fuel mixture now has to be injected into the combustion chamber at a considerably lower pressure than pure kerosene for example.

In accordance with a further embodiment the injectors 450, 480 are equipped with size-ad ustable openings. The pulsation frequency f of the fuel mixture depends namely on the diameter d of the outlet opening of the injectors 450, 480 as follows:

f - d- 1/2

The pulsation frequency can accordingly be controlled or regulated by adjusting the injection opening. Additionally or alternatively, a plurality of injection openings of different size may also be provided. Frequency control could then lead the fuel mixture to the injection openings of desired size by means of a distribution valve so as to set a desired pulsation frequency. For example the injector 450 could comprise a different outlet opening diameter compared to the injector 480. The distributor 430 could then be designed in such a way that it distributes the fuel mixture, for example, only to a respective one of the two injectors .

With the aid of the fuel mixtures described in the present case a more complete combustion process and in particular a reduction of the pollutant emissions and of the tar content in the waste gases can further be achieved. In particular, the combustion efficiency can be increased on a technical scale by using the described fuel mixtures. Since the described fuel mixtures are carriers of active oxygen, which contributes to combustion, they can ensure stable combustion, even without or with reduced external oxygen supply .

In addition, hardly any pollutant emissions of the flame of the fuel mixture were detected during measurements. On the one hand this is due to the natural turbulence of the flames, which leads to improved mixing of the fuel and ambient air and thus to a more complete combustion process. On the other hand the flame exhibits relatively low soot formation. The pollutant emission is thus reduced by the use of TBPB as a fuel. Furthermore, the TBPB acts as an effective combustion accelerator owing to the active oxygen present in the molecule. The content of pollutants and soot in the combustion products can thus be largely reduced.

The use of the described fuel mixtures with natural pulsation behaviour is advantageous, in particular, in industrial dryers. In these processes the described fuel mixtures not only provide the described natural pulsation of combustion, but simultaneously act as effective combustion accelerators owing to the active oxygen present in the TBPB molecule. The content of pollutants and tar in the combustion products can thus be largely reduced with simultaneous simplified operation of the dryer, since additional means for generating the pulsation are not necessary. This also reduces the costs of corresponding dryers. Furthermore, the external feed of an oxidant, for example air, oxygen or air enriched with oxygen can be reduced .

Furthermore, the pulsation frequency can also be affected by the geometry of the pulse ducts, in particular by their diameter. The pulse combustion can thus be controlled by the mixing ratio and the duct geometry without having to provide an active control, such as the mechatronic control known from US 2007/0028593, or the like. As has already been mentioned, this is of particular advantage for the use of the described fuel mixtures in a combustion process, as a result of which an engine can be operated in a particularly efficient, low-polluting manner and with low consumption . As described at the outset, engines are known in which a pulsating combustion process takes place in pulse ducts. In this case the pulsation of the combustion process is generated, for example, by the specifically equipped regulator 55 as a flow pulse generator. The regulator is connected to a computer-controlled control unit 68 which comprises a complex logic unit.

If the fuel mixtures described in the present case, which exhibit a natural pulsation behaviour, are used instead, the advantages of pulsating combustion processes can be obtained without having to provide additional active control means, such as the complex regulator 55. This not only reduces the costs, but also allows relatively compact constructions of the engines. A schematic view of an engine 450 according to an embodiment of the present invention is shown in Fig. 7. In this instance a combustion chamber 480 is also connected to an ejector 464 via pulse ducts 454, 456, 458, 460, the pulse ducts 454, 456, 458, 460 each ending in an associated chamber 422 of the ejector 464. By contrast to US 2007/0028593 however, the pulse ducts 454, 456, 458, 460 each have a different diameter Dl, D2, D3, D4.

Since the pulsation frequency f of the fuel mixture depends on the diameter of a pulse duct, for example the diameter d of the above-mentioned outlet opening as follows:

- d- 1 ' 2

r

the pulsation frequency in the individual pulse ducts 454, 456, 458, 460 can be adjusted by the selection of the duct geometry. These are selected in such a way that there is no positive superposition, but instead preferably a destructive superposition of the individual pressure waves from the different pulse ducts 454, 456, 458, 460. In particular, the duct geometries are selected in such a way that the pressure waves of different pulse ducts are out of phase. The noise-reduction effect described in US 2007/0028593 can thus be achieved by a passive component with the use of the fuel mixture described.

With the aid of the fuel mixtures described in the present case a more complete combustion process and in particular a reduction of the pollutant emissions and of the tar content in the waste gases can further be achieved. In particular, the combustion efficiency can be increased on a technical scale by using the described fuel mixtures. Since the described fuel mixtures are carriers of active oxygen, which contributes to combustion, they can ensure stable combustion, even without or with reduced external oxygen supply .

In addition, hardly any pollutant emissions of the flame of the fuel mixture were detected during measurements. On the one hand this is due to the natural turbulence of the flames, which leads to improved mixing of the fuel and ambient air and thus to a more complete combustion process. On the other hand the flame exhibits relatively low soot formation. The pollutant emission is thus reduced by the use of TBPB as a fuel. Furthermore, the TBPB acts as an effective combustion accelerator owing to the active oxygen present in the molecule. The content of pollutants and soot in the combustion products can thus be largely reduced.

The use of the described fuel mixtures with natural pulsation behaviour is advantageous, in particular, in engines for noise reduction. In these processes the described fuel mixtures not only provide the described natural pulsation of combustion, but simultaneously act as effective combustion accelerators owing to the active oxygen present in the TBPB molecule. The content of pollutants and tar in the combustion products can thus be largely reduced with simultaneous simplified operation of the engine, since an additional active control for phase control of the different pressure waves is not necessary. This also reduces the costs of corresponding engines. Furthermore, the external feed of an oxidant, for example air, oxygen or air enriched with oxygen can be reduced.

In particular, in accordance with one embodiment the mixing ratio between TBPB and kerosene can also be changed during the combustion process. In accordance with one embodiment TBPB and kerosene can be mixed in a mixing chamber at the respective desired ratio. In accordance with another embodiment a mixture of 60 % by wt . TBPB and 40 % by wt . kerosene can be provided. In accordance with a further example TBPB and/or kerosene can be added to an initial mixture of TBPB and kerosene, for example a 50:50 mixture, in order to alter the mixing ratio.

The present invention has been described with reference to embodiments. These embodiments should in no way be considered to limit the present invention.