The present invention relates to a fuel and the use of this fuel, in particular the use in refuse incineration.

Combustion is one of the most important chemical processes which people use. In the course of time, different fuels have therefore been found or developed for the various applications of combustion processes and have been optimized in their properties for the specific applications.

One of the main uses of combustion processes is heat generation, whether for industrial use, electricity generation or heating purposes. A further important field of use of combustion processes is mobility, since at present the vast majority of all vehicles are driven with the aid of internal combustion engines. In addition, combustion processes are also used for thermal utilization of wastes or for rendering poisonous substances harmless by means of incineration.

Common to all combustion processes is that the resulting emissions, in particular NO _x , CO and tar, pose health and environmental threats. It is therefore desirable to provide fuels or combustion processes in which such emissions are reduced.

In view of the above statements, the present invention proposes a fuel according to Claims 1, 7 and 13 and uses of the fuel according to Claims 18, 19 and 20. Further advantageous configurations, details, aspects and features of the present invention are evident from the subclaims, the description and the attached drawing. In the latter:

Fig. 1 shows the variation of the relative flame length of a tert-butyl peroxybenzoate pool flame as a function of time.

According to a first working example, a fuel is provided which comprises a compound having the empirical formula C _n H _n+3 O _n - _S , n > 9. According to a further development of the invention, the compound may have the empirical formula CnHi ₄ O ₃ ; in particular, the compound may be tert-butyl peroxybenzoate (TBPB) .

According to another working example, a fuel is provided which comprises an organic peroxide. According to a further development of the invention, the organic peroxide may be a peroxy ester, in particular tert- butyl peroxybenzoate (TBPB) .

Organic peroxides, in particular peroxy esters and among these TBPB, are known as free radical initiators for the polymerization of various monomers. However, a use of this class of substance as fuel or fuel additive is not known to the applicant.

According to yet another working example, a fuel is provided which comprises a compound whose pool flame has a Froude number which is 50 times to 100 times greater than the Froude number of a pool flame of kerosene. According to a further development, the Froude number may be 70 times to 80 times greater than the Froude number of kerosene. In particular, tert- butyl peroxybenzoate has a Froude number in this range. The pool fire is understood as meaning a generally turbulent diffusion flame whose liquid fuel is horizontally propagated. For example, pool fires are a type of frequently occurring harmful fires which may arise, for example, during storage, transport and processing of liquid fuels. The Froude number characterizes the initial pulse of the flame, small Froude numbers tending to be typical for pool fires since the flow velocity results substantially from the uplift of the combustion. Overall, the chemical and physical principles of pool fires have been thoroughly investigated and will not be further stated here.

Fuels according to the working examples described above and their further developments show a surprising burning behaviour unknown to date. Thus, Fig. 1 shows the variation of the relative flame length of a pool flame of tert-butyl peroxybenzoate as a function of time. The relative flame length is obtained as the ratio H/d of the flame length H to the diameter d of the fuel pool. The flame length H is defined as the maximum visible length of the flame, i.e. in the wavelength range between 380 nm < λ < 750 ran. Typical- values for the relative flame length H/d of conventional fuels, such as, for example, liquefied natural gas (LNG) or kerosene, are in the range between 0.8 and 4. On the other hand, Fig. 1 shows that the relative flame length H/d for tert-butyl peroxybenzoate as a function of time can increase to 18. 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 to low values of H/d « 2. This variation in the relative flame length is not unusual per se and is also observed for other fuels. However, what is surprising about the fuels described here is firstly the large variation of the relative flame length in order of magnitude and secondly the regularity of this variation. Thus, the fuel shows an approximately periodic pulsation of the relative flame length which, owing to its appearance in the diagram (cf . Fig. 1) , is also designated as a "W effect". In other words, fuels of the type described show a substantially regular variation of the relative - A - flame length over time, in the case of pool flames by a factor of 4 or more. An absolute regularity in the sense of a strict chronological periodicity is not meant thereby but a similarity of the respective time intervals of larger or smaller relative flame length and similarity of the respective increase or decrease of the relative flame length between such time intervals. In this context, it should be pointed out that the frequency f of the pulsation is given by f~(Fr*)- ^1/2 ,

in which Fr _f is the Froude number of the pool flame of the fuel. Since the Froude number of the fuels described is 50 times to 100 times greater than that of kerosene, their pulsation frequency f is accordingly 7 times to 10 times lower than that of kerosene. Furthermore, the combustion rate of the fuels described here is typically 80 times to 120 times higher than that of kerosene.

The natural pulsation of the fuels described above can be utilized in combustion processes. Thus, for example, the article by B. T. Zinn et al., "Controlling mechanisms of pulsating incineration process", Propulsion engines and missiles, Combustion and Ignition, Annual Technical Report, 30 September 1995, Report number A246992, discloses that a refuse incineration process can be improved by imposing acoustic pressure oscillations. Thus, both the combustion efficiency could be improved and the pollutant emissions could be reduced by these pressure oscillations. This is due to the improved mixing of the inflowing air with the fuel. Similar results are also obtained by Stewart in "Application of Pulse Combustion to Solid and Hazardous Waste Incineration", Comb. Sc. Tech., Vol. 94, 1993. Furthermore, the article "Combustion Instability and Emission Control by Pulsating Fuel Injection", Paschreit et al . , J. Turbomachinery, Vol. 130, pages 011012-1 to 011012-8, 2008, states that the NO _x emissions can be substantially reduced by modulated fuel injection. Likewise, Martins et al . in "Experimental measurements of the NO _x and CO concentrations operating in oscillatory and non-oscillatory burning conditions", Fuel, 85, pages 84 to 93, 2006, arrive at the result that the CO and NO _x emissions can be reduced by acoustic oscillations. In these methods known to date, the pulsation of the combustion process is artificially imposed, whether by a variation of the fuel feed or by imposing pressure variations.

In contrast, the fuels described here have a natural pulsation behaviour. If the fuels described here are therefore used in combustion processes, the advantages of pulsating combustion processes can be achieved without having to provide additional means, such as, for example, pressure generators or complex injection apparatuses. This not only reduces the costs but also permits more compact designs of the combustion devices.

With the aid of the fuels described here, more complete combustion and in particular a reduction in the pollutant emissions and in the tar content can thus be achieved.

These advantages of the fuels described here can be used in particular in the area of refuse incineration and in particular in special waste or toxic waste incineration. The fuels described firstly provide the described natural pulsation of the combustion; secondly, they simultaneously serve as a powerful combustion accelerator owing to the active oxygen present in the molecule. In this way, the pollutant and tar content of the combustion products can be greatly reduced, and this can be done with a simultaneously simpler mode of operation of the plant, since additional means for generating the pulsation are not required. Moreover, this reduces the costs of corresponding plants.

According to a further working example, the fuels described here can also be used as fuels in a liquid drive or in a hybrid drive for a rocket. In the case of liquid drive units, the thrust F is in which r& is the mass flow rate, V _e is the outflow velocity, p ₀ is the external pressure, p _e is the pressure of the outflowing gas and A _e is the area of the outlet opening. Owing to the active oxygen present in the fuels, the amount of any oxidizing agent additionally required can be substantially reduced. Furthermore, the fuels described have a substantially higher burn rate than conventional fuels, such as, for example, kerosene. Thus, an enormous gain in thrust can be achieved. Owing to the pulsating combustion, however, at the same time smaller amounts of pollutants, in particular NO _x and CO, are output. Since in particular TBPB has a higher density than kerosene, use of TBPB or another fuel having a higher density makes it possible to store more burnable mass per unit volume.

The fuels which are described here and which exhibit the pulsating combustion behaviour described may also be present as a mixture with other fuels, in particular other liquid fuels. In particular, the fuels exhibiting the pulsating combustion behaviour can be provided as a fuel additive with a proportion of 0.1% by weight to 80% by weight of the total weight of the fuel. According to a further development, said fuels can be provided with a proportion of 0.1% by weight to 20% by weight of the total weight of the fuel. The exact proportion in the fuel depends on the specific use, provided that combustion of the additive can reliably take place. Thus, in some cases, a small proportion may be sufficient to initiate the desired pulsating combustion behaviour in the total system, while in other cases a high proportion is required. In particular, the fuel may consist completely of a fuel having pulsating burning behaviour.

The present invention was illustrated with reference to working examples. These working examples are by no means intended to be understood as delimiting the present invention.