Background

Conventional combustors/burners of liquid fuels (like diesel and gasoline), are normally operating with a diffusion flame, in which the liquid fuel is evaporated directly during the combustion at the flame front which encapsulates the liquid fuel (usually droplets from an injector spray), resulting in high local temperatures which in turn leads to high emissions of soot and nitrous oxides (NOx), that are formed at the interface between the fuel and flame and can result in the pollution of the environment unless expensive clean-up methods are applied to the combustor.

In US-2012/064465A1, US-3,886,728, US-5,209,187 and US-5,015,174 there disclosed combustion apparatuses or burners according to the state of the art at the time of filing the priority application. All of these devices comprise injection zones/injection chambers for creating swirling air. However, none of them exhibits a combination of these features with further devices for enhancing the mixing of air and fuel, and for reducing the risk of hot spots occurring.

Summary of the invention

Thus, in view of the shortcomings of the prior art in preventing hotspots and in order to provide apparatus with enhanced mixing the inventors have devised a novel apparatus which is defined in claim 1.

In the method and apparatus according to the invention, a solution for complete

evaporation and mixing of the liquid fuel with air is provided, which results in a clean homogeneous combustion of the fuel at lower temperatures and conditions that result in lower emissions and complete combustion of the fuel, including elimination of carbon monoxide through the perfect mixing of air and fuel during the combustion process.

Thereby, an essentially tube shaped combustion apparatus for providing a homogeneous combustion of liquid fuels, comprises a combustion chamber 1 having a plurality of reaction zones A, B, C, one of which is an injection mixing and evaporation zone A, the other being homogeneous combustion zones for staged homogeneous combustion of evaporated fuel and air. There is also a swirler 2, comprising a swirler base 4a and swirler elements 4b, 4c for mixing fuel and air configured to operate at a swirl number between 0.6-2.5 in combination with a flow constriction plate 3 where the size of the constriction is such that the ratio of the open diameter de of the constriction to the diameter d of the tube shaped combustion apparatus 1 is <0.7 and the constrictor plate 3 is placed at a distance LI from the base of the swirler base 4a so that Ll/D _e > 1. A primary mixing plate 7 is placed downstream from the constriction plate 3 at a distance L2 from the constriction plate 3 so that the ratio L2/L1<1 to allow for maximum mixing of the homogeneous combustion process.

Preferably the combustion apparatus uses fuel in the form of any of diesel and gasoline.

In preferred embodiments the combustion apparatus comprises a secondary mixing plate, to reduce the total length of the reactor through increased homogenization and/or with a catalyst to operate the process under partial or complete catalytic conditions.

Suitably, the combustion apparatus is configured such that in operation the fuel pressure is at an elevated pressure of 3-20 bars to optimize the evaporation in the injection zone.

The constrictor plate 3 is preferably provided with a convex cone 9, to improve the recirculation of the combustion products into the injection zone A.

In another aspect there is provided a method of combustion, injecting liquid fuel into a first reaction zone A of a combustion chamber 1, by means of a high pressure nozzle 10 that operates in the region of 3-20 bars of over pressure, mixing the fuel with air that is continuously introduced axially to the combustion chamber 1 by a swirler 2 that produces a swirl strength in the range of 0.6-2.5; igniting the produced fuel/air mixture during start-up of the combustor with a ignition device that initially produces a conventional diffusion flame; forcing the combustion mixture diffusion flame after initial swirl mixing through a radial constriction 3 in the combustion chamber 1.

Brief Description of the Drawing Figures The invention will be described with reference to the attached drawings, in which Figure 1 schematically illustrates an apparatus; Figure 2a shows a radial swirler type; Figure 2b shows an axial swirler type; and Figure 3 shows an alternative constriction plate. Description of the invention

In one embodiment the combustion reactor 1, shown in Figure 1, comprises a plurality, suitably three reaction zones A, B and C, in which A is the injection zone where mixing and evaporation takes place, where the fuel is injected into the combustion chamber, mixed with air while undergoing gas phase evaporation. Zone A is separated from zone B by a flow constriction plate 3 designed for recirculation of hot combustion products into the injection zone A. Zone B and C are homogeneous combustion zones separated by a mixing device 7 for staged homogeneous combustion of evaporated fuel and air.

The constrictor plate 3 is suitably provided with a convex cone 9, to improve the

recirculation of the combustion products into the injection zone A. In operation, the liquid fuel is injected into zone A of the combustion chamber 1, by means of a high pressure nozzle 10 that operates in the region of 3-20 bars of over pressure where the fuel is mixed with air that is continuously introduced axially to the combustion chamber 1 by a swirler 2, which may be of the radial or axial type, as shown in Figs. 2a and 2b, that produces a swirl strength in the range of 0.6-2.5. Thereby, a swirler 2, comprises a swirler base 4a, and swirler elements 4b, 4c.

In the radial type the swirler elements 4b are provided as "blades" protruding inwards in the combustion chamber at an angle and disposed along a circle concentric with the periphery of the swirler base 4a. In the axial type the swirler elements 4c are provided as "blades" which are located within an inlet portion before entry into the combustion chamber." The produced fuel/air mixture is during start-up of the combustor ignited with a

conventional ignition device such as, but not limited to, a glow plug or spark plug that initially produces a conventional diffusion flame. The combustion mixture diffusion flame is after initial swirl mixing forced through a radial constriction 3 where the ratio of the open diameter of the radial constriction D _e to the tube diameter D is less than 0.7 D _e /D<0.7 and the distance LI between the base 4a of the swirler 2 and the constriction plate 3, is such so that ratio of the distance LI and the constriction open diameter D _e is greater than 1 Ll/de>l.

The radial swirler 2' shown in Fig. 2a comprises a swirler bas plate member 4a with baffle like elements 2a arranged concentrically around a nozzle 6' at a location between the nozzle and the periphery P of the swirler 2. These baffles 2a are made by punching or cutting out portions in the swirler plate 4a corresponding to circular segments, leaving one portion of the segments attached or integral with the plate 2. This creates foldable "flaps" that can be bent upwards such they project at an angle from the plane of the swirler base plate 4a.

Fig. 2b shows an axial swirler 2"having a base plate 4a and deflecting elements 2b arranged concentrically around a nozzle 6". There are numerous possible configurations of means for redirecting the air flow and apart from the one described one could envisage making the apertures themselves such that the bore forms an angle.

By introducing the constriction 3 described above, a negative flow zone is created at the center 5 of the combustion reactor 1 between zone A and B which enables the recirculation of hot combustion products to the fuel injection zone, providing a means for evaporating the fuel in the resulting hot gas mixture. By evaporating the fuel directly the residence time of the fuel in the reactor zone A is decreased and the as a result the combustion is "lifted" from directly above the nozzle 6 to the constriction plate 3 where a now completely pre-mixed gas phase combustion takes place, as the fuel is completely evaporated in the hot gas phase that is created from the recirculation of the hot combustion gases to the injection zone of the reactor zone A.

Additionally a primary mixing plate 7 is placed at a distance L2 from the constriction plate 3 to further increase the mixing of the combustion products and to reduce the risks of hotspot formation. The mixing plate 7 is placed at the distance L2 from the constriction plate 3 so that L2/L1 < 1.

In some cases a secondary mixing plate 8 can be added to the combustor 1 in order to reduce the total length L4 of the combustor 1, by further increasing the total mixing of the homogeneous combustion process. Mixing plate 8 can also be replaced by a catalyst to convert the combustor to a catalytic combustor for an optimal emission combustor.