DE2912102A1 - Stoichiometrically operated oil burner - has air blown into chamber to create cyclone for drawing fuel oil through needle valve into chamber - Google Patents

Abstract

Liq. fuel (31) and air (40) for combustion are fed in a constant ratio into a mixing and vaporisation chamber (43) in which the air forms a cyclone creating suction which draws fuel (31) into a chamber via the axis of the cyclone. The burner power is pref. controlled exclusively by the metering of air into a chamber, esp. to create a reduction in pressure of -0.04 to -0.1 bar at the fuel inlet in chamber (43). Fuel is pref. fed into chamber as a steam 0.5-0.2 mm dia. The air is pref. fed at 40-250 m/second into the chamber at 90 deg. to the fuel stream. The burner can have a chamber with 3-20, esp. 12, inlet holes or slots for air on its periphery.

Description

Improved Pumpless Burner

The invention relates to a burner arrangement in which a liquid fuel and combustion air are brought together in a mixed and atomization chamber (MZK), which is enclosed by a preferably cylindrical jacket is that has one or more openings through which the air of the MZK such can be supplied that a cyclone with a centrally located negative pressure area within the MZK is formed, and the one arranged in the negative pressure, the end wall the MZK has penetrating inlet opening for the fuel, according to patent (patent application P 28 28 319.4).

In the parent application a burner is described which does not have an atomizing nozzle for the fuel owns.

Nebulization and gassing take place with extensive smashing of the Fuel particles held in a limited volume. The burner of the parent application uses a combustion process, according to which the air is guided so that it forms a cyclone within the MZK, with the fuel in the area of the Axis of the cyclone initiated, preferably sucked in.

"Cyclone" is understood here to mean an air movement that is circular is, due to the centrifugal forces a slight compression of air to the edge of the Mixing chamber takes place. Because of this air flow, there is a negative pressure inside the cyclone, which is used to suck in the fuel. The burner therefore basically does not require a fuel pump. It is only necessary that the fuel is introduced in the area of the axis of the cyclone, because here the Experience has shown that negative pressure has reached its maximum value.

The imported fuel is caused by the turbulence within the Air movement immediately torn and divided into the finest particles and appropriate Burned soot-free.

The burner has an arrangement for carrying out the process mentioned an inlet opening for the fuel, which is enclosed by a jacket Mixing and atomizing chamber is arranged downstream. The opening or openings for The supply of combustion air is incorporated into the jacket of the MZK and allows it an air duct in which, as already mentioned, there is a cyclone within the MZK trains. In detail, reference is made to the (not previously published) documents the Referred to parent registration, in which further details of the operation and structure the burner arrangement are explained in accordance with the parent application.

The burner arrangement mentioned is suitable because of its data and Properties primarily to be used for household burners that only have a low fuel oil consumption. For example, for single family homes So-called miniature burners are required that consume oil in the order of magnitude Have 1 - 3 kg of oil per hour. With a corresponding reduction in the size of the nozzle and Adaptation of the remaining dimensions is a burner according to the principle of the parent application build that works.

It turns out, however, that the mixture of atomized oil and combustion air is relatively difficult to ignite in the range of the stoichiometric ratio. Only when the mixture is enriched with an increased proportion of oil, is an ignition of the Mixture by a spark plug, in which there is a spark between two electrodes trains, possible. The difficulty of igniting so-called blue burners, which in the Operate with a stoichiometric ratio of fuel and air, are solved in known burners that by a flap control with the help of a servomotor, the air supply is initially throttled so that a "richer" fuel-air mixture can brush past the ignition device (DE-OS 2 700 671 However, the burner system is becoming more expensive, operations more complicated and In particular, re-ignition after an unsuccessful start attempt is more difficult, if a burner is provided with such an arrangement for the regulation of the starting air is. Another disadvantage is that if the attempt to start is unsuccessful, if this is not due to a lack of fuel, including a large amount of soot and cracked products are released, which heavily foul the combustion chamber can.

It therefore arises for a burner arrangement of the type mentioned at the beginning Kind of the task of reliably initiating ignition, starting with the fuel-air mixture should be practically stoichiometric without the need for complicated additional equipment are.

Unsuccessful attempts to start when oil is present should practically be ruled out as this creates a considerable risk of soiling.

This object is achieved in that in the area of MZK a heatable incandescent body in the flow of the unburned fuel-air mixture lies.

Surprisingly, it has been shown that known electrode spark plugs, also those with lyre electrodes, obviously because of too short ignition times, because of low energy transfer or because the local ignition area is too small a fuel-poor mixture cannot ignite or can ignite only very unreliably.

If, on the other hand, an incandescent body is used, which is preferably a wire helix or ignition spiral, the mixture can sweep past such a body, the combustion reaction starts immediately when fuel is mixed with the air will. Misfires are practically ignored at all. Apparently Incandescent bodies are particularly suitable as igniters, since they are on a relatively small Area transfer a large amount of heat to the fuel-air mixture locally can, so that the combustion is reliably initiated.

The burner is switched on in several steps: a) The air supply is switched on and the combustion chamber is pre-purged. Then will the incandescent body is heated while the air supply remains switched on. The fuel supply is still interrupted.

b) After a heating-up time, during which the cooling rate of the incandescent body through the air is taken into account, a fuel valve is opened and the fuel mixed into the air - in the final ratio. It immediately comes to Ignition when the surface temperature of the mantle is abundant at this time is above the ignition temperature, i.e. has reached about 8000C. The initiation of the ignition process is a very complex process. Obviously must Local energy transfer continuously over a longer period of time to the fuel-air mixture act so that the burning reaction is initiated. oil droplets appearing on hit the surface of the incandescent body, evaporate there and result in the area of the hot surface a particularly ignitable mixture.

c) As soon as the ignition has taken place, an ignition monitor For example, an ionization sensor that displays the burning status and the ignition current switched off.

The incandescent body cools down.

In the burner construction of the parent application, the MZK designed so that they have the same cross-section from the beginning to The end is. One end face is bounded by the end wall, in which there is also the or the inlet openings for the fuel jet are located. It turned out to be Proven to be advantageous, the glow coil or the glow wire in the form of an arc segment with an opening angle between 30 and 33; 00 at a short distance from the opening to attach the MZK. The opening of the MZK is partially framed by the Incandescent body.

Furthermore, it has proven advantageous to use the incandescent body or the ignition spiral at a distance between 5 and 30 mm from the front of the combustion chamber to be arranged remotely.

If the MZK is lying horizontally, it is advantageous to remove the incandescent body or to attach the glow coil below the opening of the MZK, so that any dripping or larger droplets of oil falling downwards fall directly onto the spiral and there can also evaporate in addition to the atomization effect.

The incandescent body is generally mounted so that it is turbulent from the The mixed jet emerging from the MZK is penetrated as intensively as possible without fully to lie in the core or in the axis of this ray. Advantageous it is to be attached adjacent to the opening edge of the MZK, since it is known that tear-off vortices form at the edge. If the edge is rounded, so due to of the Coanda effect, the path of the flow is carried out of the axial direction, so this flow formation is also easy to attach the incandescent body adapt. With such an edge rounding, a flame cone forms with a opening angle between 90 and 1800. It is suggested that the incandescent body in this case nestles against the end wall or is fitted in a groove.

The incandescent body or the ignition spiral is usually located in between MZK and flame front lying, relatively cool area of those in operation Burner arrangement. This once ensures that before the start of the combustion the mixture emerging from the MZK works well with the incandescent body located at the opening comes into contact. After initiating the ignition process and switching off the heating current the incandescent body is then practically outside the flame front and is only moderate heated so that it has a long life.

The incandescent body is preferably made of ceramic or a low-scaling one Alloy, so that it can hardly or not at all scale. The shape of the mantle can be very different. It should be quick to warm up and emit heat well Own surface. Ceramic, conical incandescent bodies with internal Heating coil, electrically heated strips or coils or even platelets are used will. Strangely enough, even a relatively small area is sufficient if they Maintained continuously at a temperature of approx. 8000 C during the ignition process can be.

The heating can of course also be carried out by induction or HF heating or related procedures happen.

Embodiments of the invention are shown in the figures. The figures show: FIG. 1 a burner arrangement according to the invention; Figure 2 shows a detail the burner arrangement according to Figure 1; Figure 3 is a sectional view along line III ... III of Figure 2.

In the figure 1 is an embodiment of a burner arrangement shown. The fuel, usually EL fuel oil with a viscosity of about 5 cSt 200 C, a line 32 is from a storage container 31 liver to the actual burner fed. A float regulator 33 is installed between the storage container and the burner, that for a constant pressure between burner fuel inlet and level of the float regulator 33 ensures.

This is for the proportionality between negative pressure and quantity Fuel taken care of in the unit of time. The line 32 ends in a bore 34, which is connected to a further closable bore 30.

The closure bore 30 can with the help of a controllable valve needle 60 can be opened and closed. The further details of the locking mechanism are shown in detail in the parent application and are not required here to be discussed in more detail.

The liquid fuel emerges from the inlet opening 30 into a Mixing and atomizing chamber 43 surrounded by a cylindrical jacket is, in the axial direction one behind the other two rings of air inlet holes 44, 44 'ends. The mixing chamber is preferably designed so that it has the same cross-section from the nozzle to the mouth. These holes are from the outlet opening the bore 30 preferably measured about 5 and 8 mm away from a projection of the center of the bores 44, 44 onto the axis of the chamber 43.

It is essential that the bores 44, 44 'are so that the air at least one of the rings entering the mixing chamber at an angle of 10 - 600 is guided in deviation from the normal direction. The air becomes accordingly tangentially on the periphery of an imaginary circle within the mixing chamber 43 blown. The air reaches the nozzles 44, 44 'via an annular duct space 36, which is arranged around the axis of the mixing and atomizing chamber 43 and is charged with air via an air line 37 via a fan 40. One End wall 51 forms the conclusion of a conventional boiler, which with the usual Exchanger tubes (not shown) and side walls 52 is equipped. Because of good atomization, mixing and gasification and subsequent combustion it can be dispensed with in the burner under almost stoichiometric conditions and to install a brick lining in the boiler.

Furthermore, it is preferably provided that on the inside around the Mouth of the MZK 43 around a burner jacket 63 is arranged, the has a much larger diameter than the diameter of the MZK and whose opening surrounds concentrically. The burner jacket 63 can, for example, be cylindrical be shaped or formed like a truncated cone opening or tapering. Other Shapes are also possible.

The strong vortex movement (cyclone) that occurs inside the mixing chamber caused by the injection of the combustion and atomization air, sets accordingly continues in the direction of the burner jacket 63 and ensures the establishment of a stable, concentrated flame.

The jet of fuel does not emerge from the outlet opening 30 in droplet form, i.e. H. sprayed out, but initially in a compact jet with z. B. 1 mm diameter. With such an arrangement, the oil consumption is around 1 - 4 kg bl per hour, it may be possible to reduce the full load to 25%. By Narrowing the bore diameter and reducing the usual dimensions However, a burner can be operated economically with only about 1 kg bl per hour is working. Due to the turbulence and centrifugal forces that exist inside the cyclone act, the jet will be inside and outside the mixing chamber fully detected, divided into fine droplets and then in the area inside and outside of the burner jacket burned. This is a soot-free, essentially blue one Flame burning in progress observed.

An ignition spiral 70 is used to ignite and initiate the combustion provided, which is made of a 1 mm thick wire from a heat-resistant, low-scaling wire Chromium-nickel alloy is made. The glow wire of the ignition coil is arranged in such a way that that it emanates from the jet of the unburned mixture flowing out as it flows out the chamber 43 is penetrated and this at an intrinsic temperature of about 700 - 9000 C ignited. The ignition spiral 70 is via electrical leads 71 the Energy supplied for the annealing process. Preferably the filament is in the form of a Helix or screw wound; however, other configurations are also conceivable, for example a zigzag bend or a flat glow strip. It turned out surprisingly shown that the use of the filament allows you to start with a to drive a very lean, practically stoichiometric fuel-air mixture. It it is therefore not necessary to first adjust the air content via a movable flap to make it lower and then to increase it again after the ignition has taken place.

After the ignition process has ended, the ignition spiral 70 is switched off again. It is arranged so that it is in the area between the opening plane 73 and the flame front is, so in a relatively cool range, which makes their service life considerable is increased.

The distance from the edge of the MZK is approximately between 5 and 40 mm. The distance from the opening plane 73 or

End wall 51 is approximately between 5 and 30 mm.

FIG. 2 shows a burner arrangement that is somewhat different from that of FIG seen from above. An ionization sensor 74 is used to monitor the ignition process provided, with which it is continuously monitored whether a combustion occurs within of the burner jacket takes place or not.

FIG. 3 shows a view into the sectioned burner jacket 63. The ignition spiral 70 is in this case with the axis of the mixing and atomization chamber lying horizontally arranged so that it is mounted below the opening of the chamber 43 and in Shape of an arc segment only a relatively short distance from the opening of the chamber 43 has. At this point is to point out that the detonator or the ignition spiral can also take a different position, since it is not at all it is necessary to arrange the incandescent body below the MZK. The spiral is fulfilled the requirement that the eddies emerging from the chamber 43 should be as large as possible Space occupied by the spiral 70 prevail and thus the ignition initiate safely and reliably.

The edge 75 of the MZK is rounded outwards so that due to the Coanda effect, the path of the flow is partially pulled out of the axial direction will. This can create a very strongly expanded cone of flame, the opening angle of which is between 90 and 1800. With this design, the Incandescent bodies, in particular an ignition coil, nestle against the end wall 51 or be fitted into a groove.

Claims (11)

Claims: 1. Burner arrangement in which a liquid fuel and combustion air are brought together in a mixing and atomizing chamber (MZK), which is enclosed by a preferably cylindrical jacket, the one or has several openings through which air can be fed to the MZK in such a way that a cyclone with a central vacuum area is formed within the MZK is and the one arranged in the negative pressure area, the end wall of the MZK has penetrating inlet opening for the fuel, according to patent (patent application P 28 28 319.4), characterized in that in the area of the MZK (43) a heatable Incandescent body (70) lies in the flow of the unburned fuel-air mixture. 2. Burner arrangement according to claim 1, characterized in that the Incandescent body consists of a ceramic mass or -zusa a tinder-unyssum alloy. 3. Burner arrangement according to claim 2, characterized in that the Incandescent body consists of an electrically stimulable filament. 4. Burner arrangement according to claim 3, characterized in that the Glow wire is coiled into an ignition coil (70). 5. Burner arrangement according to claim 1, characterized in that the Incandescent body has the shape of a ribbon. 6. Burner arrangement according to claim 1, characterized in that the Incandescent body has the shape of a cylinder or cone. 7. Burner arrangement according to claim 1 or 4 or 5, characterized in that that the incandescent body or the ignition spiral in the form of an arc segment with an opening angle between 30 and 3300 at a short distance from the opening of the MZK (43). 8. Burner arrangement according to claim 7, characterized in that the Incandescent body or the ignition coil at a distance of between 5 and 30 mm from the end face (51) is arranged remotely from the combustion chamber. 9. Burner arrangement according to claim 7, characterized in that with the MZK lying horizontally, the glow wire or the ignition coil below the opening the MZK is attached. 10. Burner arrangement according to claim 1, characterized in that the incandescent body in the relatively cool area between the MZK and the flame front is arranged. 11. Burner arrangement according to claim 1 or 10, characterized in that that the edge of the MZK is rounded and therefore a flame cone with a opening angle between 90 ... 1800 results, and that the incandescent body is attached to the front wall hugs or is fitted in a groove.