STARTING METHOD AND DEVICE FOR COMBUSTION APPARATUS

Abstract: A pulsating air pump (24) is used to start an apparatus for combustion of fuel and air with the aid of a spark or corresponding ignition means, said pump delivering a starting air stream with periodically varying volume per time unit for mixing with the fuel for igniting with the spark. During starting there is thus achieved a periodically varying mixing ratio between certain limits which embrace the ignitable mixing ratio for the occasion.

Description: STARTING METHOD AND DEVICE FOR COMBUSTION APPARATUS The present invention relates to a starting arrange¬ ment for a combustion apparatus, and is of the kind dis- closed in the preamble to the accompanying main claim. The invention primarily has the object of providing a starting arrangement facilitating starting combustion apparatuses operating with pulsating combustion, but the invention can also to advantage be.applied to apparatuses operating with continuous combustion. For a combustion apparatus to start as reliably as possibly, both when the apparatus is cold as when it is hot, involves in itself certain problems. Furthermore, problems are engendered when starting with varying air temp'eratures and air humidity. And last but not least there can be problems on starting if one fuel with certain properties is changed to another fuel with other properties. In all cases- however, it is a question of providing the correct mixture ratio between air ' and fuel which it to prevail at the • ignition electrode and its spark in order to obtain ignition, The starting phase is especially sensitive with regard to correct mixing ratio. Once the apparatus has started and become warm, this sensitivity declines. To facilitate starting it is usual to vary the amount of fuel per second as well as the amount of air per second supplied until the apparatus starts. This way of starting usually requires manual control and some skill, however. On the other hand, if it is a question of an apparatus which is to be used for heating purposes, for example, the apparatus must be able to be started both quickly and reliably at short or longer intervals without the aid of manual service. Against the background of the above-mentioned problems, the invention has the object of providing a starting arrangement enabling start under different conditions involving ignition to take place under certain conditions at a certain mixture ratio, while in other cases ignition only can take place at another mixture ratio. This problem is solved by a starting arrangement having the characterizing features in accordance with the invention disclosed in the following patent claims. Fuel is usually supplied with the aid of a fuel pump delivering a predetermined quantity of fuel per time unit during starting. The invention is however not limited to fuel pumps giving a constant delivery. The flow of fuel passes through the area around the ignition electrode, and combustion air is supplied to this area also. Alternatively, the air and fuel can be mixed before this area, or the mixture can take place in this area. In accordance with the invention, a periodically varying mixture ratio is now provided in this area by the starting combustion air being fed by means of an air pump supplying a pulsating air stream, i.e. a varying air volume per time unit. Such an air pump can comprise a diaphragm pump or a membrane pump of a construction known per se, which is driven by an electro¬ magnet. The number of pump strokes per second can* thereby be controlled in a simple way by regulating the frequency of the stream to the magnet coil. In practice, it has been found sufficient to be able to vary the number of pump strokes in the area of 0.1 to 1.0 strokes per second for setting the right frequency for a given fuel. During starting, a pulsating stream of starting air is thus used, which is suitably supplied via a separate channel or conduit for directing to the area about the starting electrode. In this case, with the use of a separate channel, the combustion air will be supplied during normal operation via another channel, in which air is sucked in in the normal way as soon as the apparatus has started. In certain cases it is also possible, however, to supply the pulsating starting air in the same channel as is used for an air channel during normal operation. The pulsating starting air stream thus results in that the mixing ratio in the area at the starting electrode will vary periodically between predetermined limits, which include the pertinent ignitable mixture ratios for one and the same fuel, or for different fuels. The ignition spark, " or the corresponding hot igniting means, will thus meet a fuel-air mixture which has an ignitable mixture ratio at some time during the impulse. Practical trials of the invention have shown that the starting time has been able to be shortened considerably with the aid of the starting arrangement in accordance with the invention, simultaneously as possible starting difficulties due to fuel having different properties have been reduced considerably, or entirely eliminated. The trials have been performed with an apparatus for pulsating combustion. These and other details and advantages distinguishing the invention will be explained in detail in the following description of a starting arrangement in accordance with the invention, selected as an example, used in conjunction with an apparatus for pulsating combustion. Fig. 1 is a schematic, axial section through an apparatus for pulsating combustion, and with a starting air channel for connecting to the starting arrangement in accordance with the invention, and Fig. 2 is a schematic, axial section through a diaphragm pump used in the starting arrangement in accordance with the invention and connected to the apparatus in Fig. 1. An inlet 11 is connected to the combustion chamber 10, there being a central body 12 arranged in the inlet 11. At one end of the body 12 there is a fuel nozzle 13 connected to a fuel pump (not shown) for delivering fuel into a funnel-shaped tube 14 which guides the fuel stream into the combustion chamber 10. The nozzle 13 is conventionally substantially he i- spherical. At one side of the nozzle there is arranged an ignition electrode 15 the tip of which is at the side of the fuel jet from the nozzle during normal operation. For normal -operation, air is sucked in through an inlet 16, inlet openings 17, past a non-return valve 18 and down into a gap 19 round the body 12 and further down on the outside of the tube 14 and into the combustion chamber 10. During normal operation, the mixture of air and fuel thus takes place first in the area at the intake opening the combustion chamber. In the illustrated example there is a separate air channel 21 made in the body 12 for starting. As is apparent from Fig. 1, the channel 21 opens out into the vicinity of the nozzle 13, whereby an air stream in the channel 21 will flow out and partially be diverted round the nozzle 13 in a direction towards the area of the ignition electrode 15 spark. The air stream will thus be mixed with the fuel stream to provide a given mixture ratio in the area at the spark. The conical portion 14a of the tube 14 situated round the nozzle also contributes to this control of the air stream. A conduit 22 is connected to the channel 21, this conduit in turn being connected to an outlet 23 of the pulsating pump 24 illustrated in Fig. 2. The pump 24 in the shown example is a diaphragm pump but can to advantage be replaced by a diaphragm piston pump. The pump 24 is arranged for providing a pulsating air stream An electromagnetic coil 25 is used for intermittently driving the pump, this coil having a movable armature 26. The latter in turn is attached to a rod 27 connected to a plate 28 attached to a rubber bellows 29 defining an air space 30 which is compressible. When the rod 27 is pressed down with the aid of the electromagnet, the air space 30 wil be compressed while air is blown out through the outlet 23 and further down into the channel 21 to the area about the ignition electrode 15. The outlet 23 has a non-return valve 23a. When the force on the rod 27 ceases, the bellows 29 wil spring back into the initial position, thereby sucking in ai through an inlet 31 which is provided with a non-return valv 31a. The coil is connected via a timer 32 to the mains supply. The desired frequency can be set with the aid of thi timer to obtain the desired number of pump strokes per second. In practice it has been found sufficient to be able to regulate within the area 0.1 to 1.0 pump strokes per second. With the aid of this pulsating pump, which is only coupled in during the starting period, a periodically varying volume of starting air per time unit can thus be supplied to the area of the starting electrode 15 spark simultaneously as a certain amount of fuel is mixed into this starting air stream. The mixing ratio will thus vary periodically between certain limits, which embrace the ignitable mixing ratio for the occasion. When the spark occurs simultaneously with this mixture ratio, ignition and starting occur. The pump 24 is then disconnected and normal operation begun.

Claims: CLAIMS 1. A method of starting a combustion apparatus, including a combustion chamber with an intake connected to means for supplying air and fuel, an ignition electrode or corresponding ignition means being connectible during the starting period to generate an ignition spark or a correspoding heavy local temperature increase for igniting fuel when the supplied combustion air and the supplied fuel 0 have a mixing ratio at the ignition electrode enabling ignition, characterized in that the arrangements for supplying combustion air solely during the starting period are operated in a way such that the mixing ratio for fuel and air varies during the starting period between upper and 5 lower values for a range including the different mixing ratios which are ignitable during the different operating conditions which can occur. 2. An arrangement for starting a combustion apparatus with the method disclosed in claim 1, characterized by a 0 means (24) for supplying a periodically varying air quan¬ tity per time unit, said means being adapted for being coupled in solely until the apparatus starts. 3. An arrangement as claimed in claim 2, there being a central body (12) arranged in the intake (11) for carrying 5 the fuel nozzle (13) and electrode (15) at its inner end, the air supply during operation taking place in an air passage (19) on the outside of the central body, character¬ ized by an extra air channel (21) made in the central body (12) and having one end opening out in the area round the Q nozzle (13) and its other end connected to the means (24) which is only coupled in during the starting period to suppl a periodically varying quantity of starting air.

Inventors: OLSSON K
Applicants: MARECK BV, OLSSON K
Application year: 1980
Main classification: F23D11
IPC codes: F23D11, F23Q3