US1888694A - of detroit - Google Patents

Description

Nov. 22, 1932. M. A. POWERS ELECTRIC IGNITION FOR FLUID FUEL BURIE RS Filed May 29, 9

Patented Nov. 22, 1932 UNITED STATES PATENT oFFlca MILTON A. POWERS, OF DETROIT, MICHIGAN, ASSIGNOB TO THE TIMIEN SILENT AUTOMATIC COMPANY, E DETROIT, MICHIGAN, A CORPORATION OF MICHIGAN ELECTRIC IGNITION FOB FLUID FUEL BUBNEBS Application filed Kay 29, 1980.

My invention relates to the electric ignition of fluid fuel burners and is particularly adapted for use in connection with oil burners of "the type in which combustion takes place around the periphery of a rather large hearth ring. Heretofore gas pilot lights and the like have been the common means for lighting such burners; but there are numerset forth in my co-pending application Serial No. 369,863 filed June 10, 1929, of which the present application is in part a continuation.

The principal objects of the present improve.-

ment are to increase the heat of the ignition spark, thus improving the characteristics and size of the flaming are described in the" original application for the purpose of increasing its ability in igniting the fuel and to minimize radio interference. Other objects and advantages will appear hereinafter.

It is very evident that the simplest and best ignition system would be a jump spark properly located if it could be made to function. Such a system is cheap to make and install, requires no special control and is very reliable electrically and may be as universal in its application as the burner itself. Many attempts have been made to utilize a spark gap for ignition at the refractory ring and the results have been most discouraging. The spark between the electrodes is ext ded by the velocity of the air, and while a v ry hot spark may be used the heat is not conserved but is dissipated into the air stream. The

oil spray passes between or near the electrode and while at times it may be momentarily ignited the high velocity prevents flame propagation and failure results.

The invention consists principally in providing an electric current of high amperage (say in excess of twenty-five milliamperes) and of sufficient voltage to adequately jump the spark gap or gaps (say ten thousand volts in the "case of a single spark gap and fourteen thousand volts in the case of a double spark gap). The invention further con- Serial No. 456,940.

sists in the electric ignition f r liquid fuel burners and in themethod an in theparts and combinations and arrangements of parts hereinafter described and claimed. j

In the accompanying drawing wherein like numerals refer to like parts wherever they r occur, 7

Fig. 1 is apart elevational, part sectional view of a liquid fuel burner provided with an electric ignition system embodying my invention,:

Fig. 2 is awirin diagram, and I Fig. 3 is adetail sectional view of a portion of the hearth ring.

The drawing illustrates the invention embodied in an oil burner comprising a refractory hearth I mounted in a boiler 2 and provided with a refractory ring 3 around its out er periphery, ignition and combustion tak-- ing place around said ring. Said ring is preferabl made in accordance with the disclosure 0 said co-pending application Serial No. 369,863 filed June 10, 1929 and is provided at diametrically spaced points with a pair of ignitin devices of the construction set forth in sai application. Each igniting device includes an electrode 4 that is embedpreferably provided with amounting piece 5 of carborundum or other refractory material whose edge is shaped to conform to the shape of said ring. The other electrode 6 of each system is of heat resistant metal mounted in a suitable insulator? The burner mechanism includes any suitable motor 8 provided with a vertical rotary shaft at the top of which is an air fan 9 and suitable mechanism (not shown in the drawing) for spraying liquid fuel to the periphery ofthe hearth 1.

A transformer 10 (which in the case of a two gap system should have approximately fourteen thousand volts potential) is provided with a. secondary or hlgh tension lead wire 11 that extends to one of the metal electrodes '6. The other electrode 4 of that igniter gap of the transformer secondary. The tran.:

ded in the face of the hearth ring 3 and is former secondary is thus connected in series with the two igniter gaps.

The conventional electric ignition spark system has heretofore been installed on types of burners where the oil is initially prepared for easy ignition by atomization or by vapor] zation with the help of an independent heating means. Under such conditions the spark v need be only of suflicient strength to initiate combustion, the fuel being condition to rapidly propagate the flame without outside aid.

' On the type of burner using my ignition systerm the wet oil is depositedas-aliquid around the hearth ring 3 and combustion is extreme-- I supply a current of at least twenty-five milliamperes, which results in a flaming are instead of an intermittent spark. Ordinarily a power input in excess of seventy-five wat s is required to produce this amperage. The a:-

' rangement described produces (instead of the usual intermittent spark) a flaming arc of considerable size and of great heat intensity.

Thus the liquid or fluid-fuel is quickly vaporized and ignited, while the use of two igniting devices gratly facilitates the propagation of the flame around the entire periphs ery of the hearth ring.

In the event that only a single igniting device is used, the voltage can be reduced considerably, say to about ten thousand volts, the

I only requirement being that the voltage be suflicient to jump the gap between the two electrodes. In order, however, to retain the desired heating effect, the high amperage must be maintained. High amperage being the important consideration, the voltage is maintained only high enough to insure reliable operation across the igniting gap or gaps.

I have found that the radio interference of the usual electric ignition system is largely due to the high strain set up in the ignitionv circuit. This strain depends upon the breakdown voltage at the spark gap and due to the fact that the spark is intermittent, such strain is maintained throughout the entire operation of the ignition system, with the conventional low capacity transformer. The hot flame of the present system requires a high capacity transformer, with the result that the flaming are results in tremendous reduction of the strain in the high voltage c1rcu1t. The passing of the spark across the 'ing arc.

gap heats the air in the vicinity of the spark,

so that subsequent sparks pass with very little effort, resulting in a great lowering of the voltage and minimizing radio interference. To illustrate, a circuit which only requires two thousand volts for proper operation will cause less interference than a circuit requiring ten thousand volts to operate the gap. With the conventional low amperage transformer in the circuit and partlcularly if there is must of a blast of airacross the gap, the required potential for a given gap will be a certain amount, say ten thousand volts. This voltage will have to be attained twice each cycle before the gap breaks down resulting in a crackling blue spark and marked radio interference. With my system a high amperage secondary current is utilized and the gap preferably, although not necessarily, located at a point protected from high air currents. The operation then proceeds as follows: The maximum strain necessary to break down the gap is produced by the transformer.

However, whenthe current does pass across the gap the heating effect is so marked and the relative amount of currnt so great that the resistance of the gap is very greatly reduced during subsequent passage of the flam- I have repeatedly demonstrated this action as follows: A gap is arranged to require a one-half inch spark in operation.

While the are for this gap is being produced by my high capacityv transformer a second adjustable gap is connected in parallel wlth the first and the opening between the electrodes slowly reduced. It is possible to reduce this second gap to almost onesixteenth inch before the current passing the one-half inch gap finds it easier to transfer to the smaller gap. It is evident, from the above experiment, that the initial breakdown of an air ga by a flame-like arc discharge w1ll result 1n a subsequent much reduced breakdown voltage durmg the continuation of the are. This fact allows a greatly lessened mar imum potential in the high voltage circult resulting in the reduction of radio interference to a minimum. With the conventional low capacity transformer the above test will result in an immediate transfer of the spark to the second ap as soon as its length is less than that o the operating gap thus demonstrating that there is very little if any reduction in gap resistance after the spark is initiated.

In order to take the maximum advantage '1. The face of the ring 22 in which one of the electrodes is located is spaced away from said vertical ledge. Thus the current of air from the fan passes along close to'the hearth surface and striking the upstanding ledge 21 is deflected upwardly towards the top of the ring where combustion takes place and, for the most part passes over the space where the electrodes are located. Other suitable means could be provided for protecting the spark or are from air currents. The above described system has the important advantage of minimizingradio interference and of producing an intensely hot arc that quickly and certainly ignites the fuel. Obviously the invention is not limited to the details of construction shown but is characterized by the system which produces said very hot spark or flaming arc.

What I claim is: 1. The improvement in the process of fluid fuel burner ignition which consists in maintaining an electric current of at least ten thousand'volts and in excess of twenty-five milliamperes.

2. The improvement in the process of fluid fuel ignition which consists in maintaining a jump spark electric current of at least ten thousand volts and in excess of twenty-five I milliamperes.

3. The improvement in the process of fluid I fuel ignition which consists in maintaining a jump spark electric current of at least ten thousand volts and in excess of twenty-five milliamperes and protecting the spark from movement of gas.

4. An electric ignition system for fluid I fuel burners comprising a pair of spaced electrodes and means-for supplying said electrodes with a current of at least ten thousand volts and in excess of twenty-five milliamperes.

5. An electric ignition system for fluid fuel burners comprising a'pair of spaced electrodes and means for supplying said electrodes'with a current of at least ten thousand volts and in excess of twenty-five.milliam-' peres, said electrodes being protected against excess movement of gas.

6. An electric ignition system for fluid fuel burners comprising two pairs of spaced electrodes wired in series and means for supplying said electrodes with a current of about fourteen thousand volts and in excess of twent -five milliamperes.

7. 11 electric ignition system for fluid I fuel burners comprising two pairs of spaced May 1930.

MILTON A. PowE s.

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