US 2906094 A
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FUEL AND RAPID :[GNITION APPARATUS FOR IGNITION 0F FUEL IN RAM JETS AND ROCKETS Filed April 14, 1954 INVENTORS G'Zezznflfiamon Q go/121155600 ch FUEL AND RAPID IGNITION APPARATUS FGR IGNITION F FUEL IN RAM JETS AND ROCKETS Glenn H. Damon, Pittsburgh, and John Ribovich, McKeesport, Pa.
Application April 14, 1954, Serial No. 423,262
3 Claims. (Cl. 6039.47)
(Granted under Title 35, US. Code (1952), see. 265) This invention relates to ram jets of the solid fuel type with particular application to fuel igniters.
In solid fuel ram jets, as well as in kindred apparatus where a rapid forced heat supply is required, it is important that the time of ignition be reduced as far as possible. Heretofore, the use of a gas flame applied to the fuel bed has been prevalent but ignition by gas flame is relatively slow and requires, in the case of ram jets, that the ram air be by-passed during the ignition period. This slow ignition is disadvantageous not only in delaying heat supply but also in softening or destroying the fuel binders before full ignition and thus destroying the required geometric shapes of the fuel briquets. Also, there is a tendency to undermine the fuel effectiveness by destructive distillation of the volatile fuel components.
It is accordingly an outstanding object of the invention to provide a fuel igniter which operates positively and with high rapidity to ignite the fuel. An object, also, is to provide a fuel ignitor composition which may be readily composed and applied to a base element. Still another object is to provide an igniter which, while primarily suitable for ram jet solid fuel ignition is readily applied to gas, liquid or solid ignition in furnaces, rockets and turbojets and similar apparatus.
The invention meeting the above objects may best be understood by consideration of a specific form thereof as hereinafter described, reference being made also to the accompanying drawings in which:
Fig. l is a longitudinal view, partly in association with fuel units of'a combustion tube;
Fig. 2 is an enlarged view of the igniter in perspective showing to the tube arrangement;
Fig. 3 is a view of the igniter at the ignition end thereof; and
Fig. 4 'is a view of a modified construction of igniter apparatus.
The combustion unit of Fig. l includesthe combustion tube 11 and blower 12, the latter including the fan 13 rotatably supported in the terminal casing 14 and the driving motor 9. Three fuel briquets 15, 16 and 17 are shown in the tube 11 in series relation, each briquet being in the shape of a cylindrical drum or block with four axially parallel ducts 18 therein. In assembly, the ducts 18 of the briquets are in alignment so that the heated burning gases and materials may be carried freely therethrough to the combustion tube exit. These briquets may be of any known fuel composition, for example, powdered Bell coal with an asphalt binder (12 /2 Upstream, adjoining the briquets, is the igniter 2b. This unit consists of a cylindrical mass of castable cement in which are formed four axially parallel ducts 21, 22, 23 and 24 as in the briquets. The diameter of the igniter is the same as that of the briquets so as to permit end to end placement in tube 11. In addition to the four briquet aligning ducts the igniter has a smaller axial duct 25 for the initiator lead 26, and grooves formed at both.
Patented Sept. 29, 1959 ire ends 27 and 28 of the igniter 20. These grooves include diagonal grooves 30 and 31 between alternate ducts, as
2123 and 22-24 and grooves 32, 33, 34 and 35 be' tween adjoining ducts. In a typical installation, the igniter frame has a six inch diameter, is three inches long and the four ducts have a one and one-half inch diameter and are equally spaced on a three and one-quarter inch circle. The diameter of the briquets and the briquet ducts correspond to those of the igniter.
The grooves as mentioned, as well as the end connecting tubes 21, 22, 23 and 24 of the igniter, are coated with ignition material. This material consists of a composition having a starter component and a thermite component 35%. The starter consists of Percent Silicon (Si) 26 Potassium nitrate (KNO 35 Carbon (C) 4 the silicon and carbon being 66% in excess stoichiometrically. Carbon may be in the form of ordinary charcoal or coal.
The thermite consists of Percent Aluminum (Al) 18 Copper sulphate (CuSO 17 the aluminum being 57% in excess stoichiometrically. Anhydrous copper sulphate is used.
These materials are formed into a dry mix and then combined in a mixing operation with an 8% solution of nitrocellulose in acetone, with or without plasticizer, such as dibutylphtlialate, to form a slurry. This slurry is varied, preferably, for application to the grooves on the one hand and the duct Walls on the other hand. In the latter case the slurry is formed in the proportion of 24 grams of dry mix and 8 grams of binder solution for each duct; and in the former case, 19 grams of dry mix and 6 /3 grams of binder solution.
After slurry application the igniter is conditioned by drying in an oven at a temperature of about 55 C. until the igniter is free of the odor of acetone. An ignition initiating device is now applied to the end of the igniter in the form of a flat spiral coil 4% of No. 20 Nichrome resistance wire, one lead 26 of the coil, as previously indicated passing through the axial igniter duct 25 and the other lead 41 passing through one of the ducts 21 to 24. The spiral coil 40 overlies the cross grooves 30, 31 and on application to the combustion chamber is downstream of the igniter.
In placing the igniter into operation, an air stream flow of about cubic feet per minute (c. f.rn.) is passed through the igniter and aligned fuel briquets while at the same time electric power from any suitable source is applied to initiator leads 26 and 41. The ignition coat adjacent the initiator is immediately ignited and this ignition travels instantaneously along the connecting grooves and ducts to the opposite or upstream side of the igniter producing molten particles which are forced at once through the aligned ducts of the fuel briquets, igniting the same. The ignition action is completed in less than 20 to 30 seconds; the air flow can then be raised to the amount desired, as, for example, 400 c.f.m., within one minute of initiation of the igniter action. A typical time temperature log follows:
Time: Temperature at briquets /2 minute 1450 F.
1 minute 2150 F.
1 /2 minute 2380 F.
It is pointed out that there is no diversion or cessation of ram air in the ignition procedure, and because of the high speed of ignition (from 25 to St) times faster i 3 than that of ordinary gas ignition) there is no appreciable change in the physical or chemical characteristics of the fuel or fuel binder. Also, it is apparent that by controlling air flow, the burning'rate of the igniter'can be controlled to produce any desired ignition period. Thus, accommodation may be made for variation in fuel composition. It is observed further that the singular air flow serves the dual function not only of supplying excess oxidants for the igniter composition but also of furnishing oxidation for fuel consumption.
It is noteworthy that the heat transfer from the ignitor to the fuel is not alone by heated gases but primarily by bodily movement of molten particles each particle being a focal point of high heat supply.
Obviously, the igniter unit may be varied not only in structural features but also in composition proportions and components. For example, while the mentioned ratio of starter to the thermite portions gives a satisfactory balance between burning rate and heat release the ratio may be varied within limits where a difiierent burning rate is desired, the 50% ratio giving the fastest burning rates. It has bene ascertained that the total heat release varies with the proportion of thermite used. Further, the proportions of substances in either the starter or the thermite portions may be varied while preferably, keeping the starter-thermite ratio constant. For example, increasing the percentage of aluminum while decreasing the copper sulphate will increase the burning rate to an optimum point followed by a rate reduction, although the heat release will continue to increase due to the supply of ram air. Also, in the starter portion all or part of the silicon may be replaced by other substances such as magnesium, aluminum, boron, the hydrides of lithium, titanium, zirconium and other similar hydrides and metallic alloys. In the thermite, also, all or part of the aluminum may be replaced by other reductants such as magnesium, boron, the hydrides of titanium, lithium, and zirconium and other similar hydrides and metallic alloys. Although copper sulphate gives the best results in the thermite composition other sulphates or oxidants such as potassium nitrate (KNO sodium nitrate (NaNo ammonium perchlorate (NH ClO or potassium perchlorate (KClO may be effectively used in this material.
Tests have indicated that a fine state of subdivision of the component composition substances results in a more complete reaction and greater heat release. However, the degree of subdivision of potassium nitrate is a controlling factor in the burning rate, the rate increasing with a decrease in particle size. Thus, an additional positive control of the burning rate is supplied by the degree of subdivision of the oxidant.
While the ignition is generated by a heater coil, as disclosed, other heat means may be used, such as gas flame, black powder, black powder squibs, electric arc sparks and spontaneous chemical reactions, such as that of glycerin on powdered potassium permanganate (KMnO structurally, the igniter may be varied by form, as increasing or decreasing the number of ducts, or by position as placement external to the combustion tube.
While the described form of the combustion unit has desirable uses, the arrangement of Fig. 4 has been found more advantageous in many respects, particularly as to time of ignition, the time being reduced by the modified structure from around 20 or 30 seconds to a small fraction of a second. In Fig. 4, the casing 50 is tapered at 51 to form the exit nozzle and converged at 52 to form the inlet nozzle, as indicative of ram jet use. A diffuser 53 having a forward converging cone shape 54 and a rearward converging cone shape frustum 55 is positioned rigidly in the inlet 52, as shown, to produce initial air velocity increase followed by decreased velocity with increased compression.
At the downstream end of the diffuser section 55, a recess is formed in which is embedded the igniter 56. This 4 igniter consists of the various starter and thermite substances as described hereinabove in connection with the apparatus of Fig. l, and is provided with an initiator 57, which may take the form of an electric squib with power connecting wires 58.
Displaced down stream from the igniter are hollow fuel briquets 60 and 61, the outer diameter thereof approximating the inner diameter of the combustion shell 50, which retains them in position. While powdered coal and a binder may serve as briquet fuel, it is preferred, in this construction, to use a composition including a percentage of oxidants, so as to promote rapid ignition.
In making the briquet, the various substances are mixed thoroughly in appropriate equipment and then pressed as a powder into briquet form. The resulting briquet density ranges from 1.4 to 1.9 grm./cc., depending on the particular composition and molding pressure used. After an appropriate curing procedure, which depends on the type of binder used, the briquets are ready for use.
In operation, the desired number of briquets are placed end to end in the combustion chamber, as shown in Fig. 4. Air is then passed through the chamber and, when the desired air flow is ready, the igniter 56 is initiated by the squib 57. The hot, molten particles emitted by the igniter are carried downstream to the fuel charge by the moving air stream where they ignite the fuel surface. The fuel burns radially, the rate depending upon the burning surface area of the charge, the inherent burning rate of the fuel mixture and the pressure prevailing in the chamber. Since the quantity of oxidant is ade quate only for promotion of rapid ignition and propagation of the burning front, the oxygen of the air completes the fuel oxidation.
The utility of the described apparatus and ignition means of both modifications appears from the following considerations:
1) No complex mechanism, involving moving parts, are necessary to bring about fuel ignition.
(2) With solid fuels, the heat content per unit volume is higher than for either gas or liquid fuels, thus permitting, for example, a ram jet construction about sixteen percent shorter and nineteen percent lighter than a liquid powered ram delivering equivalent thrust.
(3) With effective solid fuel, the problem of fuel handling and storage particularly in jet use, becomes simplified.
(4) Tests indicate smooth operation of jet engines using solid fuel at high or low altitudes.
(5) Use of slag forming compositions insures fuel ignition either under quiescent conditions or under conditions of high velocity air flow.
(6) Slag fuel compositions insure positive ignition of gaseous, liquid or solid fuels.
It is apparent that modifications of the construction other than hereinabove specified, may be made. For example, the igniter, instead of being in hollowed form (Fig. 1) or solid mass form (Fig. 4), may take the form of a fluent slurry. Also, the igniter position in relation to its support may be other than at the ends thereof. The fuel beds are shown downstream from the igniters as may be desirable for ram jet use, but for other uses other locations may be desirable.
Modifications other than as above mentioned, may be made and it is to be understood that within the scope of the appended claims the invention may be practiced otherwise than as described.
The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
1. A combustion unit comprising an enclosing tubular casing having inlet and outlet end openings, a fuel mass having opp sed end Walls, a side wall conforming to the casing interior, and at least one duct passing through the mass from end to end, and an igniter for said fuel mass, said igniter comprising a support block having end walls, a side wall conforming to the enclosing casing, at least one duct extending therethrough from end to end joining the surfaces on said ends, a surface groove on each of said igniter block ends communicating with said igniter duct, a coating of heat producing materials on the walls of said grooves and igniter duct, and an igniting device for initiating ignition of said coating, the igniter being upstream of said fuel mass, and said igniter and fuel mass ducts being series connected whereby on ignition of said igniter coating and application of air pressure to the fuel tube inlet, heat for combustion is transmitted to said fuel mass.
2. A reaction motor comprising an enclosing tubular casing having inlet and outlet ends, means for applying air under pressure to the inlet end of said casing to establish air flow therethrough, a fuel mass having passage means therein for the passage of air therethrough and located in said casing, an igniter in said casing forming When ignited a source of molten particles upstream of said fuel mass and subject to said air flow, and means for igniting said igniter whereby after ignition of said igniter said particles may be transmitted by the air flow into igniting relationship throughout said fuel mass.
3. A reaction motor comprising an enclosing tubular casing having inlet and outlet ends, means for supplying air under pressure to the inlet end of said casing to establish air flow therethrough, a fuel mass in said casing having end to end ducts therein to permit air flow there through, a supporting element upstream from said fuel mass, an exothermic composition coating said supporting element, said composition when ignited becoming a source of molten particles, and means for igniting said composition, whereby said molten particles are transferred by air flow to the exposed surfaces of said fuel mass ducts.
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