Patent GB-729919-A (GB)
Title: Improvements in or relating to method and apparatus for suppressing detonation or the effects of detonation of fuel and air mixtures
IPC: F02B23/08
Filed: 1951-10-10
Abstract: 729,919. Suppressing detonation; combustion chambers ; sparking plugs ; valves. BODINE, A. G. Oct. 10, 1951, No. 23573/51. Classes 7(2), 7(4) and 7(6). [Also in Groups XII and XXVI] Harmful sound waves accompanying detonation in a gas-filled combustion chamber are acoustically attenuated with the object of suppressing detonation or the effects of detonation. As shown in Fig. 9, a watercooled engine comprises a piston 14 reciprocable in a cylinder 15, and the walls of the combustion chamber 21 and the head of the piston are provided with a number of straight, cylindrical cavities 22 functioning as pipe resonators. The edges of the openings of the cavities 22 may be chamtered or radiused, and the diameter of the cavities preferably does not exceed one-half the depth of the cavities. In Fig. 10, Helmholtz resonator cavities 22a open to the combustion chamber are used, and in Fig. 20 (not shown) such resonators are closed by thin, flexible plates acting as vibratory membranes and serving to prevent the deposition of carbon within the cavities. In Fig. 11 (not shown) the cavities have inner end portions laterally offset from the entrances of the cavities, such portions being shielded from the heat of combustion and less liable to accumulate carbon deposits. The cavities in the head of the piston may be replaced by (a) Fig. 13 (not shown), pipe resonators in the form of U-shaped tubes cast vertically in the head of the piston, (b), a pipe resonator comprising a tube 30, Fig. 15, located in a horizontal plane and extendng around threequarters of the periphery of the piston 29, the two ends of the tube opening through the top of the piston and being spaced at an angle of 90 degrees from one another, (c), Helmholtz resonators 33, (Fig. 17), of different sizes, each comprising a cylindrical body 34 rounded at the base and fitted into and spaced from the wall of a socket 32 in the head of the piston 31, the body being provided with a stem 34b riveted at 34c to secure the resonator in position, and a top wall 34d furnished with a downwardly extending tubular stem 34e, (d), Fig. 18 (not shown), resonators each comprising a bore in the head of the piston and communicating with the top surface of the piston by a bore of smaller diameter, and (e), resonators comprising a cylindrical chamber 37c, Fig. 19, annularly spaced from a bore 36a in the head of the piston 36 and a base portion 37a received and secured in a counterbore 36b, the walls of the chamber 37c being provided with ports 37e and kept free from carbon deposits by the scouring action of a loose steel ball 38. In the embodiment shown in Fig. 21, acoustic attenuators 51, 65 are screwed into ports 49, 50 in a hemispherical combustion chamber 41, the attenuator 51 comprising a plug 55 of porous material, e.g. fibre-glass confined between screens, sintered, powdered metal, ceramic or graphite granular compositions, accommodated in a tubular housing 52 closed by a plug 58, the space between the plugs and the body forming a resonator cavity 59 and preferably containing an inverted ceramic cup 60. The attenuator 65 is provided with a wall 80 of porous material and a spring-loaded valve 74 to prevent the accumulation of carbon in the resonator cavity 81, the valve being opened during the intake stroke of the engine to allow a small quantity of air to be drawn through a felt filter 85 and into the cavity 81 thereby to oxidize and remove carbonaceous matter that strays into the cavity. Also, a pad 67 of porous material is mounted on the head of the piston 42 and, if required, used in combination with resonator cavities 68. In alternative forms of attenuator, (a) Fig. 22 (not shown), a plug of porous material is disposed in a tubular housing but a resonator cavity is not provided for, (b) a perforated conical wall 101, Fig. 23, fitted inside a tubular body 100, is provided with a screwed neck 104 for mounting the device in the combustion chamber 41, Fig. 21, the space between the wall and the body being packed with fibre glass, tungsten, copper or silica fibres, and a screen 109 surrounds the wall 101 to confine the fibrous material and prevent loss thereof through the perforations 102 in the wall, (c), Fig. 24 (not shown), a plug of porous material is supported and extends downwardly within a tubular body having a screw-threaded stem for mounting the device in a port 49 or 50, Fig. 21, there being a clearance between the plug and the inner surface of the body, and a nose cap mounted on the lower end of the plug to define a resonator cavity, (d), a cylindrical body 122, Fig. 25, of porous material enclosed in a metal shell 125 has a cavity screw-threaded to receive a sparking plug 124 and an externally screw-threaded stem 121, which may be solid, for mounting the device in a cylinder head 41, Fig. 21, and preferably an external circumferential groove 126 providing a resonator cavity. In a further embodiment, a combustion chamber 137, Fig. 26, in the form of an " exponential " horn is provided, the lower part of the horn being formed by the wall 140 of a cylinder head 131 and the upper portion of the horn comprising a passageway 166 in an extension 141 screwed into the head 131 and air cooled by means of fins 172. The mouth of the horn is coextensive with the cylinder 133 of the engine, and the throat of the horn which is contained in the extension 141 is reduced at a plane 170 to a relatively small diameter, e.g. one millimetre, and communicates with a sound wave attenuator element comprising a straight uniform diameter bore 171. Alternatively, Fig. 27 (not shown), the bore 171 is increased in diameter and packed with sound attenuative material, such as fibre glass or tungsten wool, held in place by a screen and a cross-pin. The top of the piston 132 is formed with a hump 175 which is received in the mouth of the horn and may be of a porous material. The inlet valve 135 is provided with a horn-shaped passage 180 extending through the stem 144 of the valve and joining at a plane 182 with a fine uniform bore 183, e.g. one millimetre in diameter, and the exhaust valve 136 has a horn-shaped passage packed with a body 186 of fibre glass or tungsten wool held in place by a screen 187 and a cross-pin 188. In modified forms of attenuator devices for mounting in the cylinder head of an engine, (a), a sparking plug 215, Fig. 28, is screwed into a socket 214 at the lower end of a bore 212 formed in a body 204 screwed into a housing 200 provided with external cooling fins 201, the insulator portion of the plug being tightly received in an aperture 216 in the body, and the electrode of the plug being spaced from an earthed rod 218 projecting from the side of the housing 200; the body 204 has an external longitudinal curvature to form with the interior surface of the housing a longitudinal annular passage 205 the cross-section of which decreases in an upward direction to form a flared horn, (b), Fig. 29 (not shown), a housing encloses a horn-shaped chamber the throat of which continues to a bore of small diameter, e.g. one millimetre, terminating in an orifice open to atmosphere, the mouth of the chamber being larger in diameter than the opening through a screw-threaded neck portion of the housing, and (c), Fig. 30 (not shown) a horn-shaped passage opening through a screw-threaded neck portion of a housing has a throat portion terminating in a chamber. In a still further embodiment, the highest portion of the combustion chamber 258, Fig. 31, of an engine is located directly over the periphery of a piston 252 and is extended upwardly into an attenuator 260 comprising a body part 261 arcuate-shaped in cross-section and having a horn-shaped passage 270 braced by webs and connected to a coiled attenuator tube 272. Horn-type attenuators may be provided in a piston as shown in Fig. 35 wherein the head 281 of the piston 280 is formed with a number of horn-shaped passages 283, 284 and 285 angularly spaced at 45 degrees and at different levels, the mouths and throats of the passsages opening into the bevelled face 282 of the head 281. In modifications, (a), Fig. 37 (not shown) three angularly spaced and vertically disposed horn-type attenuators are formed in the wall structure of a piston, a fourth attenuator being located at the centre of the piston, (b), a bore 300, Fig. 39, in the body 301 of a piston receives a plug 302 formed with a horn-shaped chamber 303, the throat of the chamber opening at 304 through the inner end of the plug to a groove 305 communicating with a spiral groove 306 around the plug, and (c), Fig. 40, the upper portion 316 of a piston 315 is shaped to form with a cylinder wall 315a a horn-type passage which communicates at a plane 318 with a number of peripheral grooves 321. The Specification describes a method of determining the pressure wave patterns due to detonation and set up in the combustion chamber of an engine.