Combustion chamber of pulse combustion apparatus

Abstract: The curved peripheral wall (3) of the combustion chamber includes a flat inner face (6) perpendicularly intersected by a bore (4) which receives a spark plug (P). Heat transmitted to the plug (P) is uniformly dissipated by the surrounding wall portion.

Description: This invention relates to pulse combustion apparatus in which pulsating explosive combustions occur repeatedly and continuously. EP-A-0 180 417, for instance, describes pulse combustion apparatus which includes an ignition plug (spark plug) and which performs repeatedly explosive combustions in a certain cycle by making use of self-ignition and natural suction of air for combustion at the time of regular combustion, at which combustion heat is used to be applied for cooking devices etc. US-A-5 044 928 discloses pulse combustion apparatus in accordance with the pre-characterising part of claim 1. A further development of such pulse combustion apparatus is shown in Fig. 2 of the accompanying drawings. A combustion chamber R in which explosive combustions are performed is defined by a wall W having a curved face of snail's or cylindrical shape etc. with a fundamental curvature owing to the characterization of pulse combustion and so on. As an ignition device, necessary at the start of combustion, an ignition plug P is set and inserted into the curved wall W spirally by a screw part P1. Also, TP in Fig 2 denotes a tail pipe for the discharge of combustion exhaust. As the temperature inside the combustion chamber R of such pulse combustion apparatus becomes, however, very high, the top (L-shape part shown by the broken line) of the ground electrode P2 on the ignition plug P often becomes burnt away or damaged as shown in Fig. 1. Also asthe central electrode P3 expands due to high temperature and oxidization, the surrounding insulator P4 may happen to break up to cut wire inside. An object of the present invention is to provide an apparatus in which the above problem may be resolved to extend life span of the ignition plug by more efficient transfer of heat from the ignition plug to the outside through the combustion chamber. Accordingly the present invention provides pulse combustion apparatus comprising a combustion chamber defined by a peripheral wall having a curved inner surface, the wall having a bore for accommodating a spark plug for initiating pulsating explosive combustions in the combustion chamber, the combustion chamber having an inlet which is substantially tangential to the curved surface so that, in use of the apparatus, a stream of combustible mixture flows from the inlet in a curved path along the inner surface of the peripheral wall towards the spark plug, characterised in that the peripheral wall includes a substantially flat inner face through which the said bore opens into the combustion chamber, the axis of the bore being substantially perpendicular to the said face, and said face being formed by an inwardly increased thickness of the peripheral wall, the upstream edge of the said face being smoothly merged with the curved surface. In the combustion chamber of the pulse combustion apparatus according to the above structure of this invention, heat from the plug heated up during combustion is well dissipated by equal transmission through its wall, because the inner face where the ignition plug is set and inserted into is a substntially flat face which is substantially perpendicular to the axis of the plug. In the prior apparatus, an ignition plug is set and inserted generally slantwise to the wall face and furthermore due to the curved face the contact area between the ignition plug and the receiving wall is not constant around its plug. That is, as shown at letter A in Fig. 2, the plug has to have partially an exposed part to the combustion chamber. Compared to this, in the combustion chamber of this invention constant contact with the receiving wall is achieved because the inner face of the same wall is formed approximately perpendicular to the axis of the ignition plug. As a result, transfer of heat from the ignition plug to the combustion chamber wall occurs well without partial deviation. In order to clarify further the structure and function of this invention in the above, the combustion chamber of the pulse combustion of this invention is explained as below by way of a suitable practical example. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a sectional elevational view of a combustion chamber of the pulse combustion apparatus as a practical example of this invention ; Fig.2 is a sectional elevational view of a prior art apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Fig.1 is a schematic cross-sectional diagram of a combustion chamber used in a pulse combustion apparatus as a practical example. The combustion chamber 1 receives an air/fuel mixture drawn in from a mixing chamber (not shown in Fig. 1) and at a certain cycle explosive combustions are continuously repeated, and the shape is formed like a snail shell with a cavity almost circular in cross section. The entrance 2 of the combustion chamber which is connected with the mixing chamber (not shown in Fig. 1), is formed tangentially to the combustion chamber 1 in order to take in mixture well and also to prevent backfiring. In the wall 3 defining this combustion chamber 1, a screw bore 4 for installing an ignition plug ( hereinafter called plug fitting hole 4) is set and into this bore the plug P is fitted and inserted by screwing. Also the inner wall face where the plug fitting hole 4 is made is formed as a flat one perpendicular to the inserting direction of the plug P. In other words, with respect to the continuous curved face 5 forming a snail's shape, the inner wall face where the ignition plug is set is formed to become perpendicular to the axis of the ignition plug by increasing wall thickness. This part of inner wall face is hereinafter called inner plane 6. Furthermore in Fig. 1 for easy understanding, hatching is done respectively on the wall forming inner plane 6 around the plug fitting hole 4 and on the wall forming the curved face 5. However, they are one body. Also number 7 in Fig.l indicates a tail pipe to discharge the combustion products. Such a pipe 7 is provided in both side faces of combustion chamber 1. The ignition plug P in whose top are set a central electrode P3 and a ground electrode P2 bent in the form of an L and in whose central side face is set a cylindrical screw part P1, is fitted and inserted by screwing the said screw part P1 into the plug fitting hole 4. Consequently, a ring-form face P1a of the edge of screw part P1 becomes parallel to the inner plane 6, and besides in this practical example the inserting position is set so that both of these faces are approximately in one plane. Also, not shown in Figure 1, a flame rod for flame detection is set next to the ignition plug and inserted perpendicularly on the wall forming the above-said inner plane 6. In the combustion chamber 1 constructed as above, after the ignition by the ignition plug P, explosive combutions are repeated in a certain cycle and the internal temperature becomes very high. However, for the reasons mentioned below, the life span of a ground electrode P2 and a central electrode P3 of the ignition plug can be extended. That is, as heat from the ground electrode P2 and central electrode P3, whose temperature have become high by the effect of pulse combustion, is transmitted via the screw part P1 uniformly to the wall 3 of combustion chamber 1, the heat dissipation effect can be increased without deviation. In the prior device as shown in Fig. 2, effective heat dissipation can not be achieved because a part of the screw part P1 is exposed in the combustion chamber R (shown as part A in the Fig. 2), by the fact that the ignition plug P is inserted and set in the curved wall W. Furthermore, in this example, the inclined set up of the ignition plug also affects such partial exposure. If the exposure of screw part P1 is prevented by setting the ignition plug drawn outwards from the combustion chamber R, the position of both electrodes P2 and P3 will become far from the center of the chamber R, resulting in decrease of the ignition efficiency. Compared to this, in the combustion chamber 1 of the said practical example, the heat dissipation effect of the screw part P1 can be obtained at its maximum, for the face of the inner wall part where the ignition plug P is fixed by insertion is formed as a perpendicular one to the axis of the said plug. Consequently, breakages of ground electrode P2, wire of central electrode P3, or others due to combustion heat can be reduced so that the life span of the ignition plug P is extended. Temperature which reaches 900°C at the plug top of prior art can be reduced to 840°C, further to 700°C by effect of the increasing wall thickness to make the flat face 6 continuous from the fundamental curve 5 of the pulse combustion chamber, i.e. smoothly merged therewith.

Claims: Pulse combustion apparatus comprising a combustion chamber defined by a peripheral wall (3) having a curved inner surface (5), the wall (3) having a bore (4) for accommodating a spark plug (P) for initiating pulsating explosive combustions in the combustion chamber, the combustion chamber having an inlet (2) which is substantially tangential to the curved surface (5) so that, in use of the apparatus, a stream of combustible mixture flows from the inlet (5) in a curved path along the inner surface (5) of the peripheral wall (3) towards the spark plug (P), characterised in that the peripheral wall (3) includes a substantially flat inner face (6) through which the said bore (4) opens into the combustion chamber, the axis of the bore (4) being substantially perpendicular to the said face (6), and said face being formed by an inwardly increased thickness of the peripheral wall (3), the upstream edge of the said face (6) being smoothly merged with the curved surface (5). Apparatus as claimed in claim 1, in which the wall portion having the said face (6) is integral with the wall portion having the curved surface (5). Apparatus as claimed in claim 1 or 2, in which the inlet (2) and the said bore (4) are arranged side-by-side and substantially parallel to each other. Apparatus as claimed in any preceding claim, including a spark plug (P) accommodated in the said bore (4), the spark plug (P) having a cylindrical body (P1) with an end face (P1a) which is substantially co-planar with the said face (6).

Inventors: EJIRI SUSUMU, KIMURA MAKOTO, EJIRI, SUSUMU, KIMURA, MAKOTO
Applicants: PALOMA KOGYO CO LTD, PALOMA KOGYO CO., LTD.
Application year: 1992
Main classification: F23C11
IPC codes: F23Q3, F23C15