Abstract:
In order to obtain good efficiency of a pulse combustion apparatus, an ignition plug is protected to extend its life span by way of controlling the rotation of the ground electrode at the wall face of a combustion chamber wherein 100°˜200° C. may be reduced from a conventional temperature of 900° C. at the ground electrode in the ignition plug.

Description:
This application is a continuation of application Ser. No. 07/973,345 filed Nov. 9, 1992 abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a pulse combustion apparatus in which pulsating explosive combustions occur repeatedly and continuously. A pulse combustion apparatus 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, and wherein combustion heat is used for cooking devices and etc. 
     2. Description of the Prior Art 
     One example of a combustion chamber of this pulse combustion apparatus is shown in FIG. 4. A combustion chamber 1 in which explosive combustions are carried on is generally formed and sectioned by a wall 3 having a curved face similar to that of a snail with a fundamental curvature owing to the characterization of combustion and so on. An ignition plug 10 is set and inserted into the curved wall 3 spirally by the screw part 13. Also, 7 in the Figure represents a tail pipe for the discharge of combustion exhaust. 
     SUMMARY OF THE INVENTION 
     As the temperature inside the combustion chamber 1 of such pulse combustion apparatus becomes, however, very high, the edge (L letter-shape part shown by the broken line) of the ground electrode 12 on the ignition plug 10 often has been burnt and damaged as shown in FIG. 4. For this reason, the life span of the ignition plug 10 becomes short. 
     From this point, the present inventors thought it is possible to protect the ground electrode 12 if the same ground electrode 12 would be positioned near the combustion chamber wall 3, when a test result suggested a fact that temperature distribution inside the combustion chamber 1 becomes lower towards the wall 3 of the combustion chamber. 
     An object of the present invention is to provide a pulse combustion apparatus in which the above problem may be resolved to extend the life span of the ignition plug by a new plug mount structure for reducing heating of the ground electrode according to the above idea. 
     This invention is summarized as that of an ignition plug mount structure of a pulse combustion apparatus, a combustion chamber wall of which is screwed into an ignition plug whose sparks start pulsating explosive combustions, which is characterized in that a ground electrode which is positioned at the side of the top of an ignition plug is set near an inner wall face of the combustion chamber by using a spacer, which decides the inserting position of the ignition plug with the selected thickness. 
     According to the above mount structure of the ignition plug in the pulse combustion apparatus subject to this invention, the ground electrode may be positioned at a point near the inner wall of a combustion chamber by way of selecting the thickness of a spacer. That is, a prior art position of ignition plus is at a random point, because there is uncertainty in a screw-cut part of the ignition plug, the plug inserting hole in a combustion chamber and the like, or tightening torque or so on. 
     When a spacer is selectively used, the ground electrode may be set near the inner wall face of a combustion chamber. Therefore, temperature distribution becomes lower towards the wall of the combustion chamber, and temperature of the ground electrode becomes low so that heat collapse and undesirable effects may be lightened. 
     In order to clarify further the composition and function of this invention explained in the above, a suitable practical example for the ignition plug mount structure of the pulse combustion apparatus is explained as below according to this invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross-sectional front-view of a combustion chamber used in a pulse combustion apparatus as a practical example. 
     FIG. 2 is a schematic cross-sectional side-view of this example. 
     FIG. 3 is a graph of temperature characteristics at the ground electrode. 
     FIG. 4 is a schematic cross-sectional front-view of the combustion chamber in the pulse combustion apparatus of a prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, the combustion chamber 1 is a chamber where mixed air supplied from a mixing chamber not shown in the Figure is drawn in and at a certain cycle and explosive combustions are repeated, and this chamber is formed with a snail shape possessing a cave of almost circular cross section with a fundamental curvature in this practical example. The entrance 2 of the combustion chamber connected with the mixing chamber not shown in the Figure, is formed towards a tangent of the combustion chamber 1 in order to take in mixed air well and also to prevent backfire. 
     In the wall 3 composing this combustion chamber 1, a screw hole 4 for installing an ignition plug (hereinafter called a plug fitting hole 4) and a screw hole 5 for fixing a flame rod are provided therewith, and an ignition plug 10 and a flame rod 20 are respectively set and inserted into holes by screwing. 
     The ignition plug 10 has a central electrode 11 provided at the center of the top, a ground electrode 12 bent in the form of the letter L provided at the side of the central electrode, a cylindrical screw part 13 provided on the central side thereof and a stopper 14 in a ring shape with diameter larger than that of the screw part 13 provided at the end of the same screw part 13, according to a general firing device. In the conventional device, the ignition plug 10 had the screw part 13 instantly screwed into the plug fitting hole 4 formed in the combustion chamber 1. Screwing was done with use of the necessary torque until the stopper 14 is stopped and engaged with a peripheral outer-wall of the combustion chamber surrounding the plug fitting hole 4 (hereinafter called a contact face 6). Compared to this, a spacer 30 in a ring form in inserted on the screw part 13, according to this invention. Consequently, there is a state in which the spacer 30 was set between the stopper 14 and the contact face 6 of the combustion chamber 1 when the plug was screwed therein. 
     4 sizes in thickness of the spacer 30 can be used for this example, which are respectively different by 1/4 pitch in respect with the pitch of the screw part 13. In series, the spacer 30 has H, H+P/4, H+P/2, and H+3P/4, when the thickness of the thinnest space 30 is H and P is the length of one pitch. Accordingly, the ignition plug 10 can be stopped and positioned with 1/4 pitch difference subject to the thickness of the spacer 30. 
     FIG. 3 now suggests the relation between temperature and position of the ground electrode 12. Data in FIG. 3 are obtained by experiment, which presents rotating the angle of the inserted ignition plug 10 in the horizontal axis and temperature of the ground electrode 12 in the vertical axis. From the Figure, the temperature of the ground electrode 12 changes about 100° C. in response to the rotating angle, that is, the position of the inserted ignition plug 10. By this data, as the ground electrode 12 becomes nearer the center of combustion chamber 1 (point A in FIG. 3), the temperature becomes higher. In contrast, the nearer the inner wall face of combustion chamber 1 (point B in FIG. 3), the lower the temperature of ground electrode 12. In other words, when the position of the ground electrode 12 is nearest to the inner face of wall 3 in the combustion chamber 1 as shown (I) in FIG. 2, the temperature becomes lower by about 100° C. than when the ground electrode 12 faces the center of combustion chamber 1 as shown (II) in FIG. 2. 
     From the above, the practical example uses to set one of the spacers (4 sizes) by which the ground electrode 12 is positioned nearest to the inner wall face of the combustion chamber 1. The ground electrode 12 can be set to face the inner wall face of the combustion chamber 1, in spite of the precision with which the ignition plug 10 and the plug fitting hole 14 of the combustion chamber 1 are respectively screw-cut. 
     Therefore, the temperature of the ground electrode is always controlled at low, so that the life span of the ignition plug 10 may be extended with effect of lightening heat collapse of the ground electrode 12 subject to combustion heat. The temperature can be reduced to 750° C. further to 700° C. by controlling the direction of the ground electrode 12 towards the wall face of combustion chamber 1, while the temperature reached 900° C. at the ground electrode in the prior art. 
     This invention explained as the above practical example is not limited by such practical example and of course can be practiced within the limits by not deviating from the major points thereof. For example, although a spacer 30 is of 4 sizes having different thicknesses by 1/4 pitch , the number of the size may be increased so that the ground electrode 12 will be further more near the inner wall face, or otherwise reduced to be simplified. 
     From the above, the temperature can be lowered at the ground electrode of an ignition plug according to the ignition plug mount structure, and the life span of the ignition plug can be extended by lightening heat collapse of the ground electrode.