Abstract:
A double-combustor type pulsating combustion apparatus has a pair of pulsating combustors. Fuel-supplying valves are respectively provided in fuel-supplying pipes connected to the upstream sides of combustion chambers of the pair of pulsating combustors. A combustion control unit controls to stop only one pulsating combustor and to operate only the other pulsating combustor by closing one fuel-supplying valve corresponding to one pulsating combustor in a combustion range of 1/2 or less of the maximum combustion amount of the double-combustor type pulsating combustion apparatus. The combustion control unit further controls to operate both the pulsating combustors by opening both the fuel-supplying valves in a combustion range exceeding 1/2 of the maximum combustion amount.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a double-combustor type pulsating combustion apparatus for combusting a pair of pulsating combustors in reverse phase to each other. 
     2. Description of the Related Art 
     A coupling type pulsating combustion apparatus which solves a problem of noise of the defect of a pulsating combustion apparatus using one pulsating combustor is known. The apparatuses of this type are disclosed, for example, in U.S. Pat. Nos. 4,840,558 and 4,917,596. The apparatus of this type ordinarily comprises, in addition to a pair of combustion chambers formed in the same arrangement for combusting mixture gas of fuel and combustion air in a pulsating manner, tail pipes connected to the exhaust ports of the combustion chambers for exhausting exhaust gases, air-intake pipes connected at one end to the air-intake ports of the combustion chambers for supplying air necessary for combustion to the combustion chambers, an air-intake chamber connected commonly at the other end of the air-intake pipes, an exhaust chamber connected commonly at the downstream side of the tail pipes, aerodynamic valves provided in the air-intake pipes, having larger backward flow efficiency than forward flow efficiency, a fuel-supplying system for supplying fuel between the aerodynamic valves and the air-intake ports in the air-intake pipes, ignitors provided in the combustion chambers for igniting the mixture gas supplied into the combustion chambers at the time of starting, and an air-supplying fan having a small capacity, provided in or at the upstream side of the air-intake chamber. 
     In the coupling type pulsating combustion apparatus in which the aerodynamic valves are interposed in the air-intake pipes, the pressures in the two combustion chambers can be strongly interfered through two aerodynamic valves. Thus, the oscillating periods of the pulsating combustors can be differentiated at 180 degrees to reduce its noise. 
     As disclosed in U.S. patent application Ser. No. 437,187, now U.S. Pat. No. 4,946,381, filed by the inventors including ones of the present invention, a combustion amount can be varied to approx. 1/3 of the maximum combustion amount by varying the rotating speed of the air-supplying fan in response to the supplying amount of fuel at the time of operation. 
     However, when the coupling type pulsating combustion apparatus disclosed as above is applied, for example, for a domestic room heater, a request for further reducing room heating capacity is strongly desired due to advancement in high heat insulation and high density in residence. However, in the apparatus described above, the request for the further reduction in the room heating capacity cannot be coped with the combustion amount of approx. 1/3 of the maximum combustion amount. 
     In order to reduce the combustion amount to 1/3 or less of the maximum combustion amount, a method of controlling on/off a coupling type pulsating combustion apparatus is, for example, considered. However, in this manner, there arise problems of repetitive thermal stress, increase in CO concentration in combustion gas, and frosting due to condensation in a coupling type pulsating combustion apparatus by frequent on/off of a solenoid valve. 
     That is, in the conventional coupling type pulsating combustion apparatus, the varying range of the combustion amount cannot be reduced to 1/3 or less of the maximum combustion amount, and it cannot be applied to an equipment necessary for a large capacity varying range for domestic room heaters, etc. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a double-combustor type pulsating combustion apparatus in which varying range of a combustion amount can be increased. 
     According to one aspect of the present invention, there is provided a double-combustor type pulsating combustion apparatus comprising: 
     a first pulsating combustor having a first combustion chamber including a predetermined volume, a first tail pipe connected to a downstream side of the first combustion chamber, a first air-intake pipe connected to an upstream side of the first combustion chamber, and a first fuel-supplying pipe; 
     a second pulsating combustor having a second combustion chamber including the predetermined volume, a second tail pipe connected to a downstream side of the second combustion chamber, a second air-intake pipe connected to an upstream the of said second combustion chamber, and a second fuel-supplying pipe, being formed in the same arrangement as the first pulsating combustor, and having a combustion cycle of reverse phase to the first pulsating combustor; 
     a first fuel-supplying valve, provided in the first fuel-supplying pipe, for controlling supply of fuel to the first combustion chamber of the first pulsating combustor; 
     a second fuel-supplying valve provided in the second fuel-supplying pipe for controlling supply of fuel to the second combustion chamber of the second pulsating combustor; and 
     control means for controlling to operate only the second pulsating combustor by closing the first fuel-supplying valve in a combustion range of 1/2 or less of the maximum combustion amount of the double-combustor type pulsating combustion apparatus and to operate both the first and second pulsating combustors by opening the first and second fuel-supplying valves in a combustion range exceeding 1/2 of the maximum combustion amount. 
     According to another aspect of the present invention, there is provided a double-combustor type pulsating combustion apparatus, comprising: 
     a pair of pulsating combustors connected to each other to be able to perform pulsating combustions in reverse phase; and 
     combustion control means for combusting the pair of pulsating combustors while controlling combustion air supplying amounts in response to the amount of fuel supplied to the pair of pulsating combustors, and for controlling to stop combustion of one pulsating combustor when the combustion amount becomes a set combustion amount or less and to supply fuel and combustion air to the other pulsating combustor. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
     FIG. 1 is a front view partly cut out in a double-combustor type pulsating combustion apparatus according to first embodiment of the present invention; 
     FIG. 2 is a side view partly cut out in FIG. 1 line X--X; 
     FIG. 3 is a view showing the oscillating period of pulsating combustors having phases of difference of 180 degrees at the time of stable pulsating combustion; 
     FIG. 4 is an operation characteristic diagram of pulsating combustors when a combustion amount is reduced; 
     FIG. 5 is a flowchart of a combustion control unit for explaining the varying operation of the combustion amount; 
     FIG. 6 is a flowchart of a routine for operating one pulsating combustor; 
     FIG. 7 is a state characteristic diagram of combustion varying range; and 
     FIG. 8 is a operation characteristic diagram of a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 shows a first embodiment of a pulsating combustion apparatus 10 using a pair of pulsating combustors 10a, 10b connected in parallel with each other according to the present invention. The pulsating combustion apparatus 10 comprises a cylindrical air-intake chamber 12, an exhaust chamber 14, pulsating combustors 10a and 10b having the same arrangement and size and connected between the air-intake chamber 12 and the exhaust chamber 14, and a fuel-supplying system 16 for supplying fuel gas to the pulsating combustors 10 and 10b. 
     One pulsating combustor 10a has a cylindrical combustion chamber 18a having a bottom of which one end is closed by a closed bottom 20a and the other end has an exhaust port 22a. The exhaust port 22a is connected to the exhaust chamber 14 through a tail pipe 24a. 
     An air-intake port 26a is formed as shown in FIG. 2 in the peripheral wall of the combustion chamber 18a and at a position in the vicinity of the closed button 20a. An ignitor 28a with a discharge gap portion positioned within the combustion chamber 18a as shown in FIG. 2 is mounted in the peripheral wall of the combustion chamber 18a and at a position in the vicinity of the air-intake port 26a. A flame sensor 30a for detecting whether or not the mixture gas within the combustion chamber 18a is combusted is mounted in the peripheral wall of the combustion chamber 18a and at the position opposed to the ignitor 28a. 
     One end of an air-intake pipe 32a is connected to the air-intake port 26a. The other end of the air-intake pipe 32 is connected to the air-intake chamber 12. The air-intake pipe 32a is connected to the combustion chamber 18a, with the axis extending at right angle to the axis of the combustion chamber 18a but not intersecting therewith. 
     An aerodynamic valve 34a whose forward flow efficiency is greater than the backward flow efficiency is inserted at a position halfway of and within the air-intake pipe 32a. The aerodynamic valve 34a is in the form of a nozzle of which open area is gradually reduced from the air-intake chamber 12 toward the combustion chamber 18a. That is, the aerodynamic valve 34a is formed so as to have a small resistance with respect to a flow from the air-intake chamber 12 toward the combustion chamber 18a and to have a large flow resistance with respect to a flow reversed thereto. 
     The other pulsating combustor 10b has a combustion chamber 18b, a closed bottom 20b, an exhaust port 22b, a tail pipe 24b, an air-intake port 26b, an ignitor 28b, a flame sensor 30b, an air-intake pipe 32b and an aerodynamic dynamic valve 34b, and has the same arrangement and size as those of the pulsating combustor 10a. 
     Fuel-injection ports 36a and 36b are formed in a portion between portions where the aerodynamic valves 34a and 34b are positioned and positions connected to the air-intake ports 26a and 26b in the peripheral walls of the air-intake pipes 32a and 32b. A fuel-supplying port 38b is connected to the one fuel-injection port 36a. A fuel-supplying pipe 38b is connected to the other fuel-injection port 36b. The fuel-supplying pipe 36a is connected to a fuel gas supply source (not shown) through a fuel-supplying valve 40a composed of an electromagnetic valve and the fuel-supplying pipe 36b is connected to the fuel gas supply source through a fuel-supplying valve 40b composed of an electromagnetic valve. In this case, a fuel control valve 42 for controlling the flow rate of fuel is provided between the fuel-supplying valves 40a, 40b and the fuel gas supply source to control a combustion power of the pulsating combustion apparatus 10. 
     An air inlet port 44 is formed, as shown in FIG. 2, at an end in a axial direction of the air-intake chamber 12. An air-supplying fan 46 for feeding air into the air-intake chamber 12 is connected to the air inlet port 44. 
     First, when an operation command S 1  is provided from an operation unit (not shown) in response to the operation of the operation unit, a combustion control unit 48 issues a drive control command S 2  to the air-supplying fan 46 to rotate the fan 46 at low speed. By the start of the air-supplying fan 46, air flows through the air-intake chamber 12, the air-intake pipes 32a, 32b, the aerodynamic valves 34a, 34b, the air-intake ports 26a, 26b and the combustion chambers 18a, 18b. This air flow causes the gas remained in the combustion chambers 18a and 18b to be purged. 
     Next, the combustion control unit 48 provides operation start commands S 3a  and S 3b  for the ignitors 28a and 28b at different timings to start operations of the ignitors 28a and 28b, and provides an open command S 4  for the fuel control valve 42 to fully open the fuel control valve 42. When the fuel valves 42 is controlled to be &#34;fully opened&#34;, the fuel gas is injected into the combustion chambers 18a and 18a through the fuel-supplying valves 40a, 40b, the fuel-supplying pipes 38a, 38b and the fuel-injection ports 36a, 36b (at that time, both the fuel-supplying valves 40a and 40b are opened by the open commands S 3a  and S 3b  from the combustion control unit 48). In this manner, the combustion chambers 18a and 18b are filled with the mixture gas of fuel gas and air. The ignitors 28a and 28b are then fired by the mixture gas because they are already in the operating state, and the pulse combustions are started in the combustion chambers 18a and 18b. 
     At that time, the combustion control unit 48 detects whether or not the mixture gases in the combustion chambers 18a and 18b are combusted by detection signals S 6a  and S 6b  from the flame sensors 30a and 30b. When the combustion control unit 48 detects that the mixture gases are combusted in the combustion chambers 18a and 18b, the unit 48 issues a drive control command S 2  to the air-supplying fan 46 to rotate the air-supplying fan 46 at a high speed. Accordingly, the air-supplying fan 46 supplies further more air into the combustion chambers 18a and 18b through the air-intake chamber 12, the air-intake pipes 32a and 32b, the aerodynamic valves 34a, 34b and the air-intake ports 26a, 26b. In this manner, more amount of air than that before the start of the fire, i.e., the combustion is supplied into the combustion chambers 18a and 18b, and stable pulsating combustion occurs therein. 
     Namely, the temperatures of the combustion chambers 18a and 18b are low till the mixture gases in the combustion chambers 18a and 18b are fired. Accordingly, since the pressure losses of the combustion chambers 18a and 18b are low, the air-supplying fan 46 is rotated at low speed to feed a small amount of air to the combustion chambers 18a and 18b. When the mixture gases in the combustion chambers 18a and 18b are fired, the temperatures of the combustion chambers 18a and 18b rapidly increase and the pressure losses of the combustion chambers 18a and 18b also increase. In this embodiment, however, a large amount of air is forcibly supplied after firing by the air supplying fan 46, so that the stabilized combustion may continue within the combustion chambers 18a and 18b. 
     Within the combustion chambers 18a and 18b, the mixture gases intermittently explosively burn. When the mixture gases are combusted in the combustion chambers 18a and 18b as described above, pressures in the combustion chambers 18a and 18b rise, and the front pressures of the fuel-injection ports 36a and 36b also rise. Therefore, the injections of fuel into the combustion chambers 18a and 18b are automatically stopped. When the pressures in the combustion chambers 18a and 18b abruptly rise, a majority of combustion gas flows toward the exhaust chamber 14 at high speed within the tail pipes 24a and 24b. The remaining combustion gases tend to flow toward the air-intake chamber 12 passing through the aerodynamic valves 34a and 34b. However, since this aerodynamic valves 34a and 34b have a great flow resistance with respect to a flow from the combustion chambers 18a and 18b toward the air-intake chamber 12, the amount of combustion gas flowing toward the air-intake chamber 12 is suppressed to a small amount. 
     The chambers in pressure in the combustion chambers 18a and 18b caused by the explosive combustion of the mixture gas is propagated into the air-intake chamber 12 through the aerodynamic valves 34a and 34b. This propagation increases the amount of air flowing into the combustion chambers 18a and 18b through the aerodynamic valves 34a and 34b. When the combustion gas in the combustion chambers 18a and 18a flow toward the tail pipes 24a and 24b at high speed, the pressures in the combustion chamber 18a and 18a rapidly lower to a negative pressure (less than atmospheric pressure due to the interior of the combustion gas in the tail pipes 24a and 24b. 
     When the pressures in the combustion chambers 18a and 18a lower to the negative pressure, the fuel injections from the fuel injection port 36a and 36b are restarted. With this, airs flow into the combustion chambers 18a and 18a through the aerodynamic valves 34a and 34a at high speed. In this case, the air flowing into the combustion chambers 18a and 18a through the aerodynamic valves 34a and 34a impinge upon the fuel gas injected from the fuel injection ports 36a and 36b and assume the form of flow which whirls along the inner surfaces of the peripheral walls of the combustion chambers 18a and 18b. Therefore, the fuel and air are well mixed. In this manner, the combustion chambers 18a and 18a are again filled with the mixture gas of fuel and air. At this time, the remaining fire is present within the combustion chambers 18a and 18b, and therefore, the mixture gas is fired by the remaining fire to again induce the explosive combustion. 
     That is, the double combustor type pulsating combustion apparatus induces merits peculiar for the pulsating combustion by the interference of the two pulsating combustors 10a and 10b arranged in parallel with each other, i.e., (1) high heat transfer rate, (2) low NOx combustion, and (3) high load combustion, etc. by the pulsating combustion. The interference is caused by the air-intake chamber 12 and the exhaust chamber 14 connected commonly to the inlet and outlet. A noise can be reduced by repeating the pulsating combustion cycle with the phase difference of 180 degrees, i.e., in reverse phase to each other, as shown in FIG. 3. This belongs to a noise cancelling method near active control. 
     Next, the reduction in the combustion amount will be described. This case includes two types of modes of the operation using two pulsating combustors 10a and 10b, and the operation only by one pulsating combustion 10b. That is, air supplying amount by the air-supplying fan 46 and fuel supplying amount by the fuel control valve 42 are first regulated to vary the combustion amounts of both the pulsating combustors 10a and 10b from time T A  to time T B  as shown in FIG. 4. When the combustion amount is reduced more than variable combustion amount range by the regulation of the air and fuel supplying amounts, one pulsating combustor 10a is turned off, and the operation is switched to the combustion using only the other pulsating combustor 10b. 
     An operation of this combustion will be described in more detail with reference to the processing flowcharts of the combustion control unit 48 in FIGS. 5 and 6. At time T A  shown in FIG. 4, an operation command S 1  for varying a combustion amount is input from the operation unit (step ST1), and whether or not the operation command S 1  is a command for reducing the combustion amount or a command for raising the combustion amount is judged (step ST2). When the operation command S 1  is the command for reducing the combustion amount, whether or not the present combustion amount reaches the minimum combustion amount (C B ) capable by the two pulsating combustors having a combustion amount (C E ) or less of 1/2 of the maximum combustion amount (max) is judged (step ST3). If the present combustion amount does not yet arrive at the minimum combustion amount (C B ), the rotating speed of the air-supplying fan 46 and the opening of the fuel control valve 42 are regulated to vary the combustion amount (step ST4). In this case, the rotating speed of the air-supplying fan 46 is decelerated, and the opening of the fuel control valve 42 is reduced, thereby decreasing air and fuel supply amounts to reduce the combustion amount. 
     When a command for reducing a combustion amount is further received after the combustion amount reaches the minimum combustion amount (C B ) capable by the two pulsating combustors at time T B  shown in FIG. 4, a routine for operating one pulsating combustor is executed (step ST5). 
     FIG. 6 shows a detailed flowchart of this routine for operating one pulsating combustor. In order to stop the operation of one pulsating combustor 10a, the fuel-supplying valve 40a is turned off to stop the supply of fuel to the pulsating combustor 10a (step ST10). Accordingly, only the pulsating combustor 10b is operated. At this time, the rotating speed of the air-supplying fan 46 is accelerated to a high speed, and the opening of the fuel control valve 42 is increased to increase the combustion amount of the pulsating combustor 10b to the combustion amount C B  as shown in FIG. 4 (step ST12). In this manner, a continuous combustion variation is performed. 
     When a combustion amount varying operation command S 1  is further input (step ST13) to reduce the combustion amount (step ST14), whether or not the combustion amount reaches the minimum combustion amount (min) capable by one pulsating combustor is judged (step ST15). If the combustion amount does not yet reach the minimum combustion amount (min), the rotating speed of the air-supplying fan 46 and the opening of the fuel control valve 42 are regulated to vary the combustion amount (step ST16). In this case, the rotating speed of the air-supplying fan 46 is decelerated and the opening of the fuel control valve 42 is reduced, thereby reducing air and fuel supplying amounts to the combustion chamber 18b to decrease the combustion amount. 
     As described above, the combustion amount is reduced in response to the combustion amount reduction command, and the combustion amount reaches, for example, the minimum combustion amount (min) at time T C . Since the combustion amount cannot be varied even if the combustion amount reduction command is thereafter further received, the command is ignored (step ST15). 
     At time T D  shown, for example, in FIG. 4, when a command for increasing the combustion amount by the combustion amount varying command S 1  is received (step ST14), whether or not the combustion amount reaches the maximum combustion amount (C E ) capable by one pulsating combustor is judged (step ST17). If the combustion amount does not yet reach the maximum combustion amount (C E ), the rotating speed of the air-supplying fan 46 and the opening of the fuel control vale 42 are regulated to vary the combustion amount (step ST16). In this case, the rotating speed of the air-supplying fan 46 is accelerated to a high speed and the opening of the fuel control valve 42 is increased, thereby increasing the air and fuel supplying amounts to the combustion chamber 18b to increase the combustion amount. 
     However, when the combustion amount has already reached the maximum combustion amount (C E ) as at time T E  shown in FIG. 4, the fuel-supplying valve 40a is turned on to start supply of fuel to the pulsating combustor 10a (step ST18). That is, the operation by both the pulsating combustors 10a and 10b is started. At this time, the rotating speed of the air-supplying fan 46 is decelerated to a low speed and the opening of the fuel control valve 42 is reduced, thereby making the combustion amounts of both the pulsating combustors 10a and 10b uniform (step ST19). In this manner, a continuous combustion variation is performed. 
     Thereafter, the operation is returned to the operation shown in FIG. 5 as described above. Accordingly, when an operation command S 1  for varying the combustion amount is further input from the operation unit (step ST1), whether or not the operation command S 1  is a command for reducing the combustion amount or a command for raising the combustion amount is judged (step ST2). When the combustion amount is further raised, whether or not the present combustion amount reaches the maximum combustion amount (max) by the two pulsating combustors is judged (step ST6). If the combustion amount does not yet reach the maximum combustion amount, the rotating speed of the air-supplying fan 46 and the opening of the fuel control vale 42 are regulated to vary the combustion amount (step ST4). In this case, the rotating speed of the air-supplying fan 46 is accelerated to a high speed and the opening of the fuel control valve 42 is increased, thereby increasing air and fuel supplying amounts to increase the combustion amount. 
     In this manner, the combustion amount is increased in response to the command for increasing the combustion amount. For example, at time T F  shown in FIG. 4, the combustion amount reaches the maximum combustion amount (max). Thereafter, since the combustion amount cannot be varied even if the command for increasing the combustion amount is further received, the command is ignored (step ST6). 
     By the operation described above, as shown in the state characteristic diagram of the combustion varying range of the double-combustor type pulsating combustion apparatus according to a first embodiment of the present invention in FIG. 7, low combustion operation which cannot be obtained at the time of operation of both the pulsating combustors 10a and 10b can be carried out. That is, as shown, the combustion varying range can be increased as compared with that at the time of operation of both the pulsating combustors 10a and 10b. 
     With regard to noise, pressure interference by the reverse phase combustion cycle of both the pulsating combustors 10a and 10b as described above does not occur at the time of combustion of only one pulsating combustor 10b, but since a combustion load is decreased, noise is accordingly reduced. Further, the other pulsating combustor 10a which is not combusted performs a role of a muffler through the air-intake chamber 12 and the exhaust chamber 14. At this time, the pulsating combustor 10a which is not combusted becomes an ideal resonance type muffler. Accordingly, it is confirmed that an extremely low noise value ca be performed similarly to that at the time of combustion by the two pulsating combustors according to experiments. 
     As described above, the combustion by the one pulsating combustor is fundamentally different from the case that the two pulsating combustors are independently operated in parallel as described above to increase the capacity varying range at a point that both the pulsating combustors affect each other. 
     Next, a double combustor-type pulsating combustion apparatus according to a second embodiment of the present invention will be described with reference to the operation characteristic diagram in FIG. 8. In the case of the combustion control unit 48 at the time of combustion of one pulsating combustor in the first embodiment described above, as shown, the pulsating combustors operating for a predetermined period of time are exchanged. That is, when one pulsating combustor 10a is operated for a predetermined period of time, the pulsating combustor 10a is stopped, and the other pulsating combustor 10b is then operated. When the other pulsating combustor 10b is similarly operated for a predetermined period of time, it is stopped, and the one pulsating combustor 10a is then operated. 
     Both the pulsating combustors are controlled as described above to prevent the durability of both the pulsating combustors from decreasing due to the operation that either one pulsating combustor is operated for a long period of time. 
     According to the present invention as described above, when the combustion amounts of the double-combustor type pulsating combustion apparatus are desirably reduced, either one pulsating combustor is stopped to reduce the entire capacity by half to increase the varying range of the combustion amount whole holding an extremely low noise value. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices, shown and described herein. Accordingly, various modifications may be without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.