Gas engine power generation system

Abstract

To provide a power generation system with extremely high operating efficiency, which runs on fuel generated from organic matter such as food waste and animal excrement heated in an oxygen-free environment and effectively burns the combustible substances in the fuel. [Configuration] The device includes a main fuel gas container 11 for a bio-based main fuel gas G1, a support gas container 21 for a non-bio-based support gas G2, a gas engine 7, and a mixer 3 for supplying a mixed gas fuel G3 obtained by mixing the main fuel gas G1 and the support gas G2 to the gas engine 7. The gas engine 7 has two spark plugs 81, 82, an intake valve 84, and two exhaust valves 85, 85 disposed in a cylinder 71, and a flame sensor 9 for detecting the strength of a flame K is attached to an inner peripheral wall surface 71a of the cylinder 71 at a predetermined distance from both the spark plugs 81, 82, and the flame sensor 9 is connected to an ECU 4, and when the explosive power of the flame K in the cylinder 71 is equal to or less than a predetermined value, the ECU 4 supplies the support gas G2 into the cylinder 71.

Description

[Technical field]

[0001] The present invention relates to a gas engine power generation system that operates using fuel produced from organic matter such as food waste and animal manure heated in an oxygen-free environment, and that can effectively burn the combustible substances in the fuel to operate with extremely high operating efficiency. [Background technology]

[0002] In general, waste from livestock animals, food waste, and residues are steamed in an oxygen-free environment, solidified, and then buried in a landfill, and there is a problem that the gas generated during the process is released into the atmosphere, which leads to environmental pollution. In recent years, engines that run on gas generated from organic matter such as livestock animal waste, food waste, and residues (also called biogas fuel) have come to be used for power generation or normal power. Patent Document 1 (JP Patent Publication 2009-174392 A) is an example of a conventional technology that uses such biogas fuel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-174392 A Summary of the Invention [Problem to be solved by the invention]

[0004] Gas containing combustible gas is generated during the process of fermenting food waste or steaming industrial waste in an oxygen-free environment to reduce its volume. For convenience, this type of gas is referred to as S gas (main fuel gas G1). The proportion of combustible gas in the S gas (main fuel gas G1) is small, but it is 20 Mj per cubic meter, i.e., 20 Mj / m 3 However, this gas contains more carbon dioxide (CO2) than combustible gases.

[0005] CO2 inhibits combustion, and is also used in fire extinguishers. Theoretically, if the above-mentioned S gas (main fuel gas G1) could be burned inside the cylinder of an engine, and the energy of S gas (main fuel gas G1) could be converted into power to drive a generator, this could contribute greatly to energy conservation. Combustible gases in S gas (main fuel gas G1) include carbon monoxide (CO), hydrogen (H2), and methane (CH4), but the ignition temperatures of these gases are high and they cannot be ignited by the heat of compression like diesel engines.

[0006] Furthermore, there are the following problems when using crude gas made of biogas fuel in a gas engine. First, as mentioned above, crude gas is a so-called artificial gas made from livestock manure or food residues. Furthermore, crude gas may contain inorganic substances such as CO and H2. Therefore, this crude gas is produced in smaller quantities than natural gas (propane and methane). Therefore, it is difficult to secure a quantity sufficient to supply to a large gas turbine. Therefore, the Stirling engine disclosed in Patent Document 1 is an external combustion engine, and it is extremely difficult and unsuitable to apply the above-mentioned crude gas as it is to a Stirling engine.

[0007] Next, in the process of steaming or fermenting livestock manure or food residues in an oxygen-free state, combustible gas (called raw gas) is generated, which is used as fuel for gas engines, but this raw gas often contains a large amount of carbon dioxide (CO2). Normally, in the technology shown in Patent Document 1, gas turbines or Stirling engines are continuous combustion, and combustion is possible even if a certain amount of carbon dioxide is mixed in the fuel. However, spark ignition engines are intermittent combustion that repeats intake, compression, ignition expansion, and exhaust, and carbon dioxide in the fuel may interfere with ignition, the formation of the flame kernel, and the propagation of the flame. In this respect, the technology disclosed in Patent Document 1 is difficult to apply to spark ignition engines.

[0008] However, some of the components that make up raw gas are flammable. If these flammable components are not disposed of, but rather their energy can be fully utilized and this difficult-to-burn gas can be used as fuel for a spark-ignition engine of 200 kW or less, and the resulting power can be used to drive a generator and convert it into electrical energy, then this will be an effective use of recycled resources and will contribute greatly to environmental conservation.

[0009] The object of the present invention is to provide a gas engine power generation system that can make maximum effective use of biological crude gas consisting of livestock manure or food waste in a spark ignition engine, thereby contributing to the effective use of renewable resources and environmental conservation. [Means for solving the problem]

[0010] Therefore, the inventors have conducted intensive research to solve the above-mentioned problems, and as a result, the inventors have come up with the invention of claim 1, which is a gas engine power generation system comprising: a main fuel gas container in which a bio-based main fuel gas is stored; a support gas pressure container in which a non-bio-based support gas is stored; a gas engine; and a mixer that supplies a mixed gas fuel consisting of a mixture of the main fuel gas and the support gas to the gas engine, wherein the gas engine has two ignition plugs, an intake valve, and an exhaust valve disposed in a cylinder, and two flame sensors that detect the strength of a flame are attached to an inner wall surface of the cylinder at a predetermined distance from both the ignition plugs, both the flame sensors being connected to an ECU, and when the explosive power of the flame in the cylinder is equal to or less than a predetermined value, the ECU supplies the support gas into the cylinder, thereby solving the above-mentioned problems.

[0012] Claim 2The above problem has been solved by providing a gas engine power generation system according to the invention described in claim 1, wherein both of the flame sensors have a first electrode and a second electrode within an insulator section whose tips protrude from the insulator section, a gap is formed between the first electrode and the second electrode, and when flame particles reach the gap sufficiently, a current is generated in the gap and the ECU determines that the flame is stable, and when flame particles do not reach the gap sufficiently, no current is generated in the gap and the flame is determined to be unstable, and the ECU supplies the support gas.

[0013] Claim 3 The invention solves the above problem by providing a gas engine power generation system as described in claim 1 or 2, characterized in that an O2 sensor and a three-way catalyst are arranged in the exhaust system, and the O2 sensor and the three-way catalyst are provided. Effect of the Invention

[0014] The invention of claim 1 comprises a main fuel gas container in which a bio-based main fuel gas is stored, a support gas pressure container in which a non-bio-based support gas is stored, a gas engine, and a mixer that supplies a mixed gas fuel obtained by mixing the main fuel gas and the support gas to the gas engine, and the gas engine has two ignition plugs, an intake valve, an exhaust valve, and two flame sensors arranged within a cylinder.

[0015] The flame sensors are attached to the inner peripheral wall surface of the cylinder at a predetermined distance from the spark plugs and serve to detect the strength of the flame in the combustion of the gas fuel in the cylinder. The flame sensors are connected to an ECU (engine control unit) and are configured to supply the support gas into the cylinder when the explosive power of the flame in the cylinder is equal to or less than a predetermined value.

[0016] With the above configuration, when the concentration of bio-based main fuel gas in the mixed gas sent into the cylinder becomes high and the combustion condition of the mixed gas flame generated by the ignition plug deteriorates, the flame sensor detects this condition and sends a signal to the ECU, which then sends an appropriate amount of support gas into the mixer, enabling a good mixed gas to be sent into the cylinder of the gas engine via the mixer.

[0017] In this way, in the present invention, with an extremely simple configuration in which a flame sensor is mounted inside the cylinder, the ECU (engine control unit) determines the state of the fuel flame ignited by the spark from the ignition plug, and maintains a good ratio of main fuel gas and support gas in the mixed gas fuel inhaled into the cylinder via the mixer, thereby maintaining good operation of the gas engine.

[0018] Furthermore, in the invention of claim 1, the two flame sensors can more accurately detect (sense) the flames ignited from both of the spark plugs, and transmit this information to the ECU, allowing the ECU to determine whether or not to supply support gas to the gas fuel. In other words, By providing two flame sensors, the accuracy of detecting (sensing) the flames ignited from both spark plugs can be improved even more, thereby making it possible to maintain even better combustion conditions in the cylinder.

[0019] Claim 2 In the invention, the flame sensor has a first electrode and a second electrode within an insulator portion, with their tips protruding from the insulator portion, and a gap is formed between the first electrode and the second electrode.When flame particles reach the gap sufficiently, a current is generated in the gap and the ECU determines that the flame is stable, and when flame particles do not reach the gap sufficiently, no current is generated in the gap and the flame is determined to be unstable, and the ECU supplies the support gas.As a result, the flame sensor can be configured extremely simply and can detect (sense) the state of the gas fuel in the cylinder with high accuracy.

[0020] Claim 3In the invention, in the gas engine power generation system described in claim 1 or 2, an O2 sensor is provided in the exhaust system, and by using the O2 sensor in conjunction with the flame sensor, the mixture ratio of the main fuel gas and the support gas in the gas fuel (mixed gas fuel and air) in the cylinder via the mixer can be maintained at a good ratio, that is, at a stoichiometric air-fuel ratio or an approximately stoichiometric air-fuel ratio, thereby maintaining good combustion conditions in the cylinder. [Brief description of the drawings]

[0021] [Figure 1] 1 is a schematic diagram illustrating the overall configuration of the present invention; [Diagram 2] FIG. 2 is a process diagram (flowchart diagram) showing the operation of the present invention. [Diagram 3] 1A is a cross-sectional view of a main portion showing the position of a flame sensor in a cylinder head and a cylinder of a gas engine of the present invention, (B) is a cross-sectional view taken along the line Y1-Y1 of (A), (C) is a cross-sectional view taken along the line X1-X1 of (B), and (D) is an enlarged cross-sectional view of part (α) of (C). [Figure 4] 1A is a partial cross-sectional front view of the flame sensor, FIG. 1B is a longitudinal cross-sectional front view of the flame sensor, and FIG. 1C to FIG. 1E are enlarged views of each state of the (β) portion of FIG. [Diagram 5] (A) is a graph showing the state of the flame, and (B) and (C) are state diagrams of the flame and the flame sensor. [Figure 6] (A) is a graph showing the state of the flame, and (B) and (C) are state diagrams of the flame and the flame sensor. [Figure 7] 1A is a longitudinal sectional front view of a mixer, FIG. 1B is a plan view of the mixer, and FIG. 1C is a longitudinal sectional front view of a main fuel gas low pressure regulating valve and a support gas low pressure regulating valve. [Figure 8] 1A and 1B are graphs showing the duty in the present invention, and 1C is a graph showing the duty and the theoretical air-fuel ratio in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The gas engine power generation system of the present invention mainly comprises a main fuel gas container 11, a main fuel gas shutoff valve 12, a main fuel gas low pressure regulator valve 13, and a main fuel gas pressure sensor 14 as a main fuel gas system, a support gas container 21, a support gas shutoff valve 22, and a support gas low pressure regulator valve 23 as a support gas system, and further comprises a mixer 3, an ECU (engine control unit) 4, and a gas engine 7 (see FIG. 1). Furthermore, a cylinder 71 constituting the gas engine 7 is provided with a flame sensor 9 (see FIG. 3). The main fuel gas container 11 is filled with a main fuel gas G1, and the support gas container 21 is filled with a support gas G2.

[0023] The respective devices are connected to each other through pipelines (main fuel gas pipeline 51 and support gas pipeline 52). The main fuel gas G1 in the main fuel gas container 11 and the support gas G2 in the support gas container 21 are sent to the mixer 3 while their respective pressures are appropriately adjusted, and the main fuel gas G1 and the support gas G2 are mixed in the mixer 3 to generate a mixed gas fuel G3, which is then sent toward the gas engine 7 while mixing with the air G0.

[0024] With this configuration, the main fuel gas G1, which is a biomass-based raw gas, and the support gas G2, such as city gas, are mixed by the mixer 3 and supplied to the gas engine 7 as mixed gas fuel G3, which is then used to operate the gas engine 7 together with air G0, which is supplied separately (see FIG. 2). In the present invention, the main fuel gas G1 is a gas generated by heating livestock manure or food waste, such as cows and pigs, in an oxygen-free state, and is sometimes referred to as raw gas. The support gas G2 is a general gas, such as city gas.

[0025] The configuration of the gas engine power generation system of the present invention is shown as a schematic diagram in Fig. 1. Fig. 2 is a process diagram (also called a flow chart diagram) showing the operation of the gas engine power generation system of the present invention, and Fig. 2 shows the process in which the main fuel gas G1 in the main fuel gas container 11 and the support gas G2 in the support gas container 21 in the gas engine power generation system are mixed in the mixer 3 to generate the mixed gas fuel G3, and the mixed gas fuel G3 is supplied to the gas engine 7.

[0026] The main fuel gas vessel 11 and the support gas vessel 21 are connected to the mixer 3 by separate, independent main fuel gas pipes 51 and support gas pipes 52. The main fuel gas G1 in the main fuel gas vessel 11 and the support gas G2 in the support gas vessel 21 are sent to the mixer 3 via the separate main fuel gas pipes 51 and support gas pipes 52, respectively, and the main fuel gas G1 and the support gas G2 are mixed for the first time in the mixer 3, and mixed gas fuel G3 is generated inside the mixer 3.

[0027] The gas engine 7 includes a cylinder 71 and a cylinder head 72, and has a structure in which one or more cylinders 71 and cylinder heads 72 are arranged in series (see FIG. 3). A piston is housed in the cylinder 71 so as to be movable up and down, and a cylinder head 72 is provided on the upper part of the cylinder 71, and the lower surface of the cylinder head 72 is formed as a head inner top wall surface 72a. The head inner top wall surface 72a is substantially spherical, more specifically, a flattened spherical concave surface (see FIG. 3(B)). An intake port 73 and an exhaust port 74 are provided in the cylinder head 72, and an opening of the intake port 73 and an opening of the exhaust port 74 are formed in the head inner top wall surface 72a. The horizontal cross section of the cylinder 71 is a perfect circle.

[0028] The cylinder head 72 is provided with two spark plugs 81, 82, an intake valve 84, and an exhaust valve 85 (see Figs. 3(A) and (B)). When viewed from the top side of the cylinder head 72 (or the cylinder 71) in a plan view, the two spark plugs 81, 82, the intake valve 84, and the exhaust valve 85 are appropriately positioned. Specifically, the two spark plugs 81, 82, the intake valve 84, and the exhaust valve 85 are arranged around the circumference at equal intervals to divide the circumference into four equal parts (see Fig. 3(C)). The intake valve 84 opens and closes the opening of the intake port 73, and the exhaust valve 85 opens and closes the opening of the exhaust port 74.

[0029] The two spark plugs 81, 82 are identical and are mounted so that their respective gaps 81a, 82a protrude from the head inner top wall surface 72a (see FIG. 3(B)). For ease of explanation, one of the two spark plugs 8 will be referred to as a first spark plug 81 and the other as a second spark plug 82. Here, the first spark plug 81 is the first to receive the injected jet of gas fuel (a mixture of mixed gas fuel G3 and air G0) flowing into the cylinder 71 from the intake port 73 of the cylinder head 72.

[0030] Next, the flame sensor 9 will be described. The role of the flame sensor 9 is to detect the state of the flame caused by the explosion of the mixed gas of the mixed gas fuel G3, which is the fuel gas in the cylinder 71, and the air G0. Then, a signal from the flame sensor 9 that detects the strength of the flame is sent to the ECU (engine control unit) 4, which in turn determines whether the mixed state of the mixed gas fuel G3 and the air G0 is good or not, and further determines whether or not to supply the support gas G2 to the mixer 3 (see Figs. 1 and 2).

[0031] The flame sensor 9 is attached to the inner peripheral wall surface 71a of the cylinder 71 at a predetermined distance from the first spark plug 81 and the second spark plug 82 in the cylinder 71 (see Figs. 3(C), 5(B), (C), 6(B), (C)). The predetermined distance is a substantially long distance, and specifically, the flame sensor 9 is attached to the inner peripheral wall surface 71a of the cylinder 71 at a position that is a long distance from the first spark plug 81 and the second spark plug 82 in the cylinder 71. By setting the attachment position of the flame sensor 9 in the cylinder 71 as far away as possible from the first spark plug 81 and the second spark plug 82, it becomes easier to detect (sense) the overall combustion state of the fuel gas (mixed gas fuel G3 and air G0) in the cylinder 71, and it becomes easier to accurately detect the combustion state of the fuel gas and send more accurate information to the ECU 4.

[0032] Regarding the installation of the flame sensor 9 in the cylinder 71, a first imaginary line L1 connecting the first spark plug 81 and the second spark plug 82 is set in the cylinder 71, and a second imaginary line L2 in the horizontal direction perpendicular to the center of the first imaginary line L1 is also set (see FIG. 3(C)). Both the first imaginary line L1 and the second imaginary line L2 pass through the center Q of the diameter of the circumference of the cylinder 71. The first imaginary line L1 and the second imaginary line L2 are different in the height direction, and do not intersect with each other.

[0033] Next, the positions where both ends of the imaginary second straight line L2 contact the inner circumferential wall surface 71a of the cylinder 71 are defined as the installation positions of the flame sensor 9 (see FIG. 3(C)). The flame sensor 9 is provided at the intersection of the inner circumferential wall surface 71a of the cylinder 71 and the imaginary second straight line L2, and there are two intersections, so two flame sensors 9 are provided. Also, the flame sensor 9 may be provided at only one of the two intersections. That is, in this case, there is one flame sensor 9. Also, the position where the flame sensor 9 is disposed on the inner circumferential wall surface 71a of the cylinder 71 is not limited to the above conditions, and the flame sensor 9 may be provided at any position on the inner circumferential wall surface 71a, and in this case, the number of flame sensors 9 may be three or more.

[0034] In the present invention, the number of flame sensors 9 is two, and the description will be given on the assumption that the two flame sensors 9 are attached to the inner peripheral wall surface 71a of the cylinder 71. As described above, the head inner top wall surface 72a of the cylinder head 72 is a spherical concave surface, and the outer shape of this spherical surface is circular and has the same diameter as the circumference of the inner peripheral wall surface 71a of the cylinder 71. As described above, the imaginary first straight line L1 connecting the first spark plug 81 and the second spark plug 82 attached to the cylinder head 72 passes through the diametric center Q of the cylinder 71 in principle, and the center position of the imaginary first straight line L1 is the position of the diametric center Q of the cylinder 71. Therefore, the imaginary second straight line L2 that is perpendicular to the horizontal direction at the center of the imaginary first straight line L1 also passes through the diametric center Q of the cylinder 71 (see FIG. 3(C)).

[0035] As a result, the position of the flame sensor 9 is equidistant from the respective positions of the gaps 81a, 82a of the first spark plug 81 and the second spark plug 82 (see FIG. 3(C)). One or two flame sensors 9 are provided for one cylinder 71. In practice, the flame sensor 9 is provided on the inner circumferential wall surface 71a of the cylinder 71, equidistant from the respective positions of the gaps 81a, 82a of the first spark plug 81 and the second spark plug 82.

[0036] The flame sensor 9 comprises an insulator section 91, a case section 92, connector sections 93a and 93b, a first electrode 94a, a second electrode 94b, and connecting wires 95a and 95b connecting the connector section 93a to the first electrode 94a and the connector section 93b to the second electrode 94b, respectively (see Figs. 3(D), 4(A), and (B)). That is, the connector section 93a and the first electrode 94a are electrically connected by the connecting wire 95a, and the connector section 93b and the second electrode 94b are electrically connected by the connecting wire 95b. A gap is provided between the first electrode 94a and the second electrode 94b, and the gap is called a gap 94s between the first electrode 94a and the second electrode 94b (see Figs. 4(A) and (B)).

[0037] The flame sensor 9 is attached to the inner peripheral wall surface 71a of the cylinder 71 so that the flame sensor 9 is embedded in the inner peripheral wall surface 71a (see Figs. 3(C) and (D)). Specifically, an external thread 92a is formed in a part of the case portion 92 of the flame sensor 9 (see Fig. 4(A)), and a mounting hole 71b for the flame sensor 9 is formed in the inner peripheral wall surface 71a of the cylinder 71. An internal thread 71c is formed in the mounting hole 71b. The external thread 92a of the flame sensor 9 and the internal thread 71c of the mounting hole 71b are screwed together, and the flame sensor 9 is attached to the inner peripheral wall surface 71a of the cylinder 71 (see Figs. 3(C) and (D)).

[0038] As mentioned above, the flame sensor 9 serves to detect the strength of the flame K caused by the explosion of gas fuel in the cylinder 71, and transmits the state of the flame to the ECU 4 connected to the flame sensor 9, thereby allowing the ECU 4 to determine whether or not to supply support gas G2 into the mixer 3 (see Figures 5 and 6).

[0039] Hereinafter, a process of determining whether or not the support gas G2 is supplied to the mixer 3 by the flame sensor 9 and the ECU 4 will be described. First, when the gas engine 7 is in operation, the gas fuel explodes in the cylinder 71 by the first ignition plug 81 and the second ignition plug 82, and the flame particles ka of the flame K caused by this explosion surround the first electrode 94a and the second electrode 94b of the flame sensor 9 (see Fig. 4(C) and Fig. 5(B)). When a large number of flame particles ka sufficiently reach both the first electrode 94a and the second electrode 94b, an ion current is generated in the gap 94s between the first electrode 94a and the second electrode 94b, and the ECU 4 determines that the flame K is stable, and does not supply the support gas G2 (see Fig. 5(B) and Fig. 4(C)).

[0040] The situation at this time is the normal combustion region in the explanatory diagram showing the flame state in Fig. 5(A), specifically, the portion (1). Furthermore, even if the momentum of the explosion of the gas fuel weakens and the number of flame particles ka reaching the gap 94s between the first electrode 94a and the second electrode 94b of the first electrode 94a and the second electrode 94b starts to decrease, when the ECU 4 determines that the explosion can be maintained, the support gas G2 is not supplied [see Fig. 5(A) (2) and Fig. 5(C)].

[0041] Next, when flame particles ka due to the explosion of the gas fuel do not sufficiently reach the first electrode 94a and the second electrode 94b, no current is generated in the gap 94s between the first electrode 94a and the second electrode 94b, and the ECU 4 determines that the state of the flame K is unstable (see Fig. 6(B) and Fig. 4(D)). The ECU 4 determining that the state of the flame K is unstable means that the ECU 4 determines that very few flame particles ka reach the gap 94s between the first electrode 94a and the second electrode 94b of the flame sensor 9.

[0042] At this time, the ECU 4 makes a decision to supply the support gas G2, and supplies the support gas G2 to the mixer 3. The situation at this time is in the "flame reaches but is weak" region, specifically, part (3) in the explanatory diagram showing the flame state in Fig. 6(A). Also, when the flame particles ka due to the explosion of the gas fuel do not completely reach the first electrode 94a and the second electrode 94b, a misfire occurs (see Fig. 6(C) and Fig. 4(E)).

[0043] Further, to describe the state of the flame K in detail, the flame K propagates, but the outer periphery of the flame K, where the molecules are activated, is ionized and conductive. In the results of high-speed photography in a model experiment, the flame K caused by the explosion of the mixed gas of the mixed gas fuel G3 and the air G0 ignited by the spark of the first spark plug 81 (or the second spark plug 82) spreads concentrically, but the two flames K, K that grow and expand from the gaps 81a, 82a of the first spark plug 81 and the second spark plug 82, respectively, come into contact and spread in the vertical direction (see FIG. 5(B)). This is thought to be because the fronts (tip portions) of the flame K are both positive and repel each other.

[0044] The flame sensor 9 is attached to the portion where the first spark plug 81 and the second spark plug 82 are farthest from each other and where the arrival of the flame K is the latest, and detects the state and sends the result to the ECU 4. When the ECU 4 determines through the flame sensor 9 that the arrival state of the flame K is deteriorating, it increases the outlet pressure of the support gas low pressure regulating valve 23 to increase the flow rate of the support gas G2. In other words, when misfire is likely to occur in the cylinder 71, the ECU 4 issues a command to the support gas low pressure regulating valve 23 to increase the flow rate of the support gas G2, thereby controlling the pressure P2 of the support gas G2 to be slightly higher.

[0045] Next, the state of the flame K of the explosion of the mixed gas of the mixed gas fuel G3 and the air G0 ignited by the first spark plug 81 and the second spark plug 82 in the cylinder 71 and the flame sensor 9 will be described. First, as shown in FIG. 5, the flame K spreads in a concentric shape from the gaps between the first spark plug 81 and the second spark plug 82. At this time, since the flame K is charged, the flames K, K generated from the gaps 81a, 82a of the first spark plug 81 and the second spark plug 82 repel each other when their flame fronts (also called "flame fronts") approach each other, and the flame fronts spread so as to become longer along the imaginary second straight line L2 perpendicular to the imaginary first straight line L1 connecting the first spark plug 81 and the second spark plug 82. Therefore, it takes a certain time from the explosion for the two flames K, K generated by the first spark plug 81 and the second spark plug 82 to spread and reach the flame sensor 9.

[0046] The main fuel gas G1 contains a large amount of CO2, and in order to burn the main fuel gas G1, it is necessary to add the support gas G2 to make the mixed gas fuel G3 regardless of whether the air-fuel ratio is theoretical or not. When the flame K caused by the mixed gas of the mixed gas fuel G3 and the air G0 spreads in the cylinder 71, and the flame front reaches the positions of the first electrode 94a and the second electrode 94b of the flame sensor 9, a sufficient ion current flows in the gap 94s between the first electrode 94a and the second electrode 94b (see FIG. 4(C)), which indicates that stable combustion is realized (see FIG. 5(A) and (B)).

[0047] If the combustion state is poor, even if the flame front reaches both the first electrode 94a and the second electrode 94b of the flame sensor 9, the ion current becomes small (see FIG. 4(D)). Here, even if the flame K weakens somewhat, or the amount of flame particles ka reaching the first electrode 94a and the second electrode 94b decreases, the operation continues in the same state (see FIG. 5(C)). Furthermore, if the flame K does not reach the flame sensor 9, no ion current flows through the gap 94s between the first electrode 94a and the second electrode 94b of the flame sensor 9 (see FIG. 4(E)), and the ECU 4 issues a command to increase the amount of the support gas G2 (see FIG. 6(A) and (B)). Note that FIG. 6(C) shows a completely misfired state.

[0048] Next, for reference, the time it takes for flame K to reach the entire cylinder 71 after it is generated by the first spark plug 81 and the second spark plug 82 will be described. For the engine to operate stably regardless of the engine speed, the crankshaft must rotate within 120 degrees once it enters the expansion stroke. Converting this to time, in the case of 2500 rpm, it is 60 s / 2500r×120 degrees / 360 degrees=0.008 s. In other words, the time it takes for flame K to reach the entire cylinder 71 after it is generated by the first spark plug 81 and the second spark plug 82 is 8 ms.

[0049] An O2 sensor 54 may also be provided in the exhaust system (exhaust pipe on the exhaust port 74 side, etc.) of the gas engine 7 (see FIG. 1). The pressure of the gas fuel supplied to the mixer 3 is adjusted by the support gas low pressure regulating valve 23 so that the air-fuel ratio is the theoretical air-fuel ratio according to a signal from the O2 sensor 54 attached to the exhaust system. A three-way catalyst 55 is provided downstream of the exhaust system to render HC / CO / NOx in the exhaust harmless, but in order to do so, the engine must be operated at the theoretical air-fuel ratio so that neither oxygen nor combustible substances (fuel) remain after combustion in the cylinder 71.

[0050] For this purpose, the O2 sensor 54 detects the O2 concentration in the exhaust gas, and the ECU 4 performs feedback control so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. Specifically, even if the air-fuel ratio detected by the O2 sensor 54 is judged to be leaner than the stoichiometric air-fuel ratio, the flow rate of the support gas G2 is increased. The air-fuel ratio is adjusted by increasing or decreasing the flow rate of the support gas G2, not the main fuel (main fuel gas G1) whose combustible components are unclear. In this way, by using the O2 sensor 54 and the flame sensor 9 in combination, the mixture ratio of the main fuel gas G1 and the support gas G2 in the mixed gas fuel G3 in the gas fuel (mixed gas fuel G3 and air G0) in the cylinder 71 through the mixer 3 can be maintained well, that is, the mixture ratio can be maintained at the stoichiometric air-fuel ratio or approximately the stoichiometric air-fuel ratio, and a good combustion state in the cylinder 71 can be maintained.

[0051] The main fuel gas container 11 is filled with main fuel gas G1, which is a crude gas. The main fuel gas container 11 is provided with a primary pressure reducing valve 11a. The main fuel gas container 11 and the mixer 3 are connected by a main fuel gas pipe 51. A main fuel gas shutoff valve 12, a main fuel gas low pressure regulating valve 13, and a main fuel gas pressure sensor 14 are provided in series in the main fuel gas pipe 51 between the main fuel gas container 11 and the mixer 3 (see FIG. 1).

[0052] The main fuel gas G1 discharged from the main fuel gas container 11 is reduced in pressure to about 50 kPa by the primary pressure reducing valve 11a attached to the main fuel gas container 11, and is further reduced in pressure to about 3 kPa, close to atmospheric pressure, by the main fuel gas low pressure regulating valve 13. At this time, if the main fuel gas G1 discharged from the main fuel gas container 11 can be reduced in one go to a pressure of about 3 kPa, close to atmospheric pressure, by the primary pressure reducing valve 11a, the main fuel gas low pressure regulating valve 13 need not be provided and may be unnecessary.

[0053] The support gas container 21 is filled with the support gas G2. The support gas container 21 is provided with a primary pressure reducing valve 21a. The support gas container 21 and the mixer 3 are connected by a support gas pipeline 52. A support gas shutoff valve 22 and a support gas low pressure regulating valve 23 are provided in series in the support gas pipeline 52 between the support gas container 21 and the mixer 3. The support gas G2 discharged from the support gas container 21 is reduced in pressure to about 50 kPa by the primary pressure reducing valve 21a attached to the support gas container 21, and is further reduced in pressure by the support gas low pressure regulating valve 23 to a pressure close to atmospheric pressure of about 3 kPa.

[0054] In particular, the combustible gases in the main fuel gas G1 include carbon monoxide CO, hydrogen H2, and methane CH4, but these gases have high ignition temperatures and cannot be ignited by compression heat like diesel engines. Therefore, in order to ignite with an electric spark and help the flame spread, it is possible to create a spark ignition engine system in which propane C3H8, which is easy to obtain, is premixed with the main fuel gas G1 as a support gas.

[0055] The mixer 3 has a mixer body 31 and a throttle 32. The mixer body 31 has a first inlet 31a, a second inlet 31b, and an introduction pipe 31c. A venturi section 31d is formed in the introduction pipe 31c. An annular space 31e is formed on the outer periphery of the venturi section 31d via a partition wall 31f (see Figs. 7A and 7B). An annular slit 31g is formed in the partition wall 31f, and the annular space 31e communicates with the inside of the venturi section 31d via the annular slit 31g.

[0056] In addition, both the first inlet portion 31a and the second inlet portion 31b are connected to the annular space 31e. In other words, the first inlet portion 31a and the second inlet portion 31b are configured to be connected via the annular space 31e. A throttle 32 is provided on the discharge side of the venturi portion 31d. The first inlet portion 31a of the mixer 3 is connected to a main fuel gas pipe 51 of the main fuel gas system, and serves as an inlet for the main fuel gas G1. The second inlet portion 31b is connected to a support gas pipe 52 of the support gas system, and serves as an inlet for the support gas G2. The mixer 3 is sucked into the cylinder of the two-point ignition gas engine 7 through the intake manifold and the intake valve.

[0057] Next, the main fuel gas low pressure regulating valve 13 and the support gas low pressure regulating valve 23 will be described. The main fuel gas low pressure regulating valve 13 and the support gas low pressure regulating valve 23 have the same structure and differential, and the main fuel gas low pressure regulating valve 13 will be mainly described (see FIG. 7(C)). Note that the reference numerals in parentheses refer to the support gas low pressure regulating valve 23. When no signal is received from the low pressure controller or ECU 4, the seal member 13c (23c) at the tip of the armature 13a (23a) is pushed back by the spring 13b (23b) to block the nozzle 13d (23d).

[0058] When a pulse signal is received from the ECU 4, the magnetic force generated by the coil 13h (23h) pulls up the armature 13a (23a), creating a gap ks, and the main fuel gas G1 from the main fuel gas container 11 (the primary pressure reducing valve 11a) flows into the small chamber 13f (23f) partitioned by the diaphragm 13e (23e). The main fuel gas G1 then flows out to the shutoff valve or mixer 3, lowering the pressure in the small chamber 13f (23f). The main fuel gas low pressure regulating valve 13 and the support gas low pressure regulating valve 23 are formed with through holes that open to the atmosphere. These are atmosphere vent holes 13g (23g), and serve to improve the movement of the diaphragm 13e (23e).

[0059] A square-wave signal that drives the armature 13a (23a) is input from the ECU 4 to the coil 13h (23h). Figure 8(A) shows the form of this signal. When the engine is running, electricity is applied for t(S) with a period of to(s) (frequency is 1 / to). When electricity is applied, a magnetic field is generated, and the armature 13a (23a) is pulled up against the force of the spring 13b (23b), forming a gap ks through which the main fuel gas G1 (support gas G2) flows. Here, the results of a separate visualization experiment showed that the seal member 13c (23c) is not flapping, but rather the gap ks becomes larger as the duty increases. This is due to the inertia and hysteresis of the moving parts.

[0060] Moreover, reference numeral 13j denotes an inlet of the main fuel gas low pressure regulating valve 13, which communicates with the main fuel gas container 11 and the main fuel gas shutoff valve 12 via a main fuel gas pipe 51, and serves to supply the main fuel gas G1 into the main fuel gas low pressure regulating valve 13 via the main fuel gas container 11 and the main fuel gas shutoff valve 12. Reference numeral 13k denotes an outlet of the main fuel gas low pressure regulating valve 13, which communicates with the mixer 3, and serves to supply the main fuel gas G1 to the mixer 3.

[0061] Furthermore, reference symbol 23j denotes an inlet of the support gas low pressure regulating valve 23, which communicates with the support gas container 21 and the support gas shutoff valve 22 via a support gas pipe 52 and serves to supply the support gas G2 into the support gas low pressure regulating valve 23 via the support gas container 21 and the support gas shutoff valve 22. Reference symbol 23k denotes an outlet of the support gas low pressure regulating valve 23, which communicates with the mixer 3 and serves to supply the support gas G2 to the mixer 3.

[0062] Next, for reference, we will discuss whether the main fuel gas (for convenience, referred to as S gas "main fuel gas G1") produced by fermenting livestock manure or steaming food waste in an oxygen-free environment, whose volumetric composition is 40% methane (CH4), 30% carbon monoxide (CO), and 30% carbon dioxide (CO2), can be burned inside the cylinder 71.

[0063] Calculate the mass of each component in 1 mole (22.4 liters under standard conditions) of S gas (main fuel gas G1). The molecular weight of CH4 is 16, so the mass of 0.4 moles is 16 x 0.4 = 6.4g. The molecular weight of CO is 28, so the mass of 0.3 moles is 28 x 0.3 = 0.34g. The molecular weight of CO21 is 44, so the mass of 0.3 moles is 44 x 0.3 = 13.2g. Therefore, the mass of 1 mole of S gas (main fuel gas G1) is 25 g (almost equal to air). Density of S gas (main fuel gas G1) (1m 3 The mass (kg) is 28g x 1000 / 22.4 = 1.25kg / m 3

[0064] Next, calculate the calorific value of S gas (main fuel gas G1). The calorific value of CH4 is 36.1Mj / m 3 So 0.44m 3 So 36.1×0.4=14.44 The calorific value of CO is 12.66 Mj / m 3 So 0.3m 3 So 12.6×0.3=3.8 Since the calorific value of CO2 is 0, 0x0.3=0.

[0065] Therefore, S gas (main fuel gas G1) 1m 3 The calorific value is 18.2Mj / m 3 This is 90.7M j / m for propane (C3H8). 3 This is approximately 20% of the total fuel, so it is deemed worthwhile to regenerate it. However, carbon dioxide (CO2), which is also used in fire extinguishers, accounts for 30% of the main fuel, and so does not enter the flammable range within cylinder 71. This will be explained below. When the amount of exhaust gas recirculation (EGR) is increased to the engine's operating limit in a two-point ignition gasoline engine, in the case of a theoretical air-fuel ratio, the limit for stable combustion is a CO2 concentration of 10% in the mixture drawn into cylinder 71.

[0066] Therefore, assuming that the engine can be operated using only S gas (main fuel gas G1), the theoretical air-fuel ratio of S gas (main fuel gas G1) is calculated. First, the mass of air required to burn 1 mole (28 g) of S gas (main fuel gas G1) is calculated.

[0067] CH4 + 2O2=CO2 + 2H2O This means 2 moles of O2 are required. If there is 0.4 moles of CH4, then 2 moles x 0.4 = 0.8 moles of O2 are required. CO+1 / 2O2=CO2, which means 1 / 2 mole of O2 is required. If there are 0.3 moles of CO, then 0.5 moles x 0.3 = 0.15 moles of O2 are required. CO2 does not burn, so O2 is not required. To burn 1 mole of S gas (main fuel gas G1), 0.8 + 0.15 moles = 0.995 moles (30.4 g) of O2 are required.

[0068] On the other hand, the mass of O2 in 1 mole of air (28.8 g) is 32g × 0.21 = 6.72, so (30.4g / 6.72) × 28.8 = 130.3g of air is required. Therefore, the theoretical air-fuel ratio of the main fuel gas G1 is 130.3 / 28g=4.6 4 The theoretical air-fuel ratio is smaller than that of propane (15.6) and gasoline (14.7), which means that there are fewer components that can burn.

[0069] We will consider whether or not combustion can occur within the cylinder, based on a 10% standard. Omitting the chemical and mathematical formulas, 101.3 liters are required to burn 1 mole 28g of S gas (main fuel gas G1). This is equivalent to 130.2g at 4.522 molar mass. The theoretical air-fuel ratio of the main fuel gas G1 is 130.2g / 28g=4.65, That's significantly less than the 15.6 for propane and 14.7 for gasoline, which means there's less to burn.

[0070] Next, we will consider whether or not the CO2 concentration just before ignition can be burned in the cylinder based on the aforementioned standard of 10% or less. The volume ratio of the support gas to the S gas (main fuel gas G1) is calculated so that the CCb concentration in the mixture sucked into the cylinder 71 described above is 10% or less. If the amount of propane required to burn S gas (main fuel gas G1), which cannot burn on its own, by adding a combustion support gas (hereinafter, support gas) and co-firing it is X moles, then: 0.1 ≧ (number of moles of CO2 in 1 mole of S gas (main fuel gas G1)) / {(number of moles of CO2 in 1 mole of S gas (main fuel gas G1) and the number of moles of air needed to burn it) + (X moles of propane and the number of moles of air needed to burn it)} · · · (1) If we put the values ​​we have found so far into this, we get 0.1 ≧ (0.3 moles) / {(1 + 4.52 moles) + (X + 23.7X) · · · (1') Solving this, we find that X≧0.121, in other words, propane (C3 H8) is required in a volumetric proportion of 12.1% or more of the S (crude) gas (main fuel gas G1).

[0071] Even if the engine is operating at the stoichiometric air-fuel ratio with the above-mentioned support gas ratio, if the amount of support gas is small, the combustion in the cylinder 71 becomes uneven, causing large rotation fluctuations, and if it increases further, the engine will stop. Before explaining the means for controlling multi-fuel combustion, the relationship between the output signal (electromotive force) of the platinum-zirconia O2 sensor 54 and the air-fuel ratio in Figure 8(C) is shown. The electromotive force changes significantly around the stoichiometric air-fuel ratio, but 0.5 V can be said to be the stoichiometric air-fuel ratio. As shown in the upper diagram of Figure 8(C), the outlet pressure P2 of the support gas low pressure regulating valve 23 is adjusted to P50. When the duty t / t0, which will be explained next, increases, the air-fuel ratio becomes smaller (richer).

[0072] A method of controlling the pressure of the main fuel gas G1 and the support gas G2 entering the mixer 3 will be described with reference to Fig. 7(C). A square wave signal that drives the armature 13a (23a) is input from the battery 57 to the coil 13h (23h) of the main fuel gas low pressure regulating valve 13 (support gas low pressure regulating valve 23). Fig. 8(A) shows the form of this signal. When the engine is running, electricity is applied for only t(S) with a period of t0 and (s) (frequency is 1 / t0).

[0073] When electricity is applied, a magnetic field is generated and the armature 13a (23a) is pulled up against the force of the spring 13b (23b), creating a gap 58 through which gas can flow. Here, the results of a separate visualization experiment showed that the seal member 13c (23c) does not flap, but the gap becomes larger as the duty increases. This is due to the inertia and hysteresis of the moving parts.

[0074] Even if the mixture of the mixed gas fuel G3 of the main fuel gas G1 and the support gas G2 and the air obtained by the formula (1) and formula (1') is at the theoretical air-fuel ratio, the CO2 in the main fuel may hinder the flame propagation. If this causes the combustion to become disturbed, the signal of the flame sensor 9 will be disturbed. The flame detection signal appears with a delay of t (s) from the ignition signal. This t is different from the t used in the explanation of the duty in Figure 8 (A).

[0075] In Fig. 5(A), (1) shows that the flame K has correctly reached the gap 94s between the first electrode 94a and the second electrode 94b of the flame sensor 9. Also, Fig. 5(B) shows the state of Fig. 5(A) (1). In Fig. 5(A) (2), a weak flame K has reached the gap 94s between the first electrode 94a and the second electrode 94b of the flame sensor 9. In Fig. 6(A) (3), the flame K reaches the gap 94s between the first electrode 94a and the second electrode 94b of the flame sensor 9 late and is weak, but it has still propagated.

[0076] (4) in Figure 6(A) shows a misfire state in which the flame K does not reach the gap 94s between the first electrode 94a and the second electrode 94b of the flame sensor 9. This phenomenon can occur even when operating at the stoichiometric air-fuel ratio due to the extinguishing action of CO2 in the main fuel gas G1. When the ECU 4 determines that a misfire has occurred, increasing the duty cycle described above increases P2 in Figures 1 and 8(C). For example, if the pressure P1 in Figure 1 is 2.8 kPa, adjust the pressure P2 to 4.5 kPa until misfire is no longer detected. As shown in Figure 8(C), P2 is always greater than P1. The pressure P1 of the main fuel gas G1 is not changed.

[0077] If the ECU 4 judges that there is a misfire, increasing the duty as described above will increase P2 in Figures 1 and 8 (C). For example, if the pressure P1 in Figure 1 is 2.8 kPa, the pressure P2 is adjusted to 4.5 kPa, and so on, until the misfire is no longer detected. As shown in Figure 8 (B), the pressure P2 is always greater than the pressure P1. The pressure P1 of the main fuel gas G1 is not changed.

[0078] In FIG. 1, reference numeral 53 denotes a generator, reference numeral 54 denotes an O2 sensor, reference numeral 55 denotes a three-way catalyst, reference numeral 56 denotes a muffler, reference numeral 57 denotes a battery, reference numeral 58 denotes a crank sensor, reference numeral 59 denotes a flywheel, and reference numeral 14 denotes a main fuel gas pressure sensor. [Explanation of symbols]

[0079] 11...Main fuel gas cylinder, 21...Support gas pressure cylinder, 3...Mixer, 4...ECU 54...O2 sensor, 7...gas engine, 71...cylinder, 71a...inner peripheral wall surface, 81...first spark plug, 82...second spark plug, 84...intake valve, 85...exhaust valve, 9...flame sensor, 91...insulator portion, 94a...first electrode, 94b: second electrode; 94s: gap; L1: virtual first straight line; L2: virtual second line, G1: main fuel gas G1, G2: support gas, G3...mixed gas fuel, G0...air, K...flame, ka...flame particles.

Claims

1. The present invention relates to a fuel cell system for generating a fuel mixture comprising: a main fuel gas container for storing a bio-based main fuel gas; a support gas pressure container for storing a non-bio-based support gas; a gas engine; and a mixer for supplying a mixed gas fuel obtained by mixing the main fuel gas and the support gas to the gas engine; The gas engine has two ignition plugs, an intake valve, and an exhaust valve arranged in a cylinder, and two flame sensors for detecting the strength of the flame are attached to the inner wall surface of the cylinder at a predetermined distance from both of the ignition plugs, and both flame sensors are connected to an ECU, and when the explosive power of the flame in the cylinder is below a predetermined level, the ECU supplies the support gas into the cylinder.

2. 2. The gas engine power generation system according to claim 1, wherein each of the flame sensors has a first electrode and a second electrode within an insulator portion and whose tips protrude from the insulator portion, a gap is formed between the first electrode and the second electrode, and when flame particles reach the gap sufficiently, a current is generated in the gap and the ECU determines that the flame is stable, and when flame particles do not reach the gap sufficiently, no current is generated in the gap and the flame is determined to be unstable, and the ECU supplies the support gas.

3. 3. The gas engine power generation system according to claim 1, further comprising an O2 sensor disposed in the exhaust system.

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