Gas engine power generation system

Abstract

To provide a gas engine power generation system with extremely high operating efficiency, which is operated by fuel generated from organic matter such as food residues and animal excrement heated in an oxygen-free state and which operates by effectively burning combustible substances in the fuel. [Configuration] The system comprises 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 an exhaust valve 85 arranged in a cylinder 71, and a flame sensor 9 for detecting the strength of a flame K attached to an inner peripheral wall surface 71a of the cylinder 71 at a predetermined distance from both spark plugs 81, 82, the flame sensor 9 being connected to an ECU 4, and when the explosive power of the flame K in the cylinder 71 is below a predetermined level, 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 with extremely high operating efficiency that runs on fuel produced from organic matter such as food waste and animal manure heated in an oxygen-free environment, and that can operate by effectively burning the combustible substances in the fuel. [Background technology]

[0002] Typically, livestock excrement, food waste, and residues are treated by steaming them in an oxygen-free environment, solidifying them, and then landfilling them. This process generates gases that are released into the atmosphere, resulting in environmental pollution. In recent years, engines that run on gases generated from organic matter, such as livestock excrement, food waste, and residues (also called biogas fuels), have come into use for power generation or general motive power. Patent Document 1 (JP 2009-174392 A) is an example of a conventional technology using such biogas fuels. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-174392 Summary of the Invention [Problem to be solved by the invention]

[0004] When food waste is fermented or industrial waste is steamed in an oxygen-free environment to reduce its volume, gas containing combustible gas is generated. For convenience, this gas will be referred to as S gas (main fuel gas G1). Although the proportion of combustible gas in S gas (main fuel gas G1) is small, 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 S gas (main fuel gas G1) could be burned inside the engine cylinder and its energy converted into power to drive a generator, it 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 these gases have high ignition temperatures and cannot be ignited by the heat of compression like in a diesel engine.

[0006] Furthermore, the use of crude gas made from biogas fuel in a gas engine presents the following problems. First, as mentioned above, crude gas is a so-called artificial gas made from livestock manure or food waste. Furthermore, crude gas may contain inorganic substances such as CO and H2. As a result, the production volume of this crude gas is smaller than that of natural gas (propane or methane). Therefore, it is difficult to secure a quantity sufficient to power 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 directly to a Stirling engine.

[0007] Next, livestock manure or food waste is steamed or fermented in an oxygen-free environment, generating combustible gas (called crude gas). This gas is used as fuel for gas engines, but this crude gas often contains a large amount of carbon dioxide (CO2). Typically, with technologies such as those described in Patent Document 1, gas turbines or Stirling engines use continuous combustion, making it possible to burn fuel even if it contains a certain amount of carbon dioxide. However, spark-ignition engines use intermittent combustion, repeating intake, compression, ignition, expansion, and exhaust cycles, and carbon dioxide in the fuel can interfere with ignition, flame kernel formation, and flame propagation. For these reasons, 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 could be used as fuel for a spark-ignition engine of 200 kW or less, and converted into electrical energy instead of being discarded, this would be an effective use of recycled resources and would 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 use of bio-based crude gas consisting of livestock manure or food residues 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 extensive research to solve the above-mentioned problems, and as a result, have come up with the invention of claim 1, a gas engine power generation system 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 consisting of a mixture of the main fuel gas and the support gas to the gas engine, wherein the gas engine has two spark plugs, an intake valve, and an exhaust valve disposed in a cylinder, and a flame sensor for detecting the strength of a flame attached to an inner peripheral wall surface of the cylinder at a predetermined distance from both spark plugs, the flame sensor being connected to an ECU, and when the explosive power of the flame in the cylinder is below a predetermined value, the ECU supplies the support gas into the cylinder, thereby solving the above-mentioned problems.

[0011] The above problem was solved by the invention of claim 2, which is a gas engine power generation system as described in claim 1, characterized in that the flame sensor is provided at at least one of the two contact points between an imaginary second line perpendicular to the center of an imaginary first line connecting both of the ignition plugs and the inner wall surface of the cylinder.

[0012] The above problem was solved by the invention of claim 3, which is a gas engine power generation system as described in claim 1, characterized in that the flame sensors are provided at both contact points between an imaginary second line perpendicular to the center of an imaginary first line connecting both of the ignition plugs and the inner wall surface of the cylinder.

[0013] The above problem is solved by the invention of claim 4, which is a gas engine power generation system as defined in claim 1 or 2, wherein the flame sensor has a first electrode and a second electrode within an insulator section with tips protruding 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.

[0014] The invention of claim 5 is 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, thereby solving the above problem. [Effects of the Invention]

[0015] The invention of claim 1 comprises 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, and the gas engine has two ignition plugs, an intake valve, an exhaust valve, and a flame sensor arranged within a cylinder.

[0016] The flame sensor is attached to the inner wall surface of the cylinder at a predetermined distance from both the spark plugs and serves to detect the strength of the flame during combustion of gas fuel in the cylinder. The flame sensor is connected to an ECU (engine control unit) and is configured to supply the support gas into the cylinder when the explosive power of the flame in the cylinder is below a predetermined value.

[0017] 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, allowing a good mixed gas to be sent into the cylinder of the gas engine via the mixer.

[0018] In this way, in the present invention, with an extremely simple configuration in which a flame sensor is installed inside the cylinder, the ECU (engine control unit) determines the state of the flame of the fuel ignited by the spark from the spark plug, and maintains a good ratio of main fuel gas to support gas in the mixed gas fuel inhaled into the cylinder via the mixer, thereby maintaining good operation of the gas engine.

[0019] In the invention of claim 2, the flame sensor is configured to be located at at least one of the two points of contact between an imaginary second line perpendicular to the center of an imaginary first line connecting the two spark plugs and the inner wall surface of the cylinder, so that the flame sensor is positioned at an equal distance from the two spark plugs, and the flame sensor can more accurately detect (sense) the flames ignited from the two spark plugs, and transmit this information to an ECU, allowing the ECU to determine whether or not to supply support gas to the gas fuel.

[0020] In the invention of claim 3, the flame sensors are configured to be installed at both points of contact between an imaginary second line perpendicular to the center of an imaginary first line connecting both of the ignition plugs and the inner wall surface of the cylinder, so that two flame sensors are installed in the cylinder.By installing these two flame sensors, it is possible to further improve the accuracy of detecting (sensing) the flames ignited by both of the ignition plugs, and therefore it is possible to maintain even better combustion conditions in the cylinder.

[0021] In the invention of claim 4, the flame sensor has a first electrode and a second electrode within the 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.This makes the flame sensor extremely simple in configuration and capable of detecting (sensing) the state of gas fuel in the cylinder with high accuracy.

[0022] In the invention of claim 5, in the gas engine power generation system described in claim 1 or 2, an O2 sensor is arranged 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 can be maintained well via the mixer, that is, maintained at the stoichiometric air-fuel ratio or an approximately stoichiometric air-fuel ratio, and good combustion conditions can be maintained in the cylinder. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic diagram illustrating the overall configuration of the present invention. [Figure 2] FIG. 2 is a process diagram (flowchart diagram) showing the operation of the present invention. [Figure 3](A) is a cross-sectional view of the main part showing the position of the flame sensor in the cylinder and cylinder head of the gas engine of the present invention, (B) is a cross-sectional view taken along the Y1-Y1 arrow of (A), (C) is a cross-sectional view taken along the X1-X1 arrow 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 FIGS. 1C to 1E are enlarged views of the respective states of the (β) portion of FIG. 1B. [Figure 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 the mixer, FIG. 1B is a plan view of the mixer, and FIG. 1C is a longitudinal sectional front view of the main fuel gas low pressure regulating valve and the 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 stoichiometric air-fuel ratio in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] 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 system including a main fuel gas container 11, a main fuel gas shutoff valve 12, a main fuel gas low-pressure regulating valve 13, and a main fuel gas pressure sensor 14, and a support gas system including a support gas container 21, a support gas shutoff valve 22, and a support gas low-pressure regulating valve 23, as well as 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 equipped with a flame sensor 9 (see FIG. 3). The main fuel gas container 11 is filled with main fuel gas G1, and the support gas container 21 is filled with support gas G2.

[0025] The respective pieces of equipment are connected to each other by 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 air G0.

[0026] With this configuration, the main fuel gas G1, which is a biomass-based raw gas, and the supporting gas G2, such as city gas, are mixed in the mixer 3 and supplied to the gas engine 7 as a mixed gas fuel G3, which is then used to operate the gas engine 7 together with separately supplied air G0 (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 supporting gas G2 is a common gas, such as city gas.

[0027] The configuration of the gas engine power generation system of the present invention is shown as a schematic configuration diagram in Fig. 1. Fig. 2 is a process diagram (also called a flow chart) showing the operation of the gas engine power generation system of the present invention, and Fig. 2 shows the process from mixing 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 mixer 3 to generating mixed gas fuel G3 and supplying the mixed gas fuel G3 to the gas engine 7.

[0028] The main fuel gas container 11 and the support gas container 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 container 11 and the support gas G2 in the support gas container 21 are sent to the mixer 3 by 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, producing a mixed gas fuel G3 inside the mixer 3.

[0029] The gas engine 7 includes a cylinder 71 and a cylinder head 72, with one or more cylinders 71 and cylinder heads 72 arranged in series (see FIG. 3). A piston is housed in the cylinder 71 so that it can move up and down. A cylinder head 72 is provided on top of the cylinder 71, and the lower surface of the cylinder head 72 forms an inner head top wall surface 72a. The inner head top wall surface 72a has a substantially spherical shape, more specifically, a flattened spherical concave surface (see FIG. 3(B)). The cylinder head 72 is provided with an intake port 73 and an exhaust port 74, and the openings of the intake port 73 and the exhaust port 74 are respectively formed in the inner head top wall surface 72a. The horizontal cross section of the cylinder 71 is a perfect circle.

[0030] The cylinder head 72 is provided with two spark plugs 81, 82, an intake valve 84, and an exhaust valve 85 (see Figures 3(A) and 3(B)). When viewed in a plan view from the top side of the cylinder head 72 (or the cylinder 71), 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 Figure 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.

[0031] 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)). To distinguish between the two spark plugs 8 for ease of explanation, one of them will be referred to as the first spark plug 81 and the other as the second spark plug 82. Here, the first spark plug 81 is assumed to be 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.

[0032] Next, we will explain the flame sensor 9. The role of the flame sensor 9 is to detect the state of the flame caused by the explosion of a mixed gas of mixed gas fuel G3, which is the fuel gas, and air G0 inside the cylinder 71. A signal from the flame sensor 9 detecting the strength of the flame is sent to the ECU (engine control unit) 4, which then determines whether the mixed state of mixed gas fuel G3 and air G0 is good or bad, and further determines whether or not to supply support gas G2 to the mixer 3 (see FIGS. 1 and 2).

[0033] The flame sensor 9 is attached to the circumferential inner 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), and (C)). The predetermined distance is a substantially long distance, and specifically, the flame sensor 9 is attached to the inner 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 attaching the flame sensor 9 inside the cylinder 71 as far 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.

[0034] To describe in detail how the flame sensor 9 is mounted inside the cylinder 71, an imaginary first line L1 connecting the first spark plug 81 and the second spark plug 82 is set inside the cylinder 71, and an imaginary second line L2 is set in the horizontal direction perpendicular to the center of the imaginary first line L1 (see FIG. 3(C)). Both the imaginary first line L1 and the imaginary second line L2 pass through the diametric center Q of the circumference of the cylinder 71. Furthermore, the imaginary first line L1 and the imaginary second line L2 are different in the height direction and do not intersect.

[0035] Next, the locations where both ends of the imaginary second straight line L2 abut against the inner circumferential wall surface 71a of the cylinder 71 are defined as the installation positions of the flame sensors 9 (see FIG. 3(C)). The flame sensors 9 are provided at the intersections of the inner circumferential wall surface 71a of the cylinder 71 and the imaginary second straight line L2. There are two intersections, and two flame sensors 9 are provided. It is also possible to provide the flame sensor 9 at only one of the two intersections. In other words, in this case, there is only one flame sensor 9. The location 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. In this case, the number of flame sensors 9 may be three or more.

[0036] In the present invention, the number of flame sensors 9 is two, and the description will be given assuming that the two flame sensors 9 are attached to the inner circumferential wall surface 71a of the cylinder 71. As described above, the 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 circumferential wall surface 71a of the cylinder 71. As described above, the imaginary first 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 of the imaginary first line L1 is located at the diametric center Q of the cylinder 71. Therefore, the imaginary second line L2, which intersects the horizontal direction at the center of the imaginary first line L1, also passes through the diametric center Q of the cylinder 71 (see FIG. 3C).

[0037] As a result, the position of the flame sensor 9 is equidistant from the positions of the gaps 81a, 82a of the first spark plug 81 and the second spark plug 82, respectively (see FIG. 3(C)). One or two flame sensors 9 are provided for each cylinder 71. In practice, the flame sensor 9 is provided on the inner circumferential wall surface 71a of the cylinder 71, equidistant from the positions of the gaps 81a, 82a of the first spark plug 81 and the second spark plug 82.

[0038] The flame sensor 9 comprises an insulator portion 91, a case portion 92, connector portions 93a and 93b, a first electrode 94a, a second electrode 94b, and connecting wires 95a and 95b connecting the connector portion 93a to the first electrode 94a and the connector portion 93b to the second electrode 94b, respectively (see FIGS. 3(D), 4(A), and 4(B)). Specifically, the connector portion 93a and the first electrode 94a are electrically connected by the connecting wire 95a, and the connector portion 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 this gap is referred to as a gap 94s between the first electrode 94a and the second electrode 94b (see FIGS. 4(A) and 4(B)).

[0039] 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 3(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 threadedly engaged, so that the flame sensor 9 is attached to the inner peripheral wall surface 71a of the cylinder 71 (see FIGS. 3(C) and 3(D)).

[0040] 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 by transmitting the state of the flame to the ECU 4 connected to the flame sensor 9, the ECU 4 determines whether or not to supply support gas G2 into the mixer 3 (see Figures 5 and 6).

[0041] The following describes a process by which the flame sensor 9 and the ECU 4 determine whether or not the support gas G2 is being supplied to the mixer 3. First, when the gas engine 7 is running, gas fuel explodes in the cylinder 71 through the first and second spark plugs 81 and 82, and flame particles ka of the flame K caused by this explosion surround the first and second electrodes 94a and 94b of the flame sensor 9 (see FIGS. 4(C) and 5(B)). When a large number of flame particles ka reach both the first and second electrodes 94a and 94b, an ion current is generated in the gap 94s between the first and second electrodes 94a and 94b, and the ECU 4 determines that the flame K is stable and does not supply the support gas G2 (see FIGS. 5(B) and 4(C)).

[0042] This situation corresponds to the normal combustion region in the flame state diagram of 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 begins to decrease, if the ECU 4 determines that the explosion can be maintained, the support gas G2 is not supplied (see (2) in Fig. 5(A) and Fig. 5(C)).

[0043] Next, when flame particles ka resulting from the explosion of 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 FIGS. 6(B) and 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.

[0044] At this time, the ECU 4 determines to supply the support gas G2, and supplies the support gas G2 to the mixer 3. This situation corresponds to the "flame reaches but is weak" region, specifically, part (3), in the flame state diagram of FIG. 6(A). Also, if the flame particles ka resulting from the explosion of the gas fuel do not completely reach the first electrode 94a and the second electrode 94b, a misfire state occurs (see FIG. 6(C) and FIG. 4(E)).

[0045] Further, to elaborate on the state of flame K, flame K propagates, but the outer periphery of flame K, where the molecules are activated, is ionized and conductive. The results of high-speed photography from a model experiment show that flame K, which is caused by the explosion of a mixed gas of mixed gas fuel G3 and air G0 ignited by a spark from the first spark plug 81 (or second spark plug 82), spreads concentrically, but also spreads vertically where the two flames K, K that grow and expand starting from the gaps 81a, 82a of the first spark plug 81 and the second spark plug 82 come into contact (see Figure 5(B)). This is thought to be because the fronts (tips) of flame K are both positive and repel each other.

[0046] Flame sensor 9 is attached to the part between first spark plug 81 and second spark plug 82 that is the farthest away and where flame K arrives the latest, and detects the situation and sends the information to ECU 4. When ECU 4 determines via flame sensor 9 that the situation of flame K is deteriorating, it increases the outlet pressure of support gas low pressure regulating valve 23 to increase the flow rate of support gas G2. In other words, when misfire is likely to occur in cylinder 71, ECU 4 issues a command to support gas low pressure regulating valve 23 to increase the flow rate of support gas G2, thereby controlling pressure P2 of support gas G2 to be slightly higher.

[0047] Next, the state of the flame K resulting from the explosion of the mixed gas of mixed gas fuel G3 and air G0 ignited by the first spark plug 81 and the second spark plug 82 in the cylinder 71, and the state of the flame sensor 9 will be described. First, as shown in FIG. 5 , the flame K spreads concentrically from the gaps between the first spark plug 81 and the second spark plug 82. Because the flame K is electrically 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 as their flame fronts (also referred to as "flame fronts") approach each other, and the flame fronts spread so as to become longer along an imaginary second line L2 that is perpendicular to an imaginary first line L1 connecting the first spark plug 81 and the second spark plug 82. Therefore, it takes a predetermined 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.

[0048] The main fuel gas G1 contains a large amount of CO2, and in order to combust the main fuel gas G1, it is necessary to add support gas G2 to produce mixed gas fuel G3, regardless of whether the air-fuel ratio is stoichiometric or not. When the flame K caused by the mixed gas of mixed gas fuel G3 and air G0 spreads inside 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)), indicating that stable combustion has been achieved (see FIGS. 5(A) and (B)).

[0049] If the combustion condition is poor, the ion current will be small even if the flame front reaches both the first electrode 94a and the second electrode 94b of the flame sensor 9 (see FIG. 4D). Even if the flame K weakens somewhat or the number of flame particles ka reaching the first electrode 94a and the second electrode 94b decreases, the engine will continue to operate in this state (see FIG. 5C). Furthermore, if the flame K does not reach the flame sensor 9, no ion current will flow through the gap 94s between the first electrode 94a and the second electrode 94b of the flame sensor 9 (see FIG. 4E), and the ECU 4 will issue a command to increase the amount of support gas G2 (see FIGS. 6A and 6B). Note that FIG. 6C shows a completely misfired state.

[0050] 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 engine speed, the crankshaft must be rotated within 120 degrees once it enters the expansion stroke. Converting this to time, in the case of 2500 rpm, it is 60 s / 2500 r × 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.

[0051] An O2 sensor 54 may also be provided in the exhaust system of the gas engine 7 (such as the exhaust pipe on the exhaust port 74 side) (see Figure 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 stoichiometric air-fuel ratio according to the signal from the O2 sensor 54 attached to the exhaust system. A three-way catalyst 55 is provided downstream of the exhaust system to neutralize HC / CO / NOx in the exhaust, but in order to do this, the engine must be operated at the stoichiometric air-fuel ratio so that neither oxygen nor combustible substances (fuel) remain after combustion in the cylinder 71.

[0052] To achieve this, the O2 sensor 54 detects the O2 concentration in the exhaust gas, and the ECU 4 performs feedback control to adjust the air-fuel ratio to the stoichiometric air-fuel ratio. Specifically, even if the air-fuel ratio detected by the O2 sensor 54 is determined 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, rather than the main fuel (main fuel gas G1), whose combustible components are unknown. 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 gas fuel mixture G3 (mixed gas fuel G3 and air G0) in the cylinder 71 via the mixer 3 is maintained at a good ratio, i.e., at or near the stoichiometric air-fuel ratio, thereby maintaining a good combustion state in the cylinder 71.

[0053] 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 also 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).

[0054] 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. In this case, 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 may not be provided and may be unnecessary.

[0055] The support gas container 21 is filled with a support gas G2. A primary pressure reducing valve 21a is provided in the support gas container 21. 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.

[0056] 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 heat of compression like a diesel engine. Therefore, in order to ignite them with an electric spark and help the flame spread, it is possible to create a spark ignition engine system in which easily available propane (C3H8) is premixed with the main fuel gas G1 as a support gas.

[0057] 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 within the introduction pipe 31c. An annular space 31e is formed around 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.

[0058] The first inlet portion 31a and the second inlet portion 31b are both connected to the annular space 31e. That is, the first inlet portion 31a and the second inlet portion 31b are connected to each other 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. Air is drawn into the mixer 3 from the intake manifold through an intake valve and into the cylinders of the dual-ignition gas engine 7.

[0059] 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) and blocks the nozzle 13d (23d).

[0060] 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 thereof) 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 the mixer 3, causing the pressure in the small chamber 13f (23f) to drop. Note that the main fuel gas low pressure adjustment valve 13 and the support gas low pressure adjustment valve 23 are formed with through holes that are open to the atmosphere. These are atmosphere vent holes 13g (23g), and serve to facilitate the movement of the diaphragm 13e (23e).

[0061] 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 format of this signal. When the engine is running, current is applied for t(S) with a period of to(s) (frequency is 1 / to). While current 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) does not flap, but rather the gap ks increases as the duty increases. This is due to the inertia and hysteresis of the moving parts.

[0062] Furthermore, 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.

[0063] Furthermore, reference numeral 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 the 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 numeral 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.

[0064] Next, for reference, we will discuss whether or not 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.

[0065] Calculate the mass of each component in 1 mole (22.4 liters at 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

[0066] 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 x 0.4 = 14.44 The calorific value of CO is 12.66 Mj / m 3 So 0.3m 3 So 12.6 x 0.3 = 3.8 Since the calorific value of CO2 is 0, 0x0.3=0.

[0067] Therefore, S gas (main fuel gas G1) 1m 3 The calorific value is 18.2Mj / m 3 , which is propane (C3H8) 90.7M j / m 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 exhaust gas recirculation (EGR) amount is increased to the engine's operating limit in a dual-ignition gasoline engine, at the theoretical air-fuel ratio, the CO2 concentration in the mixture drawn into cylinder 71 is at the limit for stable combustion when it is 10%.

[0068] 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 combust 1 mole (28 g) of S gas (main fuel gas G1) is calculated.

[0069] CH4 + 2O2=CO2 + 2H2O This means 2 moles of O2 are required. If there are 0.4 moles of CH4, then 2 moles x 0.4 = 0.8 moles of O2 are required. CO + 1 / 2O2 = CO2, meaning 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 is required.

[0070] On the other hand, the mass of O2 in 1 mole of air (2 8.8 g) is 32 g x 0.21 = 6.72, so (3 0.4g / 6.7 2)×2 8.8 = 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), meaning that there are fewer components that can burn.

[0071] We will consider whether combustion can occur within the cylinder based on 10%. Without going into 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 in terms of 4.522 molar mass. The theoretical air-fuel ratio of main fuel gas G1 is 130.2g / 28g = 4.65, which is significantly smaller than the 15.6 for propane and the 14.7 for gasoline. This means there is less to burn.

[0072] Next, we 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 drawn into the cylinder 71 is 10% or less. If the amount of propane required to mix S gas (main fuel gas G1), which cannot burn on its own, by adding combustion support gas (hereinafter referred to as support gas) 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 air required to combust 1 mole of S gas (main fuel gas G1)) + (number of moles of propane and air required to combust X moles)} (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, meaning that propane (C3 H8) is required at a volume ratio of 12.1% or more of the S (crude) gas (main fuel gas G1).

[0073] Even if the engine is operating at the stoichiometric air-fuel ratio with the aforementioned support gas ratio, if the amount of support gas is small, combustion within the cylinder 71 will vary, resulting in increased rotational fluctuations, and if this increases further, the engine will shut down. Before explaining how to control dual combustion, Figure 8(C) shows the relationship between the output signal (electromotive force) of the platinum-zirconia O2 sensor 54 and the air-fuel ratio. This electromotive force varies significantly around the stoichiometric air-fuel ratio, but 0.5 V can be considered 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 adjustment valve 23 is adjusted to P50. As the duty cycle t / t0, explained below, increases, the air-fuel ratio decreases (becomes richer).

[0074] A method for controlling the pressure of the main fuel gas G1 and the support gas G2 entering the mixer 3 will be explained using Figure 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). Figure 8(A) shows the format of this signal. When the engine is running, current is applied for only t(S) with a period of t0 and (s) (frequency is 1 / t0).

[0075] When current 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. A separate visualization experiment showed that the seal member 13c (23c) does not flap, but rather the gap becomes larger as the duty increases. This is due to the inertia and hysteresis of the moving parts.

[0076] Even if the mixture of the main fuel gas G1, the support gas G2, the mixed gas fuel G3, and the air obtained by equations (1) and (1') is at the stoichiometric air-fuel ratio, the CO2 in the main fuel can hinder flame propagation. This disrupts combustion and the signal from the flame sensor 9. The flame detection signal appears t(s) after the ignition signal. This t is different from the t used in the explanation of the duty in Figure 8(A).

[0077] 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 (1) in Fig. 5(A). In Fig. 5(A), (2) shows that 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) shows that the flame K has reached 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.

[0078] (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 a stoichiometric air-fuel ratio due to the extinguishing effect of CO2 in the main fuel gas G1. If the ECU 4 determines that a misfire has occurred, increasing the duty cycle 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.

[0079] If the ECU 4 determines that a misfire has occurred, increasing the aforementioned duty cycle will increase P2 in Figures 1 and 8(C). For example, if pressure P1 in Figure 1 is set to 2.8 kPa, adjust pressure P2 to 4.5 kPa until misfire is no longer detected. As shown in Figure 8(B), pressure P2 is always greater than pressure P1. The pressure P1 of the main fuel gas G1 is not changed.

[0080] 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]

[0081] 11...Main fuel gas container, 21...Support gas pressure container, 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 line, L2...virtual second line, G1...main fuel gas G1, G2...supporting gas, G3...mixed gas fuel, G0...air, K...flame, ka...flame particles.

Claims

1. 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 spark plugs, an intake valve, and an exhaust valve arranged in a cylinder, and a flame sensor that detects the strength of the flame is attached to the inner wall surface of the cylinder at a predetermined distance from both spark plugs, and the flame sensor is 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 the flame sensor is provided at at least one of the two points of contact between an imaginary second line perpendicular to the center of an imaginary first line connecting the two ignition plugs and the inner wall surface of the cylinder.

3. 2. The gas engine power generation system according to claim 1, wherein the flame sensors are provided at both points of contact between an imaginary second line perpendicular to the center of an imaginary first line connecting the two ignition plugs and the inner peripheral wall surface of the cylinder.

4. 3. A gas engine power generation system according to claim 1, wherein the flame sensor has a first electrode and a second electrode within an insulator portion, the tips of which 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.

5. 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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