JP7402019B2 - combustion system - Google Patents

Description

The present invention relates to an air-fuel ratio control device that controls the air-fuel ratio, which is the ratio of air to fuel, in a mixture supplied to an internal combustion engine equipped with a burner such as a power generation boiler. The air-fuel ratio is controlled based on this.

In recent years, in spark ignition internal combustion engines, the fuel supplied to the internal combustion engine is controlled based on the detected air-fuel ratio to improve fuel efficiency and output. The air-fuel ratio is detected using an oxygen O2 sensor or an air-fuel ratio sensor, but the O2 sensor and air-fuel ratio sensor are in an inactive state, such as during a cold start of an internal combustion engine. At times, the measured values are unstable and the accuracy of air-fuel ratio control cannot be maintained. In order to solve this problem, a method is generally known in which the air-fuel ratio is detected using an ion current corresponding to ions generated by combustion in the combustion chamber of an internal combustion engine.

However, the magnitude of the detected ionic current varies due to individual differences in the surface area of the applying electrode and the grounding electrode for detecting the ionic current, so the air-fuel ratio is A problem arises in which it is difficult to accurately determine the combustion state. In addition, if carbon is deposited on the surfaces of the application electrode and the grounding electrode, the ionic current flowing between the application electrode and the grounding electrode will vary. A problem arises in which it is difficult to accurately determine the combustion state of the fuel. If the combustion state cannot be determined accurately, it may be incorrectly determined that there is insufficient fuel for the current air-fuel ratio, resulting in unnecessary fuel consumption.

An object of the present invention is to solve the above-mentioned problems, and even if the magnitude of the detected ion current changes due to individual differences in the constituent elements of the ion current detection device that detects the ion current, carbon It is an object of the present invention to provide a combustion system that accurately determines the combustion state with respect to the air-fuel ratio based on the ion current and maintains the optimum combustion state even if the fuel is deposited.

A combustion system according to the present invention is a combustion system that combusts an air-fuel mixture containing at least a main fuel, and includes a combustion tube that burns the air-fuel mixture and ions that are generated by combustion of the air-fuel mixture in the combustion tube. a detection probe; an ion current detection means for detecting an ion current as an ion current detection signal based on the ions detected by the probe; and an ion current detection means for detecting an ion current detection signal based on the ions detected by the probe, and the ion current detection signal indicating a combustion state of the main fuel in the combustion cylinder. A control means for calculating a combustion state quantity, and the control means adjust the air-fuel ratio of the main fuel in the air-fuel mixture based on the combustion state quantity.

In the combustion system of the present invention, a combustion state quantity indicating the combustion state of the main fuel is calculated from the ion current, and the air-fuel ratio of the main fuel in the air-fuel mixture is adjusted based on this combustion state quantity. Therefore, the combustion state of the main fuel can be accurately determined without depending on variations in the size of the detected ion current due to individual differences in the surface area of the applying electrode and the grounding electrode for detecting the ion current. Since it becomes possible to make a determination as to whether the combustion conditions are the same or not, it becomes possible to continue the optimum combustion state.

In one embodiment of the combustion system, the probe is located in an external recirculation region outside the mainstream of the swirling flow of the mixture.

In the combustion system of the present invention, the combustion state in the external recirculation area around the internal recirculation area generated below the output port of the combustion tube can be directly detected, so that the unburnt gas from the swirler can be directly detected. It becomes possible to further suppress the main fuel (for example, flame-retardant ammonia gas) from being ejected from the output port along the peripheral wall of the combustion cylinder. Therefore, it becomes possible to burn the main fuel more efficiently and spread the flame from the output port.

In the combustion system of one embodiment, the control means converts the ion current detection signal into a frequency spectrum by Fourier transform processing, and uses the frequency spectrum as the combustion state quantity to determine the air-fuel ratio of the main fuel in the air-fuel mixture. Adjust.

In the combustion system of this invention, the frequency spectrum converted by the Fourier transform method is used for the ion current detection signal. It becomes possible to more accurately determine the combustion state of the main fuel without depending on variations in the magnitude of the detected ion current. Therefore, it becomes possible to continue the optimum combustion state.

In one embodiment of the combustion system, the control means controls the air-fuel mixture by determining whether or not there is a frequency spectrum having a magnitude equal to or greater than a predetermined threshold near a specific frequency in the frequency spectrum. Adjusting the air-fuel ratio of the main fuel.

In the combustion system of the present invention, since only the magnitude of the frequency spectrum at a specific frequency is determined, it is possible to easily determine the combustion state of the main fuel.

In the combustion system of one embodiment, the control means determines whether or not there is a frequency spectrum having a magnitude equal to or greater than a predetermined threshold value near a specific frequency in the frequency spectrum, and if there is no frequency spectrum, the control means continues to The air-fuel ratio of the main fuel in the air-fuel mixture is adjusted, and when the main fuel exists, it is determined that the main fuel has reached an optimal combustion state, and the adjustment of the air-fuel ratio of the main fuel is stopped.

In the combustion system of the present invention, since only the magnitude of the frequency spectrum at a specific frequency is determined, it is possible to easily determine the combustion state of the main fuel. Furthermore, since adjustment of the air-fuel ratio is stopped when the combustion state of the main fuel reaches the optimum combustion state, it is possible to reduce wasteful consumption of the main fuel.

According to the combustion system according to the present invention, even if the magnitude of the detected ion current changes due to individual differences in the constituent elements of the ion current detection device that detects the ion current, carbon may be deposited on each electrode. Even if the fuel burns, it is possible to accurately determine the combustion state with respect to the air-fuel ratio based on the ion current and continue the optimum combustion state.

1 is a partially cutaway side view of a combustion system 1 according to an embodiment of the present invention and a block diagram showing peripheral components thereof. FIG. 1B is a plan view of the swirler 10 of FIG. 1A. FIG. 1A is a circuit diagram of the ion detector 61 of FIG. 1A. FIG. 1A is a simplified vertical cross-sectional view schematically showing a combustion tube 2 of the combustion system 1 of FIG. 1A. FIG. 3 is a time axis waveform diagram showing changes in ion current with respect to time of an ion current detection signal output from the ion detection circuit 51 of FIG. 2. FIG. 4A is a spectral waveform diagram showing changes in spectral intensity with respect to frequency of the ion current detection signal of FIG. 4A. FIG. 1A is a two-dimensional plan view showing a combustion state when the combustion system 1 of FIG. 1A is used. FIG.

Embodiments according to the present invention will be described below with reference to the drawings.

Embodiment 1.
FIG. 1A is a partially cutaway side view of a combustion system 1 according to an embodiment of the present invention and a block diagram showing peripheral components thereof. The combustion system 1 in FIG. 1A includes a combustion cylinder 2 having an upper wall 5 and a bottom wall 4 at the upper and lower ends of a cylindrical peripheral wall 3, and a lower side of a fuel injection port 6 formed at the center of the bottom wall 4. a swirler (swirling vane) 10 for forming a swirling flow, and a fuel supply section connected to the lower side of the swirler 10 to supply a mixture of flame-retardant ammonia gas and air, which is the main fuel, to the swirler 10. 11, a spark plug 12 that ignites the air-fuel mixture ejected from the swirler 10, and valves 34 and 36 that adjust the amounts of ammonia gas and air supplied into the fuel supply section 11, respectively.

Furthermore, the combustion system 1 of FIG. 1A includes an ion probe 21 for detecting ions that detects ions generated by combustion of the air-fuel mixture in the combustion tube 2, and an ion current generated based on the ions detected by the ion probe 21. An ion detector 61 having an ion detection circuit 51 as an ion current detection means, and control for controlling the opening/closing and opening degree of the valves 34 and 36 based on the ignition operation of the spark plug 12 and information from the ion probe 21. The control device 53 is configured to include a control device 53 as a means. Here, the combustion system 1 in FIG. 1A is a combustion system that combusts an air-fuel mixture containing at least ammonia gas, which is the main fuel.

FIG. 1B is a plan view of the swirler 10 of FIG. 1A, in which a plurality of inclined blades 10a are arranged at equal intervals in the circumferential direction, and the center of the swirler 10 is located on the cylinder axis C1. 2 clearly illustrates the centrally arranged arrangement of the bottom wall 4.

The swirler 10 sends a mixture of ammonia gas and air supplied from the fuel supply section 11 into the combustion cylinder 2 as a swirling flow. The mainstream S0 of the swirling flow sent into the combustion cylinder 2 from the inlet 6 rotates around the cylinder axis C1 and advances upward while expanding upward in a generally conical shape.

The ion probe 21 in FIG. 1A is composed of an application electrode 21a and a grounding electrode 21b that face each other on the same straight line parallel to the bottom wall 4, and is arranged in an external recirculation area Z2, which will be described later. Further, the application electrode 21a and the grounding electrode 21b are supported by a pair of support legs 25, 25 erected on the bottom wall 4 of the combustion tube 2. The electric wire 41 connected to the application electrode 21a passes through the support leg 25 in an insulated state, is led out of the combustion tube 2, and is electrically connected to the ion detection circuit 51. Here, the grounding electrode 21b is connected to the grounding wire 43 via the bottom wall 4.

The control device 53 in FIG. 1A calculates a combustion state amount indicating the combustion state of ammonia gas, which is the main fuel, in the combustion tube 2 based on the ion current detected by the ion detection circuit 51, and calculates the combustion state Based on the amount, the air-fuel ratio of ammonia gas in the mixture is adjusted. Here, the control device 53 determines the combustion state of the ammonia gas based on the detected ion current, and opens and closes the valves 34 and 36 and adjusts the degree of opening so as to maintain the optimum combustion state. With this configuration, it is possible to grasp the combustion state of ammonia gas, which is difficult to see, and control the combustion of ammonia gas to continue stably. Specifically, the control device 53 executes the following processes 1 to 3.

Processing 1: A/D converting the ion current detection signal indicating the ion current to convert the ion current detection signal into a digital signal.

Processing 2: Perform FFT (Fast Fourier Transform) processing on the ion current detection signal converted into a digital signal in Processing 1 to calculate a frequency spectrum as a combustion state quantity indicating the combustion state of ammonia gas.

Process 3: If a frequency spectrum equal to or higher than a predetermined threshold exists near a specific frequency (13 Hz in this embodiment), it is determined that a protrusion (peak) of the frequency spectrum exists, and the opening degree of the valves 34 and 36 is determined. Stop adjusting. Further, if there is no frequency spectrum equal to or higher than a predetermined threshold near a specific frequency (13Hz in this embodiment), it is determined that there is no protrusion in the frequency spectrum, and the opening degree adjustment of the valves 34 and 36 continues. It will be done.

Further, in the combustion tube 2 of FIG. 1A, an output port 9 from which flame is ejected is formed in the center of the upper wall 5 of the combustion tube 2. The swirler 10 has a cylindrical shape, and is arranged so that its axis is concentric with the cylinder axis C1 of the combustion tube 2 and extends in the vertical direction. Note that a spark plug 12 is arranged within the range of the inlet 6.

The spark plug 12 has a discharge electrode 12a with a hook-shaped tip and a ground electrode 12b with a hook-shaped tip. They are each formed so as to protrude into the inside of the cylinder 2. Note that a high voltage is applied to the discharge electrode 7a from the control device 53, and as a result, sparks are generated between the tip of the discharge electrode 12a and the tip of the ground electrode 12b, and the ammonia spouted from the swirler 10 is A mixture of gas and air is ignited.

A fuel supply pipe 31 is connected to the fuel supply section 11 in FIG. 1A, and the upstream side of the fuel supply pipe 31 branches into two branch pipes 32a and 32b. A fuel tank 33 storing ammonia gas is connected to one branch pipe 32a via a valve 34, and an air compressor 35 is connected to the other branch pipe 32b via a valve 36. Here, the opening/closing and opening degree of the valves 34 and 36 are controlled by the control device 53 so as to adjust the supply amounts of ammonia gas and air, respectively.

Ion detection circuit 51 is connected to control device 53. The signal output section of the control device 53 is connected to the drive actuators 34a, 36a of the valves 34, 36 via electric wires 54, 55. By sending the output signal of the control device 53 to each drive actuator 34a, 36a, the opening/closing and opening degree of the valves 34, 36 are controlled, and the ammonia gas (main fuel) from the fuel tank 33 and the compressed air from the air compressor 35 are controlled. The discharge amount can be adjusted.

FIG. 2 is a circuit diagram of the ion detector 61, and the ion detection circuit 51 includes a power source 51a, a resistor 51b, and a voltage measuring section 51c. The power supply 51a applies a voltage to the application electrode 21a of the ion probe 21 via the resistor 51b. In this embodiment, the power supply 51a is arranged so that a negative voltage is applied.

The voltage of the power supply 51a is, for example, -200V. When ions are present around the ion probe 21, the ions are attracted to the application electrode 21a, and a current (ion current) flows. The more ions generated by combustion, the greater the current flow. The voltage measurement unit 51c detects the potential difference generated between both ends of the resistor 51b due to the ionic current, and the value of the ionic current is calculated based on this potential difference.

FIG. 3 is a simplified vertical cross-sectional view schematically showing the combustion tube 2 of the combustion system 1 of FIG. 1A. Here, by representing the main stream S0 of the swirling flow, the internal recirculation S1, and the external recirculation S2 with simple shapes of straight lines and ellipses, the configurations of the internal recirculation region Z1 and the external recirculation region Z2 can be illustrated in more detail. It shows. As shown in FIGS. 1A and 3, the space inside the combustion cylinder 2 is formed by the main flow S0 of the swirling flow into an inner recirculation zone (IRZ) inside the main flow S0 (on the cylinder axis C1 side). Z1 and an outer recirculation zone (ORZ) Z2 outside the main stream S0. In the internal recirculation region Z1, during combustion, as the mainstream S0 of the swirling flow described above moves, the air-fuel mixture is pulled into the mainstream S0, flows upward and outward as shown by the arrow S1, and at the same time moves toward the cylinder axis at the top. Internal recirculation occurs in a spiral shape on the line C1 side. On the other hand, in the external recirculation region Z2, during combustion, the air-fuel mixture is pulled by the mainstream S0 as the mainstream S0 of the swirling flow described above moves, flows upward and outward as shown by the arrow S2, and also flows downward at the top. An external recirculation S2 is formed which curves into a spiral shape.

Here, an external recirculation area Z2 is generated around the internal recirculation area Z1 generated below the output port 9 of the combustion tube 2, and a flame is formed in the external recirculation area Z2. Therefore, it is possible to suppress unburned ammonia gas from the swirler 10 from being ejected from the output port 9 along the peripheral wall 3 of the combustion tube 2, and it is possible to efficiently burn the ammonia gas. Furthermore, since the flame is generated along the peripheral wall 3 of the combustion tube 2, it becomes possible to spread the flame from the output port 9 by the flame formed in the external recirculation area Z2. The controller 53 of FIG. 1A therefore controls the formation of a flame in the external recirculation zone Z2.

The operation of the combustion system 1 configured as above will be explained below. Here, the combustion process by the combustion system 1 is executed under the control of the control device 53.

When the combustion process of the combustion system 1 of FIG. 1A is started, first, the valves 34 and 36 are closed (step S100). Next, the ammonia gas supplied from the fuel tank 33 and the air supplied from the air compressor 35 are mixed in the fuel supply section 11 to form a mixture, and the mixture is guided by the swirler 10 as a swirling flow. It is sent into the combustion cylinder 2 (step S101). Here, the combustion cylinder 2 is divided into an internal recirculation area Z1 and an external recirculation area Z2 by the mainstream S0 of the swirling flow, and an internal recirculation S1 occurs in the internal recirculation area Z1, and an external recirculation In region Z2, external recirculation S2 occurs.

Next, the air-fuel mixture ejected by the swirler 10 is ignited by the spark plug 12, the air-fuel mixture is combusted in the combustion tube 2, and a flame is formed (step S102). Ions are generated within the combustion tube 2 due to this combustion and flame formation.

During combustion, a voltage is applied to each of the application electrodes 21a and 22a in the ion probe 21 (step S103). As a result, ions near the ion probe 21 are attracted to the application electrode 21a, and an ion current flows through the ion detection circuit 51.

Next, the control device 53 receives the ion current detection signal indicating the ion current from the ion detection circuit 51, performs AD conversion to convert it into a digital intermediate frequency signal (step S104), and converts the signal into a digital intermediate frequency signal. A frequency spectrum is calculated by performing FFT (fast Fourier transform) on the signal, and the spectral intensity for each frequency is stored in a memory (not shown) (step S105).

4A is a time axis waveform diagram showing the change in ion current with respect to time of the ion current detection signal output from the ion current detection circuit 51 of FIG. FIG. 3 is a spectral waveform diagram showing changes. Here, FIG. 4B shows a waveform diagram obtained by converting the ion current detection signal shown in FIG. 4A into a frequency spectrum that is ion current spectrum information using the fast Fourier transform method.

As shown in FIG. 4B, when a frequency spectrum equal to or higher than a predetermined threshold exists in the vicinity of 13 Hz, the control device 53 determines that a protrusion in the frequency spectrum exists, and adjusts the opening degrees of the valves 34 and 36. Stop. That is, at the time when a protrusion in the frequency spectrum appears around 13 Hz, the control device 53 determines that the highly flame-retardant ammonia gas has reached the optimal combustion state, and stops adjusting the opening degree of the valves 34 and 36. . Here, it becomes possible to stably continue combustion of ammonia gas.

Further, if there is no frequency spectrum equal to or higher than a predetermined threshold value around 13 Hz, the control device 53 determines that there is no protrusion in the frequency spectrum, and continues to adjust the opening degrees of the valves 34 and 36. The opening degree is adjusted until a protrusion in the frequency spectrum near 13 Hz appears (step S106).

FIG. 5 is a two-dimensional plan view showing a combustion state when the combustion system 1 of FIG. 1A is used. In FIG. 5, the horizontal axis shows the equivalence ratio, and the vertical axis shows the flow velocity of the air-fuel mixture ejected from the swirler 10. Here, the ● mark indicates a condition in which a flame was formed and maintained in the combustion tube 2, and the × mark indicates a condition in which the flame could not be maintained in the combustion tube 2 and disappeared. , the shaded area indicates the area where flames formed in the external recirculation area. This shaded area indicates a range in which the equivalence ratio is 1.0 to 1.1 and the flow velocity from the swirler 10 is 3 to 7 (m/s).

In Fig. 5, no flame is generated in the internal recirculation region Z1 on the fuel lean side where the equivalence ratio is up to 0.8 and on the fuel rich side where the equivalence ratio exceeds 1.4, and when the equivalence ratio is 0.8, the fuel If it changes to the rich side, there is a tendency for flame to occur in the internal recirculation zone Z1. The above-mentioned equivalent ratio is expressed below.

Equivalence ratio = theoretical air-fuel ratio / actual air-fuel ratio

In the above equation, when the actual air-fuel ratio of the air-fuel mixture matches the stoichiometric air-fuel ratio, the equivalence ratio becomes 1.0. When the actual air-fuel ratio is on the fuel lean side than the stoichiometric air-fuel ratio, the equivalence ratio is less than 1.0, and when the actual air-fuel ratio is on the fuel-rich side than the stoichiometric air-fuel ratio, the equivalence ratio is 1.0. .0 becomes larger.

Therefore, the control device 53 in FIG. 1A determines that there is no protrusion in the frequency spectrum when there is no frequency spectrum equal to or higher than a predetermined threshold around 13 Hz, and the opening degree adjustment of the valves 34 and 36 continues. The opening degrees of the valves 34 and 36 are controlled so that the equivalence ratio becomes an optimal value of 1.0 to 1.1. That is, the amount of ammonia gas in the fuel tank 33 and the amount of air in the air compressor 35 is controlled so that an optimal combustion state close to the stoichiometric air-fuel ratio is achieved.

As explained above, according to this embodiment, even if the magnitude of the detected ion current changes due to individual differences in the constituent elements of the ion current detection device that detects the ion current, carbon is not deposited on each electrode. Even if combustion occurs, the combustion state relative to the air-fuel ratio can be accurately determined based on the ion current, making it possible to accurately control the equivalence ratio, air-fuel ratio, etc. in order to maintain the optimal combustion state. .

(Modification 1)
In this embodiment, the power supply 51a of the ion detection circuit 51 is configured to apply a negative voltage to the application electrode 21a, but the present invention is not limited to this. For example, the power supply 51a of the ion detection circuit 51 may be configured to apply a positive voltage (for example, 200V) to the application electrode 21a. In this case, electrons existing around the ion probe 21 are attracted to the application electrode 21a, and an ionic current flows. The more ions that are present, that is, the more electrons there are, the larger the current flows. Even in this case, the same effects as in this embodiment can be obtained.

(Modification 2)
In this embodiment, the ion probe for ion detection was placed within the external recirculation area Z2, but the invention is not limited thereto. For example, an ion probe for ion detection is composed of an application electrode and a grounding electrode that face each other on the same straight line parallel to the bottom wall, and is placed near the cylinder axis C1 within the internal recirculation area. It may be configured so that In this case, the application electrode and the grounding electrode are supported by a pair of support legs installed on the bottom wall of the combustion tube, and the electric wire connected to the application electrode is passed through the support legs in an insulated state. is led out of the combustion tube and connected to an ion detection circuit. Even in this case, the same effects as in this embodiment can be obtained.

(Modification 3)
In this embodiment, the combustion state of ammonia gas is determined using the fast Fourier transform method, but the present invention is not limited to this. For example, it may be configured to convert the ion current caused by the ions detected by the ion probe into a pulse signal using a predetermined threshold value, and use the period of the pulse signal to determine the combustion state of the ammonia gas. good. In this case, a high level signal is output when the ion current is larger than a predetermined threshold value, and a low level signal is output when the ion current is below the predetermined threshold value. Even in this case, the same effects as in this embodiment can be obtained.

(Modification 4)
In this embodiment, the combustion state of ammonia gas is determined using the fast Fourier transform method, but the present invention is not limited to this. For example, it may be configured to apply a band pass filter (BPF) that passes only a specific frequency (13 Hz) to the ion current caused by the ions detected by the ion probe, and determine the combustion state of the ammonia gas based on the output waveform. good. In this case, the control device determines that the combustion state of ammonia gas is good when the output waveform after BPF has a peak larger than a predetermined size or when the output waveform has an area larger than a predetermined area. configured so that Even in this case, the same effects as in this embodiment can be obtained.

Although embodiments of the present invention have been described, the above embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the invention described in the claims and its equivalents.

1 Combustion system 2 Combustion tube 6 Inlet 10 Swirler 11 Fuel supply 12 Spark plug 21 Ion probe 33 Fuel tank 34, 36 Valve 35 Air compressor 51 Ion detection circuit 53 Control device 61 Ion detector Z1 Internal recirculation area Z2 External recirculation Circulation area S0 Main stream of swirling flow S1 Internal recirculation S2 External recirculation

Claims (2)

A combustion system that burns a mixture containing at least a main fuel,
a combustion tube that burns the air-fuel mixture;
a probe that detects ions generated by combustion of the air-fuel mixture in the combustion cylinder;
ion current detection means for detecting an ion current as an ion current detection signal based on the ions detected by the probe;
a control means for calculating a combustion state quantity indicating a combustion state of the main fuel in the combustion cylinder using the ion current detection signal;
Equipped with
The control means converts the ion current detection signal into a frequency spectrum by Fourier transform processing, uses the frequency spectrum as the combustion state quantity, and detects a magnitude of a predetermined threshold value or more in the vicinity of a specific frequency in the frequency spectrum. determine whether a frequency spectrum having a frequency spectrum of A combustion system that stops adjusting the air-fuel ratio of the main fuel . 2. The combustion system of claim 1, wherein the probe is located in an external recirculation region outside of the mainstream of the swirling flow of the mixture.

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