Hydrogen internal combustion engine control method based on variable pressure hydrogen rail and hydrogen supply system

Abstract

The invention relates to a hydrogen internal combustion engine control method based on a variable pressure hydrogen rail and a hydrogen injection system, and the method comprises the steps: carrying out a calibration experiment on a hydrogen internal combustion engine, and determining optimal excess air coefficients under different working conditions, and hydrogen injection amount change ranges and hydrogen injection pressures corresponding to different excess air coefficient ranges; when the hydrogen internal combustion engine operates, the current optimal excess air coefficient is determined based on the calibration result according to the current internal combustion engine rotating speed and the load requirement, and the hydrogen injection pressure is determined according to the current optimal excess air coefficient; preliminarily controlling the valve opening of the pressure regulating valve according to the required hydrogen spraying pressure; the pressure at an inlet of the hydrogen rail is measured, and the valve opening degree of the pressure regulating valve is further regulated based on the relative relation between the current hydrogen rail pressure and the needed hydrogen spraying pressure; and according to the hydrogen spraying pressure and the optimal excess air coefficient, the hydrogen spraying pulse width of the hydrogen sprayer is controlled. Compared with the prior art, the dynamic property and economical efficiency of the hydrogen internal combustion engine can be improved, and the situation that the combustion condition becomes poor due to the fact that the hydrogen injection pulse width is too large and delayed to the air cylinder combustion stage is prevented.

Description

Technical Field

[0001] This invention relates to the field of hydrogen internal combustion engine control technology, and in particular to a hydrogen supply system for a hydrogen internal combustion engine based on a variable pressure hydrogen rail and its control method. Background Technology

[0002] The engine's injection system controls the amount of fuel and air injected into the engine cylinders, along with the injection method, adjusting the air-fuel mixture concentration and spray state. This determines the in-cylinder combustion, significantly impacting the engine's power, fuel economy, and emissions characteristics. Hydrogen burns rapidly, making hydrogen internal combustion engines prone to knocking. Combustion control within the cylinders is relatively complex. Furthermore, hydrogen internal combustion engines can achieve relatively lean combustion. Therefore, the control technology of the hydrogen injection system is a key technology for achieving stable, efficient, and low-emission combustion in hydrogen internal combustion engines.

[0003] For example, Chinese patent application CN202311276714.0 discloses a method for correcting the injection quantity of each cylinder in an electronically controlled high-pressure common rail system by monitoring the pressure drop of the high-pressure fuel rail before and after each cylinder's injection. This method corrects the injection quantity of each cylinder by monitoring the pressure drop of the high-pressure fuel rail before and after each cylinder's injection, solving the problem of uneven injection between cylinders caused by wear and blockage of the common rail system injectors during use. Chinese patent application CN202310800019.3 discloses a fuel injection control method, device, electronic equipment, and storage medium. It determines the engine's required intake air volume and required fuel volume based on the torque requirements of the hydrogen internal combustion engine; determines the current throttle opening of the hydrogen internal combustion engine based on the required intake air volume; and determines the current injection pulse width of the injector based on the required fuel volume. Then, it controls the throttle to open to the target position corresponding to the current throttle opening and controls the injector to open to the current injection pulse width.

[0004] The aforementioned existing patent solutions all control the fuel injection quantity by controlling the injection pulse width of the fuel injector. However, the combustion range of a hydrogen internal combustion engine is large, and the adjustment range of the hydrogen injection quantity is also large. Controlling the hydrogen injection pulse width alone will result in an excessively large hydrogen injection pulse width. An excessively large hydrogen injection pulse width will delay the combustion stage in the cylinder, which will greatly affect the combustion and damage the hydrogen injector. To prevent the above situation, the single hydrogen injection valve has a pulse width allowable range. When the required hydrogen injection pulse width exceeds the limit of the pulse width range, the hydrogen injection quantity will not meet the requirements. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a hydrogen internal combustion engine control method and hydrogen supply system based on a variable pressure hydrogen rail.

[0006] The objective of this invention can be achieved through the following technical solutions: As a first aspect of the present invention, a method for controlling a hydrogen internal combustion engine based on a variable pressure hydrogen rail is provided, comprising the following steps: Calibration experiments were conducted on hydrogen internal combustion engines under different operating conditions to determine the optimal excess air coefficient under different operating conditions. A calibration experiment was conducted on the hydrogen injection pressure of the hydrogen internal combustion engine. The excess air coefficient range of the hydrogen internal combustion engine was divided into multiple segments. The required range of hydrogen injection quantity variation for each segment of the excess air coefficient range was calculated, and a hydrogen injection pressure was determined for each segment of the excess air coefficient range. When the hydrogen internal combustion engine starts running, the current optimal excess air coefficient is determined based on the current speed and load requirements of the hydrogen internal combustion engine and the excess air coefficient calibration results. Based on the current optimal excess air coefficient and the hydrogen injection pressure calibration results of the hydrogen internal combustion engine, the hydrogen injection pressure is determined, and the valve opening of the pressure regulating valve is initially controlled according to the required hydrogen injection pressure. The pressure on the hydrogen rail is measured, and based on the relative relationship between the current hydrogen rail pressure value and the required hydrogen injection pressure, the valve opening of the pressure regulating valve is further adjusted. The hydrogen injection pulse width of the hydrogen injector is calculated and controlled based on the hydrogen injection pressure and the hydrogen injection quantity corresponding to the optimal excess air coefficient.

[0007] As a preferred technical solution, the calibration experiment for the excess air coefficient is specifically as follows: Through engine bench testing, the power, economy, and emission characteristics of different excess air coefficients under different operating conditions were measured. The performance indicators were normalized and comprehensively evaluated to determine the optimal excess air coefficient under different operating conditions.

[0008] As a preferred technical solution, a calibration experiment is performed on the hydrogen injection pressure of the hydrogen internal combustion engine, as detailed below: Excess air coefficient of hydrogen internal combustion engine λ The range is divided into multiple segments ( λ 0 , λ 1), , ( λ 2n-2 , λ 2n-1 ); Based on intake volume m air Calculate the hydrogen injection velocity corresponding to each range of excess air coefficient ( m 0 , m 1), , ( m 2n-2 , m 2n-1 ), and set the hydrogen injection pressure for each excess air coefficient range. P 1 , ,P n ; Based on the pressure difference before and after hydrogen injection Calculate the flow velocity using Bernoulli's formula ,⋯, And calculate the hydrogen injection pulse width for each excess air coefficient range according to the formula. θ 0 , θ 1) ,⋯, ( θ 2n-2 , θ 2n-1 ).

[0009] As a preferred technical solution, the calculation of the hydrogen injection pulse width is as follows: , , , , , In the formula, ,⋯, This refers to the hydrogen injection flow rate; ,⋯, The flow rate is calculated based on the pressure difference before and after hydrogen injection and Bernoulli's formula.

[0010] As a preferred technical solution, the hydrogen injection pressure set for each excess air coefficient range ensures that the hydrogen injection pulse width variation range is within the permissible pulse width range.

[0011] As a preferred technical solution, the determination of the current optimal excess air coefficient based on the excess air coefficient calibration result is as follows: The optimal excess air coefficient MAP diagram under different operating conditions was obtained through excess air coefficient calibration experiments, and the data of the MAP diagram was imported into the hydrogen internal combustion engine control unit (ECU). When the hydrogen internal combustion engine starts running, the ECU (Engine Control Unit) detects the engine's operating conditions and obtains the optimal excess air coefficient under the current operating conditions by searching the optimal excess air coefficient MAP (Map of Optimal Excess Air Coefficient).

[0012] As a preferred technical solution, the valve opening of the pressure regulating valve is further adjusted based on the relative relationship between the current hydrogen rail pressure value and the required hydrogen injection pressure, as follows: The pressure at the hydrogen rail inlet was measured by a pressure sensor. P ; The ECU determines the relationship between the hydrogen rail inlet pressure P and the required hydrogen injection pressure Pe: If the pressure at the hydrogen rail inlet PGreater than the required hydrogen injection pressure Pe If this is the case, the pressure regulating valve will decrease, and the pressure will return to the measurement point at the hydrogen rail inlet. P ; If the pressure at the hydrogen rail inlet P Less than the required hydrogen injection pressure Pe If this is the case, the pressure regulating valve will increase, and the pressure at the hydrogen rail inlet will be measured again. P ; Adjust the valve opening of the pressure regulating valve until the pressure at the hydrogen rail inlet is reached. P With the required hydrogen injection pressure Pe equal.

[0013] As a second aspect of the present invention, a hydrogen supply system for a hydrogen internal combustion engine based on a variable pressure hydrogen rail is provided, the system including a hydrogen internal combustion engine control unit (ECU), sensors and a hydrogen injection system; The hydrogen injection system includes a hydrogen storage cylinder, a one-way valve, a safety valve, a pressure regulating valve, a hydrogen rail, and a hydrogen injector connected in sequence. The hydrogen injector is used to supply high-pressure direct-injection hydrogen to the hydrogen internal combustion engine. The sensors include a first pressure sensor for monitoring the pressure at the hydrogen rail inlet and an in-cylinder sensor for collecting the operating conditions of the hydrogen internal combustion engine. The hydrogen internal combustion engine control unit (ECU) is connected to the hydrogen internal combustion engine, the pressure regulating valve, and various sensor signals, and executes the hydrogen internal combustion engine control method based on the variable pressure hydrogen rail as described above.

[0014] As a preferred technical solution, a pneumatic shut-off valve and an explosion-proof flame arrester are also installed on the hydrogen supply pipeline between the pressure regulating valve and the hydrogen rail.

[0015] As a preferred technical solution, the sensors installed in the hydrogen supply system also include a hydrogen concentration sensor and a second pressure sensor located between the safety valve and the pressure regulating valve.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The hydrogen supply system and control method for a hydrogen internal combustion engine based on a variable pressure hydrogen rail designed in this invention can reasonably control the excess air coefficient of the in-cylinder mixture to the optimal level by real-time monitoring of the operation of the hydrogen internal combustion engine, thereby comprehensively improving the power and economy of the hydrogen internal combustion engine and improving emissions; by changing the hydrogen injection pressure, it can prevent the hydrogen injection pulse width from being too large and delayed to the cylinder combustion stage, which would lead to poor combustion and damage to the hydrogen injector. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a hydrogen internal combustion engine control method based on a variable pressure hydrogen rail according to the present invention. Figure 2 This is a schematic diagram of a hydrogen supply system for an internal combustion engine based on a variable pressure hydrogen rail, according to the present invention. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0019] Example 1 This invention addresses the wide combustion range of hydrogen internal combustion engines by proposing a control method for hydrogen internal combustion engines based on a variable pressure hydrogen rail. For example... Figure 1 As shown, the control method includes the following steps: Step 1: Calibrate the optimal excess air coefficient of the hydrogen internal combustion engine: Calibration experiments were conducted on hydrogen internal combustion engines under different operating conditions to determine the optimal excess air coefficient under different operating conditions, taking into account the power, economy and emission characteristics of the hydrogen internal combustion engine.

[0020] Step 2: Calibrate the hydrogen injection pressure of the hydrogen internal combustion engine: The excess air coefficient range of the hydrogen internal combustion engine is divided into multiple segments. The required range of hydrogen injection quantity variation for each segment is calculated. A hydrogen injection pressure is determined for each segment, and the range of hydrogen injection pulse width variation is kept within the permissible pulse width range.

[0021] Step 3: The hydrogen internal combustion engine control unit (ECU) determines the optimal excess air coefficient based on the current hydrogen internal combustion engine speed and load requirements, according to the table calibrated on the hydrogen internal combustion engine test bench.

[0022] Step 4: Determine the hydrogen injection pressure according to the table for calibrating hydrogen injection pressure of hydrogen internal combustion engines, based on the optimal excess air coefficient.

[0023] Step 5: The ECU initially controls the valve opening of the pressure regulating valve based on the required hydrogen injection pressure.

[0024] Step Six: The pressure sensor measures the pressure on the hydrogen rail and sends the current pressure value back to the ECU. When the hydrogen rail pressure... P Greater than the required hydrogen injection pressure Pe When the pressure is low, reduce the pressure regulating valve; when the hydrogen rail pressure P Less than hydrogen injection pressure Pe When the pressure is equal to the hydrogen injection pressure, increase the pressure regulating valve; when the hydrogen rail pressure is equal to the hydrogen injection pressure, proceed to the next step.

[0025] Step 7: Calculate and control the hydrogen injection pulse width of the hydrogen injector based on the hydrogen injection pressure and the hydrogen injection quantity determined by the optimal excess air coefficient.

[0026] Specifically, the calibration experiment for the optimal excess air coefficient of the hydrogen internal combustion engine in step 1 is implemented as follows: Through engine bench testing, the power, economy, and emission characteristics of different excess air coefficients under different operating conditions were measured. The performance indicators were normalized and comprehensively evaluated to determine the optimal excess air coefficient under different operating conditions, and a MAP diagram of the optimal excess air coefficient was obtained. The data of the MAP diagram was then imported into the ECU.

[0027] The specific implementation of the hydrogen injection pressure calibration experiment for the hydrogen internal combustion engine in step 2 is as follows: The excess air coefficient range of hydrogen internal combustion engines is divided into ( λ 0 , λ 1), , ( λ 2n-2 , λ 2n-1 According to the intake volume m air Formula: Calculate the hydrogen injection velocity corresponding to the excess air coefficient ( m 0 , m 1), , ( m 2n-2 , m 2n-1 The hydrogen injection pressure is set for each range. P 1 , ,P n : Based on the pressure difference before and after hydrogen injection and Bernoulli's formula Calculate the flow velocity ,⋯, And according to the formula , , , , , Calculate the width of each hydrogen injection pulse segment ( θ 0 , θ 1) ,⋯, ( θ 2n-2 , θ 2n-1 The set hydrogen injection pressure for each segment ensures that the pulse width of each hydrogen injection segment is within the permissible range.

[0028] The excess air coefficient range for each segment and its corresponding hydrogen injection pressure are input into the ECU.

[0029] like Figure 2The diagram shows a flowchart illustrating exemplary steps of a control method in an ECU.

[0030] In step 301, the hydrogen internal combustion engine starts running, the ECU detects the operating conditions of the hydrogen internal combustion engine, and finds the optimal excess air coefficient under the current operating conditions of the hydrogen internal combustion engine by searching the optimal excess air coefficient MAP.

[0031] In step 401, the ECU obtains the required hydrogen injection pressure by searching the range of excess air coefficients to which the optimal excess air coefficient belongs. Pe .

[0032] In step 501, the ECU initially controls the valve opening of the pressure regulating valve based on the required hydrogen injection pressure. In step 601, the pressure sensor measures the pressure at the hydrogen rail inlet. P .

[0033] In step 602, the ECU determines the relationship between the pressure P at the hydrogen rail inlet and the required hydrogen injection pressure Pe. If P > Pe Then return to step 501 and control the pressure regulating valve to reduce its pressure.

[0034] In step 603, the ECU determines the pressure at the hydrogen rail inlet. P With the required hydrogen injection pressure Pe If the relationship, P < Pe Then return to step 501 and control the pressure regulating valve to increase its opening.

[0035] In step 604, the ECU determines the pressure at the hydrogen rail inlet. P With the required hydrogen injection pressure Pe If the relationship, P = Pe Then proceed to the next step.

[0036] In step 701, the ECU determines the required hydrogen injection pressure. Pe And the optimal excess air coefficient, controlling the hydrogen injection pulse width of the hydrogen injector to be θ e .

[0037] The hydrogen internal combustion engine control method based on variable pressure hydrogen rail designed in this invention can reasonably control the excess air coefficient of the in-cylinder mixture of the hydrogen internal combustion engine to the optimal level by real-time monitoring of the internal combustion engine's operation, thereby comprehensively improving the engine's power, economy, and emissions; and by changing the hydrogen injection pressure, it can prevent the hydrogen injection pulse width from being too large and delayed to the cylinder combustion stage, which would lead to poor combustion and damage to the hydrogen injector.

[0038] Example 2 As another embodiment of the present invention, this embodiment also provides a hydrogen supply system for a hydrogen internal combustion engine based on a variable pressure hydrogen rail, which is used to implement the hydrogen supply method for a hydrogen internal combustion engine based on a variable pressure hydrogen rail as described in Embodiment 1. Figure 2 As shown, the system includes an ECU, sensors, and a hydrogen injection system; the hydrogen injection system includes a hydrogen storage tank, a safety valve, a check valve, a pressure regulating valve, a pneumatic shut-off valve, a flame arrester, a hydrogen rail, and a hydrogen injector.

[0039] Furthermore, one hydrogen storage cylinder is connected to the first safety valve via a pipeline, and the other hydrogen storage cylinder is connected to the hydrogen supply pipeline. A one-way valve, a second safety valve, a pressure regulating valve, a pneumatic shut-off valve, and an explosion-proof flame arrester are arranged in order from left to right on the hydrogen supply pipeline.

[0040] Furthermore, the operating conditions are measured by in-cylinder sensors, and the pressure is measured by a pressure gauge installed at the hydrogen rail inlet; the sensors and pressure gauges interact with the ECU via wired or wireless means.

[0041] Furthermore, the ECU is connected to the in-cylinder sensor, pressure gauge, concentration sensor, and pressure regulator valve, respectively, and the ECU can control the pressure regulator valve according to the signals.

[0042] The hydrogen supply system and control method for a hydrogen internal combustion engine based on a variable pressure hydrogen rail designed in this invention can reasonably control the excess air coefficient of the in-cylinder mixture to the optimal level through real-time monitoring of the hydrogen internal combustion engine's operation, thereby comprehensively improving the engine's power, economy, and emissions. Furthermore, by changing the hydrogen injection pressure, it prevents excessively wide hydrogen injection pulse widths from delaying combustion into the cylinder combustion stage, which could lead to poor combustion and damage to the hydrogen injectors. The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A control method for a hydrogen internal combustion engine based on a variable pressure hydrogen rail, characterized in that the steps include... include: Calibration experiments were conducted on hydrogen internal combustion engines under different operating conditions to determine the optimal excess air coefficient under different operating conditions. A calibration experiment was conducted on the hydrogen injection pressure of the hydrogen internal combustion engine. The excess air coefficient range of the hydrogen internal combustion engine was divided into multiple segments. The required range of hydrogen injection quantity variation for each segment of the excess air coefficient range was calculated, and a hydrogen injection pressure was determined for each segment of the excess air coefficient range. When the hydrogen internal combustion engine starts running, the current optimal excess air coefficient is determined based on the current speed and load requirements of the hydrogen internal combustion engine and the excess air coefficient calibration results. Based on the current optimal excess air coefficient and the hydrogen injection pressure calibration results of the hydrogen internal combustion engine, the hydrogen injection pressure is determined, and the valve opening of the pressure regulating valve is initially controlled according to the required hydrogen injection pressure. The pressure on the hydrogen rail is measured, and based on the relative relationship between the current hydrogen rail pressure value and the required hydrogen injection pressure, the valve opening of the pressure regulating valve is further adjusted. The hydrogen injection pulse width of the hydrogen injector is calculated and controlled based on the hydrogen injection pressure and the hydrogen injection quantity corresponding to the optimal excess air coefficient.

2. The hydrogen internal combustion engine control method based on a variable pressure hydrogen rail according to claim 1, characterized in that, The calibration experiment for the excess air coefficient is as follows: Through engine bench testing, the power, economy, and emission characteristics of different excess air coefficients under different operating conditions were measured. The performance indicators were normalized and comprehensively evaluated to determine the optimal excess air coefficient under different operating conditions.

3. The hydrogen internal combustion engine control method based on a variable pressure hydrogen rail according to claim 1, characterized in that, The hydrogen injection pressure of the hydrogen internal combustion engine was calibrated using the following methods: Excess air coefficient of hydrogen internal combustion engine λ The range is divided into multiple segments ( λ 0 ,λ 1), , ( λ 2n-2 ,λ 2n-1 ); Based on intake volume m air Calculate the hydrogen injection velocity corresponding to each range of excess air coefficient ( m 0 , m 1), , ( m 2n-2 , m 2n-1 ), and set the hydrogen injection pressure for each excess air coefficient range. P 1 , ,P n ; Based on the pressure difference before and after hydrogen injection Calculate the flow velocity using Bernoulli's formula ,⋯, And calculate the hydrogen injection pulse width for each excess air coefficient range according to the formula. θ 0 ,θ 1) ,⋯, ( θ 2n-2 ,θ 2n-1 ).

4. The hydrogen internal combustion engine control method based on a variable pressure hydrogen rail according to claim 3, characterized in that, The calculation of the hydrogen injection pulse width is as follows: , , , , , In the formula, ,⋯, This refers to the hydrogen injection flow rate; ,⋯, The flow rate is calculated based on the pressure difference before and after hydrogen injection and Bernoulli's formula.

5. The hydrogen internal combustion engine control method based on a variable pressure hydrogen rail according to claim 3, characterized in that, The set hydrogen injection pressure for each excess air coefficient range ensures that the hydrogen injection pulse width variation range is within the permissible pulse width range.

6. The hydrogen internal combustion engine control method based on a variable pressure hydrogen rail according to claim 1, characterized in that, The optimal excess air coefficient is determined based on the excess air coefficient calibration results, as follows: The optimal excess air coefficient MAP diagram under different operating conditions was obtained through excess air coefficient calibration experiments, and the data of the MAP diagram was imported into the hydrogen internal combustion engine control unit (ECU). When the hydrogen internal combustion engine starts running, the ECU (Engine Control Unit) detects the engine's operating conditions and obtains the optimal excess air coefficient under the current operating conditions by searching the optimal excess air coefficient MAP (Map of Optimal Excess Air Coefficient).

7. The hydrogen internal combustion engine control method based on a variable pressure hydrogen rail according to claim 1, characterized in that, Based on the relative relationship between the current hydrogen rail pressure and the required hydrogen injection pressure, the valve opening of the pressure regulating valve is further adjusted as follows: The pressure at the hydrogen rail inlet was measured by a pressure sensor. P ; The ECU determines the relationship between the hydrogen rail inlet pressure P and the required hydrogen injection pressure Pe: If the pressure at the hydrogen rail inlet P Greater than the required hydrogen injection pressure Pe If this is the case, the pressure regulating valve will decrease, and the pressure will return to the measurement point at the hydrogen rail inlet. P ; If the pressure at the hydrogen rail inlet P Less than the required hydrogen injection pressure Pe If this is the case, the pressure regulating valve will increase, and the pressure at the hydrogen rail inlet will be measured again. P ; Adjust the valve opening of the pressure regulating valve until the pressure at the hydrogen rail inlet is reached. P With the required hydrogen injection pressure Pe equal.

8. A hydrogen supply system for a hydrogen internal combustion engine based on a variable pressure hydrogen rail, characterized in that, The system includes a hydrogen internal combustion engine control unit (ECU), sensors, and a hydrogen injection system; The hydrogen injection system includes a hydrogen storage cylinder, a one-way valve, a safety valve, a pressure regulating valve, a hydrogen rail, and a hydrogen injector connected in sequence. The hydrogen injector is used to supply high-pressure direct-injection hydrogen to the hydrogen internal combustion engine. The sensors include a first pressure sensor for monitoring the pressure at the hydrogen rail inlet and an in-cylinder sensor for collecting the operating conditions of the hydrogen internal combustion engine. The hydrogen internal combustion engine control unit (ECU) is connected to the hydrogen internal combustion engine, the pressure regulating valve, and various sensor signals, and executes the hydrogen internal combustion engine control method based on a variable pressure hydrogen rail as described in any one of claims 1-7.

9. A hydrogen supply system for a hydrogen internal combustion engine based on a variable pressure hydrogen rail according to claim 8, characterized in that, A pneumatic shut-off valve and an explosion-proof flame arrester are also installed on the hydrogen supply pipeline between the pressure regulating valve and the hydrogen rail.

10. A hydrogen supply system for a hydrogen internal combustion engine based on a variable pressure hydrogen rail according to claim 8, characterized in that, The sensors installed in the hydrogen supply system also include a hydrogen concentration sensor and a second pressure sensor located between the safety valve and the pressure regulating valve.

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