Method for limiting load of a fixed pitch propeller diesel engine based on supercharger rotational speed

Abstract

Provided is a constant pitch propeller diesel engine load limiting method based on supercharger speed, belonging to the technical field of marine diesel engines. The method comprises: obtaining multiple main engine speeds and corresponding supercharger speed data when the diesel engine is shipped according to a standard propeller characteristic line; using a mathematical fitting method to establish a functional relationship between the supercharger speed and the main engine speed, and generating a standard operation curve; calculating the supercharger speed limit value at the corresponding speed according to the commonly used main engine speed of the ship; in actual operation, the supercharger speed is monitored in real time, and when the limit value is reached or exceeded, it is determined that the load is over-limited, and a protection measure of limiting the highest operating speed is executed. The present application indirectly monitors the diesel engine load by using the supercharger speed, provides a quantitative judgment basis by fitting the standard operation curve, and dynamically limits the highest speed when the load is over-limited, ensuring that the diesel engine always operates in a safe area. The present application has low cost and high reliability, and effectively prevents damage caused by long-term over-torque operation of the diesel engine.

Description

Technical Field

[0001] This invention belongs to the field of marine diesel engine technology, specifically relating to a load limiting method for fixed-pitch propeller diesel engines based on turbocharger speed. It is particularly suitable for ships without shaft power monitoring equipment, and is used to prevent fixed-pitch propeller diesel engines from operating under overload conditions due to a decrease in propeller efficiency after long-term operation. Background Technology

[0002] In fixed-pitch propeller (FPP) marine diesel engines, the input power of the propeller is proportional to the cube of the engine speed. To prevent damage to the diesel engine due to excessive load during continuous operation, the following two measures are typically employed in ship design: Measure 1: Considering factors such as hull fouling, decreased engine and propeller efficiency, and the maintenance cycle of ship equipment after long-term operation, a certain power reserve is included in the ship design, such as... Figure 1 As shown, the hull and propeller should be cleaned regularly to restore propeller efficiency and ensure the ship operates below the standard propeller line. During operation, changes in parameters such as exhaust temperature, burst pressure, rack and pinion count, and boost pressure are observed for auxiliary judgment.

[0003] The drawback of this approach is that the rate at which ship fouling and propeller efficiency decline is significantly affected by the operating sea area. If the reserve factor is too high, it will affect the diesel engine's power performance, leading to unnecessary power loss; if the reserve factor is too low, it will require shorter maintenance cycles, reduced on-duty time, and increased periodic maintenance costs. Furthermore, judging load status through parameter changes relies heavily on personnel's familiarity with the equipment and their experience, introducing considerable uncertainty. For example, a ship's diesel engine was designed with a reserve factor of 13%, and the plan was to clean the hull and propeller after 12,000 hours of operation. However, due to frequent operations in the South China Sea, where marine life proliferates rapidly, the operating line exceeded the standard propeller line after 6,000 hours of actual operation. Since the commonly used speed was 920 rpm, 1,000 rpm below the rated speed, although the propeller was operating above standard speed and load characteristics such as exhaust temperature and pressure had significantly increased, the threshold parameters corresponding to the rated speed had not been reached, thus failing to trigger an alarm. This resulted in the diesel engine operating under over-torque for an extended period, ultimately causing piston damage.

[0004] Measure 2: Install a shaft dynamometer and load limiting system to monitor and output the actual torque and shaft power of the host in real time, and compare them with the preset load limiting curve. If the limit is exceeded, the oil supply will be automatically reduced to achieve load limiting.

[0005] The drawback of this approach is that shaft dynamometers and load limiting systems increase the ship's construction and maintenance costs. Furthermore, for certain ships requiring guaranteed mission availability, installing sophisticated electronic sensors on high-speed rotating shafts undoubtedly increases system complexity and potential points of failure, reducing the reliability of the propulsion system.

[0006] Therefore, there is an urgent need for a simple, reliable, and low-cost emergency load limiting alternative to ensure the safe operation of diesel engines in the absence of shaft power monitoring equipment. Summary of the Invention

[0007] The technical problem solved by this invention: The purpose of this invention is to provide a load limiting method for a fixed-pitch propeller diesel engine based on turbocharger speed, thereby solving the problems existing in the background art. This method indirectly monitors the diesel engine load by controlling the turbocharger speed, achieving load limiting under shaft dynamometer-less conditions, ensuring that the diesel engine does not operate under over-torque for extended periods, and improving the safety and reliability of diesel engine operation.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A load limiting method for fixed-pitch propeller diesel engines based on turbocharger speed includes the following steps: Step 1) Obtain turbocharger speed data corresponding to multiple main engine speed points based on the diesel engine's operating state under standard propeller characteristic lines at the time of manufacture; Step 2) Based on the main engine speed and turbocharger speed data obtained in Step 1), establish a functional relationship between turbocharger speed and main engine speed using a mathematical fitting method, and generate a standard operating curve of turbocharger speed-main engine speed; Step 3) Substitute the commonly used main engine speed into the standard operating curve according to the ship's commonly used main engine speed, and calculate the turbocharger speed limit value corresponding to the standard propeller state at that commonly used speed; Step 4) Monitor the actual turbocharger speed at the current main engine speed in real time during the actual operation of the diesel engine; Step 5) Compare the actual turbocharger speed at the current main engine speed with the turbocharger speed limit value corresponding to the main engine speed in Step 3); if the actual turbocharger speed reaches or exceeds the turbocharger speed limit value, it is determined that the diesel engine load is over-limit, and load limiting protection measures are implemented.

[0009] As a further aspect of the present invention, the load limiting protection measures in step 5) include: limiting the maximum operating speed of the diesel engine to be lower than the rated speed, so as to ensure that the diesel engine always operates below 100% torque line.

[0010] As a further aspect of the present invention, the maximum operating speed limit is dynamically adjusted according to the following steps: calculating the ratio of the power corresponding to the standard propeller characteristic line to the power corresponding to 100% torque at the current commonly used speed, as a power reserve coefficient; and dynamically adjusting and setting a new maximum operating speed limit based on the power reserve coefficient and the rate of decrease in propeller efficiency during diesel engine operation.

[0011] As a further embodiment of the present invention, the mathematical fitting method in step 2) adopts one of exponential fitting, polynomial fitting or power function fitting, and the standard operating curve of the turbocharger speed-host speed is generated by data processing software to form a fitting function and curve.

[0012] As a further aspect of the present invention, the turbocharger speed limit value is used as the threshold for determining diesel engine overload, replacing the shaft dynamometer and automatic load limiting system, to achieve indirect monitoring and control of diesel engine load.

[0013] As a further aspect of the present invention, the protection measure of limiting the maximum operating speed is used to prevent the diesel engine from operating at 100% torque at normal operating speed when the operating line deviates from the standard propeller line due to hull fouling or decreased propeller efficiency after the diesel engine has been running for a long time.

[0014] As a further aspect of the present invention, the power reserve coefficient is used to assess the load margin under the current speed limit, and combined with the decrease coefficient of the reserve coefficient during the early operation of the diesel engine, to predict the safe operating time under the current maximum speed limit, thus providing a basis for decision-making on ship operation strategies.

[0015] Advantages of this invention compared to existing technologies: 1. This solution provides quantitative monitoring to improve the accuracy of judgment: By fitting the generated standard operating curve, it provides quantitative load limit parameters (turbocharger speed limit value), which solves the problem of no limit parameters for some load lines. It avoids the problem of exhaust temperature and explosion pressure not reaching the threshold value when the marine diesel engine is running at a speed lower than the rated speed for a long time due to the torque exceeding 100% during operation. It has higher timeliness and accuracy. 2. This solution simplifies the system, reduces costs and failure rates: It utilizes the diesel engine's existing turbocharger speed sensor for monitoring, eliminating the need for an expensive shaft dynamometer and complex automatic load limiting system as required by the prior art. This significantly reduces the construction and maintenance costs of the vessel, while simplifying the complexity of the power system, reducing potential failure points, and improving system reliability. 3. Flexible Strategy Adjustment: This invention not only provides immediate overload protection (limiting maximum speed), but also offers decision support for ship operation by calculating the power reserve coefficient. It can dynamically adjust the maximum speed limit based on the rate of propeller efficiency decline, predicting safe operating time and making the load limiting strategy more flexible and scientific. 4. This solution effectively prevents over-torque operation: This invention directly addresses the root cause of diesel engine damage—prolonged operation at over 100% torque. By limiting the maximum operating speed, it forces the diesel engine to operate within a safe range, fundamentally solving the problem in existing technologies where alarms cannot be triggered due to commonly used speeds being lower than the rated speed, leading to prolonged over-torque operation and eventual damage to the diesel engine. 5. Wide applicability and promotional value of this solution: This method does not change the original structure of the diesel engine, but only utilizes existing sensor data and mathematical fitting methods. It is low-cost, easy to implement, and applicable to various fixed-pitch propeller diesel engines. It has extremely high application value and promotion prospects, especially in emergency scenarios where shaft dynamometers cannot be installed or in the retrofitting of old ships. Attached Figure Description

[0016] Figure 1 This is a diagram of the diesel engine operating area in this invention; Figure 2 This is a schematic diagram of the fitting curve of the relationship between the turbocharger speed and the main engine speed when the diesel engine leaves the factory in this invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Please see Figure 1-2 The embodiments of the present invention are described in detail below.

[0019] Example This embodiment uses a certain type of marine diesel engine that malfunctioned, as mentioned in the background art, as an example to provide a detailed description of the method of the present invention.

[0020] 1. Data Acquisition and Curve Fitting The relationship between the turbocharger speed and the main engine speed when the diesel engine is manufactured, based on the propeller characteristic line, is shown in Table 1: Table 1. Correspondence between turbocharger speed and main unit speed at the factory. Using the charting function in Microsoft Excel, insert an XY scatter plot with the engine speed on the x-axis and the turbocharger speed on the y-axis (the average of columns A and B can be used). Add a trendline, select exponential trendline mode, and check "Show formulas" to fit and generate a function curve of turbocharger speed versus engine speed. The fitted function relationship is as follows: Figure 2 As shown, the fitting indicator function is .

[0021] 2. Determine the turbocharger speed limit. Substituting the commonly used main engine speed of 920 rpm into the above fitting function, the turbocharger speed limit corresponding to the standard propeller condition at this speed is calculated. For example, the calculated value is 26989 rpm. This value is the judgment threshold for subsequent operational monitoring.

[0022] 3. Overload detection and protection strategy from Figure 1 It can be seen that after prolonged operation, the diesel engine's operating line will move from the new ship's propeller characteristic line towards, and even exceed, the standard propeller characteristic line. On the same propeller characteristic line, the torque is greater at higher speeds. Therefore, to ensure that the diesel engine's torque does not exceed 100% at 100% speed, it is necessary to ensure that the diesel engine always operates below the standard propeller characteristic line. After setting the turbocharger speed-main engine speed operating limit line according to this method, it is only necessary to set the turbocharger speed operating limit value for the diesel engine's commonly used maximum speed to ensure that the diesel engine operates below the standard propeller characteristic line. At this time, the maximum operating speed is unrestricted (it can reach 100% speed). When the commonly used speed reaches the standard propeller characteristic line, by calculating the power at the current speed under the standard propeller characteristic line and at 100% torque, the power reserve coefficient at the current speed can also be calculated, allowing for judgment on the ship's subsequent operating strategy.

[0023] In actual diesel engine operation, if the actual turbocharger speed continuously approaches or exceeds 26989 rpm when the engine speed is 920 rpm, it indicates that the diesel engine's operating line has exceeded the standard propeller line and the load is over-limited. At this time, load limiting protection measures should be implemented: limit the maximum operating speed of the diesel engine. For example, limit the maximum speed to 920 rpm or lower (such as 850 rpm) to ensure the diesel engine operates safely below the 100% torque line.

[0024] 4. Dynamic adjustment and operational strategy decision-making To further refine management and forecasting, the following calculations can be performed: Calculate the power reserve coefficient: Based on the rated speed of 1000 rpm, calculate the power reserve coefficient at the commonly used speed of 920 rpm. Since the power of a standard propeller is proportional to the cube of the speed, the ratio of the linear power of the standard propeller to the power corresponding to 100% torque is (920 / 1000)^3 = 0.78.

[0025] Similarly, if the commonly used speed is 950 rpm, calculate the power corresponding to 100% torque at that speed. .

[0026] When a diesel engine runs for a long time, the propeller efficiency decreases. At the same speed, the diesel engine power will increase. According to the calculation above, the main engine speed will reach the power corresponding to 100% torque at 950 rpm. At this time, if the maximum operating speed is limited, such as to 920 rpm or a lower speed, such as 850 rpm, the diesel engine will ensure operation below 100% torque. When the main engine is at 950 rpm and the torque is 100%, the power at 920 rpm is calculated as (920 / 950)^3 = 0.90, that is, at this speed, there is still a power reserve coefficient of about 10%.

[0027] By combining the rate of decrease of the reserve coefficient during the initial operation, the safe operating time under the current maximum speed limit can be roughly estimated, providing a basis for decision-making on whether the ship needs to return to port for cleaning or continue to perform its mission.

[0028] 5. Application Validation A certain ship established a turbocharger speed-main engine speed operating line according to this method, and accordingly set a protection mechanism for the maximum main engine operating speed. After actual operation verification, the diesel engine has been operating safely for 5 years without any further piston damage caused by prolonged over-torque operation, proving the effectiveness and reliability of this invention.

[0029] The working principle of this invention is based on the following technical understanding: 1. The efficiency of diesel engine fuel combustion in converting into mechanical work does not change much when operating above the economic power level. Therefore, the diesel engine power P is approximately proportional to the number of racks in the fuel rack.

[0030] 2. The theoretical minimum air-fuel ratio for fuel combustion is a constant of 1.4. From the turbocharger MAP diagram, there is a corresponding relationship between turbocharger speed, boost pressure, and boost air flow. Therefore, there is a certain functional relationship between turbocharger speed and diesel engine power.

[0031] 3. For fixed-pitch diesel engines, their power is proportional to the cube of the speed.

[0032] Based on the above three points, a functional relationship between the turbocharger speed and the main engine speed can be fitted. When the diesel engine leaves the factory, it is operated according to the standard propeller characteristic curve. The main engine speed and turbocharger speed are measured at various operating points, and a standard operating curve of "turbocharger speed - main engine speed" is generated through mathematical fitting. This curve represents the operating characteristics of the diesel engine under standard load conditions.

[0033] In actual operation, due to hull fouling or decreased propeller efficiency, the diesel engine needs to output more power (i.e., increased torque) to maintain the same speed, which leads to a corresponding increase in turbocharger speed. Therefore, by comparing the actual monitored turbocharger speed with the corresponding speed limit on the standard operating curve, it is possible to indirectly determine whether the diesel engine is under overload. Once the actual turbocharger speed reaches or exceeds the limit, it indicates that the diesel engine load is excessive. At this point, by limiting the maximum operating speed, the diesel engine can be forced back to operate below the 100% torque line, thereby avoiding the risk of damage caused by prolonged operation under excessive torque.

[0034] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0035] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A load limiting method for a fixed-pitch propeller diesel engine based on turbocharger speed, characterized in that: Includes the following steps: Step 1) Obtain turbocharger speed data corresponding to multiple main engine speed points based on the diesel engine's operating state under standard propeller characteristic lines at the time of manufacture; Step 2) Based on the main engine speed and turbocharger speed data obtained in Step 1), establish a functional relationship between turbocharger speed and main engine speed using a mathematical fitting method, and generate a standard operating curve of turbocharger speed-main engine speed; Step 3) Substitute the commonly used main engine speed into the standard operating curve according to the ship's commonly used main engine speed, and calculate the turbocharger speed limit value corresponding to the standard propeller state at that commonly used speed; Step 4) Monitor the actual turbocharger speed at the current main engine speed in real time during the actual operation of the diesel engine; Step 5) Compare the actual turbocharger speed at the current main engine speed with the turbocharger speed limit value corresponding to the main engine speed in Step 3); if the actual turbocharger speed reaches or exceeds the turbocharger speed limit value, it is determined that the diesel engine load is over-limit, and load limiting protection measures are implemented.

2. The load limiting method for a fixed-pitch propeller diesel engine based on turbocharger speed according to claim 1, characterized in that: The load limiting protection measures in step 5) include: limiting the maximum operating speed of the diesel engine to below the rated speed, so as to ensure that the diesel engine always operates below 100% torque line.

3. The load limiting method for a fixed-pitch propeller diesel engine based on turbocharger speed according to claim 2, characterized in that: The maximum operating speed limit is dynamically adjusted according to the following steps: Calculate the ratio of the power corresponding to the standard propeller characteristic line to the power corresponding to 100% torque at the current commonly used speed, and use it as the power reserve coefficient; based on the power reserve coefficient and the rate of decrease in propeller efficiency during diesel engine operation, dynamically adjust and set a new maximum operating speed limit.

4. The load limiting method for a fixed-pitch propeller diesel engine based on turbocharger speed according to claim 1, characterized in that: The mathematical fitting method in step 2) adopts one of exponential fitting, polynomial fitting or power function fitting, and the standard operating curve of the turbocharger speed-host speed is generated by data processing software to form a fitting function and curve.

5. The load limiting method for a fixed-pitch propeller diesel engine based on turbocharger speed according to claim 1, characterized in that: The turbocharger speed limit value is used as the threshold for determining diesel engine overload, replacing the shaft dynamometer and automatic load limiting system to achieve indirect monitoring and control of diesel engine load.

6. The load limiting method for a fixed-pitch propeller diesel engine based on turbocharger speed according to claim 2, characterized in that: The aforementioned protection measure limiting the maximum operating speed is used to prevent the diesel engine from operating at 100% torque at its normal operating speed when the operating line deviates from the standard propeller line due to hull fouling or decreased propeller efficiency after the diesel engine has been running for a long time.

7. The load limiting method for a fixed-pitch propeller diesel engine based on turbocharger speed according to claim 3, characterized in that: The power reserve coefficient is used to assess the load margin under the current speed limit, and combined with the reserve coefficient reduction coefficient of the diesel engine in the early stage of operation, it predicts the safe operating time under the current maximum speed limit, providing a basis for ship operation strategy decision-making.

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