Control method for marine diesel engine nitrogen oxide emission reduction system

Abstract

The application discloses a marine diesel engine nitrogen oxide emission reduction system control method and particularly relates to the technical field of diesel engine nitrogen oxide emission reduction. By constructing a spray-wall decomposition deficiency coefficient and a local low-temperature region migration description, potential crystal deposition areas can be identified in advance and their space-time drift trends can be predicted, so that the control strategy can be adjusted in a targeted manner to inhibit the formation and accumulation of crystal deposition from the source. Meanwhile, through joint evaluation of a crystal deposition potential accumulation index and back pressure evolution characteristics, short-period crystal deposition influence and long-period degradation trends can be distinguished in closed-loop adjustment, fine compensation of injection offset can be realized, the local low-temperature effect can be corrected in time, and systematic degradation caused by continuous back pressure rise can be avoided.

Description

Technical Field

[0001] This invention relates to the field of diesel engine nitrogen oxide emission reduction technology, and more specifically, to a control method for a marine diesel engine nitrogen oxide emission reduction system. Background Technology

[0002] With the further refinement of nitrogen oxide emission standards, marine diesel engines are increasingly adopting nitrogen oxide emission reduction systems based on selective catalytic reduction (SCR) technology. This involves injecting nitrogen oxide injectors into the high-temperature exhaust gas stream and promoting a reduction reaction within the catalyst layer to achieve dynamic control of NOx emissions. However, the complex operating environment and frequent load changes of ships cause significant fluctuations in exhaust gas temperature under various operating conditions, especially low loads and extreme sea states, making it difficult to maintain stable temperature and concentration conditions required for the catalytic reaction over long periods. When the local temperature of the exhaust pipe wall falls below the decomposition range of the nitrogen oxide injectors, the evaporation and decomposition processes are incomplete, easily leading to solid crystal deposition on the wall surface. This results in localized shielding of active sites and insufficient reduction reaction. More subtly, the hull is affected by roll and pitch during long-term navigation. The low-temperature region is not fixed on the lower side of the pipe but changes periodically with the hull's attitude, causing the solidified deposition area to dynamically migrate. This not only interferes with the uniformity of the catalyst inlet flow field but also forms continuously accumulating microcrystalline zones, causing a slow decline in nitrogen oxide reduction efficiency over time. Furthermore, solidification deposition gradually alters the microstructure of the exhaust channel, causing localized back pressure increases at specific locations. This localized increase evolves into a long-term upward trend in overall exhaust back pressure, ultimately affecting the stability and combustion efficiency of the engine's exhaust process. Consequently, the control system continuously faces issues of insufficient compensation and cumulative lag in closed-loop regulation. Therefore, the coupling mismatch between the nitrogen oxide injection fluid and the pipe wall temperature not only directly affects catalytic reaction efficiency but also triggers significant long-term degradation effects during continuous ship operation, becoming one of the key practical technical challenges currently facing the stable compliance and reliable control of marine nitrogen oxide emission reduction systems. Summary of the Invention

[0003] In order to overcome the above-mentioned defects of the prior art, embodiments of the present invention provide a control method for a marine diesel engine nitrogen oxide emission reduction system to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: The control method for nitrogen oxide emission reduction systems in marine diesel engines includes the following steps: The ship's attitude, exhaust gas velocity, and local temperature field of the exhaust pipe wall are obtained. The exhaust wall temperature distribution function is constructed by sampling along the axial and circumferential directions, and the spray-wall coupled temperature field description set is formed by combining the spray position, spray angle and exhaust temperature. Based on the spray-wall coupled temperature field description set, the temperature range of nitrogen oxide spray liquid in the evaporation and decomposition stages is segmented and fitted to extract the effective decomposition temperature range and the under-decomposition temperature range, and the spray-wall decomposition insufficiency coefficient is calculated based on the proportion of the under-decomposition temperature range. Based on the insufficient coefficient of the spray-wall decomposition and the hull roll angle and roll velocity, a migration vector of the local low temperature region is constructed, and combined with the time-varying sequence of exhaust flow velocity, the spatiotemporal drift function of the low temperature region relative to the exhaust flow is obtained. The predicted amount of solidification increment is calculated based on the spatiotemporal drift trend and the local wall temperature change rate, and the potential cumulative index of solidification is obtained. The local back pressure evolution characteristics are extracted based on the potential accumulation index of solidification and the rate of change of exhaust back pressure, and a spray-wall coupled degradation state vector is constructed to obtain a degradation segment feature set. The exhaust wall temperature and back pressure are extracted based on the degradation segment feature set, and the exhaust wall temperature and back pressure are compared with the allowable wall temperature range and the back pressure safety threshold, respectively, to calculate the injection adjustment offset.

[0005] In a preferred embodiment, the process of acquiring the ship's attitude, exhaust gas velocity, and local temperature field of the exhaust pipe wall, constructing the exhaust wall temperature distribution function by sampling along the axial and circumferential directions, and forming a spray-wall coupled temperature field description set by combining the injection position, injection angle, and exhaust temperature is as follows: The ship attitude sensor, exhaust temperature infrared array measuring points and exhaust pipe wall multi-point thermocouple array are integrated into the marine diesel engine exhaust system. The ship's attitude sensor collects the ship's three-dimensional attitude angles and marks them as attitude data, and records the acquisition time sequence of each frame of attitude data; Simultaneously, exhaust temperature infrared arrays are used to collect exhaust flow temperature data, and the instantaneous temperature value of each detection point is calculated along the axial direction of the pipeline. With Zhou Xiang Establish two-dimensional coordinates based on direction; The collected attitude data and temperature data are time-series aligned and a unified sampling timestamp is used. Equally spaced sampling points will be performed along the axial direction, and the number of sampling points will be denoted as [missing information]. Equal-angle sampling will be performed along the circumferential direction, and the number of sampling points will be denoted as... ; For each ( , The temperature values ​​at the sampling points are interpolated, and the exhaust wall temperature distribution function is constructed: Where t is the sampling time; Obtain the injection position output by the injection system control unit. Spray angle ; Corresponding injection position Extract the cross-sectional temperature corresponding to the axial position from the wall temperature distribution function. ; The cross-sectional temperature was normalized to obtain the local spray-wall temperature. : ; exhaust temperature Spray angle Local spray-wall temperature The jet-wall coupling calculation module is used to obtain the angular projection value between the jet angle and the local jet-wall temperature, as well as the jet-wall coupling temperature. Finally, a spray-wall coupled temperature field description set was constructed.

[0006] In a preferred embodiment, the specific calculation logic for the spray-wall coupling calculation module to obtain the angular projection value between the spray angle and the local spray-wall temperature, and the spray-wall coupling temperature, is as follows: Add an angle projection operation between the spray angle and the local spray-wall temperature: ,in This is the angular projection value between the spray angle and the local spray-wall temperature; The angular projection value between the injection angle and the local spray-wall temperature is compared with the exhaust temperature. Perform integral calculation of spray-wall coupling temperature : .

[0007] In a preferred embodiment, the process of segmenting and fitting the temperature range of the nitrogen oxide spray liquid during the evaporation and decomposition stages according to the spray-wall coupled temperature field description set, extracting the effective decomposition temperature range and the under-decomposition temperature range, and calculating the spray-wall decomposition insufficiency coefficient based on the proportion of the under-decomposition temperature range is as follows: Extracting spray-wall coupling temperature from the spray-wall coupling temperature field description set To reduce the spray-wall coupling temperature Establish instantaneous temperature trajectories according to time series, and divide temperature ranges into intervals based on experimental data; Spray-wall coupling temperature Perform smoothing filtering and normalize to a unified temperature range reference; The normalized temperature sequence is segmented and fitted according to a preset temperature threshold to obtain the under-decomposition temperature range, the effective decomposition temperature range, and the efficient decomposition reaction zone. The time period of the under-decomposition temperature range is statistically analyzed, and the ratio of this time period to the entire injection cycle is calculated to obtain the proportion of the under-decomposition temperature range. : ,in This refers to the time period of the under-decomposition temperature range. For the entire injection cycle; Calculate the insufficient decomposition coefficient of the spray-wall decomposition based on the proportion of the under-decomposition temperature range. : ,in, The periodic average of the spray-wall coupling temperature. The threshold for complete and effective decomposition reaction.

[0008] In a preferred embodiment, the process of constructing a local cryogenic region migration vector based on the jet-wall decomposition insufficiency coefficient, the hull roll angle, and roll velocity, and combining this with the time-varying sequence of exhaust velocity to obtain the spatiotemporal drift function of the cryogenic region relative to the exhaust flow is as follows: During ship navigation, the ship's roll angle is obtained. With roll speed Time series data, and compared with the spray-wall decomposition insufficiency coefficient Perform timing alignment; Insufficient coefficient of spray-wall decomposition Multiply by the roll angle and roll velocity to construct the migration vector of the local cryogenic region. : ; Synchronous acquisition of time-varying exhaust flow velocity sequences This is then combined with the migration vector of the local low-temperature region to obtain the spatiotemporal drift function of the low-temperature region relative to the exhaust flow: ,in This is the spacetime drift function.

[0009] In a preferred embodiment, the process of calculating the predicted solidification increment based on the spatiotemporal drift trend and the local wall temperature change rate to obtain the potential solidification accumulation index is as follows: After calculating the spatiotemporal drift trend of the local low-temperature region, the spatiotemporal drift function is... With exhaust wall temperature distribution sequence Perform synchronous matching; The rate of change of local wall temperature is obtained through time difference, and the expression is as follows: ,in For the local wall temperature change rate, For time difference time intervals; By coupling the spatiotemporal drift function with the local wall temperature change rate, the predicted local solidification increment is obtained. : ; The predicted die-bonding increment is accumulated and integrated using a sliding window: ,in This is the cumulative prediction of the solidification increment. For time indexing, The length of the sliding window; The cumulative prediction is spatially integrated along the axial direction of the exhaust pipe to obtain the potential cumulative index for die bonding. : ,in and These indicate the axial positions of the exhaust pipe inlet and outlet, respectively.

[0010] In a preferred embodiment, the process of extracting local backpressure evolution features based on the potential accumulation index of solidification and the rate of change of exhaust backpressure, and constructing a nozzle-wall coupled degradation state vector to obtain a degradation segment feature set is as follows: Acquisition of exhaust back pressure sequence The exhaust back pressure was then subjected to first-order difference processing to obtain the exhaust back pressure change rate. : ,in The time interval for the first-order difference; The potential accumulation index of die bonding and the rate of change of exhaust back pressure are normalized, and a nozzle-wall coupled degradation state vector is constructed using a linear combination method. : ,in, and The weighting coefficients for the potential accumulation index of solidification and the rate of change of exhaust back pressure; The degradation state vector of the spray-wall coupling is subjected to time series analysis, and short-period disturbances and long-period accumulation processes are distinguished based on time windows to obtain a degradation segment feature set.

[0011] The technical effects and advantages of this invention are as follows: 1. This invention dynamically captures the coupling state between the injection process and the exhaust wall temperature under complex ship operating conditions, and continuously quantifies key influencing factors such as low temperature region, solidification migration and back pressure evolution. Without changing the existing selective catalytic reduction hardware structure, the injection control can be shifted from the traditional static temperature range determination to dynamic compensation based on the spray-wall relationship and its time evolution characteristics, thereby significantly enhancing the nitrogen oxide reduction efficiency under low load and extreme sea conditions.

[0012] 2. By constructing a spray-wall decomposition deficiency coefficient and a description of local low-temperature region migration, this invention can identify potential crystal-bonding regions in advance and predict their spatiotemporal drift trends, enabling the control strategy to obtain targeted adjustment capabilities and suppress the formation and accumulation of crystal-bonding deposition from the source. At the same time, through the joint evaluation of the potential accumulation index of crystal-bonding and the back pressure evolution characteristics, the short-cycle crystal-bonding effect and the long-cycle degradation trend can be distinguished in the closed-loop regulation, realizing fine compensation of spray offset, so that the local low-temperature effect can be corrected in time and the systemic degradation caused by the continuous increase of back pressure can be avoided.

[0013] 3. Compared with conventional methods that only focus on catalyst inlet temperature or overall exhaust temperature, this invention can perform fine-grained modeling of the coupling mechanism between local temperature field, solidification distribution and back pressure changes, so that injection regulation is transformed from result control to process control, significantly improving the adaptability of the control strategy to temperature disturbances under multiple operating conditions and changes in hull attitude, effectively reducing dependence on exhaust temperature and catalyst temperature window, and ultimately achieving long-term stable compliance with nitrogen oxide emissions and improving the reliability and durability of marine diesel engine emission reduction systems. Attached Figure Description

[0014] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings; Figure 1 This is a flowchart of a method according to an embodiment of the present invention. Detailed Implementation

[0015] 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.

[0016] Example: Figure 1 The present invention provides a control method for a marine diesel engine nitrogen oxide emission reduction system, comprising the following steps: The system acquires operational status data such as hull attitude, exhaust gas velocity, and local temperature field of exhaust pipe wall. It constructs exhaust wall temperature distribution function by sampling along the axial and circumferential directions, and combines injection position, injection angle, and exhaust temperature to form a spray-wall coupled temperature field description set. Based on the spray-wall coupled temperature field description set, the temperature range of nitrogen oxide spray liquid in the evaporation and decomposition stages is segmented and fitted to extract the effective decomposition temperature range and the under-decomposition temperature range. The spray-wall decomposition insufficiency coefficient is calculated based on the proportion of the under-decomposition temperature range to characterize the short-term possibility of local solidification formation. Based on the insufficient coefficient of spray-wall decomposition and the hull roll angle and roll velocity, a migration vector of the local low temperature region is constructed. Combined with the time-varying sequence of exhaust flow velocity, the spatiotemporal drift function of the low temperature region relative to the exhaust flow is obtained to measure the spatiotemporal drift trend of the potential solidification region. The predicted amount of solidification increment is calculated based on the spatiotemporal drift trend and the local wall temperature change rate, and the potential cumulative index of solidification is obtained. The local back pressure evolution characteristics are extracted based on the potential accumulation index of crystal fixation and the rate of change of exhaust back pressure, and a spray-wall coupled degradation state vector is constructed to distinguish between the short-cycle crystal fixation influence and the long-cycle degradation trend, thereby obtaining a degradation segment feature set. The exhaust wall temperature and back pressure are extracted based on the degradation segment feature set. The exhaust wall temperature and back pressure are then compared with the allowable wall temperature range and the back pressure safety threshold, respectively. The injection adjustment offset is calculated to compensate for the insufficient decomposition caused by the injection-wall temperature coupling.

[0017] In this embodiment of the invention, the process of acquiring operational status data such as hull attitude, exhaust gas velocity, and local temperature field of the exhaust pipe wall, constructing an exhaust wall temperature distribution function by sampling along the axial and circumferential directions, and forming a spray-wall coupled temperature field description set by combining the injection position, injection angle, and exhaust temperature is as follows: The ship attitude sensor, exhaust temperature infrared array measuring points and exhaust pipe wall multi-point thermocouple array are integrated into the marine diesel engine exhaust system. The hull attitude sensor acquires the three-dimensional attitude angles of the hull at a sampling frequency of 50Hz. Tilt angle, Pitch angle, The deflection angle is marked as attitude data, and the acquisition timing of each frame of attitude data is recorded; Simultaneously, exhaust temperature infrared arrays are used to collect exhaust flow temperature data, and the instantaneous temperature value of each detection point is calculated along the axial direction of the pipeline. With Zhou Xiang Establish two-dimensional coordinates based on direction; It should be noted that attitude data is used to characterize the positional relationship of the exhaust flow field offset caused by hull rolling, and exhaust temperature data is used to describe the local temperature change of the exhaust wall caused by the difference in heat transfer inside the exhaust. The collected attitude data and temperature data are time-series aligned and a unified sampling timestamp is used. It should be noted that the purpose of timing alignment is to maintain the real-time coupling relationship between exhaust temperature and hull attitude. If it is not aligned, the direct impact of hull dynamics on wall temperature distribution cannot be reflected. Equally spaced sampling points will be performed along the axial direction, and the number of sampling points will be denoted as [missing information]. Equal-angle sampling will be performed along the circumferential direction, and the number of sampling points will be denoted as... ; It should be noted that, and Determined by the structure of the exhaust system, the preferred option is... , It is understandable that too few sampling points cannot reflect local temperature differences, while too many sampling points will lead to excessive real-time computing overhead. For each ( , The temperature values ​​at the sampling points are interpolated, and the exhaust wall temperature distribution function is constructed: Where t is the sampling time; It should be noted that the exhaust wall temperature distribution function is used to reflect the two-dimensional variation characteristics of wall temperature in time and space, and can be further used for calculation of jet evaporation and wall endothermic effect.

[0018] Obtain the injection position output by the injection system control unit. (Axial position), spray angle (Relative tube axis included angle); It should be noted that the spray angle The injection angle is determined by the injector's structural parameters and the nozzle azimuth angle. Different devices have different nozzle distributions, so the injection angle is expressed in radians. Corresponding injection position Extract the cross-sectional temperature corresponding to the axial position from the wall temperature distribution function. ; It should be noted that the cross-sectional data is used to describe the circumferential distribution differences of the wall temperature in the sprayed area; The cross-sectional temperature was normalized to obtain the local spray-wall temperature. : ; It should be noted that the normalization process is used to eliminate the influence of absolute temperature differences under different load conditions; exhaust temperature Spray angle Local spray-wall temperature The jet-wall coupling calculation module is used to obtain the angular projection value between the jet angle and the local jet-wall temperature, as well as the jet-wall coupling temperature. The specific calculation logic for the spray-wall coupling calculation module to obtain the angular projection value between the spray angle and the local spray-wall temperature, and the spray-wall coupling temperature is as follows: Add an angle projection operation between the spray angle and the local spray-wall temperature: ,in This is the angular projection value between the spray angle and the local spray-wall temperature; It should be noted that the angle projection reflects the degree of overlap between the jet direction and the high-temperature area of ​​the wall, and can describe the actual contact efficiency of jet cooling. The angular projection value between the injection angle and the local spray-wall temperature is compared with the exhaust temperature. Perform integral calculation of spray-wall coupling temperature : ; It should be noted that the integral is used to describe the cumulative coupling effect between the jet and the wall in the circumferential direction; Finally, the spray-wall coupled temperature field description set is constructed: ; It should be noted that the spray-wall coupled temperature field description set realizes three-layer information association: exhaust wall temperature (spatial distribution), spray direction (geometric relationship), and exhaust gas temperature (heat source effect).

[0019] In this embodiment of the invention, based on the spray-wall coupled temperature field description set, the temperature range of the nitrogen oxide spray liquid during the evaporation and decomposition stages is segmented and fitted to extract the effective decomposition temperature range and the under-decomposition temperature range. The spray-wall decomposition insufficiency coefficient is then calculated based on the proportion of the under-decomposition temperature range to characterize the short-term probability of localized crystal formation. Extracting spray-wall coupling temperature from the spray-wall coupling temperature field description set To reduce the spray-wall coupling temperature Establish instantaneous temperature trajectories according to time series, and divide temperature ranges into intervals based on experimental data; It should be noted that the evaporation and decomposition stages of the sprayed liquid typically have two main temperature characteristic ranges: the initial evaporation rise range and the decomposition reaction range; in order to eliminate the influence of absolute temperature shifts under different loads, the spray-wall coupling temperature is... Perform smoothing filtering and normalize to a unified temperature range reference; For example, the normalization formula is: ,in, and These represent the minimum and maximum spray-wall coupling temperatures within the current operating window, respectively. This is the normalized spray-wall coupling temperature; The normalized temperature sequence is segmented and fitted according to a preset temperature threshold. The preferred segmented thresholds include: the lower evaporation limit threshold. The effective lower limit threshold of decomposition reaction The effective threshold for complete decomposition reaction ; It should be noted that the above thresholds were all calibrated by those skilled in the art based on actual reaction path experiments. Different models and spray arrangements may differ, but the zoning logic remains consistent. Three-segment fitting was performed on the normalized temperature range: The under-decomposition temperature range (lower region): ; It should be noted that the corresponding sprayed liquid in this section has not yet reached the energy level required for full decomposition, and the local evaporation and surface reaction rates are insufficient. Effective decomposition temperature range (normal zone): ; It should be noted that this section indicates that the decomposition reaction is in a stable range, and the droplet residue is significantly reduced; High-efficiency decomposition reaction zone (high zone): ; It should be noted that the decomposition reaction in this section is rapid and more efficient; The time period of the under-decomposition temperature range is statistically analyzed, and the ratio of this time period to the entire injection cycle is calculated to obtain the proportion of the under-decomposition temperature range. : ,in This refers to the time period of the under-decomposition temperature range. For the entire injection cycle; It should be noted that a higher percentage indicates a longer duration of lower temperature in the spray-wall mixing zone; Calculate the insufficient decomposition coefficient of the spray-wall decomposition based on the proportion of the under-decomposition temperature range. : in, The periodic average of the spray-wall coupling temperature. This represents the effective threshold for the complete decomposition reaction. It should be noted that the significance of the spray-wall decomposition insufficiency coefficient lies in the fact that by coupling the proportion of the under-decomposition temperature range with the degree of deviation of the average temperature, the potential for solidification deposition in local areas of the spray-wall region in a short period of time can be quantified; among them, the proportion of under-decomposition reflects the duration of the temperature insufficiency period, and the degree of deviation of the average temperature reflects the degree of insufficiency of the overall energy level. The product of the two is used to characterize the insufficiency of the local reaction. It should also be noted that the advantage of obtaining the spray-wall decomposition insufficiency coefficient is that it can provide early warning of the short-term cumulative risk of local crystal solidification before the spraying strategy has been adjusted, which helps to optimize the spraying direction, spraying amount and spraying timing, reduce surface deposition and improve the efficiency of subsequent reduction reaction.

[0020] In this embodiment of the invention, a local cryogenic region migration vector is constructed based on the spray-wall decomposition insufficiency coefficient and the hull roll angle and roll velocity. Combined with the time-varying sequence of exhaust flow velocity, a spatiotemporal drift function of the cryogenic region relative to the exhaust flow is obtained. The process of measuring the spatiotemporal drift trend of the potential solidification region is as follows: During ship navigation, the ship's roll angle is obtained. With roll speed Time series data, and compared with the spray-wall decomposition insufficiency coefficient Perform timing alignment, where The insufficient coefficient for spray-wall decomposition obtained at time t; It should be noted that the roll angle represents the instantaneous tilt angle of the hull about its longitudinal axis, and the roll speed represents the rate of change of the roll angle over time. It can be understood that these two parameters directly affect the change of the position of the low-temperature region in the exhaust pipe in the lateral direction of the pipe. Preferably, the roll angle sampling frequency is 50Hz, which can fully reflect the dynamic characteristics of the ship's roll, and the roll speed is obtained from the roll angle data through a differential method; Insufficient coefficient of spray-wall decomposition Multiply by the roll angle and roll velocity to construct the migration vector of the local cryogenic region. : ; It should be noted that the direction of the migration vector represents the dynamic movement trend of the low-temperature region in the lateral and longitudinal directions of the exhaust pipe, and the vector amplitude reflects the relative magnitude of the cumulative intensity of the low-temperature region. It should also be noted that by coupling the spray-wall decomposition insufficiency coefficient with the ship's roll dynamics, the spatial behavior of the cryogenic zone as the ship's attitude changes periodically or randomly can be characterized. Synchronous acquisition of time-varying exhaust flow velocity sequences This is then combined with the migration vector of the local low-temperature region to obtain the spatiotemporal drift function of the low-temperature region relative to the exhaust flow: ,in It is the spacetime drift function; It should be noted that, This indicates the axial position of the exhaust pipe. It can be understood that this function reflects the drift path of the low-temperature zone inside the pipe over time along the axial and lateral directions.

[0021] In this embodiment of the invention, the process of calculating the predicted solidification increment based on the spatiotemporal drift trend and the local wall temperature change rate, and obtaining the potential cumulative solidification index, is as follows: After calculating the spatiotemporal drift trend of the local low-temperature region, the spatiotemporal drift function is... With exhaust wall temperature distribution sequence Perform synchronous matching; It should be noted that the rate of change of local wall temperature is obtained through time difference, and an exemplary expression is as follows: ,in For the local wall temperature change rate, For time difference time intervals; It should be noted that the wall temperature change rate is used to reflect the rate at which the wall temperature decreases or increases over time, thereby indicating whether the thermal conditions are trending toward the low-temperature region required for solidification. By coupling the spatiotemporal drift function with the local wall temperature change rate, the predicted local solidification increment is obtained. : ; The predicted die-bonding increment is cumulatively integrated using a sliding window to offset the periodic effect of the rolling period on the instantaneous temperature drop. ,in This is the cumulative prediction of the solidification increment. For time indexing, The length of the sliding window; Understandably, this cumulative integral is used to capture the short-term cumulative trend of the possibility of solidification; The cumulative prediction is spatially integrated along the axial direction of the exhaust pipe to obtain the potential cumulative index for die bonding. : ,in and These indicate the axial positions of the exhaust pipe inlet and outlet, respectively. It should be noted that the physical meaning of the potential accumulation index of crystal bonding is that, by coupling the spatiotemporal drift trend with the local temperature decrease trend, the short-term cumulative risk of crystal bonding can be quantified, and an early warning can be given before crystal bonding has formed on a large scale. It should also be noted that the benefits of obtaining the potential accumulation index of solidification are: it can promptly identify the drift direction and accumulation intensity of potential solidification areas inside the exhaust pipe, providing accurate process quantity basis for dynamically adjusting the injection angle, injection time, injection direction and injection quantity, thereby reducing the risk of exhaust back pressure increase caused by solidification accumulation and improving the continuous performance of marine nitrogen oxide emission reduction systems.

[0022] In this embodiment of the invention, the process of extracting local backpressure evolution features based on the potential accumulation index of die-bonding and the rate of change of exhaust backpressure, and constructing a nozzle-wall coupled degradation state vector to distinguish between short-cycle die-bonding influence and long-cycle degradation trend, and obtaining a degradation segment feature set is as follows: The aforementioned potential cumulative index for die bonding was obtained. Based on this, continue to collect exhaust back pressure sequences. The exhaust back pressure was then subjected to first-order difference processing to obtain the exhaust back pressure change rate. : ,in The time interval for the first-order difference; It should be noted that the exhaust back pressure change rate is used to reflect the changing trend of the internal resistance of the exhaust system over time. It can be understood that when the local die-bonding increment causes the channel to shrink, the exhaust back pressure change rate will show a continuous upward trend. The potential accumulation index of die bonding and the rate of change of exhaust back pressure are normalized, and a nozzle-wall coupled degradation state vector is constructed using a linear combination method. : ,in, and The weighting coefficients for the potential accumulation index of solidification and the rate of change of exhaust back pressure are preferably obtained through experimental calibration or training with historical operating data. For example, the weighting coefficients can be set to make the die-bonding accumulation index more sensitive to long-term trends, while the exhaust back pressure change rate is more sensitive to short-term disturbances, in order to distinguish between short-term die-bonding effects and long-term degradation behavior. The spray-wall coupled degradation state vector is subjected to time-series analysis, and short-period perturbations and long-period accumulation processes are distinguished based on time windows to obtain a degradation segment feature set. : ,in The segmentation of short-period solidification effects is used to characterize the rapid migration trend induced by instantaneous spray-wall perturbation and local phase transition. The long-term degradation trend is segmented to describe the slow degradation channel caused by the accumulation of weak decomposition of the spray-wall coupled thermal-flow field, thereby realizing the separation, identification and feature manifestation of the degradation mechanism on the time scale. For example, the process of performing time-series analysis on the spray-wall coupled degradation state vector and distinguishing between short-period disturbances and long-period accumulation processes based on time windows is as follows: First, the spray-wall coupling degradation state vector is analyzed. Construct a time series representation and arrange it in chronological order as follows: , where n is the total number of sampling time points; And perform a difference transformation on the sequence: ,in The result of the difference transform. The time interval for the difference transformation; Secondly, a two-layer time window is set up, with separate short-period windows defined. With long period window ,in ; And a time series energy function is constructed based on the variance evolution within the window: , ,in For short-cycle windows The time-series energy function, For long period window The time-series energy function, For short-cycle windows Internal spray-wall coupled degradation state vector time series variance For long period window Internal spray-wall coupled degradation state vector time series The variance; Furthermore, a perturbation-cumulative separation factor is established by using the energy ratio of short and long windows. : ,in This is to prevent division by zero by a very small constant (generally taken as...). ); When the perturbation-cumulative separation factor When the value is higher than a preset threshold, it is determined to be dominated by short-period disturbances; when the disturbance-cumulative separation factor is higher... When the value is below a preset threshold, it is determined that the long-cycle cumulative effect is enhanced, thus obtaining a time-segmented description of the spray-wall coupling degradation state. Finally, the short-cycle perturbation interval and the long-cycle cumulative interval are output as follows: and ; It should be noted that the short-cycle die-bonding effect corresponds to the sudden insufficient spray-wall and the instantaneous drop in wall temperature caused by swaying, with high-frequency components dominating; the long-cycle degradation trend corresponds to the slow increase in exhaust back pressure caused by continuous accumulation of die-bonding, with low-frequency components dominating. Understandably, by using the degradation segmentation feature set, the short-term perturbations and long-term changes in the spray-wall coupling degradation can be decoupled, thereby identifying whether there is a continuous degradation trend, rather than relying solely on a single spray-wall event or short-term temperature changes.

[0023] In this embodiment of the invention, the process of extracting exhaust wall temperature and back pressure based on the degradation segment feature set, comparing the exhaust wall temperature and back pressure with the allowable wall temperature range and the back pressure safety threshold respectively, and calculating the injection adjustment offset to compensate for the insufficient decomposition caused by the injection-wall temperature coupling is as follows: For the short-cycle solidification effect segment and the long-cycle degradation trend segment in the degradation segment feature set, the corresponding exhaust wall temperature and back pressure are extracted respectively. exhaust wall temperature With respect to the allowable wall temperature range Perform interval comparisons to obtain the local wall temperature deviation. : ; And extract back pressure With back pressure safety threshold relative deviation : ; Constructing injection relative controllable bias parameters : ,in , These are the local wall temperature deviations. Back pressure With back pressure safety threshold relative deviation The preferred weighting coefficients are obtained through experimental calibration or training with historical operating data. The jet adjustment offset was calculated separately for the short-cycle die-bonding effect segment and the long-cycle degradation trend segment. : ,in For short-cycle injection, the relatively controllable bias parameters are used. For long-cycle injection, the relatively controllable bias parameters are used. This is a preset proportional coefficient for the controllable offset parameter of the short-cycle injection. This is the preset proportional coefficient for the controllable offset parameter of the long-cycle injection. The injection adjustment offset is used as a compensation for the injection intensity to update the injection intensity; Therefore, the injection adjustment offset will dynamically compensate for the insufficient decomposition caused by the spray-wall temperature coupling without changing the basic framework of the original injection strategy. This will cause the local wall temperature to converge near the effective temperature window of the catalyst and suppress the continuous decomposition decline caused by abnormal back pressure, thereby reducing the probability of short-cycle solidification and delaying the cumulative effect of long-cycle degradation.

[0024] This invention dynamically captures the coupling state between the injection process and the exhaust wall temperature under complex ship operating conditions, and continuously quantifies key influencing factors such as low temperature region, solidification migration and back pressure evolution. Without changing the existing selective catalytic reduction hardware structure, it enables injection control to shift from traditional static temperature range determination to dynamic compensation based on the spray-wall relationship and its time evolution characteristics, thereby significantly enhancing the nitrogen oxide reduction efficiency under low load and extreme sea conditions.

[0025] This invention, by constructing a spray-wall decomposition deficiency coefficient and a description of local low-temperature region migration, can identify potential crystal-bonding regions in advance and predict their spatiotemporal drift trends, enabling the control strategy to achieve targeted adjustment capabilities and suppress the formation and accumulation of crystal deposition from the source. At the same time, through the joint evaluation of the potential accumulation index of crystal bonding and the back pressure evolution characteristics, it can distinguish between short-cycle crystal bonding effects and long-cycle degradation trends in closed-loop regulation, achieve fine compensation of spray offset, and enable timely correction of local low-temperature effects and avoid systemic degradation caused by continuous increase in back pressure.

[0026] Compared to conventional methods that only focus on catalyst inlet temperature or overall exhaust temperature, this invention can perform fine-grained modeling of the coupling mechanism between local temperature field, solidification distribution, and back pressure changes, enabling injection regulation to shift from outcome control to process control. This significantly improves the adaptability of the control strategy to temperature disturbances under multiple operating conditions and changes in hull attitude, effectively reduces dependence on exhaust temperature and catalyst temperature window, and ultimately achieves long-term stable compliance with nitrogen oxide emissions and improves the reliability and durability of marine diesel engine emission reduction systems.

[0027] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0028] It should be understood that in the various embodiments of this application, the order of the above-mentioned processes does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0029] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A control method for a marine diesel engine nitrogen oxide emission reduction system, characterized in that: Includes the following steps: The ship's attitude, exhaust gas velocity, and local temperature field of the exhaust pipe wall are obtained. The exhaust wall temperature distribution function is constructed by sampling along the axial and circumferential directions, and the spray-wall coupled temperature field description set is formed by combining the spray position, spray angle and exhaust temperature. Based on the spray-wall coupled temperature field description set, the temperature range of nitrogen oxide spray liquid in the evaporation and decomposition stages is segmented and fitted to extract the effective decomposition temperature range and the under-decomposition temperature range, and the spray-wall decomposition insufficiency coefficient is calculated based on the proportion of the under-decomposition temperature range. Based on the insufficient coefficient of the spray-wall decomposition and the hull roll angle and roll velocity, a migration vector of the local cryogenic region is constructed, and combined with the time-varying sequence of exhaust flow velocity, the spatiotemporal drift function of the cryogenic region relative to the exhaust flow is obtained. The predicted amount of solidification increment is calculated based on the spatiotemporal drift trend and the local wall temperature change rate, and the potential cumulative index of solidification is obtained. The local back pressure evolution characteristics are extracted based on the potential accumulation index of solidification and the rate of change of exhaust back pressure, and a spray-wall coupled degradation state vector is constructed to obtain a degradation segment feature set. The exhaust wall temperature and back pressure are extracted based on the degradation segment feature set, and the exhaust wall temperature and back pressure are compared with the allowable wall temperature range and the back pressure safety threshold, respectively, to calculate the injection adjustment offset.

2. The control method for the nitrogen oxide emission reduction system of a marine diesel engine according to claim 1, characterized in that: The process of acquiring hull attitude, exhaust gas velocity, and local temperature field of the exhaust pipe wall, constructing the exhaust wall temperature distribution function by sampling along the axial and circumferential directions, and forming a spray-wall coupled temperature field description set by combining the injection position, injection angle, and exhaust temperature is as follows: The ship attitude sensor, exhaust temperature infrared array measuring points and exhaust pipe wall multi-point thermocouple array are integrated into the marine diesel engine exhaust system. The ship's attitude sensor collects the ship's three-dimensional attitude angles and marks them as attitude data, and records the acquisition time sequence of each frame of attitude data; Simultaneously, exhaust temperature infrared arrays are used to collect exhaust flow temperature data, and the instantaneous temperature value of each detection point is calculated along the axial direction of the pipeline. With Zhou Xiang Establish two-dimensional coordinates based on direction; The collected attitude data and temperature data are time-series aligned and a unified sampling timestamp is used. Equally spaced sampling points will be performed along the axial direction, and the number of sampling points will be denoted as [missing information]. Equal-angle sampling will be performed along the circumferential direction, and the number of sampling points will be denoted as... ; For each ( , The temperature values ​​at the sampling points are interpolated, and the exhaust wall temperature distribution function is constructed: Where t is the sampling time, Here are the axial position coordinates of the exhaust pipe. These are the circumferential angular coordinates of the exhaust pipe; Obtain the injection position output by the injection system control unit. Spray angle ; Corresponding injection position Extract the cross-sectional temperature corresponding to the axial position from the wall temperature distribution function. ; The cross-sectional temperature was normalized to obtain the local spray-wall temperature. : ; exhaust temperature Spray angle Local spray-wall temperature The jet-wall coupling calculation module is used to obtain the angular projection value between the jet angle and the local jet-wall temperature, as well as the jet-wall coupling temperature. Finally, a spray-wall coupled temperature field description set was constructed.

3. The control method for the nitrogen oxide emission reduction system of a marine diesel engine according to claim 2, characterized in that: The specific calculation logic for the spray-wall coupling calculation module to obtain the angular projection value between the spray angle and the local spray-wall temperature, and the spray-wall coupling temperature is as follows: Add an angle projection operation between the spray angle and the local spray-wall temperature: ,in This is the angular projection value between the spray angle and the local spray-wall temperature; The angular projection value between the injection angle and the local spray-wall temperature is compared with the exhaust temperature. Perform integral calculation of spray-wall coupling temperature : .

4. The control method for the nitrogen oxide emission reduction system of a marine diesel engine according to claim 2, characterized in that: Based on the spray-wall coupled temperature field description set, the temperature range of the nitrogen oxide spray liquid during the evaporation and decomposition stages is piecewise fitted to extract the effective decomposition temperature range and the under-decomposition temperature range. The process of calculating the spray-wall decomposition insufficiency coefficient based on the proportion of the under-decomposition temperature range is as follows: Extracting spray-wall coupling temperature from the spray-wall coupling temperature field description set To reduce the spray-wall coupling temperature Establish instantaneous temperature trajectories according to time series, and divide temperature ranges into intervals based on experimental data; Spray-wall coupling temperature Perform smoothing filtering and normalize to a unified temperature range reference; The normalized temperature sequence is segmented and fitted according to a preset temperature threshold to obtain the under-decomposition temperature range, the effective decomposition temperature range, and the efficient decomposition reaction zone. The time period of the under-decomposition temperature range is statistically analyzed, and the ratio of this time period to the entire injection cycle is calculated to obtain the proportion of the under-decomposition temperature range. : ,in This refers to the time period of the under-decomposition temperature range. For the entire injection cycle; Calculate the insufficient decomposition coefficient of the spray-wall decomposition based on the proportion of the under-decomposition temperature range. : ,in, The periodic average of the spray-wall coupling temperature. The threshold for complete and effective decomposition reaction.

5. The control method for the nitrogen oxide emission reduction system of a marine diesel engine according to claim 4, characterized in that: Based on the insufficient coefficient of the spray-wall decomposition and the hull roll angle and roll velocity, a migration vector for the local cryogenic region is constructed. Combined with the time-varying sequence of exhaust velocity, the spatiotemporal drift function of the cryogenic region relative to the exhaust flow is obtained as follows: During ship navigation, the ship's roll angle is obtained. With roll speed Time series data, and compared with the spray-wall decomposition insufficiency coefficient Perform timing alignment; Insufficient coefficient of spray-wall decomposition Multiply by the roll angle and roll velocity to construct the migration vector of the local cryogenic region. : ; Synchronous acquisition of time-varying exhaust flow velocity sequences This is then combined with the migration vector of the local low-temperature region to obtain the spatiotemporal drift function of the low-temperature region relative to the exhaust flow: ,in This is the spacetime drift function.

6. The control method for the nitrogen oxide emission reduction system of a marine diesel engine according to claim 5, characterized in that: The process of calculating the predicted solidification increment based on the spatiotemporal drift trend and the local wall temperature change rate, and obtaining the potential cumulative index of solidification, is as follows: After calculating the spatiotemporal drift trend of the local low-temperature region, the spatiotemporal drift function is... With exhaust wall temperature distribution sequence Perform synchronous matching; The rate of change of local wall temperature is obtained through time difference, and the expression is as follows: ,in For the local wall temperature change rate, For time difference time intervals; By coupling the spatiotemporal drift function with the local wall temperature change rate, the predicted local solidification increment is obtained. : ; The predicted die-bonding increment is accumulated and integrated using a sliding window: ,in This is the cumulative prediction of the solidification increment. For time indexing, The length of the sliding window; The cumulative prediction is spatially integrated along the axial direction of the exhaust pipe to obtain the potential cumulative index for die bonding. : ,in and These indicate the axial positions of the exhaust pipe inlet and outlet, respectively.

7. The control method for a marine diesel engine nitrogen oxide emission reduction system according to claim 6, characterized in that: The process of extracting local backpressure evolution features based on the potential accumulation index of solidification and the rate of change of exhaust backpressure, and constructing a nozzle-wall coupled degradation state vector to obtain the degradation segment feature set is as follows: Acquisition of exhaust back pressure sequence The exhaust back pressure was then subjected to first-order difference processing to obtain the exhaust back pressure change rate. : ,in The time interval for the first-order difference; The potential accumulation index of die bonding and the rate of change of exhaust back pressure are normalized, and a nozzle-wall coupled degradation state vector is constructed using a linear combination method. : ,in, and The weighting coefficients for the potential accumulation index of solidification and the rate of change of exhaust back pressure; The degradation state vector of the spray-wall coupling is subjected to time series analysis, and short-period disturbances and long-period accumulation processes are distinguished based on time windows to obtain a degradation segment feature set.

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