A Method for Determining and Controlling Abnormal Combustion in Hydrogen Internal Combustion Engines Based on Ion Current Signals

Abstract

This invention discloses a method for judging and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals, belonging to the field of hydrogen internal combustion engine combustion monitoring and control technology. The method includes: real-time acquisition and preprocessing of in-cylinder ion current signals; extraction of the energy and energy ratio of the signals in the low-frequency, mid-frequency, and high-frequency bands as feature values; online anomaly detection of the feature values ​​based on the robust Z-score method, accurately identifying misfire, pre-ignition, and knock, and distinguishing pre-ignition caused by in-cylinder hot spots or oil auto-ignition through the mid-frequency energy ratio; independently executing adaptive control such as delayed ignition, delayed hydrogen injection, or water injection on the single cylinder experiencing the anomaly according to the anomaly type and cause; simultaneously, statistically analyzing the abnormal combustion frequency, and executing power-limited operation or engine shutdown for inspection when exceeding limits; this invention achieves low-cost, highly disturbance-resistant, traceable, and cylinder-independent closed-loop control of hydrogen internal combustion engine combustion, significantly improving the engine's operational safety and stability.

Description

Technical Field

[0001] This invention relates to the field of combustion monitoring and control technology for hydrogen internal combustion engines, and in particular to a method for determining and controlling abnormal combustion in hydrogen internal combustion engines based on ion current signals. Background Technology

[0002] Hydrogen is a clean fuel, and in recent years, countries around the world have been actively developing hydrogen internal combustion engines and automobiles. However, due to the extremely wide combustible range, extremely low ignition energy, and high diffusivity of hydrogen fuel, it is highly susceptible to abnormal combustion phenomena under conditions such as high load, low excess air coefficient, and high residual gas content. Although backfire can be avoided through direct injection, hydrogen internal combustion engines still have a significant risk of abnormal combustion, such as pre-ignition (hydrogen combustion before ignition due to hot spots in the cylinder or spontaneous combustion of engine oil); knock (high-pressure oscillation caused by spontaneous combustion of the air-fuel mixture in the cylinder); and misfire (interruption of flame propagation).

[0003] Traditional diagnostic methods based on in-cylinder transient pressure sensors and optical endoscopy suffer from high costs, poor anti-interference capabilities, and the inability to directly analyze the causes of abnormal combustion. Furthermore, most are offline diagnostics, failing to identify, suppress, and regulate abnormal combustion simultaneously. Ion current detection technology, however, can directly sense flame ionization signals using existing spark plug electrodes, offering advantages such as high real-time performance and extremely low cost. However, current ion current research largely focuses on combustion phase identification, lacking a unified method for determining and controlling various types of abnormal combustion in hydrogen internal combustion engines.

[0004] To address the aforementioned issues and improve the combustion stability of hydrogen internal combustion engines through online diagnosis of abnormal combustion characteristics, a method for determining and controlling abnormal combustion in hydrogen internal combustion engines based on ion current signals is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining and controlling abnormal combustion in hydrogen internal combustion engines based on ion current signals, aiming to achieve low-cost, high-reliability, traceable, and cylinder-independent closed-loop control of abnormal combustion.

[0006] To achieve the above objectives, this invention provides a method for determining and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals, comprising the following steps: Step S1, Data Acquisition and Preprocessing: The operating parameters of the hydrogen internal combustion engine and the in-cylinder ion current signal are acquired synchronously through the spark plug, and the ion current signal is filtered and phase aligned. Step S2, Feature Extraction: Based on the preprocessed ion current signal, extract its time domain features and frequency domain features. The frequency domain features include low frequency energy, medium frequency energy, high frequency energy, as well as the medium / low frequency energy ratio and the high / low frequency energy ratio. Step S3, Abnormal Combustion Judgment: The robust Z-score method is used to perform online outlier detection on the frequency domain characteristics to determine whether misfire, pre-ignition, or detonation has occurred in the current cycle. If pre-ignition is determined, the cause of pre-ignition is further identified based on the medium / low frequency energy ratio. Step S4, Adaptive Control: Based on the type of abnormal combustion and its inducing cause, independently execute corresponding control actions for the cylinders where abnormal combustion occurs in order to suppress abnormal combustion; Step S5, Data Statistics and Protection: Statistically count the frequency of various abnormal combustion events within a preset number of cycles. When the frequency exceeds the first threshold, limit the engine's operating boundary. When the frequency exceeds the second threshold, issue a shutdown and inspection command.

[0007] Preferably, step S2 is performed as follows: S21, Based on time-domain ion current signal Set current threshold ,in Extract the starting angle ,in, Indicates the reference current threshold. This represents the correction function. Indicates engine speed. Indicates the average effective pressure. Indicates the air-fuel ratio. Indicates crankshaft rotation angle; S22, to Perform piecewise Fourier transform to calculate the low-frequency energy in the 0–1 kHz frequency band. Mid-frequency energy in the 1~4kHz frequency band and high-frequency energy in the 4~10kHz band The expression is as follows: ; like Calculate the mid / low frequency energy ratio High / low frequency energy ratio The expression is as follows: ; .

[0008] Preferably, the condition for determining misfire in step S3 is: the starting angle at which the ion current signal cannot be extracted. or .

[0009] Preferably, the condition for determining pre-ignition in step S3 is: .

[0010] Preferably, the method for identifying the cause of pre-ignition in step S3 is as follows: calculate the medium / low frequency energy ratio of the current cycle. robust Z-score ,like If the value is less than a preset threshold, it is determined that pre-ignition is induced by local hot spots in the cylinder; if... If the value is not less than a preset threshold, then the pre-ignition is determined to be induced by in-cylinder oil auto-ignition. The calculation expression is as follows: ; In the formula, For variables or , This represents the specific value in the k-th order during the test. For variables k In the near N The median of the cycle, It is a constant used to prevent the denominator from being 0 when all data points are the same.

[0011] Preferably, the condition for determining detonation in step S3 is: calculating the high / low frequency energy ratio of the current cycle. robust Z-score ,like If the value exceeds a preset threshold, a knocking event is determined to have occurred.

[0012] Preferably, the control actions in step S4 include: for misfire, increasing ignition energy or advancing the ignition timing; for pre-ignition induced by in-cylinder hot spots, delaying hydrogen injection timing and / or activating water injection; for pre-ignition induced by in-cylinder oil auto-ignition, delaying hydrogen injection timing and / or activating water injection; for knock, delaying ignition timing and / or activating water injection, and reducing the mean effective pressure when the knock intensity exceeds the super knock threshold.

[0013] Preferably, the control action in step S4 has single-cylinder selectivity, and the control strategy is only executed on the current cylinder that is determined to have abnormal combustion, while the original control parameters of the other cylinders remain unchanged.

[0014] Preferably, the first threshold and the second threshold in step S5 are respectively: when the total frequency of abnormal combustion exceeds 10% in the most recent 1000 cycles, the engine mean effective pressure is limited; when it exceeds 30%, the engine is shut down for inspection based on the main cause of pre-ignition.

[0015] Therefore, the present invention employs the above-mentioned method for determining and controlling abnormal combustion in hydrogen internal combustion engines based on ion current signals, which has the following beneficial effects: (1) By combining segmented frequency domain energy analysis with robust Z-fraction method, the cyclic fluctuations and sensor noise interference are suppressed, which significantly improves the robustness and accuracy of abnormal combustion identification; (2) The innovative use of medium / low frequency energy ratio distinguishes between pre-ignition induced by local hot spots in the cylinder and pre-ignition induced by spontaneous combustion of engine oil in the cylinder, thereby achieving root cause diagnosis of abnormal combustion, providing key basis for subsequent targeted control and fault diagnosis, and effectively improving control efficiency; (3) A single-cylinder independent control strategy is adopted, and intervention is only performed on abnormal cylinders to avoid the impact of global adjustment on the performance of other cylinders. At the same time, an abnormal frequency graded protection mechanism is established, which automatically limits power or prompts shutdown for inspection when the limit is exceeded, providing comprehensive protection for the long-term safe operation of the engine; (4) The spark plug is used directly as an ion current sensor, without the need to install a cylinder pressure sensor or optical equipment. This greatly reduces the system cost while ensuring diagnostic accuracy, making it easy to promote and apply in mass-produced hydrogen internal combustion engines.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a structural diagram of the method for determining and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals, as described in this invention. Figure 2 This is an overall flowchart of the method for determining and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals, according to an embodiment of the present invention. Reference numerals: 1. Direct injection hydrogen internal combustion engine; 2. Spark plug; 3. In-cylinder direct injection hydrogen nozzle; 4. Water nozzle. Detailed Implementation

[0018] The following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0019] Please see Figures 1-2 A method for determining and controlling abnormal combustion in hydrogen internal combustion engines based on ion current signals is presented. The complete detection system includes a direct-injection hydrogen internal combustion engine 1, spark plugs 2, in-cylinder direct-injection hydrogen nozzles 3, and water nozzles 4. During detection, the in-cylinder ion current signal is collected through the spark plug electrodes via sampling and low-pass filtering circuits. This signal is input into the abnormal combustion control module, and after diagnosis, ignition, H2 injection, and water injection are controlled to manage abnormal combustion in the cylinder. The specific steps are as follows: Step S1, Data Acquisition and Preprocessing: Operating parameters of the hydrogen internal combustion engine and in-cylinder ion current signals are synchronously acquired via the spark plug, and the ion current signals are filtered and phase-aligned; the specific process is as follows: S1.1 acquires the engine speed for each cycle from the ECU via spark plug 2 at a sampling rate ≥200 Hz. BMEP load, air-fuel ratio Hydrogen injection timing (SOI), ignition timing (IGT); S1.2 The ion current sampling circuit based on the bias resistor acquires the ion current signal at a sampling rate ≥20 kHz. The obtained signal is low-pass filtered at 10 kHz to eliminate high-frequency electronic signal interference. The signal is aligned with the ignition timing IGT as 0° to obtain the ion current signal as a function of crankshaft angle. ; S1.3 Each cylinder establishes an N=1000 loop real-time cache of each feature parameter and judgment threshold for subsequent online updates and statistics.

[0020] Step S2, Feature Extraction: Based on the preprocessed ion current signal, extract its time-domain and frequency-domain features. The frequency-domain features include low-frequency energy, mid-frequency energy, high-frequency energy, as well as the mid / low-frequency energy ratio and the high / low-frequency energy ratio. The specific process is as follows: S2.1 Based on time-domain ion current signal Set current threshold ,in Extract the starting angle ,in, Indicates the reference current threshold. This represents the correction function. Indicates engine speed. Indicates the average effective pressure. Indicates the air-fuel ratio. Indicates crankshaft rotation angle; S2.2 Perform piecewise Fourier transform to calculate the low-frequency energy in the 0–1 kHz frequency band. Mid-frequency energy in the 1~4kHz frequency band and high-frequency energy in the 4~10kHz band The expression is as follows: ; like Calculate the mid / low frequency energy ratio High / low frequency energy ratio The expression is as follows: ; .

[0021] Step S3, Abnormal Combustion Determination: Robust Z-score method is used to perform online outlier detection on frequency domain characteristics to determine whether misfire, pre-ignition, or detonation has occurred in the current cycle. If pre-ignition is determined, the inducing cause of pre-ignition is further identified based on the mid / low frequency energy ratio. The specific process is as follows: S3.1 If extraction fails or If a fire is detected, control method S4.1 is initiated; otherwise, control method S3.2 is initiated.

[0022] S3.2 If If combustion occurs before the start of IGT, it can be inferred that pre-ignition has occurred, and proceed to S3.2.1 to determine the specific cause and manifestation of pre-ignition; otherwise, proceed to S3.3. S3.2.1 Using the robust Z-score method to... Perform outlier detection, if If pre-ignition is caused by localized hot spots in the cylinder, control method S4.2 is initiated; otherwise, if pre-ignition is caused by spontaneous combustion of engine oil in the cylinder, control method S4.3 is initiated. The calculation expression is as follows: ; In the formula, For variables or , This represents the specific value in the k-th order during the test. For variables k In the near N The median of the cycle, It is a constant used to prevent the denominator from being 0 when all data points are the same; S3.3 Using the robust Z-score method to... Perform outlier detection, if If a knocking event is detected, proceed to control method S4.4; otherwise, proceed to step S5.

[0023] Step S4, Adaptive Control: Based on the type of abnormal combustion and its inducing cause, independently execute corresponding control actions for the cylinders where abnormal combustion occurs to suppress abnormal combustion; the specific process is as follows: S4.1 After a fire is discovered: ① The ignition charging time is increased by 10% only for the target cylinder, while the time for other cylinders remains unchanged; ②If misfire still occurs after ≥3 consecutive cycles: Pre-ignite spark plug 2 of that cylinder by 3–5°CA.

[0024] S4.2 It was found that pre-ignition caused by hot spots in the cylinder was mainly caused by residual heat of spark plug electrode 2, metal hot spots in the valve gap area, and high temperature area of ​​residual gas. ①Only the hydrogen injection time SOI 20°CA of the in-cylinder direct injection hydrogen nozzle 3 of the judgment cylinder is delayed, while other cylinders remain unchanged; ②Only open water nozzle 4 for the judgment cylinder to reduce the temperature inside the cylinder.

[0025] S4.3 found that pre-ignition caused by oil auto-ignition is mainly due to oil droplets / mist entering the combustion chamber and evaporating and auto-igniting in the high-temperature atmosphere inside the cylinder. ①Only the hydrogen injection time SOI 20°CA of the in-cylinder direct injection hydrogen nozzle 3 of the judgment cylinder is delayed, while other cylinders remain unchanged; ②Only open water nozzle 4 in the judgment cylinder to reduce the temperature inside the cylinder; After S4.4 detected a detonation: ① Only determine the delayed ignition of spark plug 2 in cylinder 2 (2–6°CA); ②Only the water nozzle 4 is turned on in the judgment cylinder to reduce the combustion temperature inside the cylinder; ③If It still exceeds the set super knock threshold, so power output needs to be controlled, injection pulse width reduced, and BMEP lowered.

[0026] Step S5, Data Statistics and Protection: Statistically analyze the frequency of various abnormal combustion events within a preset number of cycles. When the frequency exceeds a first threshold, limit the engine's operating boundaries. When the frequency exceeds a second threshold, issue a shutdown and inspection command. Specifically: For the current N loops Update the system and statistically analyze the frequency of various abnormal combustion events after operation. If the frequency of abnormal combustion exceeds the 10% threshold within the last 1000 cycles, the BMEP needs to be reduced to the limit operating boundary. If the frequency of abnormal combustion exceeds 30% within the last 1000 cycles, the machine needs to be stopped for inspection based on different causes of pre-ignition (e.g., if the cause is mainly oil self-ignition, check the oil evaporation loss and oil seal sealing; if the cause is mainly hot spot self-ignition in the cylinder, check the electrode cleanliness).

[0027] Therefore, this invention employs the aforementioned method for determining and controlling abnormal combustion in hydrogen internal combustion engines based on ion current signals. It acquires in-cylinder ion current signals in real time via spark plug electrodes, and after filtering and phase alignment, extracts the time-domain combustion initiation angle and the energy ratios of low, medium, and high frequencies as characteristic parameters. A robust Z-score method is used for online anomaly detection of these features, accurately identifying misfires, knocking, and pre-ignition. Based on the medium-frequency energy ratio, it distinguishes whether pre-ignition is caused by in-cylinder hot spots or oil auto-ignition. Depending on the type and cause of the anomaly, adaptive control such as delayed ignition, delayed hydrogen injection, or water injection is independently implemented for the cylinder experiencing the anomaly. Simultaneously, the anomaly frequency is statistically analyzed, and automatic power limiting or engine shutdown for inspection is triggered when limits are exceeded. This invention achieves low-cost, highly disturbance-resistant, traceable, and independent inter-cylinder combustion closed-loop control, significantly improving the operational safety and stability of hydrogen internal combustion engines.

[0028] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for determining and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals, characterized in that, Includes the following steps: Step S1, Data Acquisition and Preprocessing: The operating parameters of the hydrogen internal combustion engine and the in-cylinder ion current signal are acquired synchronously through the spark plug, and the ion current signal is filtered and phase aligned. Step S2, Feature Extraction: Based on the preprocessed ion current signal, extract its time domain features and frequency domain features. The frequency domain features include low frequency energy, medium frequency energy, high frequency energy, as well as the medium / low frequency energy ratio and the high / low frequency energy ratio. Step S3, Abnormal Combustion Judgment: The robust Z-score method is used to perform online outlier detection on the frequency domain characteristics to determine whether misfire, pre-ignition, or detonation has occurred in the current cycle. If pre-ignition is determined, the cause of pre-ignition is further identified based on the medium / low frequency energy ratio. Step S4, Adaptive Control: Based on the type of abnormal combustion and its inducing cause, independently execute corresponding control actions for the cylinders where abnormal combustion occurs in order to suppress abnormal combustion; Step S5, Data Statistics and Protection: Statistically count the frequency of various abnormal combustion events within a preset number of cycles. When the frequency exceeds the first threshold, limit the engine's operating boundary. When the frequency exceeds the second threshold, issue a shutdown and inspection command.

2. The method for determining and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals according to claim 1, characterized in that, The process of step S2 is as follows: S21, Based on time-domain ion current signal Set current threshold ,in Extract the starting angle ,in, Indicates the reference current threshold. This represents the correction function. Indicates engine speed. Indicates the average effective pressure. Indicates the air-fuel ratio. Indicates crankshaft rotation angle; S22, to Perform piecewise Fourier transform to calculate the low-frequency energy in the 0–1 kHz band. Mid-frequency energy in the 1~4kHz frequency band and high-frequency energy in the 4~10kHz band The expression is as follows: ； like Calculate the mid / low frequency energy ratio High / low frequency energy ratio The expression is as follows: ； 。 3. The method for determining and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals according to claim 2, characterized in that, The condition for determining misfire in step S3 is: the starting angle at which the ion current signal cannot be extracted. or .

4. The method for determining and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals according to claim 3, characterized in that, The condition for determining pre-ignition in step S3 is: .

5. The method for determining and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals according to claim 4, characterized in that, The method for identifying the cause of pre-ignition in step S3 is as follows: calculate the mid / low frequency energy ratio of the current cycle. robust Z-score ,like If the value is less than a preset threshold, it is determined that pre-ignition is induced by local hot spots in the cylinder; if... If the value is not less than a preset threshold, then the pre-ignition is determined to be induced by spontaneous combustion of engine oil in the cylinder. The calculation expression is as follows: ； In the formula, For variables or , This represents the specific value in the k-th order during the test. Let k be the median of the variable k over the last N cycles. It is a constant.

6. The method for determining and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals according to claim 5, characterized in that, The condition for determining detonation in step S3 is: calculate the high / low frequency energy ratio of the current cycle. robust Z-score ,like If the value exceeds a preset threshold, a knocking event is determined to have occurred.

7. The method for determining and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals according to claim 6, characterized in that, The control actions in step S4 include: for misfire, increasing ignition energy or advancing the ignition timing; for pre-ignition induced by in-cylinder hot spots, delaying hydrogen injection timing and / or activating water injection; for pre-ignition induced by in-cylinder oil auto-ignition, delaying hydrogen injection timing and / or activating water injection; for knock, delaying ignition timing and / or activating water injection, and reducing the mean effective pressure when the knock intensity exceeds the super knock threshold.

8. The method for determining and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals according to claim 7, characterized in that: The control action in step S4 is single-cylinder selective, and the control strategy is only executed on the current cylinder that is determined to have abnormal combustion, while the original control parameters of the other cylinders remain unchanged.

9. The method for determining and controlling abnormal combustion in a hydrogen internal combustion engine based on ion current signals according to claim 8, characterized in that, The first and second thresholds in step S5 are as follows: when the total frequency of abnormal combustion exceeds 10% in the most recent 1000 cycles, the engine mean effective pressure is limited; when it exceeds 30%, the engine is shut down for inspection based on the cause of pre-ignition.

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