Cold start emission cooperative control method of natural gas engine and control system of cold start emission cooperative control method

Abstract

The invention discloses a cold start emission cooperative control method and system for a natural gas engine. The cold start emission cooperative control method comprises the following steps that firstly, cold start recognition is conducted; 2, calculating a cold start emission index CEI in real time; step 3, strategy selection: if the CEI is less than or equal to the emission index threshold value, adopting a post-processing priority regulation strategy; if CEIgt; an in-cylinder combustion optimization collaborative regulation strategy is adopted for the emission index threshold value; and 4, quitting the cold start mode. The method has the advantages that accurate decision making is achieved, the cold start emission severity is comprehensively quantified through CEI, and intelligent strategy switching is achieved; internal and external cooperation of a machine is realized, and global optimum is realized by dynamically distributing in-cylinder and post-processing control weights according to CEI; quick warming and low emission are taken into consideration, and post-treatment ignition is accelerated at the same time; the economical efficiency is good, a fuel economical efficiency loss threshold value is set, and excessive sacrifice of fuel consumption for pursuing emission is avoided; the device is high in adaptability and can be suitable for various fuel forms such as pure natural gas and hydrogen-doped natural gas.

Description

Technical Field

[0001] This invention relates to a control method and control system for an engine, and particularly to a cold start emission coordinated control method and control system for a natural gas engine, belonging to the field of engine control technology. Background Technology

[0002] With the advancement of the global "carbon peaking and carbon neutrality" strategy, low-carbon clean fuels have become crucial for emission reduction in the transportation sector. Natural gas, as a low-carbon fossil fuel, has significantly lower carbon emissions than gasoline and diesel, and is widely used in medium and heavy-duty commercial vehicles. However, natural gas engines, especially those employing stoichiometric combustion combined with three-way catalytic converters (TWC), face a significant technical bottleneck in industrialization: the control of unburned methane (CH4) emissions, particularly during cold starts. Methane is a potent greenhouse gas. During cold starts, the low cylinder temperature leads to incomplete combustion of natural gas, producing large amounts of unburned methane. Simultaneously, TWC requires temperatures above 250°C to operate efficiently, while the exhaust temperature during the initial cold start phase is far below this threshold, leaving the catalyst in a "cold-deactivated" state. This creates a significant emission window during which the vast majority of CH4 is emitted directly without treatment.

[0003] Current technological solutions mainly revolve around three aspects: in-engine measures, catalyst improvement, and passive technologies, but all have significant limitations. In-engine measures, such as delayed ignition and shutting off exhaust gas recirculation (EGR), can forcibly increase exhaust temperature, but at the cost of fuel economy and thermal efficiency, and the control is crude. At the catalyst level, the development of low-temperature ignition and highly selective methane oxidation catalysts (MOCs) is a key focus, but balancing the catalyst's low-temperature activity, resistance to hydrothermal aging, and cost is difficult, and it is still limited by the "cold start window" before ignition. Passive technologies, such as exhaust thermal management and tightly coupled catalyst arrangement, can shorten ignition time, but cannot fundamentally eliminate the emission window, and may be limited by installation space and cost. Specific existing technological solutions are as follows:

[0004] Option 1: Single-point in-cylinder temperature control. This involves using single or combined in-cylinder control methods such as retarding the ignition timing, turning off exhaust gas recirculation (EGR), or increasing idle speed to raise the exhaust temperature, thereby accelerating the heating process of aftertreatment systems such as the three-way catalytic converter (TWC).

[0005] Option 2: Simple aftertreatment temperature trigger control. Based on the inlet temperature sensor signal of the aftertreatment system (such as TWC), a fixed temperature threshold is set. When the temperature is below this threshold, a fixed in-cylinder heating strategy is executed (as described above); when the temperature is above the threshold, intervention is stopped or the system switches to normal control mode.

[0006] Option 3: Open-loop fuel with hydrogen blending assistance. During the cold start phase, a certain proportion of hydrogen is blended into the natural gas. The faster combustion speed and wider lean-burn limit of hydrogen are used to improve in-cylinder combustion, aiming to reduce the original CH4 emissions.

[0007] Based on existing technology and practical needs, the following disadvantages of natural gas engine aftertreatment systems can be identified:

[0008] 1. Lack of coordination between internal and external systems, and singular control objectives: The above-mentioned solutions (especially solutions 1 and 2) typically only have "increasing exhaust temperature" or "achieving a certain temperature in the aftertreatment system" as a single objective, failing to consider the optimization of in-cylinder combustion state in conjunction with the real-time efficiency of the aftertreatment system. This results in a lack of linkage in the control process, making it impossible to achieve a globally optimal balance between reducing raw emissions and accelerating catalyst ignition.

[0009] 2. The control strategy is crude and lacks quantitative assessment and adaptive capabilities: It relies on fixed thresholds (such as Scheme 2) to trigger control, and cannot make dynamic and fine adjustments according to the severity of cold start emission problems. The timing and intensity of control intervention depend on experience calibration, which has poor adaptability and is prone to over-adjustment or under-adjustment under changing operating conditions or environmental conditions.

[0010] 3. Excessive fuel economy loss: In pursuit of rapid warm-up, the in-cylinder measures in Scheme 1 (such as significantly delaying ignition and turning off EGR) often lead to a significant deterioration in fuel economy, and this deterioration continues throughout the entire cold start period, lacking a constraint and management mechanism for the loss of economy.

[0011] 4. The hydrogen blending strategy is isolated and costly: In Scheme 3, hydrogen blending control is usually a simple open-loop or table lookup based on operating conditions, without closed-loop coordination with other in-cylinder control parameters (such as ignition angle, EGR) and aftertreatment status. At the same time, due to the high cost of hydrogen, continuous or high-proportion hydrogen blending is uneconomical, and existing methods lack an intelligent mechanism to dynamically adjust the hydrogen blending ratio according to actual needs to balance effect and cost.

[0012] Therefore, existing technical solutions generally suffer from the problem of "poor economic efficiency of in-machine optimization and waiting for external catalysis to heat up". Summary of the Invention

[0013] Purpose of the invention: The purpose of this invention is to solve the following problems in natural gas engine emission aftertreatment systems:

[0014] 1. Insufficient and singular control strategies: Existing controls often employ fixed or simple temperature thresholds to trigger single actions, failing to dynamically adjust based on the severity of emission issues. The lack of a core decision parameter that comprehensively assesses both "in-cylinder combustion status" and "aftertreatment requirements" leads to a disconnect between in-cylinder optimization and aftertreatment control, hindering the achievement of globally optimal coordinated control.

[0015] 2. Lack of quantitative decision-making and adaptive capabilities: The control process relies on empirical thresholds and lacks real-time, quantitative assessment of the severity of cold-start emissions. It cannot intelligently distinguish the root cause of the problem (whether it is mainly due to poor combustion or failure of aftertreatment to ignite), which leads to inaccurate timing and inappropriate intensity of control intervention, potentially resulting in insufficient intervention or excessive sacrifice of economic efficiency.

[0016] 3. Imbalance between emission control and fuel economy: In the pursuit of rapid warm-up, there is a tendency to overuse methods such as retarding ignition and increasing idling speed, which leads to a significant increase in fuel consumption and fails to keep the economic losses caused by emission control within a reasonable range.

[0017] A method and control system for coordinated cold start emissions of natural gas engines are proposed. An adaptive coordinated method is proposed that can quantify cold start emissions in real time and intelligently switch in-cylinder and after-treatment control strategies accordingly, so as to achieve rapid and accurate control of pollutants during the cold start stage while ensuring fuel economy.

[0018] Technical solution: A method for coordinated control of cold start emissions of a natural gas engine, comprising the following steps:

[0019] Step 1: Cold start recognition. If the engine coolant temperature is less than the set value and the TWC temperature is less than the ignition temperature, it is determined that the cold start control mode has been entered.

[0020] Step 2: Calculate the Cold Start Emission Index (CEI) in real time based on the engine data collected in real time.

[0021] Step 3: Strategy selection. If CEI ≤ emission index threshold, adopt the aftertreatment priority control strategy; if CEI > emission index threshold, adopt the in-cylinder combustion optimization and synergistic control strategy.

[0022] Step 4: Exit cold start mode. When the water temperature is ≥ the set value and the TWC temperature is stable in the high efficiency window, exit cold start collaborative control and switch to normal emission control mode.

[0023] Preferably, the cold start emission index (CEI) is calculated in step two as follows:

[0024] CEI is defined as a weighted function of the in-cylinder unburned hydrocarbon equivalent and the ignition temperature difference of the aftertreatment system, and the calculation formula is as follows:

[0025]

[0026] in, This is a dynamic weighting factor for in-cylinder emissions, which is based on coolant temperature. The engine load L is adjusted in real time. When both are extremely low, it indicates poor in-cylinder combustion conditions, and the control value of optimizing raw emissions through in-cylinder means is low. At this time, α is reduced to decrease the sensitivity of CEI to changes in raw in-cylinder emissions, thereby avoiding the control system from adopting an aggressive control strategy that is too detrimental to fuel economy under conditions with limited optimization space.

[0027] : A scaling factor used to adjust the weight of post-treatment heating requirements in CEI. This factor is based on the TWC temperature. and exhaust flow Real-time adjustments are needed. When both are very low, it indicates that the post-processing system will face a slow, natural temperature rise. At this point, increasing... This value will amplify the impact of the "difference between target temperature and actual temperature" in CEI, thereby directing the optimization of the control system to focus more on solving the after-treatment inertia problem, prompting the adoption of in-cylinder measures to increase exhaust temperature earlier or more proactively.

[0028] These represent the volume concentrations of the corresponding components in the original emissions;

[0029] The target ignition temperature for TWC (e.g., 250°C);

[0030] This refers to the actual TWC temperature.

[0031] The higher the CEI value, the more serious the cold start emission problem, and the more proactive control strategies need to be adopted.

[0032] CEI range:

[0033] 0 1.0 (Ideal Range): After-treatment complete ignition, extremely low emissions, when the engine is fully warmed up ( When combustion is perfect (original emission concentration is extremely low), the CEI value will approach 0.

[0034] 1.0 3.0 (Transitional Range): Corresponds to "Strategy 1 Range". This indicates that the post-processing is heating up and has some purification capacity, but further optimization and control are still needed.

[0035] 3.0 6.0 (Severe Range): Corresponds to "Strategy 2 Range". This indicates that during the initial cold start phase, emissions are severe, requiring intervention in in-cylinder combustion.

[0036] 6.0 10.0 (Extreme / Failure Range): Indicates extreme low temperatures (e.g., This could be due to a system malfunction. During extreme low-temperature cold starts (e.g., -30°C), the concentration of unburned hydrocarbons is extremely high, and the catalyst temperature difference is at its maximum, at which point the CEI will reach its maximum value.

[0037] The preferred option is that the post-processing priority control strategy in step three is as follows:

[0038] The aftertreatment subsystem includes a selective catalytic reduction system (SCR unit) that monitors the NOx concentration at the SCR outlet; if the concentration exceeds the concentration threshold, urea injection is initiated.

[0039] The injection volume is adjusted based on NOx concentration and CEI value: When the CEI is high, it indicates that the system is in a stage of serious emissions or urgent need for post-treatment heating. The urea injection volume can be appropriately increased to utilize the endothermic reaction process of urea hydrolysis and the exothermic reaction process of NH3 oxidation to assist the post-treatment system to heat up quickly and enhance NOx purification. When the CEI is low, the precise and economical injection mode is returned to avoid urea waste and the risk of ammonia leakage.

[0040] The amount of urea injected Dynamic correction based on NOx concentration and CEI is performed, and the calculation formula is as follows:

[0041]

[0042] in, It is obtained in real time based on a preset pulse spectrum (MAP) or model, or by a combination of both. This indicates the concentration of nitrogen oxides in the exhaust gas, expressed in ppm. This value is measured in real time by a NOx sensor installed upstream of the SCR catalytic converter. This indicates exhaust flow rate, expressed in kg / h.

[0043] It is a monotonically non-decreasing function of CEI, and its mapping relationship is determined by calibration.

[0044] When CEI≤ hour, ≈1.0, implementing precision injection with a focus on economy.

[0045] when hour, As CEI increases, it grows linearly or piecewise from 1.0 to (1.3) to appropriately enhance control,

[0046] When CEI> hour, = To perform enhanced injection within the maximum permissible range, in order to rapidly increase catalyst activity and control pollutants;

[0047] and These are two threshold values ​​that are set, where: This is the low threshold for a state of "minor" emissions; it is the dividing line for determining whether a cold start emissions problem is in a "minor" state. Set to 1.5, 1.0 1.5 is the system's "comfort zone". When the CEI drops below 1.5, it indicates that the catalyst temperature is excellent (e.g., >280°C), no additional chemical heat is required, and returning to standard control is the most cost-effective. This is the high threshold value under severe emission conditions; it serves as the dividing line for determining whether cold-start emission issues are in a "severe" state (and meets the following conditions). ). Set to 2.5, 2.5 3.0 is the "edge zone" of Strategy 1. When CEI is in this range, the system may deteriorate at any time and revert to Strategy 2 (>3.0). Therefore, it is necessary to intervene early at 2.5 to maximize injection and forcefully "pull" the system back to the safe zone.

[0048] Objective: To maintain the post-processing system at its highest efficiency, avoiding overheating or overspray.

[0049] Preferably, the theoretical urea aqueous solution injection rate in step three... Preset pulse map (MAP) method:

[0050] I. Creating a MAP

[0051] MAP structure: X-axis represents exhaust mass flow rate. (kg / h), step size setting covers from idle low flow rate to maximum load flow rate during cold start; Y-axis represents SCR inlet NOx concentration. (ppm), covering the range of high emission fluctuations during cold starts; Z-axis (output value) is the theoretical urea aqueous solution injection rate. (mg / s);

[0052] In bench experiments, the optimal amount of urea required to complete the conversion of NOx was determined in advance under different NOx concentrations and different exhaust flow rates, and these data were filled into a two-dimensional table, namely a MAP diagram.

[0053] II. Real-time Calculation

[0054] ECU reads the current status in real time and The ECU finds the coordinates corresponding to these two values ​​in the MAP table; Linear interpolation: If the current value falls between two scale marks in the table, the ECU will perform linear interpolation to calculate the accurate value. value.

[0055] Preferably, the theoretical urea aqueous solution injection rate Model calculation method:

[0056] Based on the chemical reaction ratio of NOx and NH3 in the SCR system, combined with exhaust flow rate and NOx concentration, the theoretically required amount of urea is calculated, and then corrected according to factors such as catalytic converter efficiency and temperature.

[0057]

[0058] in: This represents the stoichiometric ratio of urea to NOx. This is the estimated conversion efficiency of the current SCR system.

[0059] The preferred option is that the in-cylinder combustion optimization and coordinated control strategy in step three is as follows:

[0060] Step S2.1: Optimize in-cylinder combustion parameters while ensuring that fuel economy loss is ≤ fuel economy loss threshold;

[0061] Step S2.2: Recalculate CEI. If CEI ≤ emission index threshold, proceed to strategy 1; otherwise, proceed to step S2.3.

[0062] Step S2.3: Determine whether the actual temperature of TWC is ≥ the temperature threshold. If it is, it indicates that the post-treatment has basically ignited, and proceed to Strategy 1 for fine maintenance; otherwise, proceed to step S2.4.

[0063] Step S2.4: Determine whether the engine load rate is ≥ the engine load rate threshold. If yes, return to step S2.1; otherwise, proceed to step S2.5.

[0064] Step S2.5: Determine whether hydrogen doping mode is enabled. If enabled, return to step S2.1; otherwise, proceed to step S2.6.

[0065] Step S2.6: Determine whether the TWC temperature is ≥ the temperature threshold. If yes, stop the active heating strategy; otherwise, output a diagnostic code and maintain the current optimal in-cylinder control state until the exit condition of step four is met.

[0066] Preferably, the optimization of in-cylinder combustion parameters is achieved through the following steps:

[0067] S2.1.1 Determine the economic budget: Calculate the difference between the current fuel economy loss and the fuel economy loss threshold, denoted as the economic budget Y. Budget Y>0 indicates available optimization space;

[0068] S2.1.2 Establish a "cost-benefit" mapping table: pre-calibrate a mapping relationship for each adjustable parameter to describe the CEI reduction (benefit) and fuel economy loss increase (cost) caused by each unit of parameter adjustment.

[0069] S2.1.3, Allocate budget iteratively according to priority:

[0070] a. Sorting: Based on the current operating conditions, sort the above parameter adjustment methods from high to low according to the "benefit / cost" ratio to form an optimization sequence.

[0071] b. Allocation and Adjustment: Starting from the first position of the sequence, adjust it to the extent that most effectively reduces CEI within the budget Y, apply this adjustment, and update the remaining budget. ;

[0072] c. Loop: Repeat step b, processing the next parameter sequentially, until: ① CEI drops below the emission index threshold; ② Budget... Exhausted; ③ All parameters have no further adjustment margin;

[0073] S2.1.4 Output: Obtain a set of optimized parameter correction values; recalculate CEI. If CEI ≤ emission index threshold, switch to strategy 1; otherwise, proceed to subsequent judgment (S2.3-S2.6).

[0074] A control system for implementing the aforementioned cold start emission coordinated control method for a natural gas engine includes an in-cylinder control subsystem, an aftertreatment subsystem, and a control unit (ECU).

[0075] The in-cylinder control subsystem includes a natural gas supply system, an optional hydrogen supply system, an EGR system, an ignition system, and in-cylinder temperature, pressure, and air-fuel ratio sensors.

[0076] The aftertreatment subsystem includes a three-way catalytic converter (TWC), which can be expanded to a diesel oxidation catalytic converter (DOC), a diesel particulate filter (DPF), a selective catalytic reduction system (SCR), and an ammonia slip catalytic converter (ASC); it is equipped with TWC inlet / outlet temperature sensors and a NOx sensor.

[0077] The control unit (ECU) is used to acquire sensor signals in real time, calculate CEI, execute strategy judgments, and output control commands.

[0078] The preferred option is that the engine uses a dual-fuel supply system with natural gas as the main fuel and a small proportion of diesel or methanol as ignition or auxiliary fuel, and is equipped with two independent fuel injectors or one dual-fuel injector.

[0079] A method for coordinated cold start emission control of a natural gas engine, comprising the following steps:

[0080] During cold start, a small amount of highly active pilot fuel is injected in the early stage of the compression stroke to allow it to undergo partial premixed combustion, thereby increasing the initial temperature and pressure in the cylinder. Natural gas is then injected in the subsequent main injection.

[0081] By controlling the ratio of dual fuels, injection timing and pulse width, the exhaust heat flow during the cold start phase is maximized while ensuring stable combustion, thus providing a sufficient heat source for TWC.

[0082] After ignition, switch back to pure natural gas mode or a very low proportion of ignition mode.

[0083] Working principle:

[0084] 1. Dual-mode adaptive switching mechanism based on CEI threshold judgment: Based on real-time comparison of CEI and preset thresholds, an adaptive switching mechanism is constructed that combines two fundamentally different control logics: "aftertreatment priority control" and "in-cylinder combustion optimization and coordinated control". This mechanism can intelligently identify whether the essence of the current emission problem is "insufficient aftertreatment efficiency" or "poor in-cylinder combustion", and thus call the most suitable control strategy, solving the problems of single strategy and conflicting objectives in traditional methods.

[0085] 2. Layered Iterative Optimization and Exit Logic in Strategy 2: In the "In-Cylinder Combustion Optimization and Coordinated Control" strategy, a closed-loop process including effect evaluation, state judgment, and conditional looping is designed. It is not a one-time operation, but rather an iterative process of "optimization-evaluation-re-decision". Multiple conditional exits are set, including load judgment, fuel enhancement (hydrogen blending) feasibility, and aftertreatment base temperature, to ensure that the optimal or most feasible solution is found under limited control freedom and constraints (economic loss), and to provide a systematic diagnosis when the potential is exhausted.

[0086] 3. Dynamic transition and smooth exit mechanism for coordinated control: The dynamic transition path between the two strategies and between cold start mode and normal mode is clearly defined. In particular, when in-cylinder optimization reduces CEI, it can automatically switch to fine control of the aftertreatment; finally, the exit criterion is the "dual stability" of water temperature and aftertreatment temperature, which ensures seamless connection of the control process and smooth transition of system state, avoiding the shock caused by mode switching.

[0087] Beneficial effects: This invention achieves precise decision-making by comprehensively quantifying the severity of cold-start emissions through CEI and realizing intelligent strategy switching; it achieves synergy between internal and external systems by dynamically allocating in-cylinder and aftertreatment control weights based on CEI to achieve global optimization; it balances rapid warm-up with low emissions by prioritizing in-cylinder combustion optimization in Strategy 2 to reduce pollutants at the source while accelerating aftertreatment ignition; it offers good fuel economy by setting a fuel economy loss threshold to avoid excessively sacrificing fuel consumption for emissions targets; and it is highly adaptable to various fuel forms such as pure natural gas and hydrogen-blended natural gas, as well as different aftertreatment configurations. Attached Figure Description

[0088] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0089] Figure 1 This is the control flowchart of the present invention. Detailed Implementation

[0090] 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.

[0091] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0092] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0093] like Figure 1 As shown, a cold start emission coordinated control method for a natural gas engine includes the following steps:

[0094] Step 1: Cold start identification. If the engine coolant temperature is less than the set value (e.g., 60°C) and the TWC temperature is less than the ignition temperature, it is determined that the cold start control mode is entered.

[0095] Step 2: Calculate the Cold Start Emission Index (CEI) in real time based on the engine data collected in real time.

[0096] The Cold Start Emission Index (CEI) is calculated as follows:

[0097] CEI is defined as a weighted function of the in-cylinder unburned hydrocarbon equivalent and the ignition temperature difference of the aftertreatment system, and the calculation formula is as follows:

[0098]

[0099] in, This is a dynamic weighting factor for in-cylinder emissions, which is based on coolant temperature. And adjust the engine load L in real time.

[0100] When both are extremely low, it indicates poor in-cylinder combustion conditions, making the control value of optimizing raw emissions through in-cylinder means relatively low. In this case, α is reduced to decrease the sensitivity of CEI to changes in raw in-cylinder emissions, thereby preventing the control system from employing aggressive control strategies that excessively harm fuel economy under conditions with limited optimization space.

[0101] : A scaling factor used to adjust the weight of post-treatment heating requirements in CEI. This factor is based on the TWC temperature. and exhaust flow Real-time adjustments are needed. When both are very low, it indicates that the post-processing system will face a slow, natural temperature rise. At this point, increasing... This value will amplify the impact of the "difference between target temperature and actual temperature" in CEI, thereby directing the optimization of the control system to focus more on solving the after-treatment inertia problem, prompting the adoption of in-cylinder measures to increase exhaust temperature earlier or more proactively.

[0102] These represent the volume concentrations of the corresponding components in the original emissions;

[0103] The target ignition temperature for TWC (e.g., 250°C);

[0104] This refers to the actual TWC temperature.

[0105] CEI range:

[0106] 0 1.0 (Ideal Range): After-treatment complete ignition, extremely low emissions, when the engine is fully warmed up ( When combustion is perfect (original emission concentration is extremely low), the CEI value will approach 0.

[0107] 1.0 3.0 (Transitional Range): Corresponds to "Strategy 1 Range". This indicates that the post-processing is heating up and has some purification capacity, but further optimization and control are still needed.

[0108] 3.0 6.0 (Severe Range): Corresponds to "Strategy 2 Range". This indicates that during the initial cold start phase, emissions are severe, requiring intervention in in-cylinder combustion.

[0109] 6.0 10.0 (Extreme / Failure Range): Indicates extreme low temperatures (e.g., This could be due to a system malfunction. During extreme low-temperature cold starts (e.g., -30°C), the concentration of unburned hydrocarbons is extremely high, and the catalyst temperature difference is at its maximum, at which point the CEI will reach its maximum value.

[0110] The higher the CEI value, the more serious the cold start emission problem, and the more proactive control strategies need to be adopted.

[0111] Step 3: Strategy Selection

[0112] If CEI ≤ threshold A, adopt strategy 1: prioritize post-processing control;

[0113] If CEI > threshold A, adopt strategy 2: in-cylinder combustion optimization and coordinated regulation;

[0114] Threshold A is the emission index threshold.

[0115] Strategy 1: Prioritize post-processing control

[0116] If the aftertreatment subsystem includes an SCR unit, then the following steps are performed: Monitor the NOx concentration at the SCR outlet; if the concentration is greater than threshold B, initiate urea injection, with the injection rate adjusted based on the NOx concentration and CEI: when the CEI is high, it indicates that the system is in a stage of severe emissions or urgent need for aftertreatment heating, and the urea injection rate can be appropriately increased to utilize the endothermic reaction process of urea hydrolysis and the exothermic reaction process of NH3 oxidation to assist the aftertreatment system in rapidly heating up and enhancing NOx purification; when the CEI is low, revert to the precise and economical injection mode to avoid urea waste and the risk of ammonia leakage.

[0117] Threshold B is the NOx concentration threshold.

[0118] The amount of urea injected The calculation formula is based on dynamic correction of NOx concentration and CEI:

[0119]

[0120] in:

[0121] It can be calculated in real time based on a preset pulse map (MAP) or a model. Among them: This indicates the concentration of nitrogen oxides in the exhaust gas, expressed in ppm. This value is typically measured in real time by a NOx sensor installed upstream of the SCR catalytic converter. This indicates the exhaust flow rate, measured in kg / h, and is calculated by the ECU.

[0122] (1) Preset pulse map (MAP) mode:

[0123] I. Creating a MAP

[0124] The structure of the MAP is as follows: X-axis: exhaust mass flow rate (kg / h), step size setting covers from idle low flow rate to maximum load flow rate during cold start; Y-axis: SCR inlet NOx concentration (ppm), covering the range of high emission fluctuations during cold starts; Z-axis (output value): theoretical urea aqueous solution injection rate. (mg / s). Different NO levels were pre-tested in bench experiments. X At different concentrations and exhaust flow rates, NO can be converted. X Determine the optimal amount of urea required and populate this data into a two-dimensional table (i.e., a MAP).

[0125] II: Real-time computing

[0126] 1. The ECU reads the current data in real time. (e.g., 500ppm) and (e.g., 200 kg / h).

[0127] 2. The ECU finds the coordinates corresponding to these two values ​​in the MAP table.

[0128] 3. Linear Interpolation: If the current value falls between two scales on the table (e.g., between 200 kg / h and 250 kg / h), the ECU will automatically perform linear interpolation to calculate an accurate value. value.

[0129] (2) Model calculation method:

[0130] Based on chemical reaction equations, mass conservation, and catalytic conversion efficiency models, the required amount of urea is calculated in real time.

[0131] For example, based on the chemical reaction ratio of NOx to NH3 in the SCR system (usually 1:1), combined with the exhaust flow rate and NOx concentration, the theoretical amount of urea required is calculated, and then corrected according to factors such as catalyst efficiency and temperature.

[0132]

[0133] in: This is the stoichiometric ratio of urea to NOx (e.g., in a 32.5% urea aqueous solution, approximately 1.05 grams of urea are required per gram of NOx). The estimated conversion efficiency of the current SCR system (related to temperature and space velocity).

[0134] In practical engine control, a hybrid strategy of "MAP as the primary method and model as the secondary method" is usually adopted. (A basic MAP is used to provide the injection quantity for mainstream operating conditions, and an efficiency model is used to make real-time corrections for extreme temperatures or aging conditions.)

[0135] For a monotonically non-decreasing function of CEI, its mapping relationship can be determined by calibration, for example:

[0136] when ≤ (Minor emission range) ≈1.0, implementing precision injection with economic priority.

[0137] when Time (transition adjustment range), As CEI increases, it grows linearly or piecewise from 1.0 to (1.3) to appropriately enhance control.

[0138] when > (During the severe emissions period) = Execute enhanced injection within the maximum permissible range to rapidly increase catalyst activity and control pollutants.

[0139] This is the lower limit of the emission index threshold. This represents the upper limit of the emission index threshold.

[0140] and These are two threshold values ​​that are set, where: This is the low threshold for a state of "minor" emissions; it is the dividing line for determining whether a cold start emissions problem is in a "minor" state. Set to 1.5, 1.0 1.5 is the system's "comfort zone". When the CEI drops below 1.5, it indicates that the catalyst temperature is excellent (e.g., >280°C), no additional chemical heat is required, and returning to standard control is the most cost-effective. This is the high threshold value under severe emission conditions; it serves as the dividing line for determining whether cold-start emission issues are in a "severe" state (and meets the following conditions). ). Set to 2.5, 2.5 3.0 is the "edge zone" of Strategy 1. When CEI is in this range, the system may deteriorate at any time and revert to Strategy 2 (>3.0). Therefore, it is necessary to intervene early at 2.5 to maximize injection and forcefully "pull" the system back to the safe zone.

[0141] Main objective: To maintain the post-processing system at its highest efficiency, avoiding overheating or overspray.

[0142] Strategy 2: In-cylinder combustion optimization and coordinated regulation

[0143] Step S2.1: Optimize in-cylinder combustion parameters (ignition angle, EGR rate, air-fuel ratio, and optional hydrogen blending) under the premise that the fuel economy loss is ≤ threshold D.

[0144] The optimization is achieved through the following steps: 1. Determine the economic budget: Calculate the difference between the current fuel economy loss and the threshold D, and denote it as the economic budget. 1. Budget Y > 0 indicates available optimization space. 2. Establish a "cost-benefit" mapping table: Pre-calibrate a mapping relationship for each adjustable parameter (ignition angle retarding, EGR rate reduction, air-fuel ratio enrichment, hydrogen blending ratio increase) to describe the CEI reduction (benefit) and fuel economy loss increase (cost) caused by each unit parameter adjustment (e.g., 1° ignition angle retarding). 3. Iteratively allocate the budget according to priority: a. Sorting: Based on the current operating conditions, sort the above parameter adjustment methods from high to low according to the "benefit / cost" ratio to form an optimization sequence. b. Allocation and correction: Starting from the first position in the sequence, attempt to adjust it to the most effective CEI reduction achievable within the budget Y. Apply this correction and update the remaining budget. c. Loop: Repeat step b, processing the next parameter sequentially, until: ① CEI drops below threshold A; ② Budget ③ All parameters have no further adjustment margin. 4. Output: Obtain a set of optimized parameter correction values. Recalculate CEI. If CEI ≤ A, proceed to Strategy 1; otherwise, proceed to subsequent judgments (S2.3-S2.6). Step S2.2: Recalculate CEI. If CEI ≤ threshold A, proceed to Strategy 1; otherwise, proceed to step S2.3. Step S2.3: Determine if the actual TWC temperature ≥ threshold C. If yes, it indicates that the aftertreatment has basically ignited, and proceed to Strategy 1 for fine maintenance; otherwise, proceed to step S2.4. Step S2.4: Determine if the engine load rate ≥ threshold E. If yes, return to step S2.1; otherwise, proceed to step S2.5. Step S2.5: Determine if hydrogen blending mode is enabled (if a hydrogen source is available). If enabled, return to step S2.1; otherwise, proceed to step S2.6. Step S2.6: Determine if the TWC temperature ≥ threshold C. If yes, stop the active heating strategy; otherwise, output a diagnostic code and maintain the current optimal in-cylinder control state until the exit condition of S3 is met. Step S3: Exit Cold Start Mode When the water temperature is ≥ the set value and the TWC temperature is stable in the high efficiency window, exit the cold start collaborative control and switch to normal emission control mode.

[0145] Threshold C is the temperature threshold, threshold D is the fuel economy loss threshold, and threshold E is the engine load rate threshold.

[0146] The aforementioned thresholds (A, B, C, D, E) can be predetermined through bench calibration and experiments based on the specific engine model, after-treatment system configuration, and target emission regulations, and stored in the control unit (ECU).

[0147] Based on a chemical thermal management scheme using dual-fuel staged injection and in-cylinder reaction heat, this scheme starts with fuel supply and in-cylinder chemical reaction, utilizing the differences in fuel characteristics to generate more usable waste heat.

[0148] 1. System Composition:

[0149] The engine employs a dual-fuel supply system (e.g., primarily supplied by natural gas, with a small proportion of diesel or methanol as ignition or auxiliary fuel). It is equipped with two independent fuel injectors or one dual-fuel injector.

[0150] 2. Control Logic:

[0151] During cold start, a small amount of highly reactive pilot fuel (such as diesel) is injected early in the compression stroke to allow for partial premixed combustion, significantly increasing the initial temperature and pressure inside the cylinder. Natural gas is then injected in the subsequent main injection. Because the cylinder environment has become high-temperature and high-pressure due to the pilot fuel combustion, the natural gas burns faster and more completely, with a later center of heat release, directly producing exhaust gases with higher temperatures and enthalpies. By precisely controlling the dual-fuel ratio, injection timing, and pulse width, the exhaust heat flow during the cold start phase is maximized while ensuring stable combustion, providing a sufficient heat source for the TWC (Transmission Welding). After ignition, the system switches back to pure natural gas mode or a very low-ratio pilot ignition mode.

[0152] The key feature of this approach is that it addresses the emission temperature from the energy source (combustion chemistry), requiring direct hardware modifications. However, it necessitates the addition of a fuel system and presents significant control complexity. Its technical path differs markedly from the main approach (CEI-based internal and external co-optimization), yet both offer different solutions to cold-start emissions problems.

[0153] The specific implementation example of this control method is as follows: When a natural gas engine is cold-started in an environment of 5°C, the system first identifies that both the water temperature and the TWC temperature are lower than the set values, and determines that it is entering the cold start mode.

[0154] The real-time calculated cold start emission index (CEI) is 5.2, which is higher than the decision threshold (set to 3.0). Therefore, the second start strategy is to implement the in-cylinder combustion optimization and coordinated control system, which, under the premise of ensuring that the fuel economy loss does not exceed 3%, delays the ignition angle by 8°, shuts off EGR, and starts a low proportion (2%) of natural gas with hydrogen blending to increase the exhaust temperature and improve combustion.

[0155] Approximately 2 minutes later, the CEI was recalculated and dropped to 2.8, which was below the threshold. At this point, the control logic automatically switched to Strategy 1: post-treatment priority control. The system detected that the TWC temperature had risen to 230℃, so it controlled the exhaust temperature to rise steadily to protect the catalyst, while simultaneously injecting a small amount of urea based on the NOx concentration (25ppm) at the SCR outlet.

[0156] Approximately 5 minutes later, the engine coolant temperature reached 65°C, and the TWC temperature stabilized at the efficient operating window of 320°C. The system met the exit conditions and automatically switched to the conventional emission control mode.

[0157] This embodiment fully demonstrates the dual-strategy adaptive switching process based on real-time CEI assessment, achieving a smooth transition from "in-cylinder active optimization" to "precise aftertreatment control". Within 5 minutes, it simultaneously achieves the core objectives of rapid warm-up, emission compliance, and fuel economy protection, verifying the effectiveness and engineering applicability of the proposed collaborative control method.

[0158] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0159] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for coordinated cold start emission control of a natural gas engine, characterized in that, Includes the following steps: Step 1: Cold start recognition. If the engine coolant temperature is less than the set value and the TWC temperature is less than the ignition temperature, it is determined that the cold start control mode has been entered. Step 2: Calculate the Cold Start Emission Index (CEI) in real time based on the engine data collected in real time. Step 3: Strategy selection. If CEI ≤ emission index threshold, adopt Strategy 1, the aftertreatment priority control strategy; if CEI > emission index threshold, adopt Strategy 2, the in-cylinder combustion optimization and synergistic control strategy. Step 4: Exit cold start mode. When the water temperature is ≥ the set value and the TWC temperature is stable in the high efficiency window, exit cold start collaborative control and switch to normal emission control mode.

2. The cold start emission coordinated control method for a natural gas engine according to claim 1, characterized in that, The method for calculating the cold start emission index (CEI) in step two is as follows: CEI is defined as a weighted function of the in-cylinder unburned hydrocarbon equivalent and the ignition temperature difference of the aftertreatment system, and is calculated as follows: ； in, The dynamic weighting factor for in-cylinder emissions. This is an amplification factor used to adjust the weight of post-treatment heating requirements in CEI. These represent the volume concentrations of the corresponding components in the original emissions. The target ignition temperature for TWC. This refers to the actual TWC temperature. The higher the CEI value, the more serious the cold start emission problem, and the more proactive control strategies need to be adopted.

3. The cold start emission coordinated control method for a natural gas engine according to claim 2, characterized in that, The post-processing priority control strategy in step three is as follows: The aftertreatment subsystem includes a selective catalytic reduction system (SCR unit) that monitors the NOx concentration at the SCR outlet; if the concentration exceeds the NOx concentration threshold, urea injection is initiated. Urea injection volume Dynamic correction based on NOx concentration and CEI is performed using the following calculation method: ； in: It is obtained in real time based on a preset pulse spectrum (MAP) or model, or by a combination of both. This indicates the concentration of nitrogen oxides in the exhaust gas, expressed in ppm. This value is measured in real time by a NOx sensor installed upstream of the SCR catalytic converter. This indicates exhaust flow rate, expressed in kg / h. It is a monotonically non-decreasing function of CEI, and its mapping relationship is determined by calibration. When CEI≤ hour, ≈1.0, implementing precision injection with a focus on economy. when hour, As CEI increases, it grows linearly or piecewise from 1.0 to (1.3) to appropriately enhance control; When CEI> hour, = To perform enhanced injection within the maximum permissible range, in order to rapidly increase catalyst activity and control pollutants; and These are two threshold values ​​that are set, where: This represents the low threshold for a state of minimal emissions. This represents the high threshold value under severe emission conditions. Objective: To maintain the post-processing system at its highest efficiency, avoiding overheating or overspray.

4. The cold start emission coordinated control method for a natural gas engine according to claim 3, characterized in that, The theoretical urea aqueous solution injection rate in step three Preset pulse map (MAP) method: I. Creating a MAP MAP structure: X-axis represents exhaust mass flow rate. (kg / h), step size setting covers from idle low flow rate to maximum load flow rate during cold start; Y-axis represents SCR inlet NOx concentration. (ppm), covering the range of high emission fluctuations during cold starts; Z-axis (output value) represents the theoretical urea aqueous solution injection rate. (mg / s); In bench experiments, the optimal amount of urea required to complete the conversion of NOx was determined in advance under different NOx concentrations and different exhaust flow rates, and these data were filled into a two-dimensional table, namely a MAP diagram. II. Real-time Calculation ECU reads the current status in real time and The ECU finds the coordinates corresponding to these two values ​​in the MAP table; Linear interpolation: If the current value falls between two scale marks in the table, the ECU will perform linear interpolation to calculate the accurate value. value.

5. The cold start emission coordinated control method for a natural gas engine according to claim 3, characterized in that, The theoretical urea aqueous solution injection rate Model calculation method: Based on the chemical reaction ratio of NOx and NH3 in the SCR system, combined with exhaust flow rate and NOx concentration, the theoretically required amount of urea is calculated, and then corrected according to factors such as catalytic converter efficiency and temperature. ； in: This represents the stoichiometric ratio of urea to NOx. This is the estimated conversion efficiency of the current SCR system.

6. The cold start emission coordinated control method for a natural gas engine according to claim 1, characterized in that, The in-cylinder combustion optimization and coordinated control strategy in step three is as follows: Step S2.1: Optimize in-cylinder combustion parameters while ensuring that fuel economy loss is ≤ fuel economy loss threshold; Step S2.2: Recalculate CEI. If CEI ≤ emission index threshold, proceed to strategy 1; otherwise, proceed to step S2.

3. Step S2.3: Determine whether the actual temperature of TWC is ≥ the temperature threshold. If it is, it indicates that the post-treatment has basically ignited and proceeds to Strategy 1 for fine maintenance. Otherwise proceed to step S2.4; Step S2.4: Determine whether the engine load rate is ≥ the engine load rate threshold. If yes, return to step S2.

1. Otherwise proceed to step S2.5; Step S2.5: Determine whether hydrogen doping mode is enabled. If enabled, return to step S2.

1. Otherwise proceed to step S2.6; Step S2.6: Determine whether the TWC temperature is ≥ the temperature threshold. If yes, stop the active heating strategy; otherwise, output a diagnostic code and maintain the current optimal in-cylinder control state until the exit condition of step four is met.

7. The cold start emission coordinated control method for a natural gas engine according to claim 6, characterized in that, The optimization of in-cylinder combustion parameters is achieved through the following steps: S2.1.1 Determine the economic budget: Calculate the difference between the current fuel economy loss and the fuel economy loss threshold, denoted as the economic budget Y. Budget Y>0 indicates available optimization space; S2.1.2 Establish a "cost-benefit" mapping table: pre-calibrate a mapping relationship for each adjustable parameter to describe the CEI reduction (benefit) and fuel economy loss increase (cost) caused by each unit of parameter adjustment. S2.1.3, Allocate budget iteratively according to priority: a. Sorting: Based on the current operating conditions, sort the above parameter adjustment methods from high to low according to the "benefit / cost" ratio to form an optimization sequence; b. Allocation and Adjustment: Starting from the first position of the sequence, adjust it to the extent that most effectively reduces CEI within the budget Y, apply this adjustment, and update the remaining budget. ; c. Loop: Repeat step b, processing the next parameter sequentially, until: ① CEI drops below the emission index threshold; ② Budget... Exhausted; ③ All parameters have no further adjustment margin; S2.1.4 Output: Obtain a set of optimized parameter correction values; recalculate CEI. If CEI ≤ emission index threshold, switch to strategy 1; otherwise, proceed to subsequent judgment (S2.3-S2.6).

8. A control system for implementing the cold start emission coordinated control method for a natural gas engine according to any one of claims 1-7, characterized in that: Including the in-cylinder control subsystem, aftertreatment subsystem, and control unit ECU, The in-cylinder control subsystem includes a natural gas supply system, an optional hydrogen supply system, an EGR system, an ignition system, and in-cylinder temperature, pressure, and air-fuel ratio sensors. The aftertreatment subsystem includes a three-way catalytic converter (TWC), which can be expanded to a diesel oxidation catalytic converter (DOC), a diesel particulate filter (DPF), a selective catalytic reduction system (SCR), and an ammonia slip catalytic converter (ASC); it is equipped with TWC inlet / outlet temperature sensors and a NOx sensor. The control unit (ECU) is used to acquire sensor signals in real time, calculate CEI, execute strategy judgments, and output control commands.

9. The control system for realizing the cold start emission coordinated control method of a natural gas engine according to claim 8, characterized in that: The engine uses a dual-fuel supply system with natural gas as the main fuel and a small proportion of diesel or methanol as ignition or auxiliary fuel, and is equipped with two independent fuel injectors or one dual-fuel injector.

10. The cold start emission coordinated control method for a natural gas engine according to claim 9, characterized in that, Includes the following steps: During cold start, a small amount of highly active pilot fuel is injected in the early stage of the compression stroke to allow it to undergo partial premixed combustion, thereby increasing the initial temperature and pressure in the cylinder. Natural gas is then injected in the subsequent main injection. By controlling the ratio of dual fuels, injection timing and pulse width, the exhaust heat flow during the cold start phase is maximized while ensuring stable combustion, thus providing a sufficient heat source for TWC. After ignition, switch back to pure natural gas mode or a very low proportion of ignition mode.

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