Diesel particulate filter regeneration optimization method based on external heat proportion

Abstract

The application discloses a diesel particulate filter regeneration optimization method based on external heat proportion, comprising the following steps: S1, constructing a DPF single-channel model and a solid-phase control body energy transmission model; S2, defining the external heat proportion as the ratio of the external heat flow rate to the total heat flow rate of the system; S3, calculating the soot combustion heat release rate and the external heat flow rate based on the model, and determining the external heat proportion; S4, identifying the stage of the regeneration process according to the change trend of the external heat proportion with the regeneration time or the solid-phase temperature; and S5, based on the stage identification result and the real-time value of the external heat proportion, synergistically controlling at least one parameter in the oxygen concentration, the initial temperature, the soot load and the exhaust mass flow rate, so that the system completes the transition from the external heating dominance to the soot self-sustaining combustion within the safe temperature window. The application improves the relative weight of external heating and soot self-ignition heat release to the level of heat source composition for unified measurement, and identifies the regeneration process and controls based on the external heat proportion.

Description

Technical Field

[0001] This invention belongs to the field of diesel engine aftertreatment technology, specifically a method for regenerating and optimizing a diesel engine particulate filter based on the proportion of external heat. Background Technology

[0002] Diesel engines have long held an important position in the transportation sector due to their high thermal efficiency and reliability. However, particulate matter (PM) in diesel engine exhaust poses a serious threat to the ecological environment and human health. Diesel particulate filters (DPFs), as the most effective aftertreatment device for reducing particulate matter emissions, have become an essential component for meeting China VI and higher emission standards.

[0003] Thermal management during the active regeneration process of a DPF directly affects its operational safety and service life. The heat generated during regeneration originates from the combined effects of external heating and the exothermic reaction of soot combustion; the relative weight of these two factors directly influences the evolution of the temperature field and the distribution of thermal stress. Traditional research often focuses on the independent effects of various operating parameters, such as exhaust temperature, oxygen concentration, soot load, or exhaust flow rate, on the maximum regeneration temperature or regeneration efficiency. However, this parameterized approach fails to reveal the dynamic competition between external heating and internal exothermic reaction at the level of heat source composition. It lacks a unified parameter to quantitatively characterize their relative importance, leading to insufficient understanding of the fundamental laws governing regeneration thermal behavior under different operating conditions.

[0004] If the system's dependence on external energy input during regeneration cannot be quantitatively measured, it is difficult to accurately determine the stage of the regeneration process (such as the preheating stage, the combustion self-sustaining stage, etc.), and it is also difficult to formulate a refined control strategy accordingly. For example, if external heating is not withdrawn or reduced in time after soot ignition, it may lead to excessively high local temperatures and excessive thermal stress, threatening the service life of the DPF; conversely, if external heating is withdrawn too early, when the soot load is insufficient or the oxygen concentration is low, combustion may not be self-sustaining and the flame may go out, reducing regeneration efficiency. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a diesel particulate filter regeneration optimization method based on the external heat ratio. The method defines the external heat ratio as a quantitative parameter, elevates the relative weight of external heating and soot auto-combustion heat release to the level of heat source composition for unified measurement, identifies the physical stage of the regeneration process based on the external heat ratio, and adjusts at least one operating parameter to enable the system to quickly complete the transition from preheating to self-sustaining combustion within a safe temperature window.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The diesel particulate filter regeneration optimization method based on the proportion of external heat includes the following steps: Step S1: Construct a single-channel model of the diesel particulate filter and an energy transfer model of the solid-phase control body. The solid-phase control body is a micro-element composed of the filter wall and the particulate layer. Its energy transfer includes heat carried in by the intake air permeation, convective heat transfer in the inlet channel, heat release from carbon soot combustion, convective heat transfer in the outlet channel, heat carried out by the exhaust air permeation, and axial heat conduction in the solid phase; Step S2: Define the proportion of external heat as the ratio of the external heat flux to the total heat flux of the system. The total heat flux of the system is the sum of the external heat flux and the heat release rate from carbon soot combustion, wherein the external heat flux is the ratio of the heat carried in by the intake air permeation, the heat carried out by the exhaust air permeation, the heat carried out by the exhaust air permeation, and the heat transfer rate from the exhaust air permeation. The sum of the convective heat transfer in the inlet channel, the convective heat transfer in the outlet channel, the heat carried out by the exhaust seepage, and the heat conduction by the solid phase axial direction; Step S3: Based on the energy transfer model of the solid phase control body, calculate the soot combustion heat release rate and the external heat flow rate to determine the external heat ratio; Step S4: Based on the trend of the external heat ratio with regeneration time or solid phase temperature, identify the stage of the regeneration process; Step S5: Based on the identification results and the real-time value of the external heat ratio, coordinately regulate at least one of the oxygen concentration, initial temperature, soot load, and exhaust mass flow rate to enable the system to complete the transition from external heating-dominated to soot self-sustaining combustion within a preset safe temperature window.

[0008] The single-channel model of the diesel particulate filter consists of four parts: an inlet channel, a particulate layer, a wall, and an outlet channel. The inlet channel is the internal passage of the diesel particulate filter, through which exhaust gas enters and flows axially. The outlet channel is blocked at the outlet end, forcing the exhaust gas to seep radially through the wall into the outlet channel. The particulate layer is a layer of carbon soot particles attached to the surface and pores of the wall, forming the core area for filtration and regeneration. The wall is a porous ceramic filter wall, serving as the key filtration medium for gas passage and particulate retention, and also as the carrier for the regeneration reaction and the thermal management structure. The outlet channel is the passage through which the filtered exhaust gas flows out. The outlet channel is blocked at the inlet end; that is, the inlet and outlet channels employ an alternating blocking design. The exhaust gas flows axially within the outlet channel until it exits the diesel particulate filter, with the axial direction aligned with the length of the diesel particulate filter.

[0009] Exhaust gas refers to the waste gas emitted after a diesel engine is running. Its main components include carbon dioxide, nitrogen oxides, water vapor, and unburned particulate matter. This exhaust gas needs to enter the particulate filter through the inlet channel inside the diesel particulate filter, where the particulate matter is captured by the filter material.

[0010] The solid-phase control volume energy transfer model is a micro-element in the solid phase composed of a wall and a microparticle layer. The axial direction of this micro-element is the length of the micro-element along the length direction of the diesel engine particulate trap, the radial direction is from the inner side of the wall to the outer side of the wall, and the circumferential direction is the unit width. The inner side of the wall refers to the junction of the inlet channel and the solid phase, and the outer side of the wall refers to the junction of the outlet channel and the solid phase.

[0011] As a further improvement to the above technical solution:

[0012] In step S3, the soot combustion heat release rate is calculated based on the reaction rate of soot being oxidized by oxygen to produce carbon monoxide and its calorific value, as well as the reaction rate of soot being oxidized by oxygen to produce carbon dioxide and its calorific value.

[0013] Step S4 specifically includes: when the external heat ratio is within a preset high threshold range, it is determined to be the external heat-dominated stage; when the external heat ratio rapidly decreases from the preset high threshold range, it is determined to be the combustion development and dominance stage; when the external heat ratio rises again after decreasing, it is determined to be the post-combustion stage.

[0014] The preset high threshold is a numerical range in which the external heat ratio is close to 1.

[0015] In step S3, in order to calculate the heat release rate of carbon soot combustion and the external heat flow rate, the set of governing equations to be solved includes: the mass conservation equation of the inlet channel, the mass conservation equation of the outlet channel, the momentum conservation equation of the inlet channel, the momentum conservation equation of the outlet channel, the gas phase energy conservation equation of the inlet channel, the gas phase energy conservation equation of the outlet channel, and the solid phase energy conservation equation.

[0016] In step S5, the exhaust mass flow rate is controlled within a preset flow window. The lower limit of the preset flow window is the minimum flow rate to ensure sufficient oxygen supply, and the upper limit is the maximum flow rate to prevent excessive cooling of the reaction zone, thereby inhibiting self-sustaining combustion.

[0017] The preset flow window is determined by calibrating the decreasing curve of the external heat ratio under different exhaust mass flow rates, and the flow range that makes the external heat ratio drop to a preset low level within the target solid phase temperature range is selected as the preset flow window.

[0018] In step S5, the oxygen concentration is adjusted within the range of 5% to 20%. When the real-time value of the external heat ratio is higher than the target value, the intake oxygen concentration is increased within this range to accelerate the decrease of the external heat ratio.

[0019] In step S5, the carbon soot loading is adjusted so that the initial carbon soot loading is greater than a preset critical threshold. The preset critical threshold is a value between 4 g / L and 12 g / L. When the initial carbon soot loading is lower than this threshold, the heat released by carbon soot combustion is insufficient to sustain the regeneration process.

[0020] The beneficial effects of this invention are:

[0021] (1) The external heat ratio is defined as a quantitative parameter to characterize the proportion of heat input from external heat sources to the total heat during the regeneration process. This elevates the relative weight of external heating and soot self-combustion heat release to the level of heat source composition for unified measurement. This provides a new quantitative tool for understanding the regeneration thermal behavior of DPF, reveals the common laws of regeneration thermal behavior under different operating conditions, and overcomes the problem of fragmented laws caused by traditional methods that analyze only a single operating parameter independently.

[0022] (2) Based on the dynamic evolution of the external heat ratio, the physical stages of the regeneration process can be clearly identified: when the external heat ratio is close to 1, it is the stage dominated by external heating; when it drops rapidly, it is the stage dominated by combustion development; and when it rises again, it indicates the entry into the post-combustion stage. This helps to accurately judge the regeneration process and provides a key theoretical basis for formulating a phased and refined thermal management and control strategy.

[0023] (3) The mechanism by which key operating parameters affect the proportion of external heat was revealed: oxygen concentration is a sensitive parameter that promotes the transition of the system to combustion dominance; initial temperature determines the total amount of sensible heat required for the system to cross the ignition threshold; soot load has a critical threshold for self-sustaining regeneration; and exhaust flow rate has a non-monotonic effect on the proportion of external heat through the coupling of oxygen transport and convective cooling mechanisms, thereby determining the existence of an optimal flow window. Based on these principles, the system can quickly transition from preheating to self-sustaining combustion within a safe temperature window by synergistically controlling oxygen concentration, initial temperature, and exhaust flow rate, while avoiding the decrease in regeneration efficiency due to insufficient external heat or excessive cooling, or the risk of thermal stress caused by local overheating, thus balancing the safety and efficiency of DPF regeneration. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a single-channel DPF model.

[0025] Figure 2 This is a schematic diagram of a single-channel DPF control unit.

[0026] Figure 3 This is a schematic diagram showing the change of the external heat ratio in each axis of a single channel of a DPF over time, according to an embodiment of the present invention.

[0027] Figure 4 This is a schematic diagram of the external heat ratio of a single-channel DPF controller according to an embodiment of the present invention, with an inlet temperature of 620°C, an oxygen concentration of 5%, an initial temperature of 23°C, a soot load of 20 g / L, and an exhaust flow rate of 4.5 g / s.

[0028] Figure 5This is a schematic diagram of the external heat ratio of a single-channel DPF controller according to an embodiment of the present invention, with an inlet temperature of 620°C, an oxygen concentration of 10%, an initial temperature of 23°C, a soot load of 20 g / L, and an exhaust flow rate of 4.5 g / s.

[0029] Figure 6 This is a schematic diagram of the external heat ratio of a single-channel DPF controller according to an embodiment of the present invention, with an inlet temperature of 620°C, an oxygen concentration of 20%, an initial temperature of 23°C, a soot load of 20 g / L, and an exhaust flow rate of 4.5 g / s.

[0030] Figure 7 This is a schematic diagram of the external heat ratio of a single-channel DPF controller according to an embodiment of the present invention, with an inlet temperature of 620°C, an oxygen concentration of 10%, an initial temperature of 23°C, a soot load of 20 g / L, and an exhaust flow rate of 12.3 g / s.

[0031] Figure 8 This is a schematic diagram of the external heat ratio of a single-channel DPF controller according to an embodiment of the present invention, with an inlet temperature of 620°C, an oxygen concentration of 10%, an initial temperature of 300°C, a soot load of 20 g / L, and an exhaust flow rate of 12.3 g / s.

[0032] Figure 9 This is a schematic diagram of the external heat ratio of a single-channel DPF controller according to an embodiment of the present invention, with an inlet temperature of 620°C, an oxygen concentration of 10%, an initial temperature of 500°C, a soot load of 20 g / L, and an exhaust flow rate of 12.3 g / s.

[0033] Figure 10 This is a schematic diagram of the external heat ratio of a single-channel DPF controller according to an embodiment of the present invention, with an inlet temperature of 620°C, an oxygen concentration of 10%, an initial temperature of 23°C, a soot load of 4 g / L, and an exhaust flow rate of 36.5 g / s.

[0034] Figure 11 This is a schematic diagram of the external heat ratio of a single-channel DPF controller according to an embodiment of the present invention, with an inlet temperature of 620°C, an oxygen concentration of 10%, an initial temperature of 23°C, a soot load of 12 g / L, and an exhaust flow rate of 36.5 g / s.

[0035] Figure 12 This is a schematic diagram of the external heat ratio of a single-channel DPF controller according to an embodiment of the present invention, with an inlet temperature of 620°C, an oxygen concentration of 10%, an initial temperature of 23°C, a soot load of 20 g / L, and an exhaust flow rate of 36.5 g / s.

[0036] Figure 13This is a schematic diagram of the external heat ratio of a single-channel DPF controller according to an embodiment of the present invention, with an inlet temperature of 620°C, an oxygen concentration of 10%, an initial temperature of 300°C, a soot load of 20 g / L, and an exhaust flow rate of 36.5 g / s.

[0037] Figure 14 This is a schematic diagram of the external heat ratio of a single-channel DPF controller according to an embodiment of the present invention, with an inlet temperature of 620°C, an oxygen concentration of 10%, an initial temperature of 500°C, a soot load of 20 g / L, and an exhaust flow rate of 36.5 g / s. Detailed Implementation

[0038] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0039] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0040] The diesel engine particulate filter regeneration optimization method based on the proportion of external heat includes the following steps:

[0041] Step S1: Construct a single-channel DPF model and a solid-state control volume energy transfer model.

[0042] Step S11: Construct a single-channel DPF model.

[0043] The DPF single-channel model is the basic unit for describing the internal physicochemical processes of a diesel particulate filter. Since the DPF consists of numerous parallel channels, and the airflow distribution at the inlet and the material distribution are uniform across all channels, one-dimensional modeling is sufficient to model all channels. This model can describe momentum transfer (flow), heat transfer (temperature evolution), and reaction phenomena (carbon dioxide oxidation) within the filter. It can also be applied to the time-varying concentration, temperature, and energy conditions during active regeneration in actual cycles, thereby calculating the proportion of external heat.

[0044] like Figure 1 As shown, the DPF single-channel model consists of four parts: inlet channel 1, particulate layer 2, wall surface 3, and outlet channel 4. Inlet channel 1 is the channel through which exhaust gas enters the DPF, flowing axially (Z-direction) within the channel, while some gas permeates outward through wall surface 3. Particulate layer 2 is a layer of carbon soot particles attached to the surface and pores of wall surface 3, forming the core area for filtration and regeneration. Wall surface 3 is a porous ceramic filter wall with specific porosity and permeability, serving both filtration and heat transfer functions. Outlet channel 4 is the channel through which filtered gas flows out; adjacent channels are alternately blocked, forcing the gas to pass through wall surface 3. Figure 1 In this context, X represents the radial direction.

[0045] The DPF single-channel model describes the following key processes: flow process, heat transfer process, and soot oxidation process.

[0046] During the flow, exhaust gas flows in from the inlet channel 1 and flows downstream axially (Z direction). Some of the gas, driven by the pressure difference, seeps through the wall 3 into the outlet channel 4. The seepage velocity is determined by the pressure difference across the wall 3 and the permeability of the wall 3.

[0047] For the heat transfer process, convective heat transfer occurs between the gas and the solid phase (wall 3 + particle layer 2) in the inlet channel 1 and outlet channel 4; there is axial and radial heat conduction inside the solid phase; seepage heat transfer occurs as the gas seeps from the inlet channel 1 into the wall 3 and then from the wall 3 into the outlet channel 4; the chemical heat released by the carbon soot oxidation reaction is the main heat source for regeneration.

[0048] For the carbon soot oxidation process, when the solid phase temperature reaches the carbon soot ignition temperature (approximately 550~600°C), the carbon soot undergoes an oxidation reaction with oxygen. There are two main reaction pathways:

[0049] Incomplete oxidation: (Generates carbon monoxide) (1)

[0050] Complete oxidation: (2) (Generates carbon dioxide)

[0051] The DPF single-channel model is a one-dimensional physical model that describes the flow, heat transfer, and soot oxidation reaction of exhaust gas in an alternately blocked channel. It is a fundamental tool for calculating the proportion of external heat and optimizing regeneration control strategies.

[0052] Step S12: Construct a solid-state control volume energy transfer model.

[0053] To calculate the proportion of external heat, a local energy transfer model of the DPF single-channel control volume was constructed. The control volume selected in the model is a micro-element in the solid phase (3 layers of wall + 2 layers of microparticles), such as... Figure 2 The red box clearly marks the boundary of this micro-element, and the arrow in the red box indicates the direction of gas flow. The axial length of this micro-element is taken along the length of the DPF, the radial length is from the inner side of wall 3 (the junction of inlet channel 1 and wall 3) to the outer side of wall 3 (the junction of outlet channel 4 and wall 3), and the circumferential length is taken as the unit width.

[0054] This is a solid-phase control volume, excluding the gas phase within the channel; in other words, the control volume consists of two parts: wall 3 and particle layer 2. The local energy transfer model of the constructed DPF single-channel control volume is as follows: Figure 2 As shown, this energy transfer model system describes various energy exchanges at the boundary of the control volume during the regeneration process. The model includes six energy transfer methods: First, heat carried in by inlet gas permeation, where exhaust gas carries heat into the control volume as it permeates from inlet channel 1 into wall surface 3; the heat carried into the control volume per unit time through this method is the inlet gas permeation heat carry-in rate. Second, convective heat transfer through inlet channel 1, which is the heat exchange between the gas and the solid phase surface within inlet channel 1; the heat exchanged through this method per unit time is the inlet channel convective heat transfer rate. Third, exothermic combustion of soot, which is the chemical heat released by the oxidation reaction of soot, the core driving source of solid phase temperature rise during regeneration; the heat released through this method per unit time is the soot combustion exothermic heat. The model is based on the following six energy parameters: First, the heat exchange rate; second, the heat transfer rate; third, the heat exchange between the solid phase and the gas in the outlet channel 4; fourth, the heat exchange rate through this method per unit time; fifth, the heat carried away by the exhaust gas as it seeps from the wall 3 into the outlet channel 4, carrying heat away from the control body; and sixth, the heat transfer along the solid phase axis described by Fourier's law of thermal conductivity, which helps to smooth the axial temperature gradient and reduce the risk of thermal stress. The heat transferred along this method per unit time is the solid phase axial thermal conductivity. This model is based on the principle of energy conservation, where the rate of change of the solid phase energy within the control body is equal to the algebraic sum of the above six energy parameters, providing a complete energy balance framework for the quantitative analysis of the proportion of external heat.

[0055] Step S2: Define the external heat ratio as the ratio of the external heat flow rate to the total heat flow rate, where the total heat flow rate is the sum of the external heat flow rate and the soot combustion heat release rate.

[0056] The heat generated during the regeneration process originates from two parallel and coupled heat sources: one is the heat input from an external heat source (such as high-temperature exhaust convection heat transfer, electric heating, microwave heating, etc.), and the other is the chemical heat released by the carbon soot oxidation reaction. The relative weights of these two sources in the total heat directly affect the temperature field evolution characteristics of the regeneration process. The heat generated during particulate filter regeneration comes from upstream or downstream heat transfer and combustion heat release. The ignition temperature of carbon soot is typically between 550°C and 600°C, while the exhaust temperature of a diesel engine under normal operating conditions (especially in urban driving) is often only between 200°C and 400°C, which is insufficient to spontaneously ignite carbon soot. Therefore, an external heat transfer stage is needed to increase the temperature within the DPF.

[0057] In the DPF regeneration process, there are two main energy sources: external heat transfer and heat release from soot combustion. External heat transfer comes from two sources: one is direct heating of the exhaust gas through methods such as post-injection of fuel, installing a burner or electric heater before the DPF; the other is the enthalpy of the exhaust gas itself, i.e., the heat carried by the high-temperature exhaust gas generated by the engine through adjustments to operating conditions. External heat transfer can raise the temperature of the DPF and soot, bringing them to the ignition temperature. This energy is passive and comes from outside the system. The heat release from soot combustion originates from the soot particles in particulate layer 2 (the main component of which is carbon). ) and oxygen ( The chemical reaction that occurs. Once the carbon soot is ignited, it becomes a powerful heat source itself. This energy is active and comes from within the system.

[0058] To quantitatively describe the relative importance of external heat transfer and particulate combustion heat release during the entire regeneration process, this invention defines the external heat ratio F as the proportion of the heat flux provided by external heat transfer (i.e., external heat flux) to the total heat flux of the system (the sum of external heat flux and soot combustion heat release rate), that is:

[0059] (3)

[0060] in, External heat flux, in W; This represents the heat release rate of carbon soot combustion, expressed in W.

[0061] This parameter reflects the degree to which the regeneration process depends on external energy input. The closer F is to 1, the more the regeneration is driven by external heating; conversely, the smaller F is, the more dominant the exothermic reaction of soot combustion becomes. This parameter describes the proportion of external heating to the total heating intensity at any given moment during the regeneration process, and can reveal the dynamic competition between reaction exotherm and external heating.

[0062] The external heat flow rate in the external heat ratio includes the heat carried in by the inlet air seepage, the convective heat transfer rate of the inlet channel, the convective heat transfer rate of the outlet channel, the heat carried out by the exhaust air seepage, and the solid phase axial heat conduction rate.

[0063] The introduction of the external heat ratio provides a new perspective for understanding the regenerative heat behavior of DPF: traditional studies have focused on the independent effects of various operating parameters, while the external heat ratio elevates the issue to the level of heat source composition, which helps to reveal the common laws of regenerative heat behavior under different operating conditions.

[0064] Step S3: Calculate the heat release rate of carbon soot combustion and the external heat flow rate based on the energy transfer model, and determine the proportion of external heat.

[0065] The formula for calculating the heat release rate of carbon soot combustion is as follows:

[0066] (4)

[0067] It is a carbon soot oxidation reaction. The reaction rate; Carbon soot oxidation reaction The calorific value of combustion, in units of . The oxidation of soot during active regeneration can be divided into two cases: soot is... Oxidation generation As shown in formula (1); the carbon soot is Oxidation generation As shown in formula (2). Furthermore, the oxidation reaction is of first order. These two... The reaction rate expressions for the oxidation of carbon soot are shown below:

[0068] (5)

[0069] (6)

[0070] Carbon soot oxidation The reaction rate, in units of ; For carbon soot oxidation The reaction rate, in units of ; for The concentration, in units of ; for The concentration, in units of ; For solid-state temperature, specifically... The temperature of the particulate filter wall 3 or the soot temperature is defined in the model, which assumes that both temperatures are the same. The solid-state temperature.

[0071] (7)

[0072] For carbon soot oxidation The calorific value of combustion, in units of Carbon soot oxidation generates calorific value The variation within the DPF regeneration temperature range is less than 1%, and it is taken as a constant in engineering calculations, with a value range of 1.0 × 10⁻⁶. 7 ~1.1×10 7 J / kg, in this embodiment, is taken as ; For carbon soot oxidation The calorific value of combustion, in units of Carbon soot oxidation generates calorific value It is approximately constant within the DPF regeneration temperature range, and takes a value of [value missing]. In this embodiment, Therefore, the heat release rate of carbon soot combustion is expressed as a function of temperature, carbon monoxide concentration, and oxygen concentration.

[0073] (8)

[0074] The external heat flux is:

[0075] (9)

[0076] in, Represents the solid phase porosity; Represents the thermal conductivity of the solid phase; Represents the axial direction; This represents the convective heat transfer coefficient between the gas in inlet channel 1 and the wall 3. This represents the geometric specific surface area of ​​the diesel particulate filter. This represents the exhaust temperature inside inlet channel 1; The convective heat transfer coefficient between the gas in the outlet channel 4 and the wall 3; This represents the exhaust temperature inside outlet channel 4; The specific heat capacity at constant pressure representing the gas phase; The gas phase density inside the inlet channel 1 of the diesel particulate filter; This represents the velocity at which exhaust gas flows into wall 3 from inlet channel 1; This represents the gas phase density inside the diesel particulate filter outlet channel 4. The velocity of the exhaust gas flowing out of the wall 3 in the outlet channel 4 represents the exhaust gas velocity.

[0077] To calculate the soot combustion heat release rate and external heat flow rate, we need to solve equation (8) in... and and in equation (9) , , , , With parameters such as [parameter quantification], a system of equations was constructed and solved. Considering the influence of the inlet region, the heat and mass transfer between the fluid in the channel and the filter wall 3 were calculated using the Sieder-Tate correlation and the Hawthorn relation, respectively.

[0078] The remaining assumptions of the DPF model in the active regeneration process are as follows: (a) airflow distribution at the inlet and uniform material distribution in all channels; (b) axial diffusion in the gas phase is ignored; (c) the radial outer wall is completely adiabatic; (d) the heat capacity and thermal conductivity of the gas within wall 3 are ignored; (e) the particulate matter is assumed to be soot; (f) the heat release rate only considers the combustion of carbon and ignores other reactions; (g) the active regeneration time is short and particulate matter deposition during regeneration is ignored.

[0079] Based on the above assumptions, the main governing equations of the single-channel model in the active regeneration process of DPF include: mass conservation equation for inlet channel 1, mass conservation equation for outlet channel 4, effective flow area equation for inlet channel 1, mass continuity equation for wall 3, equilibrium relationship satisfied by the concentration distribution of gas components in the solid phase along the wall thickness direction (radial), seepage velocity equation for wall 3, total reaction consumption rate equation, momentum conservation equation for inlet channel 1, momentum conservation equation for outlet channel 4, gas phase energy conservation equation for inlet channel 1, gas phase energy conservation equation for outlet channel 4, heat transfer coefficient calculation equation, solid phase energy conservation equation, and soot mass calculation equation for diesel particulate filter.

[0080] The mass conservation equation for import channel 1 is as follows:

[0081] (10)

[0082] in, For axial coordinates, the unit is . ; The gas flow rate within inlet channel 1 is expressed in units of... ; The effective circulation area of ​​import channel 1, in units of ; Indicates time; The seepage velocity at wall 3 of inlet channel 1 is expressed in units of... ; The wet cycle of the import channel is 1. .

[0083] The mass conservation equation for exit channel 4 is as follows:

[0084] (11)

[0085] in, The gas flow rate within outlet channel 4 is expressed in units of... ; The cross-sectional area of ​​exit channel 4 is equal to the initial cross-sectional area of ​​the clean channel, in units of... ; The seepage velocity at wall 3 of outlet channel 4 is expressed in units of... ; The wet perimeter of the outlet channel is 4, and the unit is... Cleanliness refers to the state where no particulate layer 2 is attached to the corresponding channel.

[0086] The equation for the effective circulation area of ​​import channel 1 is as follows:

[0087] (12)

[0088] in, The initial cross-sectional area of ​​the clean inlet channel 1, in units of ; The mass of carbon soot deposition is expressed in units of... ; Carbon soot deposition density, in units of ; Total number of channels; Channel length, in units of .

[0089] The effective flow area and diameter of the inlet channel 1 change with time and axial position, initially equal to the diameter of the clean channel; as soot is deposited, the thickness of the particulate layer 2 increases, and the effective diameter decreases. The relationship between the effective diameter and the thickness of the particulate layer 2 is determined by geometric relationships, and the thickness of the particulate layer 2 is jointly determined by the local soot mass, channel density, and soot density.

[0090] The continuity equation for the mass of wall 3 is as follows:

[0091] (13)

[0092] The mass flow rate through wall 3 is continuous on both sides of wall 3, meaning that the mass flow rate of inlet channel 1 penetrating into wall 3 is equal to the mass flow rate of inlet channel 3 penetrating into outlet channel 4. This relationship couples the flow in inlet channel 1 and outlet channel 4 together.

[0093] The flow distribution is established based on equations (10) to (13) as the basic input for calculating the proportion of external heat.

[0094] The equilibrium relationship satisfied by the concentration distribution of gaseous components in the solid phase along the wall thickness direction (radial) is as follows:

[0095] (14)

[0096] in, For radial coordinates (from the surface of wall 3 inwards); The seepage velocity at the wall surface is given in units of 3. ; Components Concentration (mass fraction or mole fraction); Components The effective diffusion coefficient, in units of . ; Components Total reaction consumption rate, in units of .

[0097] Inside the DPF wall 3 and particulate layer 2, components such as oxygen in the exhaust gas diffuse into the wall 3 while undergoing an oxidation reaction with soot. Along the wall thickness direction (radial), the concentration distribution of each gas component is determined by the balance of convection, diffusion, and chemical reaction.

[0098] Convection term: Exhaust gas carrying gas components is transported radially into the interior of wall 3. The magnitude of the convection contribution is determined by the seepage velocity at wall 3. With component concentration The product determines the product.

[0099] Diffusion term: Due to the concentration gradient between the surface and interior of wall 3, gas components diffuse deeper into particle layer 2. The diffusion flux follows Fick's law and is proportional to the effective diffusion coefficient and the concentration gradient. The effective diffusion coefficient is affected by the porosity and pore tortuosity of wall 3.

[0100] Reaction source term: During diffusion, oxygen reacts with carbon soot to undergo oxidation, consuming oxygen and generating... and The reaction consumption rate is determined by Arrhenius-type reaction kinetics and is related to the solid-phase temperature, local oxygen concentration, and soot density. Stoichiometric coefficients reflect the consumption or formation relationships of components in the reaction.

[0101] On the surface of particle layer 2 (at the junction with inlet channel 1), the component concentration is equal to the gas phase concentration inside inlet channel 1, constituting a first-type boundary condition. On the leeward side of wall 3 (at the junction with outlet channel 4), the concentration gradient is zero, constituting a flux-free boundary condition.

[0102] This equation is used to solve for the oxygen concentration distribution inside wall 3, and then to determine the local reaction rate of soot oxidation, which serves as the basis for calculating the soot combustion heat release rate.

[0103] Pressure difference across wall 3 This is the driving force propelling the gas through the porous wall 3, and it is related to the seepage velocity of wall 3 via Darcy's law. The equation for the seepage velocity of wall 3 is as follows:

[0104] (15)

[0105] in: The wall permeability is given in units of 3. ; Wall thickness 3, unit is ; The exhaust pressure within inlet channel 1, in units of ; The exhaust pressure within outlet channel 4, in units of ; Exhaust dynamic viscosity, in units of .

[0106] The above equation applies to the seepage velocity at wall surface 3. It is coupled with the seepage term in the mass conservation equation.

[0107] The equation for the total reaction consumption rate is as follows:

[0108] (16)

[0109] in, Specific surface area of ​​particles, in units of , Stoichiometric coefficients The oxidation reaction when carbon soot is oxidized by oxygen. The reaction rate, in units of .

[0110] The momentum conservation equation for inlet channel 1 is as follows:

[0111] (17)

[0112] in: This is the shear stress loss coefficient (dimensionless, related to channel geometry and flow state). The hydraulic diameter of inlet channel 1 is given in units of... .

[0113] The rate of change of gas momentum in the axial direction (i.e. The axial gradient consists of two parts: one is the pressure gradient. The first factor is the acceleration / deceleration effect of the gas; the second is the momentum loss caused by friction on the wall 3. The friction loss term is proportional to the exhaust dynamic viscosity, local flow velocity, and friction loss, reflecting the shear stress between the gas and the channel wall 3.

[0114] The momentum conservation equation for exit channel 4 is as follows:

[0115] (18)

[0116] in: The hydraulic diameter of outlet channel 4, in units of .

[0117] The momentum balance relationship of outlet channel 4 is similar to that of inlet channel 1, but the flow direction is reversed (gas in outlet channel 4 seeps into the wall 3 and flows downstream). The friction loss term is also related to dynamic viscosity, flow velocity, and loss coefficient. However, since the diameter of outlet channel 4 is usually constant (no soot deposition), its loss term expression includes a term of the square of the channel diameter to reflect the influence of channel geometry on friction loss.

[0118] The pressure and velocity distribution inside the DPF are established based on the conservation of momentum in inlet channel 1 and outlet channel 4, serving as inputs for the flow parameters in the calculation of the external heat ratio.

[0119] The energy conservation equation for the gas phase in inlet channel 1 is as follows:

[0120] (19)

[0121] in, . It is the isobaric specific heat capacity of the gas phase.

[0122] The rate of change of gas phase enthalpy flow per unit axial length is contributed by two parts: convective heat transfer between the gas and solid phases, and energy carried away by seepage through wall 3. The convective heat transfer term is determined by the heat transfer coefficient, the wetted perimeter of the channel, and the gas-solid temperature difference; the seepage term through wall 3 reflects the energy carried by the gas as it seeps into wall 3 from inlet channel 1. Assuming that the seeping gas and solid phase reach thermal equilibrium at the surface of wall 3, the energy carried away is related to the solid phase temperature.

[0123] The energy conservation equation for the gas phase at outlet channel 4 is as follows:

[0124] (20)

[0125] in, . Let the initial cross-sectional area of ​​inlet channel 1 be . The initial cross-sectional area of ​​the clean exit channel 4.

[0126] The energy balance within outlet channel 4 is similar to that within inlet channel 1, but the flow direction is reversed. As gas seeps from wall 3 into outlet channel 4, it carries heat from the solid phase. The rate of change of gas phase enthalpy per unit axial length is contributed by two parts: convective heat transfer between the gas and solid phases, and the energy carried in by the seepage from wall 3.

[0127] The equation for calculating the heat transfer coefficient is as follows:

[0128] heat transfer coefficient The Sieder-Tate correlation is used for calculations related to the flow velocity, gas properties, and channel geometry within the channel.

[0129] (twenty one)

[0130] in, The thermal conductivity is the vapor phase. The hydraulic diameter of the channel. Let Reynolds number be 1. It is a Prandtl number.

[0131] (twenty two)

[0132] in, The exhaust dynamic viscosity, The hydraulic diameter of the channel, For exhaust density, This represents the exhaust velocity. The subscript indicates the exhaust speed. 'a' or 'b' represents the parameter corresponding to import channel 1 or export channel 4, respectively.

[0133] (twenty three)

[0134] The energy in the inlet channel 1 and the outlet channel 4 is coupled: the energy loss (carried away by seepage) in the inlet channel 1 and the energy gain (carried in by seepage) in the outlet channel 4 are coupled through the energy balance phase of the wall 3, and together they constitute the convective heat transfer source term in the solid phase energy conservation equation.

[0135] The temperature distribution inside the DPF is established based on the above energy conservation relationship, and used as the input for the temperature parameter in the calculation of the proportion of external heat.

[0136] The solid-state energy conservation equation is as follows:

[0137] (twenty four)

[0138] Among them, the gas-solid convection heat transfer rate of inlet channel 1 and outlet channel 4 Percolation heat transfer rate . This represents the solid phase reduced specific heat capacity. It is the solid-phase reduced density.

[0139] The temperature evolution of the DPF solid phase (including filter wall 3 and particle layer 2) is determined by the law of conservation of energy. The rate of change of internal energy per unit volume of solid phase is equal to the algebraic sum of the four contributions: axial heat conduction, exothermic chemical reaction, gas-solid convection heat transfer, and percolation heat transfer.

[0140] Solid phase internal energy change: The rate of change of solid phase temperature with time is determined by the solid phase density, solid phase heat capacity, and solid phase volume fraction. Porosity reflects the volume proportion of pores within the wall surface and affects the total heat capacity of the solid phase.

[0141] Axial thermal conduction: Along the axial direction of the DPF, heat transfer within the solid phase is described by Fourier's law of thermal conductivity. Thermal conduction contributes to the diffusion of heat from high-temperature regions to low-temperature regions, helping to smooth the axial temperature gradient and reduce the risk of thermal stress.

[0142] Exothermic chemical reaction: The chemical heat released by the carbon soot oxidation reaction is the main energy source for the solid phase temperature rise during the regeneration process. The exothermic power is obtained by summing the products of the reaction rates and the enthalpy changes of each reaction. As the solid phase temperature rises to the carbon soot ignition temperature (approximately 550~600°C), the reaction rate increases exponentially, and the exothermic power increases rapidly.

[0143] Gas-solid convective heat transfer: The convective heat transfer between the solid phase and the gas phase in inlet channel 1 and outlet channel 4 is determined by the heat transfer coefficient, geometric specific surface area, and gas-solid temperature difference. This is the main pathway for heat dissipation from the solid phase to the gas phase.

[0144] Percolation heat transfer: During the process of gas percolating from inlet channel 1 into wall 3 and then from wall 3 into outlet channel 4, heat is carried and transferred. The percolation heat transfer term is determined by the percolation velocity, gas phase density, gas phase isobaric specific heat capacity, and solid phase temperature. The gas percolating at the inlet side carries away heat from the solid phase, while the gas percolating at the outlet side carries in heat; the difference between the two constitutes the net effect of percolation heat transfer.

[0145] The solid-phase temperature distribution inside the DPF is calculated based on the solid-phase energy conservation equation, and is used as a reference in the calculation of the proportion of external heat. And the core input of temperature parameters.

[0146] The equation for calculating the carbon soot mass of a diesel engine particulate filter is as follows:

[0147] (25)

[0148] in, For carbon soot quality; This refers to the density of carbon soot.

[0149] The deposited soot is oxidized and consumed in a high-temperature, oxygen-rich environment. The oxidation rate is determined by the solid-phase temperature, local oxygen concentration, and intrinsic reactivity of the soot, following Arrhenius-type reaction kinetics. When the solid-phase temperature is below the ignition temperature (approximately 550°C), the oxidation rate is extremely low; when the temperature exceeds the ignition temperature, the oxidation rate increases exponentially. The soot mass is related to the effective cross-sectional area equation of inlet channel 1.

[0150] The boundary conditions for the constructed diesel particulate trap model are set as follows: Inlet boundary: given inlet exhaust temperature, inlet channel 1 flow velocity and concentration of each component, outlet channel 4 exhaust velocity is 0; Outlet boundary: outlet pressure is atmospheric pressure. The exhaust velocity of inlet channel 1 is 0; the boundary of wall 3: the radial outer wall is set as an adiabatic boundary, that is, the radial heat flux is zero; the boundary is symmetrical at the center line of the channel; on the surface of particle layer 2 (at the junction with inlet channel 1), the component concentration is equal to the gas phase concentration in inlet channel 1; on the leeward side of wall 3 (at the junction with outlet channel 4), the concentration gradient is zero, indicating a no-flux boundary.

[0151] The initial conditions for the constructed diesel particulate filter model are set as follows: Temperature field: The internal temperature of the DPF is uniformly distributed at the initial moment, and the initial temperature of the diesel particulate filter is given; Carbon soot distribution: The carbon soot load is uniformly distributed along the axial direction at the initial moment; Velocity field: The flow velocity in the channel is zero at the initial moment, and is gradually established by the inlet flow rate after startup; Concentration field: The oxygen concentration is uniformly distributed along the internal DPF at the initial moment, and is equal to the inlet oxygen concentration.

[0152] Step S4: Identify the stage of the regeneration process based on the trend of the external heat ratio changing with regeneration time or solid phase temperature.

[0153] The proportion of external heat exhibits a typical trend of first increasing and then decreasing over time (or as the temperature of wall surface 3 increases), eventually stabilizing. Figure 3 As shown, this clearly reflects a complete physical stage of the DPF regeneration process:

[0154] External heat-dominated stage (high F, increased solid-phase temperature, and F≥0.9): In the initial stage of regeneration, the DPF temperature is low, and the combustion reaction has not yet started or is at an extremely low rate. At this time, energy analysis: ≈0 (because it has not yet burned); >0 (and is the primary energy source). The system's temperature rise depends entirely on external heat transfer, with external heat accounting for nearly 1%. This means the system is almost 100% dependent on external energy input. The goal at this stage is to inject energy and cross the ignition temperature as quickly as possible.

[0155] Combustion development and dominant stage (rapid decrease in flammability, flammability < 0.9): As the temperature rises to near the soot ignition temperature (550~600°C), the combustion reaction is triggered and rapidly accelerates. The external heat transfer increases dramatically, becoming the primary heat source for the system. Although external heat transfer may increase or decrease due to changes in inlet conditions, its relative contribution is diluted by the surge in internal heat release, leading to a rapid decrease in the proportion of external heat. Once the combustion reaction has fully developed, the system enters a quasi-steady-state phase dominated by combustion heat release. At this point, the proportion of external heat drops to a low level and tends to stabilize, indicating that the system has successfully transitioned from an external energy input-dependent mode to an internal heat release-based self-sustaining mode.

[0156] Post-combustion stage (F increases again, solid phase temperature decreases, and F≥0.9): Most of the soot has been burned off, and the remaining soot is sparsely distributed, making it difficult to maintain the chain reaction. It rapidly decays to 0. Due to the reduction in soot, the heat released during combustion decreases, and external heating may need to be restarted to burn off the remaining, more difficult-to-burn soot. The proportion of external heating then rises back to a higher value. When When the ratio is 0, the external heat ratio returns to 1.0, and the regeneration process ends.

[0157] Step S5: Adjust operating parameters to optimize the regeneration process.

[0158] The external heat ratio F characterizes the transition process at a certain location within the DPF from dependence on external energy input to achieving self-sustaining combustion. The external heat ratio is influenced by multiple operating parameters, including oxygen concentration, the initial temperature of the DPF, soot load, and exhaust mass flow rate. Therefore, at least one of the following control methods can be used to enable the system to transition from external heating-dominated to soot self-sustaining combustion within a preset safe temperature window: (a) When the real-time value of the external heat ratio is higher than the target value, the decrease in the external heat ratio is accelerated by increasing the intake oxygen concentration. For the oxygen concentration control threshold: when the external heat ratio F > 0.9, the target oxygen concentration is set to 15%~20%; when F < 0.5, the oxygen concentration can be reduced to 5%~10% to reduce the risk of thermal runaway. (b) When the real-time value of the external heat ratio is higher than the target value, the initial temperature of the particulate filter is increased by preheating or other methods to reduce the dependence of the regeneration process on external energy input. For example, the DPF inlet temperature can be increased to 400°C through electric heating or a post-injection strategy. o C~500 o C. Reduce the external heat ratio to below 0.5 within a short period after regeneration begins. (c) Ensure the initial soot load exceeds a preset critical threshold, which is the minimum soot load required for the soot combustion heat release to sustain the regeneration process. For example, the critical soot load is determined to be 6-8 g / L through model calibration; below this range, active regeneration is prohibited or auxiliary heating is required. (d) Control the exhaust mass flow rate within a preset flow window, where the lower limit of the preset flow window is the minimum flow rate to ensure sufficient oxygen supply, and the upper limit is the maximum flow rate to prevent excessive cooling of the reaction zone, thus inhibiting self-sustaining combustion. For example, set the target exhaust mass flow rate to 10-25 g / s; if this range is exceeded, adjust via the throttle or variable geometry turbocharger.

[0159] During the external heat-dominated stage, when F ≥ 0.9 and the temperature of DPF wall surface 3 is less than 600℃, start the electric heater or post-injection, with the target power causing the wall surface 3 temperature to rise at a rate ≥ 5℃ / s; if the oxygen concentration is < 15%, increase it to 15%; if the exhaust flow rate is... , actively reduce to .

[0160] In the combustion development stage, when 0.5 < F < 0.9, maintain the oxygen concentration at 12% - 18%; gradually reduce the external heating power (such as reducing by 10% every 10 seconds); monitor dF / dt: if the decrease is too slow ( ), increase the oxygen concentration by 2%; if the decrease is too fast ( ), appropriately increase the exhaust gas flow rate ( ) to inhibit the temperature rise. When the combustion development is completed and enters the combustion-dominated stage, when F ≤ 0.5, completely turn off the external heating; the oxygen concentration can be reduced to 10% - 12% (only to maintain stable combustion); keep the exhaust gas flow rate at ; monitor the upper limit of the temperature of wall 3: if the temperature of wall 3 is greater than 800 °C, increase the exhaust gas flow rate or reduce the oxygen concentration.

[0161] In the post-combustion stage, when F rises back to ≥ 0.9, continue to regenerate using the waste heat. If there is more residual soot and the loading is less than the critical soot loading, the auxiliary heating can be restarted, but it is required to be at low power to avoid thermal shock.

[0162] Figures 4 to 6 The influence laws of different oxygen concentrations (5%, 10%, 20%) on the proportion of external heat under the same working conditions (inlet temperature = 620 o °C, initial temperature = 23 o °C, soot loading = 20 g / L, mass flow rate = 4.5 g / s) were compared.

[0163] It can be seen from Figure 4 that under a low oxygen concentration (5%), the proportion of external heat remains at a level close to 100% for a long time in the initial stage of regeneration. As the temperature of wall 3 slowly rises, the decrease in the proportion of external heat is extremely gentle, and it is still higher than 50% until the DPF regeneration starts. During the whole regeneration process, external heat transfer always dominates. It can be seen from Figure 5 that at a medium oxygen concentration (10%), the proportion of external heat starts to decrease significantly around 140 seconds and has dropped to the lowest value at about 235 seconds, indicating that the system successfully transitions to the combustion-dominated stage. It can be seen from Figure 6 that at a high oxygen concentration (20%), the proportion of external heat starts to drop sharply around 130 seconds and approaches the lowest value at about 210 seconds, and the system very quickly achieves self-sustaining combustion.

[0164] Therefore, the oxygen concentration is the key reactant for the soot oxidation reaction, directly affecting the reaction rate and the soot combustion heat release rate According to the Arrhenius-type rate equation, increasing oxygen concentration directly increases the reaction rate. At low oxygen concentrations (5%), the reaction rate is limited, and the heat release rate from soot combustion is insufficient to counteract the dominance of external heating, making it difficult for the system to transition to self-sustaining combustion, resulting in a persistently high proportion of external heat. As the oxygen concentration increases (10%), the reaction accelerates. quickly surpass The external heat percentage transitions from 1 to 0 within a narrow temperature window. A high oxygen concentration (20%) further intensifies this process, causing the system to enter a combustion-dominated state at a lower ignition temperature, resulting in a steeper decrease in the external heat percentage. This pattern reveals that oxygen concentration is one of the most sensitive parameters controlling the regeneration transition process; excessively low oxygen concentrations may lead to unsustainable regeneration, while excessively high oxygen concentrations may exacerbate the risk of thermal runaway.

[0165] Figures 7 to 9 , Figures 12 to 14 Comparison of different initial temperatures (23) o C, 300 o C, 500 o C) The influence of the proportion of external heat.

[0166] Depend on Figure 7 , Figure 12 It can be seen that the low initial temperature (23) o In case C), the proportion of external heat remains high during the initial stage of regeneration and requires a relatively long heating process to decrease. The starting temperature window for the decrease in the proportion of external heat is relatively wide. Figure 8 , Figure 13 It can be seen that the moderate initial temperature (300) o In case C), the descent process is significantly accelerated. At the same wall surface temperature, the proportion of external heat is significantly lower than in the case of lower initial temperature. (From...) Figure 9 , Figure 14 It can be seen that a high initial temperature (500) o In step C), the descent process occurs much earlier, and the initial external heat percentage has already dropped below 50%. The system almost skips the preheating stage and directly enters the combustion development and dominant state.

[0167] As shown above, the initial temperature determines the total sensible heat required for the system to reach the soot ignition temperature. According to the solid-state energy conservation equation, a higher initial temperature means less external heat is needed for the local temperature to cross the reaction activation energy barrier. When the initial temperature approaches the ignition temperature, even a small amount of heat released during combustion can trigger a self-accelerating reaction cycle. The external heat quickly becomes dominant, and its proportion drops sharply. This pattern indicates that increasing the initial temperature is an effective way to reduce the dependence of regeneration on external energy and achieve a rapid and stable transition, but the temperature tolerance limit of the downstream catalyst must be weighed.

[0168] Figures 10 to 12Comparison under the same operating conditions (inlet temperature) =620 o C, initial temperature =23 o C, Oxygen concentration = 10%, Mass flow rate The influence of different initial soot loadings (4 g / L, 12 g / L, 20 g / L) on the proportion of external heat at a value of 36.5 g / s.

[0169] Depend on Figure 10 It can be seen that, with a low carbon soot load (4 g / L), the proportion of external heat remains at a high level (>60%) throughout the regeneration process, even when the wall surface temperature exceeds 600°C. o C, the system has not yet fully transitioned to a combustion-dominated state. Figure 11 It can be seen that under medium carbon soot load (12 g / L): the proportion of external heat begins to decrease significantly around 50 seconds, reaching its lowest value at approximately 110 seconds. This lowest external heat proportion is significantly lower than that under low carbon soot load conditions. Figure 12 It can be seen that with high carbon soot load (20 g / L): the proportion of external heat begins to drop sharply around 40 seconds, and drops to the lowest value at about 90 seconds. The lowest value of the proportion of external heat then drops slightly, and the system quickly enters a self-sustaining combustion state.

[0170] As shown above, the soot loading determines the total amount of fuel available for reaction per unit volume. This is based on the expression for the soot combustion heat release rate. It is directly proportional to the soot loading (when reaction kinetics are not limited by mass transfer). Therefore, the higher the soot loading, the greater the instantaneous exothermic power under the same reaction conditions. The easier it is to surpass This causes the proportion of external heat to decrease rapidly. However, at a low carbon load (4g / L), even with complete oxidation, the total heat released is limited and cannot form a self-sustaining heat source, causing the system to always rely on external heating to maintain the regeneration temperature.

[0171] Figure 5 , Figure 7 , Figure 12 Comparison under the same operating conditions (inlet temperature) =620 o C, initial temperature =23 o The influence of different exhaust mass flow rates (4.5 g / s, 12.3 g / s, 36.5 g / s) on the proportion of external heat under C (oxygen concentration = 10%, soot load = 20 g / L).

[0172] Depend on Figure 5It can be seen that at low flow rates (4.5 g / s), the proportion of external heat begins to decrease significantly around 50 seconds, reaching its lowest value at approximately 110 seconds. The decrease curve is relatively steep. Figure 7 It can be seen that at a medium flow rate (12.3 g / s), the final stable value of the external heat ratio is lower than that under low flow rate conditions. From... Figure 12 It can be seen that at high flow rate (36.5 g / s), the external heat ratio eventually stabilizes at over 40%, which is higher than that of medium flow rate conditions.

[0173] As shown above, the effect of exhaust mass flow rate on the proportion of external heat exhibits a complex, non-monotonic relationship. This is the result of the competition between its convective cooling effect and oxygen transport effect: at low flow rates, convective cooling is weak, and heat easily accumulates. Rapid flow rate is dominant. However, excessively low flow rates may limit oxygen supply, and the reaction weakens after local oxygen depletion. At medium flow rates, oxygen supply is sufficient, but the cooling effect begins to appear, requiring higher temperatures to achieve the desired effect. overwhelming The curve showing a decrease in the proportion of external heat shifts to the right and flattens out. At high flow rates, strong convection cooling dominates. Although the inlet enthalpy flow is increased, the heat is rapidly carried away from the reaction zone. The inability to accumulate and form a self-accelerating reaction results in a consistently high proportion of external heat.

[0174] This principle reveals the dual role of exhaust gas mass flow rate in the regeneration process: an appropriate exhaust gas mass flow rate promotes self-sustaining combustion by optimizing oxygen transport, while an excessively high exhaust gas mass flow rate suppresses the dominant role of combustion heat release due to overcooling, making it difficult for the system to complete the transition from external heating to internal heat release. There exists an optimal range of inlet exhaust gas mass flow rates within which: heat transfer efficiency is high enough for effective preheating; oxygen supply is sufficient but not excessive; and the airflow velocity ensures the oxygen required for the reaction without extinguishing the flame or causing overcooling. Under this optimal exhaust gas mass flow rate, the DPF regeneration process can achieve: rapid preheating to stable ignition, a rapid decrease in the proportion of external heat to a low level, and finally, efficient, self-sustaining stable combustion. Whether the inlet exhaust gas mass flow rate is too low or too high, this balance will be disrupted, preventing the proportion of external heat from being effectively reduced during the combustion phase, thus making the regeneration process inefficient, expensive, and risky.

[0175] Finally, it is necessary to state that the above embodiments are only used to further illustrate the technical solution of the present invention in detail, and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for optimizing the regeneration of diesel particulate filters based on the proportion of external heat, characterized in that, Includes the following steps: Step S1: Construct a single-channel model of the diesel particulate filter and an energy transfer model of the solid phase control body. The solid phase control body is a micro-element composed of the filter wall and the particulate layer. Its energy transfer includes heat carried in by the intake air permeation, convective heat transfer in the inlet channel, heat release from carbon soot combustion, convective heat transfer in the outlet channel, heat carried out by the exhaust air permeation, and axial heat conduction of the solid phase. The single-channel model of the diesel particulate filter consists of four parts: an inlet channel, a particulate layer, a wall surface, and an outlet channel. The inlet channel is the internal channel of the diesel particulate filter, through which exhaust gas enters and flows axially. The inlet channel is blocked at the outlet end, forcing the exhaust gas to seep radially through the wall surface into the outlet channel. The particulate layer is a layer of carbon soot particles attached to the surface and pores of the wall surface, which is the core area for filtration and regeneration. The wall surface is a porous ceramic filter wall. The outlet channel is the channel through which the filtered exhaust gas flows out. The outlet channel is blocked at the inlet end, and the exhaust gas flows axially through the outlet channel until it exits the diesel particulate filter. The axial direction is consistent with the length direction of the diesel particulate filter. The solid-phase control volume energy transfer model is a micro-element in the solid phase composed of a wall and a microparticle layer. The axial direction of this micro-element is the length of the micro-element along the length direction of the diesel engine particulate trap, the radial direction is from the inner side of the wall to the outer side of the wall, and the circumferential direction is the unit width. The inner side of the wall refers to the junction of the inlet channel and the solid phase, and the outer side of the wall refers to the junction of the outlet channel and the solid phase. Step S2: Define the external heat ratio as the proportion of external heat flow rate to the total heat flow rate of the system. The total heat flow rate of the system is the sum of the external heat flow rate and the soot combustion heat release rate. The external heat flow rate is the sum of the heat carried in by the inlet air permeation, the convective heat transfer in the inlet channel, the convective heat transfer in the outlet channel, the heat carried out by the exhaust air permeation, and the solid phase axial heat conduction. Step S3: Based on the solid-state control body energy transfer model, calculate the carbon soot combustion heat release rate and external heat flow rate, and determine the proportion of external heat. Step S4: Identify the stage of the regeneration process based on the trend of the external heat ratio changing with regeneration time or solid phase temperature; Step S5: Based on the identification results and the real-time value of the external heat ratio, coordinate and regulate at least one of the following: oxygen concentration, initial temperature, soot load, and exhaust mass flow rate, so that the system can complete the transition from external heating-dominated to soot self-sustaining combustion within a preset safe temperature window.

2. The optimization method according to claim 1, characterized in that: In step S3, the soot combustion heat release rate is calculated based on the reaction rate of soot being oxidized by oxygen to produce carbon monoxide and its calorific value, as well as the reaction rate of soot being oxidized by oxygen to produce carbon dioxide and its calorific value.

3. The optimization method according to claim 1, characterized in that: Step S4 specifically includes: when the external heat ratio is within a preset high threshold range, it is determined to be the external heat-dominated stage; when the external heat ratio rapidly decreases from the preset high threshold range, it is determined to be the combustion development and dominance stage; when the external heat ratio rises again after decreasing, it is determined to be the post-combustion stage.

4. The optimization method according to claim 1, characterized in that: In step S3, in order to calculate the heat release rate of carbon soot combustion and the external heat flow rate, the set of governing equations to be solved includes: the mass conservation equation of the inlet channel, the mass conservation equation of the outlet channel, the momentum conservation equation of the inlet channel, the momentum conservation equation of the outlet channel, the gas phase energy conservation equation of the inlet channel, the gas phase energy conservation equation of the outlet channel, and the solid phase energy conservation equation.

5. The optimization method according to claim 1, characterized in that: In step S5, the exhaust mass flow rate is controlled within a preset flow window. The lower limit of the preset flow window is the minimum flow rate to ensure sufficient oxygen supply, and the upper limit is the maximum flow rate to prevent excessive cooling of the reaction zone, thereby inhibiting self-sustaining combustion.

6. The optimization method according to claim 5, characterized in that: The preset flow window is determined by calibrating the decreasing curve of the external heat ratio under different exhaust mass flow rates, and the flow range that makes the external heat ratio drop to a preset low level within the target solid phase temperature range is selected as the preset flow window.

7. The optimization method according to claim 1, characterized in that: In step S5, the oxygen concentration is adjusted within a range of 5% to 20%. When the real-time value of the external heat ratio is higher than the target value, the intake oxygen concentration is increased within this range to accelerate the decrease of the external heat ratio.

8. The optimization method according to claim 1, characterized in that: In step S5, the carbon soot loading is adjusted so that the initial carbon soot loading is greater than a preset critical threshold. The preset critical threshold is a value between 4 g / L and 12 g / L. When the initial carbon soot loading is lower than this threshold, the heat released by carbon soot combustion is insufficient to sustain the regeneration process.

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