Method for estimating hydrocarbon storage in a catalytic device

Abstract

Method for estimating hydrocarbon storage in a catalytic device of an exhaust gas treatment system, the method comprising: Determining hydrocarbon absorption by the catalytic device over a period of time, hydrocarbon desorption by the catalytic device over a period of time, and hydrocarbon oxidation in the catalytic device over a period of time; Estimating the hydrocarbon storage of the catalytic device using a controller from the equation: Ω d θ HC dt = Δ [ HC ] absorp − Δ [ HC ] desorp − Δ [ HC ] oxitres 1 + tres Δ t where Ω d θ HC dt The rate of change of hydrocarbon storage per unit volume of the catalytic device is Δ[HC] absorpthe amount of hydrocarbons absorbed in the catalytic device per unit volume of exhaust gas, Δ[HC] desorp the amount of hydrocarbons desorbed in the catalytic device per unit volume of exhaust gas, Δ[HC] oxi the amount of hydrocarbons oxidized in the catalytic device per unit volume of exhaust gas, t res where Δt is the residence time of the exhaust gas in the catalytic device and Δt is the change in time (i.e., duration); and Controlling the exhaust gas treatment system based on the hydrocarbon storage of the catalytic device to heat the catalytic device to a start-up temperature in order to regenerate the catalytic device.

Description

TECHNICAL AREA

[0001] The invention relates generally to a method for estimating a quantity or mass of hydrocarbon storage in a catalytic device of an exhaust gas treatment system. BACKGROUND

[0002] Vehicles with an internal combustion engine (ICE) include an exhaust aftertreatment system to reduce the toxicity of the engine's exhaust gases. This system typically incorporates at least one, and often several, catalytic devices. If the engine is a diesel engine, these catalytic devices may include, for example, one or more diesel particulate filters, diesel oxidation catalysts, catalytic converters, and / or selective catalytic reduction (SCR) devices. Each catalytic device contains a catalyst that reduces nitrogen oxides in the exhaust gas to nitrogen and carbon dioxide or water, and also oxidizes carbon monoxide (CO) and unburned hydrocarbons (HCs) to carbon dioxide and water. The catalyst may include, but is not limited to, platinum group metals (PGMs).The catalytic converter must be heated to its activation temperature before it can function. Accordingly, the exhaust gas must heat the catalytic converter to this activation temperature before the reaction between the converter and the exhaust gas begins. The catalytic converter can also be intentionally heated to this activation temperature during a regeneration process to burn off accumulated hydrocarbons.

[0003] To determine when the exhaust aftertreatment system needs regeneration, the vehicle can use a model to predict when the catalytic converter(s) will require regeneration. The model provides an estimate of the hydrocarbons accumulated in the catalytic converter based on one or more actual vehicle operating conditions. The engine operation can then be controlled by the model based on the estimated hydrocarbon accumulation or storage to heat the catalyst to the activation temperature necessary for regenerating the catalytic converter(s).

[0004] A model for optimizing the injection of hydrocarbons into an exhaust stream upstream of an active lean NOₓ x-Catalysator (ALNC) is described in: D. Aswani, MJ van Nieuwstadt, JA Cook, JW Grizzle, Control Oriented Modeling of a Diesel Active Lean NOx Catalyst Aftertreatment System, ASME Journal of Dynamic Systems, Measurement, and Control, Volume 127, Issue 1, March 2005. SUMMARY

[0005] A method for estimating hydrocarbon storage in a catalytic device of an exhaust gas treatment system is provided. The method comprises calculating the amount of hydrocarbons absorbed in the catalytic device per unit volume of exhaust gas over a given time period, the amount of hydrocarbons desorbed in the catalytic device per unit volume of exhaust gas over a given time period, and the amount of hydrocarbons oxidized in the catalytic device per unit volume of exhaust gas over a given time period.The amount of hydrocarbons oxidized and desorbed in the catalytic device is subtracted from the amount of hydrocarbons absorbed to determine the amount of hydrocarbons stored in the catalytic device. The exhaust aftertreatment system is then controlled based on this estimated hydrocarbon storage to heat the catalytic device to a start-up temperature for regeneration.

[0006] A method for estimating hydrocarbon storage in a catalytic device of an exhaust gas treatment system is also provided. The method comprises estimating the hydrocarbon storage of the catalytic device from Equation 1). ΩdθHCdt=Δ[HC]absorp−Δ[HC]desorpΔ[HC]oxitres1+tresΔt.

[0007] Referring to equation 1 above, ΩdθHCdt the rate of change of hydrocarbon storage per unit volume of the catalytic device, Δ[HC] absorp is the amount of hydrocarbons absorbed in the catalytic device per unit volume of exhaust gas, Δ[HC] desorp Δ[HC] is the amount of hydrocarbons desorbed in the catalytic device per unit volume of exhaust gas. oxi is the amount of hydrocarbons oxidized in the catalytic device per unit volume of exhaust gas, t res is the residence time of the exhaust gas in the catalytic device, and Δt is the change in time (i.e., duration). The exhaust gas treatment system is then controlled based on the estimated hydrocarbon storage of the catalytic device.

[0008] Accordingly, Equation 1 is a mass equilibrium equation that balances the incoming mass of hydrocarbons with the outgoing mass of hydrocarbons to estimate the amount of hydrocarbons stored in the catalytic device.

[0009] The above features and advantages, as well as further features and advantages of the present invention, will be readily apparent from the following detailed description of the best ways of carrying out the invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a flowchart showing a method for estimating hydrocarbon storage in a catalytic device. Fig. Figure 2 is a schematic diagram showing a mapping structure for determining a normalized hydrocarbon storage desorption rate (k desorp ) shows. Fig. Figure 3 is a schematic diagram showing a mapping structure for determining the amount of hydrocarbon absorbed in the catalytic device per unit volume of exhaust gas, (Δ[HC] absorp ) shows. Fig. Figure 4 is a schematic diagram showing a mapping structure for determining the amount of O2 (oxygen) consumed in the catalytic device per unit volume of exhaust gas (Δ[O2]). DETAILED DESCRIPTION

[0010] The person skilled in the art will recognize that terms such as "above," "below," "upwards," "downwards," "above," "below," etc., are used descriptively for the figures and do not represent any limitations regarding the scope of protection of the invention as defined by the appended claims. Furthermore, the invention may be described herein in terms of functional and / or logical block components and / or various processing steps. It is understood that such block components may consist of any number of hardware, software, and / or firmware components configured to perform the specified functions.

[0011] Referring to the figures in which the same reference numerals in the different views denote the same parts, a flowchart showing a method for estimating hydrocarbon storage in a catalytic device of an exhaust gas treatment system is generally described in Fig. Figure 1 shows that the exhaust aftertreatment system treats the flow of exhaust gas from an engine, such as, but not limited to, a diesel engine or a gasoline engine. The exhaust aftertreatment system may include one or more devices containing a catalyst, such as, but not limited to, a catalytic converter. If the engine is a diesel engine, the catalytic device may, but is not limited to, a diesel oxidation catalyst, a diesel particulate filter, or a selective catalytic reduction system. To properly control the catalytic device, a vehicle controller must estimate the amount of hydrocarbons stored in the catalytic device. The controller uses this estimated amount of hydrocarbons stored in the catalytic device to determine when to regenerate the hydrocarbons stored in the catalytic device, i.e., when to remove them.to burn down, are.

[0012] As noted above, the vehicle has a controller to manage and / or monitor the operation of the engine and / or an exhaust aftertreatment system, including the catalytic converter. The controller may include a computer and / or processor and all the software, hardware, memory, algorithms, connections, sensors, etc., necessary to manage, monitor, and control the operation of the engine and the exhaust aftertreatment system. Therefore, the procedure described below can be executed as a program that can be run on the controller.It should be noted that the controller may include any device capable of analyzing data from various sensors, comparing data, making the necessary decisions required to control the operation of the engine and / or exhaust treatment system, and performing the various calculations required to calculate the estimated hydrocarbon storage of the catalytic device.

[0013] Referring to Fig. 1. The method for estimating the amount of hydrocarbon storage in the catalytic device includes calculating the amount of hydrocarbons absorbed in the catalytic device per unit volume of exhaust gas over a period of time, as generally shown in Box 20; calculating the amount of hydrocarbons desorbed in the catalytic device per unit volume of exhaust gas over a period of time, as generally shown in Box 22; and calculating the amount of hydrocarbons oxidized in the catalytic device per unit volume of exhaust gas over a period of time, as generally shown with Box 26.The amount of hydrocarbons oxidized 26 in the catalytic device and the amount of hydrocarbons desorbed 22 in the catalytic device are subtracted from the amount of hydrocarbons absorbed 20 in the catalytic device, as generally indicated by Box 28, to determine the amount of hydrocarbons stored in the catalytic device, as generally indicated by Box 30. Accordingly, the method uses a mass equilibrium between hydrocarbon absorption 20, hydrocarbon desorption 22, and hydrocarbon oxidation 26 to determine the hydrocarbon storage of the catalytic device.

[0014] The hydrocarbon storage of the catalytic device can be estimated from Equation 1: ΩdθHCdt=Δ[HC]absorp−Δ[HC]desorpΔ[HC]oxitres1+tresΔt; where ΩdθHCdt The rate of change of hydrocarbon storage per unit volume of the catalytic device is Δ[HC] absorp the amount of hydrocarbons absorbed in the catalytic device per unit volume of exhaust gas, Δ[HC] desorp the amount of hydrocarbons desorbed in the catalytic device per unit volume of exhaust gas, Δ[HC] oxi the amount of hydrocarbons oxidized in the catalytic device per unit volume of exhaust gas, t res where Δt is the residence time of the exhaust gas in the catalytic device and Δt is the change in time (i.e., duration).

[0015] The amount of hydrocarbons desorbed in the catalytic device per unit volume (Δ[HC] desorp ) can be calculated from equation 2: Δ[HC]desorp=(tres1+tresΔt)Ωkdesorp where t reswhere Δt is the residence time of the exhaust gas in the catalytic device, Δt is the change in time (i.e., duration), Ω is the maximum amount of hydrocarbon storage per unit volume of the catalytic device, and k desorp The normalized desorption rate for hydrocarbon storage is...

[0016] Referring to Fig. 2 can be a value for the normalized desorption rate for hydrocarbon storage (k desorp ), as generally specified by Box 32, can be obtained from a desorption rate table 34 stored in the controller's memory. Obtaining the normalized desorption rate for hydrocarbon storage, as generally specified by Box 36, is used to determine the amount of hydrocarbons desorbed in the catalytic device per unit volume (Δ[HC] ). desorpCalculating ) may involve referring to desorption rate table 34 to determine the normalized desorption rate for hydrocarbon storage (k desorp ) 32. The desorption rate table 34 can be defined as a two-dimensional table that uses two input values ​​to define an output value. The normalized desorption rate for hydrocarbon storage (k desorp ) 32 is based on a temperature of the catalytic device (T) 38 and a normalized hydrocarbon storage of the catalytic device (θ HC ) 40. Accordingly, the controller can determine the temperature of the catalytic device (T) 38 and a normalized hydrocarbon storage of the catalytic device (θ ). HC ) 40 as the two inputs in the desorption rate table 34 to determine the value for the normalized desorption rate for hydrocarbon storage (k desorp) 32 to look up and / or define which represents the output of the desorption rate table.

[0017] The amount of hydrocarbons oxidized in the catalytic device per unit volume of exhaust gas (Δ[HC] oxi ) can be calculated from equation 3: Δ[HC]oxi=∑[O2]ratio_O2_HC; where Δ[O2] is the O2 (oxygen) consumed in the catalytic device per unit volume of exhaust gas, and ratio stöch_O2_HC The stoichiometric ratio of the reaction of O2 and hydrocarbon is.

[0018] Referring to Fig. 3 is the O2 consumed in the catalytic device per unit volume of exhaust gas 44 (Δ[O2]) a function of an oxygen combustion efficiency ratio 46 and an amount of O2 available for reaction with hydrocarbons per unit volume of exhaust gas 48. The amount of O2 available for reaction with hydrocarbons per unit volume of exhaust gas 48 can be calculated from equation 4: ηdiff([O2]in+[O2]−1tresΔt1+tresΔt); where η diff The diffusion efficiency ratio of the oxidation catalyst is [O2] in The inlet O2 concentration of the oxidation catalyst is [O2] -1 the O2 concentration in the catalytic device at a final time increment is, t res where Δt is the residence time of the exhaust gas in the catalytic device and Δt is the change in time (i.e., duration).

[0019] As in Fig. As shown in Figure 3, a value for the oxygen combustion efficiency ratio 46 can be obtained from a combustion efficiency table 50 stored in the controller's memory. Obtaining the value, as generally specified by Box 52, for the oxygen combustion efficiency ratio 46, which is used to calculate the O2 consumed in the catalytic device per unit volume of exhaust gas 44 (Δ[O2]), can involve referring to the combustion efficiency table 50 to look up the value for the oxygen combustion efficiency ratio 46. The combustion efficiency table 50 can be defined as a two-dimensional table that uses two input values ​​to define an output value. The oxygen combustion efficiency ratio 46 is based on a temperature of the catalytic device 38 (T) and a first intermediate variable for hydrocarbon oxidation 54.Accordingly, the controller can use the temperature of the catalytic device 38 (T) and the first intermediate variable for hydrocarbon oxidation 54 as the two inputs to the combustion efficiency table 50 to look up and / or define the value for the oxygen combustion efficiency ratio 46, which represents the output of the combustion efficiency table 50.

[0020] As in Fig. As shown in Figure 3, the first intermediate variable for hydrocarbon oxidation 54 is a function of a second intermediate variable for hydrocarbon oxidation 56 (ζ O2 ) and a diffusion efficiency ratio 58 of the oxidation catalyst. The second intermediate variable for hydrocarbon oxidation 56 (ζ O2 ) can be calculated from equation 5: ςO2=Ωf(θHC)tres1+tresΔt where Ω is the maximum amount of hydrocarbon storage per unit volume of the catalytic device, f(θ HC) is a function of the normalized hydrocarbon storage of the catalytic device, t res where Δt is the residence time of the exhaust gas in the catalytic device and Δt is the change in time (i.e., duration).

[0021] As in Fig. As shown in Figure 3, a value for the diffusion efficiency ratio 58 of the oxidation catalyst can be obtained from a diffusion efficiency table 60 stored in the controller's memory. Obtaining the value, as generally specified by Box 62, for the diffusion efficiency ratio 58 for the oxidation catalyst, which is used to calculate the first intermediate variable for hydrocarbon oxidation 54, can involve referring to the diffusion efficiency table 60 to look up the value for the diffusion efficiency ratio 58 for the oxidation catalyst. The diffusion efficiency table can be defined as a one-dimensional table that uses an input value to define a single output value. The diffusion efficiency ratio 58 for the oxidation catalyst is based on a residence time of the exhaust gas in the catalytic device 64 (t resAccordingly, the controller can determine the residence time of the exhaust gas in the catalytic device 64 (t res ) as the single input to the diffusion efficiency table 60 to look up and / or define the value for the diffusion efficiency ratio 58 for the oxidation catalyst, which represents the output of the diffusion efficiency table 60.

[0022] As in Fig. As shown in 3, once the diffusion efficiency ratio 58 for the oxidation catalyst is obtained from the diffusion efficiency table 60 and the second intermediate variable for hydrocarbon oxidation 56 (ζ) O2The first intermediate variable for hydrocarbon oxidation 54 is calculated from Equation 5 by division, as generally specified in Box 66, and the second intermediate variable for hydrocarbon oxidation 56 is calculated by division by the diffusion efficiency ratio 58 for the oxidation catalyst. The first intermediate variable for hydrocarbon oxidation 54 and the temperature of the catalytic device 38 (T) are then used as the inputs to the combustion efficiency table 50 to obtain the oxygen combustion efficiency ratio 46. The oxygen combustion efficiency ratio 46 is then multiplied by the amount of O2 available to react with hydrocarbons per unit volume of exhaust gas 48, as specified in Box 68, to define and / or calculate the O2 consumed in the catalytic device per unit volume of exhaust gas 44 (Δ[O2]).

[0023] Referring to Fig. 4 is the amount of hydrocarbons absorbed in the catalytic device per unit volume of exhaust gas 72 (Δ[HC] absorp ) a function of a hydrocarbon absorption efficiency ratio 74 and a hydrocarbon concentration available for absorption 76. The hydrocarbon concentration available for absorption 76 is calculated from equation 6: ηdiff([HC]in+[HC]−1tresΔt1+tresΔt)+(tres1+tresΔt)Ωkϕdesorp; where η diff the diffusion efficiency ratio of the oxidation catalyst is, [HC] in an inlet hydrocarbon concentration of the oxidation catalyst, [HC] -1 the hydrocarbon concentration in the catalytic device at the last time increment is t reswhere Δt is the residence time of the exhaust gas in the catalytic device, Δt is the change in time (i.e., duration), Ω is the maximum amount of hydrocarbon storage per unit volume of the catalytic device, and k desorp The normalized desorption rate for hydrocarbon storage is...

[0024] As in Fig. As shown in Figure 4, a value for the hydrocarbon absorption efficiency ratio 74 can be obtained from an absorption efficiency table 78 stored in the controller's memory. Obtaining the value, generally specified by Box 80, for the hydrocarbon absorption efficiency ratio 74, which is used to calculate the amount of hydrocarbons absorbed in the catalytic device per unit volume of exhaust gas 72 (Δ[HC] absorp), may include referencing absorption efficiency table 78 to look up the value for the hydrocarbon absorption efficiency ratio 74. Absorption efficiency table 78 may be defined as a two-dimensional table that uses two input values ​​to define an output value. The hydrocarbon absorption efficiency ratio 74 is based on a temperature of the catalytic device 38 (T) and a first intermediate variable for hydrocarbon absorption 82. Accordingly, the controller may use the temperature of the catalytic device 38 (T) and the first intermediate variable for hydrocarbon absorption 82 as the two inputs to absorption efficiency table 78 to look up and / or define the value for the hydrocarbon absorption efficiency ratio 74, which represents the output of absorption efficiency table 78.

[0025] As in Fig. As shown in Figure 4, the first intermediate variable for hydrocarbon absorption 82 is a function of a second intermediate variable for hydrocarbon absorption 84 (ζ HC_absorp ) and the diffusion efficiency ratio 58 for the oxidation catalyst. The second intermediate variable for hydrocarbon absorption 84 (ζ HC_absorp ) can be calculated from equation 7: ςHC_absorp=Ω(1−θHC)tres1+tresΔt; where Ω is the maximum amount of hydrocarbon storage per unit volume of the catalytic device, θ HC the normalized hydrocarbon storage of the catalytic device is, t res where Δt is the residence time of the exhaust gas in the catalytic device and Δt is the change in time (i.e., duration).

[0026] As in Fig. As shown in Figure 4, a value for the diffusion efficiency ratio 58 of the oxidation catalyst can be obtained from the diffusion efficiency table 60, which is stored in the controller's memory. Obtaining the value, as generally specified by Box 86, for the diffusion efficiency ratio 58 of the oxidation catalyst, which is used to calculate the first intermediate variable for hydrocarbon oxidation 82, may involve referring to the diffusion efficiency table 60 to look up the value for the diffusion efficiency ratio 58 for the oxidation catalyst. The diffusion efficiency table 60 may be defined as a one-dimensional table that uses an input value to define a single output value. The diffusion efficiency ratio 58 for the oxidation catalyst is based on the residence time of the exhaust gas in the catalytic device 64 (t). resAccordingly, the controller can determine the residence time of the exhaust gas in the catalytic device 64 (t res ) as the single input to the diffusion efficiency table 60 to look up and / or define the value for the diffusion efficiency ratio 58 of the oxidation catalyst, which represents the output of the diffusion efficiency table 60.

[0027] As in Fig. As shown in Figure 4, once the diffusion efficiency ratio 58 for the oxidation catalyst is obtained from the diffusion efficiency table 60 and the second intermediate variable for hydrocarbon absorption 84 (ζ) HC_absorp ) calculated from equation 7, the first intermediate variable for hydrocarbon absorption 82 by diffusion, as generally indicated by box 88, the second intermediate variable for hydrocarbon absorption 84 (ζ HC_absorp) by the diffusion efficiency ratio 58 for the oxidation catalyst. The first intermediate variable for hydrocarbon absorption 82 and the temperature of the catalytic device 38 (T) are then used as the inputs to the absorption efficiency table 78 to obtain the absorption efficiency ratio 74 for hydrocarbon absorption. The hydrocarbon absorption efficiency ratio 74 is then multiplied by the hydrocarbon concentration available for absorption 76, as generally specified by Box 90, to define and / or calculate the amount of hydrocarbons absorbed in the catalytic device per unit volume of exhaust gas 72, (Δ[HC] absorp ).

[0028] The vehicle's operation can be controlled based on the estimated hydrocarbon storage of the catalytic device. For example, the engine can be controlled to heat the catalyst to the activation temperature in order to regenerate the catalytic device(s), or fuel can be injected into the exhaust gas flow for combustion to further heat the catalyst.

[0029] The detailed description and the drawings or figures support and describe the invention; however, the scope of protection of the invention is defined exclusively by the claims. While some of the best designs and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments for carrying out the invention, as defined in the attached claims, are also present.

Claims

[1] Method for estimating hydrocarbon storage in a catalytic device of an exhaust gas treatment system, the method comprising: Determining hydrocarbon absorption by the catalytic device over a period of time, hydrocarbon desorption by the catalytic device over a period of time, and hydrocarbon oxidation in the catalytic device over a period of time; Estimating the hydrocarbon storage of the catalytic device using a controller from the equation: ΩdθHCdt=Δ[HC]absorp−Δ[HC]desorp−Δ[HC]oxitres1+tresΔt where ΩdθHCdt The rate of change of hydrocarbon storage per unit volume of the catalytic device is Δ[HC] absorp the amount of hydrocarbons absorbed in the catalytic device per unit volume of exhaust gas, Δ[HC] desorpthe amount of hydrocarbons desorbed in the catalytic device per unit volume of exhaust gas, Δ[HC] oxi the amount of hydrocarbons oxidized in the catalytic device per unit volume of exhaust gas, t res where Δt is the residence time of the exhaust gas in the catalytic device and Δt is the change in time (i.e., duration); and Controlling the exhaust gas treatment system based on the hydrocarbon storage of the catalytic device to heat the catalytic device to a start-up temperature in order to regenerate the catalytic device. [2] Method according to claim 1, wherein Δ[HC] desorp calculated from the equation: Δ[HC]desorp=(tres1+tresΔt)Ωkdesorp where t reswhere Δt is the residence time of the exhaust gas in the catalytic device, Δt is the change in time (i.e., duration), Ω is the maximum amount of hydrocarbon storage per unit volume of the catalytic device, and k desorp The normalized desorption rate for hydrocarbon storage is... [3] Method according to claim 1, wherein Δ[HC] oxi calculated from the equation: Δ[HC]oxi=Δ[O2]Ratio_O2_HC where Δ[O2] is the O2 (oxygen) consumed in the catalytic device per unit volume of exhaust gas, and ratio stöch_O2_HC The stoichiometric ratio of the reaction of O2 and hydrocarbons is. [4] Method according to claim 3, wherein the O2 consumed in the catalytic device per unit volume of exhaust gas (Δ[O2]) is a function of an oxygen combustion efficiency ratio and an amount of O2 available to react with hydrocarbons per unit volume of exhaust gas, wherein the amount of O2 available to react with hydrocarbons per unit volume of exhaust gas is calculated from the equation: ηdiff([O2]in+[O2]−1tresΔt1+tresΔt) where η diff the diffusion efficiency ratio of the oxidation catalyst is, [O2] in the inlet O2 concentration of the oxidation catalyst is, [O2] -1 the O2 concentration in the catalytic device at the last time increment is, t res where Δt is the residence time of the exhaust gas in the catalytic device and Δt is the change in time (i.e., duration). [5] Method according to claim 4, further comprising obtaining a value for the oxygen combustion efficiency ratio from a table based on a temperature of the catalytic device (T) and a first intermediate variable for hydrocarbon oxidation. [6] Method according to claim 5, wherein the first intermediate variable for hydrocarbon oxidation is a function of a second intermediate variable for hydrocarbon oxidation (ζ O2 ) and a diffusion efficiency ratio of the oxidation catalyst; where ζ O2 The following is calculated from the equation: ζO2=Ωf(θHC)tres1+tresΔt where Ω is the maximum amount of hydrocarbon storage per unit volume of the catalytic device, f(θ HC ) is a function of the normalized hydrocarbon storage of the catalytic device, t reswhere Δt is the residence time of the exhaust gas in the catalytic device and Δt is the change in time (i.e., duration). [7] Method according to claim 6, further comprising obtaining a value of the diffusion efficiency ratio of the oxidation catalyst from a table based on the residence time of the exhaust gas in the catalytic device (tres). [8] Method according to claim 1, wherein Δ[HC] absorp a function of a hydrocarbon absorption efficiency ratio and a hydrocarbon concentration available for absorption, where the hydrocarbon concentration available for absorption is calculated from the equation: ηdiff([HC]in+[HC]−1tresΔt1+tresΔt)+(tres1+tresΔt)Ωkdesorp where η diff the diffusion efficiency ratio of the oxidation catalyst is, [HC] in the inlet hydrocarbon concentration of the oxidation catalyst is, [HC] -1the hydrocarbon concentration in the catalytic device at the last time increment is t res where Δt is the residence time of the exhaust gas in the catalytic device, Δt is the time change (i.e., duration), Ω is the maximum amount of hydrocarbon storage per unit volume of the catalytic device, and k desorp The normalized desorption rate for hydrocarbon storage is... [9] Method according to claim 8, further comprising obtaining a value for the hydrocarbon absorption efficiency ratio from a table based on the temperature of the catalytic device (T) and a first intermediate variable for hydrocarbon absorption. [10] Method according to claim 9, wherein the first intermediate variable for hydrocarbon absorption is a function of a second intermediate variable for hydrocarbon absorption (ζ HC_absorp ) and a diffusion efficiency ratio of the oxidation catalyst, where ζHC_absorp The following is calculated from the equation: ζHC_absorp=Ω(1−θHC)tres1+tresΔt where Ω is the maximum amount of hydrocarbon storage per unit volume of the catalytic device, θ HC the normalized hydrocarbon storage of the catalytic device is, t res where Δt is the residence time of the exhaust gas in the catalytic device and Δt is the change in time (i.e., duration).

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