KR20180110623A - Method and control unit for operating a particle filter - Google Patents

Abstract

The invention relates to a method for operating a particulate filter (25) in an exhaust after-treatment system of an internal combustion engine, in particular for performing regeneration of the particulate filter and/or for heating the particulate filter, wherein the exhaust after-treatment system includes at least a first lambda sensor, a first catalyst, a secondary air inlet and the particulate filter in the flow direction of the exhaust gas along an exhaust passage. According to the method, the lambda of the exhaust gas in the upstream portion of the first catalytic converter is regulated using the signal of the first lambda sensor, and the lambda of the exhaust gas in the upstream portion of a particle filter is adjusted by a controlled supply of secondary air into the exhaust passage between the first catalyst and the particulate filter, therefore lambda adjustment of the exhaust gas in the upstream portion of the particle filter in the flow direction, which is suitable for the operation of the particle filter, is carried out. Moreover, the invention relates to a control unit for carrying out the method. The method and the control unit enable optimized operation of the particulate filter.

Description

METHOD AND CONTROL UNIT FOR OPERATING A PARTICLE FILTER < RTI ID = 0.0 >

The present invention relates to a method for operating a particle filter in an exhaust gas aftertreatment system of an internal combustion engine, in particular for performing regeneration of the particle filter and / or for heating the particle filter, At least a lambda sensor, a first catalytic converter, a secondary air inlet, and a particle filter along the exhaust gas channel in the flow direction of the exhaust gas.

The present invention also relates to a control unit for operation of a particle sensor in an exhaust gas channel of an internal combustion engine, wherein the internal combustion engine is assigned an exhaust gas aftertreatment system, the exhaust gas aftertreatment system comprising: Wherein at least one output signal of the first lambda sensor is supplied to the control unit and the control unit is connected to the internal combustion engine via an internal combustion engine, It is connected to the fuel metering system of the engine.

In today's engine control systems, lambda sensors are used for detection of oxygen concentration in the exhaust gas and lambda control of the engine. In this case, a broadband lambda sensor and a discrete level lambda sensor are used.

Typically, a broadband lambda sensor is used where the rich or lean lambda value must be measured accurately, or where the lambda = 1 range of measurements is sufficient with limited accuracy. A discontinuous level lambda sensor is used where the exhaust lambda in the vicinity of lambda = 1 should be measured with high accuracy.

Typical applications for broadband lambda sensors are lambda control upstream of the catalytic converter and balancing of the inflow and outflow of oxygen during the diagnosis of the catalytic converter. Typical applications of discontinuous level lambda sensors are very precise regulation of lambda = 1 downstream of the catalytic converter and detection of breakthrough of rich or lean exhaust gases at the time of diagnosis of the catalytic converter.

In particular, in order to comply with legal emissions and diagnostic requirements (e.g. SULEV), recent internal combustion engines, and in particular typical exhaust gas systems of gasoline engines, are equipped with a first lambda sensor downstream of the internal combustion engine, in particular a broadband lambda sensor, A first three-way catalytic converter, a second lambda sensor, particularly a discrete level lambda sensor, and an unmonitored second three-way catalytic converter.

Future tighter emissions and diagnostic requirements (eg China 6) require an exhaust aftertreatment system in which a second catalytic converter is also to be monitored. At the same time, the number of particles in the exhaust gas must be limited. To achieve this, it may be desired to combine the second three-way catalytic converter with a particle filter, or to use a catalyst-coated particle filter (a catalytic converter) instead of a second catalytic converter.

Further, a secondary air inlet may be provided between the first catalytic converter and the second catalytic converter. The secondary air inlet may be merged into the exhaust gas channel upstream or downstream of the second lambda sensor in the flow direction of the exhaust gas. With the aid of the secondary air inlet, fresh air (secondary air) can be introduced into the exhaust gas channel upstream of the second catalytic converter, and thus upstream of the particle filter.

With the aid of the particle filter, the soot particles generated from the exhaust gas upon combustion of the internal combustion engine are filtered. When the storage capacity of the particle filter is reached, regeneration of the particle filter should be performed. To this end, the temperature of the particle filter rises until the accumulated soot burns in the exothermic reaction. An internal engine action or fuel injection into the exhaust gas channel may be performed to raise the temperature. There must be enough oxygen in the exhaust gas to allow soot combustion. Accordingly, a lean exhaust gas (lambda greater than 1) must be present upstream of the particle filter. In view of this, Document D1 (DE 10 2011 100 677 A1) describes a method of operating a diesel engine with an exhaust gas control system consisting of an oxidation catalytic converter, preferably a three-way catalytic coating, a particulate filter and an SCR catalytic converter . For regeneration of the particle filter, the diesel engine is operated with at least one lambda to achieve a good conversion of the harmful substances of the oxidation catalytic converter. Air is guided into the exhaust gas channel between the oxidizing catalytic converter and the particulate filter so that combustion of soot particles of the particulate filter is simultaneously possible. The secondary air supply is controlled in particular to produce a pre-adjusted soot burning speed. To this end, the exhaust gas temperature difference for the particle filter is used as the control variable.

In order to realize the catalysis of a three-way catalytic converter or catalytic-coated particle filter combined with a particle filter, the particle filter must have a sufficient operating temperature. For example, after cold starting of the internal combustion engine, or after prolonged operation in the costing mode, the internal combustion engine is operated as a rich mixer and the catalytic converter / particle filter A method of introducing secondary air into an exhaust gas duct of an internal combustion engine from upstream is known. Hydrocarbons in the exhaust gas are then combusted in the catalytic converter either upstream of or in the catalytic converter by the oxygen of the secondary air to heat the catalytic converter. In this case, preferably at least one lambda is regulated upstream of the particle filter.

In order to precisely adjust the lambda of the exhaust gas upstream of the particle filter (as a combination of the three-way catalytic converter and the particle filter or as the second catalytic converter as the catalyst-coated particle filter) for the regeneration or rapid heating of the particle filter, The amount of car air can be controlled by a second lambda sensor that is disposed between the first catalytic converter and the particle filter. To this end, the inflow of secondary air has to be carried out upstream of the second lambda sensor in the flow direction.

A precondition for precise control of the supplied secondary air is that a clear relationship is established between the actual lambda of the exhaust gas at the mounting position of the second lambda sensor and the signal of the lambda sensor, The accuracy of the control based on the signal is insufficient and excessively high discharge or damage of the particle filter may occur. Since the signals are receiving normally different exhaust gas component such as influenced by the different cross-sensitivity of the lambda sensor of the CO, CO _2, H _2, H ₂ O, HC, NO _x, O ₂ from the lambda sensor, And because the exhaust gas composition may be different even though the exhaust gas lambda is the same under different operating conditions of the internal combustion engine, the precondition is not usually satisfied in a broadband lambda sensor as well as a discrete level lambda sensor.

Thus, for example, at the downstream of the three-way catalytic converter, the time-varying ratio between hydrogen (H ₂ ) and carbon monoxide (CO) is regulated under constant rich lambda conditions. The cause is the so-called water gas conversion reaction, in which the catalytic converter can not be continuously balanced. After a lambda = 1 or a change from a lean lambda to a constant rich lambda, the catalytic converter initially supplies an amount of H ₂ corresponding to approximately equilibrium. However, over time, the catalytic converter apparently supplies too much CO compared to H ₂ . Even though the lambda at the sensor location is constant, due to the different cross sensitivities to H ₂ and CO, the lambda sensor indicates a signal that is temporarily strongly fluctuating downstream of the three-way catalytic converter.

According to another undesirable effect, the pre-catalytic action of H ₂ by O ₂ in the lambda sensor, for the different cross sensitivities of lambda sensors to H ₂ , CO and O ₂ , It affects. Since only a small amount of O ₂ present can be converted by the catalytic action in the lambda sensor, this fraction is highly dependent on the amount of O ₂ present. Here again, even if the lambda at the sensor position is constant, other sensor signals of the lambda sensor are adjusted depending on the composition of the exhaust gas.

Therefore, complicated modeling of the exhaust gas composition downstream of the first catalytic converter and the cross sensitivity of the second lambda sensor is required in order to achieve the accuracy required for metering supply of the secondary air.

It is an object of the present invention to provide a method for enabling optimized operation of a particle filter disposed downstream of a first catalytic converter and a subsequent secondary air inlet.

A further object of the present invention is to provide a control unit suitable for carrying out the method.

An object of the present invention related to the apparatus is to control the lambda of the exhaust gas upstream of the first catalytic converter using the signal of the first lambda sensor; As the lambda of the exhaust gas upstream of the particle filter is adjusted by the controlled secondary air supply into the exhaust gas channel between the first catalytic converter and the particle filter; This is solved by performing lambda adjustment of the exhaust gas upstream of the particle filter in the flow direction, which is suitable for the operation of the particle filter. The first lambda sensor is used for normal operation of the internal combustion engine, lambda control upstream of the catalytic converter, and, in some cases, balancing the inflow and outflow of oxygen during the diagnosis of the catalytic converter. Optionally, the cross sensitivity of the first lambda sensor is corrected through relatively simple modeling for normal operation of the exhaust aftertreatment system as known in the prior art. Thus, the lambda of the exhaust gas upstream of the first catalytic converter can be accurately measured and adjusted by the first lambda sensor. As the storage capacity of the first catalytic converter is exceeded, the lambda regulated upstream of the first catalytic converter is also present downstream of the first catalytic converter. If the lambda at the downstream of the first catalytic converter is known, it is possible to determine the amount of secondary air that must be supplied to the exhaust gas upstream of the particle filter to adjust the lambda suitable for operation of the particle filter. This allows the exhaust gas lambda upstream of the particle filter to be precisely adjusted through the supply of the controlled secondary air according to the invention. The amount of secondary air supplied is determined by the lambda regulated upstream of the first catalytic converter. It is unnecessary to use the signal of the second lambda sensor disposed between the first catalytic converter and the particle filter. Thus, a complicated correction of the cross sensitivity of the second lambda sensor can be omitted.

In order to provide optimum operating conditions for the regeneration of the particulate filter, a lambda of less than or equal to 1, particularly between 0.95 and 1.00, is regulated upstream of the first catalytic converter to effect regeneration of the particulate filter, It is possible to regulate the lean lambda, particularly the lambda in the range of 1.05 to 1.2, upstream of the particle filter through the controlled supply. Thereby, not only unburned hydrocarbons but also enough oxygen are present in the exhaust gas to raise the temperature of the particle filter so that combustion of soot particles occurs. In this case, the burning rate of the soot particles can be influenced by a suitable fluctuation of the lambda of the exhaust gas upstream of the first catalytic converter and / or the volumetric flow rate of the supplied secondary air.

Rapid heating of the particulate filter to the desired operating temperature is achieved by regulating the rich lambda upstream of the first catalytic converter to effect the heating of the particulate filter, particularly the lambda within the range of 0.85 to 0.95, By adjusting at least one lambda upstream of the particle filter.

The adjustment accuracy of the lambda required respectively upstream of the particle filter can be improved by considering the current exhaust gas mass flow in a controlled supply of secondary air. If the lambda upstream of the first catalytic converter as well as the lambda downstream of the first catalytic converter are known and if the exhaust gas mass flow is known then it must be added to the exhaust gas to precisely adjust the lambda upstream of the required particle filter The secondary air demand can be accurately determined and adjusted.

Monitoring of the correct performance of the heating or regeneration of the particulate filter is achieved by regenerating and / or regenerating the particulate filter through the output signal of the second lambda sensor downstream of the secondary air inlet in the flow direction of the exhaust gas and upstream of the particulate filter, Or whether or not a condition of lean lambda or lambda = 1 has been established to carry out the heating can be monitored. The detection of such a lean lambda can be performed with sufficient accuracy without the correction of the cross sensitivity of the second lambda sensor.

According to one preferred embodiment of the present invention, the function of the secondary air inlet can be monitored through the output signal of the second lambda sensor. For example, the failure of the secondary air pump supplying the secondary air of the secondary air inlet can be recognized simply and quickly. This can be reliably detected when there is a defect in the secondary air inlet and thus the lambda required for optimum operation of the particle filter can not be adjusted.

In order to optimally operate the particle filter, in particular for the purpose of carrying out rapid heating or regeneration of the particle filter, it is desirable to adjust the lambda not to be 1 both upstream of the first catalytic converter and downstream of the first catalytic converter. Thus, according to a preferred variant of the invention, it is possible that the lambda upstream of the first catalytic converter is regulated using a broadband lambda sensor. With such a broadband lambda sensor, the oxygen concentration of the exhaust gas is detected within a wide range around lambda = 1, and the lambda can be correspondingly adjusted.

Preferably, the lambda of the exhaust gas upstream of the particle filter can be adjusted by the controlled supply of the secondary air as the storage capacity of the first catalytic converter is exceeded and the breakdown of the rich exhaust gas appears. From the rich exhaust gas, the lambda upstream of the particle filter can be adjusted to lambda 1 or lean by a corresponding supply of secondary air. In this case, the lambda of the exhaust gas downstream of the first catalytic converter and the exhaust of the rich exhaust gas corresponds to the lambda upstream of the first catalytic converter. This lambda is accurately known through measurements by the first lambda sensor disposed upstream of the first catalytic converter, so that the secondary air demand that must be supplied to the exhaust gas to adjust the desired lambda upstream of the particle filter can be accurately determined.

The method can preferably be used for a particle filter or a catalyst coated particle filter (a catalytic converter) in combination with a three-way catalytic converter.

An object of the present invention relating to a control unit is to control the lambda of the exhaust gas upstream of the first catalytic converter through the control of the fuel metering supply system in accordance with the output signal of the first lambda sensor, Wherein the control unit is adapted to control the control of the air / fuel mixture supplied to the internal combustion engine to a pre-adjusted value, wherein the control unit controls the air / Through control of the controlled secondary air supply, to adjust the lambda of the exhaust gas upstream of the particle filter to a value suitable for regeneration or heating of the particle filter. In this way, the control unit makes it possible to carry out the above-mentioned method.

The present invention will be described in more detail below based on the embodiments shown in the drawings.

1 is a schematic diagram of an exhaust gas aftertreatment system of an internal combustion engine having a secondary air inlet disposed downstream of a second lambda sensor.
Figure 2 is a schematic diagram of an exhaust aftertreatment system of an internal combustion engine having a secondary air inlet disposed upstream of a second lambda sensor.

Figure 1 is a schematic diagram of an exhaust aftertreatment system 20 of an internal combustion engine 10 having a secondary air inlet 27 disposed downstream of a second lambda sensor 24.

The exhaust gas 11 of the internal combustion engine 10 is guided through the exhaust gas aftertreatment system 20 along the exhaust gas channel 21. [ At this time, the first catalytic converter 23 is arranged in the flow direction of the exhaust gas 11 along the exhaust gas channel 21, and thereafter, the particle filter 25 is disposed in the exhaust gas channel 21. A first lambda sensor (22) is provided between the internal combustion engine (10) and the first catalytic converter (23). The second lambda sensor 24 is disposed directly behind the first catalytic converter 23 in the exhaust gas channel 21. [ A third lambda sensor 26 is disposed downstream of the particle filter 25 in the exhaust gas channel 21. A secondary air inlet 27 is connected to the exhaust gas channel 21 between the first catalytic converter 23 and the particulate filter 25. At this time, the secondary air inlet is disposed downstream of the second lambda sensor 24 in the flow direction. The secondary air 12 may be supplied to the exhaust gas channel 21 through the secondary air inlet 27.

2 is a schematic diagram of an exhaust aftertreatment system 20 of an internal combustion engine 10 having a secondary air inlet 27 disposed upstream of a second lambda sensor 24. As shown in FIG. Is identical to the structure of the exhaust gas after-treatment system 20 shown in Fig. 1, except that the arrangement of the secondary air inlet 27 and the second lambda sensor 24 is reversed. The same elements are therefore marked identically.

The internal combustion engine 10 shown in Figs. 1 and 2 is mainly implemented as a gasoline engine. The first lambda sensor 22 is a broadband lambda sensor. This lambda sensor is used to control the air / fuel mixture ratio supplied to the internal combustion engine 10. [ To this end, the signal of the first lambda sensor 22 is supplied to an engine control unit (not shown). The correction of the lambda value measured by the first lambda sensor 22 in the engine control section is performed. As a result, the error caused by the cross sensitivity of the first lambda sensor to the different exhaust gas constituents is corrected. Such cross-sensitivities are formed, for example, for carbon monoxide, carbon dioxide, hydrogen, water, hydrocarbons, nitrogen oxides and oxygen. Through the corresponding correction of this cross sensitivity, the lambda of the exhaust gas 11 upstream of the first catalytic converter 23 can be accurately detected.

The first catalytic converter 23 is implemented as a three-way catalytic converter. These three-way catalytic converters have limited storage capacity for oxygen and unburned hydrocarbons. When reaching the limit of the storage capacity of the three-way catalytic converter after a corresponding supply of lean exhaust gas or rich exhaust gas, the lean exhaust gas or lean breakthrough, which is passed through the three- way catalytic converter unconverted, ) Or rich breakthrough occurs. This lean or rich break can be detected by the second lambda sensor 24. [ For this, the cross sensitivity of the second lambda sensor 24 need not be corrected.

The particle filter 25 is here implemented with a catalyst coated particle filter 25. This catalyst-coated particle filter 25 is also referred to as a copropower converter. It is also conceivable to combine the particle filter 25 with a three-way catalytic converter as a constituent unit.

During operation of the internal combustion engine (10), the detected soot particles are filtered from the exhaust gas (11) by the particle filter (25). When the storage capacity of the particle filter 25 is full, the particle filter must be regenerated. In this case, the accumulated fine grains are burnt.

In order to maintain the conversion ability of the catalyst coating of the particle filter 25, the particle filter 25 must have the required operating temperature. In this case, the operating temperature must be reached as soon as possible after the cold start of the internal combustion engine 10, for example, to prevent the emission of harmful substances from being increased.

With the third lambda sensor 26, a lean or rich breakthrough of the coated particle filter 25 can be detected.

By supplying the secondary air 12 into the exhaust gas channel 11 upstream of the particle filter 25 in the rich combustion chamber mixing ratio so that the particle filter 25 is heated faster to its operating temperature, Lt; RTI ID = 0.0 > exothermic < / RTI > In order to prevent unwanted emissions, at least one average lambda lambda upstream of the particle filter 25 should be kept as precisely as possible.

When the temperature of the particle filter 25 is sufficiently high, combustion of the soot trapping amount and consequent regeneration of the particle filter 25 can be accomplished. To this end, a thin lambda should be maintained as defined upstream of the particle filter 25. At the same time, the lambda 1 is adjusted in the combustion chamber of the internal combustion engine 10 during regeneration, in order to ensure as much as possible a good conversion of the first catalytic converter 23.

The following lambda goal values are thus presented for optimal operation of the particle filter 25:

입자 필터의 가열:

Heating particle filter:

- lambda downstream of the first catalytic converter (23): rich (e.g. lambda = 0.9)

- lambda upstream of the particle filter (25): 1 (or at least greater than 1)

입자 필터의 재생:

Regeneration of particle filter:

Lambda "1 or slightly rich (e.g. lambda = 0.99) downstream of the first catalytic converter 23,

- lambda upstream of the particle filter (25): lean (eg lambda = 1.1)

Controlling the lambda upstream of the particle filter 25 in the flow direction of the exhaust gas 11 using the second lambda sensor 24 is advantageous in that the exhaust gas composition at the location of the second lambda sensor 24, Is not possible without considering the cross sensitivity of the second lambda sensor to the gas component because the sensor can indicate a different signal even if the exhaust gas lambda is the same if the exhaust gas composition is different.

Therefore, according to the present invention, the lambda upstream of the first catalytic converter 23 can be adjusted to the corresponding target value by the first lambda sensor 22, so that the necessary lambda downstream of the first catalytic converter 23 can be adjusted .

The lambda regulated upstream of the first catalytic converter 23 is regulated as soon as its storage capacity is exceeded, even downstream of the first catalytic converter 23. In this case, the lambda can be precisely adjusted upstream of the first catalytic converter 23 and accordingly also downstream of the first catalytic converter 23, based on the output signal of the first lambda sensor 22, This is because the cross sensitivity of the sensor 22 is corrected. In accordance with the present invention, to adjust the desired lambda upstream of the particulate filter 25 through the combination of the exhaust lambda upstream of the secondary air inlet 27 and the metered secondary air 12, There is provided a configuration for pilot-controlling the supply of the secondary air 12 through the inlet 27. Preferably, in determining the amount of secondary air to be metered, the current exhaust gas mass flow in addition to the exhaust gas lambda is also considered.

When the secondary air inlet 27 is located upstream of the second lambda sensor 24, as shown in Fig. 2, the signal of the second lambda sensor 24 is actually upstream of the particle filter 25 Can be used to detect whether there is a lean lambda required for regeneration or heating. This detection is not adversely affected by the above-mentioned cross sensitivity of the second lambda sensor 24. Likewise, the functionality of the secondary air inlet 27 can be monitored using the second lambda sensor 24.

Claims (10)

A method for operating the particulate filter 25 in the exhaust aftertreatment system 20 of the internal combustion engine 10 and in particular for regenerating the particulate filter 25 and / or for heating the particulate filter 25 The exhaust aftertreatment system 20 includes at least a lambda sensor 22, a first catalytic converter 23, a secondary air inlet 27, and a second catalytic converter 23 along the exhaust gas channel 21 in the flow direction of the exhaust gas 11. [ , And a particle filter (25), the method comprising:
The lambda of the exhaust gas 11 upstream of the first catalytic converter 23 is regulated using the signal of the first lambda sensor 22; The lambda of the exhaust gas 11 upstream of the particulate filter 25 is regulated by the supply of the controlled secondary air 12 into the exhaust gas channel 21 between the first catalytic converter 23 and the particulate filter 25 By doing so; Characterized in that a lambda adjustment of the exhaust gas (11) upstream of the particle filter (25) in the flow direction, suitable for the operation of the particle filter (25), is carried out. 2. A method according to claim 1, characterized in that in order to carry out regeneration of the particulate filter (25), a lambda of less than or equal to 1, in particular between 0.95 and 1.00, is regulated upstream of the first catalytic converter (23) Characterized in that a regulated lambda is regulated upstream of the particulate filter (25) through a controlled supply, in particular a lambda in the range of 1.05 to 1.2. A method according to any one of the preceding claims, characterized in that in order to effect the heating of the particulate filter (25), a rich lambda, in particular a lambda in the range of 0.85 to 0.95, is regulated upstream of the first catalytic converter (23) Characterized in that at least one lambda is regulated upstream of the particulate filter (25) via a controlled supply of particulate filter (12). 4. A method according to any one of claims 1 to 3, characterized in that during the controlled supply of secondary air (12), the current exhaust gas mass flow is taken into account. 5. A lambda sensor according to any one of claims 1 to 4, further comprising a second lambda sensor (24) disposed downstream of the secondary air inlet (27) in the flow direction of the exhaust gas (11) Characterized in that, through an output signal of the particle filter (25), whether a condition of lean lambda or lambda = 1 is established to carry out regeneration and / or heating of the particle filter (25) is monitored. Method according to claim 5, characterized in that the function of the secondary air inlet (27) is monitored via the output signal of the second lambda sensor (24). 7. A method according to any one of claims 1 to 6, characterized in that the lambda upstream of the first catalytic converter (23) is regulated using a broadband lambda sensor. 8. A method according to any one of claims 1 to 7, characterized in that as the storage capacity of the first catalytic converter (23) is exceeded and a breakthrough of dense exhaust gas is indicated, a controlled supply of secondary air (12) Characterized in that the lambda of the exhaust gas (11) upstream of the particle filter (25) is regulated by means of the filter (25). Use of a process according to any one of claims 1 to 8 for a particle filter (25) or a catalyst coated particle filter (25) (a catalytic converter) in combination with a three-way catalytic converter. An exhaust gas aftertreatment system (20) is assigned to an internal combustion engine (10) as a control unit for operation of a particle sensor (23) in an exhaust gas channel (21) of an internal combustion engine (10) The first catalytic converter 23, the secondary air inlet 27 and the particulate filter (not shown) are arranged along the exhaust gas channel 21 in the flow direction of the exhaust gas 11. At least the first lambda sensor 22, the first catalytic converter 23, 25), wherein the control unit is supplied with one or more output signals of a first lambda sensor (22) and the control unit is connected to a fuel metering supply system of an internal combustion engine (10)
The control unit adjusts the lambda of the exhaust gas 11 upstream of the first catalytic converter 23 through the control of the fuel metering supply system in accordance with the output signal of the first lambda sensor 22, , To control the pre-adjusted value of the air / fuel mixture supplied to the internal combustion engine 10,
The control unit controls the particulate filter 25 through the control of the secondary air pump and the supply of the controlled secondary air 12 into the exhaust gas channel 21 upstream of the particle filter 25, Is designed to adjust the lambda of the upstream exhaust gas (11) to a value suitable for regeneration or heating of the particle filter (25).

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