Patent Application
20240159179
The present invention relates to an exhaust gas aftertreatment system and method for reducing harmful emissions from internal combustion engines.
There is a rising demand for cleaner and more efficient internal combustion engines, especially diesel engines. In response to these demands, new standards continue to be proposed for reduction of exhaust emissions and in particular reduction of particulate and NOx(NO and NO2) emissions. Exhaust aftertreatment systems (EAT) in engine exhaust systems have been developed to meet these standards.
The EAT system 10 includes an electronic control system 26 including one or more electronic control units (ECU), indicated schematically at 28 in
The electronic control system 26 also includes a number of sensors for monitoring various operating parameters of the EAT system. These include:
The sensors provide inputs for use by the ECU 28 in regulating operation of the EAT system in a variety of operating conditions. Control of the EAT system is carried out using a combination of mathematical modelling to predict operating conditions and parameters at various locations within the system and closed loop feedback control, both using inputs from the various sensors. Inputs from other sensors associated with the engine and/or the exhaust gas system upstream of the EAT system may also be utilised. These may provide data relating to engine state, speed, load and temperatures, for example, as inputs to the EAT control system.
During operation, the DPF 12 may become filled by particulates (referred to herein as soot loading) which can affect correct operation of the engine and EAT system. Excess soot is oxidised in a process known as regeneration. Soot is oxidised by NO2 reduction with the DPF in a temperature range in the order of 300-500 deg C. This occurs during normal operation of the vehicle and is therefore termed passive regeneration. However, if the soot loading becomes too high, a more aggressive regeneration is required in which the soot is oxidised at a DPF temperature in excess of 500 deg C. This is termed active regeneration as the process is actively triggered when the soot loading in the DPF exceeds a predetermined limit. For regeneration purposes, the temperature of the DPF is determined principally using the second temperature sensor 38.
It is known to monitor soot loading of the DPF using two approaches. In a first method, monitoring of the soot loading in the DPF is carried out by the ECU 28 using a model based approach in which three EAT models are used:
A further sensor based monitoring of the soot loading in the DPF 14 is also carried out using inputs from, amongst other things, the DPF pressure differential sensor 40, the EGT measured downstream of the DOC by second temperature sensor 38, the EGT upstream of the SCR unit 22 measured by third temperature sensor 42, and the soot loading as modelled by the DPF model. This method compares the measured differential pressure over the DPF catalyst against a threshold value. If the sensor value exceeds the threshold value, this may trigger an active regeneration of the DPF.
Dosing of the DEF is controlled by the ECU 28 and may be controlled using a model-based DEF dosing control strategy. DEF dosing is allowed only when the engine is running and the DEF dosing strategy is adjusted according to the particular operating state of the engine. The main target of the dosing control is to reach the required tailpipe emissions of NOx while minimizing NH3 slip and excessive use of DEF.
The SCR DEF dosing control model utilizes in particular the two NOx sensors 30, 32 and the third and fourth temperature sensors 42, 44, located up and downstream of the SCR unit 22 to provide temperature data. Chemical reactions for the NOx components (NO and NO2) in the EAT system are different. Therefore accurate modelling of NOx conversion requires differentiation between NO and NO2. The upstream NOx sensor 30 cannot differentiate between NO and NO2. However, the DOC and DPF models provide separate concentrations for NO and NO2 which are used as input for the SCR model. Accordingly, accurate modelling of the DOC and DPF are required both for monitoring the soot loading of the DPF and DEF dosing control.
A problem with known EAT systems is the amount of space that is required to accommodate the system on a vehicle. This is a particular issue for agricultural vehicles such as tractors where it is becoming more difficult to find space for an exhaust aftertreatment system in addition to a simultaneous need to accommodate an increasing number of other systems and components that customers require.
It is an objective of the present invention to provide an alternative EAT system which occupies less space than the known EAT systems.
It is a further objective of the invention to provide an alternative method of operating an EAT system which enables the EAT system to occupy less space than the known EAT systems.
According to a first aspect of the invention, there is provided an exhaust gas aftertreatment (EAT) system for receiving exhaust gases from an internal combustion engine, the EAT system having an oxidation catalyst (OC) upstream of and adjacent to a particulate filter (PF) and a pressure differential sensor configured to measure a pressure differential across the OC and the PF.
In the EAT system according to the invention, the OC and PF are positioned adjacent one another providing a shorter package for the OC and PF than in the known system where the OC and PF are spaced apart to enable the pressure difference across the PF and the EGT between the OC and PF to be measured directly.
The EAT system is preferably provided on a vehicle or machine which may be an off-road vehicle or machine. The EAT system may be provided on an agricultural vehicle or machine, such as a tractor, combine harvester or the like, or on an industrial or construction vehicle or machine (which may be mobile or static), or on a generator.
The PF may have a catalytic coating and may be a CSF.
The EAT system may be configured to receive exhaust gases from a diesel engine. In which case, the OC may be a diesel oxidation catalyst (DOC) and the PF may be a Diesel Particulate Filter (DPF). Alternatively, the EAT system may be configured to receive exhaust gases from an internal combustion engine which burns an alternative fuel such as hydrogen. In this case, the OC and PF may be adapted to the type of fuel burned.
In the EAT system there may not be any sensors for directly sensing a parameter of the exhaust gases located between the OC and the PF.
The OC and PF may be provided as an integral module.
There may be a gap of no more than 15 mm between the OC and the PF, or a gap of no more than 12 mm between the OC and the PF, or a gap of no more than 10 mm between the OC and PF, or a gap of no more than 8 mm between the OC and PF, or a gap of no more than 5 mm between the OC and PF.
In an embodiment, a selective catalytic reduction (SCR) system is provided downstream of the PF, the SCR system including an exhaust fluid (EF) dosing module for introducing an EF into the exhaust gas flow downstream of the PF and a SCR catalyst downstream of the EF dosing unit. The EF is a reducing agent which reacts in the SCR catalyst to reduce NOx levels in the exhaust and may be a DEF. The EF may be urea (which may be a urea water mixture).
The EAT system may comprise an upstream NOx sensor for detecting NOx levels in the exhaust gases upstream of the OC, a downstream NOx sensor for detecting NOx levels in the exhaust gas downstream of the SCR catalyst, an upstream OC temperature sensor for sensing the exhaust gas temperature (EGT) upstream of the OC, and at least one intermediate temperature sensor for sensing the EGT downstream of the PF and upstream of the SCR catalyst. The EAT system may also comprise a downstream SCR temperature sensor for sensing the EGT downstream of the SCR catalyst.
In an embodiment, there are two intermediate temperature sensors, one downstream of the PF and upstream of the EF dosing module and one downstream of the EF dosing module and upstream of the SCR catalyst.
Alternatively, the EAT system has a single intermediate temperature sensor, wherein the single intermediate temperature sensor is located either:
The EAT system may also comprise a mixer for mixing the EF in the exhaust gases downstream of the EF dosing module and upstream of the SCR catalyst
The SCR system may comprise an ammonia slip catalyst (ASC). The ASC may be provided as a separate catalytic coating zone after the SCR catalyst coating in an SCR unit or it may be provided in a separate unit downstream of the SCR.
The EAT system may having an electronic control system including at least one programmable electronic control unit (ECU) configured and programmed to control and regulate operation of the EAT system in accordance with a number of pre-defied protocols depending on operating conditions using a combination of mathematical modelling and closed loop feedback control. The at least one ECU may be programmed and configured to carry out a method according to the second aspect of the invention as set out below.
In accordance with a second aspect of the invention, there is provided a method of controlling an EAT system according to the first aspect of the invention, the method comprising: measuring an actual pressure drop between a first measurement position upstream of the OC and a second measurement position downstream of the PF using the differential pressure sensor, mathematically modelling a pressure drop occurring in the system between the first measurement position and an inlet face of the PF and between the outlet of the PF and the second measurement position, and determining the pressure drop across the PF using the measured pressure drop and the modelled pressure drop.
The method may comprise subtracting the modelled pressure drop from the measured pressure drop to derive the pressure drop across the PF. In other words, the pressure drop occurring in any part of the system between the first and second measurement positions outside of the PF is modelled and subtracted from the measured pressure drop.
The method may comprise mathematically modelling the temperature of the exhaust gases entering or in the PF. Where the EAT system has an electronic control system including at least one programmable electronic control unit (ECU) configured and programmed to control and regulate operation of the EAT system in accordance with a number of pre-defied protocols depending on the operating conditions using a combination of mathematical modelling and closed loop feedback control, the control system may include a mathematical model for predicting soot loading of the PF and the method may comprise using the modelled temperature value as an input to the PF model.
Embodiments of the invention will now be described, by way of example only, with reference to the remaining accompanying drawings, in which:
The drawings are provided by way of reference only, and will be acknowledged as not necessarily to scale. Like reference numbers are used to represent the same features, or features which perform substantially the same function, in each of the embodiments.
The EAT system 110 is provided for reducing particulate and NOx emissions in the exhaust gases emitted to atmosphere. The EAT system is similar to that of the known system described above in relation to
The EAT system 110 includes an electronic control system 126 including one or more electronic control units (ECU), indicated schematically at 128 in
The electronic control system 126 also includes a number of sensors for monitoring various operating parameters of the EAT system. These include:
The EAT system 110 according to the first embodiment is similar the prior art EAT system 10 illustrated in
Exhaust gases are directed from the engine into the common housing 146 through a first exhaust conduit section 148. The upstream NOx sensor 130 and the first temperature sensor 134 are located between the engine and the DOC 112. They can be located in the first exhaust conduit section 148 as shown. Alternatively, one or both could be located in an inlet chamber of the DOC 112. In an embodiment, exhaust gases exiting the DPF 114 and the housing 146 are directed to the SCR unit 122 through a second or intermediate exhaust conduit section 150. The second and third temperature sensors 138, 142, the DEF dosing module 116, and the mixer 118 are all mounted to the intermediate exhaust conduit section 150. The second temperature sensor 138 is located proximal the outlet of the DPF 114 and housing 146, upstream of the DEF dosing module 116 and the mixer 118 and could be mounted to an outlet end of the DPF 114. The third temperature sensor 142 is located proximal to the inlet to the SCR unit 122. In an embodiment, the exhaust gases exiting the SCR unit 122 are directed to atmosphere through a third exhaust conduit section or tailpipe 152. The fourth temperature sensor 144 and the downstream NOx sensor 132 are both mounted to the tailpipe 152 close to the SCR unit 122. The fourth temperature sensor 144 and the downstream NOx sensor are typically mounted close together. Whilst the fourth temperature sensor 144 is shown as being positioned upstream of the downstream NOx sensor 132, this order can be reversed.
The DOC 112, DPF 114, SCR catalyst 120, and ASC 124 can be of any suitable types known in the art and so will not be described in detail.
The change in sensor layout to enable the DOC and DPF to be positioned closer together requires a modification in the control system and methods of controlling the EAT system.
In general, the electronic control system 126 is constructed and functions in a similar manner to that of the prior art control system 26 as described above, to which the reader should refer. Accordingly, the sensors provide inputs for use by the ECU 128 in regulating operation of the EAT system in a variety of operating conditions. Control of the EAT system is carried out using a combination of mathematical modelling to predict operating conditions at various locations within the system and closed loop feedback control, both using inputs from the various sensors. Inputs from other sensors associated with the engine and or exhaust gas system upstream of the EAT system may also be utilised. These may provide data relating to engine state, speed, load and temperatures, for example, as inputs to the EAT control system.
As in the prior art EAT system, monitoring of the soot loading in the DPF is carried out using a model based approach utilising three EAT models:
A “sensor based” monitoring of the soot loading in the DPF 114 is also carried out. In the prior art system, the sensor based monitoring compares a measured differential pressure across the DPF catalyst against a threshold value. However, the modified sensor layout in the EAT system 110 does not allow direct measurement of the pressure differential across the DPF. To compensate for this, the EAT modelling includes an additional model to predict the pressure drop occurring in any part of the system between the first measurement position 140a and the second measurement position 140b but outside of the DPF. Typically this would require modelling a pressure drop occurring between the first measurement position 140a and the inlet face of the DPF 114 (including the pressure drop across the DOC 112) and modelling of a pressure drop occurring between the outlet of the DPF and the second measurement position 140b. The output from this model is used together with the measured pressure drop across both the DOC and DPF obtained from the differential pressure sensor 140 to derive a pressure drop across the DPF. For example, the modelled pressure drop can be subtracted from the pressure drop measured by the pressure differential sensor 140 to derive the pressure drop across the DPF. This derived value for the pressure drop across the DPF is used as part of the sensor based monitoring of the soot loading in the DPF in place of the directly measure pressure differential used in the prior art method. The derived value for the pressure across the DPF and the threshold value are compared periodically. If the derived pressure value exceeds the threshold value, this may trigger an active regeneration of the DPF. The threshold value may be obtained from a look up table or a model of predicated pressure value for the operating conditions.
A further input required for secondary monitoring of the soot loading of the DPF is the EGT of the gas entering the DPF. Since this also cannot be measured directly with the modified sensor layout, the EAT modelling is further modified to generate a modelled temperature value. This might be calculated from the EGT measured at the first temperature sensor 134, using a thermal model of the DOC to predict the DOC outlet temperature. Alternatively, the EGT of the gas entering the DPF can be calculated using the EGT measured by the first and second temperature sensors 134, 138, taking into account relevant effects such as heat transfer and thermal losses to the ambient, e.g. allowing for the higher heat capacity between the first and second temperature sensors 134,138. The modelled temperature value can also be used as an input to the DPF model and can also be used to control the temperature of the DPF during regeneration, especially active regeneration. Indeed, various models which form part of the EAT control system may require recalibration and/or additional modelling to take account of the fact that the second temperature sensor 138 is measuring the EGT downstream of the DPF.
The EAT systems 110′, 110″ of
Whilst embodiments of an EAT system and method in accordance with the invention have been described in relation to a mobile agricultural machine 101 in the form of a tractor, it should be understood that the inventive EAT system and method can be applied to a range of vehicles and machines (whether static or mobile) which use an internal combustion engine and especially a diesel engine. This includes, without limitation, tracked vehicles, combine harvesters, industrial and construction vehicles, and generators. Furthermore, whilst the invention has been described in relation to an EAT configured to receive exhaust gases from a diesel engine, the principles may be applied where the EAT system is used in respect of an engine which burns an alternative fuel such as hydrogen. In this case, the EAT may have an oxidation catalyst (OC) upstream of and adjacent to a particulate filter (PF) which are adapted to the type of fuel burned in place of the DOC and the DPF. Typically, the OC and PF would be constructed and function in similar manner to a DOC and DPF but would be configured for use with the particular type of fuel. Similarly, the DEF may be referred to simply as an exhaust fluid (EF) or a reducing agent where the engine is not a diesel engine.
The invention is not limited to the embodiments or examples described herein, and may be modified or adapted without departing from the scope of the present invention. For example, it should be understood that whilst the relative positons of the DOC, DPF, DEF dosing module, and SCR catalyst will remain the same, the physical layout of the EAT system may be varied. For example, the DOC, DPF, DEF dosing module, and SCR catalyst could all be contained in a common housing unit without the need for a smaller diameter intermediate exhaust conduit section. The required sensors will be mounted to the housing unit in the same relative positions as in the disclosed embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2106257.5 | Apr 2021 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/052049 | 3/8/2022 | WO |
