Patent Application
20110153179
This application claims priority to British Patent Application No. 0920017.1, filed Nov. 16, 2009, which is incorporated herein by reference in its entirety.
The technical field generally relates to a method for operating a Diesel engine system, in particular a turbocharged Diesel engine system.
A turbocharged Diesel engine system generally comprises a Diesel engine having an intake manifold and an exhaust manifold, an intake line for feeding fresh air from the environment into the intake manifold, an exhaust line for discharging the exhaust gas from the exhaust manifold into the environment, and a turbocharger which comprises a compressor located in the intake line, for compressing the air stream flowing therein, and a turbine located in the exhaust line, for driving said compressor. The intake line comprises an intercooler, also indicated as Charge Air Cooler (CAC), which is located downstream the compressor of turbocharger, for cooling the air stream before it reaches the intake manifold. The exhaust line comprises a diesel oxidation catalyst (DOC), which is located downstream the turbine of the turbocharger, for degrading residual hydrocarbons (HC) and carbon oxides (CO) contained in the exhaust gas, and a diesel particulate filter (DPF), which is located downstream the DOC, for capturing and removing diesel particulate matter (soot) from the exhaust gas.
In order to reduce polluting emission, most turbocharged Diesel engine system actually comprises an exhaust gas recirculation (EGR) system, which is provided for routing back and mixing an appropriate amount of exhaust gas with the fresh induction air aspired into the Diesel engine. Such amount of exhaust gas has the effect of reducing the amount of oxides of nitrogen (NOx) produced within the Diesel engine during the combustion process.
Conventional EGR systems comprise an EGR conduit for fluidly connecting the exhaust manifold with the intake manifold, an EGR cooler located in the EGR conduit, and valve means for regulating the flow rate of exhaust gas through the EGR conduit. Since the EGR conduit directly connects the exhaust manifold with the intake manifold, it defines a short route EGR (SRE) which routes back high temperature exhaust gas.
Improved EGR systems further comprise an additional EGR conduit for fluidly connecting the exhaust line downstream the DPF to the intake line upstream the compressor of turbocharger, an additional EGR cooler located in the additional EGR conduit, and additional valve means for regulating the flow rate of exhaust gas through the additional EGR conduit. As a matter of fact, these improved EGR systems are provided with a long route EGR (LRE), which comprises the above mentioned additional EGR conduit and the portion of the intake line between the additional EGR conduit and the Diesel engine. The LRE has the function of routing back exhaust gas having lower temperature than that routed back by the SRE.
According to this design, these improved EGR systems are configured for routing back the exhaust gas partially through the SRE and partially through the LRE, to thereby maintaining the temperature of the induction air in the intake manifold at an optimal intermediate value in any engine operating condition. The total amount of exhaust gas, and the rate of exhaust gas coming from the LRE, are determined by the Electronic Control Unit (ECU) from empirically determined data sets or maps, which correlate the total amount of EGR and the LRE rate to a plurality of engine operating parameters, such as for example engine speed, engine load and engine coolant temperature. The efficiency of a LRE is generally bound to the efficiency of its single components, including the additional cooler, the additional valve means, the compressor of turbocharger, and the Charge Air Cooler. It has been found that the efficiency of each LRE component generally decreases more or less quickly depending on several conditions, such as for example the component aging, the thermal stress to which the component is subject, and the composition of the exhaust gas which flows through the component.
These conditions are taken into account when designing the LRE components, in order to realize a LRE whose global efficiency can be expected to remain above a minimum allowable value over the entire LRE lifetime. Since the LRE is configured for getting the exhaust gas downstream the DPF, its components are generally designed considering a condition in which the exhaust gas passing therein contains only a minimum amount of soot. However, in case of DPF filtration performance loss, due for example to possible cracks during real world engine lifetime, accidental damages or breakings, it may happen that an unexpectedly high amount of soot is contained in the exhaust gas downstream the DPF and hence in the LRE.
The soot contained in the exhaust gas is generally hot and moist, so that it tends to stick to the internal walls of the LRE conduits and to the mechanical organs of the LRE components, to thereby reducing their efficiency below the minimum allowable value before the ending of the expected lifetime. For example, soot fouling in a heat exchanger such as the LRE cooler or the CAC causes an early loss of cooling efficiency and permeability, increasing the polluting emissions and deteriorating the Diesel engine performance. Regarding this problem, have been actually proposed only diagnostic methods based on LRE component efficiency monitoring, which are able to detect the soot fouling of the LRE component once onset, but which are unable to prevent it.
In view of the foregoing, at least one object is to provide a strategy for protecting the LRE components against excessive soot contamination, in order to prevent, or at least to positively reduce, the above mentioned problem. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.
A method is provided for operating a Diesel engine system, wherein the Diesel engine system generally comprises a Diesel engine, an intake line for feeding fresh induction air into the Diesel engine, an exhaust line for discharging exhaust gas from the Diesel engine, a Diesel Particulate Filter (DPF) located in the exhaust line, and an Exhaust Gas Recirculation (EGR) system for routing back exhaust gas into the Diesel engine, and wherein the EGR system generally comprises a long route EGR (LRE) which gets exhaust gas from the exhaust line downstream the DPF.
According to the invention, the operating method comprises the steps of setting a soot threshold representing the maximum allowable amount of soot which can flows into the LRE, determining the actual amount of soot (Saa) flowing into the LRE, and activating a LRE protection routine, if said actual amount of soot (Saa) exceeds said soot threshold (Sth). The protection routine is generally provided for lowering the amount of soot entering the LRE, to thereby reducing the risk of an early LRE efficiency loss.
According to an embodiment, the determination of the actual amount of soot flowing into the LRE comprises the steps of determining the amount of soot entering the DPF, determining the DPF filtration efficiency, and calculating the amount of soot flowing into the LRE, in function of said determined amount of soot entering the DPF and said DPF filtration efficiency. The amount of soot entering the DPF can be estimated by means of a Diesel engine-out soot model. The DPF filtration efficiency can be determined in function of the amount of soot entering the DPF.
According to an embodiment, the determination of the DPF filtration efficiency comprises the steps of determining the amount of soot which is trapped by the DPF, and calculating the DPF filtration efficiency in function of said trapped amount of soot and the amount of soot entering the DPF. In this case, the amount of soot which is trapped by the DPF can be estimated by means of a DPF soot loading model.
According to another embodiment of the invention, the determination of the DPF filtration efficiency comprises the steps of determining the amount of soot exiting the DPF, and calculating the DPF filtration efficiency in function of said amount of soot exiting the DPF and the amount of soot entering the DPF. In this case, the amount of soot exiting the DPF can be measured by means of a soot sensor located in the exhaust line downstream the DPF itself.
According to another embodiment, the LRE protection routine generally provides for regulating at least one combustion managing parameter which affects the soot production within the Diesel engine, in order to decrease the soot production itself. Such combustion managing parameter can be for example the total amount of exhaust gas which is routed back by the EGR system, including SRE and LRE, or the amount of exhaust gas which is routed back by the LRE with respect to the total amount.
As a matter of fact, while the Diesel engine system works normally, these combustion managing parameters are generally regulated according to a respective set point, which is determined by the ECU in function of one or more engine operating parameters, such as for example engine speed, engine load, intake air mass flow and engine coolant temperature.
In this contest, the LRE protection routine preferably provides for determining a correction index to be applied to said set point, in order to decrease the soot production. The correction index can be determined in function of the difference between the calculated amount of soot and the soot threshold, and eventually also in function of one or more engine operating parameters, such as for example engine speed, engine load, intake air mass flow and engine coolant temperature.
The method according to the embodiments can be realized in the form of a computer program comprising a program-code to carry out all the steps of the method of the invention, and in the form of a computer program product comprising means for executing the computer program.
The computer program product comprises, according to a preferred embodiment of the invention, a microprocessor based control apparatus for an IC engine, for example the ECU of the engine, in which the program is stored so that the control apparatus defines the invention in the same way as the method. In this case, when the control apparatus execute the computer program all the steps of the method according to the invention are carried out.
The method according to the embodiments can be also realized in the form of an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represent a computer program to carry out all steps of the method of the invention.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and:
The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description.
The turbocharged Diesel engine system comprises a Diesel engine 1 having an intake manifold 10 and an exhaust manifold 11, an intake line 2 for feeding fresh air from the environment in the intake manifold 10, an exhaust line 3 for discharging the exhaust gas from the exhaust manifold 11 into the environment, and a turbocharger 4 which comprises a compressor 40 located in the intake line 2, for compressing the air stream flowing therein, and a turbine 41 located in the exhaust line 3, for driving said compressor 40.
The turbocharged Diesel engine system further comprises an intercooler 20, also indicated as Charge Air Cooler (CAC), located in the intake line 2 downstream the compressor 40 of turbocharger 4, for cooling the air stream before it reaches the intake manifold 10, and a valve 21 located in the intake line between the CAC 20 and the intake manifold 10.
The turbocharged Diesel engine system further comprises a diesel oxidation catalyst (DOC) 30 located in the exhaust line 3 downstream the turbine 41 of turbocharger 4, for degrading residual hydrocarbons (HC) and carbon oxides (CO) contained in the exhaust gas, and a diesel particulate filter (DPF) 31 located in the exhaust line 3 downstream the DOC 30, for capturing and removing diesel particulate matter (soot) from the exhaust gas.
In order to reduce polluting emission, the turbocharged Diesel engine system comprises an exhaust gas recirculation (EGR) system, for routing back and feeding exhaust gas into the Diesel engine 1. The EGR system comprise a first EGR conduit 50 for fluidly connecting the exhaust manifold 11 with the intake manifold 10, a first EGR cooler 51 for cooling the exhaust gas, and a first electrically controlled valve 52 for determining the flow rate of exhaust gas through the first EGR conduit 51. Since the first EGR conduit 51 directly connects the exhaust manifold 11 with the intake manifold 10, it defines a short route EGR (SRE) which routes back high temperature exhaust gas. The EGR system further comprise a second EGR conduit 60, which fluidly connects a branching point 32 of the exhaust line 3 with a leading point 22 of the intake line 2, and a second EGR cooler 61 located in the second EGR conduit 60.
The branching point 32 is located downstream the DPF 31, while the leading point 22 is located downstream an air filter 23 and upstream the compressor 40 of turbocharger 4. The flow rate of exhaust gas through the second EGR conduit 60 is determined by a second electrically controlled three-way valve 62, which is located in the leading point 22. As a matter of fact, the EGR systems is provided with a long route EGR (LRE), which comprises the second EGR conduit 60, including the second EGR cooler 61, and the portion of the intake line 2 between the leading point 22 and the Diesel engine 1, including the second valve 62, the compressor 40 of turbocharger 4, the CAC 20, and the valve 21. Flowing along the long route EGR, the exhaust gas become considerably colder than the exhaust gas which flows through the first EGR conduit 50, to thereby reaching the intake manifold 10 at a lower temperature.
The turbocharged Diesel engine system is operated by a microprocessor based controller (ECU), which is provided for generating and applying control signals to the valves 52 and 62, in order to route back the exhaust gas partially through the SRE and partially through the LRE, to thereby maintaining the temperature of the induction air in the intake manifold 10 at an optimal intermediate value in any engine operating condition. As a matter of fact, the ECU is configured for: determining a set point of the total amount of EGR to be fed into the exhaust manifold 10, determining a set point of the LRE rate, and controlling the valves 52 and 62 accordingly.
These set points are determined by the ECU from empirically determined data sets or maps, which respectively correlate total EGR amount and LRE rate to a plurality of engine operating parameters, such as for example engine speed, engine load, intake air mass flow and engine coolant temperature. The ECU is also provided for protecting the LRE circuit and its components (chiefly the second EGR cooler 61, the compressor 40 and the CAC 20) against excessive soot contamination in case of DPF 31 filtration performance loss. The protection strategy performed by the ECU is schematically illustrated in
This strategy provides for setting a soot threshold Sth representing the maximum allowable amount of soot which can flow into the LRE. The amount of soot is intended to be a soot mass flow, which can be expressed for example in terms of milligrams of soot per second, per minute, per hour, or per kilometer covered by the vehicle on which the Diesel engine system is mounted. The soot threshold Sth can be determined by means of an empirical calibration activity, which is performed on a test Diesel engine system having the same characteristics of the real one.
The calibration activity provides for setting a minimum allowable LRE lifetime. The minimum allowable LRE lifetime preferably coincides with the entire vehicle lifetime, which is generally fixed to at least 160.000 km with regard to polluting emission. The calibration activity further provides for setting a minimum allowable value of a LRE efficiency parameter.
Since the LRE efficiency is generally bound to the efficiency of each LRE component, the LRE efficiency parameter can be chosen as the efficiency of the LRE component which is the most sensitive to soot contamination. For example, the LRE efficiency parameter can be the cooling efficiency of the second EGR cooler 61, the mechanical efficiency of the compressor 40, or the cooling efficiency of the CAC 20, depending on which of said components manifests a quicker performance loss due to soot fouling. As a matter of fact, it has been found that the most sensitive component probably is the cooler 61, so that the cooling efficiency of the latter can be effectively used as LRE efficiency parameter.
Finally, the calibration activity provides for empirically determining the maximum amount of soot flowing into the LRE, for which the chosen LRE efficiency parameter remains above the preset minimum allowable value, until the end of the preset LRE lifetime. The resultant maximum amount of soot is then assumed as soot threshold Sth, and is stored in a memory module of the Diesel engine system.
The protection strategy further provides for monitoring the amount of soot Saa which actually flows into the LRE, during the real Diesel engine system functioning. In order to determine the amount of soot Saa, the strategy provides for determining the amount of soot DPF in entering the DPF 31 and the DPF filtration efficiency DPFeff. The DPFin can be estimated by means of a known Diesel engine-out soot model.
According to the present example, the DPFeff can be determined in two different ways. The first way provides for determining the amount of soot DPFtrap which is captured by the DPF 31, and for calculating the DPF filtration efficiency DPFeff as the ratio between the trapped amount of soot DPFtrap and the total amount of soot DPFin entering the DPF 31, according to the equation:
The amount of soot DPFtrap can be estimated by means of known DPF soot loading model, using the pressure drop across the DPF 31.
The second way provides for determining the amount of soot DPFout exiting the DPF 31, and for calculating the DPF filtration efficiency DPFeff as the difference between the unitary efficiency and the ratio between the exiting amount of soot DPFout and the total amount of soot DPFin entering the DPF 31, according to the equation:
The amount of soot DPFout which exits from the DPF 31, can be estimated by means of known soot sensor 33, which is located in the exhaust line 3 downstream the DPF 31.
The DPF filtration efficiency DPFeff and the amount of soot DPFin entering the DPF 31 are then sent to a computing module CM, which calculates the amount of soot Saa flowing into the LRE, in function of said amount of soot DPFin entering the DPF and said DPF filtration efficiency DPFeff. As a matter of fact the amount of soot Saa can be calculated according to the equation:
Where MLRE is the exhaust gas mass flow routed into the second EGR conduit 60, and Mout is the exhaust mass flow emitted by the exhaust line 3 into the environment. MLRE and Mout can be measured by means of mass flow sensors (not shown), which are respectively located in the second EGR conduit 60 and in the exhaust line 3 downstream the branching point 32.
The amount of soot Saa is sent to an adder A1, which calculates the difference E between the memorized soot threshold Sth and said amount of soot Saa. The difference E is then supplied to governor G, which is provided for selectively activating a LRE protection routine in response of the above named difference E. In particular, if the actual amount of soot Saa does not exceeds the soot threshold Sth, it means that the LRE does not risk manifesting an early efficiency loss.
In this case, the difference E is not negative and the governor G remains inactive, so that the Diesel engine system continues to operate normally. If conversely the actual amount of soot Saa exceeds the soot threshold Sth, it means that the LRE risks to manifest an efficiency loss quicker than that expected. In this case, the difference E is negative and the governor G activates the LRE protection routine. The LRE protection routine generally provides for regulating at least one combustion managing parameter which affects the soot production within the Diesel engine 1, to thereby decreasing the soot production itself.
In the present example, the governor G is configured for reducing the total amount of exhaust gas which is routed back by the EGR system, including LRE and SRE, and/or for reducing the rate of exhaust gas which is routed back by the LRE. In fact, it is known that a reduction of total EGR amount and/or a reduction of LRE rate has the effect of limiting the soot production within the Diesel engine 1, which consequently results in soot decreasing into LRE.
As previously described, the total EGR amount and the LRE rate are normally regulated according to respective set points, EGRsp and LREsp, which are determined by the ECU in function of one or more engine operating parameters, such as engine speed, engine load, intake air mass flow and engine coolant temperature. In this contest, the governor G provides for determining a correction index Cegr and/or a correction index Clre, to be respectively applied to said set points EGRsp and LREsp, in order to decrease soot production.
The correction index Cegr and/or Clre is determined proportionally to the modulus of the difference E, and can eventually be adjusted in function of one or more engine operating parameters, such as for example engine speed, engine load, intake air mass flow and engine coolant temperature. As a matter of fact, the correction indexes Cegr and Clre are determined from empirically determined data sets or maps, M1 and M2, which respectively correlates the correction index Cegr and Clre to the modulus of the difference E, and to one or more of said engine operating parameters.
In greater detail, the correction index Cegr of the total EGR amount is sent to an adder A2, which calculates the difference between the normal set point EGRsp and said correction index Cegr, in order to provide a lower set point EGRsp* to be used for operating the Diesel engine system. Analogously, the correction index Clre of the LRE rate is sent to an adder A3, which calculates the difference between the normal set point LREsp and said correction index Clre, in order to provide a lower set point LREsp* to be used for operating the Diesel engine system.
In case that the governor G provides for regulating the LRE rate only, the ECU must regulate the SRE rate in order to obtain the unchanged total EGR amount set point EGRsp. If subsequently the DPF Out soot estimation Saa does not exceed the soot threshold Sth, the adder A1 will return a not negative difference E, and the governor G will deactivate the protection routine, by setting to zero the correction indexes Cegr and/or Clre, so that the ECU will operate the Diesel engine system normally.
While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0920017.1 | Nov 2009 | GB | national |
