GB2475319A

GB2475319A - Protecting a diesel engine long-route EGR system from excessive soot contamination

Info

Publication number: GB2475319A
Application number: GB0920020A
Authority: GB
Inventors: Frederico Luigi Guglielmone; Cristian Taibi; Alberto Vassallo
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2009-11-16
Filing date: 2009-11-16
Publication date: 2011-05-18
Also published as: GB0920020D0

Abstract

A method for operating a Diesel engine system which has a Diesel Particulate Filter (DPF) 31, and an exhaust gas recirculation EGR system 50, 60 comprising a long EGR route (LRE) 60 which gets exhaust gas from the exhaust line 3 downstream of the DPF 31, comprises the steps of setting a soot threshold Sth for the amount of soot (soot mass flow) flowing into the exhaust line 3 downstream of the DPF 31, determining the actual amount of soot Saa flowing into the exhaust line 3 downstream of the DPF 31, and activating a LRE protection routine if said actual amount of soot Saa exceeds the threshold Sth. The actual amount of soot Saa may be determined using a soot sensor. The LRE protection routine may comprise regulating at least one combustion management parameter affecting soot production, eg total amount of gas routed back by the EGR system 50,60 and/or the amount of exhaust gas routed back by the long EGR route 60.

Description

METRCX) FOR OPEPTTING A DTWET. EMGflTh SYSTE!4

TEIL FID

The present invention generally relates to a method for operating a Diesel engine system, in particular a turbocharged Diesel engine sys-tern.

A turbocharged Diesel engine system generally corrprises a Diesel en-gine having an intake manifold and an exhaust manifold, an intake line for feeding fresh air from the environment into the intake mani- fold, an exhaust line for discharging the exhaust gas from the ex- haust manifold into the environment, and a turbocharger which com-prises 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 tur-bocharger, 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 (NO) produced within the Diesel engine during the combustion process.

Conventional EGR systems comprise an EGR conduit for fluidly connect- ing the exhaust manifold with the intake manifold, an EGR cooler lo-cated 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 (SPE) 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 coo-ler 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 par-tially 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 corning 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 operat-ing parameters, such as for example engine speed, engine load, intake air mass flow and engine coolant temperature.

The efficiency of a LRE is generally bound to the efficiency of its single components, including the additional cooler, the addition-al 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 quick depending on several conditions, such as for example the component aging, the thermal stress to which the corn-ponent is subject, and the composition of the exhaust gas which flows through the component.

These conditions are taken into account when designing the LRE cornpo- nents, in order to realize a LRE whose global efficiency can be ex-pected 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 condi-tion 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 dam-ages or brea kings, 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 permeabiJ.-ity, 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.

DISCLOSURE

An object of the present invention is to provide a strategy for pro-tecting the LRE components against excessive soot contamination, in order to prevent, or at least to positively reduce, the above men-tioned problem.

An object of an embodiment of the invention is attained by the char-acteristics of the invention as reported in independent claims. The dependent claims recite preferred and/or especially advantageous fea-tures of the invention.

The invention provides a method 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 Di- esel engine, an exhaust line for discharging exhaust gas from the Di-esel 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 gener-ally comprises a long route EGR (LPE) which gets exhaust gas from the exhaust line downstream the DPF.

According to the invention, the operating method comprises the steps of: setting a threshold for the amount of soot flowing into the ex-haust line downstream the DPF, determining the actual amount of soot flowing into the exhaust line downstream the DPF, and activating a IRE protection routine, if said actual amount of soot exceeds said soot threshold.

Since the LRE communicates with the exhaust line downstream the DPF, the amount of soot flowing in the latter is expected to be propor-tional to the amount of soot routed into the LBE, so that the above named soot threshold can be chosen to correspond to a maximum allowa-ble amount of soot flowing into the LRE.

The protection routine is then generally provided for lowering the amount of soot entering the LRE, to thereby reducing the risk of an early LRE efficiency loss.

If subsequently the amount of soot is determined to be below the soot threshold, the method preferably provides for deactivating the LRE protection routine.

According to an aspect of the invention, the actual amount of soot is preferably measured by means of a soot sensor, which can be located in the exhaust line downstream the DPF.

Soot sensors are known for measuring the content of soot in the ex-haust gas downstream the DPF, but at present they are only used for diagnostic purpose, in order to generate an alarm signal if the amount of soot exceeds a predetermined level fixed by the anti-polluting standards.

A soot sensor which is already used for this diagnostic purpose, can effectively be used for performing also a method according the present invention.

In this case, the preset soot threshold is preferably greater than the soot level fixed by anti-polluting standards.

According to another aspect of the invention, the LRE protection routine generally provides for regulating at least one combustion managing parameter which affects the soot production within the Di-esel 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, includ-ing 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 accord-ing to a respective set point, which is determined by the ECU in function of one or more engine operating parameters, such as for ex- ample engine speed, engine load, intake air mass flow and engine coo-lant 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 actual amount of soot and the soot threshold, and even-tually 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.

According to another aspect of the invention, the soot threshold is determined by means of a calibration activity, which is performed on a test Diesel engine system, and which preferably comprises the steps of: setting a minimum allowable LRE lifetime, setting a minimum allowable value of a LRE efficiency parameter, and empirically determining the maximum amount of soot flowing into the exhaust line downstream the DPF, for which said efficiency para-meter remains above the preset minimum allowable value until the end of the preset LRE lifetime.

Since the IRE efficiency is bound to the efficiency of the LRE compo-nents, the LRE efficiency parameter can be chosen as the efficiency of the component which is the most sensitive to the soot contamina-tion.

while reducing the soot production, it may happen that the LRE protection routine contemporaneously causes a nitrogen oxides (NO) production increasing.

For this reason, the method according to the invention can be im-proved with the steps of: setting a nitrogen oxides threshold, representing the maximum allowable amount of nitrogen oxides which can be emitted into the en-vironment, determining the actual amount of nitrogen oxides emitted into the environment, and performing a special procedure if said actual amount of nitrogen oxides exceeds said nitrogen oxides threshold.

According to the present embodiment, said special procedure can pro- vide for deactivating the LRE protection routine, and/or for generat-ing an alarm signal.

The method according to the invention 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 com-puter program product comprising means for executing the computer program.

The computer program product comprises, according to a preferred em-bodiment 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 appara- tus execute the computer program all the steps of the method accord-ing to the invention are carried out.

The method according to the invention 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.

BRIEF DESQIPTXi OF THE DRAIJINGS The present invention will now be described, by way of example, with reference to the accompanying drawing, in which: -figure 1 schematically illustrates a turbocharged Diesel engine system; -figure 2 is a flowchart which illustrates an operating method ac-cording to the invention; -figure 3 is a flowchart which illustrates an improved operating method according to the invention.

DESIPTI OF THE PREBERRED E2BCDD4ENT The present invention is hereinafter disclosed with reference to a turbocharged Diesel engine system of a vehicle.

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 mani-fold 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 compress-ing 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 inter-cooler 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 in-take manifold 10.

The turbocharged Diesel engine system further comprises a diesel oxi-dation catalyst (WC) 30 located in the exhaust line 3 downstream the turbine 41 of turbocharger 4, for degrading residual hydrocarbons (HC) and carbon oxides (CC) contained in the exhaust gas, and a die- sel particulate filter (DPF) 31 located in the exhaust line 3 down- stream the EXX 30, for capturing and removing diesel particulate mat-ter (soot) from the exhaust gas.

In order to reduce polluting emission, the turbocharged Diesel engine system comprises an exhaust gas recirculation (EGR) system, for rout-ing back and feeding exhaust gas into the Diesel engine 1.

The EGR system corrrise 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 con-trolled 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 fluid-ly 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 de-termined 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 tempera-ture.

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 op-erating 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 deter-mined 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.

According to the invention, the ECU is also provided for protecting the LPE circuit and its components (chiefly the second cooler 62, 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 illu-strated in figure 2.

This strategy provides for setting a threshold S-th for the amount of soot flowing into the exhaust line 3 downstream the DPF 31, which generally corresponds to a 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 S-th is determined by means of an empirical cali-bration activity, which is performed on a test Diesel engine system having the same characteristics of the real one.

Said calibration activity provides for setting a minimum allowable LRE lifetime.

The minimum allowable LRE lifetime preferably coincides with the en-tire vehicle lifetime, which is generally fixed to at least 160.000km with regard to polluting emission.

The calibration activity further provides for setting a minimum al-lowable 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 ef-ficiency of the LRE component which is the most sensitive to the soot contamination.

For example, the LRE efficiency parameter can be the cooling effi-ciency 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 corrponents manifests a quicker performance loss due to soot fouling.

Finally, the calibration activity provides for empirically deterrnin- ing the maximum amount of soot flowing into the exhaust line 3 down- stream the DPF 31, for which the chosen LRE efficiency parameter re-mains 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 thre-shold S-th, and is stored in a memory module of the Diesel engine system.

The protection strategy further provides for monitoring the amount of soot S-aa which actually flows into the exhaust line 3 downstream the DPF 31, during the real Diesel engine system function-ing.

In the present example, said amount of soot S-aa is determined by means of a known soot sensor 33, which is located in the exhaust line 3 downstream the branching point 32, and about 50cm downstream the DPF 31.

As a matter of fact, the soot sensor 33 measures the amount of soot with a frequency which corresponds to the refresh timing of the soot sensor 33 itself.

The refresh time of the soot sensor 33 depends in turn on the soot concentration, and generally can vary from one second to several mi-flutes.

The actual amount of soot S-aa is sent to an adder Al, which calcu-lates the difference E between the memorized soot threshold S-th and said actual amount of soot S-aa.

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 S-aa does not exceeds the soot threshold S-th, it means that the LRE does not risk to manifest an early efficiency loss.

In this case, the difference E is not negative and the governor G re-mains inactive, so that the Diesel engine system continues to operate normally.

If conversely the actual amount of soot S-aa exceeds the soot thresh-old S-th, it means that the LiRE risks to manifest an efficiency loss quicker than that expected.

In this case, the difference E is negative and the governor G acti-vate the LRE protection routine.

The LiRE protection routine generally provides for regulating at least one combustion managing parameter which affects the soot production within the Diesel engine lr to thereby decreasing the soot production itself.

In the present exartple, 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 a soot de-creasing into LRE.

As previously described, the total EGR amount and the LRE rate are normally regulated according to respective set points, EGR-sp and LRE-sp, which are 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 governor G provides for determining a correction index C-egr and/or a correction index C-ire, to be respectively ap-plied to said set points EGR-sp and LRE-sp, in order to decrease soot production.

The correction index C-egr and/or C-ire 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 ex- ample engine speed, engine load, intake air mass flow and engine coo-lant temperature.

As a matter of fact, the correction indexes C-eqr and C-ire are de-termined from empirically determined data sets or maps, Ml and M2, which respectively correlates the correction index C-egr and C-ire to the modulus of the difference E, and to one or more of said engine operating parameters.

In greater detail, the correction index C-egr of the total EGR amount is sent to an adder A2, which calculates the difference between the normal set point EGR-sp and said correction index C-egr, in order to provide a lower set point EGR_sp* to be used for operating the Diesel engine system.

Analogously, the correction index C-ire of the LRE rate is sent to an adder A3, which calculates the difference between the normal set point LRE-sp and said correction index C-ire, in order to provide a lower set point LRE_sp* to be used for operating the Diesel engine system.

If subsequently the soot sensor 33 will measure an amount of soot S-aa which does not exceed the soot threshold S-th, the adder Al will return a not negative difference E, and the governor G will deactivate the protection routine, by setting to zero the correction indexes C-egr and/or C-ire, so that the ECU will operate the Diesel engine system normally.

While decreasing the soot production, a reduction of total EGR amount and/or a reduction of LRE rate usually causes a nitrogen oxides (NO) production increasing.

For this reason, it has been proposed an improved strategy which is schematically illustrated in figure 3.

This improved strategy differs from the preceding one, in that it provides for setting a nitrogen oxides threshold NOx-th, which represents the maximum amount of nitrogen oxides which can be emitted in the environment.

The nitrogen oxides threshold NOx-th can be determined from polluting emission standards, and then stored in a memory module.

The improved strategy further provides for determining the actual amount of nitrogen oxides NOx-aa which is emitted in the environment.

The actual nitrogen oxides amount NOx-aa can be either measured with a sensor, or estimated.

The actual nitrogen oxides amount NOx-aa is then sent to an adder A4, which calculates the difference E' between the memorized nitrogen oxides threshold NOx-th and said actual nitrogen oxides amount NOx-aa.

The difference E' is then supplied to a governor G2, which is config-ured for performing a special procedure if said difference E' is negative, that is, if the actual nitrogen oxides amount NOx-aa ex-ceeds the nitrogen oxides threshold NOx-th.

In particular, the special procedure provide for the governor G2 to deactivate the LRE protection routine if any, and eventually for ge-nerating an alarm signal.

While the present invention has been described with respect to cer- tain preferred embodiments and particular applications, it is under-stood that the description set forth herein above is to be taken by way of example and not of limitation. Those skilled in the art will recognize various modifications to the particular embodiments are within the scope of the appended claims. Therefore, it is intended that the invention not be limited to the disclosed embodiments, but that it has the full scope permitted by the language of the following claims.

Claims

1. Method for operating a Diesel engine system, wherein the diesel engine system comprises a Diesel engine (1), an intake line (2) for feeding fresh induction air into the Diesel engine (1), an exhaust line (3) for discharging exhaust gas from the Diesel engine (1), a Diesel Particulate Filter DPF (31) located in the exhaust line (3), and an Exhaust Gas Recirculation EGR system (50, 60) for routing back exhaust gas into the Diesel engine (1), said EGR system comprising a long EGR route LRE (60) which gets exhaust gas from the exhaust line (3) downstream the DPF (31), characterized in that the method comprises the steps of: setting a threshold (S-th) for the amount of soot flowing into the exhaust line (3) downstream the DPF (31), determining an actual amount of soot (S-aa) flowing into the ex-haust line (3) downstream the DPF (31), and activating a LRE protection routine, if said actual amount of soot (S-aa) exceeds said soot threshold (S-th).

2. Method according to claim 1, characterized in that the actual amount of soot (S-aa) is measured by means of a soot sensor (33).

3. Method according to claim 1, characterized in that the LRE pro- tection routine provides for regulating at least one combustion man-aging parameter which affects the soot production within the Diesel engine (1), in order to decrease the soot production.

4. Method according to claim 3, characterized in that the LRE pro-tection routine provides for determining a correction index (C-egr, C-ire) to be applied to a set point (EGR-sp, LRE-sp) of said combus-tiori managing parameter.

5. Method according to claim 4, characterized in that said correc-tion index (C-egr, C-ire) is determined in function of the difference (E) between the actual amount of soot (S-aa) and the soot threshold (S-th).

6. Method according to claim 3, characterized in that said combus-tion managing parameter is the total amount of exhaust gas which is routed back by the EGR system (50, 60).

7. Method according to claim 3, characterized in that said cornbus-tion managing parameter is the amount of exhaust gas which is routed back by the long EGR route (60).

8. Method according to claim 1, characterized in that the setting of the soot threshold (s-th) comprises the steps of: setting a minimum allowable LRE lifetime, setting a minimum allowable value of a LRE efficiency parameter, and empirically determining the maximum amount of soot flowing into the exhaust line (3) downstream the DPF (31), for which said effi-ciency parameter remains above said minimum allowable value until the end of the LRE lifetime.

9. Method according to claim 1, characterized in that the method further comprises the steps of: setting a threshold (NOx-th) for the amount of nitrogen oxides which can be emitted in the environment, determining the actual amount of nitrogen oxides (NOx-aa) emit-ted in the environment, and performing a special procedure if said actual amount of nitrogen oxides (NOx-aa) exceeds said nitrogen oxides threshold (NOx-th).

10. Method according to claim 9, characterized in that said special procedure provides for deactivating the LRE protection routine.

11. Method according to claim 9, characterized in that said special procedure provides for generating an alarm signal.

12. Computer program comprising a computer-code for carrying out a method according to any of the preceding claims.

13. Computer program product comprising a computer program according to claim 12.

14. Computer program product as in claim 13, comprising a control apparatus wherein the computer program is stored.

15. I\n electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 12.