METHOD FOR INJECTING GASEOUS AMMONIA INTO A COMBUSTION ENGINE EXHAUST LINE

Abstract

Disclosed is a device for injecting ammonia in gaseous form into an exhaust line of a combustion engine, the device including a supervisor, an evaporation chamber incorporating a heater for heating a quantity of reducing agent thus releasing ammonia in gaseous form that exits the evaporation chamber via a pipe opening into the exhaust line. The control supervisor is associated with an internal first pressure sensor housed in the evaporation chamber and with a second pressure sensor intended to be housed in the exhaust line, including a calculator calculating a quantity of ammonia to be injected into the exhaust line at a given instant as a function of the pressure values from the first and second pressure sensors.

Claims

1. A method for injecting ammonia in gaseous form into a combustion engine exhaust line, a reducing agent being heated in an evaporation chamber so as to release ammonia in gaseous form which is thereafter introduced into the exhaust line by a pipe at the outlet of the evaporation chamber, wherein, with the pressure in the evaporation chamber and the pressure of the exhaust gases in the exhaust line being measured or estimated, a quantity Q of ammonia is injected in gaseous form into the exhaust line at a given instant and estimated in accordance with the following equation:
[Math. 1]
Q=√{square root over ([(P1−P2)/K])} P1 being the pressure prevailing in the evaporation chamber, P2 the prevailing pressure of the exhaust gases in the exhaust line and K a constant dependent on a cross section of the pipe and on a density of the quantity of ammonia in gaseous form injected into the exhaust line.

2. The method as claimed in claim 1, wherein a temperature in the evaporation chamber is measured and controlled so that the temperature is greater than a conversion temperature at which the reducing agent can convert into ammonia at the measured or estimated pressure prevailing in the evaporation chamber.

3. The method as claimed in claim 2, wherein a concentration of ammonia in gaseous form in the evaporation chamber is measured or estimated, and when this concentration of ammonia in gaseous form is below a minimum concentration, reducing agent is reintroduced into the evaporation chamber.

4. The method as claimed in claim 1, wherein a flow rate of exhaust gas is measured or estimated in the exhaust line, the nitrogen oxides discharged from the combustion engine into the exhaust line being estimated as a function of this measured or estimated flow rate, a total quantity of ammonia in gaseous form being estimated in a determined time interval for reducing the quantity of nitrogen oxides discharged during this time interval in the exhaust line, the total quantity of ammonia in gaseous form being injected as a succession of quantities of ammonia in gaseous form at given instants in the time interval.

5. A device for injecting ammonia in gaseous form into an exhaust line of a combustion engine, the device comprising a control supervisor, an evaporation chamber incorporating heating means for heating a quantity of reducing agent thus releasing ammonia in gaseous form that exits the evaporation chamber via a pipe opening into the exhaust line, the device implementing a method as claimed in claim 1, wherein the control supervisor is associated with an internal first pressure sensor housed in the evaporation chamber and with a second pressure sensor intended to be housed in the exhaust line, comprising calculation means for calculating a quantity of ammonia to be injected into the exhaust line at a given instant as a function of the pressure values from the first and second pressure sensors.

6. The device as claimed in claim 5, wherein the supervisor is associated with a temperature sensor and with an ammonia sensor which are housed in the evaporation chamber, the supervisor being associated with a mass flow rate sensor for sensing the mass flow rate of the exhaust gases and which is intended to be housed in the exhaust line and estimating means for estimating the flow rate of nitrogen oxides in the line on the basis of the mass flow rate or comprising a model for estimating a flow rate of nitrogen oxides as a function of operating parameters of a combustion engine, these parameters comprising at least an engine speed and an engine torque.

7. The device as claimed in claim 6, wherein the outlet pipe comprises a communication interface communicating with the evaporation chamber, a metering valve downstream of the communication interface and controlled by actuating means under the control of the supervisor so as to deliver a quantity of ammonia to be injected at a given instant and a restriction on the pipe downstream of the metering valve, a cross section of the restriction being considered to be the cross section of the pipe and the supervisor comprises estimating means for estimating the density of the quantity of ammonia in gaseous form that is injected into the exhaust line as a function of the temperature measured by the temperature sensor in the evaporation chamber.

8. The device as claimed in claim 6, wherein the pipe is intended to open into the exhaust line via a passive injector.

9. The device as claimed in claim 6, wherein the supervisor comprises actuating means for actuating a metering valve for metering reducing agent into the evaporation chamber, the reducing agent metering valve being positioned upstream of an inlet interface for entry into the evaporation chamber.

10. The device as claimed in claim 5, wherein the heating means for heating the evaporation chamber are electrical heating means and the reducing agent is a mixture of water and of urea.

11. The method as claimed in claim 2, wherein a flow rate of exhaust gas is measured or estimated in the exhaust line, the nitrogen oxides discharged from the combustion engine into the exhaust line being estimated as a function of this measured or estimated flow rate, a total quantity of ammonia in gaseous form being estimated in a determined time interval for reducing the quantity of nitrogen oxides discharged during this time interval in the exhaust line, the total quantity of ammonia in gaseous form being injected as a succession of quantities of ammonia in gaseous form at given instants in the time interval.

12. The method as claimed in claim 3, wherein a flow rate of exhaust gas is measured or estimated in the exhaust line, the nitrogen oxides discharged from the combustion engine into the exhaust line being estimated as a function of this measured or estimated flow rate, a total quantity of ammonia in gaseous form being estimated in a determined time interval for reducing the quantity of nitrogen oxides discharged during this time interval in the exhaust line, the total quantity of ammonia in gaseous form being injected as a succession of quantities of ammonia in gaseous form at given instants in the time interval.

13. A device for injecting ammonia in gaseous form into an exhaust line of a combustion engine, the device comprising a control supervisor, an evaporation chamber incorporating heating means for heating a quantity of reducing agent thus releasing ammonia in gaseous form that exits the evaporation chamber via a pipe opening into the exhaust line, the device implementing a method as claimed in claim 2, wherein the control supervisor is associated with an internal first pressure sensor housed in the evaporation chamber and with a second pressure sensor intended to be housed in the exhaust line, comprising calculation means for calculating a quantity of ammonia to be injected into the exhaust line at a given instant as a function of the pressure values from the first and second pressure sensors.

14. A device for injecting ammonia in gaseous form into an exhaust line of a combustion engine, the device comprising a control supervisor, an evaporation chamber incorporating heating means for heating a quantity of reducing agent thus releasing ammonia in gaseous form that exits the evaporation chamber via a pipe opening into the exhaust line, the device implementing a method as claimed in claim 3, wherein the control supervisor is associated with an internal first pressure sensor housed in the evaporation chamber and with a second pressure sensor intended to be housed in the exhaust line, comprising calculation means for calculating a quantity of ammonia to be injected into the exhaust line at a given instant as a function of the pressure values from the first and second pressure sensors.

15. A device for injecting ammonia in gaseous form into an exhaust line of a combustion engine, the device comprising a control supervisor, an evaporation chamber incorporating heating means for heating a quantity of reducing agent thus releasing ammonia in gaseous form that exits the evaporation chamber via a pipe opening into the exhaust line, the device implementing a method as claimed in claim 4, wherein the control supervisor is associated with an internal first pressure sensor housed in the evaporation chamber and with a second pressure sensor intended to be housed in the exhaust line, comprising calculation means for calculating a quantity of ammonia to be injected into the exhaust line at a given instant as a function of the pressure values from the first and second pressure sensors.

16. The device as claimed in claim 7, wherein the pipe is intended to open into the exhaust line via a passive injector.

17. The device as claimed in claim 7, wherein the supervisor comprises actuating means for actuating a metering valve for metering reducing agent into the evaporation chamber, the reducing agent metering valve being positioned upstream of an inlet interface for entry into the evaporation chamber.

18. The device as claimed in claim 8, wherein the supervisor comprises actuating means for actuating a metering valve for metering reducing agent into the evaporation chamber, the reducing agent metering valve being positioned upstream of an inlet interface for entry into the evaporation chamber.

19. The device as claimed in claim 6, wherein the heating means for heating the evaporation chamber are electrical heating means and the reducing agent is a mixture of water and of urea.

20. The device as claimed in claim 7, wherein the heating means for heating the evaporation chamber are electrical heating means and the reducing agent is a mixture of water and of urea.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Further features, aims and advantages of the present invention will become apparent from reading the following detailed description, and with reference to the accompanying drawing, which is provided by way of non-limiting example, and in which:

[0040] FIG. 1 is a diagrammatic representation of a view of a device for injecting ammonia in gaseous form into a combustion engine exhaust line according to one embodiment according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] With reference to FIG. 1, the present invention relates to a method for injecting ammonia in gaseous form into a combustion engine exhaust line 10. Exhaust gases pass through the exhaust line 10 on leaving the combustion engine in the direction indicated by the arrow F.

[0042] In this method, a reducing agent, advantageously an ammonia-precursor reducing agent, being urea or a urea derivative, notably a mixture known by the brand name AdBlue®, is heated in an evaporation chamber 3 in order to release ammonia in gaseous form.

[0043] This ammonia in gaseous form or NH3 is then introduced into the exhaust line 10 by a pipe 16 at the outlet of the evaporation chamber 3.

[0044] The quantity of ammonia in gaseous form that is injected is dependent on the difference in pressure between the pressure prevailing, on the one hand, in the evaporation chamber 3 and, on the other hand, in the exhaust line 10.

[0045] According to the invention, the pressure in the evaporation chamber 3 and the pressure of the exhaust gases in the exhaust line 10 are measured or estimated, advantageously measured. A quantity Q of ammonia is injected in gaseous form into the exhaust line 10 at a given instant, this quantity being estimated in accordance with the following equation:

[Math. 1]

Q=√{square root over ([(P1−P2)/K])}

[0046] The quantity Q of ammonia in gaseous form is the quantity of ammonia equal to the square root of the ratio of difference in pressure between the pressure prevailing in the evaporation chamber 3 and the prevailing pressure of the exhaust gases in the exhaust line 10 divided by a constant K.

[0047] In this equation, P1 is the pressure prevailing in the evaporation chamber 3, P2 the prevailing pressure of the exhaust gases in the exhaust line 10, and K a constant dependent on a cross section of the pipe 16 and on a density of the quantity of ammonia in gaseous form injected into the exhaust line 10.

[0048] The monitoring of the temperature in the evaporation chamber 3 is important so as to control the temperature in the evaporation chamber 3 to ensure that it is at a value sufficiently high that there is always ammonia present in the gaseous phase having been obtained following thermolysis and hydrolysis of the urea.

[0049] The formation of the NH3 reducing compound from the reducing agent, frequently a product known by the name of AdBlue® which is a mixture of 32.5% urea and of water, occurs in two steps.

[0050] The first step is the thermolysis of the urea according to the following chemical reaction

[Math. 2]

(NH.sub.2).sub.2CO.fwdarw.NH.sub.3+HNCO

[0051] The second step is the hydrolysis of the isocyanic acid according to the following chemical reaction:

[Math. 3]

HNCO+H.sub.2O.fwdarw.NH.sub.3+CO.sub.2

[0052] These two steps, and especially the first one, require temperatures of at least 180° to 200° C.

[0053] A temperature in the evaporation chamber 3 may be measured and controlled so that it is greater than a conversion temperature at which the reducing agent can convert into ammonia at the measured or estimated pressure prevailing in the evaporation chamber 3.

[0054] Preferably, the temperature and pressure prevailing in the evaporation chamber 3 may be measured by a temperature sensor 11 and a pressure sensor 12, as shown in FIG. 1.

[0055] To replace the gaseous-form ammonia consumed in the exhaust line 10, a concentration of ammonia in gaseous form in the evaporation chamber 3 can be measured or estimated. Preferably, the concentration of ammonia in gaseous form may be measured by an ammonia sensor 13, as shown in FIG. 1.

[0056] When this concentration of ammonia in gaseous form is below a minimum concentration, reducing agent may be reintroduced into the evaporation chamber 3, this being from a tank of reducing agent sited some distance away from the evaporation chamber 3, that tank not being shown in FIG. 1.

[0057] In order to calculate the quantity Q of ammonia in gaseous form introduced at a given instant, a flow rate of exhaust gas in the exhaust line 10 may be measured or estimated.

[0058] In a first alternative, an estimate of the nitrogen oxides discharged from the combustion engine into the exhaust line 10 may be performed as a function of this measured flow rate by using the first equation set out hereinabove, this being done in a determined time interval in order to reduce the quantity of nitrogen oxides discharged during this time interval.

[0059] In a second alternative, a total quantity of ammonia in gaseous form for reducing the nitrogen oxides may be estimated in a determined time interval for reducing the quantity of nitrogen oxides discharged into the exhaust line 10 during this time interval.

[0060] For these two alternatives, the total quantity of ammonia in gaseous form can be injected as a succession of quantities of ammonia in gaseous form at given instants in the time interval.

[0061] The invention relates to a device 1 for injecting ammonia in gaseous form into an exhaust line 10 of a combustion engine. The injection device 1 comprises a control supervisor 4, an evaporation chamber 3 incorporating heating means 6 for heating a quantity of reducing agent thus releasing ammonia in gaseous form.

[0062] The ammonia in gaseous form leaves the evaporation chamber 3 via a pipe 16 opening into the exhaust line 10.

[0063] The injection device 1 implements a method as described hereinabove. In order to do so, the control supervisor 4 is associated with an internal first pressure sensor 12 housed in the evaporation chamber 3 and with a second pressure sensor 14 intended to be housed in the exhaust line 10.

[0064] As mentioned previously, the pressure in the exhaust line 10 may also be estimated by being supplied by the engine control electronic unit which calculates it on the basis of the current operating parameters of the combustion engine.

[0065] That allows the pressure prevailing in the evaporation chamber 3 and the prevailing pressure of the exhaust gases in the exhaust line 10 to be measured simultaneously.

[0066] The control supervisor 4 incorporates calculation means for calculating a quantity of ammonia to be injected at a given instant into the exhaust line 10 as a function of the pressure values from the first and second pressure sensors 12, 14, this being performed according to the first equation mentioned hereinabove, incorporating also the constant K.

[0067] In addition, the supervisor 4 may be associated with a temperature sensor 11 and with an ammonia sensor 13 which are housed in the evaporation chamber 3. In addition, the supervisor 4 may be associated with a mass flow rate sensor 15 for sensing the mass flow rate of the exhaust gases and which is intended to be housed in the exhaust line 10 and comprising estimating means for estimating the flow rate of nitrogen oxides in the line 10 on the basis of the mass flow rate, this being a first optional embodiment.

[0068] In a second optional embodiment, the supervisor 4 comprises a model for estimating a flow rate of nitrogen oxides as a function of operating parameters of a combustion engine, these parameters comprising at least an engine speed and an engine torque, this model being a model of the exhaust gas emissions that takes account of the operating parameters.

[0069] The model may be corrected using measurements from a nitrogen oxide probe present in the exhaust line 10.

[0070] Specifically, if the quantity of nitrogen oxides leaving the engine is underestimated by the model, the supervisor 4 commands an under-injection of ammonia in gaseous form, which leads to the SCR post-treatment system of which the device 1 forms part not being effective enough to conform to the pollution-control standards.

[0071] In the case where the quantity of nitrogen oxides leaving the engine is overestimated by the model, the supervisor 4 commands an over-injection of ammonia in gaseous form, leading to ammonia being released at the outlet of the exhaust.

[0072] The estimation model may be calibrated on a nominal engine and not take account of the peculiarities of the combustion engine specific to the motor vehicle, and notably the ageing or drift in settings thereof. However, with the spread of the engines produced and the ageing of these engines the estimation error may be significant. Thus, it is sensible to correct the estimation model if need be, this being done through a learning process.

[0073] The outlet pipe 16 may comprise a communication interface 7 interfacing with the evaporation chamber 3, positioned on the wall of the evaporation chamber 3 and locally passing through same.

[0074] The outlet pipe 16 may then comprise a metering valve 8 downstream of the communication interface 7 and controlled by actuating means under the control of the supervisor 4 so as to deliver a quantity of ammonia in gaseous form that is to be injected at a given instant, this being as a function of the difference in pressure in the evaporation chamber 3 and in the exhaust line 10, as estimated according to the first equation mentioned hereinabove.

[0075] The outlet pipe 16 may finally comprise a restriction 17 on the pipe 16 downstream of the metering valve 8. This restriction 17 influences the value of the constant K in the first equation. A cross section of the restriction is then taken as being the cross section of the pipe 16 in the first equation.

[0076] To calculate the constant K, the supervisor 4 may additionally comprise means for estimating the density of the quantity of ammonia in gaseous form injected into the exhaust line 10 as a function of the temperature measured by the temperature sensor 11 in the evaporation chamber 3.

[0077] Because of the presence of the metering valve 8 upstream of the injector 9, which forms the interface between the pipe 16 and the exhaust line 10, the pipe 16 can open into the exhaust line 10 via a passive injector 9, which is to say an injector which exerts no control over the flow rate of ammonia in gaseous form passing through it.

[0078] Upstream of the evaporation chamber 3 in the injection device 1, the supervisor 4 may comprise actuating means for actuating a metering valve 2 for metering reducing agent into the evaporation chamber 3. The reducing agent metering valve 2 may thus be positioned upstream of an inlet interface 5 for entry into the evaporation chamber 3.

[0079] The heating means 6 the heating the evaporation chamber 3 may be electrical heating means 6.

[0080] The invention is in no way limited to the embodiments described and illustrated, which have been given solely by way of example.