Method for controlling combustion inside burner of exhaust gas aftertreatment system

Abstract

A method for controlling combustion inside a combustion chamber (22) of a combustor (21) of an exhaust gas aftertreatment system (14) is described. The burner (21) is designed to introduce the exhaust gas into the exhaust duct (10). The method provides a step of placing a first pressure sensor (33, 34) along a first conduit (25, 35) of the exhaust aftertreatment system (14); a step of acquiring a signal detected by the first pressure sensor (33, 34) in a first mobile listening interval between the initial time (t1) and the final time (t2); a step of processing the signal detected by the first pressure sensor (33, 34) in order to determine its energy content; a step of calculating a combustion index indicating an indicator of combustion inside the combustion chamber (22) on the basis of the energy content of the signal detected by the first pressure sensor (33, 34); a step of comparing the combustion index with a first threshold value (TVOFF); and a step of identifying a failed combustion event inside the combustion chamber (22) if the combustion index is less than the first threshold value (TVOFF).

Description

[0001] Cross - reference to related applications

[0002] This patent application claims the priority of Italian Patent Application No. 102023000027690, filed on December 21, 2023, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] The present invention relates to a method for controlling combustion inside the combustion chamber of a burner (or combustor) for an exhaust gas after - treatment system. Background art

[0004] As is well known, an internal combustion engine typically has a plurality of cylinders, each cylinder being connected to an intake manifold and an exhaust manifold. An exhaust pipe is connected to the exhaust manifold, and the exhaust pipe supplies the exhaust gas generated by combustion to an exhaust system, which discharges the gas generated by combustion into the atmosphere.

[0005] An exhaust gas after - treatment system generally includes: a pre - catalyst, which is arranged along the exhaust pipe; a particulate filter, which is also arranged along the exhaust pipe downstream of the pre - catalyst; and a catalytic converter, which is arranged along the exhaust pipe upstream of the particulate filter. Finally, the exhaust gas after - treatment system also includes a burner, which is designed to introduce exhaust gas (and thus heat) into the exhaust pipe in order to accelerate the heating of the catalytic converter and to facilitate the regeneration of the particulate filter.

[0006] There is an increasing need to be able to ascertain the combustion inside the burner in a fast and reliable manner; in particular, it is of the utmost importance to be able to identify, in a fast and reliable manner, the time at which a failed combustion event (misfire) occurs inside the burner. Summary of the invention

[0007] An object of the present invention is to provide a method for controlling combustion inside a burner of an exhaust gas after - treatment system that does not have the above - mentioned drawbacks and is, in particular, easy to implement and cost - effective.

[0008] According to the present invention, there is provided a method for controlling combustion inside a burner of an exhaust gas after - treatment system, the burner being designed to introduce exhaust gas into an exhaust pipe, the method comprising:

[0009] - placing a first pressure sensor along a first pipe of the exhaust gas after - treatment system;

[0010] - a step of collecting the signal detected by the first pressure sensor in a first moving listening interval between an initial moment and a final moment;

[0011] - a step of processing the signal detected by the first pressure sensor to determine its energy content;

[0012] - Calculating a combustion index based on the energy content of the signal detected by the first pressure sensor, the combustion index being an indicator representing the combustion inside the combustion chamber;

[0013] - A step of comparing the combustion index with a first threshold; and

[0014] - A step of identifying a failed combustion event inside the combustion chamber when the combustion index is less than the first threshold.

[0015] In some embodiments, the processing step includes a sub-step of applying a filter within the distinctive oscillation frequency range of the burner.

[0016] In some embodiments, the filter can alternatively be a hardware filter or a software filter.

[0017] In some embodiments, the filter is a band-pass filter.

[0018] In some embodiments, the distinctive oscillation frequency range of the burner is variable depending on the layout of the exhaust gas aftertreatment system, the geometry of the burner, and the physical characteristics of the exhaust gas.

[0019] In some embodiments, the filter is applied within a frequency range from 250 to 350 Hz.

[0020] In some embodiments, the distinctive oscillation frequency range of the burner is near the injection frequency.

[0021] In some embodiments, the method includes a step of identifying a combustion event, the step providing:

[0022] - A sub-step of comparing the combustion index with a second threshold, wherein the first threshold is preferably greater than the second threshold; and

[0023] - A sub-step of identifying the occurrence of a combustion event inside the combustion chamber when the combustion index is greater than the second threshold.

[0024] In some embodiments, the first moving listening interval between the initial time t1 and the final time t2 has a duration defined based on the characteristics of the burner and corresponds to a plurality of pulsations of the signal detected by the first pressure sensor, preferably three or four pulsations.

[0025] In some embodiments, the first movement monitoring interval between an initial time t1 and a final time t2 has a duration ranging from 5 ms to 15 ms; preferably, the first movement monitoring interval has a duration of 10 ms.

[0026] In some embodiments, the method includes a further step of calculating a combustion index of the first movement monitoring interval by means of an effective RMS value at the final time t2:

[0027]

[0028] n: the number of samples; and

[0029] Pf i : the filtered value of the i-th pressure sample.

[0030] In some embodiments, the method includes a further step of calculating a combustion index of the first movement monitoring interval by means of a moving average absolute deviation S at the final time t2:

[0031]

[0032] n: the number of samples;

[0033] x i : the value (filtered or unfiltered) of the i-th pressure sample; and

[0034] M: the moving average value of the value x i .

[0035] In some embodiments, the method includes using the ratio of the sum of the squares of the differences between the value x of the i-th pressure sample i and the moving average value M of the value x of the pressure samples i to the number of samples n to calculate a further step of the combustion index of the first movement monitoring interval.

[0036] In some embodiments, the method includes a further step of calculating the combustion index of the first movement monitoring interval by means of the square root of the ratio of the sum of the squares of the differences between the value x of the i-th pressure sample i and the moving average value M of the value x of the pressure samples i to the number of samples n.

[0037] In some embodiments, the method includes the following additional steps:

[0038] - calculating the value of the combustion index in a second movement interval, the duration of the second movement interval being greater than the duration of the first movement monitoring interval; and

[0039] - Calculate a moving average M1 of the combustion index of the second moving monitoring interval and use it as an indicator of the combustion intensity inside the burner.

[0040] In some embodiments, the second moving interval has a duration ranging from 80 ms to 120 ms; preferably, the second moving monitoring interval has a duration of at least 100 ms.

[0041] In some embodiments, the method includes another step of calculating a moving standard deviation σ of the combustion index of the second moving interval and using it as an indicator of the combustion stability inside the burner.

[0042] In some embodiments, the step of collecting the signal detected by the first pressure sensor is performed at a frequency that is at least twice the characteristic oscillation frequency of the burner and preferably at least 10 kHz.

[0043] In some embodiments, the first pressure sensor is configured to detect the pressure of the exhaust gas flowing out of the burner and is positioned along a first outlet pipe connecting the burner to the exhaust duct.

[0044] In some embodiments, the first pressure sensor is configured to detect the pressure of the air flow supplied to the burner along the first pipe.

[0045] In some embodiments, the method includes the following additional steps:

[0046] - Place the first pressure sensor along a first outlet pipe connecting the burner to the exhaust duct so as to detect the pressure of the exhaust gas flowing out of the burner;

[0047] - Place a second pressure sensor along a second pipe, the second pressure sensor being configured to detect the pressure of the air flow supplied to the burner;

[0048] - Process the signals detected by the first pressure sensor and the second pressure sensor; and

[0049] - Use the difference between the signals detected by the first pressure sensor and the second pressure sensor to calculate the combustion index.

[0050] In some embodiments, the first pressure sensor is a differential sensor and is configured to detect the difference between the pressure of the air flow supplied to the burner along a second pipe and the pressure of the exhaust gas flowing out of the burner along the first outlet pipe connecting the burner to the exhaust duct. Description of the Drawings

[0051] The present invention will now be described with reference to the accompanying drawings, which illustrate non - limiting exemplary embodiments of the present invention, in which:

[0052] - Figure 1 an internal combustion engine provided with an exhaust gas after - treatment system and an electronic control unit for the purpose of implementing the method of the present invention is schematically shown; and

[0053] - Figure 2 is schematically illustrated Figure 1 of the exhaust gas after - treatment system. Detailed Description of the Invention

[0054] In Figure 1 , the reference numeral 1 generally indicates a supercharged internal combustion engine, which is provided with an exhaust system 2 for the exhaust gas in a motor vehicle (not shown) and has a plurality of cylinders 3, each cylinder 3 being connected to an intake manifold 4 and an exhaust manifold 5 via at least one respective exhaust valve (not shown).

[0055] The intake manifold 4 receives a gas mixture including both exhaust gas and fresh air (i.e., air from the external environment through the intake duct 6), the intake duct 6 being provided with an air filter for the fresh air flow and being regulated by a throttle valve 8. A flowmeter 9 (better known as an air flowmeter) is also arranged downstream of the air filter 7 along the intake duct 6.

[0056] An exhaust duct 10 is connected to the exhaust manifold 5, the exhaust duct 10 supplying the exhaust gas generated by combustion to the exhaust system 2, and the exhaust system 2 discharging the gas generated by combustion into the atmosphere.

[0057] The supercharged internal combustion engine 1 includes a supercharging system of the internal combustion engine 1, the supercharging system being made up of a turbocharger 11, the turbocharger 11 being provided with a turbine 12 and a compressor 13. The turbine 12 is arranged along the exhaust duct 10 and is adapted to rotate at high speed under the action of the exhaust gas discharged from the cylinders 3, and the compressor 13 is arranged along the intake duct 6 and is mechanically connected to the turbine 12 so as to be driven by the turbine 12 to rotate, thereby increasing the pressure of the air present in the supply duct 6.

[0058] The exhaust system 2 of the gas is provided with an exhaust gas after - treatment system 14, the exhaust gas after - treatment system 14 including a pre - catalyst 15 arranged downstream of the turbocharger 11 along the exhaust duct 10 and a particulate filter 16 (also known as a gasoline particulate filter) also arranged downstream of the pre - catalyst 15 along the exhaust duct 10. According to a preferred variant, the exhaust gas after - treatment system 14 is provided with a catalytic converter 17, the catalytic converter 17 being arranged upstream of the particulate filter 16 along the exhaust duct 10. According to a preferred embodiment, the catalytic converter 17 and the particulate filter 16 are arranged one after another inside a common tubular container.

[0059] According to a preferred variant, the internal combustion engine 1 is also provided with: a linear oxygen probe (probe, or also called a probe or detector) 18 of the UHEGO or UEGO type, which is positioned along the exhaust duct 10 and inserted between the turbocharger 11 and the pre-catalyst 15; a lambda probe 19, which is positioned along the exhaust duct 10 and inserted between the pre-catalyst 15 and the assembly defined by the catalytic converter 17 and the particulate filter 16, for detecting the oxygen concentration inside the exhaust gas downstream of the pre-catalyst 15; and finally, a lambda probe 20, which is positioned along the exhaust duct 10 and arranged downstream of the assembly defined by the catalytic converter 17 and the particulate filter 16, for detecting the oxygen concentration inside the exhaust gas downstream of the assembly defined by the catalytic converter 17 and the particulate filter 16.

[0060] Then, the exhaust gas aftertreatment system 14 includes a burner 21, which is designed to introduce exhaust gas (and thus heat) into the exhaust duct 10 in order to accelerate the heating of the pre-catalyst 15 and / or the catalytic converter 17 and in order to facilitate the regeneration of the particulate filter 16. The burner 21 is arranged to introduce exhaust gas into the exhaust duct 10 upstream of the pre-catalyst 15 or upstream of the catalytic converter 17.

[0061] According to Figure 2 what is better illustrated in, a combustion chamber 22 is defined inside the burner 21, and the combustion chamber 22 receives fresh air (i.e., air from the external environment) via an air supply circuit 23. The air supply circuit 23 is provided with a pumping device 24 (of a known type and not specifically described), preferably inserted with an air filter element, and supplies air to the burner 21 by means of a pipe 25. According to the first embodiment, the pumping device 24 is of the fixed flow rate type, and a shut-off valve 26 is provided, which is positioned along the pipe 25 (arranged downstream of the pumping device 24), for regulating the air flow rate. Alternatively, the pumping device 24 is of the variable flow rate type (controlled by PWM), and a check valve 26 is provided, which is positioned along the pipe 25 (arranged downstream of the pumping device 24).

[0062] The combustion chamber 22 also receives fuel from an injector 27, which is arranged to inject fuel inside the combustion chamber 22. In addition, a spark plug 28 is connected to the burner 21 for determining the ignition of the mixture present inside the combustion chamber 22. Then, the internal combustion engine 1 includes a fuel supply circuit 29, which is provided with a pumping device 30, which extracts fuel from a tank 39 and supplies fuel by means of a pipe 31 regulated by a valve 38.

[0063] The air-fuel mixture introduced into the combustion chamber 22 is defined as rich (or rich) when the fuel is in excess relative to the stoichiometric value, and is defined as lean (or lean) when the air is in excess relative to the stoichiometric value. As is well known, generally, lambdaλ represents a coefficient of excess air relative to the air-fuel mixture under stoichiometric conditions. For a rich mixture, lambdaλ is less than 1, and for a lean mixture, lambdaλ is greater than 1.

[0064] The probes 18, 19, 20 are configured to detect / measure the amount of oxygen present in the exhaust gas and alternatively to provide a binary output of the on / off type or a linear output indicating the oxygen content in the exhaust gas for allowing an electronic control unit (commonly referred to as an "ECU") to calculate the air / fuel ratio of the exhaust gas. In other words, the probes 18, 19 and 20 provide an output indicating whether the value of lambda λ detected for the exhaust gas is above or below the stoichiometric value (i.e. 1).

[0065] The internal combustion engine 1 finally comprises a control system 32 suitable for supervising the operation of the internal combustion engine 1. The control system 32 comprises at least an electronic control unit which supervises the operation of the different components of the internal combustion engine 1. Obviously, the electronic control unit ECU introduced in the previous discussion can be a dedicated electronic control unit ECU supervising the operation of the burner 21, or it can be an electronic control unit ECU supervising the operation of the internal combustion engine 1. The spark plug 28 is driven by the electronic control unit ECU for generating a spark strike between its own electrodes and therefore for determining the ignition of the compressed gases inside the combustion chamber 22.

[0066] Finally, the control system 32 comprises a plurality of sensors connected to the electronic control unit ECU. These sensors comprise in particular: a temperature and pressure sensor 33 of the air flow supplied to the burner 21, preferably positioned along the duct 25 (in other words, the sensor 33 is positioned along the duct 25 downstream of the pumping device 24, preferably interposed between the pumping device 24 and the shut-off valve 26); a pressure sensor 34 of the exhaust gases flowing out of the burner 21, positioned along the outlet duct 35; a pressure sensor 36 of the fuel supplied to the burner 21, positioned along the duct 31. The electronic control unit ECU is also connected to a linear oxygen probe 18 and lambda probes 19, 20 of the UHEGO or UEGO type, from which it receives signals indicating the air / fuel ratio of the exhaust gases.

[0067] Hereinafter, a method for controlling combustion inside the combustion chamber 22 of the burner 21 implemented by the electronic control unit ECU is described.

[0068] First, the method provides for acquiring the signal detected by the pressure sensor 34. More specifically, the signal is acquired by the electronic control unit ECU at a frequency of at least 10 kHz.

[0069] Preferably, the signal is acquired by the electronic control unit ECU at a frequency at least twice the listening frequency, which is the characteristic oscillation frequency of the burner 21 (which will be better described in the following discussion).

[0070] During normal operation, the intensity of the pressure signal generated by combustion in the burner 21 is thus detected by means of the sensor 34 and stored in the buffer memory.

[0071] The pressure signal stored in the buffer memory relates to a first moving listening interval between two instants t1 and t2; where t1 represents the initial instant of the moving listening interval and t2 represents the final instant of the moving listening interval. Preferably, the first moving listening interval has a predetermined and constant duration. Advantageously, the first moving listening interval has a duration ranging from 5 ms to 15 ms; in particular, the first moving listening interval has a duration of 10 ms.

[0072] Advantageously, the first moving listening interval between the two instants t1 and t2 has a duration defined based on the characteristics of the burner 21 and corresponds to a plurality of pulsations, preferably three or four pulsations, of the signal detected by the pressure sensor 33.

[0073] A given number n of time-based samples detected by the pressure sensor and related to the first moving listening interval are stored in the storage buffer.

[0074] Subsequently, the electronic control unit ECU is preferably configured to apply a filter within the characteristic oscillation frequency range of the burner 21. In other words, the electronic control unit ECU is configured to filter the evolution of the pressure signal over time with a filter, which can alternatively be a hardware filter or a software filter. Preferably, the filter is a band-pass filter; that is, a first-order filter that allows frequencies within the passband of the listening frequency to pass through and attenuates frequencies outside the passband.

[0075] In particular, the applicant has experimentally determined that when the burner 21 is ignited, the pressure signal detected by the sensor 34 has a marked component around 300 Hz (a value representing the listening frequency). Advantageously, the listening frequency is the frequency of a quarter-wavelength oscillation.

[0076] Specifically, observing the trend of pressure over time, with the internal combustion engine 1 burning at 1500 rpm and varying the fuel injection frequency in the burner 21 (i.e., at 50, 100, and 150 Hz), the applicant experimentally determined that the main pulsations of pressure remained the same, essentially around 300 Hz. This value represents the quarter - wavelength pressure oscillation in the burner 21; more specifically, the burner 21 is assimilated to an equivalent pipe with a first open end (which identifies the confluence point in the exhaust pipe 10) and a second closed end. It was further observed that the quarter - wavelength pressure oscillation in the burner 21 is essentially independent of the injection frequency and combustion. Each combustion determines a local increase in pressure, which causes the burner 21 to resonate in a quarter - wavelength manner; according to the following relationship, the frequency f is proportional to the speed of sound V S and inversely proportional to four times the pipe length:

[0077] f=(2n + 1)*V S / 4L

[0078] where 2n + 1 is the harmonic number, where n = 0, 1, 2, 3….

[0079] According to the following relationship, the speed of sound V S is in turn a function of the temperature T, the gas constant R, and the specific heat ratio γ at constant pressure c P and at constant volume c V (i.e., γ = c P / c V ):

[0080] V S =(γ*R*T) 1 / 2

[0081] Therefore, the first harmonic with n = 0 has a frequency f1 = V S / 4L. Considering the average cross - section of the flow velocity V and radius r in the burner 21, the oscillation period T P and the relative frequency f C can be calculated as follows:

[0082] T P =2*(L + 0.6r)*(1 / (V S +V)+1 / (V S -V))

[0083] f C =1 / T P

[0084] Assuming an average temperature of 1000 °C, a burner length L equal to 0.52 m, an average radius r equal to 0.03 m, and an air mass flow rate of 30 kg / h with stoichiometric combustion, the frequency will be equal to 341 Hz.

[0085] Advantageously, the listening frequency or the passband ranges from 250 to 350 Hz. In other words, the band - pass filter is made to allow the frequencies within the characteristic oscillation frequency range of the burner 21 to pass.

[0086] The range of the listening frequency is related to the pressure oscillations in the burner 21 and in the pipe system. Therefore, the range of the listening frequency varies depending on the layout of the exhaust gas after - treatment system (basically depending on the length of the pipe system), the geometry of the burner 21, and the physical characteristics of the gas (pressure, temperature, etc.).

[0087] Subsequently, an electronic control unit ECU is set to calculate the combustion index of the first moving listening interval. The combustion index is an indicator of whether a combustion event has occurred inside the burner 21.

[0088] More specifically, the combustion index represents an indicator of combustion inside the combustion chamber 22 based on the energy content of the detected pressure signal. The energy content of the pressure signal refers to its variation over time in the first moving listening interval relative to its average value in the first moving listening interval. If the pressure signal is constant in the first moving listening interval, the energy content is zero, while if the signal varies relative to its average value in the first moving listening interval, the energy content will be greater than zero. Substantially, the energy content can be evaluated as the average integral of the absolute deviation relative to the average value in the first moving listening interval.

[0089] More specifically, according to the first and preferred embodiment, the combustion index of the first moving listening interval is defined by the effective value or RMS (root - mean - square) value at time t2, calculated as follows:

[0090]

[0091] n: the number of samples; and

[0092] Pf i : the value of the pressure signal of the i - th sample filtered by the band - pass filter.

[0093] In this case, it is not necessary to evaluate the deviation relative to the average value because we use the value of the pressure signal of the i - th sample filtered by the band - pass filter; the band - pass filter is made to provide oscillation components tending towards zero value.

[0094] Advantageously, according to the second embodiment, the combustion index of the first moving monitoring interval is defined by the moving average absolute deviation S (as an alternative to the RMS value) at time t2, and is calculated as follows:

[0095]

[0096] n: number of samples;

[0097] x i : the value of the pressure signal of the i-th sample filtered by the band-pass filter; and

[0098] M: the moving average of the combustion index of the first moving monitoring interval.

[0099] Advantageously, according to the third embodiment, the combustion index of the first moving monitoring interval is defined by the moving variance σ 2 (as an alternative to the RMS value or the moving average absolute deviation S) and is calculated as follows:

[0100]

[0101] n: number of samples;

[0102] x i : the value of the pressure signal of the i-th sample filtered by the band-pass filter; and

[0103] M: the moving average of the combustion index of the first moving monitoring interval.

[0104] In other words, with respect to formula [2] or [3], the sum of the squares of the differences between the value x i of the i-th pressure sample and the moving average M of the values x i of the pressure samples is used to calculate the combustion index of the first moving monitoring interval.

[0105] Advantageously, according to the fourth and last embodiment, the combustion index of the first moving monitoring interval is defined by the moving standard deviation σ or the moving mean square deviation at time t2 (as an alternative to the RMS value or the moving average absolute deviation S or the moving variance σ 2 ) and is calculated as follows:

[0106]

[0107] n: number of samples;

[0108] x i : the value of the pressure signal of the i-th sample filtered by the band-pass filter; and

[0109] M: the moving average of the combustion index of the first moving monitoring interval.

[0110] In other words, regarding formula [2], the value x of the i-th pressure sample is used i and the difference between the value x of the pressure sample i and the moving average M, the square root of the ratio between the sum of the squares of the differences and the number of samples n is calculated for the combustion index of the first moving monitoring interval.

[0111] Once the combustion index of the first moving monitoring interval has been calculated, the electronic control unit ECU is set to compare the combustion index with at least one threshold. More specifically, the electronic control unit ECU is set to compare the combustion index with the (first) threshold TV OFF and the (second) threshold TV ON . Advantageously, the (first) threshold TV OFF is greater than the (second) threshold TV ON .

[0112] In the case where the combustion index is less than the (first) threshold TV OFF , the electronic control unit ECU is set to identify a failed combustion event (misfire) inside the burner 21. Generally speaking, the electronic control unit ECU is set to identify the absence of combustion.

[0113] Similarly, in the case where the combustion index is greater than the (second) threshold TV ON , the electronic control unit ECU is set to identify the occurrence of a combustion event inside the burner 21. In particular, the electronic control unit ECU is arranged to identify the moment of the start of combustion (also known as SOC - Start of Combustion).

[0114] According to a preferred embodiment, during normal operation, the combustion index values related to the (second) moving monitoring interval between two moments t3 and t4 are stored in the buffer memory; where t3 represents the initial moment of this moving interval, and t4 represents the final moment of this moving interval. Advantageously, the moment t4 corresponds to the moment t2. Preferably, the second moving interval has a predetermined and constant duration. Advantageously, the second moving interval has a duration ranging from 80 ms to 120 ms; in particular, the second moving monitoring interval has a duration of 100 ms.

[0115] The duration of the second moving monitoring interval is greater than the duration of the first moving monitoring interval.

[0116] A given number n of time-based samples having combustion intensity values related to the second moving interval are stored in the storage buffer.

[0117] Subsequently, the electronic control unit ECU is set to calculate the moving average M1 of the combustion index for the second moving interval. The moving average M1 of the combustion index for the second moving interval is used as an indicator of the combustion intensity inside the burner 21. Also in this case, once the moving average M1 of the combustion index for the second moving interval has been calculated, the electronic control unit ECU is set to compare the moving average M1 of the combustion index for the second moving interval with a corresponding threshold value. In the case where the moving average M1 of the combustion index for the second moving monitoring interval is less than the corresponding threshold value, a fault signal is issued.

[0118] Finally, the electronic control unit ECU is set to calculate the moving standard deviation σ or the moving mean square deviation of the moment t4 for the second moving interval as follows:

[0119]

[0120] m: number of samples;

[0121] x i : the i-th value of the combustion index; and

[0122] M1: the moving average of the combustion index for the second moving interval.

[0123] The moving standard deviation σ of the second moving monitoring interval is used as an indicator of the combustion stability inside the burner 21. Also in this case, once the moving standard deviation σ has been calculated, the electronic control unit ECU is set to compare the moving standard deviation σ with a corresponding threshold value. In the case where the moving standard deviation σ is less than the corresponding threshold value, a fault signal is issued.

[0124] In the previous discussion, explicit reference was made to the case of collecting the signal detected by the pressure sensor 34; alternatively, the pressure signal of the air flow supplied to the burner 21 detected by the temperature and pressure sensor 33 or the difference between the pressure signals detected by the pressure sensors 33 and 34 can also be used to advantageously apply the method described so far.

[0125] Alternatively, the pressure signal detected by a differential sensor can also be used to advantageously apply the method described so far, and the differential sensor is configured to detect the difference between the pressure of the air flow supplied to the burner 21 along the pipe 25 and the pressure of the exhaust gas flowing out of the burner 21 along the pipe 35.

[0126] List of reference numerals

[0127] 1 Internal combustion engine

[0128] 2 Exhaust system

[0129] 3 Cylinders

[0130] 4 Intake Manifold

[0131] 5 Exhaust Manifold

[0132] 6 Intake Pipe

[0133] 7 Air Filter

[0134] 8 Throttle Valve

[0135] 9 Flow Meter

[0136] 10 Exhaust Pipe

[0137] 11 Turbocharger

[0138] 12 Turbine

[0139] 13 Compressor

[0140] 14 Aftertreatment System

[0141] 15 Pre - Catalyst

[0142] 16 Particulate Filter

[0143] 17 Catalytic Converter

[0144] 18 Linear Probe

[0145] 19 λ Probe

[0146] 20 λ Probe

[0147] 21 Burner

[0148] 22 Combustion Chamber

[0149] 23 Air Supply Circuit

[0150] 24 Pumping Device

[0151] 25 Pipe

[0152] 26 Shut - off Valve

[0153] 27 Injector

[0154] 28 Spark Plug

[0155] 29 Fuel Supply Circuit

[0156] 30 Pumping Device

[0157] 31 Pipe

[0158] 33 Sensors P, T

[0159] 34 Sensors P, T

[0160] 35 Outlet pipe

[0161] 36 Sensors P, T

[0162] 38 Valve

[0163] 39 Fuel tank

[0164] ECU Electronic Control Unit

Claims

1. A method for controlling combustion inside a combustion chamber (22) of a burner (21) of an exhaust gas aftertreatment system (14), the burner (21) being designed to introduce exhaust gas into an exhaust duct (10); the method providing: - a step of placing a first pressure sensor (33, 34) along a first conduit (25, 35) of the exhaust gas aftertreatment system (14); - a step of collecting a signal detected by the first pressure sensor (33, 34) in a first movement monitoring interval between an initial moment (t1) and a final moment (t2); - a step of processing the signal detected by said first pressure sensor (33, 34) to determine its energy content; - a step of calculating a combustion index based on the energy content of the signal detected by the first pressure sensor (33, 34), the combustion index being indicative of the combustion inside the combustion chamber (22); - comparing the combustion index with a first threshold value (TV OFF ) a step of comparing; and - when the combustion index is less than the first threshold value (TV OFF ), a step of identifying a failed combustion event inside the combustion chamber (22).

2. The method according to claim 1, wherein: The processing step comprises a sub-step of applying a filter within the characteristic oscillation frequency range of the burner (21).

3. The method according to claim 2, wherein: The filter may alternatively be a hardware filter or a software filter.

4. The method according to claim 2, wherein: The filter is a bandpass filter.

5. The method according to any one of claims 2 to 4, wherein: The characteristic oscillation frequency range of the burner (21) is variable depending on the layout of the exhaust gas aftertreatment system (14), the geometry of the burner (21) and the physical characteristics of the exhaust gas.

6. The method according to any one of claims 2 to 4, wherein: The filter is applied in the frequency range from 250 to 350 Hz.

7. The method according to any one of claims 2 to 4, wherein: The burner (21) has a characteristic oscillation frequency range near the injection frequency.

8. A method according to any one of claims 1 to 4, comprising the step of identifying a combustion event, said step providing: - comparing the combustion index with a second threshold value (TV ON ) is compared, wherein the first threshold value (TV OFF ) is preferably greater than the second threshold (TV ON );as well as - when the combustion index is greater than the second threshold value (TV ON ), a sub-step of identifying the occurrence of a combustion event inside the combustion chamber (22).

9. The method according to any one of claims 1 to 4, wherein: The first movement listening interval between the initial moment (t1) and the final moment (t2) has a duration defined based on characteristics of the burner (21) and corresponds to a plurality of pulsations, preferably three or four pulsations, of the signal detected by the first pressure sensor (33, 34).

10. The method according to claim 9, wherein: The first movement listening interval between the initial time (t1) and the final time (t2) has a duration ranging from 5ms to 15ms; preferably, the first movement listening interval has a duration of 10ms.

11. The method according to any one of claims 1 to 4, comprising a further step of calculating a combustion index of the first mobile listening interval by means of the effective RMS value at the final moment (t2): n: the sample size; and Pf i : The filtered value of the i-th pressure sample.

12. The method according to any one of claims 1 to 4, comprising a further step of calculating the combustion index of the first mobile listening interval by means of a moving average absolute deviation (S) at the final moment (t2): n: sample size; x i : the (filtered or unfiltered) value of the ith pressure sample; and M: value x i The moving average of .

13. The method according to claim 12, comprising using the value (x i ) and the value of the pressure sample (x i ) and the ratio between the sum of squares of the differences between the moving averages (M) of the first moving listening interval and the number of samples (n) to calculate the combustion index of the first moving listening interval.

14. The method according to claim 13, comprising: using the value (x i ) and the value of the pressure sample (x i ) and the square root of the ratio between the sum of squares of the moving averages (M) of the first moving listening interval and the number of samples (n).

15. The method according to any one of claims 1 to 4, comprising the following further steps: - Calculate the second moving interval (t3, t 2, t4), the duration of the second moving interval is greater than the duration of the first moving monitoring interval; and - calculating a moving average value (M1) of the combustion index in the second moving monitoring interval and using it as an indicator of the combustion intensity inside the burner (21).

16. The method according to claim 15, wherein: The second movement interval has a duration ranging from 80 ms to 120 ms; preferably, the second movement listening interval has a duration of at least 100 ms.

17. The method according to claim 15, comprising a further step of calculating a moving standard deviation (σ) of the combustion index of the second moving interval and using it as an indicator of the combustion stability inside the burner (21).

18. The method according to any one of claims 1 to 4, wherein: The step of acquiring the signal detected by the first pressure sensor (33, 34) is performed at a frequency at least twice the characteristic oscillation frequency of the burner (21), and preferably at least 10 kHz.

19. The method according to any one of claims 1 to 4, wherein: The first pressure sensor (34) is configured to detect the pressure of the exhaust gas flowing out of the burner (21) and is located along a first outlet duct (35) connecting the burner (21) to the exhaust duct (10).

20. The method according to any one of claims 1 to 4, wherein: The first pressure sensor (33) is configured to detect the pressure of an air flow supplied to the burner (21) along the first duct (25).

21. The method according to any one of claims 1 to 4, comprising the following further steps: - placing the first pressure sensor (34) along a first outlet duct (35) connecting the burner (21) to the exhaust duct (10) in order to detect the pressure of the exhaust gas flowing out of the burner (21); - a second pressure sensor (33) is placed along the second duct (25), the second pressure sensor (33) being configured to detect the pressure of the air flow supplied to the burner (21); - processing the signals detected by the first pressure sensor (34) and the second pressure sensor (33); as well as - calculating the combustion index using the difference between the signals detected by the first pressure sensor (34) and the second pressure sensor (33).

22. The method according to any one of claims 1 to 4, wherein: The first pressure sensor is a differential sensor and is configured to detect a difference between the pressure of the air flow supplied to the burner (21) along the second duct (25) and the pressure of the exhaust gas flowing out of the burner (21) along the first outlet duct (35) connecting the burner (21) to the exhaust duct (10).

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