Apparatus and control method for reducing NOx emissions from a diesel engine

Abstract

The application discloses a device and a control method for reducing NOx emission of a diesel engine, relates to tail gas aftertreatment, and adds a combustor at the outlet of a supercharger; the diesel oil consumption of the combustor is calculated according to the catalytic temperature requirement value of an SCR; and equivalent diesel oil is injected into the combustor for combustion according to the diesel oil consumption, so that heat is generated, and the actual temperature of the SCR reaches the catalytic temperature requirement value. The application achieves the purpose of reducing hidden troubles such as the increase of negative pressure in the cylinder and the increase of oil consumption caused by the use of a throttle valve, reduces the influence caused by the T6 model temperature hysteresis, and reduces the risk of the increase of NOx emission of the diesel engine caused by the decrease of the SCR temperature due to the combustor failure.

Description

Technical Field

[0001] This invention relates to exhaust aftertreatment, and more specifically, to a device and control method for reducing NOx emissions from diesel engines. Background Technology

[0002] Nitrogen oxides (NOx) and particulate matter are the main pollutants from diesel engines. To effectively suppress these two exhaust pollutants, China VI diesel engines typically employ an aftertreatment system with a DOC+DPF+SCR structure. Among these, the SCR is a key component for reducing NOx emissions. By injecting urea, under high-temperature conditions, urea hydrolyzes to produce ammonia, which, along with the NOx emissions from the exhaust, is converted into nitrogen by the SCR catalytic converter. However, its conversion efficiency is highly dependent on the temperature of the catalytic converter. To increase the catalytic converter temperature and thus its conversion efficiency, current methods mainly involve increasing the throttle opening and increasing the amount of fuel injected afterward. However, these technologies have certain limitations. Relying solely on these technologies can have other negative impacts on the engine, such as increased in-cylinder negative pressure due to the increased throttle opening, and increased oil consumption. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a device and control method for reducing NOx emissions from diesel engines, thereby reducing potential problems such as increased negative pressure in the cylinder and increased oil consumption caused by the use of the throttle valve.

[0004] The present invention discloses a method for controlling NOx emissions from a diesel engine, which involves adding a burner at the outlet of the turbocharger, calculating the amount of diesel fuel used in the burner based on the catalytic temperature requirement of the SCR, and injecting an equivalent amount of diesel fuel into the burner for combustion to generate heat, thereby bringing the actual temperature of the SCR to the required catalytic temperature.

[0005] To further improve the design, the diesel fuel consumption of the burner is calculated using the following formula:

[0006]

[0007] In the formula, M0 is the diesel fuel consumption of the burner; Q1 is the heat required for the SCR to reach the required catalytic temperature; Q2 is the heat absorbed by DOC; Q3 is the heat absorbed by DPF; Q4 is the heat dissipated by SCR; Hu is the calorific value of diesel fuel; and η is the combustion efficiency of the burner.

[0008] Furthermore, based on the temperature difference between the required catalytic temperature and the current SCR temperature, and the product relationship between the exhaust flow rate through the SCR and the exhaust specific heat capacity, the amount of heat required for the SCR to reach the required catalytic temperature is calculated.

[0009] The heat absorbed by the DOC is calculated based on the product relationship between the carrier mass of the DOC and the specific heat capacity of the exhaust gas flowing through the DOC.

[0010] The heat absorbed by the DPF is calculated based on the product relationship between the carrier mass of the DPF and the specific heat capacity of the exhaust gas flowing through the DPF.

[0011] The heat dissipated by the SCR is calculated based on the product relationship between the ambient temperature and the heat dissipation coefficient of the SCR.

[0012] Further improvements are made by obtaining the real-time exhaust volume after SCR; when the real-time exhaust volume is less than the exhaust volume of the previous cycle, a positive correction coefficient is introduced to correct the diesel consumption; when the real-time exhaust volume is greater than the exhaust volume of the previous cycle, an inverse correction coefficient is introduced to correct the diesel consumption.

[0013] Furthermore, the corrected diesel consumption is compared with the set maximum and minimum fuel consumption limits. If the corrected diesel consumption is greater than the maximum fuel consumption limit, then the maximum fuel consumption limit is used as the corrected diesel consumption limit; if the corrected diesel consumption is less than the minimum fuel consumption limit, then the minimum fuel consumption limit is used as the corrected diesel consumption limit.

[0014] Furthermore, a reference value for the fuel injection quantity is set based on the temperature difference between the required catalytic temperature and the current SCR temperature, and the amount of supplemental air for the burner is calibrated based on the reference value for the fuel injection quantity.

[0015] Furthermore, when the actual fuel injection quantity of the burner is less than the reference value of the fuel injection quantity, the mass ratio of the supplementary air quantity to the actual fuel injection quantity is calibrated to 4-6; when the actual fuel injection quantity of the burner is greater than or equal to the reference value of the fuel injection quantity, the mass ratio of the supplementary air quantity to the actual fuel injection quantity is calibrated to 6-8.

[0016] To make further improvements, the actual temperature rise energy and theoretical temperature rise energy of the burner are obtained, and the burner rationality coefficient is calculated based on the ratio between the actual temperature rise energy and the theoretical temperature rise energy. The burner rationality coefficient is then compared with a set burner rationality coefficient threshold.

[0017] If the burner rationality coefficient is less than or equal to the burner rationality coefficient threshold, then the burner ignites normally.

[0018] If the burner's rationality coefficient is greater than the burner's rationality coefficient threshold, a second ignition attempt is made, and the coefficient is compared again. If the burner ignites more than three times and the burner's rationality coefficient is still greater than the burner's rationality coefficient threshold, a burner malfunction is indicated.

[0019] A device for reducing NOx emissions from a diesel engine includes a turbocharger, a DOC (Digital Oxide Charge), a DPF (Digital Power Filter), an SCR (Stable Radiation Regulator), and an ECU (Electronic Control Unit). A combustor is disposed between the outlet end of the turbocharger and the DOC. The ECU is used to apply the control method described above to inject an equivalent amount of diesel fuel into the combustor for combustion.

[0020] As a further improvement, the burner includes a mixing chamber, an injection system, an ignition system, and a supplementary gas system.

[0021] Beneficial effects

[0022] The advantages of this invention are:

[0023] 1. A burner was added to the outlet of the turbocharger, thereby eliminating the original throttle valve configuration and reducing potential problems such as increased negative pressure in the cylinder and increased oil consumption caused by the use of the throttle valve.

[0024] 2. In controlling the fuel injection quantity and intake air quantity of the burner, a closed-loop control based on the catalytic temperature requirement value, i.e., the T6 model temperature, was adopted to ensure that the SCR operates in the efficient temperature range. At the same time, the fuel injection quantity of the burner was corrected based on the change in exhaust volume, reducing the impact of the T6 model temperature hysteresis.

[0025] 3. When the burner is in operation, the burner diagnostic model, constructed based on the actual temperature rise energy and the theoretical temperature rise energy, can determine whether the burner ignition has failed. This allows for timely information on the burner's operating condition and reduces the risk of increased NOx emissions from diesel engines due to a decrease in SCR temperature caused by burner failure. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the device for reducing NOx emissions from diesel engines according to the present invention;

[0027] Figure 2 This is a schematic diagram of the internal structure of the burner of the present invention;

[0028] Figure 3 This is a schematic diagram of the control method logic of the present invention;

[0029] Figure 4 This is a schematic diagram of the burner misfire detection logic of the present invention. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made by any person within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0031] See Figures 1-4 This invention discloses a method for reducing NOx emissions from diesel engines. It eliminates the throttle valve's function in the aftertreatment system and adds a combustor at the turbocharger outlet. The diesel fuel consumption in the combustor is calculated based on the catalytic reduction temperature requirement of the SCR (Selective Catalytic Reduction) system. By burning diesel fuel in the combustor to generate heat, the exhaust temperature is increased, bringing the actual SCR temperature up to the required catalytic reduction temperature. Unburned CO and HC in the combustor undergo oxidation upon passing DOC, converting to CO2 and H2O and releasing heat. This further increases the temperature of the SCR catalyst carrier, improving conversion efficiency and ultimately reducing NOx emissions.

[0032] The working logic of the control method of the present invention is as follows: Figure 2 As shown. When the engine is running, various sensors and actuators output the current status in real time, such as catalyst temperature, vehicle speed, gear position, engine speed, and circulating oil volume. These parameters will serve as input conditions for subsequent logic.

[0033] Step 1: Based on the required catalytic temperature (i.e. Figure 1 The heat required for the SCR to reach the required catalytic temperature is calculated by taking the temperature difference between the T6 model temperature of the medium temperature sensor T6 and the current SCR temperature, the product of the current exhaust flow rate through the SCR catalytic unit and the exhaust specific heat capacity, and denoted as Q1.

[0034] The heat absorbed by the DOC is calculated based on the product of the carrier mass of the DOC and the specific heat capacity of the exhaust gas flowing through the DOC, and denoted as Q2.

[0035] The heat absorbed by the DPF is calculated based on the product of the carrier mass of the DPF and the specific heat capacity of the exhaust gas flowing through the DPF, and is denoted as Q3.

[0036] The heat dissipated by the SCR is calculated based on the product relationship between the ambient temperature and the heat dissipation coefficient of the SCR, and is denoted as Q4.

[0037] Step 2: Based on the required heat and heat loss calculated in Step 1, obtain the energy required for the SCR to reach the target heat level:

[0038] Q = Q1 + Q2 + Q3 + Q4.

[0039] The third step is to calculate the diesel fuel mass requirement of the burner based on the burner's combustion efficiency η and the diesel fuel's calorific value Hu. The calculation formula is as follows:

[0040]

[0041] When the burner is first started, it is injected and burned according to the diesel fuel mass M0. Here, diesel fuel mass M0 is the amount of diesel fuel injected in one combustion cycle.

[0042] Because the actual injection combustion process has errors, in order to prevent the errors from increasing with the increase of burner working time, this invention introduces a correction factor for diesel fuel consumption.

[0043] The fourth step is to adjust the fuel injection quantity of the burner based on the maximum fuel quantity limit, minimum fuel quantity limit, and the trend of exhaust volume changes.

[0044] Specifically, the real-time exhaust volume after SCR is obtained. When the real-time exhaust volume is less than that of the previous cycle, a positive correction coefficient (>1) is introduced to adjust the diesel consumption, thereby increasing the exhaust volume in the next cycle by increasing the diesel quantity and preventing the reduced exhaust volume from affecting the SCR catalytic effect. When the real-time exhaust volume is greater than that of the previous cycle, a negative correction coefficient (<1) is introduced to adjust the diesel consumption, thereby increasing the exhaust volume in the next cycle by decreasing the diesel quantity.

[0045] The specific correction factor can be obtained through experimentation by calibrating the relationship between the correction factor and the rate of change of exhaust volume. The calibration method is basically the same as the calibration method for fuel and intake / exhaust volume in an engine, and is existing technology; therefore, it will not be discussed further.

[0046] Once the diesel fuel consumption is determined, the fuel injection quantity reference value can be set based on the temperature difference between the required catalytic temperature and the current SCR temperature, and the burner's air supply quantity can be calibrated based on the fuel injection quantity reference value.

[0047] Specifically, when the actual fuel injection quantity of the burner is less than the reference value, the mass ratio of the make-up air quantity to the actual fuel injection quantity should be calibrated between 4 and 6. This can prevent unstable ignition and slow temperature rise caused by excessive make-up air quantity. When the actual fuel injection quantity of the burner is greater than or equal to the reference value, the mass ratio of the make-up air quantity to the actual fuel injection quantity should be calibrated between 6 and 8. This can enhance fuel-air mixing and limit the phenomenon of temperature overshoot caused by rapid temperature rise.

[0048] Furthermore, the burner of this invention is also equipped with a misfire detection function. When the burner is activated, the ignition system, fuel injection system, and air supply system of the burner work together under the control of the ECU. Temperature sensors Ta and Tb are respectively arranged at both ends of the burner. By monitoring the temperature sensors Ta and Tb, the actual temperature rise energy under the operating conditions of the burner is obtained.

[0049] like Figure 4As shown, the actual temperature rise energy E1 = (Ta - Tb) × C × V. Where C is the exhaust specific heat capacity; V is the exhaust flow rate; Ta is the actual measured value of temperature sensor Ta; and Tb is the actual measured value of temperature sensor Tb.

[0050] The theoretical temperature rise energy is calculated based on parameters such as fuel injection quantity and combustion efficiency. Theoretical temperature rise energy E2 = (Ta - Tb) st )×C×V. Where, Tb st The calibration temperature value for temperature sensor Tb is the temperature model for temperature sensor Tb. st = (Hu×η) / (C×V)+Ta.

[0051] The burner rationality coefficient is calculated based on the ratio between the actual temperature rise energy and the theoretical temperature rise energy. This coefficient is then compared to a set threshold. If the burner rationality coefficient is less than or equal to the threshold, the burner ignites normally. If the coefficient is greater than the threshold, a second ignition attempt is made, and the coefficient comparison is repeated. If the burner ignites more than three times, and the rationality coefficient remains greater than the threshold in each comparison, a burner malfunction is detected, prompting on-site personnel to perform timely maintenance. This significantly reduces the risk of increased NOx emissions from diesel engines due to reduced SCR temperature caused by burner malfunction.

[0052] like Figure 1 and Figure 2 As shown, a device for reducing NOx emissions from a diesel engine includes a turbocharger, DOC (Digital Oxide Charge), DPF (Digital Fluid Filter), SCR (Self-Regulating Catalytic Reduction), ECU (Electronic Control Unit), and burner. The burner of this invention mainly consists of a mixing chamber, a fuel injection system, an ignition system, and a supplementary air system. The fuel injection system, ignition system, and supplementary air system are all installed in the mixing chamber. The fuel injection system, ignition system, and supplementary air system are all controlled by the engine's ECU using the aforementioned control method. Based on the SCR's catalytic temperature requirement, i.e., the T6 model temperature, an equivalent amount of diesel fuel is injected, and the supplementary air quantity is determined based on the amount of diesel fuel injected. The ECU controls the fuel injection system and supplementary air system to execute relevant commands and ignites the diesel fuel injected into the burner through the ignition system.

[0053] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention, and these will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A control method for reducing NOx emissions from a diesel engine, characterized in that, A burner is added at the outlet of the turbocharger. The amount of diesel fuel used in the burner is calculated based on the catalytic temperature requirement of the SCR. An equivalent amount of diesel fuel is then injected into the burner for combustion to generate heat, so that the actual temperature of the SCR reaches the catalytic temperature requirement. Obtain the real-time exhaust volume after SCR; When the real-time exhaust volume is less than the exhaust volume of the previous cycle, a positive correction coefficient is introduced to correct the diesel consumption. When the real-time exhaust volume is greater than the exhaust volume of the previous cycle, an inverse correction coefficient is introduced to correct the diesel consumption. The corrected diesel fuel consumption is compared with the set maximum and minimum fuel consumption limits. If the corrected diesel fuel consumption is greater than the maximum fuel consumption limit, the maximum fuel consumption limit is used as the corrected diesel fuel consumption limit; if the corrected diesel fuel consumption is less than the minimum fuel consumption limit, the minimum fuel consumption limit is used as the corrected diesel fuel consumption limit.

2. The control method for reducing NOx emissions from a diesel engine according to claim 1, characterized in that, The diesel fuel consumption of the burner is calculated using the following formula: ； In the formula, M0 is the diesel fuel consumption of the burner; Q1 is the heat required for the SCR to reach the required catalytic temperature; Q2 is the heat absorbed by DOC; Q3 is the heat absorbed by DPF; Q4 is the heat dissipated by SCR; Hu is the calorific value of diesel fuel; and η is the combustion efficiency of the burner.

3. The control method for reducing NOx emissions from a diesel engine according to claim 2, characterized in that, The amount of heat required for the SCR to reach the required catalytic temperature is calculated based on the temperature difference between the required catalytic temperature and the current SCR temperature, as well as the product relationship between the exhaust flow rate through the SCR and the exhaust specific heat capacity. The heat absorbed by the DOC is calculated based on the product relationship between the carrier mass of the DOC and the specific heat capacity of the exhaust gas flowing through the DOC. The heat absorbed by the DPF is calculated based on the product relationship between the carrier mass of the DPF and the specific heat capacity of the exhaust gas flowing through the DPF. The heat dissipated by the SCR is calculated based on the product relationship between the ambient temperature and the heat dissipation coefficient of the SCR.

4. A control method for reducing NOx emissions from a diesel engine according to any one of claims 1-3, characterized in that, The fuel injection quantity reference value is set according to the temperature difference between the required catalytic temperature and the current SCR temperature, and the gas injection quantity of the burner is calibrated according to the fuel injection quantity reference value.

5. The control method for reducing NOx emissions from a diesel engine according to claim 4, characterized in that, When the actual fuel injection quantity of the burner is less than the reference value of the fuel injection quantity, the mass ratio of the supplementary air quantity to the actual fuel injection quantity is calibrated to 4-6; when the actual fuel injection quantity of the burner is greater than or equal to the reference value of the fuel injection quantity, the mass ratio of the supplementary air quantity to the actual fuel injection quantity is calibrated to 6-8.

6. A control method for reducing NOx emissions from a diesel engine according to any one of claims 1-3, characterized in that, The actual temperature rise energy and theoretical temperature rise energy of the burner are obtained. The burner rationality coefficient is calculated based on the ratio between the actual temperature rise energy and the theoretical temperature rise energy. The burner rationality coefficient is then compared with a set burner rationality coefficient threshold. If the burner rationality coefficient is less than or equal to the burner rationality coefficient threshold, then the burner ignites normally. If the burner's rationality coefficient is greater than the burner's rationality coefficient threshold, a second ignition attempt is made, and the coefficient is compared again. If the burner ignites more than three times and the burner's rationality coefficient is still greater than the burner's rationality coefficient threshold, a burner malfunction is indicated.

7. A device for reducing NOx emissions from a diesel engine, comprising a turbocharger, DOC, DPF, SCR, and ECU, characterized in that, A burner is provided between the outlet end of the turbocharger and the DOC, and the ECU is used to apply the control method as described in any one of claims 1-6 to inject an equivalent amount of diesel fuel into the burner for combustion.

8. The device for reducing NOx emissions from a diesel engine according to claim 7, characterized in that, The burner includes a mixing chamber, an injection system, an ignition system, and a gas supply system.

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