Device and method for improving misfire of natural gas engine

Abstract

The purpose of the present invention is to provide a device and method for improving misfire of a natural gas engine, comprising an engine, an ECU, an intake pipe, and an exhaust pipe, wherein the intake pipe is connected to the engine through an intake manifold, the exhaust pipe is connected to the engine through an exhaust manifold, a natural gas supply system is installed on the intake pipe, a natural gas flow sensor is installed on the natural gas supply system, an air flow sensor is installed on the intake pipe before the natural gas supply system, a dimethyl ether injection device is installed on the intake manifold, a dimethyl ether injection device is installed with a dimethyl ether injection device flow sensor, and a wide-range oxygen sensor is installed on the exhaust manifold; the ECU is respectively connected to the natural gas flow sensor, the air flow sensor, the dimethyl ether injection device, and the wide-range oxygen sensor. The present invention can effectively monitor misfires in the cylinder of a natural gas engine, and improve the combustion condition by injecting combustion-supporting fuel, and can effectively improve the operation of the natural gas engine under low load.

Description

Technical Field

[0001] The invention relates to an engine, in particular to a device and a method for improving misfire of a natural gas engine. Background Art

[0002] Engine misfire is currently mainly diagnosed through cylinder pressure and speed. For cylinder pressure, the knock sensor signal is integrated, and the integral difference at multiple different time periods is used to determine whether it meets the pre-determined numerical range. When it exceeds this range, it is considered that the cylinder has misfired. Or it can be determined whether there is a misfire based on the combustion condition in the cylinder reflected by the pre-turbine pressure. For speed, the current main technical path is to achieve it through the rate of change of crankshaft speed, but this method still has great difficulties in locating the cylinder where the misfire has occurred, and is greatly affected by external environmental conditions, which can easily lead to misjudgment or missed judgment. Summary of the invention

[0003] The object of the present invention is to provide a device and method for improving misfire of a natural gas engine which can effectively monitor misfire conditions in the cylinder of the natural gas engine.

[0004] The object of the present invention is achieved in that:

[0005] The invention discloses a device for improving misfire of a natural gas engine, which is characterized by comprising an engine, an ECU, an intake pipe and an exhaust pipe, wherein the intake pipe is connected to the engine through an intake manifold, the exhaust pipe is connected to the engine through an exhaust manifold, a natural gas supply system is installed on the intake pipe, a natural gas flow sensor is installed on the natural gas supply system, an air flow sensor is installed on the intake pipe before the natural gas supply system, a dimethyl ether injection device is installed on the intake manifold, a dimethyl ether injection device flow sensor is installed on the dimethyl ether injection device, and a wide-range oxygen sensor is installed on the exhaust manifold; and the ECU is respectively connected to the natural gas flow sensor, the air flow sensor, the dimethyl ether injection device and the wide-range oxygen sensor.

[0006] The present invention provides a method for improving misfire of a natural gas engine, which is characterized in that: when the engine is in a normal operating state, the ECU obtains the total air flow and the total natural gas flow measured by the reference air flow sensor and the natural gas flow sensor as well as the dimethyl ether flow measured by the dimethyl ether flow sensor in each cycle, i.e., the duration of two crankshaft rotations, and then the ECU calculates the theoretical oxygen concentration in the exhaust gas by the following formula, and then obtains the theoretical pump oxygen battery current value Ipth by comparing the working characteristics of the wide-range oxygen sensor of the subsystem input in advance:

[0007]

[0008] Wherein, mair is the total mass of air entering the engine in each cycle measured by the air flow sensor, mNG is the total mass of natural gas entering the engine in each cycle measured by the natural gas flow sensor, and mDME is the mass of dimethyl ether entering the cylinder in each cycle measured by the dimethyl ether flow sensor; th,NG ,λ th,DME The amount of oxygen theoretically required for complete combustion of natural gas NG and dimethyl ether DME per unit amount of substance; Δ n,NG , Δ n,DME The theoretical unit amount of natural gas NG and dimethyl ether DME will cause the amount of material in the cylinder to change after complete combustion; C1 and C2 are correction coefficients;

[0009] In the same cycle of the ECU acquiring the dimethyl ether flow sensor, when the exhaust valve opens, the ECU starts to acquire the pump oxygen battery current value Ip of the wide-range oxygen sensor until the intake valve opens, and integrates and averages this signal to obtain the average pump oxygen battery current value during this period. in If the fuel is not completely burned, It will be greater than the theoretical value Ipth. When it exceeds the set deviation degree, the deviation degree is expressed by the correction coefficient C3, that is, , the cylinder misfires in this cycle.

[0010] A method for improving misfire of a natural gas engine according to the present invention may further include:

[0011] 1. When a fire occurs, The degree of deviation controls the dimethyl ether injection device to inject a fixed amount of dimethyl ether into the intake manifold. The calculation formula for the deviation degree Δ is:

[0012] The lower limit of Δ is 0

[0013] Supply of dimethyl ether m DME is the deviation degree Δ and the corrected mass C of natural gas entering the cylinder 2 m NG The binary function of

[0014]

[0015] HNG and HDME are the lower heating values ​​of natural gas and dimethyl ether, respectively;

[0016] The adjustment process for misfire is based on cycles, and the device remains operational throughout the entire engine operation process.

[0017] 2. When the engine is in the starting state, during the intake stage, dimethyl ether (30% of the total fuel energy) is injected into the cylinder through the dimethyl ether injection device, where the total fuel energy is determined by the original engine speed control device; during this process, the misfire monitoring device remains inoperative, and when the engine speed stabilizes, it starts to monitor whether there is misfire in the cylinder, and the ECU The degree of deviation Δ controls the fuel supply of the dimethyl ether injection device.

[0018] 3. During the operation of the engine, C 1 , C 2 , C 3 It is dynamic and improves the recognition of engine misfire by adjusting the parameter values. The initial values ​​of the three coefficients are:

[0019] n is the number of cylinders of the engine.

[0020] The advantages of the present invention are:

[0021] 1. The misfire diagnosis method mentioned in the present invention reflects the combustion condition in the cylinder through oxygen, can monitor the working condition of each cycle, and can quantitatively analyze the misfire degree in the cylinder through the deviation degree between the wide-range oxygen sensor signal and the theoretical value.

[0022] 2. The subsystem of the misfire improvement device mentioned in the present invention is applicable to all cylinders of the engine, so it can accurately and timely diagnose the misfire phenomenon of a cylinder in the engine in a certain cycle, and control the supply of dimethyl ether according to the degree of misfire. Therefore, in actual work, the carrying amount of dimethyl ether can be greatly reduced, avoiding the fuel storage problem caused by the dual-fuel engine.

[0023] 3. As a fuel with a high cetane number, dimethyl ether has a low saturated vapor pressure under normal pressure. It will boil quickly after injection and eventually enter the cylinder in a gaseous state. Compared with diesel, dimethyl ether has a stronger combustion-supporting effect on natural gas. In addition, because it is injected into the intake manifold, the complexity of the cylinder structure and the cost of modification are reduced, and dimethyl ether is mixed with air more evenly. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the present invention;

[0025] Figure 2 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0026] The present invention is described in more detail below with reference to the accompanying drawings:

[0027] Combination Figure 1-2The present invention is divided into two parts: a main system and a subsystem. The main system includes an intake pipe 1, an air flow sensor 2, a natural gas supply system 3, a natural gas flow sensor 4, and a controller ECU 12. The subsystem includes an intake manifold 5, a dimethyl ether injection device 6, a dimethyl ether flow sensor 7, an intake valve 8, an exhaust valve 9, an exhaust manifold 10, and a wide-range oxygen sensor 11. Taking the connection between the main system and any group of subsystems as an example, an air flow sensor 2 is installed at the front end of the intake pipe 1, and then a natural gas supply system 3 is installed. A natural gas flow sensor 4 is installed in the natural gas supply system 3. The intake pipe 1 is connected to the intake manifold 5. A dimethyl ether injection device 6 is installed in the intake manifold 5. A dimethyl ether flow sensor 7 is installed in the dimethyl ether injection device 6. The intake manifold 5 is connected to the intake duct and the intake valve 8; the exhaust manifold 10 is connected to the exhaust duct and the exhaust valve 9, and a wide-range oxygen sensor 11 is installed in the exhaust manifold 10. The air flow sensor 2 of the main system, the natural gas flow sensor 4, the dimethyl ether flow sensor 7 of the subsystem, and the wide-range oxygen sensor 11 are connected to the controller ECU 12 of the main system, and the controller ECU 12 controls the dimethyl ether injection device 6 of the subsystem.

[0028] The number of subsystems required for an engine is determined by demand, with the upper limit being the number of engine cylinders. The dimethyl ether flow sensors 7 and wide-range oxygen sensors 11 in all subsystems are connected to the controller ECU 12 of the main system, and the controller ECU 12 of the main system controls the dimethyl ether injection device 6 of the corresponding subsystem, and each subsystem is independent of each other.

[0029] The operation of the engine is divided into two states, namely, the starting state and the normal operation state. The operating state of the engine is determined by the controller ECU12 according to the speed sensor and the car clock.

[0030] Taking the device composed of the main system and a group of subsystems as an example, when the engine is in normal operation, the device works in each cycle. The controller ECU12 first obtains the total air flow and natural gas flow measured by the reference air flow sensor 2 and the natural gas flow sensor 4 as well as the dimethyl ether flow measured by the dimethyl ether flow sensor 7 of the subsystem in each cycle, i.e., the duration of two crankshaft rotations, and then the controller ECU12 calculates the theoretical oxygen concentration in the exhaust gas by the following formula, and then obtains the theoretical pump oxygen battery current value Ipth by comparing the working characteristics of the wide-range oxygen sensor 11 of the subsystem input in advance.

[0031]

[0032] mair: The total mass of air entering the engine per cycle as measured by the air flow sensor;

[0033] mNG: The total mass of natural gas entering the engine in each cycle measured by the natural gas flow sensor;

[0034] mDME: the mass of dimethyl ether entering the cylinder in each cycle measured by the dimethyl ether flow sensor;

[0035] λ th,NG ,λ th,DME : The amount of oxygen theoretically required for complete combustion of natural gas NG and dimethyl ether DME per unit amount of substance;

[0036] Δ n,NG , Δ n,DME :Theoretically, the complete combustion of natural gas NG and dimethyl ether DME per unit amount of substance will cause a change in the amount of substance in the cylinder. Usually, Δ n,DME =1,Δ n,NG You need to refer to the chemical composition of the natural gas used by the engine. Pure methane is 0;

[0037] C1, C2: Correction coefficients. Taking into account the unevenness of the intake of each cylinder, the air and natural gas entering the cylinder are corrected through the coefficients. Each subsystem has an independent correction coefficient.

[0038] The controller ECU 12 obtains the same cycle of the dimethyl ether flow sensor 7. When the exhaust valve 9 opens (EVO), the controller starts to obtain the pump oxygen battery current value Ip of the wide-band oxygen sensor 11 until the intake valve 8 opens (IVO), and integrates and averages this signal to obtain the average pump oxygen battery current value during this period. in If the fuel is not completely burned, It will be greater than the theoretical value Ipth. When it exceeds a certain deviation, the deviation is expressed by the correction coefficient C3, that is, The controller ECU12 believes that the cylinder has misfired in this cycle.

[0039] When the controller ECU thinks that a misfire has occurred, The degree of deviation controls the dimethyl ether injection device 6 to inject a fixed amount of dimethyl ether into the intake manifold. The calculation formula for the deviation degree Δ is:

[0040] The lower limit of Δ is 0

[0041] Supply of dimethyl ether m DME is the deviation degree Δ and the corrected mass C of natural gas entering the cylinder 2 m NG The binary function of

[0042]

[0043] HNG, HDME: lower heating value of natural gas and dimethyl ether, kJ / kg;

[0044] The adjustment process for misfire is based on cycles, and the device remains operational throughout the entire engine operation process.

[0045] Take the device composed of the main system and a group of subsystems as an example. When the engine is in the starting state, because the working condition of the supercharger is poor, the intake pressure is low, and the temperature in the cylinder is low, it is difficult for natural gas to ignite, thus affecting the engine starting. In this case, during the intake stage of the cylinder, dimethyl ether accounting for 30% of the total fuel supply energy is injected into the cylinder through the dimethyl ether injection device to achieve the purpose of promoting the normal combustion of the fuel, where the total fuel supply is determined by the original engine speed control device. In this process, the device for monitoring misfires remains inoperative, and when the engine speed stabilizes, the device begins to monitor whether there is a misfire in the cylinder, and the controller ECU12 follows The degree of deviation Δ controls the amount of oil supplied to the dimethyl ether injection device 6 .

[0046] In normal operation of the engine, the correction coefficients C1, C2, and C3 of each subsystem can be adjusted according to the operating status to improve the accuracy and sensitivity of the monitoring system. 1 , C 2 , C 3 It is dynamic, and the recognition of engine misfire can be improved by adjusting the parameter value. The initial values ​​of the three coefficients are n is the number of cylinders of the engine.

Claims

1. A method for improving misfire of a natural gas engine, characterized by: When the engine is in normal operation, the ECU obtains the total air flow and natural gas flow measured by the reference air flow sensor and natural gas flow sensor as well as the dimethyl ether flow measured by the dimethyl ether flow sensor in each cycle, i.e., two crankshaft rotations. The ECU then calculates the theoretical oxygen concentration in the exhaust gas using the following formula, and then obtains the theoretical pump oxygen battery current value Ipth by comparing the working characteristics of the wide-range oxygen sensor of the subsystem input in advance: Wherein, mair is the total mass of air entering the engine in each cycle measured by the air flow sensor, mNG is the total mass of natural gas entering the engine in each cycle measured by the natural gas flow sensor, and mDME is the mass of dimethyl ether entering the cylinder in each cycle measured by the dimethyl ether flow sensor; th，NG ,λ th，DME The amount of oxygen theoretically required for complete combustion of natural gas NG and dimethyl ether DME per unit amount of substance; Δ n，NG , Δ n，DME The theoretical unit amount of natural gas NG and dimethyl ether DME will cause the amount of material in the cylinder to change after complete combustion; C1 and C2 are correction coefficients; In the same cycle of the ECU acquiring the dimethyl ether flow sensor, when the exhaust valve opens, the ECU starts to acquire the pump oxygen battery current value Ip of the wide-range oxygen sensor until the intake valve opens, and integrates and averages this signal to obtain the average pump oxygen battery current value during this period. in If the fuel is not completely burned, It will be greater than the theoretical value Ipth. When it exceeds the set deviation degree, the deviation degree is expressed by the correction coefficient C3, that is, , the cylinder misfires in this cycle.

2. A method for improving misfire of a natural gas engine according to claim 1, characterized in that: When a fire occurs, The degree of deviation controls the dimethyl ether injection device to inject a fixed amount of dimethyl ether into the intake manifold. The calculation formula for the deviation degree Δ is: The lower limit of Δ is 0 Supply of dimethyl ether m DME is the deviation degree Δ and the corrected mass of natural gas entering the cylinder C2m NG The binary function of HNG and HDME are the lower heating values ​​of natural gas and dimethyl ether, respectively; The adjustment process for misfire is based on cycles, and the device remains operational throughout the entire engine operation process.

3. The method for improving misfire of a natural gas engine according to claim 1, characterized in that: When the engine is in the starting state, during the intake stage, dimethyl ether (30% of the total fuel energy) is injected into the cylinder through the dimethyl ether injection device, where the total fuel energy is determined by the original engine speed control device; during this process, the misfire monitoring device remains inoperative, and when the engine speed stabilizes, it starts to monitor whether there is misfire in the cylinder, and the ECU responds according to The degree of deviation Δ controls the fuel supply of the dimethyl ether injection device.

4. The method for improving misfire of a natural gas engine according to claim 1, characterized in that: During the operation of the engine, C1, C2, and C3 are dynamic. The recognition of engine misfire is improved by adjusting the parameter values. The initial values ​​of the three coefficients are: C3=10%, n is the number of cylinders of the engine.

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