JP2016166564A - Natural gas engine and operation method thereof - Google Patents

Abstract

A natural gas engine capable of suppressing the occurrence of misfire due to a change in the composition of natural gas and a method of operating the same are provided.
SOLUTION: Natural gas from an injector 17 is set so that a detection value of a lambda sensor 28 installed in an exhaust passage 25 matches a target λ value set in advance based on the engine speed and engine load of the natural gas engine. In the natural gas engine that controls the supply amount of 8, the ECU 27 presets the output value V of the vibration sensor 33 that detects the vibration value generated in the cylinder 12 based on the engine speed R and the throttle opening D. When the misfire determination value F is less than or equal to, the control is performed to decrease the target λ value until the output value V exceeds the misfire determination value F.
[Selection] Figure 1

Description

  The present invention relates to a natural gas engine and an operation method thereof, and more particularly to a natural gas engine and an operation method thereof that can suppress the occurrence of misfire caused by a change in composition of natural gas.

  Conventionally, a natural gas engine using compressed natural gas (CNG) as a fuel has been proposed as an internal combustion engine mounted on a vehicle or the like. Generally, this natural gas engine uses a spark ignition system in which an air-fuel mixture of CNG decompressed gas and intake air is ignited by a spark of a spark plug and burned (see, for example, Patent Document 1).

  It is known that the composition of natural gas, which is a raw material for CNG, varies depending on the place and time of production. Therefore, in Japan, the composition of natural gas is adjusted by refining or the like so that CNG can be used in general households. On the other hand, since the use of CNG is almost limited to vehicles overseas, CNG made of natural gas that is normally produced is used as fuel for natural gas engines.

  However, if this CNG contains a large amount of non-combustible substances such as nitrogen and carbon dioxide, the mixture will be burnt without being burned even if it is spark-ignited, which may affect the operation of the natural gas engine. There is.

JP 2004-124710 A

  The objective of this invention is providing the natural gas engine which can suppress generation | occurrence | production of misfire resulting from the composition change of natural gas, and its operating method.

  The natural gas engine of the present invention that achieves the above object is characterized in that an injector for supplying natural gas to an intake passage provided with a throttle for adjusting an air flow rate, and an air-fuel mixture of the air and the natural gas are provided in an ignition plug. A cylinder that is ignited by sparks and burned; a lambda sensor installed in an exhaust passage; and a control means, wherein the control means detects the detected value of the lambda sensor and the engine speed and engine load of the natural gas engine. In a natural gas engine that controls the supply amount of natural gas from the injector so as to coincide with a target λ value determined based on the above, a vibration sensor that detects a vibration value generated in the cylinder is installed, and the control means includes When the output value of the vibration sensor is equal to or lower than a misfire determination value set in advance based on the engine speed and the opening of the throttle. Is characterized in performing control of the output value decreases the target λ value until the misfire judgment value greater.

  Further, the operating method of the natural gas engine of the present invention for achieving the above object is to ignite and burn a mixture of natural gas and air sucked into a cylinder with a spark, and to change the combustion gas of the mixture. In the natural gas engine operation method for controlling the supply amount of the natural gas so that the λ value matches the target λ value determined based on the engine speed and the engine load, the vibration value generated in the cylinder includes the vibration value described above. The target λ value is decreased until the vibration value exceeds the misfire determination value when the misfire determination value is less than a preset misfire determination value based on the engine speed and the air flow rate. It is.

  According to the natural gas engine and the method of operating the same of the present invention, when a misfire occurs in the cylinder due to a change in the composition of the natural gas, the target λ value is reduced to an appropriate level to enrich the air-fuel mixture. Since it is made easier to ignite sparks, misfires in natural gas engines can be suppressed.

It is a block diagram of the natural gas engine which consists of embodiment of this invention. It is an example of the map data which determines target lambda value. It is a flowchart explaining the operating method of the natural gas engine which consists of embodiment of this invention. It is an example of the map data which determines a misfire determination value.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a natural gas engine according to an embodiment of the present invention.

  In this natural gas engine, the air A drawn into the intake passage 2 from the intake port 1 is compressed by the compressor 4 of the turbocharger 3, cooled by the intercooler 5, and the flow rate is adjusted by the throttle 6. Then, the air A whose flow rate has been adjusted passes through the intake manifold 7 and is then mixed with the natural gas 8 that becomes the fuel to become the air-fuel mixture 9, which is formed in the cylinder block 11 when the intake valve 10 is opened. Are supplied to the plurality of cylinders 12 (four in this example).

  The natural gas 8 is supplied from a plurality of CNG containers 13 mounted on the vehicle body into the intake port of each cylinder 12 through an injector 17 connected to a CNG pipe 16 provided with a shut-off valve 14 and a regulator 15. The

  After the air-fuel mixture 9 supplied into the cylinder 12 is ignited at an appropriate timing by the spark of the spark plug 18, the engine piston 20 in the cylinder 19 is reciprocated to rotate the crankshaft 21. When the exhaust valve 22 is opened, it becomes combustion gas 23 and is exhausted from the exhaust manifold 24 to the exhaust passage 25.

  The combustion gas 23 exhausted into the exhaust passage 25 is discharged as exhaust gas G to the outside of the vehicle through the turbine 26 of the turbocharger 3 and a purification device (not shown).

  In the operation of this natural gas engine, the excess air ratio (λ value) of the combustion gas 23 installed in the exhaust passage 25 on the downstream side of the turbine 26 is controlled by the ECU 27 serving as the control means in order to maintain the optimum operation state. Control is performed so as to adjust the supply amount of the natural gas 8 from the injector 17 so that the detection value of the lambda sensor 28 for detecting the λ value coincides with the target λ value determined based on the engine speed and the engine load. It has become.

  The engine speed is measured by a rotation sensor 30 installed in the engine body 29. The engine load is estimated from the measured values of the pressure sensor 31 and the intake air temperature sensor 32 that measure the flow rate of the air A installed in the intake passage 2 on the downstream side of the throttle 6.

  FIG. 2 shows an example of map data for determining the target λ value. In this map data, the target λ value is increased as the engine speed and the engine load increase, and the air-fuel mixture 9 is set to be in a lean state when the natural gas engine is operated at high speed and high load.

  In the natural gas engine, a vibration sensor 33 is attached to the cylinder block 16. The vibration sensor 33 has a function of outputting the vibration generated by the combustion pressure when the air-fuel mixture 9 is spark-ignited and combusted in the cylinder 12 to the ECU 27 as a voltage signal. As the vibration sensor 33, a knock sensor used for detecting knocking of a gasoline engine is desirably used.

  The number of vibration sensors 33 is not particularly limited. For example, in the configuration example of FIG. 1, one to four vibration sensors 33 can be attached to the cylinder block 11.

  Such a natural gas engine operating method will be described below as a function of the ECU 27 with reference to FIG.

  The ECU 27 operates the natural gas engine according to the map data (see FIG. 2) for determining the target λ value (S10), while inputting the output value V of the vibration sensor 33 (S20) and detecting the rotation sensor 30. The value R and the opening degree D of the throttle 6 are input (S30). Next, a misfire determination value F for determining the presence or absence of misfire in the cylinder 12 is determined from the detected value R and opening degree D and preset map data (S40).

  FIG. 4 shows an example of map data for determining the misfire determination value F. This map data uses an average value of the output values of the vibration sensor 33 as a comparison target, and is set in advance by experiment or calculation. In this example, the misfire determination value is set to be constant with respect to the engine speed, while being set to have a positive correlation with the opening of the throttle 6.

  Then, the ECU 27 compares the output value V of the vibration sensor 33 with the misfire determination value F (S50). If the output value V exceeds the misfire determination value F, it is determined that no misfire has occurred in the cylinder 12. The determination is made (S60), and the process returns to Step 10.

  On the other hand, if the output value V is equal to or less than the misfire determination value F, it is determined that a misfire has occurred in the cylinder 12 (S70), and until the output value V exceeds the misfire determination value F, In the map data shown in FIG. 2, the target λ value corresponding to the operating condition is repeatedly reduced by a predetermined decrement c (S80 to S10). The magnitude of the target c decrement c in step 80 is appropriately set according to the specifications of the natural gas engine, the composition of the natural gas 8, and the like.

  As described above, when misfire occurs in the cylinder 12 due to the composition change of the natural gas 8, the target λ value related to the operation is decreased to an appropriate level, thereby enriching the air-fuel mixture 9 and facilitating spark ignition. Therefore, misfire due to the composition change of the natural gas 8 can be suppressed.

2 Intake passage 6 Throttle 8 Natural gas 9 Mixture 11 Cylinder block 12 Cylinder 17 Injector 18 Spark plug 23 Combustion gas 25 Exhaust passage 27 ECU
28 Lambda sensor 30 Rotation sensor 31 Pressure sensor 32 Intake air temperature sensor 33 Vibration sensor

Claims (3)

Installed in the exhaust passage, an injector for supplying natural gas to an intake passage provided with a throttle for adjusting the air flow rate, a cylinder for igniting and burning a mixture of the air and the natural gas with a spark of a spark plug Lambda sensor and control means,
The control means controls the supply amount of natural gas from the injector so that the detected value of the lambda sensor matches a target λ value determined based on the engine speed and engine load of the natural gas engine. In natural gas engines,
Install a vibration sensor to detect the vibration value generated in the cylinder,
The control means, when the output value of the vibration sensor is equal to or less than a misfire determination value set in advance based on the engine speed and the throttle opening, the output value exceeds the misfire determination value. A natural gas engine that performs control to decrease the target λ value until   The natural gas engine according to claim 1, wherein the vibration sensor is a knock sensor. The mixture of natural gas and air sucked into the cylinder is ignited by sparks and burned, and the λ value of the combustion gas of the mixture is determined based on the engine speed and the engine load. In the operation method of the natural gas engine for controlling the supply amount of the natural gas so as to coincide with
When the vibration value generated in the cylinder is equal to or less than a misfire determination value set in advance based on the engine speed and the air flow rate, the target λ value is maintained until the vibration value exceeds the misfire determination value. Natural gas engine operating method characterized by reducing

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