JP6485129B2 - Natural gas engine and operation method thereof - Google Patents

Description

  The present invention relates to a natural gas engine and an operation method thereof, and more particularly, to a natural gas engine capable of maintaining an operation performance regardless of a change in composition of natural gas and an operation method thereof.

  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, even when the same amount of CNG is used, the thermal energy generated when the air-fuel mixture burns decreases, There is a risk of affecting the operating performance of natural gas engines.

JP 2004-124710 A

  An object of the present invention is to provide a natural gas engine capable of maintaining the operation performance regardless of the change in the composition of the natural gas, and an operation method thereof.

  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 ignited by a spark. And a lambda sensor installed in the exhaust passage, and a control means, the control means based on the detected value of the lambda sensor based on the engine speed and engine load of the natural gas engine. In the natural gas engine that controls the supply amount of the natural gas from the injector so as to coincide with the target λ value determined in the above, the control means supplies the natural gas from the injector based on a detection value of the lambda sensor. Increase or decrease the amount, and increase the fuel with reference to the engine speed and the engine load and preset first map data And determining a correction value from the determined fuel increase ratio, the engine load, and preset second map data, and performing control to correct the target λ value by the correction value. It is what.

  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 a method of operating a natural gas engine in which the supply amount of the natural gas is controlled so that a λ value matches a target λ value determined based on an engine speed and an engine load, the natural gas engine is operated with the λ value of the combustion gas. The fuel supply amount is increased / decreased, the fuel increase ratio is determined with reference to the engine speed and the engine load and the first map data set in advance, and the determined fuel increase ratio and the engine load are determined. A correction value is determined from preset second map data, and the target λ value is corrected with the correction value.

  According to the natural gas engine and the operating method of the present invention, when the thermal energy generated by the combustion of the air-fuel mixture in the cylinder is reduced due to the change in the composition of the natural gas, the supply amount of the natural gas is increased. At the same time, by reducing the target λ value related to operation to an appropriate level, the mixture is enriched and the thermal energy of combustion is increased, so that the operation performance can be maintained regardless of the composition of natural gas. it can.

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 fuel increase ratio. It is an example of the map data which determines the correction value of misfire prevention.

  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.

  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 by determining the supply amount of the natural gas 8 from the injector 17 according to the map data (see FIG. 2) for determining the target λ value (S10). On the other hand, the ECU 27 measures the engine speed R from the detection value of the rotation sensor 30, and estimates the engine load L from the detection values of the pressure sensor 31 and the intake air temperature sensor 32 (S20).

  Then, referring to the engine speed R and the engine load L and the fuel correction data which is the first map data adapted with the natural gas 8 having a preset reference composition (S30), the fuel increase ratio Z is determined (S40).

  FIG. 4 shows an example of fuel correction data. The fuel increase ratio is an increase in the supply amount of natural gas 8 necessary for obtaining engine performance when using natural gas 8 having a reference composition (for example, natural gas used in Japan), When it exceeds 1.0, it covers the decrease in thermal energy due to the presence of non-combustible substances such as nitrogen and carbon dioxide. In this example, the fuel increase ratio is set to have a positive correlation with the engine speed and the engine load.

  Next, the ECU 27 determines a correction value H from the engine load L and the fuel increase ratio Z and preset second map data (S50).

  Then, correction is performed by subtracting the correction value H from the target λ value corresponding to the operating condition in the map data shown in FIG. 2 (S60), and the process returns to Step 10.

  FIG. 5 shows an example of the second map data. Each correction value is determined based on an experiment or the like in advance so that the target λ value is too low in the natural gas 8 having the reference composition and no misfire occurs in the cylinder 17. In this example, the correction value is set to have a positive correlation with both the fuel increase ratio and the engine load. Accordingly, when the natural gas engine is operated at a high speed and a high load, each target λ value in FIG. 2 is corrected to be small, and the air-fuel mixture 9 is enriched.

  Thus, when the thermal energy generated by the combustion of the air-fuel mixture 9 in the cylinder 12 is reduced due to the composition change of the natural gas 8, the supply amount of the natural gas 8 is increased and the target λ value related to the operation is set. By reducing the gas mixture 9 to an appropriate level, the mixture 9 is enriched to increase the thermal energy of combustion, so that the operation performance can be maintained regardless of the composition change of the natural gas 8.

2 Intake passage 6 Throttle 7 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

Claims (2)

An injector for supplying natural gas to an intake passage having a throttle for adjusting an air flow rate, an ignition plug for igniting and burning an air-fuel mixture of the air and the natural gas, and an exhaust passage A 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,
The control means increases or decreases the supply amount of the natural gas from the injector by a detection value of the lambda sensor, and refers to the engine speed and engine load and preset first map data as a fuel. An increase ratio is determined, a correction value is determined from the determined fuel increase ratio, the engine load, and preset second map data, and control is performed to correct the target λ value with the correction value. Natural gas engine characterized by 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
While increasing or decreasing the supply amount of the natural gas by the λ value of the combustion gas, the fuel increase ratio is determined with reference to the engine speed and engine load and preset first map data,
Operation of a natural gas engine, wherein a correction value is determined from the determined fuel increase ratio and the engine load and preset second map data, and the target λ value is corrected with the correction value Method.

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