JP6536195B2 - Combustion control method and apparatus for CNG engine - Google Patents

Description

  The present invention relates to a CNG engine using compressed natural gas (CNG) as a fuel, and more particularly to a combustion control method and device in a CNG engine capable of appropriately controlling the ignition timing according to the component of natural gas.

  CNG engines using compressed natural gas are being promoted because they can achieve exhaust gas cleaning with much less black smoke and SOx like diesel engines.

  The CNG engine is a fuel injector arranged for each cylinder after the intake-controlled air is supplied to the intake manifold with a throttle valve that regulates the air flow rate, and the compressed natural gas from the CNG container is depressurized by the fuel pressure reducing valve. The mixture of air and natural gas is drawn into the cylinder and ignited and burned by sparks from the spark plug. In this CNG engine, all controls from the combustion system to the exhaust system are controlled by the electronic system by the ECU (Engine Control Unit) to optimize the mixture ratio of air and fuel according to the running condition of the CNG car. The combustion state is optimized to clean the exhaust gas.

  The combustion control by the CNG engine increases or decreases the amount of intake air at the throttle valve and the amount of natural gas supplied from the fuel injector so as to match the target λ value determined based on the engine speed and the engine load. The combustion can be performed in a lean state by controlling the mixing ratio and determining the fuel amount ratio with reference to the engine rotational speed and the engine load and the map data fitted with the preset fuel.

Japanese Patent Application Publication No. 2003-166439 Japanese Utility Model Publication No. 05-006136 Unexamined-Japanese-Patent No. 2004-225680 Unexamined-Japanese-Patent No. 2002-276519

  In this CNG container, natural gas compressed to about 20 MPa is stored, but in Japan, natural gas derived from liquefied natural gas has a substantially constant gas composition.

  However, natural gas differs in composition depending on the place of production, and in particular, natural gas mined in Southeast Asia such as Thailand contains a large amount of, for example, about 16% of an inert gas such as carbon dioxide gas or nitrogen. In the case of fuel compressed as it is at the production area and stored in a CNG container, the air-fuel ratio changes unlike in the case where natural gas used in normal domestic fuel is used as a fuel. There is a problem that can not be the same control.

  Therefore, an object of the present invention is to solve the above-mentioned problems and provide a combustion control method and apparatus in a CNG engine capable of performing appropriate combustion control even when a fuel containing a large amount of inert gas is stored. It is.

When using as a fuel a compressed natural gas having an inert gas content higher than that of a compressed natural gas having a predetermined inert gas content, it is more preferable than a spark plug having a compressed natural gas having a predetermined inert gas content as a fuel And a fuel supply amount is set such that the air fuel ratio becomes a target λ value based on the engine speed and the engine load, and the fuel supply amount is set to a predetermined value. The present invention provides a combustion control method for a CNG engine , which determines the amount of increase in fuel based on the amount of fuel supplied when using compressed natural gas with an inert gas content as the fuel and advances the ignition timing based on the amount of increase in fuel. Do.

When knocking occurs at the ignition timing advanced based on the fuel increase amount, based on the ignition timing advanced based on the fuel increase amount so as to be an appropriate ignition timing where knocking does not occur. It is preferable to retard the ignition timing .

In addition, when using compressed natural gas having a higher inert gas content than compressed natural gas having a predetermined inert gas content as fuel, it is possible to use compressed natural gas having a predetermined inert gas content as fuel. A combustion control device in a CNG engine for advancing an ignition timing by an ignition plug, wherein a lambda sensor for detecting an air-fuel ratio, and a fuel supply such that the air-fuel ratio becomes a target λ value based on an engine speed and an engine load A combustion injection control means for setting an amount and determining a fuel increase amount based on the fuel supply amount and a fuel supply amount when using a compressed natural gas having a predetermined inert gas content as the fuel, and the fuel increase amount; An ignition timing control means for advancing an ignition timing based on the above, and provides a combustion control device in a CNG engine.

It is preferable that the ignition timing control means advances the ignition timing based on the ignition timing when using a compressed natural gas having a predetermined inert gas content as a fuel.

The knocking sensor detects knocking, and when knocking is detected at the ignition timing advanced based on the fuel increase amount, the fuel increase amount is advanced based on the fuel increase amount so that knocking is not detected. It is preferable to further include knocking control means for retarding the ignition timing based on the keratinized ignition timing .

  The present invention exhibits an excellent effect that combustion can be properly controlled even when a fuel containing a large amount of inert gas is used.

It is a figure which shows one embodiment of this invention.

  Hereinafter, a preferred embodiment of the present invention will be described in detail based on the attached drawings.

  FIG. 1 shows an engine system in a combustion control method and device of a CNG engine according to the present invention.

  The cylinder block 11 of the engine 10 is provided with a piston 14 that moves up and down from the crankshaft 12 via a connecting rod 13 for each cylinder 11 c. In the cylinder head 15 on the cylinder block 11, an ignition plug 16 is provided for each cylinder 11c, and an intake valve 17 and an exhaust valve 18 are provided.

  The intake air to the engine 10 flows from the air cleaner 22 through the intake pipe 23, flows into the intake manifold 25 via the intake throttle valve 24, and is mixed with the natural gas from the fuel injector 26 provided for each cylinder 11c of the engine 10. It is introduced into the cylinder 11 c and ignited and burned by the spark plug 16.

  Exhaust gas from each cylinder 11 c is exhausted to an exhaust manifold 27 via an exhaust valve 18, and then supplied from an exhaust pipe 28 to an oxidation catalyst 30 via an exhaust brake throttle 29. In the oxidation catalyst 30, CO, NMHC ( The non-methane hydrocarbon) is removed and exhausted to the atmosphere through the silencer 31.

  Natural gas is supplied to the fuel supply pipe 35 from any of the CNG containers 32A and 32B through the fuel shutoff valves 33A and 33B and the flow path switching valve 34, and the pressure is reduced through the fuel shutoff valve 36 from the fuel supply pipe 35. The pressure is reduced to a constant pressure by a device (regulator) 37, and then supplied to the intake manifold 25 by the fuel injector 26, mixed with the intake air, and supplied to each of the cylinders 11c.

  A fuel pressure sensor 38 is provided in the flow path switching valve 34, and the detected value is displayed by a fuel pressure gauge 39. Further, a gas filling port 40 for filling the CNG containers 32A and 32B with the compressed natural gas is connected to the flow path switching valve 34.

  The fuel cutoff valves 33A and 33B, the flow path switching valve 34, and the fuel cutoff valve 36 are controlled to open and close by a CNG engine control unit 50 described later.

  A throttle opening degree sensor 41 for detecting the opening degree of the intake throttle valve 24 is provided integrally with the intake throttle valve 24 in the intake pipe 23. The intake pipe 23 between the intake throttle valve 24 and the intake manifold 25 receives intake air. A temperature sensor 42 and an intake pressure sensor 43 are provided, and detection values of the throttle opening degree sensor 41, the intake temperature sensor 42, and the intake pressure sensor 43 are input to the CNG engine control unit 50.

  A fuel temperature sensor 44 and a fuel pressure sensor 45 are provided on the fuel supply pipe 35 extending from the pressure reducing device 37 to the fuel injector 26. Detection values of the fuel temperature sensor 44 and the fuel pressure sensor 45 are input to the CNG engine control unit 50. Be done.

  The engine 10 includes a coolant temperature sensor 46 for detecting engine coolant temperature, a knocking sensor 47 for detecting knocking from vibration of the cylinder block 11, a crank angle sensor 48 for detecting a crank angle of the crankshaft 12, and an intake valve 17 A cam angle sensor 49 is provided which discriminates each cylinder from the angle of the cam 51 which opens and closes the exhaust valve 18. The detected values of the coolant temperature sensor 46, the knocking sensor 47, the crank angle sensor 48 and the cam angle sensor 49 are CNG. It is input to the engine control unit 50.

  The exhaust pipe 28 is provided with a lambda sensor 54 for detecting the air-fuel ratio from the oxygen concentration of the exhaust gas exhausted from the exhaust manifold 27. The detected value of the lambda sensor 54 is input to the CNG engine control unit 50.

  In the purification of the exhaust gas by the oxidation catalyst 30, the CNG engine control unit 50 performs target λ control so that the combustion becomes stable based on the detection value of the lambda sensor 54.

  The exhaust brake throttle 29 is connected to the vacuum air tank 57 via the suction pipe 58 and the opening of the suction pipe 58 is adjusted by the exhaust brake actuating valve 59.

  The detection value of the atmospheric pressure sensor 60 is input to the CNG engine control unit 50, and the detection value of the accelerator opening degree sensor 62 that detects the depression amount of the accelerator 61 is also input.

  The CNG engine control unit 50 controls the opening degree of the intake throttle valve 24 and the fuel injector 26 via the driver unit 52 based on the detection values from the various sensors 42 to 49, 54, 60, 62, and the spark plug The ignition timing of 16 is controlled, and the exhaust brake actuating valve 59 is controlled to control the opening degree of the exhaust brake throttle 29.

  The CNG engine control unit 50 controls the intake air amount and the fuel supply amount based on the map data adapted to the domestic fuel according to the engine speed and the engine load, and supplies the fuel based on the detection value of the lambda sensor 54 The detected values of fuel injection control means 64 for increasing and decreasing the amount, ignition timing control means 65 for controlling the spark ignition timing with the spark plug 16 based on the detected values of the crank angle sensor 48 and cam angle sensor 49, and the knocking sensor 47 And knocking control means 66 for delaying the ignition timing of the spark plug 16 to avoid knocking.

  The fuel injection control means 64 controls the opening degree of the intake throttle valve 24 via the driver unit 52 based on the detected value of the accelerator opening degree sensor 62, and the fuel injector 26 controls the fuel injection degree based on the opening degree. More specifically, the fuel temperature sensor calculates the amount of air introduced into the intake manifold 25 based on the detection values of the intake temperature sensor 42, the intake pressure sensor 43, and the atmospheric pressure sensor 60. 44. Based on the detection value of the fuel pressure sensor 45, the fuel injector 26 is controlled to supply the amount of natural gas corresponding to the calculated amount of air to the cylinder 11c.

  At this time, the fuel injection control means 64 controls the fuel injector 26 by determining the fuel injection amount with reference to map data adapted with the preset domestic fuel.

  However, when the fuel composition is different, that is, when the amount of inert gas increases, the substantial amount of fuel decreases and the consumption of oxygen decreases, so the air-fuel ratio detected by the lambda sensor 54 also changes.

  Therefore, the fuel injection control means 64 increases the amount of fuel injected from the fuel injector 26 so that the oxygen concentration in the exhaust gas becomes the same as the oxygen concentration of the appropriate fuel, that is, the air fuel ratio becomes the target λ value. The fuel increase ratio is used as the different fuel correction to control the fuel injector 26.

  The ignition timing control means 65 controls the ignition timing of the spark plug 16 to ignite in the vicinity of the compression top dead center of each cylinder 11c based on the detection values of the crank angle sensor 48 and the cam angle sensor 49. It is determined from the amount of air, fuel and engine speed calculated by the fuel injection control means 64 as in the above, and the mixture of air and natural gas is sucked into the cylinder and ignited by the spark at the determined time and burned. Let

  At this time, if the amount of inert gas contained in the natural gas increases, the combustion speed is slowed, so control is made to advance the ignition timing of the spark plug 16 with respect to the ignition timing set optimally for domestic fuel. Do. The range of this advance is advanced by 2 to 3 degrees in crank angle (deg) with respect to the ignition timing with the domestic fuel when the inert gas is contained 16%.

  Knocking control means 66 detects the presence or absence of knocking on the basis of the detection value of knocking sensor 47 which detects the vibration generated by the combustion pressure when the air-fuel mixture is spark-ignited and burned in cylinder 11 c to control the ignition timing. Means 65 corrects the ignition timing determined by the ignition timing control means 65 in order to avoid knocking that occurs when the ignition timing is advanced.

  In this knocking control, natural gas containing a large amount of inert gas has a slow burning speed, and when advancing and performing ignition, the ignition speed of the mixture is slow, but depending on the temperature in the cylinder (in the cylinder) A mixture of unburned fuel at a distant place is ignited, and adiabatic compression causes self-ignition to easily cause knocking. Therefore, the ignition timing advanced based on the degree of knocking by the knocking sensor 47 is retarded so that knocking does not occur continuously.

  The advancing by the ignition timing control means 65 and the retarding by the knocking control means 66 will be further described.

  First, the fuel injection control means 64 determines the amount of supplied fuel based on the engine speed and the engine load, but when the engine speed is low, the target λ changes as little as 1.0, 1.1 and 1.2, When the engine rotational speed is high, the target λ is set to sequentially increase to 1.0, 1.0, 1.2... 1.6.

  The ignition timing control means 65 performs control for advancing the ignition timing and igniting when the target λ is large when the fuel supply amount increases due to the increase of the engine load. The advancement of the ignition timing control means 65 due to the increase of the engine load is set to an optimal value which does not cause knocking in the domestic fuel.

  However, in natural gas that contains a large amount of inert gas, the combustion rate is slow, so even if the advanced ignition timing set with appropriate fuel does not complete combustion, the advance angle value (deg) set with appropriate fuel Further, combustion can be completed by advancing by a few degrees (2 to 3 deg), but depending on the temperature in the cylinder, knocking tends to occur by advancing.

  Therefore, when natural gas containing a large amount of inert gas is used as the fuel, the fuel injection control means 64 determines the amount of fuel increase for the appropriate fuel, and the ignition timing control means 65 determines the appropriate fuel based on the amount of fuel increase. The ignition timing is further advanced (2 to 3 deg) with respect to the injection timing determined including the advancement based on the engine speed and the engine load at the engine ignition, and ignition is performed by the spark plug 16, and this combustion causes knocking control means 66 detects the presence or absence of knocking, and retards the advanced ignition timing, for example, every 0.5 deg to determine an optimum ignition timing that can avoid knocking.

  As described above, according to the present invention, the fuel injection control means 64 controls the amount of supplied fuel and the air fuel ratio to become the target λ value based on the engine speed and the engine load. At this time, when a fuel containing a large amount of inert gas is used, the air fuel ratio detected by the lambda sensor 54 largely fluctuates with respect to the air fuel ratio of the proper fuel. The amount of supplied fuel is increased to achieve the target λ value set in accordance with the engine load. Further, in response to the increase in fuel, the ignition timing control means 65 advances the ignition timing of the spark plug 16 based on the amount of fuel increase, and the knocking control means 66 generates ignition timing control means from the detection value of the knocking sensor 47. It is judged whether or not knocking occurs at the ignition timing advanced at 65, and if knocking occurs, the advanced ignition timing is retarded to advance to an appropriate ignition timing that can avoid knocking. It is possible to correct the angle of keratinization.

  Although the EGR circuit (exhaust gas recirculation) is not shown in the above embodiment, the amount of air is reduced and the air fuel ratio is also changed when the exhaust gas recirculation is performed in the EGR circuit. The ignition timing may be controlled at 65.

Reference Signs List 10 engine 11 c cylinder 16 spark plug 26 fuel injector 32A, 32B CNG container 50 CNG engine control unit 54 lambda sensor

Claims (5)

When using as a fuel a compressed natural gas having an inert gas content higher than that of a compressed natural gas having a predetermined inert gas content, it is more preferable than a spark plug having a compressed natural gas having a predetermined inert gas content as a fuel A combustion control method for a CNG engine that advances the ignition timing by
Set the fuel supply amount so that the air-fuel ratio becomes the target λ value based on the engine speed and the engine load,
The fuel increase amount is determined based on the fuel supply amount and the fuel supply amount when using a compressed natural gas with a predetermined inert gas content as the fuel,
A combustion control method for a CNG engine, comprising advancing the ignition timing based on the amount of fuel increase . When knocking occurs at the ignition timing advanced based on the fuel increase amount, based on the ignition timing advanced based on the fuel increase amount so as to be an appropriate ignition timing where knocking does not occur. The method for controlling combustion in a CNG engine according to claim 1 , wherein the ignition timing is retarded . When using as a fuel a compressed natural gas having an inert gas content higher than that of a compressed natural gas having a predetermined inert gas content, it is more preferable than a spark plug having a compressed natural gas having a predetermined inert gas content as a fuel A combustion control device for a CNG engine that advances the ignition timing by
A lambda sensor for detecting an air fuel ratio;
The fuel supply amount is set so that the air-fuel ratio becomes a target λ value based on the engine speed and the engine load, and the fuel supply amount when using the above-mentioned fuel supply amount and compressed natural gas with a predetermined inert gas content as fuel Combustion injection control means for determining the amount of fuel increase based on the amount;
Ignition timing control means for advancing the ignition timing based on the fuel increase amount;
Equipped with
A combustion control device in a CNG engine characterized by: The ignition timing control means advances the ignition timing based on the ignition timing when using a compressed natural gas having a predetermined inert gas content as a fuel
The combustion control device in a CNG engine according to claim 3. A knocking sensor that detects knocking;
When knocking is detected at the ignition timing advanced based on the fuel increase, reference is made to the ignition timing advanced based on the fuel increase so as to obtain an appropriate ignition timing at which knocking is not detected. Knocking control means for retarding the ignition timing to
Further comprising
The combustion control device in a CNG engine according to claim 3 or 4.