JP4265283B2 - CNG engine fuel property control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel property control method for a CNG engine using compressed natural gas (CNG) as fuel, and more particularly, to a fuel property of a CNG engine that can be operated optimally even if the fuel property changes. It relates to a control method.
[0002]
[Prior art]
In recent years, CNG engines that use compressed natural gas (CNG) as fuel for internal combustion engines for automobiles have been actively developed from the viewpoint of energy measures and environmental measures, etc., for optimal control of the CNG engines. Various techniques have been proposed.
[0003]
[Problems to be solved by the invention]
By the way, although the main component of CNG fuel is methane, it is known that this CNG fuel has a variation in gas component composition depending on its production area, production time, season, etc., and its calorific value is different.
[0004]
Therefore, if the CNG engine is operated with the same fuel injection amount, the combustion state also changes every time the fuel property changes, and the engine performance assumed in advance may not be obtained. In addition, a sensor (for example, a methane sensor) that accurately detects fuel properties has not been put into practical use.
[0005]
As described above, although there is a demand for providing a fuel property control method for a CNG engine capable of optimal operation even when the fuel property changes, it has not been provided yet.
[0006]
In particular, in a direct injection type CNG engine in which a fuel injection valve is provided in the combustion chamber, it is necessary to change the fuel injection amount due to a change in fuel properties, but if the fuel injection amount is changed during stratified combustion, Other combustion parameters (for example, fuel injection period, fuel injection timing, ignition timing, etc.) need to be changed in a complicated manner, and it has been desired to provide a control method therefor.
[0007]
In addition, the technique which ensures optimal ignition timing irrespective of the gas composition of gaseous fuel is proposed (refer patent document 1). That is, this technique makes the actual air-fuel ratio coincide with the stoichiometric air-fuel ratio by controlling the fuel injection amount based on the output signal of the oxygen sensor provided in the exhaust manifold. Further, by detecting the actual air-fuel ratio with an air-fuel ratio sensor provided in the exhaust pipe, the stoichiometric air-fuel ratio determined according to the gas composition of the CNG fuel is detected. Then, the relationship between the theoretical air-fuel ratio of CNG fuel and the optimal ignition timing is obtained in advance, and the ignition timing is corrected according to the detected theoretical air-fuel ratio of CNG fuel.
[0008]
Further, as related technologies for determining the fuel properties, a technology for determining the gasoline fuel properties by calculating the combustion speed of the fuel from the in-cylinder pressure (see Patent Document 2), and a fuel property sensor (methane sensor) in a gas fuel vehicle A technique for discriminating fuel properties and correcting the fuel remaining amount display (see Patent Document 3) has been proposed.
[0009]
[Patent Document 1]
JP 10-54305 A [Patent Document 2]
Japanese Patent Publication No. 7-50098 [Patent Document 3]
Japanese Patent No. 3164336 [0010]
The present invention has been made in view of the above, and it is possible to operate a CNG engine with an optimal fuel injection amount even when the fuel property changes, and to provide a CNG engine that can sufficiently exhibit engine performance. An object of the present invention is to provide a fuel property control method.
[0011]
In addition, the present invention provides a fuel property control method for a CNG engine that can perform stratified charge combustion operation with optimum combustion parameters even when the fuel property changes, and can sufficiently exhibit engine performance. For the purpose.
[0012]
[Means for Solving the Problems]
To achieve the above object, the fuel property-based control method for CNG engine according to the present invention comprises a fuel injection valve for injecting CNG fuel provided into the combustion chamber of the CNG engine, for detecting the pressure of the combustion chamber A fuel property control method for a CNG engine equipped with an in-cylinder pressure sensor, comprising a plurality of stratified map areas in advance, and when a CNG fuel cylinder that stores CNG fuel is newly filled with CNG fuel, The fuel property is determined based on the in-cylinder pressure when the predetermined property determining operation condition is met. After the fuel property is determined, if the CNG engine is not in the stratified lean burn operation region, a fuel amount correction coefficient is set for each fuel property. If the CNG engine is in the stratified lean burn operation region after the fuel property determination and correcting the fuel injection amount, the corresponding fuel property is determined based on the fuel property. A stratification map area is selected, and operation is performed using data of each combustion parameter for each stratification map area .
[0013]
Therefore, according to the present invention, even if the fuel property changes, the CNG engine can be operated with the optimum fuel injection amount, and the engine performance can be sufficiently exhibited.
[0015]
Further , according to the present invention, the stratified combustion operation of the CNG engine can be performed with the optimal combustion parameters even when the fuel property changes, and the engine performance can be sufficiently exhibited.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a fuel property control method for a CNG engine according to the present invention will be described below in detail with reference to the drawings. Although the present invention is applied to an in-cylinder direct injection CNG engine and one cylinder is illustrated and described, the present invention is not limited to this embodiment.
[0017]
Reference example.
FIG. 1 is a cross-sectional view illustrating a schematic configuration of a CNG engine according to a reference example . As shown in FIG. 1, the CNG engine 10 is a direct injection type in which CNG fuel is directly injected into a combustion chamber 10a by an injector (fuel injection valve) 23 described later, and is configured to have a stratified lean burn operation region. . The combustion chamber 10 a is configured by a cylinder bore 11, a cylinder head 13, and a piston 12 disposed in the cylinder bore 11 so as to reciprocate.
[0018]
A spark plug 14 is disposed substantially at the center of the combustion chamber 10a. An intake valve 16 is disposed at the intake port 15 facing the combustion chamber 10a, and an exhaust valve 20 is disposed at the exhaust port 18 facing the combustion chamber 10a. An injector 23 that directly injects CNG fuel into the combustion chamber 10a is disposed near the intake valve 16 in the combustion chamber 10a. An in-cylinder pressure sensor 25 that detects the pressure in the combustion chamber 10a is disposed in the vicinity of the exhaust valve 20 in the combustion chamber 10a.
[0019]
The CNG engine 10 includes an exhaust gas recirculation device (EGR device), a variable valve timing mechanism (VVT), and the like (not shown) and other basic components included in a normal direct injection gasoline engine. .
[0020]
As described above, the CNG engine 10 basically has the same configuration as that of a normal direct injection type gasoline engine. However, in order to supply CNG fuel, the configuration of the fuel supply system is the same as that of the gasoline engine. It is different from the case. This fuel supply system has the following configuration although an example of illustration is omitted.
[0021]
That is, the CNG fuel cylinder for storing the CNG fuel is configured to store the CNG fuel in a high pressure state (for example, a maximum of 20 MPa), and detects a pressure sensor for detecting the internal pressure and an internal temperature. A temperature sensor is provided. The CNG fuel cylinder and the delivery pipe of the CNG engine 10 are connected by a fuel supply pipe.
[0022]
This delivery pipe is for distributing the CNG fuel fed by the fuel supply pipe to each injector 23, and includes a pressure sensor for detecting the pressure in the delivery pipe and a temperature sensor for detecting the temperature. ing. The fuel supply pipe is provided with a high pressure regulator that adjusts the CNG fuel pumped from the CNG fuel cylinder to a predetermined pressure. In addition, a fuel filling port for the CNG fuel cylinder is provided with a filling port opening / closing sensor that detects an open / closed state of the filling port.
[0023]
The CNG engine 10, spark plug 14, intake valve 16, exhaust valve 20, injector 23, high pressure regulator (not shown), CNG fuel cylinder shut-off valve, exhaust gas recirculation device (EGR device) EGR valve, variable valve The timing mechanism (VVT) and the like are controlled by an electronic control unit (ECU) (not shown) based on various sensor information such as a pressure sensor, a temperature sensor, an in-cylinder pressure sensor 25, and the like.
[0024]
The open / close state of the fuel filling port is detected by the filling port opening / closing sensor, and the detection signal is monitored by the electronic control unit (ECU).
[0025]
FIG. 2 is a flowchart showing a fuel property control method for the CNG engine 10, and FIG. 3 is a map diagram showing an example of in-cylinder pressure and fuel amount correction coefficient for each fuel property under designated operating conditions.
[0026]
As shown in FIG. 2, first, it is determined whether or not a CNG fuel cylinder (not shown) is newly filled with CNG fuel (step S10). This is because the fuel property (gas composition) in the CNG fuel cylinder is changed by the new fuel filling. The presence / absence of fuel filling is determined from an ignition off signal, a signal from the filling port opening / closing sensor (not shown), and a pressure signal in the CNG fuel cylinder. That is, the pressure in the CNG fuel cylinder before the ignition is turned off is compared with the pressure in the cylinder after the ignition is turned off, the fuel filling port is opened and closed, and the ignition is turned on again. If the cylinder internal pressure after the ignition is turned on again becomes higher than the internal pressure of the CNG fuel cylinder before the ignition is turned off, it can be determined that the CNG fuel is newly filled.
[0027]
If the CNG fuel is newly charged (Yes at Step S10), it is determined that the fuel property has changed, and it is determined whether or not the CNG engine 10 is in a predetermined operating condition for performing the fuel property determination (Step S10). S11). The predetermined operating condition is an operating region that always runs at a general driving level, and is specified in advance.
[0028]
Further, as shown in FIG. 3, a cylinder pressure (for example, maximum value Pmax of cylinder pressure) map is previously provided for each of the above operating conditions. That is, in-cylinder pressure Pmax and fuel amount correction coefficient corresponding to each fuel property (fuel A, B, C,...) Are prepared in advance for each operation condition (operating conditions 1, 2,...). It is.
[0029]
If the fuel property determination is in a predetermined operating condition (Yes in step S11), the map of the in-cylinder pressure Pmax (see FIG. 3) is used to determine the operating condition and the operating condition. The fuel property is determined based on the measured value of the in-cylinder pressure Pmax (measured value by the in-cylinder pressure sensor 25) (step S12).
[0030]
Then, a fuel amount correction coefficient corresponding to this fuel property is obtained, and an optimal fuel injection amount is calculated by using this fuel amount correction coefficient (step S13), and the CNG engine 10 is operated with the optimal fuel injection amount (step S13). Step S14). In addition, what is necessary is just to interpolate from the said map when various fuel properties are mixed.
[0031]
Further, if the CNG fuel is not newly charged (No at Step S10), it can be determined that the fuel property has not changed, and therefore, the fuel injection amount under the current operating conditions may be operated (Step S14). Further, even if the CNG fuel is newly charged, if the fuel property is not in the predetermined operating condition for which the fuel property is to be determined, the fuel property is not determined and the process waits until the operating condition is satisfied (Yes in step S10, step S10). S11 negative, step S12).
[0032]
As described above, according to the fuel property control method of the CNG engine 10 according to this reference example , when the CNG fuel cylinder is newly filled with CNG fuel, the cylinder when the predetermined property determination operation condition is met. The fuel property is determined based on the internal pressure, and the fuel injection amount can be corrected by obtaining the fuel amount correction coefficient for each fuel property. Therefore, even if the fuel property changes, the CNG engine 10 can be operated with the optimum fuel injection amount. Can be driven, and the engine performance can be fully exhibited.
[0033]
For a multi- cylinder engine, the present invention can be applied to each cylinder.
[0034]
Embodiment .
4 is a flowchart showing a fuel property-specific control method for the CNG engine 10 according to the embodiment of the present invention, and FIG. 5 is a map diagram showing an example of a stratification map area corresponding to the fuel property. These are map figures which show an example of the data of each combustion parameter for every stratification map area.
[0035]
In the present embodiment , in addition to the control shown in the reference example (steps S10 to S12 in FIG. 2), when the CNG engine 10 is in the stratified lean burn operation region after the fuel property determination, the fuel property is based on the fuel property. A corresponding stratification map area (see FIG. 5) is selected, and operation is performed using data of each combustion parameter for each stratification map area (see FIG. 6).
[0036]
That is, as shown in FIG. 4, first, it is determined whether or not a CNG fuel cylinder (not shown) is newly filled with CNG fuel (step S20). If the CNG fuel is newly charged (Yes at Step S20), it is determined that the fuel property has changed, and it is determined whether or not the CNG engine 10 is under a predetermined operating condition for performing the fuel property determination (Step S20). S21). The predetermined operating condition is an operating region that always runs at a general driving level, and is specified in advance.
[0037]
If the fuel property determination is in a predetermined operating condition (Yes in step S21), the operating condition is determined by using the map of the in-cylinder pressure Pmax (see FIG. 3 shown in the above reference example ) The fuel property is determined based on the measured value of the in-cylinder pressure Pmax under the operating conditions (measured value by the in-cylinder pressure sensor 25) (step S22).
[0038]
Next, it is determined whether or not the CNG engine 10 is in the stratified lean burn operation region (step S23). In the stratified lean burn operation region, it is necessary to simultaneously control various combustion parameters, for example, fuel injection period, fuel injection timing, ignition timing, EGR valve opening, throttle opening, and valve opening / closing timing using a variable valve timing mechanism. This is because it is necessary to perform control different from that during homogeneous combustion.
[0039]
If it is in the stratified lean burn operation region (Yes at Step S23), the stratified map area (see FIG. 5) corresponding to this is selected based on the fuel property determined at Step S22. That is, as shown in FIG. 5, for example, when the fuel property is A, the stratification map area 1 is selected.
[0040]
As shown in FIG. 6, for example, the selected stratification map area 1 further includes the combustion parameters (1) fuel injection period, (2) fuel injection timing, (3) ignition timing, (4) A map is prepared for each EGR valve opening degree and the like.
[0041]
In the map relating to the fuel injection period, for example, an optimal injection period corresponding to the rotational speed of the CNG engine 10 and the fuel amount per stroke is set. Similarly, a map in which optimum values are set for fuel injection timing, ignition timing, EGR valve opening, and the like is prepared. As for the other stratified map areas (2, 3, 4,...), Optimum maps are prepared in the same manner as described above.
[0042]
Thus, a stratification map area (see FIG. 5) is prepared in advance for each fuel property, and a map for each combustion parameter (see FIG. 6) is further prepared in this stratification map area selected according to the fuel property. Therefore, by controlling using these maps, it is possible to realize stratified combustion that is optimal for the fuel properties (step S24).
[0043]
On the other hand, when it is not the stratified lean burn operation region (No at Step S23), that is, when it is the operation region of homogeneous combustion, the fuel amount correction coefficient is calculated from the map of the in-cylinder pressure Pmax (see FIG. 3 shown in the above reference example ). And the optimal fuel injection amount is calculated by using this fuel amount correction coefficient, and the CNG engine 10 is operated with the optimal fuel injection amount (step S25).
[0044]
If the CNG fuel is not newly charged (No at Step S20), it can be determined that the fuel property has not changed, and therefore, the fuel injection amount under the current operating conditions may be operated (Step S26).
[0045]
As described above, according to the fuel property control method for the CNG engine 10 according to the present embodiment, when a plurality of stratification map areas are provided in advance and the CNG engine 10 is in the stratified lean burn operation region after the fuel property determination. Selects the corresponding stratified map area based on its fuel properties and operates using the data of each combustion parameter for each stratified map area, so even if the fuel properties change, the stratified charge combustion operation with the optimal combustion parameters The engine performance can be fully exhibited.
[0046]
Further, at the time of homogeneous combustion operation, the fuel amount correction coefficient is obtained from the map of the in-cylinder pressure Pmax, the optimum fuel injection amount is calculated by using this fuel amount correction coefficient, and the CNG engine 10 is operated with the optimum fuel injection amount. The engine performance can be fully exhibited.
[0047]
【The invention's effect】
As described above, according to the fuel property control method for a CNG engine according to the present invention, when a CNG fuel cylinder is newly filled with CNG fuel, the in-cylinder engine is in a predetermined property determination operation condition. The fuel property is determined based on the pressure, and the fuel injection amount is corrected by obtaining the fuel amount correction coefficient for each fuel property. Therefore, even if the fuel property changes, the CNG engine can be operated with the optimum fuel injection amount. The engine performance can be fully exhibited.
[0048]
Further, according to the fuel property control method for a CNG engine according to the present invention, when the CNG engine is in the stratified lean burn operation region after the fuel property determination, the corresponding stratification map area is selected based on the fuel property. In addition, since the operation is performed using the data of each combustion parameter for each stratified map area, even if the fuel property changes, the CNG engine can be operated in the stratified combustion mode with the optimal combustion parameter, and the engine performance can be sufficiently exhibited. be able to.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a schematic configuration of a CNG engine according to a reference example .
FIG. 2 is a flowchart showing a fuel property control method for a CNG engine.
FIG. 3 is a map diagram showing an example of in-cylinder pressure and fuel amount correction coefficient for each fuel property under specified operating conditions.
4 is a flow chart showing a fuel property based control method CNG engine according to the embodiment of the present invention.
FIG. 5 is a map diagram showing an example of a stratification map area corresponding to a fuel property.
FIG. 6 is a map diagram showing an example of data of each combustion parameter for each stratification map area.

Claims (1)

A fuel injection valve for injecting CNG fuel provided to the combustion chamber of the CNG engine,
An in-cylinder pressure sensor for detecting the pressure in the combustion chamber;
A fuel property control method for a CNG engine equipped with
It has a plurality of stratified map areas in advance,
When the CNG fuel cylinder that stores the CNG fuel is newly filled with CNG fuel, the fuel property is determined based on the in-cylinder pressure under the predetermined property determination operation condition,
If the CNG engine is not in the stratified lean burn operation region after the fuel property determination, the fuel injection amount is corrected by obtaining a fuel amount correction coefficient for each fuel property ,
When the CNG engine is in the stratified lean burn operation region after the fuel property determination, the corresponding stratified map area is selected based on the fuel property, and the operation is performed using the data of each combustion parameter for each stratified map area. A fuel property control method for a CNG engine.

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