JP4356075B2 - Multi-fuel engine - Google Patents

Description

  The present invention relates to a multi-fuel engine that operates by switching a plurality of types of fuel, and in particular, relates to an engine that takes into account the treatment of sulfur components contained in the fuel.

  In recent years, CNG (Compressed Natural Gas) and LPG (Liquid Petrol Gas) have been used as alternatives to liquid fuels such as gasoline and light oil in automobiles and the like from the viewpoint of improving emissions and saving resources. Gas fuels such as these are attracting attention. However, since the energy density of gaseous fuel is lower than that of liquid fuel, a vehicle equipped with an engine that uses gaseous fuel has a shorter cruising distance than a vehicle equipped with an engine that uses liquid fuel. In addition, due to delays in infrastructure development, the number of gas fuel filling stations is not sufficient, and there are concerns about long-distance travel. Therefore, a multi-fuel engine capable of supplying such a gaseous fuel and a liquid fuel to a common combustion chamber, that is, a bi-fuel engine has been proposed.

  In such a bi-fuel engine, generally, during normal control, gaseous fuel is supplied to the engine and supply of liquid fuel is stopped, and when the residual gaseous fuel amount becomes less than a lower threshold value, It is assumed that the supply of gaseous fuel is stopped while supplying liquid fuel (see, for example, Patent Document 1). In addition, when supplying gaseous fuel at the start for the purpose of suppressing the discharge of unburned gas due to the adhering fuel at the start (for example, refer to Patent Document 2), or paying attention to the point that liquid fuel has excellent output characteristics, In some cases, liquid fuel is supplied (see, for example, Patent Document 3).

Recently, a NOx occlusion reduction type three-way catalyst (hereinafter referred to as a lean NOx catalyst) that stores NOx during operation at a lean air-fuel ratio and reduces NOx at a rich air-fuel ratio has been proposed. In such a lean NOx catalyst, the purification rate may decrease due to the influence of sulfur in the fuel, and therefore, poisoning recovery control must be performed periodically. This poisoning recovery control is to maintain the high temperature by placing the catalyst in a rich atmosphere . However, since execution of such poisoning recovery control promotes deterioration of fuel consumption and catalyst deterioration, it is desirable to suppress the execution time and number of executions.

Japanese Patent Laid-Open No. 11-294212 JP 2000-213394 A JP 2003-206762 A

  On the other hand, under the high-rotation and high-load operating conditions, a rich air-fuel ratio equivalent to the poisoning recovery control is realized even with the normal control without the poisoning recovery control. Sulfur is released, and so-called poisoning recovery is realized.

  Therefore, an object of the present invention is to suppress execution of poisoning recovery control by utilizing poisoning recovery by normal control in a multi-fuel engine.

The first invention is a multi-fuel engine that operates by switching the CNG or LPG and gasoline, and selection means for selecting one of the CNG or LPG and gasoline, based on a predetermined selection criterion, a predetermined In the multi-fuel engine comprising an unburned component increasing means for increasing the unburned component of CNG or LPG for sulfur desorption of the catalytic device when the increasing condition is satisfied, the selecting means includes the predetermined unit Even if CNG or LPG is to be selected based on the selection criteria of the above, the predetermined operation in which sulfur desorption ability during normal control by CNG or LPG is low and sulfur desorption during normal control by gasoline is possible in the area, select a gasoline, a multi-fuel engine and executes a normal control by the gasoline.

In the first aspect of the present invention, the selection means has a low sulfur desorption capacity during normal control by CNG or LPG and normal by gasoline even if CNG or LPG should be selected based on a predetermined selection criterion. Gasoline is selected in a predetermined operation region where sulfur desorption during control is possible. Therefore, in the first aspect of the present invention, by utilizing poisoning recovery under normal control with gasoline, it is possible to suppress execution of sulfur desorption (poisoning recovery) control by the unburned component increasing means for CNG or LPG. it can.

  If the predetermined operating range in the first aspect of the present invention is determined by the rotational speed and the required load as in the second aspect of the present invention, the expected effect of the present invention can be realized with a simple configuration. it can.

The normal control in the present invention is preferably a control for determining the fuel injection amount and the injection timing without considering the sulfur desorption of the catalyst device .

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  First, an outline of a bi-fuel engine 100 to which the present invention is applied will be described with reference to FIG. 101 is an engine body, 102 is a cylinder block, 103 is a cylinder head, 104 is a piston, 105 is a combustion chamber, 106 is an intake port, 107 is an exhaust port, and 109 is a spark plug disposed at the top of the combustion chamber 105. Show. The intake port 106 is connected to a surge tank 111 via an intake manifold 110, and the surge tank 111 is connected to an air cleaner 113 via an intake duct 112. A throttle valve 115 driven by a step motor 114 is disposed in the intake duct 112.

  The engine 100 in FIG. 1 includes a gaseous fuel supply system and a liquid fuel supply system, and uses CNG as the gaseous fuel and gasoline as the liquid fuel. The gaseous fuel supply system includes a CNG in-cylinder injection valve 120 arranged to be able to inject into the in-cylinder combustion chamber 105, and the CNG in-cylinder injection valve 120 is connected to a CNG cylinder 124 through a CNG supply line 122. Has been. Note that a fuel cutoff valve and a high-pressure regulator 126 (not shown) are arranged in the CNG supply line 122.

  The CNG filled in the CNG cylinder 124 with the filling pressure PF (for example, 20 MPa) is reduced to a constant high adjustment pressure PH (for example, 0.5 MPa) by the high pressure regulator 126. In a normal engine control state, The high control pressure PH is injected from the CNG in-cylinder injection valve 120 into the cylinder in the compression stroke. The high adjustment pressure PH is a pressure at which in-cylinder injection is always possible in the compression stroke regardless of the operating state.

  Similarly, the liquid fuel supply system includes a gasoline injection valve 130 that can be injected into an intake passage in the intake manifold 110. The gasoline injection valve 130 is a liquid fuel container that is mounted on the vehicle via a gasoline supply line 132. As a gasoline tank 134. Further, a fuel pump 133 is disposed in the gasoline supply line 132. These CNG in-cylinder injection valve 120 and gasoline injection valve 130 are controlled based on output signals from an electronic control unit (hereinafter referred to as ECU) 300, respectively.

  The exhaust port 107 is connected to the catalyst device 147 via an exhaust manifold 146, and the exhaust side of the catalyst device 147 is opened to the outside via a silencer (not shown).

  The catalyst device 147 is a NOx occlusion reduction type three-way catalyst (lean NOx catalyst) that occludes NOx during operation at a lean air-fuel ratio and reduces NOx at a rich air-fuel ratio. The catalyst device 147 has, for example, alumina as a carrier, and an alkali metal such as potassium K, sodium Na, lithium Li, and cesium Cs, an alkaline earth such as barium Ba and calcium Ca, lanthanum La, and yttrium. At least one selected from rare earths such as Y and a noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir are supported.

  The catalyst device 147 stores NOx when the average air-fuel ratio of the inflowing exhaust gas is lean, and stores NOx when the reducing gas is contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas decreases. Accumulate and reduce the amount of NOx stored by reducing the amount of NOx.

  The detailed mechanism of the accumulation and reduction action of the lean NOx catalyst has not been fully clarified. However, the mechanism currently considered can be briefly described as follows, taking as an example the case where platinum Pt and barium Ba are supported on a support.

That is, when the air-fuel ratio of the exhaust gas flowing into the lean NOx catalyst becomes considerably leaner than the stoichiometric air-fuel ratio, the oxygen concentration in the inflowing exhaust gas greatly increases and oxygen O ₂ becomes O ₂ ⁻ or O ^2−. It adheres to the surface of platinum Pt. On the other hand, NO in the inflowing exhaust gas adheres to the surface of platinum Pt and reacts with O ₂ ⁻ or O ²⁻ on the surface of platinum Pt to become NO ₂ (NO + O ₂ → NO ₂ + O ^* , where O ^{* Indicates} active oxygen). Next, a part of the produced NO ₂ is further oxidized on platinum Pt while being absorbed into the catalyst and combined with barium oxide BaO, and diffuses in the form of nitrate ions NO ₃ ⁻ . In this way, NOx is stored in the catalyst.

On the other hand, when the air-fuel ratio of the exhaust gas flowing into the lean NOx catalyst becomes rich or the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas decreases, the amount of NO ₂ generated decreases, and the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO + 2O ^* ), and thus nitrate ions NO ₃ ⁻ in the catalyst are released from the catalyst in the form of NO. If the exhaust gas contains a reducing agent, that is, HC and CO, the released NOx reacts with the HC and CO to be reduced. When NOx no longer exists on the surface of platinum Pt in this way, NOx is released from the catalyst to the next and reduced, and the amount of NOx stored in the catalyst gradually decreases.

It is also possible to store NOx without forming nitrate and to reduce NOx without releasing NOx. If attention is focused on the active oxygen O ^* , the lean NOx catalyst can be regarded as an active oxygen generating catalyst that generates active oxygen O ^* as NOx is accumulated and released.

  The ECU 300 is composed of a digital computer and, as is well known, is connected to a ROM (read only memory), a RAM (random access memory), a CPU (microprocessor), and a constant power supply that are connected to each other via a bidirectional bus. A B-RAM (backup RAM), an input port, an output port, and the like are provided.

  A pressure sensor 140 that generates an output voltage proportional to the absolute pressure in the surge tank 111 is attached to the surge tank 111 connected to the intake manifold 110. A CNG residual pressure sensor 141 and a fuel temperature (high pressure) sensor 151 that generate an output voltage proportional to the amount of residual CNG in the CNG cylinder 124, that is, the residual pressure, are disposed in the CNG supply line 122 at the outlet of the CNG cylinder 124. The gasoline tank 134 is provided with a gasoline remaining amount sensor 142 that generates an output voltage proportional to the amount of gasoline remaining in the gasoline tank 134. Further, a fuel pressure (low pressure) sensor 152 and a fuel temperature (low pressure) sensor 153 are arranged downstream of the high pressure regulator 126 in the CNG supply line 122, and an accurate fuel amount is calculated by these.

  Further, a manual switch 160 for selecting the type of fuel to be used by the driver's operation is installed in the passenger compartment, and the manual switch 160 is operated according to the operation position of “CNG” or “gasoline”. A signal is output. The output voltages of the sensors 140, 141, 142, 150, 151, 152, 153 and the switch 160 are respectively input to the input ports of the ECU 300 via corresponding AD converters.

  Further, the input port includes a rotation speed sensor 143 that generates an output pulse representing the engine rotation speed N, a throttle opening sensor 144 that detects the rotation angle of the throttle valve 115, and an accelerator pedal depression amount (corresponding to the required load L). Accelerator opening sensor 145 that detects the temperature of the engine cooling water, a water temperature sensor 150 that detects the temperature of the engine coolant, and the like are connected via corresponding AD converters. On the other hand, the output ports of ECU 300 are connected to ignition plug 109, step motor 114, CNG in-cylinder injection valve 120, gasoline injection valve 130, fuel pump 133, and the like via corresponding DA converters and drive circuits, respectively. Yes.

  In this embodiment, for each of CNG and gasoline, as normal control, operation control based on the fuel injection amount and injection timing determined without considering the sulfur desorption of the catalyst device 147 from the engine speed N, the required load L, etc. Is done. In this embodiment, as will be described later, the operation at the rich air-fuel ratio, which is realized in the region of high rotation and high load in the normal control, is used for sulfur desorption of the catalyst.

  In the present embodiment, as shown in FIG. 2, the engine operating region determined by the engine speed N and the required load L is set loads L1 (N) and L2 (N ) Is divided into three regions. The set load L1 (N) defines a boundary indicating that sulfur can be desorbed by normal control with gasoline at a higher rotation speed or higher load side. The set load L2 defines a boundary indicating that sulfur can be desorbed by normal control with CNG at higher rotation speed or higher load side. That is, among the three regions divided by the set loads L1 (N) and L2 (N), in the first region I on the lowest load side, sulfur desorption during normal control is performed by both gasoline and CNG. In the third region III on the highest load side, sulfur desorption is possible or sufficiently high in any of gasoline and CNG. In the second region II, which is a region between the first region I and the third region III, sulfur desorption is impossible or the sulfur desorption ability is extremely low during normal control by CNG, and during normal control by gasoline. Sulfur desorption is possible or the sulfur desorption capacity is sufficiently high. The sulfur desorption capacity can be specified experimentally based on, for example, the sulfur reduction rate per unit time / gas supply amount. The setting of these operation areas is stored in advance in a predetermined area of the ROM of the ECU 300 as an operation area map that is a data file in a table format.

  An example of the operation of the present embodiment configured as described above will be described. FIG. 3 shows a fuel selection processing routine executed in the ECU 300 of the present embodiment. This processing routine is repeatedly executed by interruption every predetermined set crank angle on condition that the ignition switch is turned on and cranking is started by the starter operation.

  First, when the detection value of each sensor is read (S10), it is then determined whether the CNG operation condition is satisfied (S20). Arbitrary conditions can be used as the CNG operating conditions, for example, on condition that the remaining amount of CNG fuel exceeds a predetermined lower threshold or that CNG is selected in the manual switch 160. The fuel may be selected according to the driver's will while the remaining amount of CNG fuel is sufficient, and the gasoline may be forcibly selected when the remaining CNG amount is low.

  In the case of negative in step S20, normal control with gasoline is performed (S140). Further, an estimation calculation of the supply amount of sulfur to the catalyst device 147 and the discharge amount of sulfur from the catalyst device 147 is performed according to the air-fuel ratio at that time, and subtraction or addition to the sulfur accumulation amount A of the catalyst device 147 is performed. Performed (S150).

  In the normal control with gasoline in step S140, when the sulfur accumulation amount A is equal to or greater than a predetermined desorption start threshold value At1, the catalyst device is obtained by adding a predetermined addition value to the fuel injection amount. Poisoning recovery control is performed in which 147 is placed in a rich atmosphere to maintain a high temperature. In this poisoning recovery control, the intake air amount is increased, the fuel injection amount is increased accordingly, and the ignition timing is retarded according to a separate processing routine. The increase in the intake air amount is performed by a process of reflecting the increased throttle opening obtained from the engine water temperature or the like previously given in the map in the base opening of the throttle valve 115. In response to the increase in the intake air amount, the fuel is controlled by normal fuel injection control, which is a separate process, that is, by a series of controls for driving the gasoline injection valve 130 to realize the fuel injection amount corresponding to the intake air amount. The injection amount is increased. The ignition timing retardation is obtained by using the increase retardation amount obtained in advance in the map, that is, the increase retardation amount obtained from the engine speed, air amount, valve timing amount, engine water temperature, etc., as the base ignition timing of the spark plug 109. This is done by the process of reflecting. As a result of these processes, the unburned HC in the exhaust gas from the combustion chamber 105 is increased as compared with the case where the fuel injection amount is not increased and the ignition timing is not retarded.

  If the determination in step S20 is affirmative, that is, if the CNG operation condition is satisfied, it is next determined whether the CNG lean control condition is satisfied (S30). The CNG lean control condition here is that the required load L at the current engine speed N is less than a predetermined set load, and the sulfur accumulation amount A of the catalyst device 147 is not more than a predetermined value. When the CNG lean control condition is satisfied, lean control with CNG is performed (S40). Further, based on the estimation calculation of the sulfur supply amount to the catalyst device 147 according to the air-fuel ratio at that time and the sulfur discharge amount from the catalyst device 147, the sulfur increase amount which is the difference between them is the sulfur of the catalyst device 147. It is added to the deposition amount A (S50).

  If negative in step S30, that is, if the CNG lean control condition is not satisfied, it is next determined whether or not the operation region allows sulfur desorption by normal control in CNG (S60). This determination is made by determining whether the required load L at the current engine speed N exceeds the set load L2 by referring to the operation region table using the engine speed N and the required load L. If the determination in step S60 is affirmative, that is, if the operation range is that sulfur can be desorbed by CNG normal control, the amount of sulfur supplied to the catalyst device 147 according to the air-fuel ratio at that time, and the amount of sulfur from the catalyst device 147 Subtraction from the sulfur accumulation amount A of the catalyst device 147 is performed based on the estimation calculation of the emission amount (S120). Further, normal control by CNG is performed (S130).

  In the normal control with CNG performed in step S130, when the sulfur deposition amount A is equal to or greater than the predetermined desorption start threshold value At1, the catalyst device 147 is placed in a rich atmosphere to maintain a high temperature. Poison recovery control (unburned component increase control) is performed. In this poisoning recovery control, the intake air amount is increased, the fuel injection amount is increased accordingly, and the ignition timing is retarded according to a separate processing routine. The increase in the intake air amount is performed by a process of reflecting the increased throttle opening obtained from the engine water temperature or the like previously given in the map in the base opening of the throttle valve 115. In response to the increase in the intake air amount, a normal fuel injection control, which is a separate process, that is, a series of controls for driving the CNG injection valve 120 to realize a fuel injection amount corresponding to the intake air amount, The injection amount is increased. The ignition timing retardation is obtained by using the increase retardation amount obtained in advance in the map, that is, the increase retardation amount obtained from the engine speed, air amount, valve timing amount, engine water temperature, etc., as the base ignition timing of the spark plug 109. This is done by the process of reflecting. As a result of these processes, the unburned HC in the exhaust gas from the combustion chamber 105 is increased as compared with the case where the fuel injection amount is not increased and the ignition timing is not retarded.

  In the case of negative in step S60, it is next determined whether or not the operation region can be desorbed by normal control with gasoline (S70). This determination is made by determining whether the required load L at the current engine speed N exceeds the set load L1 by referring to the operation region table using the engine speed N and the required load L. If negative in step S70, that is, if the sulfur is not desorbed by the normal control with gasoline or the operation range is extremely low, the normal control with CNG is performed (S130).

  If the determination in step S70 is affirmative, it is next determined based on the sulfur accumulation amount A of the catalyst device 147 whether the current sulfur accumulation amount A is equal to or greater than a predetermined desorption start threshold value At1 (S80). ). This desorption start threshold value At1 is such a value that the influence on the catalyst performance by sulfur poisoning can be ignored in practice when the sulfur deposition amount A in the catalyst device 147 is lower than this (for example, the limit deposition amount of 10 %) Shall be experimentally determined in advance. When the sulfur accumulation amount A is less than the desorption start threshold value At1, normal operation with CNG is performed (S130). If negative in step S70 or S80, sulfur desorption is not possible or the sulfur desorption capability is extremely low by normal control with CNG, and normal operation with CNG (S130) is performed. However, the subtraction (S120) for the sulfur accumulation amount A is skipped.

  If the determination in step S80 is affirmative, that is, CNG is to be selected based on the predetermined selection criteria in step S20, sulfur desorption during the normal control by CNG is impossible or the sulfur desorption ability is low. In a predetermined operating region that is very low (S60) and that allows sulfur desorption during normal control with gasoline (S70), gasoline is selected as the fuel. Specifically, normal control with gasoline is performed (S90), and subtraction from the sulfur accumulation amount A of the catalyst device 147 according to the air-fuel ratio at that time is performed (S100).

  Such normal control with gasoline (S90) and subtraction of sulfur accumulation amount A (S100) are repeatedly executed until the sulfur accumulation amount A becomes equal to or less than a predetermined desorption end threshold value At2 (S110). . This desorption end threshold value At2 is a value sufficiently smaller than the desorption start threshold value At1 in order to avoid a situation in which the sulfur accumulation amount A continues to rise and fall in the vicinity of the desorption start threshold value At1 described above ( For example, it is experimentally determined in advance within a predetermined error range from 0% of the limit deposition amount. Then, the process is returned on condition that the sulfur accumulation amount A becomes equal to or less than the desorption end threshold value At2, and thereafter the CNG operation is performed until the sulfur accumulation amount A again becomes equal to or greater than the desorption start threshold value At1. There is no sulfur desorption due to the choice of gasoline while the conditions are met.

  As described above, in the present embodiment, CNG is to be selected based on the predetermined selection criteria in step S20, and the sulfur desorption capability during normal control by CNG is low (S60), and normal by gasoline In a predetermined operation region where sulfur desorption during control is possible (S70), gasoline is selected as the fuel. Therefore, in the present embodiment, it is possible to suppress the poisoning recovery control (unburned component increase control) for CNG by utilizing the poisoning recovery in the normal control with gasoline.

  Further, in the present embodiment, the predetermined operating range is determined by the engine speed N and the required load L, so that the expected effect of the present invention can be realized with a simple configuration.

  In the above embodiment, the sulfur desorption capacity during normal control by each fuel is estimated based on the engine speed N and the required load L. In addition to or in place of these parameters, the water temperature sensor 150, a catalyst temperature sensor installed in the vicinity of the catalyst device 147, an oil temperature sensor installed in an engine oil pan or the like, or installed in an exhaust pipe A detection value such as an exhaust temperature sensor may be used.

  In the above-described embodiment, an example in which CNG is used as the first fuel and gasoline is used as the second fuel has been described. However, the present invention can be widely applied when using a plurality of types of fuels having different sulfur desorption capacities during normal control, and hydrocarbons such as gasoline, diesel oil, isooctane, hexane, heptane, diesel oil, kerosene, or Liquid fuels such as butane, propane-like hydrocarbons, or methanol that can be stored in a liquid state, as well as natural gas and petroleum gas as primary fuel, or coal conversion gas and petroleum conversion gas as secondary fuel, hydrogen A combination of a plurality of gaseous fuels such as DME (dimethyl ether) can be used. As the catalyst material, various substances capable of eliminating sulfur during normal control, such as various three-way catalysts and oxidation catalysts, can be selected.

  In each of the above embodiments, the CNG fuel is in-cylinder direct injection, while the gasoline is so-called port injection. However, in the present invention, each fuel supply method is arbitrary, and both liquid and gas are used. In-cylinder direct injection type or port injection type, or at least one of carburetor type or mixer type can be used.

BRIEF DESCRIPTION OF THE DRAWINGS It is a whole line figure which shows the outline | summary and embodiment of the bi-fuel engine to which this invention is applied. It is a graph which shows the structural example of a driving | operation area | region map. It is a flowchart which shows an example of the fuel selection process routine in embodiment of this invention.

Explanation of symbols

100 Bi-fuel engine 120 CNG in-cylinder injection valve 124 CNG cylinder 130 Gasoline injection valve 134 Gasoline tank 147 Catalytic device 150 Water temperature sensor 300 Electronic control unit L1, L2 Set load I, II, III Operation range

Claims (3)

A multi-fuel engine that operates by switching between CNG or LPG and gasoline, and selection means for selecting either CNG or LPG or gasoline based on a predetermined selection criterion, and a predetermined increase condition is established In a multi-fuel engine equipped with an unburned component increasing means for increasing the unburned component of CNG or LPG for sulfur desorption of the catalyst device,
Even if CNG or LPG should be selected based on the predetermined selection criteria, the selection means has a low sulfur desorption capability during normal control by CNG or LPG , and sulfur desorption during normal control by gasoline. the release is a predetermined operating region as possible, a multi-fuel engine, characterized in that selecting the gasoline, it executes normal control by the gasoline. The multi-fuel engine according to claim 1,
The multi-fuel engine, wherein the predetermined operating range is determined by an engine speed and a required load. A multi-fuel engine according to claim 1 or 2,
The normal control is a control for determining the fuel injection amount and the injection timing without considering the sulfur desorption of the catalyst device.

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