JP6589937B2 - Compression ignition engine - Google Patents

Description

  The present invention relates to a compression ignition engine.

  Patent Document 1 describes a diesel engine. This diesel engine includes an exhaust gas purification system using a three-way catalyst for the purpose of omitting an expensive selective reduction catalyst system. In order to purify exhaust gas using a three-way catalyst, this diesel engine adjusts the size and injection pressure of injection holes for injecting diesel fuel (that is, light oil) into the combustion chamber. As a result, the diesel fuel is diffused throughout the combustion chamber to burn the stoichiometric air-fuel mixture.

  Patent Document 2 describes a diesel engine that introduces gasoline as secondary fuel through a carburetor on an intake passage and injects diesel fuel into a combustion chamber. Patent Document 2 describes that the ratio of diesel fuel to gasoline is 50% or more of diesel fuel with respect to the total fuel amount.

  Patent Document 3 describes a diesel engine that introduces vaporized naphtha into a combustion chamber from an intake passage and injects liquid naphtha into the combustion chamber. Patent Document 3 describes that the amount of naphtha supplied into the combustion chamber through the intake passage does not exceed 50% of the total fuel amount.

Japanese Patent No. 5620715 British Patent No. 714672 British Patent No. 8221725

  The diesel engine described in Patent Document 1 establishes combustion of a stoichiometric air-fuel mixture by uniformly diffusing diesel fuel throughout the combustion chamber. However, since diesel fuel is difficult to vaporize, the diesel engine described in Patent Literature 1 has a problem that a portion where the fuel concentration is locally increased occurs in the combustion chamber. When the fuel concentration is locally increased, soot and carbon monoxide (CO) are generated in the combustion chamber.

  Therefore, the present invention suppresses generation of soot and CO and improves fuel consumption in a compression ignition type engine.

  In order to solve the above-described problems, the present invention provides a relatively high pressure or temperature required for self-ignition and is easily vaporized, and a relatively low pressure or temperature required for self-ignition and vaporization. Combined with a difficult second fuel, the engine's geometric compression ratio was kept low.

The compression ignition engine disclosed here is
An engine body having a combustion chamber;
A first fuel supply unit configured to supply naphtha as the first fuel to the combustion chamber;
A second fuel supply unit configured to supply, to the combustion chamber, a second fuel having at least one of pressure and temperature leading to compression ignition lower than that of the first fuel and less likely to vaporize than the first fuel; ,
An exhaust gas recirculation passage for recirculating a part of the exhaust gas from the exhaust passage to the intake passage;
An ignition assist device for forcibly igniting the air-fuel mixture in the combustion chamber by spark ignition;
The first fuel supply unit and the second fuel supply unit are configured such that the first fuel is supplied to the combustion chamber in the entire engine operating range, and the first fuel is supplied in the medium load range and the high load range in the engine operating range. in addition the second fuel supplied to the combustion chamber, and many feed weight to the combustion chamber of the first fuel than the feed weight to the combustion chamber of the second fuel, the second fuel A controller that controls the weight supplied to the combustion chamber to be 10% or less of the total fuel weight supplied to the combustion chamber ;
The control unit closes an intake valve that opens and closes the opening of the combustion chamber after the intake bottom dead center of the engine, and closes the intake valve in a low load region of the engine operation region than in the medium load region and a high load region. Execute the intake late closing control that delays the timing,
The control unit operates the ignition assist device in the low load region where the intake air intake closing control is executed,
The control unit executes recirculation of exhaust gas through the exhaust gas recirculation passage in the high load region where the first fuel and the second fuel are supplied to the combustion chamber,
The geometric compression ratio is set to 13 or more and 18 or less.

  According to this configuration, the weight supplied to the combustion chamber is greater for the first fuel than for the second fuel. The second fuel is that “at least one of pressure and temperature leading to compression ignition is lower than that of the first fuel and is less likely to vaporize than the first fuel”. This means that the second fuel is easily ignited by compression.

  Therefore, in this compression ignition type engine, torque is generated mainly by the first fuel that is supplied to the combustion chamber with a large weight and is easily vaporized, and the ignition of the mixture of the first fuel is easy to cause compression ignition. It will be supplemented by fuel. In short, the first fuel is the main fuel for torque generation, and the second fuel is the ignition fuel.

  Here, when the geometric compression ratio of the engine is increased, the ignitability of the air-fuel mixture related to the first fuel is improved, but there is a concern that the premature ignition is caused.

  Therefore, the present invention does not ignite the air-fuel mixture related to the first fuel by increasing the compression ratio, but uses the second fuel that is easily ignited by compression to ignite the air-fuel mixture. The geometric compression ratio is 13 or more and 18 or less.

  Therefore, it is possible to form a homogeneous air-fuel mixture in which the first fuel is vaporized in the combustion chamber without pre-igniting the first fuel, which is advantageous for suppressing the generation of soot and CO. In addition, since the ignition delay of the air-fuel mixture can be suppressed by the second fuel that is easily compressed and ignited, it is advantageous for improving the fuel consumption. In other words, the ignition timing of the air-fuel mixture related to the first fuel is controlled by the second fuel that is easy to compress and ignite, and the combustion center of gravity is brought to the time when the thermal efficiency becomes high. In other words, the combustion peak is set to the expansion stroke of the engine. You can bring it around right after the start.

Thus, in the low load region of the engine, the intake air slow closing control can suppress the pump loss and improve the fuel efficiency, and even if the effective compression ratio is reduced by the control, the air-fuel mixture is discharged by spark ignition. Since it can be ignited reliably, the engine operation excellent in economic efficiency can be stably performed using inexpensive naphtha as fuel.

In the middle load region and the high load region, in addition to the first fuel (naphtha), a second fuel that is lower in pressure and temperature leading to compression ignition than the first fuel and is less likely to vaporize is supplied to the combustion chamber. Therefore, even in a low compression ratio engine having a geometric compression ratio of 13 to 18, the fuel consumption can be improved by suppressing the ignition delay of the air-fuel mixture using the second fuel as an ignition fuel. The weight of the second fuel supplied to the combustion chamber is 10% or less of the total fuel weight. Therefore, since the ignition delay can be suppressed while using a large amount of inexpensive naphtha even in the middle load region and the high load region, it is possible to stably perform the engine operation excellent in economy.

Moreover, in the high load region, the combustion chamber temperature becomes high, and the air-fuel mixture related to the first fuel is likely to be pre-ignited. Pre-ignition is suppressed by the recirculation of the exhaust gas (inert gas), An appropriate ignition timing capable of generating high engine torque can be obtained.

Here, after the first fuel is supplied to the combustion chamber, the second fuel is supplied to the combustion chamber, so that a homogeneous vaporized mixture is formed by the first fuel. The ignition timing can be appropriately controlled by the second fuel . This ensures, together with the second fuel can be used in compression ignition of the mixture of the first fuel, by adjusting the supply timing of the second fuel, it becomes easy to adjust the compression ignition and combustion timing .

  The second fuel may have a higher boiling point than the first fuel.

  By doing so, the first fuel is vaporized under conditions where the pressure and temperature in the combustion chamber are low, so that it is possible to supply fuel from an intake stroke where the pressure in the combustion chamber is low, and early fuel supply timing and vaporization performance can be achieved. Therefore, even if the fuel supply amount is increased, the first fuel can form a homogeneous air-fuel mixture, which can suppress the generation of soot and CO, improve torque and improve fuel efficiency. Improvements can be made.

The second fuel can be configured to include diesel fuel. Naphtha as the first fuel is easier to vaporize than diesel fuel, and is advantageous in forming a homogeneous air-fuel mixture in the combustion chamber. Since diesel fuel is easier to ignite than naphtha, the air-fuel mixture can be compressed and ignited at an appropriate timing. Moreover, since naphtha is relatively inexpensive, the use of naphtha is excellent in economic efficiency.

In one embodiment, the pre-Symbol controller, wherein when the first fuel and the second fuel supply to said combustion chamber, in some areas or the entire area of the engine operation range, the exhaust gas by the exhaust gas recirculation passage To reflux.

  The exhaust gas recirculation through the exhaust gas recirculation passage functions to suppress temperature rise in the combustion chamber due to the amount of heat, combustion as an inert gas, and ignition, and thus can be utilized for each engine operating region.

  Accordingly, exhaust gas recirculation through the exhaust gas recirculation passage may be executed in the engine operating region on the low load side.

As the engine load decreases, the combustion chamber temperature decreases, and the exhaust gas recirculation increases the combustion chamber temperature, thereby improving the ignitability of the air-fuel mixture related to the first fuel. In addition, the recirculation of the exhaust gas makes it easy to adjust the amount of air introduced into the combustion chamber to achieve the desired air-fuel ratio .

Also, in the engine operating region of the high-speed side, to perform a reflux of exhaust gases by said exhaust gas recirculation passage may be.

  As the engine speed increases, the supply crank angle of the first fuel becomes longer, and the time interval from the end of the supply of the first fuel to the vicinity of the compression top dead center is remarkably shortened, so that a homogeneous mixture of the first fuel is formed. However, the deterioration of homogenization is suppressed by the promotion of vaporization of the first fuel due to the recirculation of EGR gas (exhaust gas), so that no soot is generated and the engine torque can be increased. As described above, when EGR gas is recirculated mainly with diesel fuel, soot is increased. Therefore, recirculation of EGR gas is impossible, but in the present invention, the engine torque can be increased rather by recirculation of EGR gas. .

In one embodiment, a three-way catalyst for purifying exhaust gas is disposed in the exhaust passage, and the control unit has an air-fuel ratio A / F in the combustion chamber corresponding to a purification window for the three-way catalyst 14. The recirculation of the exhaust gas is controlled so as to be in the range of 5 to 15.0. The air-fuel ratio A / F is a ratio between the total weight of the first fuel and the second fuel supplied to the combustion chamber and the weight of air filled in the combustion chamber.

This eliminates the need to reduce NOx in the exhaust gas in a high oxygen atmosphere as in a conventional compression ignition engine, and facilitates the exhaust gas post-treatment with a three-way catalyst .

  A three-way catalyst is disposed in the exhaust passage, and the control unit controls the first air-fuel ratio so that an air-fuel ratio of exhaust gas upstream of the three-way catalyst (hereinafter referred to as exhaust gas air-fuel ratio) becomes a stoichiometric air-fuel ratio. Fuel and the second fuel may be supplied to the combustion chamber.

  If the air-fuel ratio of the exhaust gas is set to the stoichiometric air-fuel ratio, the exhaust gas CO, HC and NOx can be purified by the three-way catalyst, and the emission performance of the compression ignition engine is further improved. Further, NOx in the exhaust gas can be purified by a three-way catalyst without using a NOx storage reduction catalyst or a urea SCR (selective catalyst reduction) system, which is advantageous in reducing the cost of exhaust aftertreatment.

  The air-fuel ratio range of 14.5 to 15.0 corresponds to the purification window of the three-way catalyst. However, if the stoichiometric air-fuel ratio is set, the purification of the three-way catalyst becomes more reliable.

  In addition, in the conventional diesel engine, it is necessary to increase the supercharging capability to make the air-fuel ratio at the time of combustion lean and to reduce soot, CO, and NOx, but in this configuration, the exhaust gas is exhausted by supplying the first fuel. The air-fuel ratio can be made the stoichiometric air-fuel ratio, and the combination with the three-way catalyst can reduce NOx as well as reducing soot and CO without relying on supercharging as in the prior art. Therefore, it is possible to provide an inexpensive engine that is not equipped with a supercharger.

  In one embodiment, the first fuel supply unit injects the first fuel into the intake port of the engine body, and the second fuel supply unit injects the second fuel directly into the combustion chamber.

  When the first fuel is injected into the intake port, the first fuel diffuses into the combustion chamber by the intake air flow, which is advantageous for forming a homogeneous air-fuel mixture. Therefore, generation of soot and CO can be suppressed.

  Since the second fuel supply unit directly injects the second fuel into the combustion chamber, the second fuel can be supplied into the combustion chamber at an appropriate timing before compression top dead center, and the air-fuel mixture is compressed at an appropriate timing. Can be ignited and burned.

As described above, according to the compression ignition type engine according to the present invention, it is possible to suppress the generation of soot and CO, which is advantageous for improving exhaust emission, and is effective for low engine load and medium load. By using a large amount of inexpensive naphtha as a fuel in the entire region of the engine and the high load region, it is possible to stably perform the engine operation with excellent economic efficiency.

FIG. 1 is a schematic view illustrating the configuration of an engine system. FIG. 2 is a block diagram illustrating a configuration related to control of the engine system. FIG. 3 is a diagram illustrating fuel injection timing. FIG. 4 is a diagram illustrating a preferred operation region of the engine system. FIG. 5 is a diagram for explaining the intake air late closing control. FIG. 6 is a flowchart showing a specific example of control of the engine system. FIG. 7 is a diagram showing main specifications of the engine system. FIG. 8 is a diagram illustrating the relationship between the indicated mean effective pressure (IMEP) and the indicated fuel consumption rate (gross ISFC) according to the embodiment. FIG. 9 is a diagram illustrating the relationship between the indicated mean effective pressure (IMEP) and the NOx emission amount according to the embodiment. FIG. 10 is a diagram illustrating a change in the cylinder pressure of the embodiment with respect to the crank angle.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or its use.

  FIG. 1 shows a schematic configuration of the engine system. FIG. 2 illustrates a configuration related to control of the engine system. The engine system is mounted on a four-wheel vehicle. The engine system disclosed herein is suitable for large vehicles such as large trucks. However, the engine system disclosed herein can be widely applied to various four-wheeled vehicles regardless of the size of the vehicle.

  The engine system includes a diesel engine 1 as a compression ignition engine. The vehicle advances by the operation of the diesel engine 1.

  This engine system is configured to supply the diesel engine 1 with diesel fuel (that is, light oil or fuel mainly composed of light oil) and a different type of fuel having different characteristics from the diesel fuel. The heterogeneous fuel has a characteristic that at least one of pressure and temperature leading to compression ignition is higher than that of diesel fuel, and its boiling point is lower than that of diesel fuel. Heterogeneous fuels are easier to vaporize than diesel fuels and are less likely to ignite than diesel fuels. The heterogeneous fuel corresponds to the first fuel, and the diesel fuel corresponds to the second fuel. The heterogeneous fuel is mainly a fuel for generating torque. Diesel fuel is mainly a fuel for ignition.

  The different type of fuel is specifically naphtha. Naphthas that can be used in this engine system include light naphtha, heavy naphtha, and whole range naphtha. Light naphtha, heavy naphtha and whole range naphtha have different boiling ranges. Also, a modified naphtha in which a small amount of crude oil or heavy oil is mixed with naphtha may be used for this engine system.

  The heterogeneous fuel may be gasoline other than naphtha. Further, the heterogeneous fuel is not limited to one type of fuel, and may be a mixture of two or more types of fuel. For example, a mixed fuel of naphtha and gasoline, a mixed fuel of naphtha and other fuel, or a mixed fuel of gasoline and other fuel may be used as the different fuel.

  In the following, an engine system that supplies diesel fuel and naphtha to the diesel engine 1 will be described.

<Engine system configuration>
The diesel engine 1 includes a cylinder block 11 provided with a plurality of cylinders 11a (only one is shown in FIG. 1), a cylinder head 12 disposed on the cylinder block 11, and a lower side of the cylinder block 11. And an oil pan 13 in which lubricating oil is stored. A piston 14 is fitted into each cylinder 11a of the diesel engine 1 so as to reciprocate along the cylinder central axis. The piston 14 is connected to the crankshaft 15 via a connecting rod 14b. A cavity that defines a reentrant combustion chamber 14 a is formed on the top surface of the piston 14. The diesel engine 1 has a geometric compression ratio of 13 or more and 18 or less.

  In the cylinder head 12, an intake port 16 and an exhaust port 17 are formed for each cylinder 11a. The intake port 16 is provided with an intake valve 21 for opening and closing the opening of the combustion chamber 14a. The exhaust port 17 is provided with an exhaust valve 22 for opening and closing the opening of the combustion chamber 14a.

  The diesel engine 1 includes an intake S-VT (Sequential-Valve Timing) 71 that makes the valve timing variable as a valve operating mechanism that drives the intake valve 21 (see FIG. 2). The intake S-VT 71 can employ various known configurations such as a hydraulic type or an electric type. The diesel engine 1 changes the valve timing of the intake valve 21 according to the operating state.

  A naphtha injector 19 as a first fuel supply unit and a diesel fuel injector 18 as a second fuel supply unit are attached to the cylinder head 12.

  The naphtha injector 19 is configured to inject naphtha into the intake port 16. That is, the naphtha injector 19 is arranged such that the injection hole for injecting the naphtha faces the intake port 16 of each cylinder 11a. The naphtha injector 19 is supplied with naphtha stored in the first fuel tank 191 through a naphtha supply path (not shown).

  The diesel fuel injector 18 is configured to directly inject diesel fuel into the combustion chamber 14a. That is, the diesel fuel injector 18 is disposed such that the injection hole for injecting diesel fuel faces the cylinder 11 a from the bottom surface of the cylinder head 12. In the illustrated example, the diesel fuel injector 18 is disposed on the central axis of the cylinder 11a. However, the diesel fuel injector 18 may be disposed at an appropriate position. Diesel fuel stored in the second fuel tank 181 is supplied to the diesel fuel injector 18 through a diesel fuel supply path (not shown).

  An ignition assist device is also attached to the cylinder head 12. The ignition assist device assists ignition of the air-fuel mixture when the diesel engine 1 is in a specific operation state. Specifically, the ignition assist device is an ignition device 20 that ignites an air-fuel mixture by spark ignition. Although the detailed illustration of the ignition device 20 is omitted, an electrode is disposed facing the combustion chamber 14a. The ignition assist device may be a glow plug that improves the ignitability of the fuel by warming the air in the cylinder 11a instead of the ignition device.

  An intake passage 30 is connected to one side of the diesel engine 1. The intake passage 30 communicates with the intake port 16 of each cylinder 11a. The intake passage 30 introduces air and EGR gas into each cylinder 11a. An exhaust passage 40 is connected to the other side of the diesel engine 1. The exhaust passage 40 communicates with the exhaust port 17 of each cylinder 11a. The exhaust passage 40 discharges burned gas from each cylinder 11a. The intake passage 30 and the exhaust passage 40 are provided with a turbocharger 61 that supercharges air, which will be described in detail later.

  An air cleaner 31 that filters air is disposed at the upstream end of the intake passage 30. A surge tank 33 is disposed near the downstream end of the intake passage 30. The intake passage 30 downstream of the surge tank 33 constitutes an independent passage that branches for each cylinder 11a. The downstream end of each independent passage is connected to the intake port 16 of each cylinder 11a.

  Between the air cleaner 31 and the surge tank 33 in the intake passage 30, a compressor 61 a of the turbocharger 61, an intercooler 35 that cools the air compressed by the compressor 61 a, and a throttle valve 36 that adjusts the air amount, Is arranged. The intercooler 35 may be configured as an air cooling type or a water cooling type. The throttle valve 36 is basically fully open, but is throttled to generate a negative pressure in the intake passage 30 when, for example, a large amount of EGR gas is returned to the intake passage 30.

  The upstream portion of the exhaust passage 40 is constituted by an exhaust manifold. The exhaust manifold has a plurality of independent passages branched for each cylinder 11 a and connected to the outer end of the exhaust port 17, and a collecting portion where the plurality of independent passages gather.

  A turbine 61b of the turbocharger 61, an exhaust purification device 41 that purifies harmful components in the exhaust gas, and a silencer 42 are disposed downstream of the exhaust manifold in the exhaust passage 40 in order from the upstream side. ing.

  The exhaust purification device 41 has a three-way catalyst 41a. The three-way catalyst 41a simultaneously purifies hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) in the exhaust gas. The three-way catalyst 41a oxidizes hydrocarbons to water and carbon dioxide, oxidizes carbon monoxide to carbon dioxide, and reduces nitrogen oxides to nitrogen. The three-way catalyst 41a can sufficiently purify the exhaust gas when the exhaust gas air-fuel ratio (weight ratio of air to fuel) is at the stoichiometric air-fuel ratio, but the air-fuel ratio is 14.5 to 15.0. It is possible to purify the exhaust gas even when it is in the substantially theoretical air-fuel ratio purification window.

  The exhaust purification device 41 may include a particulate filter that collects particulates such as soot contained in the exhaust gas in addition to the three-way catalyst 41a.

  An exhaust gas recirculation passage 51 is interposed between the intake passage 30 and the exhaust passage 40. The exhaust gas recirculation passage 51 recirculates a part of the exhaust gas to the intake passage 30. The upstream end of the exhaust gas recirculation passage 51 is connected to a portion of the exhaust passage 40 between the exhaust manifold and the turbine 61b (that is, a portion upstream of the turbine 61b). The downstream end of the exhaust gas recirculation passage 51 is connected to a portion of the intake passage 30 between the surge tank 33 and the throttle valve 36 (that is, a portion downstream of the compressor 61a). The exhaust gas recirculation passage 51 is provided with an EGR valve 51a for adjusting the recirculation amount of the exhaust gas to the intake passage 30 and an EGR cooler 52 for cooling the exhaust gas with engine cooling water.

  The turbocharger 61 has a compressor 61 a disposed in the intake passage 30 and a turbine 61 b disposed in the exhaust passage 40. The compressor 61a and the turbine 61b are mutually connected, and the compressor 61a and the turbine 61b rotate integrally. The compressor 61 a is disposed between the air cleaner 31 and the intercooler 35 in the intake passage 30. The turbine 61 b is disposed between the exhaust manifold and the exhaust purification device 41 in the exhaust passage 40. As the turbine 61b rotates due to the exhaust gas flow, the compressor 61a rotates and compresses the air.

  An exhaust bypass passage 65 that bypasses the turbine 61b is connected to the exhaust passage 40. The exhaust bypass passage 65 is provided with a waste gate valve 65 a for adjusting the amount of exhaust flowing through the exhaust bypass passage 65. The wastegate valve 65a is configured to be in a fully open state (normally open) when no power is supplied.

<Configuration of engine control device>
As shown in FIGS. 1 and 2, the diesel engine 1 is controlled by a powertrain control module (hereinafter referred to as PCM) 10. The PCM 10 includes a microprocessor having a CPU, a memory, a counter timer group, an interface, and a path connecting these units. The PCM 10 constitutes a control device (and a control unit). As shown in FIG. 2, detection signals from various sensors are input to the PCM 10. The sensors included here are a water temperature sensor SW1 that detects the temperature of engine cooling water, a supercharging pressure sensor SW2 that is attached to the surge tank 33 and detects the pressure of air supplied to the combustion chamber 14a, and the temperature of the air. Intake temperature sensor SW3 to detect, crank angle sensor SW4 to detect the rotation angle of the crankshaft 15, accelerator opening sensor SW5 to detect the accelerator opening corresponding to the operation amount of the accelerator pedal (not shown) of the vehicle, three-way catalyst 41a is attached to an exhaust passage upstream and downstream of 41a, detects an oxygen concentration in the exhaust gas, an O ₂ sensor SW6, an exhaust pressure sensor SW7 detects an exhaust pressure upstream of the turbine 61b in the exhaust passage 40, an intake passage 30 is an air flow sensor SW8 that detects the intake flow rate drawn into the air 30 and E that detects the opening degree of the EGR valve 51a. A GR valve opening sensor SW9, an intake valve phase angle sensor SW10 that detects the phase angle of the intake valve 21, and a wastegate valve opening sensor SW11 that detects the opening of the wastegate valve 65a.

  The PCM 10 performs various calculations based on the detection signals of these sensors SW1 to SW11, thereby determining the state of the diesel engine 1 and the vehicle, and the diesel fuel injector 18, the naphtha injector 19, the ignition device 20, Control signals are output to the actuators of the intake S-VT 71, throttle valve 36, EGR valve 51a, and wastegate valve 65a.

<Engine control>
The basic control of the diesel engine 1 by the PCM 10 is to determine the target torque mainly based on the accelerator opening, and cause the diesel fuel injector 18 and the naphtha injector 19 to perform fuel injection corresponding to the target torque. It is.

  The PCM 10 also adjusts the amount of air introduced into the cylinder 11 a according to the operating state of the diesel engine 1. Specifically, the PCM 10 controls the opening of the throttle valve 36 and the EGR valve 51a (that is, EGR control) and / or controls the valve timing of the intake valve 21 by the intake S-VT 71 (that is, intake late closing control). To adjust the air volume. The intake valve 21 is closed within the range of 60 ° to 120 ° after the intake bottom dead center in the middle stage of the compression stroke (the middle period when the crank angle 180 ° of the compression stroke is divided into three equal parts). By performing the late closing control (defining the time when the lift height of the intake valve 21 is 0.4 mm as the valve closing timing), the amount of air introduced into the cylinder 11a can be adjusted without increasing the pump loss. In addition, when the EGR gas is recirculated, the amount of air introduced into the cylinder 11a can be adjusted, and the temperature in the cylinder 11a can be increased (compression with a decrease in the effective compression ratio by the intake air late closing control). Although the temperature rise in the cylinder 11a in the vicinity of the top dead center is insufficient, this can be complemented to improve the ignitability of the air-fuel mixture. Furthermore, when the EGR gas is recirculated in a high load region where the temperature in the cylinder 11a is high, the low-temperature inert gas that has circulated in the EGR cooler 52 is recirculated to the combustion chamber 14a. Thus, the air-fuel mixture can be ignited at an appropriate ignition timing capable of generating high engine torque.

The PCM 10 further performs air-fuel ratio feedback control that adjusts the air amount and the fuel amount based on the oxygen concentration in the exhaust gas detected by the O ₂ sensor SW 6 and the intake air flow rate detected by the air flow sensor SW 8. The PCM 10 sets the air-fuel ratio of the air-fuel mixture in the combustion chamber 14a (that is, the weight ratio (A / F) between the air (A) and the fuel (F) in the combustion chamber 14a) to the stoichiometric air-fuel ratio from the combustion chamber 14a. Set the air / fuel ratio of the exhaust gas to the stoichiometric air / fuel ratio.

  Since A / F = 14.5 to 15.0 is an air-fuel ratio corresponding to the purification window of the three-way catalyst 41a, the air-fuel ratio in the combustion chamber 14a is substantially equal to the stoichiometric air-fuel ratio (14.5 to 15. 0), and the air-fuel ratio of the exhaust gas discharged from the combustion chamber 14a may be in the range of 14.5 to 15.0. The amount of fuel here is the total amount of fuel including both diesel fuel and naphtha. This engine system performs air-fuel ratio feedback control over the entire operating range of the diesel engine 1. Thus, the engine system purifies the exhaust gas using the three-way catalyst 41a over the entire operation range of the diesel engine 1.

(Fuel injection control)
Next, fuel injection control executed by the PCM 10 will be described. As described above, this engine system supplies the diesel engine 1 mainly with naphtha for torque generation and diesel fuel for ignition mainly. When comparing the supply weight of naphtha with the supply weight of diesel fuel, the supply weight of naphtha is larger than the supply weight of diesel fuel. The diesel fuel is 10% or less by weight with respect to the total amount of fuel supplied to the combustion chamber 14a. Diesel fuel may be 5% of the total fuel weight, for example.

  Since naphtha has a boiling point lower than that of diesel fuel, it is easily vaporized in the combustion chamber 14a. Therefore, an air-fuel mixture that is homogeneous and close to the stoichiometric air-fuel ratio is formed in the combustion chamber 14a by naphtha. This suppresses the generation of soot and the generation of CO.

  On the other hand, naphtha has at least one of pressure and temperature leading to compression ignition higher than diesel fuel. In other words, naphtha has low ignitability. As described above, the diesel engine 1 is configured to have a low compression ratio of 13 or more and 18 or less, which is disadvantageous for fuel ignition.

  Therefore, in this engine system, diesel fuel excellent in ignitability is supplied into the combustion chamber 14a. Since the diesel fuel functions as an ignition fuel, the air-fuel mixture can be reliably compressed and ignited at a predetermined timing. An air-fuel mixture containing naphtha and diesel fuel burns.

  FIG. 3 illustrates the injection timing of naphtha and diesel fuel at a predetermined engine speed. The naphtha injector 19 attached to the intake port 16 injects naphtha into the intake port 16 during the intake stroke period when the intake valve 21 is open. The naphtha injection timing may be set within the period from the middle to the previous period of the intake stroke. Here, the first period and the middle period of the intake stroke may be the first period and the middle period when the intake stroke is divided into three equal periods of the first period, the middle period, and the second period, respectively. In the period from the middle to the previous period of the intake stroke, the intake flow in the cylinder 11a increases. By injecting the naphtha during this period, the naphtha can be diffused throughout the combustion chamber 14a by utilizing the intake air flow, and the air-fuel mixture can be homogenized.

  The diesel fuel injector 18 attached facing the combustion chamber 14a injects diesel fuel into the combustion chamber 14a during the compression stroke period. The injection timing of diesel fuel may be set in the vicinity of compression top dead center, specifically, within a period of 30 to 10 ° CA before compression top dead center. By doing so, the air-fuel mixture is compressed and ignited near the compression top dead center, and combustion can be started. If the combustion center of gravity of this combustion is 5 to 10 ° CA after compression top dead center, the thermal efficiency of the diesel engine 1 is increased. Moreover, since the geometric compression ratio of the diesel engine 1 is low as described above, it is possible to avoid premature ignition of the air-fuel mixture including naphtha before injecting diesel fuel. By adjusting the injection timing of the diesel fuel, the timing at which the air-fuel mixture is compressed and ignited can be adjusted.

  Here, in the present embodiment, diesel fuel is used as an ignition fuel in the medium load region (S1 region) and high load region (S2 region) of the operating range of the engine 1 shown in FIG. In the low load region (P region) and when the engine 1 is cold or forcedly started (CS region), diesel fuel is not supplied and the fuel is ignited by the ignition assist device so that the naphtha fuel becomes 100%. .

  When the engine load is low and the engine is cold, the combustion chamber temperature is low, so that it is difficult to obtain the desired ignitability even if diesel fuel is supplied. Moreover, the effective compression ratio of the engine is lowered by the above-described intake air late closing control, and the ignitability of the fuel is deteriorated.

  Therefore, in the low load region (P region) and when the engine 1 is cold or forcibly started (CS region), diesel fuel is not used and the fuel is ignited by the ignition assist device. Diesel fuel may be supplied to activate the ignition assist device.

(EGR control)
As described above, the PCM 10 supplies both naphtha and diesel fuel to the combustion chamber 14a in order to make the air-fuel ratio A / F of the combustion chamber 14a substantially the stoichiometric air-fuel ratio and to enhance the ignitability of the fuel. Controls the EGR valve 51a at least in the operating region on the low load side to recirculate a part of the exhaust gas from the exhaust passage 40 to the intake passage 30 (EGR).

  In the operating range of the engine 1 shown in FIG. 4, the middle load range (S1 range) and the high load range (S2 range) are operating ranges in which both naphtha and diesel fuel are supplied to the combustion chamber 14a, and at least the low load side thereof. The EGR is executed in the middle load range (S1 range), which is the operation range.

  In the present embodiment, the PCM 10 executes EGR in the low load range (P range), medium load range (S1 range), and high load range (S2 range) of the engine 1 shown in FIG. In the operating region where the engine load is high, the EGR rate (the ratio of the recirculated exhaust gas amount to the total amount of the recirculated exhaust gas amount and the intake air amount) is made lower than in the low operating region. Specifically, the EGR valve 51a is controlled so that the EGR rate is 40% in the low load region (P region) and the middle load region (S1 region), and in the high load region (S2 region), the EGR rate is The EGR valve 51a is controlled such that the EGR rate decreases as the load increases in the range of 30% to 0%.

(Intake slow closing control)
In order to make the air-fuel ratio A / F of the combustion chamber 14a approximately the stoichiometric air-fuel ratio, the PCM 10 performs intake late-closed control by the intake S-VT 71 in the engine low load region (P region) in addition to the above-described EGR control. Execute.

  Here, the throttle valve 36 is basically controlled for the EGR so as to obtain the intake negative pressure in the closing direction. That is, as a means for making the air-fuel ratio A / F substantially the stoichiometric air-fuel ratio (means for reducing the amount of fresh air introduced), it is possible to use the throttle control. Become.

  Therefore, in the present embodiment, in the air-fuel ratio control, the intake valve 21 is closed late (control in which the valve opening period in the compression stroke becomes longer).

  In FIG. 5, the phantom line indicates the valve timing that serves as a reference for the intake valve 21, and in this embodiment, the closing timing is 30 ° CA after the intake bottom dead center. The PCM 10 delays the closing timing of the intake valve 21 so that the intake air amount decreases as the engine load decreases. The solid line in FIG. 5 indicates the valve timing in which the closing timing of the intake valve 21 is delayed so as to be 90 ° CA after the intake bottom dead center. The closing timing of the intake valve 21 is defined as the time when the lift amount of the intake valve 21 is reduced to 0.4 mm.

<Specific examples of engine control>
As shown in FIG. 6, the detection signals of the sensors SW1 to SW11 are read, and it is determined whether or not the operating state of the engine 1 is in the CS range (during cold or forced start) (S1, S2). .

  When the operating state of the engine 1 is in the CS region, the process proceeds to step S3, and the wastegate valve 65a is opened. As a result, the exhaust gas bypasses the turbine 61b and is sent to the three-way catalyst 41a. Therefore, it is possible to avoid heat from being exhausted from the exhaust gas to the turbine 61b, which is advantageous for early temperature rise of the three-way catalyst 41a by the heat of the exhaust gas. In the subsequent step S4, the naphtha injector is supplied at a predetermined timing of the intake stroke so that the fuel supplied to the combustion chamber 14a becomes 100% naphtha and the air-fuel ratio becomes equal to or lower than the theoretical air-fuel ratio (A / F is 15 or less rich). 19 is driven. In the following step S5, the ignition device 20 is operated so that the fuel is ignited at a predetermined timing near the compression top dead center.

  In step S2, when the operating state of the engine 1 is not in the CS region, the process proceeds to step S6 to determine whether or not the operating state of the engine 1 is in the P region (low load region).

  When the operating state of the engine 1 is in the P region, the process proceeds to step S7, and the opening degree of the EGR valve 51a is controlled so that the EGR rate becomes 40%. In the subsequent step S8, the intake S-VT 71 is driven so that the closing timing of the intake valve 21 becomes a predetermined delayed closing timing. In the subsequent step S9, the fuel supplied to the combustion chamber 14a becomes naphtha 100% and the air-fuel ratio becomes the stoichiometric air-fuel ratio (A / F = 14.7), at a predetermined timing of the intake stroke, the naphtha injector 19 Is driven. In the subsequent step S10, the ignition device 20 is operated so that the fuel is ignited at a predetermined timing near the compression top dead center.

  In step S6, when the operating state of the engine 1 is not in the P range, the process proceeds to step S11 to determine whether or not the operating state of the engine 1 is in the S1 region (medium load region).

  When the operating state of the engine 1 is in the S1 region, the process proceeds to step S12, and the opening degree of the EGR valve 51a is controlled so that the EGR rate becomes 40%. Further, the valve timing of the intake valve 21 is controlled to be the reference timing (the phantom line in FIG. 5). In subsequent step S13, the naphtha injector 19 is driven at a predetermined timing of the intake stroke so that naphtha becomes 95% of the total amount of fuel supplied to the combustion chamber 14a and the air-fuel ratio becomes the stoichiometric air-fuel ratio. In the following step S14, the diesel fuel injector 19 is driven at a predetermined timing in the latter half of the compression stroke so that the diesel fuel becomes 5% of the total amount of fuel supplied to the combustion chamber 14a and the air-fuel ratio becomes the stoichiometric air-fuel ratio.

  In step S11, when the operating state of the engine 1 is not in the S1 region, the operating state of the engine 1 is in the S2 region (high load region). At this time, the process proceeds to step S15, and the opening degree of the EGR valve 51a is controlled so that the EGR rate becomes 30% or less. Further, the valve timing of the intake valve 21 is controlled to be the reference timing (the phantom line in FIG. 5). In subsequent step S13, the naphtha injector 19 is driven at a predetermined timing of the intake stroke so that naphtha becomes 95% of the total amount of fuel supplied to the combustion chamber 14a and the air-fuel ratio becomes the stoichiometric air-fuel ratio. In the following step S14, the diesel fuel injector 19 is driven at a predetermined timing in the latter half of the compression stroke so that the diesel fuel becomes 5% of the total amount of fuel supplied to the combustion chamber 14a and the air-fuel ratio becomes the stoichiometric air-fuel ratio.

<Control example>
FIG. 7 shows combustion control in the low load range (P range), medium load range (S1 range), and high load range (S2) at an engine speed of 1500 rpm in the engine 1 having a geometric compression ratio of 16. An example of the main specifications concerning is shown. In addition, the numerical value shown here is an illustration and can be changed according to a specification. Each numerical value indicates a reference value, and may include some variation in practical use.

  In the low load region, the EGR rate is 40%, and a relatively large amount of EGR gas is introduced into the combustion chamber. The intake valve closing timing (IVC) is set to 90 ° CA after the intake bottom dead center by performing intake late closing control. In addition to the reduction in effective compression ratio due to the slow intake closing control, it is difficult to achieve stable compression ignition, so forced ignition is performed by the ignition assist device. Only naphtha that can form a gas and is advantageous in reducing emissions is used.

  In the medium load region, the EGR rate is 40%, which is the same as that in the low load region, and a relatively large amount of EGR gas is introduced into the combustion chamber. The closing timing (IVC) of the intake valve is returned to the reference setting, and is 30 ° CA after the intake bottom dead center. Since stable compression ignition is possible, the ignition assist device is not used and combustion is performed by compression ignition. By adding 5% diesel fuel to naphtha, the main fuel, stable compression ignition can be performed. Then, since the relatively low temperature inert gas (EGR gas) cooled by the EGR cooler 52 is introduced into the combustion chamber, the steep rise of combustion after the mixture ignition is suppressed, and combustion noise increases, Increase in load is suppressed.

  In the high load range, the EGR rate is 30%, and the air amount is relatively increased in order to realize efficient combustion. The intake valve closing timing (IVC) is set to 30 ° CA after the intake bottom dead center, similarly to the middle load range, and stable compression ignition is possible, so that combustion is performed by compression ignition. As for the fuel, 5% diesel fuel and 95% naphtha are used as in the medium load range. And since the comparatively low temperature inert gas (EGR gas) cooled by the EGR cooler 52 is introduced into the combustion chamber, the pre-ignition of the air-fuel mixture (naphtha) is suppressed, and the ignition timing at which high engine torque can be generated. It can be.

  Even in the engine high speed range, the EGR rate is 30%, and the air amount is relatively increased in order to realize efficient combustion. The intake valve closing timing (IVC) is a timing at which the intake charge amount can be increased in the high speed range, and is approximately 45 ° CA after the intake bottom dead center. In the high speed range, the crank angle elapsed time from the intake stroke to the compression stroke is shorter than that in the low speed range, so that the naphtha supply period through the intake port 16 when viewed from the crank angle is long, while the naphtha supply is Although the time interval from the end point to the vicinity of the compression top dead center is remarkably shortened and the formation of a homogeneous mixture of naphtha is reduced, the deterioration of homogenization is suppressed by promoting the vaporization of naphtha by the reflux of EGR gas. There is no generation and the engine torque can be increased. Even in the high speed range, 5% diesel fuel and 95% naphtha are used, but the optimal ignition timing cannot be obtained due to the balance between the engine speed and the time interval from the supply of naphtha to the vicinity of compression top dead center. In this case, 100% naphtha may be supplied and forced ignition by the ignition assist device may be performed.

  As described above, when the EGR gas is recirculated in the high speed range, the soot increases when the main fuel is diesel fuel, so that the EGR gas cannot be recirculated. Is effective.

  FIG. 8 shows the relationship between the indicated mean effective pressure (IMEP) and the indicated fuel consumption rate (gross ISFC) in the embodiment according to the control specifications shown in FIG. 7 and the conventional example (diesel fuel 100%). In the embodiment, since the air-fuel ratio is substantially the stoichiometric air-fuel ratio, the illustrated fuel consumption rate is lower than the conventional example in which lean operation is performed at low load, medium load, and high load. That is, the engine system disclosed herein has improved engine torque and fuel efficiency compared to conventional diesel engine systems.

  FIG. 9 illustrates the relationship between the indicated mean effective pressure (IMEP) and the NOx emission amount in the above-described embodiment and the conventional example. In the conventional example, as the engine load increases, the NOx emission amount from the combustion chamber increases. On the other hand, the embodiment shows the exhaust amount in the tail pipe downstream from the three-way catalyst 41a. The air-fuel ratio of the exhaust gas discharged from the combustion chamber 14a is made the stoichiometric air-fuel ratio, and the three-way Since NOx is purified by the catalyst 41a, the NOx emission is substantially zero. In other words, the engine system disclosed herein has improved emission performance over the conventional diesel engine system.

  FIG. 10 shows the change of the in-cylinder pressure of the above embodiment with respect to the crank angle. According to the figure, both the case of IMEP = 852 (medium load range) and the case of IMEP = 1440 (high load range) using diesel fuel as ignition fuel up to around 20 ° CA after compression top dead center. There is a peak in cylinder pressure. It can be seen that the fuel (naphtha and diesel fuel) burns at the timing when the thermal efficiency is increased by ignition with diesel fuel.

  As described above, this engine system supplies naphtha for torque generation and diesel fuel for ignition to the diesel engine 1. Generation of soot and CO can be suppressed by forming an air-fuel mixture that is homogeneous and close to the stoichiometric air-fuel ratio in the entire combustion chamber 14a by naphtha having excellent vaporization performance. Further, with respect to the air-fuel mixture in the combustion chamber 14a, the weight ratio (A / F) of fuel and air including both naphtha and diesel fuel is set to a substantially stoichiometric air-fuel ratio, and exhaust gas discharged from the combustion chamber 14a. By setting the air-fuel ratio to the stoichiometric air-fuel ratio, the exhaust gas can be purified using the three-way catalyst 41 a provided in the exhaust passage 40. The post-treatment system for purifying NOx, which is necessary in the conventional diesel engine, can be omitted, and the engine system can be simplified and the cost can be reduced. Further, the engine system can improve the engine torque since the air-fuel ratio of the air-fuel mixture is substantially the stoichiometric air-fuel ratio compared to the conventional diesel engine that has been operating lean.

  Note that the invention disclosed herein is not limited to the above-described configuration. For example, the air-fuel ratio of the air-fuel mixture may be made leaner than the stoichiometric air-fuel ratio (for example, A / F = 30 to 45) in a low load region or light load region where the total fuel injection amount is small. When the air-fuel ratio is set to about 30 to 45, generation of NOx in the combustion chamber 14a can be suppressed. The naphtha (first fuel) can be directly injected into the combustion chamber.

  In the above configuration, the turbocharger 61 is mounted, but the turbocharger need not always be mounted. That is, in a conventional diesel engine, it is necessary to install a supercharger to make the air-fuel ratio at the time of combustion lean, reduce soot and CO, and reduce NOx using a high-cost selective reduction catalyst. However, by installing a plurality of superchargers, the supercharging pressure is greatly increased, the air-fuel ratio at the time of combustion is greatly leaned, and the compression ratio of the engine body is lowered to lower the combustion temperature, so that the soot and CO However, in the present invention, since the air-fuel ratio of the air-fuel mixture can be set in the range of 14.5 to 15.0 by supplying the first fuel, the three-way catalyst 41a is required. With this combination, NOx can be sufficiently purified along with reduction of soot and CO without relying on supercharging, so that an inexpensive engine without a supercharger can be provided.

1 Diesel engine 1 (engine body)
10 PCM10 (control unit)
14a Combustion chamber 16 Intake port 18 Diesel fuel injector (second fuel supply unit)
19 Naphtha injector (first fuel supply)
30 Intake passage 40 Exhaust passage 41a Three-way catalyst 51 Exhaust gas recirculation passage

Claims (9)

An engine body having a combustion chamber;
A first fuel supply unit configured to supply naphtha as the first fuel to the combustion chamber;
A second fuel supply unit configured to supply, to the combustion chamber, a second fuel having at least one of pressure and temperature leading to compression ignition lower than that of the first fuel and less likely to vaporize than the first fuel; ,
An exhaust gas recirculation passage for recirculating a part of the exhaust gas from the exhaust passage to the intake passage;
An ignition assist device for forcibly igniting the air-fuel mixture in the combustion chamber by spark ignition;
The first fuel supply unit and the second fuel supply unit are configured such that the first fuel is supplied to the combustion chamber in the entire engine operating range, and the first fuel is supplied in the medium load range and the high load range in the engine operating range. in addition the second fuel supplied to the combustion chamber, and many feed weight to the combustion chamber of the first fuel than the feed weight to the combustion chamber of the second fuel, the second fuel A controller that controls the weight supplied to the combustion chamber to be 10% or less of the total fuel weight supplied to the combustion chamber ;
The control unit closes an intake valve that opens and closes the opening of the combustion chamber after the intake bottom dead center of the engine, and closes the intake valve in a low load region of the engine operation region than in the medium load region and a high load region. Execute the intake late closing control that delays the timing,
The control unit operates the ignition assist device in the low load region where the intake air intake closing control is executed,
The control unit executes recirculation of exhaust gas through the exhaust gas recirculation passage in the high load region where the first fuel and the second fuel are supplied to the combustion chamber,
A compression ignition engine having a geometric compression ratio of 13 or more and 18 or less. In claim 1,
The control unit controls the first fuel supply unit and the second fuel supply unit so that the second fuel is supplied to the combustion chamber after the first fuel is supplied to the combustion chamber. A compression ignition engine characterized by that. In claim 1 or claim 2,
The compression ignition engine, wherein the second fuel includes diesel fuel. In any one of Claim 1 thru | or 3 ,
The compression ignition engine, wherein the second fuel has a boiling point higher than that of the first fuel. In any one of Claims 1 thru | or 4 ,
Before SL control section, when supplying the first fuel and the second fuel into the combustion chamber, the engine operating region of lower load side, to perform a reflux of exhaust gases by said exhaust gas recirculation passage Characteristic compression ignition engine. In any one of Claims 1 thru | or 5 ,
The controller is configured to perform exhaust gas recirculation through the exhaust gas recirculation passage in an engine operating region on a high speed side when supplying the first fuel and the second fuel to the combustion chamber. Ignition engine. In any one of Claims 1 thru | or 6 ,
In the exhaust passage, a three-way catalyst that purifies the exhaust gas is arranged,
The control unit controls the recirculation of the exhaust gas so that the air-fuel ratio A / F in the combustion chamber is in a range of 14.5 or more and 15.0 or less corresponding to a purification window of the three-way catalyst. Characteristic compression ignition engine. In any one of Claims 1 thru | or 6 ,
In the exhaust passage, a three-way catalyst that purifies the exhaust gas is arranged,
The compression ignition engine, wherein the control unit supplies the first fuel and the second fuel to the combustion chamber so that an air-fuel ratio of exhaust gas upstream of the three-way catalyst becomes a stoichiometric air-fuel ratio. In any one of Claims 1 thru | or 8 ,
The first fuel supply unit injects the first fuel into an intake port of the engine body,
The compression ignition engine, wherein the second fuel supply unit directly injects the second fuel into the combustion chamber.

Images