JP2001107809A - Gas fuel internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark ignition type natural gas internal combustion engine provided with no throttle valve and control a load by an injection amount and to improve fuel consumption in a low load area. SOLUTION: This internal combustion engine comprises a main fuel injection valve 11 to inject natural gas in the cavity combustion chamber 14 of a piston 7; an auxiliary fuel injection valve 12 to inject natural gas to an ignition chamber 9; and an ignition plug 10 situated at the ignition chamber 9. Since, during idling, fuel is fed only from the auxiliary injection valve 12 and ignited and burnt in the ignition chamber 9, stable operation at a high excess air factor is practicable. At a partial load area, fuel is injected from the main fuel injection valve 11, and before fuel is excessively diffused in a cavity combustion chamber 14, flame generated due to combustion in the ignition chamber 9 is injected through a communication hole 13 for ignition and combustion. At a total load area, fuel is injected from the main fuel injection valve 11 in the vicinity of a bottom dead center and brought into a state approximately equal to premixture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark-ignition gas-fueled internal combustion engine which uses a gas fuel such as natural gas to realize lean combustion.

[0002]

2. Description of the Related Art At present, many large vehicles are driven by a diesel engine. However, such a medium to large diesel engine is technically difficult to reduce NOx and exhaust particulates as air pollutants. In recent years, an internal combustion engine using natural gas as a fuel has been attracting attention as a substitute for emitting a large amount of carbon dioxide that causes global warming.

[0003] As a gas-fueled internal combustion engine using compressed natural gas (CNG) or liquefied natural gas (LNG) as a fuel, fuel is supplied into an intake pipe upstream of an intake valve, and a spark plug is provided, similarly to a general gasoline engine. In this case, a throttle valve for restricting the amount of intake air according to the load is required in the intake passage (for example, see Japanese Patent Application Laid-Open No. H10-61460). .

[0004]

The natural gas internal combustion engine of this type can reduce NOx and exhaust particulates as compared with a diesel engine, but is inferior to a diesel engine in terms of thermal efficiency. In particular,
Since there is a pumping loss due to the throttle valve, the thermal efficiency is lower than that of the diesel engine in a low load region, and for example, when the vehicle interior is being cooled or heated in an idling state, the fuel efficiency is significantly deteriorated. In the partial load range, the diesel engine burns with an ultra-lean mixture, but the flammability limit of the natural gas internal combustion engine according to the above method is that the excess air ratio λ is 1.8.
And cannot be burned with a leaner mixture.
In practice, λ = 1.6 is the practical limit from the viewpoint of engine stability. Therefore, there is a limit to the improvement in fuel efficiency in the partial load range.

[0005] As described above, the fuel efficiency is inferior to that of a diesel engine in an area where the load is small, which is a major factor hindering the spread of a natural gas internal combustion engine. Also, from the viewpoint of reducing carbon dioxide, natural gas emits less carbon dioxide per calorific value, but consumes more fuel, so that the merits of reducing carbon dioxide are reduced as a whole.

A sub-chamber is provided separately from the main combustion chamber, and a relatively rich air-fuel mixture is generated in the sub-chamber, ignited by a spark plug, and the main combustion chamber is ignited by a flame ejected from the communication hole into the main combustion chamber. A sub-chamber type gas-fueled internal combustion engine in which a relatively thin air-fuel mixture in a room is ignited has also been proposed (for example, Japanese Patent Application Laid-Open No. H11-178814). It is intended to promote the combustion in the main combustion chamber using swirl,
If the throttle valve is not provided, it is necessary to ignite a super-lean homogeneous air-fuel mixture in an idling or low load range, and stable operation cannot be realized at all.

[0007]

In order to solve the above-mentioned problems, a gas-fueled internal combustion engine according to the present invention has a main fuel injection valve for supplying gas fuel to a main combustion chamber in a cylinder, and a cylinder head. An ignition chamber formed in the main combustion chamber and communicating with the main combustion chamber through a communication hole, an auxiliary fuel injection valve for supplying gas fuel to the ignition chamber, an ignition plug provided in the ignition chamber, and engine operating conditions. Accordingly, a control means for optimally controlling the fuel injection amount and the injection timing of the main fuel injection valve and the sub fuel injection valve, and the ignition timing of the ignition plug, respectively, is provided.

More specifically, the throttle valve is not provided in the intake system, and the load of the internal combustion engine is controlled by the total fuel injection amount of the main fuel injection valve and the auxiliary fuel injection valve. It is supposed to be.

That is, in the gas-fueled internal combustion engine of the present invention, gaseous fuel such as natural gas is injected and supplied into the ignition chamber, and the mixture formed here is ignited by the ignition plug. As a result, combustion occurs in the ignition chamber, and a flame is blown out toward the main combustion chamber through the communication hole. In addition, gas fuel is injected into the main combustion chamber from the main fuel injection valve at an appropriate timing before the flame is jetted out, and before the fuel is diffused beyond the lean burn limit, the flame causes Combustion in the main combustion chamber starts. Therefore, stable combustion with a high excess air ratio as a whole is possible.

According to the present invention, the cavity combustion chamber constituting the main combustion chamber is recessed in the top surface of the piston, and the top end of the communication hole is located at the top dead center of the piston. It is desirable to open toward.

By providing the cavity combustion chamber in this way, the gas fuel injected from the main fuel injection valve stays in the cavity combustion chamber without excessively diffusing. Then, the flame ejected from the communication hole goes into the cavity combustion chamber, and the air-fuel mixture formed here ignites. Therefore, even if the excess air ratio is high as a whole,
Reliable ignition combustion is possible in the main combustion chamber. In addition, the squish area left around the cavity combustion chamber generates a squish flow near top dead center, thereby promoting combustion in the main combustion chamber.

According to the fourth aspect of the present invention, the injection amount of the main fuel injection valve becomes zero during idling, and all the necessary fuel amount is injected from the auxiliary fuel injection valve.

By performing the idling operation only with the fuel of the auxiliary fuel injection valve as described above, even if the combustion becomes extremely lean as a whole without the throttle valve, the ignition chamber is kept in the ignition chamber beyond the lean combustion limit. Since a sufficiently rich air-fuel mixture exists, stable operation is possible.

According to a fourth aspect of the present invention, the fuel injection amount of the auxiliary fuel injection valve is minimized for ignition in a low load region which leads to idling, and the remaining fuel determined by the load is reduced. The quantity is injected from the main fuel injector.

That is, when the fuel injection of the main fuel injection valve is started as it is when the load is slightly increased from idling, a certain minimum injection amount is determined for the main fuel injection valve. Cannot be performed, a step occurs in the total fuel injection amount, and the torque becomes discontinuous. Therefore, in the invention of claim 5, when the engine shifts from idling to the low load range, the fuel injection amount of the auxiliary fuel injection valve temporarily decreases to a minimum necessary for ignition, and the remaining fuel is mainly injected from the main fuel injection valve. It is injected into the combustion chamber. As a result, the total fuel injection amount can have a continuous characteristic from the idling to the low load region.

The fuel injection start timing and ignition timing of the sub-fuel injection valve during idling, and the fuel injection start timing and ignition timing of the main and sub-fuel injection valves in the partial load range are determined by the engine rotation. Depending on the engine speed, the higher the engine speed is, the more advanced it is set.

Further, in the present invention, the fuel injection start timing of the main fuel injection valve is earlier than the fuel injection start timing of the sub fuel injection valve, and the difference (τ) between the two start timings is large, so that the load is large. It is given as much as possible.

Further, according to the present invention, at the time of full load, the fuel injection start timing of the main fuel injection valve is at the beginning of the compression stroke.

That is, when the load increases and the fuel injection amount increases, a partially rich region is likely to occur in the main combustion chamber. Therefore, under operating conditions where the fuel injection amount is large, it is desirable to inject fuel earlier so as to promote mixing with air. In particular, at the time of full load, it is preferable to make the total air-fuel mixture approach the state of λ = 1 as uniformly as possible.
The fuel injection of the main fuel injection valve is started in the early stage of the compression stroke to bring the state close to premixing.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows the overall configuration of a gas-fueled internal combustion engine according to the present invention. The internal combustion engine body 1 is configured as a four-cycle engine, and a piston 7 can slide within a cylinder 6. , And an exhaust valve 3 for opening and closing the intake passage 2 and an exhaust valve 5 for opening and closing the exhaust passage 4 are provided for each cylinder. The intake passage 2
In addition, no throttle valve is provided. The internal combustion engine main body 1 includes an ignition chamber 9 separately from a main combustion chamber 8 formed by a piston 7 in a cylinder 6, and an ignition plug 10 is arranged facing the ignition chamber 9.

A main fuel injection valve 11 for injecting gaseous fuel into the main combustion chamber 8 is provided at the center of the upper surface of the main combustion chamber 8, and an auxiliary fuel injection valve is provided in the ignition chamber 9. 12 are provided.

As shown in FIG. 2, the ignition chamber 9 is formed inside the cylinder head 15 at a position deviated to one side of the cylinder bore, and has a communication hole 13 extending obliquely toward the center of the cylinder bore. Through the main combustion chamber 8. The auxiliary fuel injection valve 12 is located above the ignition chamber 9, and the ignition plug 10 faces the upper end of the communication hole 13 from the side of the ignition chamber 9. The main fuel injection valve 11
It is arranged vertically substantially along the center axis of the cylinder bore, and supplies gas fuel from the center of the cylinder bore to the entire circumference. At the center of the top surface of the piston 7, a deep dish-shaped cavity combustion chamber 14 is recessed, and the tip injection hole of the main fuel injection valve 11 is located at the center of the cavity combustion chamber 14. . At the top dead center position of the piston 7, most of the volume of the main combustion chamber 8 is
Occupied by. The lower end of the communication hole 13 opens toward the cavity combustion chamber 14 at the top dead center position of the piston 7.
In other words, the communication hole 13 is not blocked on the top surface of the piston 7 which is a squish area remaining around the cavity combustion chamber 14. In the case where the cylinder bore diameter is large, for example, it is desirable to form a plurality of the communication holes 13 so that the flame is ejected toward a plurality of locations of the cavity combustion chamber 14.

Each of the main fuel injection valve 11 and the auxiliary fuel injection valve 12 is of a mechanical type that opens and closes by hydraulic pressure, and generates hydraulic pressure for opening each of them as shown in FIG. Valve control actuator 2 for
1 and 22 are provided respectively. The injection valve control actuators 21 and 22 generate a hydraulic pressure in response to the injection valve pulse signal output from the engine control unit 23, and open the injection valves 11 and 12 for substantially the same period as the injection valve pulse signal. It is to let. Further, in this embodiment, as the gas fuel have been used compressed natural gas (CNG) is gas stored in the fuel tank 24 is pressure regulated to 70kg / cm ² ~100kg / cm ² approximately constant pressure It is introduced into each of the injection valves 11 and 12 via a pressure regulator 25 and a surge tank 26 for suppressing pressure pulsation. Therefore, when the main fuel injection valve 11 or the auxiliary fuel injection valve 12 is opened based on the injection valve pulse signal, the natural gas is injected by its own pressure, and the amount of the gas substantially proportional to the pulse width of the injection valve pulse signal is increased. Is supplied.

The engine control unit 23 has a crank angle sensor 27 for detecting the rotational speed of the internal combustion engine.
And the detection signal of the accelerator opening sensor 28 for detecting the depression amount of the accelerator pedal as a load, and based on these operating conditions, the main fuel injection valve 11 and the sub fuel injection valve 12 The respective injection amounts and injection timings, and the ignition timing of the ignition plug 10 are optimally controlled.

As the volume of the ignition chamber 9 increases, the heat loss increases and the thermal efficiency of the engine decreases. However, in order to dispose the auxiliary fuel injection valve 12 and the ignition plug 10, the minimum size is is necessary. Therefore, the volume is set in the range of 3 to 20%, more preferably 5 to 12% with respect to the volume of the entire combustion chamber at the top dead center position of the piston 7. The cross-sectional area D of the communication hole 13 is optimally set according to the volume V of the ignition chamber 9 so that D / V is within a predetermined range. The size of the communication hole 13 determines the position at which the flame reaches the main combustion chamber 8 and the speed of the flame.

Next, specific control under each operating condition will be described. FIG. 3 shows the respective injection amounts of the respective fuel injection valves 11 and 12 corresponding to the load, and the total injection amount which is the sum of both.

First, in idling, the ignition chamber 9
The gas fuel is injected only from the auxiliary fuel injection valve 12 provided in the main fuel injection valve 11, and the injection amount of the main fuel injection valve 11 becomes zero. The fuel injection timing (injection start timing) of the auxiliary fuel injection valve 12 is set near top dead center, specifically, 20 ° to 70 ° BTDC. The ignition timing is 50 ° to 5 ° C from the injection start timing.
A Set to the position delayed. Here, the higher the idling speed, the earlier the fuel injection timing. In the present invention, since the throttle valve is not provided, the excess air ratio λ becomes extremely high as a whole at the time of idling, but the fuel is supplied only to the ignition chamber 9 so that the ignition chamber 9 can be ignited. The air-fuel mixture is reliably formed, and stable operation is possible. This makes it possible to obtain fuel efficiency close to that of a diesel engine during idling.

Next, in the partial load region, prior to the fuel supply on the ignition chamber 9 side, gas fuel is injected and supplied from the main fuel injection valve 11 of the main combustion chamber 8 toward the cavity combustion chamber 14,
The flame that is jetted from the ignition chamber 9 through the communication hole 13 into the air-fuel mixture formed in the cavity combustion chamber 14,
Ignition is performed. The injection amount of each fuel injection valve 11, 12 is:
As shown in FIG. 3, control is performed so that the total injection amount according to the load, that is, the accelerator opening, is obtained. In particular, when shifting from idling to the low load region, as is apparent from FIG. 3, the fuel injection amount of the auxiliary fuel injection valve decreases from the fuel amount required for idling to the minimum amount required for ignition,
The injection amount of the main fuel injection valve 11 is added to this. Therefore, despite the fact that the minimum injection amount of the main fuel injection valve 11 is a certain amount, the total injection amount continuously changes from idling to a low load range, and the torque change is smoothly continuous. Become. In the example of FIG. 3, the fuel injection amount of the auxiliary fuel injection valve 12 is constant in a region excluding idling, but may be gradually reduced according to the load. When the load increases and the total injection amount increases, the overall excess air ratio λ decreases. Therefore, even if the fuel injection amount of the auxiliary fuel injection valve 12 is gradually reduced, ignition and combustion can be sufficiently performed.

FIG. 4 shows the fuel injection timing and ignition timing of the main fuel injection valve 11 and the auxiliary fuel injection valve 12 in the partial load range. As shown in FIG. Gas fuel is injected into the chamber 14, and fuel injection of the auxiliary fuel injection valve 12 is performed with a delay. Then, ignition is normally performed during the fuel injection period of the auxiliary fuel injection valve 12. These timings are set so that the gaseous fuel injected from the main fuel injection valve 11 into the cavity combustion chamber 14 is ignited by igniting a flame from the ignition chamber 9 before diffusing beyond the lean combustion limit. It is set according to. Each injection start timing is earlier as the engine speed is higher. Further, the delay period τ from the injection start timing of the main fuel injection valve 11 to the injection start timing of the sub fuel injection valve 12 is given larger as the load increases. In other words, when the load is small and the injection amount is small, the fuel is injected from the main fuel injection valve 11 near the top dead center so that the fuel is not excessively diffused in the cavity combustion chamber 14, and the load is large. When the amount is large, injection is started early to promote mixing with air so as not to generate a partially rich region in the cavity combustion chamber 14.

In the full load range, the fuel injection start timing of the main fuel injection valve 11 is the earliest, and is at the beginning of the compression stroke, that is, near the bottom dead center. FIG. 5 shows the fuel injection timing and the ignition timing in this full load range. By injecting fuel from the main fuel injection valve 11 near the bottom dead center in this way, mixing with air is promoted, and a state close to premixing is achieved. Therefore, all the mixture is uniformly λ
= 1 and good combustion is ensured. Note that, in the full load range, λ = 1, so that even if the fuel injection from the auxiliary fuel injection valve 12 is stopped, the ignition is sufficient.
It is desirable to inject a minimum amount of fuel in the same manner as in the partial load range, in order to avoid discontinuous characteristics during transition. Further, the ignition timing is controlled to an advanced position, that is, an MBT point where the maximum torque is obtained in a range where knocking does not occur.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a 1000 cc single cylinder internal combustion engine, 8
An ignition chamber 9 having a percent volume ratio was provided and configured as shown in FIG. The injection start timing of the auxiliary fuel injection valve 12 in the ignition chamber 9 is 50 ° BTDC, and the ignition timing is 18 ° to 4 ° BTD.
When the idling operation was performed with only the fuel of the auxiliary fuel injection valve 12 as C (the higher the rotation speed, the more the advance angle), as shown in FIG. 6, the excess air ratio λ was about 2.5 to 3.5. Stable operation was possible with an ultra-lean mixture. It is also shown that self-sustaining operation is possible at around 250 rpm to 300 rpm. Therefore, it is sufficiently possible to start the internal combustion engine by cranking using a general starter motor.

[0033]

As is apparent from the above description, according to the gas-fueled internal combustion engine of the present invention, the injection start timing and the injection amount of the main fuel injection valve of the main combustion chamber and the auxiliary fuel injection valve of the ignition chamber are determined. By performing the optimal control, a stable operation at a high excess air ratio can be performed without using an intake throttle such as a throttle valve, and a high thermal efficiency comparable to a diesel engine can be obtained in a low load region including idling. Therefore, it is possible to improve the practical fuel consumption, which is a major drawback of the internal combustion engine using a gas fuel such as natural gas.

In particular, by operating only the fuel of the auxiliary fuel injection valve on the ignition chamber side at the time of idling, stable idling operation with a high excess air ratio becomes possible, and fuel efficiency at the time of idling is improved. .

When the load is increased from the idling operation in which the fuel injection of the main fuel injection valve is stopped to start the fuel injection of the main fuel injection valve, the fuel injection of the auxiliary fuel injection valve is started. By making the fuel amount lower than at the time of idling, the connection from idling to the low load region can be made very smooth.

According to the seventh aspect of the present invention, by setting the delay period from the fuel injection start timing of the main fuel injection valve to the fuel injection start timing of the sub fuel injection valve according to the load, the fuel amount, that is, An optimal flame ejection timing according to the excess air ratio can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing the overall configuration of a gas-fueled internal combustion engine according to the present invention.

FIG. 2 is an enlarged sectional view of an ignition chamber portion.

FIG. 3 is a characteristic diagram showing a relationship between an injection amount and a load.

FIG. 4 is a time chart showing a fuel injection timing and an ignition timing in a partial load region.

FIG. 5 is a time chart showing a fuel injection timing and an ignition timing in a full load range.

FIG. 6 is a characteristic diagram showing the relationship between the number of revolutions and the excess air ratio during idling operation in the internal combustion engine of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine main body 8 ... Main combustion chamber 9 ... Ignition chamber 10 ... Spark plug 11 ... Main fuel injection valve 12 ... Sub fuel injection valve 13 ... Communication hole 14 ... Cavity combustion chamber

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F02D 41/08 330 F02D 41/08 330A 41/34 41/34 C 43/00 301 43/00 301H 301J 301B F02F 3 / 26 F02F 3/26 A F02P 5/15 F02P 5/15 CF term (reference) 3G022 AA01 CA03 CA06 CA07 CA08 CA09 DA01 GA01 GA05 GA08 3G084 AA05 BA13 BA15 BA17 CA00 CA03 CA09 DA02 DA13 EB08 FA10 FA33 FA38 3G092 AA07 AB07 AB08 BA09 BB01 BB06 EA03 EC09 FA24 GA03 GA04 GA05 GA16 HE03Z HF08Z 3G301 HA04 HA05 HA22 JA02 KA06 KA07 KA08 KA23 LA00 LB04 LB05 MA11 MA18 MA23 NC02 PE01Z PE03Z PF03Z

Claims (8)

[Claims] A main fuel injection valve for supplying gaseous fuel toward a main combustion chamber in a cylinder; an ignition chamber formed in a cylinder head and communicating with the main combustion chamber through a communication hole; A fuel injection valve for supplying gaseous fuel to the fuel tank, an ignition plug provided in the ignition chamber, and a fuel injection amount, an injection timing of the main fuel injection valve and the auxiliary fuel injection valve according to engine operating conditions, and Control means for optimally controlling the ignition timing of each spark plug. 2. The load of the internal combustion engine is controlled by a total fuel injection amount of the main fuel injection valve and the auxiliary fuel injection valve without having a throttle valve in the intake system. Gas fueled internal combustion engine. 3. A cavity combustion chamber constituting the main combustion chamber is recessed in a top surface of a piston, and a tip of the communication hole is opened toward the cavity combustion chamber at a piston top dead center. The gas-fueled internal combustion engine according to claim 1 or 2, wherein: 4. The gas according to claim 1, wherein the injection amount of the main fuel injection valve becomes zero during idling, and all the necessary fuel amount is injected from the auxiliary fuel injection valve. Fuel internal combustion engine. 5. In a low load range that leads to idling, the fuel injection amount of the auxiliary fuel injection valve becomes a minimum necessary for ignition,
5. The gas-fueled internal combustion engine according to claim 4, wherein the remaining fuel amount determined according to the load is injected from the main fuel injection valve. 6. The fuel injection start timing and the ignition timing of the main and auxiliary fuel injection valves during idling and in a partial load range are set to be more advanced as the engine speed increases according to the engine speed. The gas-fueled internal combustion engine according to any one of claims 1 to 5, characterized in that: 7. The fuel injection start timing of the main fuel injection valve is earlier than the fuel injection start timing of the sub fuel injection valve, and the difference (τ) between the two start timings is given larger as the load increases. The gas-fueled internal combustion engine according to claim 1. 8. The gas-fueled internal combustion engine according to claim 7, wherein at full load, the fuel injection start timing of the main fuel injection valve is at the beginning of the compression stroke.