JPS61205322A - Fuel injection control method of direct-injection diesel engine - Google Patents

Abstract

PURPOSE:To promote the quick ignition of fuel and its complete combustion, by executing preliminary injection of a small amount of fuel in the vicinity of the intake top dead center prior to the main injection of fuel executed in the vicinity of the compression top dead center and forming a fuel vapor phase in the vicinity of the wall surface of a combustion chamber. CONSTITUTION:A piston 2 forms in its top surface a combustion chamber 8 consisting of a spherical hollowed part. While a cylinder head 3 mounts a fuel nozzle 9, and its jet 9a is opened in an tangential direction of the combustion chamber 8. Further an intake port 10 forms a swirl port. An engine in the above connects a fuel receiving port 9b of the fuel nozzle 9 with a fuel pipe 11 further the fuel pipe 11 with different fuel injection pumps 12a, 12b by each branch pipe 11a, 11b. And the engine sets the pump 12a to execute main injection from the fuel nozzle 9 in the vicinity of the compression top dead center of the piston 2 further the pump 12b to execute preliminary injection from the fuel nozzle 9 in the vicinity of the intake top dead center of the piston 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel injection control method for a direct injection diesel engine.

[Conventional technology]

A direct injection diesel engine that injects fuel through a fuel injection nozzle at compression top dead center during the intake stroke, causing self-ignition during the swirl created in the combustion chamber by a swirl boat installed in the cylinder head. Various combustion methods have been proposed (for example, see "Internal Combustion Engine" by Fujio Nagaya). Among them, the shape of the combustion chamber provided in the piston is approximately spherical, and the combustion chamber is created by a swirl boat. There is already a method (hereinafter referred to as a single-term fog method) in which fuel is injected into the swirl flow from an injection nozzle having a single injection hole toward the bottom of the combustion chamber in the tangential direction of the swirl flow. It is used in medium-sized and larger engines.

In the single-spray combustion method, as mentioned above, a single spray is injected in a swirl flow, and part of the fuel reaches the wall of the combustion chamber due to its penetration power and wets the wall, while the rest is It spreads inside the combustion chamber in a swirl flow. Therefore, in the high engine rotation range where the swirl flow velocity is high, the fuel that wets the wall surface quickly evaporates, and the fuel that does not reach the wall surface is quickly diffused in the high-velocity swirl flow, resulting in rapid ignition and combustion. This results in good combustion with low smoke concentration and high average effective pressure. However, in the low rotation range, the swirl flow rate is slow and the evaporation and diffusion of fuel is also slow, resulting in poor ignition and combustion, resulting in high smoke concentration and a large amount of unburned HC components, resulting in extremely poor combustion conditions. However, only a low average effective pressure can be obtained. These shortcomings at low speeds can be improved to some extent by measures such as strengthening the swirl flow or lengthening the fuel injection time, but the former measures lead to a decrease in volumetric efficiency at high speeds, and the latter measures The injection period becomes too long in the high-speed range, leading to poor mixing and deterioration of fuel efficiency.Therefore, the conventional method has the problem that it is not possible to lower the smoke concentration and obtain a high average effective pressure from low to low speeds. be.

[Means for solving problems]

According to the present invention, a substantially spherical combustion chamber is provided at the top of the piston, a swirl port is provided for generating a swirl flow during the intake stroke, and a single fuel injection nozzle is provided for injecting fuel in the tangential direction of the combustion chamber. A fuel injection control method is provided in a direct injection diesel engine, in which a small amount of preliminary injection is performed near intake top dead center prior to main injection performed near compression top dead center.

[For production]

The bottom wall of the combustion chamber was wetted by a small amount of preliminary injection performed near intake top dead center! During the suction stroke, the fuel is spread in the form of a film over the entire wall surface of the combustion chamber by the swirl flow from the swirl port. Next, when the compression stroke begins, the film-like fuel evaporates, forming a fuel vapor phase near the wall surface of the combustion chamber.

The vapor phase is ignited or ready to ignite before the piston reaches compression top dead center. The main injection is performed from the nozzle near the compression top dead center, and since the area near the wall surface is in a state of ignition or preparation for ignition, the fuel injected by the main injection is quickly ignited.

〔Example〕

To explain with reference to the drawings below, 1 is a cylinder block;
2 is a piston, 3 is a cylinder head, 4 is an intake valve, 5 is a valve spring, 6 is a sparkling shim, 7 is a camshaft, and 10 is an intake port.

A spherical recess is formed in the top surface of the piston 2, forming a combustion chamber 8. A fuel nozzle, designated by 9, is attached to the cylinder head 3, and its injection port 9a opens in the tangential direction of the combustion chamber 8. 'The intake boat 10 is a so-called swirl board, and can form an intake swirl. ``The fuel nozzle 9 has its fuel receiving port 9b connected to a fuel pipe 11, and the fuel pipe 11 is a branch pipe 11a.

Separate fuel injection pump 12a by 11b.

12b. The first fuel injection pump 12a is
The main injection is performed from the fuel nozzle 9 near the compression top dead center of the piston 2, and the second fuel injection pump 12b performs preliminary injection from the fuel nozzle '9 near the intake top dead center of the piston 2. do. FIG. 2 shows the first pump 12a and the second pump 1.
2b shows the fuel injection characteristics versus crank angle. Here, the crank angle 0° is taken as the intake top dead center, and the crank angle is 18
o° is the intake bottom dead center, and a crank angle of 360° is the compression top dead center. Although not shown in Fig. 2, a crank angle of 540° is the explosion bottom dead center. Near the intake top dead center (5-10°C after the intake top dead center), the second pump 12b ■ A small amount of preliminary injection from nozzle 9 depending on the fuel.

is carried out, and the main injection is performed from the nozzle 9 using the fuel from the first pump 12a near the compression top dead center.As shown in FIG. The preliminary injection amount' is approximately 10% of the main injection amount by the first pump.
It is about 30%. In addition, the injection timing is set to i, which has a valve overlapping period near the intake top dead center, and after the exhaust valve closing period □. That is, it is approximately □ approximately 10' CA after top dead center. Furthermore, it is desirable that the injection period be as long as possible in order to improve the wall surface adhesion distribution of the injected fuel, but in internal combustion engines using this fuel system, a bottle nozzle is usually used, and the crank angle
The temperature should be approximately 1°℃.

Incidentally, the fuel injection pumps 12a and 12b may be of a sub-type or other types, and their rotational shafts are connected to the pulley 16a.
, 16b and a belt 18 to the crankshaft. A difference in injection timing of approximately 360°C is required between main injection and preliminary injection. For example, in the case of a 4-stroke, 4-cylinder engine, the injection nozzle of the first cylinder is
The injection pipe for the first cylinder of a and the fourth cylinder of the second injection pump are connected. First injection pump 12
a is adjusted to have almost the same rotation speed-injection amount characteristics and injection timing characteristics as a normal compression ignition diesel engine, while the second injection pump 12b is adjusted to have approximately the same rotation speed-injection amount characteristics and injection timing characteristics as a normal compression ignition diesel engine, while the second injection pump 12b The injection amount characteristics and injection timing are adjusted to inject a small amount of fuel. Figure 4 (a) shows the second
Examples of the rotational speed-injection amount characteristic of the injection pump 12b and the injection timing characteristic are shown in (b).

The fuel injection control method of the present invention will be explained below while following the operation of the engine.

At the intake top dead center of the piston 2, a small amount of fuel is discharged from the second fuel injection pump 12b through the fuel injection nozzle 9 into the fuel chamber 8.
is introduced from the tangential direction as shown in Fig. 5i. Second
Since the fuel injected by the discharge action of the injection pump 12b is a small amount, the injection pressure is weak and the penetration force is small, but since the ambient temperature is low, it does not evaporate and remains a liquid.
Furthermore, since almost no swirl flow has been generated in the fuel chamber yet, the swirl flow reaches the combustion chamber wall surface 8' and is deposited there as shown in f.

In FIG. 6, during the intake process, the piston 2 descends and is introduced from the intake port through the intake valve 4 while forming a swirl S. Therefore, a swirl S is also induced in the piston combustion chamber 8. During the intake process, the ambient temperature is low and the fuel adhering to the wall surface is spread in a film form f' by the swirl S on the combustion chamber wall 8' while remaining in a liquid state.

Next, when entering the compression stroke shown in Fig. 7, the piston 2 moves upward, and the temperature of the atmosphere rises due to the compression.As a result, the fuel that has spread on the combustion chamber wall 8' evaporates, but the swirl S causes the center of the combustion chamber to rise. Diffusion toward the combustion chamber is suppressed, and a fuel vapor phase V is formed near the wall surface of the combustion chamber.

Main injection of fuel pumped by the first pump 12a is performed near compression top dead center (360° C.A). This main injection is injected toward the vapor phase V near the wall surface of the combustion chamber, and this vapor phase has already been ignited near the compression top dead center and is in a coal-coated state or has completed the ignition preparation stage, so the main injected fuel is It is activated near the wall surface 8' and ignites quickly. As a result, the above-mentioned problems of extremely poor ignition conditions such as the low rotational speed range of the engine, slow progress of combustion, and high smoke concentration even at low loads have been solved, and the smoke concentration remains low from low to high speeds. A low and high average effective pressure will be obtained.

In the first embodiment described above, it is assumed that the fuel injection nozzle 9 has a one-step valve opening pressure. Alternatively, a two-stage open pressure nozzle can be used. The two-stage valve opening pressure nozzle 9 is the eighth
As shown in the figure, two springs 20 and 22 are provided, and the first stage lift of the needle 24 is performed until it hits the stopper 24 at the first valve opening pressure determined by the first spring 20.
Second valve opening pressure determined by spring 22 (>first valve opening pressure)
The second lift will take place. During preliminary injection at intake top dead center, the bridge is held only by this first stage lift. Since this first-stage injection has a small lift, the nozzle flow rate coefficient can be kept low, and if the preliminary injection amount is the same as in the first embodiment, the injection engine can be extended as shown in FIG. 3I'.

Therefore, there is an advantage that the fuel can reach the wall surface of the combustion chamber over a wider range. The main injection is performed in the second stage near the top dead center of the compression.The characteristic number at the time of injection at 0 is 3°↓ wealth = 2 degrees; tFRI'Jt'l+# 7. 'e
Two such as 12a and 12b are used for IllJj injection and preliminary injection. However, it is not limited to using only two fuel injection pumps;
, =□ Can be shared with main injection. In this case, if a sub-type pump is used, two cam and piston combinations are required for each cylinder, one for preliminary injection and one for main injection.

〔effect〕

A small amount of fuel is preliminarily injected near the intake top dead center to prevent it from adhering to the combustion chamber wall, and during the compression stroke, the fuel is evaporated and a strong swirl generated within the combustion chamber creates steam near the combustion chamber wall. By forming a phase, main injection is performed on the vapor phase at compression top dead center, and rapid ignition combustion occurs, the smoke concentration is low from low rotation range to high rotation range, and high average effective pressure is achieved. can get. In addition, starting performance has been improved, and the blue color when starting,
White smoke is reduced. Furthermore, THC due to wall quenching
CO is also reduced by reducing production and promoting complete combustion. Moreover, rapid ignition reduces NOx.

[Brief explanation of the drawing]

FIG. 1 is an overall diagram of the fuel injection system of this invention. FIG. 2 is an injection rate characteristic diagram with respect to crank angle in the first embodiment of the present invention. FIG. 3 is an injection rate characteristic diagram in the second embodiment. FIG. 4 is a diagram showing (a) the injection amount and (b) the injection timing characteristics in preliminary injection, respectively. FIG. 5, FIG. 6, and FIG. 7 are perspective views illustrating details of the present invention in each step. FIG. 8 is a sectional view of the nozzle part of the two-stage injection nozzle. 2... Piston 4... Intake valve 8... Combustion chamber 9... Fuel injection nozzle lO... Intake boat

Claims (1)

[Claims] In a direct injection diesel engine that is equipped with a roughly spherical combustion chamber at the top of the piston, a swirl port that generates a swirl flow during the intake stroke, and a single fuel injection nozzle that injects fuel in the tangential direction of the combustion chamber. , a fuel injection control method in which a small amount of preliminary injection is performed near intake top dead center prior to main injection performed near compression top dead center.