JP2002285849A - Combustion system for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set a proper average swirl ratio for improving an air use rate and reducing smoke in a combustion system for a direct injection type diesel engine provided with an injector having a plurality of two kinds of nozzle holes having different injection open angles. SOLUTION: This combustion system for the diesel engine is provided with a combustion chamber provided in the top part of a piston arranged in a cylinder so as to reciprocate and a fuel injection device having the injector for injecting fuel toward the combustion chamber. The plurality of two kinds of nozzle holes having the different injection open angles of the injector are alternately arranged in the direction of its circumference. The average swirl ratio of a swirl formed in the cylinder in a suction stroke is set to be 0.5 to 1.9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine combustion system for directly injecting fuel into a combustion chamber in a cylinder.

[0002]

2. Description of the Related Art Diesel engines are broadly divided into a sub-combustion chamber type (hereinafter referred to as a sub-chamber type) and a direct injection type (hereinafter referred to as a direct injection type). Direct-injection diesel engines, which have less heat loss than sub-chamber systems, are increasingly used.

[0003] In a direct injection type diesel engine, a combustion chamber is provided on the top surface of a piston in a cylinder, and fuel is directly injected into the combustion chamber. Then, when the air in the combustion chamber is compressed and reaches the ignition temperature, the fuel self-ignites and starts burning, the inside of the cylinder expands, and the piston is lowered to convert it into rotational energy.

[0004] As described above, a diesel engine does not have an ignition device (spark plug) unlike a gasoline engine, so it is necessary to compress the inside of a cylinder to a higher pressure than a gasoline engine. In particular, in a direct injection diesel engine, fuel is injected into a cylinder in a highly compressed atmosphere, so that the fuel injection pressure also becomes high. As the fuel injection pressure becomes high, the reach of the fuel spray in the combustion chamber also increases, and the amount of fuel adhering to the wall of the combustion chamber increases, which hinders atomization of the fuel and mixing with the air in the combustion chamber. Injection-type diesel engines may cause deterioration of exhaust gas (black smoke) despite a large excess air ratio.

On the other hand, in recent diesel engines, a pressure-accumulation type fuel injection system, which is not a distribution type fuel injection device that performs pressure feeding in response to one fuel injection with one pump operation, or a line type fuel injection device, has been developed. It has become widely adopted. As shown in FIG. 5, the pressure-accumulation type fuel injection system includes a supply pump 1 driven by an engine, a supply pump control valve 2 for adjusting a supply amount of the supply pump, and a high pressure fuel supplied from the supply pump 1 through a pipe 3. A common rail 4 for accumulating pressure, an injector 6 connected to the common rail 4 by a pipe 5, a solenoid valve 10 for ON / OFF control of the start and end of fuel injection of the injector, and a pipe for discharging fuel leaked from the injector to the fuel tank 8. 7, a pipe 9 for sending fuel from the fuel tank 8 to the supply pump 1, a pressure sensor 11 for detecting a pressure in the common rail, and a supply pump control valve 2.
And an engine control unit (ECU) 12 for controlling the engine including the solenoid valve 10 of the injector.

[0006] Engine control unit (ECU)
Reference numeral 12 inputs detection signals from an accelerator opening sensor (not shown) and an engine rotation speed sensor, and determines the fuel injection amount using the detection values of these sensors as parameters. Then, the engine control unit (ECU) 12
The target pressure of the common rail is determined from the fuel injection amount and the engine rotation speed, the pumping amount of the supply pump 1 is determined from the deviation from the current common rail pressure detected by the pressure sensor 11, and the supply amount of the supply pump is adjusted. The opening / closing timing of the solenoid valve 2 is controlled.

Fuel is accumulated in the common rail 4 at a pressure corresponding to the operation state of the engine, and fuel injection is performed by controlling ON / OFF of a solenoid valve 10 provided in the injector 6. The fuel injection amount is controlled by the pressure in the common rail and the injection period. Further, the fuel pressure of the common rail can be changed depending on the operation state of the engine, and the fuel pressure feeding of the supply pump 1 and the ON / OFF control of the solenoid valve 10 of the injector 6 are executed separately. Therefore, in the accumulator type fuel injection system, fuel can be injected at any timing and at any injection pressure, and the number of injections can be freely set.

As described above, the high-pressure direct injection diesel engine has a problem that the exhaust gas (black smoke) is rather deteriorated by the fuel injection pressure. As a countermeasure, attempts have been made to increase the diameter of the multiple injection holes and small injection holes in order to further atomize the spray. However, the overlap of adjacent sprays causes the air utilization rate in the combustion chamber to deteriorate, and the exhaust gas (black smoke) ) May be worsened, and it is not possible to uselessly increase the number of nozzles or reduce the diameter of the spray.

In consideration of the above-mentioned problem, as shown in FIG. 6, the injection hole of the injector b facing the combustion chamber a of the piston P is made multi-hole, and the opening angle of the injection is changed for each injection hole. Staggered arrangements have been proposed. This is to prevent the sprays from overlapping when the injector b has multiple injection holes, thereby preventing deterioration of exhaust gas, especially black smoke.

Conventionally, in a direct injection diesel engine, mixing of air and fuel in a combustion chamber is performed by a swirl of air flowing from an intake port, that is, a swirl. Therefore, as shown in FIG. 6, the shape of the combustion chamber has a deep shape with excellent swirl preservability, that is, a so-called deep dish combustion chamber, and a so-called reentrant type in which the piston top side of the combustion chamber is narrowed. The combustion chamber was the mainstream. However, when the fuel injection pressure is increased as in recent years, increasing the swirl does not always lead to improvement of exhaust gas, especially black smoke.The diameter of the injection hole is reduced to atomize the fuel spray, and the excess air ratio in the spray is reduced. Combustion systems have been diversified by improving the generation of smoke by increasing the number, and by using shallow dish-type combustion chambers with low heat loss for the purpose of further improving fuel efficiency.

[0011]

Regarding the injection hole of the injector irrespective of the shape of the combustion chamber, it is considered that it is effective to improve the exhaust gas to arrange the injection opening angle by changing the injection opening angle for each injection hole. Although it is important to consider swirl in order to carry out combustion in which sprays do not overlap and improve air utilization rate, conventionally, optimal combustion system conditions in relation to swirl have conventionally been determined. Not disclosed.

The present invention has been made in view of the above points,
The main technical problem is that in a direct injection diesel engine combustion system with an injector having two types of injection holes with different injection opening angles, an appropriate average swirl ratio to improve air utilization and reduce smoke is set. To set.

[0013]

In order to achieve the above technical object, according to the present invention, there is provided a combustion chamber provided at a top of a piston reciprocally disposed in a cylinder, and a combustion chamber provided in the combustion chamber. A fuel injection device having an injector for injecting fuel toward the diesel engine, wherein a plurality of two types of injection holes having different injection opening angles of the injector are alternately arranged in a circumferential direction. A combustion system for a diesel engine is provided, wherein an average swirl ratio of swirl formed in the cylinder during a stroke is set to be 0.5 to 1.9.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A combustion system for a diesel engine according to the present invention will be described below with reference to the embodiments shown in FIGS. FIG. 1 shows an injector 13 in which a plurality of fuel injection holes 16 and 17 each having a different injection opening angle with respect to a center axis (O) are alternately arranged, a piston 14, and a shallow dish type provided on the top of the piston 14. A combustion chamber 15 is shown. Note that the injection opening angle is a spray angle with respect to the center axis (O) of the injector and the axis of the sprays F1 and F2 based on the fuel injection holes 16 and 17. FIG. 2 is a view in which the tip of the injector 13 is viewed from below, and the injection holes 16 and 17 are alternately arranged in a circumferential direction in a so-called staggered manner.

FIG. 3 shows the relative value of smoke when the average swirl ratio of swirl formed in the cylinder during the intake stroke is changed from zero. Note that the relative values of smoke shown in FIG. 3 are values obtained by performing a simulation under the full load under the following fuel injection conditions. That is, the fuel injection conditions are as follows: the diameter of the injection holes 16 and 17 is 0.20 mm, the number of injection holes is 5 each for the injection holes 16 and 17 (a total of 10 injection holes), and the injection opening angle of the injection holes 16 (Β1) is β1 = 77.
5 °, the injection opening angle (β2) of the injection hole 17 is β2 = 60
°, the diameter of the combustion chamber 15 (diameter at the top of the piston) is 78 m
m. It is generally known that the average swirl ratio as an engine characteristic is a value mainly set by the shape of the intake port, and the shape of the intake port will not be described in detail here. The average swirl ratio will be described below.

The average swirl ratio (Ksm) is a value obtained by estimating the in-cylinder swirl ratio at the end of the intake stroke of the engine using the steady-state swirl ratio (Ks). The steady-state swirl ratio (Ks) is a value obtained by dividing the angular velocity of the air supplied from the intake port into the cylinder at the flow rate corresponding to the average piston velocity Cm [m / s] by the engine rotational angular velocity (from the intake port to the cylinder). (Angular velocity of supplied air ÷ engine rotational angular velocity). The average swirl ratio will be described below using mathematical expressions.

In determining the average swirl ratio Ksm used in the present invention, the following assumptions are made. (1) The fluid (intake) is incompressible and does not transfer heat. (2) Swirl is one vortex centered on the cylinder center. (3) The axial flow velocity of the swirl cylinder is assumed to be uniform. (4) The volume efficiency is 100%. (5) From (1), the flow rate is assumed to be proportional to the piston speed. (6) From (1), the integration interval is TDC (piston top dead center)
BDC (bottom dead center of piston). Assuming that the average piston speed is Cm, the steady swirl ratio is Ks, and the engine rotational angular speed is Ne, the angular speed ωs of the air supplied into the cylinder is expressed by the following equation (1).

[0018]

(Equation 1)

When the piston moves at the instantaneous piston speed C [m / s], the angular velocity of the air supplied from the intake port into the cylinder is ωs × C / Cm [rad / s]. Mass M of the disk (where a portion surrounded by the upper surface of the piston and the cylinder bore and the cylinder head lower surface), the cylinder bore radius R, the air density [rho, when a disc thickness h, the moment of inertia of the disc is ^{MR 2/2 = ρπR 4 h} / Therefore, the angular momentum per unit time supplied from the intake port into the cylinder when the piston is moving at the instantaneous piston speed C is expressed by the following equation (2).

[0020]

(Equation 2)

From equation (2), the angular momentum of intake air supplied into the cylinder during the entire intake stroke is expressed by equation (3).

[0022]

(Equation 3)

On the other hand, the moment of inertia of air in the cylinder at the end of the intake stroke (ρπR ⁴ h / 2) is expressed by the following equation ( ⁴ ).

[0024]

(Equation 4)

From the above equations (3) and (4), the angular velocity of the air in the cylinder at the end of the intake stroke is expressed by the following equation (5).

[0026]

(Equation 5)

If Equation 5 is converted into a unit of the swirl ratio, the average swirl ratio Ksm is expressed by the following Equation 6.

[0028]

(Equation 6)

Further, the instantaneous piston speed C and the average piston speed Cm are the crank angle θ, the distance r between the crank shaft O1 and the crank pin O2 shown in the model of the crankshaft, connecting rod and piston as shown in FIG. When expressed as a function of the distance CL between the crankpin axis O2 and the piston pin axis O3, the connection ratio η = r / CL, and the stroke S (= 2r), the following equations 7 and 8 are obtained.

[0030]

(Equation 7)

[0031]

(Equation 8)

From the above, the average swirl ratio Ksm can be obtained by the following equation (9).

[0033]

(Equation 9)

Next, the relationship between the average swirl ratio as engine characteristics and smoke will be discussed with reference to FIG.
In FIG. 3, the horizontal axis is the average swirl ratio, and the vertical axis is the smoke relative value. In the above-described fuel injection conditions, the smoke value when the average swirl ratio is set to 0 is plotted as 1, and all the smoke relative values are averaged. This is a relative value to the smoke value when the swirl ratio is 0. The average swirl ratio 0 is given by setting the intake port so that no swirl occurs in the intake air supplied to the cylinder. As is clear from FIG. 3, the peak value with the least smoke has an average swirl ratio of 0.9.
In this case, the average swirl ratio was reduced by about 85% as compared with the case where the average swirl ratio was set to 0. Conversely, it was also found that increasing the average swirl ratio further increased the smoke. When the average swirl ratio exceeded 2.2, the average swirl ratio was reduced to 0.
It turned out to be worse than if they had done so.

Further, as is apparent from FIG. 3, the average swirl ratio is 0.9 to 0.9 as compared with the case where the average swirl ratio is set to 0.
It can be seen that the smoke is halved in the range of the average swirl ratio of 0.5 to 1.9 with the low smoke peak around 1.6. Therefore, in a combustion system employing an injector in which two types of injection holes having different injection opening angles are alternately arranged in the circumferential direction, the above-described average swirl ratio is 0.5 to 1.9.
The design may be performed with the range of the target as a target.

[0036]

According to the present invention, in a diesel engine combustion system in which two types of injection holes having different injection opening angles are alternately arranged in the circumferential direction in the injector, the injection system includes Since the average swirl ratio of the swirls to be formed is set to be 0.5 to 1.9, it is possible to improve the air utilization rate in the combustion chamber and reduce black smoke.

[Brief description of the drawings]

FIG. 1 is a diagram of a combustion system configured according to the present invention.

FIG. 2 is a view showing an arrangement of injection holes of the injector shown in FIG. 1;

FIG. 3 is a diagram showing a relationship between an average swirl ratio and a smoke relative value of the combustion system shown in FIG. 1;

FIG. 4 is a model diagram of a crankshaft, a connecting rod, and a piston.

FIG. 5 is an overall view of an accumulator type fuel injection device.

FIG. 6 shows a conventional example in which the injection holes of the injector are arranged in a staggered manner.

[Explanation of symbols]

 13: Injector 14: Piston 15: Combustion chamber 16, 17: Injection hole

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 61/18 320 F02M 61/18 320D (72) Inventor Yoshinori Ishii 8 Tsuchiya, Fujisawa City, Kanagawa Prefecture, Ltd. F term in Isuzu Central Research Laboratory (reference) 3G023 AA03 AB05 AC05 AD02 AD06 AD29 3G066 AA07 AB02 AC09 BA24 CC06U CC28 CC48 CE21

Claims (1)

[Claims] 1. A fuel injection device having a combustion chamber provided on a top of a piston reciprocally disposed in a cylinder, and an injector for injecting fuel toward the combustion chamber. In a combustion system of a diesel engine in which two kinds of injection holes having different injection opening angles are alternately arranged in a circumferential direction, an average swirl ratio of swirl formed in the cylinder during an intake stroke is 0.5 to Set to be 1.9,
A combustion system for a diesel engine, characterized in that: