JP2003097274A - Fuel combustion device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To safely intensity a vertical eddy generating in a reentrance type cavity 8 formed at the upper part of a piston 1 even under an operation condi tion in which the temperature in the cavity is relatively high. SOLUTION: This fuel combustion device is provided with a fuel injection valve 9 for injecting a fuel toward a lip 11 of an opening edge of the cavity 8 of the piston 1, and is composed such that the region of fuel vapor 16 is formed near the lip 11 by making the fuel sprayed by the injection valve 9 reach the lip 11 during ignition delay, and an expansion flow is generated by igniting the fuel vapor 16 at the front of fuel injection direction to induce the fuel vapor in the front of ignition position to the bottom of the cavity 8 by applying to the peripheral wall face 12 thereof. Further, the device is provided with a control means for extending an ignition delay period to a prescribed one or more in either one of the cases that an engine load is a prescribed one or heavier, that a supercharging pressure P applied to the intake air is a prescribed one P0 or higher, or that an intake temperature Tin is a predetermined one Tin0 or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technical field of a diesel engine fuel combustion apparatus for combusting a fuel directly injected into a reentrant type cavity formed in a piston.

[0002]

2. Description of the Related Art A direct injection diesel engine having a reentrant cavity at the top of a piston is generally known. For example, JP-A-9-41
In the 975 publication, the fuel spray and the air are sprayed by defining the cavity shape so that the fuel injected toward the lip portion of the piston is separated from the side wall of the cavity when it goes from the lip portion to the bottom portion of the cavity. It is described that the mixing with and to suppress the generation of soot.

Also, Vol.31, No.3, Ju
ly 2000, pp. 51-56, if the bottom center of the reentrant cavity of the piston is raised, a vertical vortex is formed to flow downward along the side wall below the lip during the compression stroke. , The fuel spray is drawn into the vertical vortex to form a flow that rotates downward along the side wall below the lip, and increasing the lip diameter weakens the reverse squish flow and suppresses the outflow of the air-fuel mixture to the squish area. The vertical vortex becomes a spiral vortex due to the influence of swirl, and the spiral vortex promotes mixture formation and combustion in the cavity.
It is described that the air-fuel mixture is discharged to the squish area and oxidizes the unburned soot.

[0004]

However, it is not only the soot that is generated by the driving operation of the direct injection type diesel engine. That is, there is a problem that NOx is also produced at the same time by oxidizing the nitrogen in the air taken into the combustion chamber. However, in each of the above-mentioned conventional ones, although soot discharge is suppressed, not only soot but N
It is difficult to suppress the generation of Ox at the same time.

Therefore, fuel spray is injected from the fuel injection valve with a predetermined penetration (spray penetration degree), and during the ignition delay period which is the period from the start of fuel injection to self-ignition, the fuel vapor is generated near the lip portion. By forming a region in a relatively cohesive state and inducing a part of this fuel vapor to the bottom of the cavity by the fuel gas expansion flow after ignition to generate and strengthen vertical vortices, both NOx and soot are generated. Can be reduced respectively.

On the other hand, when the engine load is relatively large, the intake supercharging pressure is relatively high, the intake air temperature is relatively high, etc., the temperature in the combustion chamber having the cavity rises and fuel spray is generated. Easier to evaporate. That is, since the fuel spray self-ignites before a sufficient fuel vapor region is formed near the lip portion, a part of the fuel vapor can be sufficiently guided to the cavity bottom portion by the expansion flow after ignition. Therefore, it becomes difficult to generate a strong vertical vortex in the cavity. As a result, when the engine load, the intake supercharging pressure, and the intake temperature are relatively high as described above, there is a problem that the production of NOx and soot cannot be effectively reduced.

The present invention has been made in view of the above points, and an object of the present invention is to enhance the longitudinal vortices generated in the cavity and, in particular, to perform an operation in which the temperature in the cavity becomes relatively high. In the state, the vertical vortices can be stably strengthened to reduce the production amounts of both NOx and soot as much as possible.

[0008]

In order to achieve the above object, in the present invention, a part of the fuel vapor is guided to the bottom of the cavity by the expansion flow generated by ignition to strengthen the longitudinal vortex, and The ignition delay period is controlled to be equal to or longer than the predetermined period during a predetermined operation state in which the temperature inside the cavity is relatively high.

Specifically, according to the first aspect of the invention, a piston having a reentrant type cavity formed in the top thereof, the diameter of which becomes smaller toward the opening end, and a lip portion forming a cavity opening edge of the piston are provided. A fuel injection valve for injecting fuel, the fuel spray injected from the fuel injection valve reaches the lip portion during an ignition delay period to form a region of fuel vapor near the lip portion, and the fuel injection valve The fuel is ignited in the front of the fuel injection direction, and the expansion flow of the combustion gas due to this ignition causes the fuel vapor in front of the ignition position to impinge on the peripheral wall surface of the cavity toward the bottom of the cavity, and the flame A diesel engine fuel combustor configured to propagate to the bottom of the cavity is of interest. The ignition delay period is set when the engine load is equal to or higher than a predetermined load, the supercharging pressure applied to the intake air is equal to or higher than a predetermined pressure, or the intake air temperature is equal to or higher than a predetermined temperature. A control means for controlling for a predetermined period or more is provided.

According to the above invention, the fuel spray is injected from the fuel injection valve and reaches the lip portion during the ignition delay period, whereby a region of fuel vapor is formed near the lip portion. Since the ignition position (ignition point) of the fuel spray is the upstream position in the fuel injection direction in the region of the fuel vapor, a strong expansion flow explosively spreading from the ignition position to the downstream side is generated by the combustion due to this ignition. To be done.

The fuel vapor in the vicinity of the lip portion on the downstream side of the fuel vapor region is caused by the expansion flow to form an inner peripheral wall surface of the cavity (in particular, a lip portion and a portion recessed outward of the lip portion in the radial direction of the piston). Around the boundary), the strong vertical vortex is generated by being guided to the bottom side of the cavity along the inner wall surface of the cavity. Further, as the flame propagates following the fuel guided to the bottom of the cavity, vertical vortices grow further.

With the flow of this vertical vortex, the flame also wraps around from the lip to the bottom of the cavity. As a result, the heat spot (local high temperature region) spreads from the vicinity of the lip portion to the bottom of the cavity, while the fuel vapor decreases near the lip portion, so the heat spot near the lip portion disappears promptly. That is, by the end of fuel injection, the highest temperature portion in the cavity moves from the lip portion to the cavity bottom side and is dispersed.

Therefore, the heat spot is prevented from existing at a specific position in the cavity for a long time, or the heat spot is quickly extinguished, so that the amount of NOx produced can be effectively reduced. Further, since the vertical vortices are strengthened, the mixing of the fuel and the air in the cavity and the mixing of the combustion gas and the air in the latter half of the combustion are respectively promoted, so that the soot generation amount is effectively reduced. be able to.

By the way, when the engine load is above a predetermined load, the boost pressure applied to the intake air is above a predetermined pressure, or the intake air temperature is above a predetermined temperature, The ambient temperature inside the cavity rises, and the fuel spray evaporates and combustion becomes easier. On the other hand, according to the present invention, in such an operating state that the atmospheric temperature in the cavity is relatively high, the control means controls the ignition delay period to be equal to or longer than the predetermined period. A sufficient fuel vapor region can be formed near the portion. Then, after that, the fuel spray self-ignites, so that a part of the fuel vapor in the vicinity of the lip can be effectively guided to the cavity bottom by the expansion flow after ignition. As a result, strong longitudinal vortices can be generated in the cavity to reduce NOx and soot generation.

A second invention is characterized in that, in the first invention, the control means controls the effective compression ratio of the engine to a predetermined value or less.

According to the above-mentioned invention, the amount of intake air into the cavity is reduced by the control means so that the effective compression ratio is controlled to a predetermined value or less, so that the temperature of the air in the cavity is raised by pressurization and compression. Can be suppressed. That is, since excessive evaporation of the fuel spray is suppressed, it is possible to prevent the ignition delay period from becoming shorter than the predetermined period.

According to a third aspect of the present invention, in the second aspect of the present invention, a variable valve mechanism for varying the closing timing of the intake valve is provided, while the control means controls the closing timing of the variable valve mechanism. It is characterized by

According to the above invention, for example, when the engine is in the high rotation and high load state, the control means controls the valve closing timing of the variable valve mechanism to set the intake valve closing timing to the retard side. Shift by an angle (slow closing of the intake valve). then,
Part of the air-fuel mixture inside the combustion chamber is pushed back into the intake passage by the piston that rises in the early stage of the compression stroke. As a result, the amount of intake air in the cavity is reduced, so that it is possible to prevent the air from being excessively pressurized and compressed in the cavity to reach a high temperature. That is, the ignition delay period can be appropriately maintained.

According to a fourth aspect of the present invention, in any one of the first to third aspects of the invention, the control means is such that the engine load is equal to or higher than a predetermined load and the supercharging pressure applied to the intake air is equal to or higher than a predetermined pressure. And the case where the intake air temperature is equal to or higher than a predetermined temperature, the fuel injection pressure of the fuel injection valve is controlled to a predetermined value or higher.

According to the above invention, the engine load is equal to or higher than a predetermined load, the supercharging pressure applied to the intake air is equal to or higher than a predetermined pressure, or the intake air temperature is equal to or higher than a predetermined temperature. In this case, since the ambient temperature inside the cavity rises as described above, the ignition delay period becomes short. On the other hand, according to the present invention, the control means controls the fuel injection pressure from the fuel injection valve to be equal to or higher than a predetermined value under such an operating condition that the atmospheric temperature in the cavity is relatively high. Therefore, the penetration of the fuel spray (degree of penetration of the spray) can be increased, and a sufficient fuel vapor region can be formed near the lip portion. Therefore, an expansion flow is generated by the subsequent self-ignition of the fuel spray, a strong longitudinal vortex is generated in the cavity, and the generation of NOx and soot can be effectively reduced.

In a fifth aspect of the invention, in any one of the first to fourth aspects of the invention, the penetration Sp is defined as the arrival distance of the fuel spray when 0.42 ms has elapsed from the fuel injection start of the fuel injection valve. The cone angle Θ of the fuel spray of the fuel injection valve and the minimum diameter Dlip at the lip portion of the cavity are expressed by the following equation Dlip = k × Sp × sin (Θ / 2) (where k = 1.4 to 1.8). ) Is satisfied.

That is, according to the present invention, the fuel is injected from the fuel injection valve toward the lip portion, and the fuel spray reaches the lip portion during the ignition delay period of the fuel so that the fuel vapor is formed near the lip portion. Is what you are trying to do. Therefore, the minimum diameter Dlip of the cavity is 0.4, which is a typical ignition delay period during medium load operation from the start of fuel injection.
It is determined based on the fuel spray arrival distance Sp (spray penetration) when 2 ms has elapsed. Si on this Sp
The reason for multiplying by n (Θ / 2) is that the fuel spray is carried out with the cone angle Θ, and therefore the reaching distance of the fuel spray in the horizontal direction is obtained.

By the way, when the above-mentioned k value is less than 1.4 and the minimum diameter Dlip of the cavity becomes relatively small, the fuel injected from the fuel injection valve as a liquid jet flows until it reaches the lip portion. As it does not split sufficiently, it becomes an incomplete spray state. Therefore, the formation of fuel vapor becomes insufficient, and the expansion flow of the combustion gas does not work effectively. Furthermore, the core of the fuel spray (the liquid column portion existing in the fuel spray injected from the fuel injection valve or the portion having a very high fuel concentration) collides with the lip portion to deteriorate the combustion and reduce the output. However, even if the NOx generation amount decreases, the soot generation amount increases.

On the other hand, when the above k value exceeds 1.8, the above D
If the lip becomes too large, the distance from the ignition point to the lip becomes longer, so even if the expansion flow of the combustion gas due to ignition acts on the fuel vapor in front of it, that fuel vapor will not reach the lip. Disperse around. Therefore, since the fuel vapor cannot be guided toward the bottom of the cavity by the expansion flow, the NOx generation amount increases.

Therefore, from the above, it is desirable that the above k value is k = 1.4 to 1.8. Further, from such a viewpoint, as the above k value, k = 1.5
It is more preferable that it is set to be 1.7.

[0026]

1 is a schematic diagram showing the structure of a direct injection diesel engine equipped with a fuel combustion system according to an embodiment of the present invention. In the figure, 2 is a cylinder block, 2a is a cylinder formed in the cylinder block 2, and 1 is a piston provided in the cylinder 2a.
Further, 3 is a flat type cylinder head mounted on the upper portion of the cylinder block 2.

At the top of the piston 1, there is formed a concave reentrant type cavity 8 whose diameter becomes smaller as it approaches the opening end. As shown enlarged in FIG.
Reference numeral 11 denotes an annular lip portion that protrudes inward at the piston top surface portion so as to form the opening edge of the cavity 8, and reference numeral 12 denotes an annular recess portion that follows the lip portion 11 and is recessed radially outward of the piston. In addition, the piston 1 has a cavity 8
At the center of the bottom of the cavity, a protrusion 13 is formed which is raised toward the opening of the cavity 8.

A fuel injection valve 9 is attached and fixed to the lower portion of the cylinder head 3 with an injection nozzle 10 at the tip thereof facing the inside of the cylinder 2a. As also shown in FIG. 4, the fuel injection valve 9 transfers the fuel from the injection nozzle 10 to the lip portion 1.
This is for directly injecting the fuel into the cavity 8 by uniformly injecting radially toward 1, for example, 6 directions. The fuel injection valve 9 outputs signals from an electromagnetic crank angle sensor 22 that detects a rotation angle of a crankshaft (not shown), an accelerator opening sensor 23 that detects an accelerator pedal opening (accelerator operation amount), and the like. Based on the above, the operation is controlled by a control unit (hereinafter referred to as ECU) 40. Further, the fuel injection valve 9 is connected to a common rail (not shown) that stores fuel in a high pressure state equal to or higher than its injection pressure, and a fuel pressure sensor 29 for detecting the internal fuel pressure is arranged on this common rail. There is.

Reference numeral 4 is an intake port (helical port) formed in the lower portion of the cylinder head 3 for supplying air into the cavity 8. Reference numeral 5 is similarly formed in the lower portion of the cylinder head 3 from the inside of the cavity 8. An exhaust port for exhausting exhaust gas. As shown in FIG. 2, for example, two intake ports 4 and two exhaust ports 5 are provided, respectively. Upright intake valve 6 in intake port 4
However, similar exhaust valves 7 are provided in the exhaust ports 5, respectively.

The intake valve 6 and the exhaust valve 7 have a plurality of cam shafts 31, 31 arranged in the cylinder head 3 driven by a crankshaft (not shown) via a timing belt to rotate. Each cylinder is opened and closed at a predetermined timing. In addition, the intake side camshaft 31 is a known variable valve mechanism 33 (Valiable Valve Mechanism) that changes the closing timing of the intake valve by continuously changing the rotation phase with respect to the crankshaft within a predetermined angle range. Timing: Hereinafter, abbreviated as VVT) is attached, and the opening / closing operation timing of the intake valve 6 is changed by the operation of this VVT 33.

The VVT 33 has a rotor 33a fixed to the end of the cam shaft 31, as shown in the schematic structure of FIG.
And a casing 33c disposed so as to cover the rotor 33a and fixedly attached to the sprocket 33b. Four vanes that radially project outward are provided on the outer periphery of the rotor 33a, while four partition walls that extend inward are provided on the inner periphery of the casing 33c. A plurality of hydraulic operating chambers 33d, 33e, ... Are respectively formed between the vanes and the partition walls, and the hydraulic pressure of the engine oil supplied to these hydraulic operating chambers 33d, 33e ,. The rotor 33a and the casing 33 are adjusted by the control valve 33f (hereinafter referred to as OCV).
c, that is, the cam shaft 31 and the sprocket 33b are relatively rotated, and the rotation phase of the cam shaft 31 with respect to the crank shaft is continuously changed. The OCV 33f is controlled by the ECU 40.

More specifically, the hydraulic working chamber of the VVT 33 is composed of advance side and retard side hydraulic working chambers 33d, 33e, ... Arranged alternately in the circumferential direction, and the advance working hydraulic chamber 33d. , 33d, ... Rotate the rotor 33a in the direction in which the cam shaft 31 rotates with respect to the casing 33c (indicated by the arrow A in FIG. 6), which is indicated by the broken line in FIG. As described above, the valve opening timing IO and the valve closing timing IC of the intake valve 6 are shifted to the advance side. On the other hand, when the hydraulic pressure in the hydraulic working chambers 33e, 33e, ... On the retard side increases, the rotor 33a is rotated with respect to the casing 33c in the direction opposite to the direction in which the cam shaft 31 rotates. As indicated by a phantom line in FIG. 7, the valve opening timing IO and the valve closing timing IC of the intake valve 6 are shifted to the retard side.

In FIG. 7, for example, the valve opening timing IO and the valve closing timing IC of the intake valve 6 are the start end and the end of the valve lift curve excluding the buffer portion as shown in the drawing.

Further, as shown in FIG. 1, the intake ports 4,
4, the intake passages 24, 24 are respectively connected,
Exhaust passages 25, 25 are connected to the exhaust ports 5, 5, respectively. The upstream sides of the intake passages 24, 24 in the intake direction of air are connected to the surge tank 21 in a communicating state. That is, the respective intake passages 24, 24 are merged in the surge tank 21. Further, in the surge tank 21, a supercharging pressure sensor 27 for detecting a pressure state of intake air pressure-fed by a turbocharger 41, which will be described later,
An intake air temperature sensor 28 that detects the temperature state of intake air is provided.

Then, as shown in the same figure, the intake passage 2
4, a blower 42 that is driven by a turbine 43 to be described later and compresses intake air in order from the upstream side in the air intake direction;
An intercooler 35 that cools the intake air compressed by the blower 42 and an intake throttle valve 26 that is a butterfly valve are respectively provided. The intake throttle valve 26 is controlled by the ECU 40 to open and close according to the output of the accelerator opening sensor 23. I am trying to do it.

Further, one of the two intake passages 24, 24 is provided with a swirl control valve 30 for changing the flow rate of the intake air in the one intake passage 24.
The swirl control valve 30 is, for example, a butterfly valve, and is opened and closed by being driven by an actuator. Then, as shown in FIG. 2, the swirl control valve 3
When 0 is completely closed, intake air flows into the cavity 8 only from the other intake passage 24, and
It is configured to generate a relatively strong swirl as indicated by an arrow in FIG.

Then, as the swirl control valve 30 gradually opens from the completely closed state, the two intake passages 2
The intake air flows in from both 4, 4 and 24, and the tumble component of the intake air is strengthened and the swirl component is weakened. This swirl control valve 30 is an ECU
By 40, for example, when the engine speed Ne is relatively small, the valve opening degree is controlled so as to strengthen the swirl.

On the other hand, the exhaust passage 25 is provided with a turbine 43 which is rotationally driven by the exhaust flow. This turbine 43 and the blower 42 of the intake passage 24 are
Are integrally fixed to each other by rotation. Then, the blower 42 rotates with the rotation of the turbine 43 due to the exhaust flow, so that the intake air is supplied to the surge tank 21 in a pressurized state. This blower 4
2, the turbine 43, and the rotating shaft 44 form a turbocharger 41.

The fuel combustion apparatus according to the present embodiment causes the fuel spray injected from the fuel injection valve 9 to reach the lip portion 11 during the ignition delay period which is a period from the start of fuel injection to self ignition. A region for the fuel vapor 16 is formed near the lip portion 11. Further, the fuel is ignited at a predetermined position in front of the fuel injection valve 9 in the fuel injection direction, and the expansion flow of the combustion gas caused by the ignition causes the fuel vapor in front of the ignition position to hit the inner peripheral wall surface of the cavity 8 and the cavity. 8 is directed towards the bottom of the cavity 8 and the flame is propagated to the bottom of the cavity 8.

That is, the fuel combustion device for the diesel engine is constructed as follows. The arrival distance Sp (penetration) of the fuel spray when 0.42 ms has elapsed from the start of fuel injection of the fuel injection valve 9 and the fuel injection valve 9
The cone angle Θ of the fuel spray and the minimum diameter (hereinafter, referred to as lip diameter) Dlip in the lip portion 11 of the cavity 8 have a relationship satisfying the following equation.

Dlip = k × Sp × sin (Θ / 2) (1) However, k = 1.4 to 1.8, and k = 1.5 to 1.7.
Is more preferable. Also, the cone angle Θ =
It is preferably 153 to 157 degrees, and Θ = 154 to
More preferably, it is 156 degrees.

Here, 0.42 time from the start of fuel injection
ms is a typical ignition delay period in the emission operation mode (during medium load operation). Further, the penetration Sp is a penetration degree (also referred to as penetration force) of the fuel spray, and is the injection direction length of the fuel spray formed in the ignition delay period (for example, 0.42 ms described above), that is, the injection nozzle 1
It is represented by the reaching distance from 0 to the fuel spray tip.

In the present invention, the fuel injection valve 9 to the lip portion 11 are used.
The fuel is injected toward and the fuel spray reaches the lip portion 11 during the ignition delay of the fuel so that the fuel vapor 16 is formed in the vicinity of the lip portion 11.
Therefore, the minimum diameter Dlip of the cavity 8 is determined based on the arrival distance Sp (penetration) of the fuel spray when the ignition delay period 0.42 ms elapses from the start of fuel injection. This Sp is multiplied by sin (Θ / 2) because the fuel is injected with the cone angle Θ, so that the reaching distance of the fuel spray in the horizontal direction is obtained.

The reach distance Sp is a constant vessel experiment (fuel injection pressure 80 MPa, atmospheric pressure 2.5 MPa, temperature 20 ° C.)
Required by. If there is no constant container experimental data, it can be estimated from Hiroan's formula. Hiro's formula is an empirical formula that relates the reaching distance Sp and the nozzle diameter of the fuel injection valve 9, and is as follows.

Sp = Spb + 2.95 × (ΔP × 10 ⁶ / ρf) ^0.25 ×
(Dn × (t-tb)) ^0.5 Spb = 0.39 × (2 × ΔP × 10 ⁶ / ρf) ^0.5 × tb tb = 28.65 × (ρf × Dn × 10 ^-3 ) / (ρA × ΔP × 10 ⁶ ) ^0.5 / 10 ^-3 However, ΔP: differential pressure (MPa) between container pressure and injection pressure, ρ
f: light oil density (kg / m ³ ), Dn: nozzle diameter (mm), t: time after injection start (0.42 ms), ρA: container air density.

The cylinder bore diameter B has a relationship satisfying the following equation.

B = K × Dlip (2) However, it is preferable that K = 1.8 to 2.5, and K =
More preferably, it is 2.0 to 2.3.

For example, when the reach distance Sp = 27 mm and the cone angle Θ = 154 degrees, the lip diameter Dlip = 38.94-
44.20 mm, bore diameter B = 77.87-100.
It will be 33 mm. The height of the convex portion 13 may be about 0.2 to 0.25 times the lip diameter Dlip.

The spray angle of the fuel spray is preferably 15 to 24 degrees, more preferably 18 to 23 degrees. The fuel injection pressure P of the fuel injection valve 9 is preferably P = 50 MPa or more, and more preferably P = 80 MPa or more. The upper limit of injection pressure is, for example, 150MP
a, and further 200 MPa.

When the fuel spray injected from the fuel injection valve 9 first reaches the lip 11 of the cavity 8 of the piston, the ratio of the swirl momentum to the momentum of the fuel spray in the lip 11 is 0.9. The ratio of momentum is preferably 1.5 to 1.5, and more preferably 1.1 to 1.3. This momentum ratio can be calculated by the following equation.

Momentum ratio = ((ρa / ρao) × Va) / ((ρs / ρso) × Vs) (3) where, ρa: filled air density, ρao: air density in standard state, Va: compression Swirl velocity at the lip portion 11 at the top dead center of the stroke, ρs: Density of fuel spray in constant container experiment, ρs
o: Density of fuel spray in the standard state, Vs: Spray speed when the lip reaches in the constant container experiment. Standard condition is 20 ℃,
It is 1 atm (0.1013 MPa).

Here, ρa / ρao = (Pin / 101.3) / (Tin / 293.3), Va = ρa × SRi × (Dlip / B / 2)) ² × (N × 2π / 60) × Dl
ip ,. It is possible to set ρs / ρso = 1.

Where Pin: pressure in the intake manifold (k
Pa), Tin: temperature in intake manifold, SRi: swirl ratio in rig test, N: engine speed (rpm).

Next, the effect of the k value on the amount of NOx produced will be described. That is, as is clear from the above equation (1), the magnitude of the k value is reflected as the magnitude of the lip diameter Dlip, and if the reaching distance Sp is constant, the strength of the vertical vortex is affected. Therefore, the amount of NO produced when the k value was changed was examined. The result is shown in FIG.

In the figure, the data of k = 1.9 shows the reentrant rate R = 1 and the convex portion 1 at the center of the cavity 8.
It is a PAN type that does not have 3. The reentrant rate R is a Dlip / Dmax value when the maximum inner diameter of the cavity 8 is Dmax. The data of k = 1.73 is a reentrant type having a reentrant rate R = 1.73 / 1.9 and a convex portion 13 at the center of the cavity 8. The respective data of k = 1.65 and k = 1.54 are the amount of recess Re from the lip 11 of the recess 12 (FIG. 3 (B)).
(Ref.) Is the same as that of k = 1.73.

According to FIG. 5, the NO generation amount decreases as the k value decreases. This is because the expansion flow of the combustion gas at the initial stage of combustion strongly acts on the inner peripheral wall surface of the cavity 8 due to the smaller lip diameter, and the vertical vortex is promoted.
Furthermore, the distance between the recessed portion 12 and the protruding portion 13 becomes short, and vertical vortices are easily generated.

However, when the k value is less than 1.4 and the minimum diameter Dlip of the cavity 8 becomes relatively small, the fuel injected from the fuel injection valve 9 as a liquid jet flows to the lip portion 11. It does not split sufficiently before reaching, resulting in incomplete atomization. Therefore, the formation of the fuel vapor 16 is also insufficient, and the expansion flow does not work effectively. Further, the core of the fuel spray (the liquid column portion existing in the fuel spray injected from the fuel injection valve 9 or the portion having a very high fuel concentration) collides with the lip portion 11 to deteriorate the combustion and reduce the output. Therefore, even if the NOx generation amount decreases, the soot generation amount increases.

On the other hand, when the k value exceeds 1.8, the minimum aperture D
If the lip becomes relatively large, the distance from the ignition point to the lip portion 11 becomes large, so even if the expansion flow acts on the fuel vapor 16 in front of it, the fuel vapor 16
Disperse around the periphery before hitting the lip 11. Therefore, since the fuel vapor 16 cannot be guided toward the bottom of the cavity by the expansion flow, the NOx generation amount increases.

From this, as the above k value, k = 1.
It is desirable that it is 4 to 1.8. Further, from such a viewpoint, it is more preferable that the above k value is k = 1.5 to 1.7.

The fuel combustion apparatus according to the present embodiment uses the turbocharger when the engine load is equal to or higher than the predetermined load (in other words, the fuel injection amount Qb is equal to or higher than the predetermined injection amount Q ₀ ). When the supercharging pressure P applied to the intake air by the machine 41 is equal to or higher than the predetermined pressure P ₀ and when the intake air temperature Tin
A control means is provided for controlling the ignition delay period to be equal to or longer than the predetermined temperature Tin ₀ when the temperature is equal to or higher than the predetermined temperature Tin ₀ . The control means is composed of the ECU 40 that controls the valve closing timing of the VVT 33 described above. And V
The VT 33 changes the closing timing IC of the intake valve 6 so that the inside of the cylinder 2a (that is, the inside of the cavity 8) is changed.
It is configured to reduce the amount of intake air into. As a result, the intake pressure in the cylinder 2a is reduced, and the effective compression ratio of the engine is controlled to a predetermined value or less.

Further, the control means, when the engine load is equal to or higher than the predetermined load, the boost pressure P is equal to or higher than the predetermined pressure P ₀ , and the intake air temperature Tin is equal to or higher than the predetermined temperature Tin _{0, as described} above. In either case, the fuel injection pressure Pr of the fuel injection valve 9 is controlled to be equal to or higher than a predetermined value Pr ₀ . The fuel injection pressure Pr is the fuel pressure in a common rail (not shown) detected by the fuel pressure sensor 29. Then, the fuel injection pressure Pr is changed by controlling the operation of a high-pressure supply pump (not shown) that supplies fuel to the common rail.

Next, the combustion concept of the diesel engine of the present invention will be described with reference to FIGS. As shown in the figure (A) of the ignition delay period, a vertical vortex (the lip portion 11 of the cavity 8 is formed in the cavity 8).
From the fuel injection valve 9 to the lip portion 11 of the piston 1 when the flow from the fuel injection valve 9 to the lip portion 13 through the concave portion 12, the deepest portion, and the convex portion 13 to the lip portion 13 is not substantially generated. . Fuel spray 1 during the ignition delay period of this fuel
5 reaches the lip portion 11 to form a region of the fuel vapor 16 near the lip portion 11. Then, the fuel vapor 16 is ignited at a position on the upstream side in the fuel injection direction in this fuel vapor pool region. The ignition point is indicated by a star in the figure (A). The reason why the ignition point is located on the upstream side of the fuel vapor 16 region is that a strong vertical vortex is not formed in the compression stroke.
While the fuel becomes excessively rich in the vicinity of the lip portion 11,
It is considered that the concentration is suitable for ignition at a place slightly away from the lip portion 11.

In this case, by increasing the spray penetration Sp, the fuel vapor 1
Six regions can be formed. This is advantageous for inducing a large amount of the fuel vapor 16 toward the recess 12 by the expansion flow described below. In addition, it is preferable to increase the cone angle Θ (θ = 153 to 157 degrees) to the lip portion 1.
1 is advantageous in forming the region of the fuel vapor 16 in the vicinity of 1.

As shown in the initial combustion state in FIG.
The ignition causes a strong expansive flow that explosively expands toward the downstream side. The fuel vapor 16 in the vicinity of the lip portion on the downstream side (in front of the ignition position) in the fuel vapor region is formed by the expansion flow of the combustion gas 17 on the inner wall surface of the cavity 8 (especially the lip portion 11 and the piston 1 more than the lip portion 11). It contacts the vicinity of the boundary with the recessed portion 12 that is recessed radially outward. Then, the fuel vapor 16 is guided to the bottom side of the cavity 8 along the inner peripheral wall surface of the cavity 8 to generate a strong vertical vortex. Further, as the flame propagates following the fuel guided to the bottom of the cavity 8, the vertical vortex grows further.

In this case, the above-mentioned spray penetration Sp
When is increased, the expansion flow forward in the injection direction is increased, which is advantageous in promoting vertical vortices. Further, the smaller the lip diameter Dlip, the more advantageous it is for the expanded flow to be strongly applied to the inner peripheral wall surface of the cavity 8 to guide the fuel vapor toward the bottom of the cavity. However, if the lip diameter Dlip becomes too small, the maximum output of the engine becomes low. Therefore, the lip diameter Dlip is preferably larger than 1/2 of the bore diameter B.

As shown in the state of the latter stage of combustion in FIG. 6C, the convex portion 13 at the center of the cavity 8 extends along the rising surface of the convex portion 13 of the combustion gas 17 from the deepest portion of the cavity bottom. Promote winding.

As described above, the maximum temperature portion in the cavity 8 is moved to the bottom side of the cavity 8 rather than the lip portion 11 by the end of fuel injection. Therefore, the heat spot does not become large at a specific portion in the cavity 8, the heat spot disappears quickly, and NOx can be reduced. Further, since the combustion gas 17 and oxygen remaining above the central portion of the cavity 8 are mixed by the above-mentioned winding in the latter stage of combustion, and further the combustion gas 17 flows into the squish area, the air utilization rate is increased, and the combustion gas 17
Reburning of the soot inside is promoted, and soot emissions are reduced.

Next, with reference to the flow chart shown in FIG. 8, a specific processing procedure of the fuel combustion control of the diesel engine according to the embodiment of the present invention will be described. First,
In step S1 after the start, output signals from various sensors such as the crank angle sensor 22, the accelerator opening sensor 23, the boost pressure sensor 27, the intake air temperature sensor 28, the fuel pressure sensor 29, etc. are input to the ECU 40.

Then, in step S2, the ECU 4
With 0, the engine speed Ne is calculated based on the output from the crank angle sensor 22, and the target torque (engine load state) is calculated based on the output from the accelerator opening sensor 23.

Then, the basic fuel injection amount Qb is calculated and set by the ECU 40 based on the engine speed Ne and the target torque. This basic fuel injection amount Q
The setting of b is performed based on the map of the fuel injection amount recorded in the memory of the ECU 40 in advance. The fuel injection amount map is a basic fuel injection amount Q that is experimentally determined according to changes in the engine load state and the engine speed Ne.
The optimum value of b is recorded, and this basic fuel injection amount Qb
Is set to be larger as the target torque (engine load state) is larger and the engine speed is higher.

Further, the basic injection timing Ib is calculated and set by the ECU 40 based on the engine speed Ne and the target torque. The setting of the basic injection timing Ib is performed based on the injection timing map recorded in the memory of the ECU 40 in advance. Further, the basic injection pressure Pb of the fuel spray injected from the fuel injection valve 9 is based on the basic fuel injection amount Qb and the engine speed Ne and the ECU 4
Calculated by 0. This set of basic injection pressure Pb is also
This is performed based on the map of the fuel injection pressure recorded in the memory of the ECU 40 in advance. In this fuel injection pressure map, the basic fuel injection pressure Pb is the basic fuel injection amount Qb.
Is set to be larger and the engine speed Ne is set to be larger. In this way, after the basic fuel injection amount Qb, the basic injection timing Ib, and the basic injection pressure Pb are set in step S2, the process proceeds to step S3.

At step S3, the basic valve timing Ivb of the intake valve 6, that is, the valve opening timing IO and the valve closing timing IC are calculated by the ECU 40 based on the engine speed Ne and the target torque. This basic valve timing Ivb
The setting is also performed based on a valve timing map (VVT map) recorded in advance in the memory of the ECU 40. The VVT map records the optimum value of the basic valve timing Ivb experimentally determined according to the load condition of the engine and the change of the engine speed Ne. For example, in the idling state, it is slightly retarded, The basic valve timing Ivb is set finely such that the valve is slightly advanced in the high load state.

After that, the routine proceeds to step S4, where it is judged if the basic injection amount Qb calculated at step S2 is equal to or larger than a predetermined threshold injection amount Q ₀ . In other words, it is determined whether the engine load is greater than or equal to a predetermined value. Then, the basic injection amount Qb is equal to or larger than the predetermined injection amount Q ₀ (the engine load is equal to or larger than the predetermined value), YE.
If it is determined to be S, the process proceeds to step S5.

In step S5, the fuel injection pressure Pr actually injected from the fuel injection valve 9 into the cavity 8 is corrected to a predetermined value Pr ₀ or more by increasing the basic injection pressure Pb by a predetermined pressure ΔPr. Then, it progresses to step S6.

In step S6, the target valve timing Iv of the intake valve 6 is calculated. That is, first EC
From the map of U40, the basic effective compression ratio set according to each operating state is obtained in a state where the opening and closing valve timing of the intake valve is standard (solid line in FIG. 7). Then, the ECU 40 calculates the variation amount ΔIv of the valve timing so that the effective compression ratio becomes equal to or lower than a predetermined value, the temperature inside the cavity 8 becomes relatively low, and the generation of NOx is suppressed. In this way, the valve operating timing Iv is obtained by performing correction by adding this variation amount ΔIv to the basic valve operating timing Ivb (Iv = Iv
b + ΔIv). That is, for example, as shown by the phantom line (two-dot chain line) in FIG. 7, the basic valve timing Ivb is shifted to the retard side as a whole, so the closing timing of the intake valve 6
The IC also shifts to the retard side.

In this case, in the diesel engine,
If the valve timing is controlled so as to advance the intake valve opening timing,
Since the piston 1 and the intake valve 6 are easily buffered,
The lift amount of the intake valve 6 is set so that the intake valve 6 does not buffer the piston 1 during this buffer period.

After that, the routine proceeds to step S7, where the ECU 40 is operated based on the valve timing Iv obtained at step S6.
Outputs a signal as an operation command to the OCV 33f of the VVT 33 to drive the VVT 33. Then,
In step S8, the fuel injection from the fuel injection valve 9 is executed by the ECU 40 based on the basic injection timing Ib, the basic injection amount Qb, and the fuel injection pressure Pr. At this time,
While the fuel injection pressure from the fuel injection valve 9 is increased and the penetration Sp is increased, the valve timing is shifted to the retard side and the effective compression ratio is decreased. Then return.

By the way, in step S4, it is determined that the basic injection amount Qb calculated in step S2 is less than the predetermined threshold injection amount Q ₀ (the engine load is less than the predetermined value) and NO. If so, step S9
Proceed to. In step S9, it is determined whether or not the supercharging pressure P detected by the supercharging pressure sensor 27 is equal to or higher than the predetermined pressure P ₀ . If the boost pressure P is equal to or higher than the predetermined pressure P ₀ and YES is determined, the above step S
Control after 5 is performed.

On the other hand, if the supercharging pressure P is less than the predetermined pressure P ₀ and it is judged NO in step S9, the process proceeds to step S10. In this step S10,
It is determined whether the intake air temperature Tin is equal to or higher than the predetermined temperature Tin ₀ . Then, the intake air temperature Tin is equal to the predetermined temperature T
If it is equal to or greater than in ₀ and YES is determined, the control from step S5 onward is performed.

In step S10, the intake air temperature Tin
Is less than the predetermined temperature Tin ₀ , and if NO is determined, the control from step S7 is performed. That is, in step S7, VV is calculated based on the basic valve timing Ivb.
Drive T33. Subsequently, in step S8, the ECU 40 executes fuel injection from the fuel injection valve 9 based on the basic injection timing Ib, the basic injection amount Qb, and the basic injection pressure Pb. At this time, penetration S
The p and the effective compression ratio are not corrected and are set to normal values based on the basic injection pressure Pb and the basic valve timing Ivb.

As described above, according to this embodiment, the fuel vapor 16 near the lip portion 11 in the fuel vapor region formed during the ignition delay period is expanded by the ignition flow and the inner peripheral wall surface of the cavity 8 is expanded. Along the cavity 8
Since it is guided to the bottom side, a strong vertical vortex can be generated. Furthermore, since the flame propagates following the fuel guided to the bottom of the cavity 8, vertical vortices can be further grown. The vertical vortex causes the flame to propagate toward the bottom of the cavity 8 and the heat spot to move to the lip portion 1.
1 spreads from the vicinity of 1 to the bottom of the cavity 8 while the lip 1
Since the fuel vapor 16 decreases in the vicinity of 1, the lip portion 1
The heat spot near 1 disappears promptly. Therefore, by the end of the fuel injection, the highest temperature portion in the cavity 8 can move from the vicinity of the lip portion 11 to the bottom side of the cavity 8 and be dispersed.

That is, the heat spot is the cavity 8.
Since it is possible to prevent the heat spot from existing at a specific position for a long time and to extinguish the heat spot quickly, the amount of NOx produced can be effectively reduced. In addition, since the vertical vortices are strengthened, the mixing of the fuel and the air in the cavity 8 and the mixing of the combustion gas and the air in the latter half of the combustion are promoted, respectively, so that the soot generation amount is made effective. Can be reduced.

When the engine load becomes less than the predetermined value and the amount of NOx produced by combustion becomes relatively small, the swirl in the cavity 8 is strengthened by the swirl control means in preference to the vertical vortex. As a result, the enhanced swirl further promotes the mixing of the fuel and air in the cavity 8 and the mixing of the combustion gas and air in the latter half of combustion, so that the soot generation is effectively performed. Can be suppressed.

In addition to that, when the engine load is a predetermined load or more, the supercharging pressure P applied to the intake air is a predetermined pressure P ₀ or more, and the intake air temperature Tin is a predetermined temperature Tin ₀ or more. In either case, the atmospheric temperature inside the cavity 8 rises, and the fuel spray evaporates and burns easily. However, in the present invention, the atmospheric temperature inside the cavity 8 is relatively high. In such an operating state, the ignition delay period is controlled by the control means to be equal to or longer than the predetermined period, so that a sufficient region of the fuel vapor 16 can be formed near the lip portion 11. Then, after that, the fuel spray self-ignites, so that a part of the fuel vapor 16 in the vicinity of the lip portion 11 can be effectively guided to the cavity bottom portion by the expansion flow after ignition.
As a result, as described above, the engine load and the boost pressure P
Even when either of the intake air temperature and the intake air temperature Tin becomes equal to or higher than a predetermined value, strong vertical vortices can be generated in the cavity 8 to reduce the generation of NOx and soot.

Further, since the amount of intake air into the cavity 8 is reduced by the control means and the effective compression ratio is controlled to be equal to or less than the predetermined value, the temperature rise of the air in the cavity 8 due to pressurization and compression is suppressed. be able to. That is, since excessive evaporation of the fuel spray is suppressed, it is possible to prevent the ignition delay period from becoming shorter than the predetermined period.

Further, when the engine is in a high rotation and high load condition, the ECU 40 as a control means controls the valve closing timing IC of the VVT 33 to retard the valve closing timing IC of the intake valve 6 by a predetermined angle ΔIv. Only (the intake valve 6 is closed late). At that time, a part of the air-fuel mixture inside the combustion chamber is pushed back to the intake passage 24 by the piston 1 rising in the early stage of the compression stroke. As a result, the amount of intake air in the cavity 8 decreases, so that it is possible to prevent the air from being excessively pressurized and compressed in the cavity 8 to reach a high temperature. That is, the ignition delay period can be appropriately maintained.

On the other hand, whether the engine load is a predetermined load or more, the supercharging pressure P applied to the intake air is a predetermined pressure P ₀ or more, or the intake air temperature Tin is a predetermined temperature Tin ₀ or more. In that case, as described above, the ambient temperature inside the cavity 8 rises, but at that time,
According to the present invention, the control means controls the fuel injection pressure Pr from the fuel injection valve 9 to be equal to or higher than the predetermined value Pr _0. Therefore, the penetration Sp of the fuel spray is increased,
A sufficient area of the fuel vapor 16 can be formed near the lip portion 11. Therefore, an expansion flow can be generated by the self-ignition of the fuel spray thereafter, and a strong vertical vortex can be generated in the cavity 8.

In the above embodiment, the engine load is equal to or higher than the predetermined load, the boost pressure P is equal to or higher than the predetermined pressure P ₀ , and the intake air temperature Tin is equal to or higher than the predetermined temperature Tin ₀ . In either case, the ECU 40 and VV
By changing the closing timing IC of the intake valve 6 by T33, the effective compression ratio of the engine is controlled to a predetermined value or less, the ignition delay period is controlled to a predetermined period or more, and the fuel injection valve 9 Although the fuel injection pressure Pr is controlled to be equal to or higher than the predetermined value Pr ₀ , the present invention is not limited to this. That is, as described above, when any one of the engine load, the supercharging pressure P, and the intake air temperature Tin becomes a predetermined value or more, only the ignition delay period may be controlled to be a predetermined period or more. Pr
May be controlled to a predetermined value Pr ₀ or more.

[0089]

As described above, according to the first aspect of the present invention, a piston having a reentrant type cavity formed on the top thereof, the diameter of which decreases as it approaches the opening end, and a lip portion forming the cavity opening edge of the piston. A fuel injection valve for injecting fuel toward the fuel injection valve, and makes the fuel spray injected from the fuel injection valve reach the lip portion during the ignition delay period to form a region of fuel vapor near the lip portion. Diesel engine configured to ignite fuel in the front of the fuel injection direction and to cause the fuel vapor in front of the ignition position to impinge on the peripheral wall surface of the cavity toward the bottom of the cavity by the expansion flow of combustion gas resulting from this ignition In the fuel combustion device of No. 1, when the engine load is equal to or higher than a predetermined load, the supercharging pressure applied to the intake air is equal to or higher than a predetermined pressure, In any one of the case where the temperature is equal to or higher than a constant temperature, by providing a control means for controlling the ignition delay period to a predetermined period or longer, it is possible to prevent the heat spot from existing for a long time at a specific position in the cavity, While effectively reducing the amount of NOx produced, promoting the mixing of fuel or combustion gas and air in the cavity,
The amount of soot generated can be effectively reduced. In addition to that, when the engine load is above a predetermined load,
Since the ignition delay period is controlled to be the predetermined period or longer when the supercharging pressure is equal to or higher than the predetermined pressure or when the intake air temperature is equal to or higher than the predetermined temperature, it is possible to ensure that the ignition delay period is sufficiently close to the lip portion. It is possible to form a region of a large fuel vapor, generate a strong vertical vortex in the cavity, and effectively reduce the generation of NOx and soot.

According to the second aspect of the invention, the control means controls the effective compression ratio of the engine to be equal to or lower than a predetermined value to suppress the temperature rise of the air in the cavity due to the pressurization and compression.
It is possible to prevent the ignition delay period from becoming short.

According to the third aspect of the invention, the control means includes a variable valve mechanism for varying the closing timing of the intake valve, while the control means controls the closing timing of the variable valve mechanism. The valve closing timing of the intake valve is shifted to the retard side by a predetermined angle by the variable valve mechanism to reduce the amount of intake air in the cavity, thus suppressing excessive pressurization and compression of air in the cavity to a high temperature. can do.

According to the fourth aspect of the invention, the control means controls when the engine load is a predetermined load or more, the supercharging pressure applied to the intake air is a predetermined pressure or more, and the intake air temperature is a predetermined temperature or more. In either case, by controlling the fuel injection pressure of the fuel injection valve to a predetermined value or more, the penetration of the fuel spray is increased to form a sufficient fuel vapor region near the lip portion and It can generate a powerful vertical vortex.

According to the fifth aspect of the invention, the penetration Sp, which is the reaching distance of the fuel spray when 0.42 ms has elapsed from the start of fuel injection of the fuel injection valve, the cone angle Θ of the fuel spray of the fuel injection valve, and the lip of the cavity. The minimum diameter Dlip in the section is such that Dlip = k × Sp × sin (Θ / 2) (where k = 1.4 to 1.8) is satisfied, so that from the fuel injection valve to the lip section. To inject fuel toward
During the fuel ignition delay period, the fuel spray can reach the lip portion and the fuel vapor can be appropriately formed near the lip portion.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram showing a fuel combustion device for a diesel engine according to an embodiment of the present invention.

FIG. 2 is an enlarged plan view showing a main part of the fuel combustion device.

FIG. 3 is an explanatory diagram showing a combustion concept of the present invention.

FIG. 4 is a plan view showing a combustion chamber in which fuel spray is injected.

FIG. 5 is a graph showing the relationship between k value and NO production amount.

FIG. 6 is a perspective view showing a VVT partially broken away.

FIG. 7 is a time chart diagram schematically showing a change in valve timing by VVT.

FIG. 8 is a flowchart showing fuel combustion control in the fuel combustion device.

[Explanation of symbols]

Sp Penetration (penetration force, fuel spray reach distance) Θ Fuel spray cone angle Dlip Lip minimum diameter IC valve closing timing Tin Intake temperature P Supercharging pressure Pr Fuel injection pressure 1 Piston 6 Intake valve (intake valve) 8 Cavity 9 Fuel injection valve 11 Lip part 12 Recessed part (circumferential wall surface of cavity) 16 Fuel vapor 22 Crank angle sensor (control means) 23 Accelerator opening sensor (control means) 27 Supercharging pressure sensor (control means) 28 Intake temperature sensor ( Control means) 29 Fuel pressure sensor (control means) 33 VVT (variable valve mechanism) 40 ECU (control means)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 15/00 F02D 15/00 E 3G301 23/02 23/02 Z 41/04 351 41/04 351 370 370 395 395 43/00 301 43/00 301S 301Z 45/00 312 512/00 312H 360 360F F02M 61/18 360 F02M 61/18 360J (72) Inventor Yasuyuki Terazawa Shinchi Fuchu-cho, Hiroshima Prefecture Mazda Incorporated (72) Inventor Hiroshi Hayashibara 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. F-term (reference) 3G018 AB17 BA33 CA20 EA02 EA11 EA32 EA35 FA27 GA08 3G023 AA07 AB05 AC05 AD02 AD07 AD09 AD12 AD14 AG01 AG02 3G066 AA07 AB02 AC09 AD12 BA24 BA25 CC48 CD28 3G084 AA01 AA04 BA07 BA08 BA14 BA15 BA22 BA23 CA04 EA11 EB08 FA00 FA02 FA13 FA18 FA33 3G092 AA02 AA09 AA10 AA11 AA18 BB06 DA01 DA10 DD03 DG05 DG09 EA04 EA16 EC10 FA22 GA06 HA11Z HA13X HA13Z HB01Z HB02X HB03 PA08 NA08Z29 MA08HA08 HA08 HA02 HA08 HA01 HA01 HA01 HA01 HA01 HA01 HA01 HA01 HA01 HA01 HA02 HA08 HA01 HA18 HA01 HA02 HA08 HA01 HA18 HA01 HA01 HA02 HA08 HA01 HA18 HA01 HA01 HA02 HA08 HA01 HA18 HA01 HA01 HA18 HA01 HA01 HA18 HA01 HA01 HA01 PE01Z PE10Z

Claims (5)

[Claims] 1. A piston having a reentrant type cavity formed on the top thereof, the diameter of which decreases as it approaches the opening end, and a fuel injection valve for injecting fuel toward a lip portion forming the cavity opening edge of the piston. The fuel spray injected from the fuel injection valve reaches the lip portion during an ignition delay period to form a fuel vapor region near the lip portion, and the fuel is ignited in front of the fuel injection direction of the fuel injection valve. Let
Due to the expansion flow of the combustion gas due to this ignition, the fuel vapor in front of the ignition position is applied to the peripheral wall surface of the cavity to guide it toward the bottom of the cavity, and the flame is propagated to the bottom of the cavity. In a fuel combustion device for a diesel engine, whether the engine load is a predetermined load or more, the supercharging pressure applied to the intake air is a predetermined pressure or more, or the intake air temperature is a predetermined temperature or more. In such a case, a fuel combustion device for a diesel engine, comprising a control means for controlling the ignition delay period to a predetermined period or longer. 2. The fuel combustion device for a diesel engine according to claim 1, wherein the control means controls the effective compression ratio of the engine to a predetermined value or less. 3. The fuel combustion apparatus for a diesel engine according to claim 2, further comprising a variable valve mechanism for varying the valve closing timing of the intake valve, while the control means controls the valve closing timing of the variable valve mechanism. A fuel combustion device for a diesel engine, which is characterized by: 4. The fuel combustion device for a diesel engine according to any one of claims 1 to 3, wherein the control means controls when the engine load is equal to or higher than a predetermined load and when the supercharging pressure applied to the intake air is equal to or higher than a predetermined pressure. A fuel combustion device for a diesel engine, wherein the fuel injection pressure of a fuel injection valve is controlled to be a predetermined value or higher in either of a case where the intake air temperature is equal to or higher than a predetermined temperature. 5. The fuel injection device for a diesel engine according to claim 1, wherein the penetration Sp is defined as the reaching distance of the fuel spray when 0.42 ms has elapsed from the start of fuel injection of the fuel injection valve. And the cone angle Θ of the fuel spray of the fuel injection valve,
Diesel engine characterized in that the minimum diameter Dlip at the lip portion of the cavity satisfies the following expression Dlip = k x Sp x sin (Θ / 2) (where k = 1.4 to 1.8) Fuel combustion equipment.