JPH08226332A - Direct injection diesel engine - Google Patents

Abstract

(57) [Summary] [Purpose] To improve the exhaust emission of direct injection diesel engines. A direct injection diesel engine equipped with a combustion control means for increasing the EGR rate and delaying the fuel injection timing in the low-speed low-load range compared with the medium-speed medium-load range is provided with a piston 15
A piston combustion chamber 16 defined on the top of the piston combustion chamber 16 and an injection nozzle 17 for injecting fuel facing the center of the piston combustion chamber 16 from the injection nozzle 17 to the piston combustion chamber 16
A means for flattening the form of the fuel spray injected into is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a direct injection diesel engine.

[0002]

2. Description of the Related Art In order to suppress the generation of NOx which is a harmful component in exhaust gas, so-called EGR (Exhaust Gas) in which an inert exhaust gas is recirculated through an intake pipe.
Recirculation) devices are well known. In this EGR device, an EGR valve is attached to an EGR passage (a passage for returning a part of exhaust gas to the intake pipe),
Open the EGR valve in the required area of
The maximum temperature during combustion is lowered by mixing (GR gas) with the intake air.

By the way, when the EGR rate (= (EGR amount / fresh air amount) × 100) [%] increases, the smoke emission concentration increases. Therefore, in JP-A-60-162018, the swirl is strengthened as the EGR rate increases.

This is because when the EGR rate becomes large, the swirl is strengthened to improve the mixing of air and fuel at the time of combustion to reduce the smoke emission amount.

[0005]

However, in the above device, if the swirl is excessively increased in order to suppress the smoke emission amount when the EGR rate is significantly increased, the intake resistance is increased and the fuel consumption is increased. The smoke emission increases due to the shortage of the intake air amount.

Further, as a measure for reducing the amount of smoke discharged, there has been a method in which a protrusion for colliding fuel spray injected from an injection nozzle is formed in a combustion chamber of a piston to promote mixing of fuel and air ( See Japanese Utility Model Laid-Open No. 58-51204 and Japanese Utility Model Laid-Open No. 62-122127).

However, if the ignition delay period is not sufficiently obtained in the low speed and low load region, the fuel injection pressure decreases, and
There is a problem that the fuel spray injected from the injection nozzle and the air are not sufficiently mixed and the smoke emission amount increases.

An object of the present invention is to solve the above problems and improve the exhaust emission of a direct injection diesel engine.

[0009]

A direct-injection diesel engine according to a first aspect of the present invention is provided with a direct-injection type diesel engine having combustion control means for increasing an EGR rate in a low-speed low-load range from a medium-speed medium-load range and delaying a fuel injection timing. In a diesel engine, a combustion chamber defined at the top of the piston is provided, an injection nozzle is provided to inject fuel toward the center of the combustion chamber, and the form of fuel spray injected from the injection nozzle into the combustion chamber is planar. It is equipped with a means.

According to a second aspect of the present invention, in the direct injection type diesel engine according to the first aspect of the invention, an injection nozzle for injecting fuel is formed, and a needle for opening and closing the injection port is provided inside the injection nozzle. A spray pin that penetrates the nozzle is projected from the tip of the needle to form an umbrella portion that gradually increases in diameter from the middle of the spray pin to the tip thereof.

According to a third aspect of the present invention, there is provided the direct injection diesel engine according to the first aspect of the present invention, including a collision table which is bulged from the bottom surface of the combustion chamber defined at the top of the piston so as to face the injection nozzle. A guide surface that reflects the fuel spray injected from the injection nozzle is formed on the collision table.

According to a fourth aspect of the present invention, in the direct injection type diesel engine according to the first aspect of the invention, a collision table facing the injection nozzle is suspended from the cylinder head through a column and is injected from the injection nozzle to the collision table. Forming a guide surface for reflecting the fuel spray.

According to a fifth aspect of the present invention, in the direct injection diesel engine according to any one of the first to fourth aspects, a combustion control means for delaying the fuel injection timing from the top dead center is provided in the low speed and low load region. .

[0014]

In the direct injection type diesel engine according to the first aspect, the fuel injected from the injection nozzle is combusted through atomization, evaporation and mixing with air.

Since the injection nozzle has a structure in which the form of fuel spray is planar, it is difficult to increase the fuel injection speed as compared with an injection nozzle having a plurality of injection holes each having a small opening diameter.

When the EGR rate is lowered in the low speed and low load region and the combustion control is performed so that the fuel injection timing is advanced from the top dead center, the ignition delay period is short, so that the fuel injection pressure is reduced in the low speed and low load region. As a result, the penetrating force of the fuel spray that is planarly injected from the injection nozzle is insufficient.

On the other hand, according to the present invention, in the low speed low load region, the combustion control is performed so that the EGR rate is higher than that in the medium speed medium load region and the fuel injection timing is delayed, so that the combustion is gentle in the low speed low load region. Since the ignition delay period becomes long, even if the fuel injection pressure falls in the low speed and low load region, the penetrating force of the fuel spray injected in a plane from the injection nozzle is sufficiently secured.

Therefore, even in the low speed and low load region, the fuel spray injected from the injection nozzle reaches a wide range of the combustion chamber during the long ignition delay period, so that the swirl force generated in the combustion chamber is exerted. It can be weakened. By weakening the power of the swirl, it is possible to reduce the intake resistance to reduce the fuel consumption, and it is possible to prevent the exhaust particulate amount from increasing due to the shortage of the intake air amount.

In the direct-injection diesel engine according to the second aspect of the present invention, the fuel pressure-fed into the injection nozzle is a flow defined between the injection port and the spray pin as the needle opens the injection port of the injection nozzle. Ejects from the road into the combustion chamber.
The fuel ejected from the injection port into the combustion chamber collides with the enlarged diameter umbrella portion at the tip of the spray pin, and spreads into the combustion chamber in the form of a conical spray.

Combustion control is performed in which the EGR rate is increased in the low speed / low load range compared to the medium / medium speed / medium load range and the fuel injection timing is delayed.
By lengthening the ignition delay period, the penetration force of the fuel spray injected from the injection nozzle in a conical surface shape is sufficiently secured.

In the direct injection type diesel engine according to the present invention, the fuel injected from the injection nozzle into the combustion chamber is reflected by the guide surface of the collision table raised from the bottom surface of the combustion chamber of the piston to form a planar spray form. And spread to the combustion chamber.

Combustion control is performed in which the EGR rate is increased in the low speed / low load range compared to the medium / medium speed / medium load range and the fuel injection timing is delayed.
By lengthening the ignition delay period, the penetration force of the fuel spray that is reflected by the guide surface of the collision table and spreads in a plane is sufficiently ensured.

In the direct-injection diesel engine according to the present invention, the fuel injected from the injection nozzle into the combustion chamber is reflected by the guide surface of the collision table suspended from the cylinder head to form a planar spray form. Spread to the combustion chamber.

Combustion control is performed in which the EGR rate is increased in the low-speed low-load range compared with the medium-speed medium-load range and the fuel injection timing is delayed.
By lengthening the ignition delay period, the penetration force of the fuel spray that is reflected by the guide surface of the collision table and spreads in a plane is sufficiently ensured.

In the direct-injection diesel engine according to the present invention, a low-speed low-speed low-load region is constituted by combustion control in which the EGR rate is higher than in the medium-speed medium-load region and the fuel injection timing is delayed from the top dead center. Since the combustion is gentle in the load range and the ignition delay period is long, even if the fuel injection pressure drops in the low speed and low load range, sufficient penetration force of the fuel spray injected in a plane from the injection nozzle is secured. To be done.

Therefore, even in the low speed and low load region, the fuel spray injected from the injection nozzle reaches a wide range of the combustion chamber during the long ignition delay period, so that the swirl force generated in the combustion chamber is exerted. It can be weakened. By weakening the power of the swirl, it is possible to reduce the intake resistance to reduce the fuel consumption, and it is possible to prevent the exhaust particulate amount from increasing due to the shortage of the intake air amount.

[0027]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, 20 is a fuel injection pump in which the fuel injection timing and the fuel injection amount are electronically controlled.
Fuel pumped from the fuel injection pump 20 is guided to the injection nozzle 17 through the pipe 18.

Reference numeral 23 is an intake passage, 25 is an exhaust passage, 41 is a filter for collecting particulate matter in the exhaust gas, 4
An exhaust muffler 2 reduces exhaust noise.

Reference numeral 26 is an EGR passage that connects the exhaust passage 25 and the intake passage 23, and 27 is a diaphragm type EGR valve that responds to control negative pressure.

Reference numeral 28 denotes a negative pressure control valve, which adjusts the constant negative pressure from the vacuum pump 29 in three stages according to the duty signal from the control unit 31. For example, the OFF duty to the negative pressure adjusting valve 28 (OFF at a constant cycle)
The time ratio) is the maximum value and the constant negative pressure remains unchanged.
50% of the exhaust gas is recirculated when it is introduced into.
This is because the EGR rate (= EGR amount / fresh air amount x 100%) is 1
Equivalent to 00%. When the OFF duty decreases stepwise, the EGR valve 27 decreases in EGR valve 27 due to the decrease in the control negative pressure.
The valve opening becomes smaller and the EGR flow rate becomes smaller. That is, the EGR rate becomes 6 each time the OFF duty is reduced.
It becomes as small as 0% and 30%.

The three-stage EGR rate thus obtained is set as shown in FIG. 5 for the operating conditions. In the figure, the EGR rate is 100 in the medium-speed / medium-load range and the low-speed full-load range.
%. On the other hand, in the high speed and high load region, the combustion period is long and the generation of smoke cannot be completely suppressed. Therefore, the intake air temperature rises due to the increase in the exhaust gas temperature and the increase in the EGR flow rate. Because the effect of NOx reduction is reduced, the EGR rate is 60%,
It has been gradually reduced to 30%.

In order to control the EGR rate according to the operating conditions of the engine, the control unit 3 comprising a microcomputer
1, the control unit 31 includes a sensor for detecting an accelerator opening (accelerator pedal opening), a signal from an air flow meter 33 for detecting an intake air amount Q taken into the intake passage 23 via an air cleaner 35, and The EGR flow rate is controlled stepwise based on a reference pulse and a scale pulse described later.

In order to obtain the characteristics of the EGR rate (target EGR rate) shown in FIG. 5 with respect to the torque generated by the engine and the engine speed, the accelerator opening (engine load equivalent amount) Acc and the engine speed Ne are obtained. Is set as a parameter (not shown) and the map is looked up to obtain the target EGR rate at that time. The EGR flow rate is calculated from this and the air flow meter flow rate (new air amount) by the following equation: EGR flow rate = air flow meter flow rate × target EGR rate, and the OFF duty to the negative pressure control valve 28 is determined so that the EGR gas of this flow rate flows. Of.

As shown in FIGS. 6 and 7 (not shown in FIG. 1), a so-called helical intake port 46 (generally linear intake air) is used as a means for producing swirl in the intake air flowing into the combustion chamber 16. Path 46a and spiral path 46b around intake valve axis
And a rotary blade 47 rotatably provided near the spiral path 46b), a link mechanism 49 connected to the blade 47, and a link mechanism 49.
The swirl ratio can be adjusted by the rotational position of the blade 47. For example, the high swirl ratio at the blade position in FIG.
Comes to the position shown in FIG. 7, the swirl ratio becomes low. This rotating blade system has a quick response and can control swirl in a wide range. Therefore, it is suitable for controlling the HC that reacts sensitively to the swirl ratio.

FIG. 8 shows the characteristics of swirl ratio with respect to operating conditions.
As shown in, the swirl ratio is increased as the speed decreases.
In the high speed range, the volume efficiency decreases with the high swirl ratio, and the improvement of combustion by increasing the injection pressure weakens the need for swirl.Therefore, the swirl ratio decreases stepwise as the rotational speed increases. is there.

The actuator for the variable swirl is a diaphragm type actuator with a two-stage spring (not shown), and the actuator is provided with a three-stage control negative pressure by diluting the atmosphere to a constant negative pressure from a negative pressure source. It is composed of a negative pressure control valve.

By the way, when the EGR rate is increased, NOx
Although the concentration can be reduced, the smoke concentration sharply rises. In this case, the smoke concentration at the high EGR rate cannot be sufficiently reduced if the countermeasure is simply to improve the mixing during the diffusion combustion by strengthening the swirl.

In order to deal with this, the control unit 31 increases the EGR rate and swirl ratio in the low speed low load region lower than 1/2 load based on the map shown in FIG. Control to delay from the top dead center. By delaying the fuel injection timing from the top dead center, the proportion of premixed gas combustion is made larger than that of diffusion combustion, and both the NOx concentration and the smoke concentration are reduced.

In the control unit 31, the solenoid valve 14
Controls the opening timing (equivalent to the injection timing). FIG.
Reference numeral 0 is a flow chart for controlling the fuel injection timing and the injection period (injection amount), which is executed at regular intervals.

First, the engine speed Ne, the accelerator opening Acc, the cooling water temperature TW and the fuel temperature TF are read (step 1). The engine speed Ne is calculated from the reference pulse (one pulse per one rotation of the injection pump 20) and the scale pulse (36 pulses per one rotation of the injection pump 20). The cooling water temperature TW and the fuel temperature TF are detected by the sensors 34 and 35.

From the read engine speed Ne and the accelerator opening Acc, the respective maps of the basic fuel injection timing Itm and the basic fuel injection period Avm are looked up and obtained (step 2).

The map of the basic injection timing Itm is based on the accelerator opening Ac so that a predetermined injection timing characteristic can be obtained.
It is a map (not shown) in which c and the engine speed Ne are defined as parameters. The basic injection period Avm is shown in FIG.
As described above, the longer the accelerator opening Acc is, the longer the accelerator opening Acc is.

On the other hand, the injection timing correction amount ΔItm is calculated from the fuel temperature TF and the cooling water temperature TW, and this is used as the basic injection timing I.
The fuel injection timing is corrected by adding it to tm (steps 3 and 4).

The injection timing correction amount ΔItm is two correction amounts Δ
12 is the sum of Itm ₁ and ΔItm ₂ , and FIG.
Itm ₁ characteristics, and FIG. 13 shows the water temperature correction amount ΔItm ₂ characteristics. In any of the characteristics, the reason why the advance angle correction amount is increased as the temperature becomes lower is that the combustion speed becomes slower as the temperature becomes lower. In other words, temperature compensation is performed.

The injection timing IT (= Itm + Δ obtained in this way
Itm) and the basic injection period Avm are stored at predetermined addresses (step 5). The electromagnetic valve 14 is closed at the injection timing IT, and the electromagnetic valve 14 is opened at the timing when the basic injection period Avm has elapsed from the valve closing timing.

FIG. 14 shows the concentration characteristics of NOx and smoke with respect to the EGR rate when the fuel injection timing is before the top dead center and after the top dead center, and the injection timing before the top dead center (IT
= -4 ATDC), as the EGR rate increases, N
Although the Ox concentration decreases, the smoke concentration rises with a sharp curve.

On the other hand, the injection timing after the top dead center (IT
= + 4ATDC), the smoke concentration shows a decreasing tendency. The reason why the smoke concentration decreases in this way is, as can be seen from the heat generation pattern shown in the figure, due to the combination of the extreme delay in the injection timing and the high EGR rate, the ignition delay period becomes significantly longer and It seems that most of the combustion is due to premixed combustion. That is, EG
If the fuel injection timing is delayed until after TDC when the R rate is not too high, it is not possible to suppress the rising tendency of the smoke concentration as shown in FIG. 15, but in this example most of the combustion Results in premixed combustion, resulting in high EGR
The smoke concentration can be greatly reduced even in the operating range of the rate.

FIG. 14 shows an example in which the crank angle after top dead center is 4 degrees, but the critical points of premixed combustion and diffusion combustion differ depending on the engine model, so how many times after top dead center Whether to do it will be determined by matching for each engine.

Further, when the characteristics of the fuel consumption rate are shown in FIG. 16, the equal volume is deteriorated by the delay of the injection timing in this example, but on the other hand, the cooling loss is significantly reduced by the decrease of the combustion temperature. However, delaying the fuel injection timing does not deteriorate the fuel consumption rate. Note that the equal volume means work conversion efficiency, and the work conversion efficiency is the work conversion efficiency = the work shown in the figure / the amount of heat generation = the shown efficiency / (1-
Cooling loss) is the value defined by.

In this example, the temperature is compensated by advancing the fuel injection timing as the fuel temperature and the cooling water temperature become lower, so that the same ignition timing as at high temperature can be obtained at low temperature.

In FIG. 2, 10 is a cylinder head, 1
Reference numeral 1 is a cylinder, and 15 is a piston. A piston combustion chamber 16, which is a cylindrical space, opens at the top of the piston 15, and a clearance combustion chamber 14, which is a disk-shaped space, is defined between the top of the piston 15 and the cylinder head 10 near the top dead center. Is made.

The cylinder head 10 has a piston combustion chamber 1
An injection nozzle 17 facing the center of 6 is provided.

As shown in FIG. 3, a needle 9 is provided inside the injection nozzle 17. The injection nozzle 17 has a seat surface 8 on which the needle 9 is seated, and an injection port 7 opened at the tip of the seat surface 8. The seat surface 8 is formed in a conical shape like the needle 9 joined to the seat surface 8. The injection port 7 is formed in a cylindrical shape and is arranged coaxially with the needle 9.

The needle 9 is pressed against the seat surface 8 via a return spring (not shown), and the needle 9 moves from the seat surface 8 as the pressure of the fuel sent from the fuel injection pump 20 to the injection nozzle 17 rises. It lifts and injects fuel from the injection port 7.

A spray pin 6 penetrating the injection port 7 is formed at the tip of the needle 9 as a means for making the form of fuel spray flat. The spray pin 6 has an umbrella portion 5 whose diameter gradually increases from the portion protruding from the injection port 7 to the tip. The tip of the umbrella portion 5 is formed into a curved surface along a conical surface having a central angle θ.

The spray pin 6 causes the fuel injected from the injection port 7 to collide with the scab 5, and the form of the fuel spray injected from the injection nozzle 17 into the combustion chamber 16 is shown in FIGS. 1 and 4, respectively. Then, make it a conical surface (umbrella shape).

The spread angle of the fuel spray is substantially equal to the central angle θ of the tip of the umbrella portion 5. The central angle θ of the tip of the umbrella portion 5 is arbitrarily set so that the direction of fuel injection is directed to the side wall portion 19 of the piston combustion chamber 16 when the piston 15 is near the top dead center as shown in FIG. To

With the above construction, the operation will be described below.

The fuel injected from the injection nozzle 17 is atomized, evaporated, and mixed with air to reach combustion.

However, since the injection port 7 of the injection nozzle 17 defines an annular flow path between the injection port 17 and the spray pin 6, the injection of fuel is more difficult than the conventional injection nozzle having a plurality of injection ports each having a small opening diameter. It is difficult to increase speed.

Therefore, in the low-speed low-load range, the ignition delay period is short if the EGR rate is higher than in the medium-speed medium-load range and the combustion control for delaying the fuel injection timing from the top dead center is not performed. With the decrease in fuel injection pressure,
The penetration force of the fuel spray injected from the injection nozzle 17 is insufficient. Therefore, the fuel spray injected from the injection nozzle 17 cannot spread to the side wall portion 19 of the piston combustion chamber 16, and the problem that the air near the side wall portion 19 of the piston combustion chamber 16 is difficult to use is considered. To be

On the other hand, according to the present invention, in the low speed low load region, the combustion control is performed such that the EGR rate is higher than that in the medium speed medium load region and the fuel injection timing is delayed from the top dead center. Is gradually performed and the ignition delay period becomes long, so that even if the fuel injection pressure falls in the low speed and low load region, the fuel injected in the conical shape from between the injection port 7 of the injection nozzle 17 and the spray pin 6 The penetration force of the spray is sufficiently secured.

Therefore, even in the low speed and low load region, the fuel spray injected from the injection nozzle 17 spreads to the side wall portion 19 of the piston combustion chamber 16 during the long ignition delay period, and near the side wall portion 19 of the piston combustion chamber 16. Take in the air in and burn it.

Since the fuel spray injected in a plane from the injection nozzle 17 reaches a wide range of the piston combustion chamber 16, the swirl force generated in the piston combustion chamber 16 can be weakened. Becomes By weakening the power of the swirl, it is possible to reduce the intake resistance to reduce the fuel consumption, and it is possible to prevent the exhaust particulate amount from increasing due to the shortage of the intake air amount.

Next, another embodiment shown in FIG. 17 will be described. It should be noted that the same reference numerals will be used for portions corresponding to those in FIG.

As a means for making the form of the fuel spray into a planar shape, the piston 15 is provided with a collision table 32 protruding from the center of the bottom surface 12 of the piston combustion chamber 16 in a cylindrical shape.

In the collision table 32, the guide surface 36 facing the injection port of the injection nozzle 17 is formed in a plane shape orthogonal to the cylinder axis.

In this case, when the piston 15 is near the top dead center, the fuel injected from the injection nozzle 17 into the piston combustion chamber 16 is reflected on the guide surface 36 of the collision table 32 as shown in FIG. It expands in a disk shape toward the side wall portion 19 of the chamber 16.

In the low-speed low-load range, the EGR rate is made higher than that in the medium-speed medium-load range, the combustion control is performed to delay the fuel injection timing from the top dead center, and the ignition delay period is lengthened to inject fuel into the low-speed low-load range. Even if the pressure drops, the penetration force of the fuel spray that is reflected by the collision table 32 and spreads in a disk shape is sufficiently secured.

Therefore, even in the low speed and low load region, the collision table 32
The fuel spray that is reflected by and spreads in a disk shape spreads to the side wall portion 19 of the piston combustion chamber 16 during the long ignition delay period, and takes in the air in the vicinity of the side wall portion 19 in the piston combustion chamber 16 and burns it. As a result, the piston combustion chamber 16
It is possible to weaken the swirl forces that occur in.

Next, another embodiment shown in FIG. 18 will be described. It should be noted that the same reference numerals will be used for portions corresponding to those in FIG.

A collision table 37 is attached to the cylinder head 10 so as to be suspended from the cylinder head 10 via a support column 39 as a means for making the form of fuel spraying planar.

The collision table 37 has a guide surface 38 facing the injection port of the injection nozzle 17. The guide surface 38 of the collision table 37 is formed in a plane shape orthogonal to the cylinder axis.

In this case, the fuel injected from the injection nozzle 17 is reflected by the guide surface 38 of the collision table 37 and spreads in a disk shape toward the side wall portion 19 of the piston combustion chamber 16 as shown in the figure.

In the low-speed low-load range, the EGR rate is made higher than that in the medium-speed medium-load range, the combustion control is performed to delay the fuel injection timing from the top dead center, and the ignition delay period is lengthened to inject fuel into the low-speed low-load range. Even if the pressure decreases, the penetration force of the fuel spray that is reflected by the collision table 37 and spreads in a disk shape is sufficiently secured.

Therefore, even in the low speed and low load range, the collision table 37
The fuel spray that is reflected by and spreads in a disk shape spreads to the side wall portion 19 of the piston combustion chamber 16 during the long ignition delay period, and takes in the air in the vicinity of the side wall portion 19 in the piston combustion chamber 16 and burns it. As a result, the piston combustion chamber 16
It is possible to weaken the swirl forces that occur in.

[0078]

As described above, the direct injection diesel engine according to the first aspect of the present invention is provided with the combustion control means for increasing the EGR rate in the low speed and low load range compared with the medium speed and medium load range and delaying the fuel injection timing. In an injection diesel engine, a combustion chamber defined at the top of a piston is provided, an injection nozzle is provided to face the center of the combustion chamber and inject fuel, and the form of fuel spray injected from the injection nozzle into the combustion chamber is Since the fuel spray injected from the injection nozzle reaches a wide range of the combustion chamber during the long ignition delay period even in the low speed and low load range, the swirl of the swirl generated in the combustion chamber is provided. It can weaken power, reduce fuel consumption, and improve exhaust emission.

According to a second aspect of the present invention, in the direct injection diesel engine according to the first aspect of the invention, an injection nozzle is provided with an injection port for injecting fuel, and a needle for opening and closing the injection port is provided inside the injection nozzle. Since the spray pin that penetrates the injection port is projected from the tip of the needle and the umbrella part that gradually expands in diameter from the middle of the spray pin to the tip is formed, the fuel ejected from the injection port to the combustion chamber spreads at the tip of the spray pin. By colliding with the diametrical umbrella part, it becomes a cone-shaped spray form and spreads to the combustion chamber, and reaches a wide range of the combustion chamber during a long ignition delay period, and exhaust emission can be improved. .

A direct injection type diesel engine according to a third aspect of the present invention is the direct injection type diesel engine according to the first aspect of the present invention, further comprising: a collision table that rises from the bottom surface of the combustion chamber defined at the top of the piston so as to face the injection nozzle. Since the guide surface for reflecting the fuel spray injected from the injection nozzle is formed on the collision table, the fuel ejected from the injection nozzle into the combustion chamber is reflected on the guide surface of the collision table raised from the bottom surface of the combustion chamber of the piston. It spreads to the combustion chamber in the form of a uniform spray, reaches a wide range of the combustion chamber during a long ignition delay period, and can improve exhaust emission.

According to a fourth aspect of the present invention, in the direct injection type diesel engine according to the first aspect of the invention, a collision table facing the injection nozzle is suspended from the cylinder head through a column and is injected from the injection nozzle to the collision table. Since the guide surface that reflects the fuel spray is formed, the fuel injected from the injection nozzle into the combustion chamber is reflected by the guide surface of the collision table suspended from the cylinder head to form a planar spray form. And reach a wide area of the combustion chamber during a long ignition delay to improve exhaust emissions.

In the direct injection type diesel engine according to the fifth aspect of the present invention, the combustion control is performed so that the fuel injection timing is delayed from the top dead center in the low speed and low load range, so that the combustion is gentle in the low speed and low load range and the ignition delay is delayed. Since the period becomes long, even if the fuel injection pressure drops in the low speed and low load region, the penetration force of the fuel spray injected in a plane from the injection nozzle is sufficiently secured, and the exhaust emission can be improved.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view of the engine.

FIG. 3 is a sectional view of an injection nozzle.

FIG. 4 is a perspective view of a piston and the like.

FIG. 5 is a characteristic diagram of an EGR rate.

FIG. 6 is a perspective view showing the position of a rotating blade during high swirl.

FIG. 7 is a perspective view showing a position of a rotating blade at a low swirl.

FIG. 8 is a characteristic diagram of swirl ratio.

FIG. 9 is a map in which an operating range for heating intake air is set.

FIG. 10 is a flowchart for explaining control of injection timing and injection period.

FIG. 11 is a characteristic diagram of a basic injection period Avm.

FIG. 12 is a characteristic diagram of a fuel temperature correction amount ΔItm ₁ .

FIG. 13 is a characteristic diagram of a fuel temperature correction amount ΔItm ₂ .

FIG. 14 is a characteristic diagram of each concentration of smoke and NOx with respect to the EGR rate.

FIG. 15 is a concentration characteristic diagram of smoke and NOx with respect to injection timing.

FIG. 16 is a characteristic diagram of cooling loss, equal volume, and fuel consumption rate with respect to EGR rate.

FIG. 17 is a sectional view of an engine showing another embodiment.

FIG. 18 is a cross-sectional view of an engine showing still another embodiment.

[Explanation of symbols]

 6 Spray Pin 7 Nozzle 9 Needle 10 Cylinder Head 15 Piston 16 Piston Combustion Chamber 17 Injection Nozzle 20 Fuel Injection Pump 21 Direct Injection Diesel Engine 23 Intake Passage 25 Exhaust Passage 26 EGR Passage 27 EGR Valve 28 Negative Pressure Control Valve 31 Control Unit 32 Collision Platform 36 Guide surface 37 Collision platform 38 Guide surface 39 Post

Claims (5)

[Claims] 1. A direct injection diesel engine having combustion control means for increasing the EGR rate and delaying the fuel injection timing in the low-speed low-load range compared with the medium-speed medium-load range, comprising a combustion chamber defined at the top of the piston. A direct injection diesel engine, comprising: an injection nozzle that injects fuel toward the center of the combustion chamber, and means for planarizing the form of fuel spray injected from the injection nozzle into the combustion chamber. 2. An injection nozzle for injecting fuel is formed in the injection nozzle, a needle for opening and closing the injection port is provided inside the injection nozzle, and a spray pin penetrating the injection port is projected from the tip of the needle. The direct-injection diesel engine according to claim 1, characterized in that an umbrella portion having a diameter gradually increasing from the front to the tip thereof is formed. 3. A collision table, which is bulged from the bottom surface of the combustion chamber defined on the top of the piston, facing the injection nozzle, and a guide surface for reflecting the fuel spray injected from the injection nozzle is formed on the collision table. The direct injection diesel engine according to claim 1, wherein 4. The cylinder head is provided with a collision table, which is opposed to the injection nozzle, hung from the cylinder via a support column, and a guide surface for reflecting fuel spray injected from the injection nozzle is formed on the collision table. Direct injection diesel engine described in. 5. The direct injection diesel engine according to claim 1, further comprising combustion control means for delaying the fuel injection timing from the top dead center in the low speed and low load region.