JPS59165857A - Fuel injection device for diesel engine - Google Patents

Abstract

PURPOSE:To reduce NOx concentration and smoke with reduction in an initial heat generation rate, by dividing a flow passage of a fuel injection pipe into a main flow passage and a sub flow passage and thereby reducing an initial injection rate. CONSTITUTION:A flow passage from A to B of a high pressure injection pipe 2 is divided into a main flow passage 15 and a sub flow passage 16. A length of the sub flow passage 16 is set smaller than that of the main flow passage 15, and a diameter of the sub flow passage 16 is set smaller than that of the main flow passage 15. A pressure wave created by movement of a plunger in an injection pump 1 is transmitted through the main flow passage 15 and the sub flow passage 16 to meet at the point B. The pressure wave transmitted through the sub flow passage 16 reaches earlier than the pressure wave transmitted through the main flow passage 15 by the time corresponding to a difference in lengths of the flow passages 15 and 16, and loses more pressure than that of the main flow passage 15 by the pressure corresponding to a difference in diameters thereof. Accordingly, a lower pressure wave in the sub flow passage 16 serves to operate an initial injection of an injection nozzle 4, thus reducing HC concentration in operation of main injection.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel injection device for a diesel engine, particularly a direct injection diesel engine.

Direct-injection diesel engines are often used for relatively large, low-speed engines, and this type is also used for high-speed engines because of its low fuel consumption and good startability.

The fuel injection system for such an engine is shown in Fig. 1 (Nichise Jidosha Co., Ltd.: Technical Manual "Diesel Engine" published March 1973, p. 57 or 93, 1980) and the inside of the fuel tank (not shown). , is supplied to a fuel injection pump 1 (shown as a distribution type injection pump) by a fuel supply pump.

The injection pump 1 not only makes the fuel high-pressure, but also adjusts the optimum injection amount according to the engine load, and pumps the high-pressure fuel to the injection nozzle 4 via the high-pressure injection pipe 2 at an appropriate injection timing. .

The injection nozzle 4 injects this high-pressure fuel into a fine mist into a single combustion chamber 7 formed between a cylinder head 5 and a piston 6 of the engine.

Note that a nozzle holder 3 is used to attach the injection nozzle 4 to the cylinder head 5, and this nozzle holder 3 guides the fuel to the injection nozzle 4 and at the same time
The injection start pressure (valve opening pressure) can be adjusted.

Therefore, in such a direct injection diesel engine, the fuel is injected in the form of a mist and mixed with air by diffusion.
Since the aim is to facilitate the generation of a mixture suitable for combustion, in many cases a hole-type injection nozzle 4 (multi-hole type) as shown in Fig. 2 is used to further promote this. It is injected at a high pressure of 150 to 300'/7.

The needle valve 11 of this hole-type injection nozzle 4 is seated and urged downward by a nozzle spring (not shown), and is connected to the pressure chamber 12 from a fuel passage (not shown) on the side of the nozzle body 10. When the pressure of the sent fuel exceeds the downward biasing force of the nozzle spring (the opening pressure of the injection nozzle 4), the needle valve 11 is pushed upward, and the fuel flows from the nozzle hole 13 at the tip of the nozzle body 10 into the pressure chamber 12. is injected into the combustion chamber 7 (FIG. 1).

In such a hole-type injection nozzle 4, since the injection hole area increases from the beginning of the lift of the needle pulp 11, the injection rate (injection amount per unit crank angle) characteristics are as follows.
Rapid rise immediately after opening of injection nozzle 4 (Figure 3)
, the required injection amount is to be supplied to the combustion chamber at once at the beginning of injection.

During combustion in a diesel engine, fuel is injected in the form of a mist, heated by compressed high-temperature air in the combustion chamber, and there is an ignition delay period from injection approaching the ignition temperature to ignition. After ignition, the air-fuel mixture formed by the evaporated fuel and air is rapidly promoted to burn, and the heat release rate peaks at υ (initial combustion period).After the initial combustion, the injected fuel droplets evaporate. Once the fuel has been burned, it is mixed with air and the fuel shifts to diffusion fuel combustion, where it is burned without being stored at all (main combustion period).

For this reason, with the hole-type injection nozzle 4 as described above, most of the required fuel is injected into the combustion chamber during the ignition delay period, which increases the initial heat release rate at the beginning of combustion and increases the in-cylinder temperature. There was a problem in that the concentration of nitrogen oxides (NOx) increased as the temperature increased, resulting in an increase in smoke.

Therefore, an object of the present invention is to reduce the injection rate at the initial stage of injection to reduce the NOx concentration and smoke due to the lower initial heat generation rate.

For this reason, the present invention provides a diesel engine in which high-pressure fuel from a fuel injection pump is injected from an injection nozzle into a combustion chamber via a high-pressure injection pipe.
45 into a main flow path and a sub flow path, and the length of the sub flow path is shorter than that of the main flow path, and its pipe diameter is also smaller than that of the main flow path. In addition to injecting most of the fuel (main injection), a small amount of fuel is injected (sub-injection) at a crank angle corresponding to the ignition delay period to ignite prior to the main injection. Configure.

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 4 shows a schematic configuration diagram of an embodiment of the present invention applied to a direct injection diesel engine.

In the figure, the flow path A-B in the middle of the high-pressure injection pipe 2 is branched into a main flow path 15 and a sub flow path 16, and the length of the sub flow path 16 is shorter than that of the main flow path 15, and the pipe diameter of the sub flow path 16 is The main flow path 15 is also smaller than υ.

Further, the injection nozzle 4 is configured to have two stages of valve opening pressure. That is, FIG. 5 is an enlarged sectional view of the injection nozzle 4 and the nozzle holder 3, and in the figure, the nozzle body 10 of the injection nozzle 4 is connected to the nozzle holder body 18 of the nozzle holder 3.
is screwed to the nozzle nut 19, and is attached by a flange (not shown) etc. provided on the nozzle holder body 18,
A needle valve 11 is seated in the nozzle body 10 and is urged downward by a first nozzle spring 20 via a retainer 21 to block the nozzle hole 13. . Further, the valve @ 23 fixed to the retainer 22 is connected to the second nozzle spring 2
4, and is positioned with a gap provided between it and the retainer 21.

Fuel from the fuel injection pump 1 is guided into the pressure chamber 12 through the fuel passage 25, and pressure waves generated by the movement of a syringe (not shown) inside the injection pump 1 move into the pressure chamber 12. , and the fuel pressure in the pressure chamber 12 exceeds the first valve opening pressure set by the urging force of the first nozzle spring 20. However, at the first valve opening pressure, the second nozzle spring 24 The valve 4d23 is not pushed up against the downward urging force, and a small amount of fuel is injected from the nozzle hole 13 according to the lift amount, and then the fuel pressure in the pressure chamber 12 is increased to 2.
When the second valve opening pressure set by the total urging force of the two nozzle and helmet springs 20 and 24 is exceeded, the needle valve 11 is pushed up together with the valve stem 23 even after contacting the valve stem 23. The main fuel is injected according to the amount of lift.

Reference numeral 26 is an adjustment screw for adjusting the second valve opening pressure.

The rest of the configuration is the same as that in FIG. 1, so the same components are given the same reference numerals and their explanations will be omitted.

The effect of the above configuration will be explained.

The pressure wave generated by the movement of the plunger (not shown) in the injection pump 1 propagates to the injection nozzle 4 via the high-pressure injection pipe 2, but since the flow path branches at point A, the pressure wave The waves propagate through the main flow path 15 and the sub flow path 16, respectively, and merge at point B.

Since the length of the sub-channel 16 is shorter than that of the main channel 15 and its diameter is smaller than that of the main channel 15, the pressure waves propagating through the sub-channel 16 tilt the main channel 15. For pressure waves,
The time is increased by the time corresponding to the difference in the length of the two flow paths 15 and 16, and the pressure is lost by the amount corresponding to the difference in the pipe diameter.

Therefore, when they merge at point B, a pressure wave is created in which a high-pressure wave that has propagated through the main channel 15 and a low-pressure wave that has propagated through the sub-channel 16 prior to this wave overlap.

Here, the pipe diameter of the sub flow path 16 is set so that the pressure caused by the low pressure wave is greater than the first valve opening pressure of the injection nozzle 4 but does not reach the second valve opening pressure. When the above-mentioned superimposed pressure waves reach the pressure chamber 12 of the injection nozzle 4, the low-pressure pressure wave causes the syn-needle valve 11 to rise by a gap and pass through the retainer 21 to the valve shaft 23. (the valve stem 23 is not pushed up due to contact with L), a small amount of fuel is injected for a predetermined period of time according to the lift amount determined by L.

Since the pressure caused by the high pressure wave exceeds the second valve opening pressure, this high pressure wave causes the needle valve 11 to
is largely pushed up together with the valve shaft 23, and fuel corresponding to the lift amount at this time is injected for a predetermined period of time.

In this case, the injection amount due to the high-pressure pressure wave is determined by the lift amount of the needle valve 11, the predetermined time during which the second valve opening pressure is exceeded, etc., and the injection amount due to the low-pressure pressure wave is determined by the lift amount of the needle valve 11. It is determined by the amount L (constant), the predetermined time during which the first valve opening pressure is exceeded, etc., and the injection timing is determined by the following: injection by high-pressure pressure waves (main injection), injection by low-pressure pressure waves (sub-injection) are the times when the pressure exceeds the second valve opening pressure and the eleventh valve opening pressure, respectively.

The total injection amount, which is the sum of the main injection and sub-injection, is adjusted by the injection pump 1 according to the engine condition.This total injection amount is divided into two, and most of the fuel is injected. The main injection is performed near the compression top dead center of the piston, and the sub-injection in which the remaining small amount of fuel is injected is performed prior to the main injection by a crank angle corresponding to the ignition delay period.
The length and diameter of the main flow path 15 and the sub flow path 16 are selected.

Therefore, the fuel injected into the combustion chamber by sub-injection during the ignition delay period is small because the injection rate is low, and if this fuel is combusted immediately after the ignition delay period has elapsed, the heat release rate will decrease. When the peak is alleviated and main injection starts after this initial combustion, the air in the combustion chamber becomes hot due to the heat generation of the fuel by the sub-injection, so the main injection After injection, the fuel undergoes diffusion combustion in which the droplets that have completely evaporated are sequentially mixed with air and burned.

Therefore, the heat release rate of the combustion chamber does not have a sharp peak, which makes it possible to suppress fuel consumption rate and smoke, and reduce NOx concentration.

As described above, the present invention branches the flow path in the middle of the high-pressure injection pipe into the main flow path and the sub flow path, and makes the length of the sub flow path shorter than that of the main flow path, and its pipe diameter smaller than that of the main flow path. In particular, the fuel injection during one cycle is divided into two times, and most of the fuel is injected (main injection) when the piston is near compression top dead center, and the crank angle corresponding to the ignition delay period is However, prior to the main injection, a small amount of fuel that can ignite is injected (sub-injection), which has the effect of suppressing the fuel consumption rate and deterioration of smoke, as well as reducing the NOx concentration. It will be done.

In addition, in the conventional device, the fuel injected at once during the ignition delay period collided with the wall surface of the combustion chamber, but in the present invention, the fuel injected into the combustion chamber by the main injection is In an atmosphere where the temperature is high due to combustion due to irradiation, the HC concentration can be reduced because evaporation and ignition occur before collision and adhesion.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of a fuel injection system for a conventional direct injection diesel engine, Figure 2 is a cross-sectional view of the main part of a hole-type injection nozzle, Figure 3 is a conventional injection rate characteristic diagram, and Figure 4 is a diagram of the main part of the main injection nozzle. FIG. 5 is an enlarged sectional view showing an example of the injection nozzle and nozzle holder used in the present invention. 1...Fuel injection pump, 2...High pressure injection pipe, 4...
・Top injection nozzle, 7... Combustion chamber, 15... Main flow path, 1
6... Sub-channel. Patent applicant Nissan Motor Co., Ltd. Figure I' Figure 2 Figure 3 Crank Porcupine

Claims (1)

[Claims] In a diesel engine that injects high-pressure fuel from a fuel injection pump into a combustion chamber from an injection nozzle via a high-pressure injection pipe, the flow path in the middle of the high-pressure injection pipe is branched into a main flow path and a sub flow path, and the sub flow path is A fuel injection device for a diesel engine, characterized in that the length of the pipe is shorter than that of the main flow path, and the diameter of the pipe is smaller than that of the main flow path.